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Studies directed towards the step-growth
photopolymerization of carbonyl compounds
Spanomanolis, Constantinos
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2
STUDIES DIRECTED TOWARDS THE STEP-GROWTH PHOTOPOLYMERIZATION
OF CARBONYL COMPOUNDS
by
Constantinos Spanoraanolis, B.Sc.
(Graduate Society)
The copyright of this thesis rests with the author.
No quotation from it should be published without
his prior written consent and information derived
from it should be acknowledged.
A t h e s i s submitted t o the U n i v e r s i t y o f Durham f o r the Degree of
Doctor o f Philosophy
197B
13 DEC 1978
si HOM
Non s i e n l e g e n t i , ancor, troppo s i c u r e
a g i u d i c a r , s i comme quel che stima
l e blade i n campo p r i a che s i e n mature:
ch' i ' ho veduto t u t t o i l verno prima
l o prun m o s t r a r s i r i g i d o e f e r o c e ,
p o s c i a p o r t a r l a rosa i n su l a cima;
e legno v i d i g i a d r i t t o e v e l o c e
c o r r e r l o mar per t u t t o suo cammino,
perire al fine a l l
1
i n t r a r de l a foce.
Dante A l i g h i e r i , 'La D i v i n a Commedia
Paradiso, Canto X I I I , 130 - 138.
'So a l s o l e t not the people be too sure i n judging, l i k e
those t h a t reckon the corn i n the f i e l d before i t i s r i p e :
for I have seen the b r i a r f i r s t show a l l harsh and r i g i d
through the w i n t e r and l a t e r bear the rose upon i t s top;
and once I saw a s h i p t h a t ran s t r a i g h t and s w i f t over the
sea through a l l i t s course and p e r i s h a t the l a s t e n t e r i n g
the harbour.'
- ii -
To the Memory of my Mother
- iii
-
ABSTRACT
Studies D i r e c t e d Towards the Step-Growth Photopolymerization
of Carbonyl Compounds
T h i s t h e s i s d e s c r i b e s some work c a r r i e d out i n the r e l a t i v e l y new area
of step-growth photopolymerization of carbonyl compounds.
The p o s s i b i l i t y of extending the photoreductive polymerization of
aromatic diketones (leading to the s y n t h e s i s of polybenzopinacols) to the
photochemical s y n t h e s i s of pentaphenylglycerols and higher analogues
investigated;
was
however examination of the model photochemical r e a c t i o n between
benzophenone and t r i p h e n y l g l y c o l e s t a b l i s h e d t h a t t h i s g l y c o l
(and the
r e l a t e d 1,2,2,2-tetraphenylethanol) i s not a hydrogen donor f o r t r i p l e t
benzophenone.
I n an attempt to examine the p o s s i b i l i t y of extending the photoreductive
a d d i t i o n of benzophenone to diphenylmethane to polymer s y n t h e s i s , m-dibenzoylbenzene and m- and p-dibenzylbenzenes were prepared and c h a r a c t e r i z e d .
I r r a d i a t i o n of the diketone i n the presence of an equimolar amount of e i t h e r
of the dibenzylbenzenes afforded low molecular weight products, shown by ^"H
and ^ C n.m.r. spectroscopy to c o n t a i n benzopinacol, tetraphenylethane and
1,1,2,2-tetraphenylethanol type of u n i t s , i n a d d i t i o n to benzophenone-type
carbonyl and benzyl groups.
R e s u l t s obtained from the p y r o l y t i c
decomposition
or treatment w i t h dehydrating agents of one of the products were c o n s i s t e n t
with the proposed
structure.
I r r a d i a t i o n of t e r e - or iso-phthalaldehyde i n the s o l i d s t a t e y i e l d e d
mostly s t a r t i n g m a t e r i a l s whereas branched low molecular weight products were
obtained from the i r r a d i a t i o n of e i t h e r of these aromatic dialdehydes i n the
presence of the hydrogen-donating
isopropanol.
An i n v e s t i g a t i o n on the s t r u c t u r e of the 'photopolymer
i r r a d i a t i n g benzaldehyde
1
produced on
i n the l i q u i d phase, by means of conventional
- iv -
spectroscopic
'Classical
1
analyses d i d not lead to a convincing
s t r u c t u r a l hypothesis.
chemical r e a c t i o n s proved to be more u s e f u l i n t h i s case;
i t was
thus shown t h a t the 'photopolymer', which has the same elemental composition
as benzaldehyde but a molecular weight 9 - 1 1 times a s high, can be a c e t y l a t e d ,
oxidized and i s r e a c t i v e towards s u l p h u r i c a c i d ;
i t i s furthermore s t a b l e to
i r r a d i a t i o n i n benzene s o l u t i o n a t 300nm i n the absence o f a i r and non-photor e d u c i b l e i n isopropanol;
i t i s however reduced by e i t h e r sodium borohydride
or sodium bis(2-methoxyethoxy)-aluminium hydride g i v i n g r i s e to a d i f f e r e n t
s t r u c t u r e i n each case.
F i n a l l y an extension
of the Paterno-Btichi r e a c t i o n of perfluoro
compounds to polymer s y n t h e s i s was attempted by examining the c y c l o a d d i t i o n
of p e r f l u o r o g l u t a r y l f l u o r i d e to two p e r f l u o r o o l e f i n s under a v a r i e t y of
experimental c o n d i t i o n s .
T h i s work was l a r g e l y u n s u c c e s s f u l and the
r a t i o n a l i z a t i o n of the r e s u l t s obtained w i l l be found i n the l a s t Chapter o f
this thesis.
-
V -
ACKNOWLEDGEMENTS
The author i s indebted to Dr. W.J. F e a s t f o r h i s continued help
and encouragement u n f a i l i n g l y given during the s u p e r v i s i o n of t h i s work.
His patience and understanding, both on the p r o f e s s i o n a l and personal l e v e l ,
have been i n v a l u a b l e to the author.
Thanks are due to Dr. R.S. Matthews f o r running n.m.r. s p e c t r a ,
Dr. B.J. Cromarty f o r t r a n s l a t i n g papers from German, and Drs. G.M. Brooke
and C D . B a r t l e t t f o r h e l p f u l suggestions.
A s s i s t a n c e from members of the t e c h n i c a l and laboratory s t a f f i s
g r e a t l y appreciated;
i n p a r t i c u l a r a s s i s t a n c e from Mrs. S.E. Robson f o r
running i . r . s p e c t r a and Mr. D. Hunter f o r p r a c t i c a l advice i s g r a t e f u l l y
acknowledged.
D i s c u s s i o n s with the other members o f the Research Laboratory '25'
have been p a r t i c u l a r l y h e l p f u l and t h e i r c o l l a b o r a t i o n i s a l s o a p p r e c i a t e d .
The author thanks the European Research O f f i c e o f the U.S. Array f o r the
award of a maintenance grant and Mr. Apostolos Spanomanolis of
'Christos Spanomanolis Sons', Athens, Greece, f o r some f i n a n c i a l
support.
F i n a l l y thanks are due to Mrs. E . Duddy and Miss A. Laing f o r typing
t h i s t h e s i s , and Mr. M. Strange f o r helping with some of the drawings.
- vi -
MEMORANDUM
The work described i n t h i s t h e s i s was c a r r i e d out i n the
Chemistry L a b o r a t o r i e s of the U n i v e r s i t y of Durham between September
1975 and August 1978.
T h i s work has not been submitted f o r any other
degree and i s the o r i g i n a l work of the author, except where acknowledged
by r e f e r e n c e .
- vii -
STUDIES DIRECTED TOWARDS THE STEP-GROWTH PHOTOPOLYMERIZATION OF CARBONYL
COMPOUNDS
TABLE OF CONTENTS
Page No.
Abstract
i i i
Acknowledgements
Memorandum
v
vi
Table of Contents
v i i
CHAPTER 1: GENERAL INTRODUCTION AND BACKGROUND
1.1.
Photopolymerization Redefined
1
1.2.
Photopolymerization V i a the S i n g l e t Manifold
2
1.3.
Photopolymerization V i a the T r i p l e t Manifold
4
1.4.
Photopolymerization V i a a R e a c t i v e Ground S t a t e Species
8
Formed i n an I n i t i a l Photochemical Reaction
1.5.
Step-Growth Photopolymerization i n the S o l i d S t a t e
9
1.6.
O r i g i n s o f Current Work
10
1.7.
B r i e f I n t r o d u c t i o n i n t o the Photochemistry of Carbonyl
13
Compounds
CHAPTER 2; PHOTOREDUCTIVE POLYMERIZATION OF AROMATIC BISKETONES
2.1.
Introduction
17
2.1.a.
H i s t o r i c a l Background
17
2.1.b.
Some Aspects of Relevant Photochemistry
32
2.1.b.i.
Introductory Survey
2.1.b.ii
Spin F l i p p i n g and Reactions w i t h i n the Solvent Cage
2.1.b.iii.
The Yellow Intermediate Observed i n the Photoreduction
32
38
41
of Aromatic Ketones
2.1.b.iv.
Complex Formation between K e t y l R a d i c a l and Ketone
43
2.1.b.v.
E f f e c t o f S t r u c t u r e on Photoreduction o f Aromatic Ketones
47
- viii
-
Page No.
2.1.b.vi.
S t e r i c E f f e c t s on Photoreduction
50
2.1.b.vii.
The Temperature E f f e c t on Photoreduction
52
2.1.b.viii.
Photoreductive Addition of Ketones to Methylene Groups
53
2.1. e.
2.2.
O b j e c t i v e s of the Study
54
Attempts to Synthesize Poly(pentaphenylglycerols) and
57
Higher Analogues
2.2.a.
I n t r o d u c t i o n to the Idea
57
2.2.b.
How One Event Led to Another
59
2.2.c.
The
'Prehistory' of Organic Photochemistry
- the Nature of
61
a Dispute
2.2.d.
The Resolution of the Dispute
64
2.2.e.
Ground S t a t e S y n t h e s i s of T r i p h e n y l g l y c o l
67
2.2.f.
The Benzophenone/Triphenylglycol
67
2.2.g.
The P h o t o r e a c t i v i t y of 1,2,2,2-Tetraphenylethanol
72
2.2.h.
Some Relevant Photoreactions
73
2.2.i.
Attempts to Prepare Pentaphenylglycerol V i a Ground S t a t e
74
Photoreaction
Chemistry
2.2.j .
Experimental
2.2.j.i.
Readily Available Materials
2.2.j . i i .
2.2.j.iii.
2.2. k.
2.3.
Solvents
M a t e r i a l s Synthesized from Simpler Chemicals
D i s c u s s i o n and Conclusions
Use of the Diphenylmethane/Benzophenone Reaction as the
79
79
80
80
85
89
Polymer B u i l d i n g Step
2.3.a.
D e t a i l s of Model Reaction
90
2.3.a.i.
D i s c u s s i o n of L i t e r a t u r e
90
2.3.a.ii.
Experimental R e s u l t s
94
2.3.a.iii.
Comments on L i t e r a t u r e Claims i n the L i g h t of
Present R e s u l t s
97
- ix -
Page No.
2.3.b.
S y n t h e s i s of Monomers
104
2.3.b.i.
D i s c u s s i o n of P o s s i b l e Routes
104
2.3.b.ii.
S e l e c t i o n of Routes
105
2.3.b.iii.
Reasons f o r F a i l u r e
114
2.3.b.iv.
P u r i f i c a t i o n and Proof o f S t r u c t u r e
116
2.3.C.
Polymerization Runs
117
2.3.c.i.
A Preliminary Investigation
117
2.3.c.ii.
Examination of the E f f e c t o f Concentration
118
2.3.c.iii.
Large S c a l e Experiments
121
2.3.d.
C h a r a c t e r i z a t i o n o f Products
123
2.3.e.
Reactions o f Polymers
128
2.3.e.i.
Depolymerization
128
2.3.e.ii.
Treatment with Dehydrating Agents
129
2.3.e.iii.
P a r a l l e l Model Compound S t u d i e s
131
2.3.f.
Experimental
134
2.3.f.i.
Readily Available Materials
134
2.3.f.ii.
Solvents
134
2.3.f.iii.
M a t e r i a l s Synthesized from Simpler Chemicals
135
2.3.g.
D i s c u s s i o n and Conclusions
CHAPTER 3:
135
THE PRODUCTS OF IRRADIATION OF BENZALDEHYDE AND ITS
DIFUNCTIONAL ANALOGUES
3.1.
Introduction
141
3.1.a.
E a r l y Photochemical I n v e s t i g a t i o n s
141
3.1.b.
Ground S t a t e Polymerization of Benzaldehyde and i t s
145
Difunctional
Analogues
3.I.e.
The Photochemistry of Phthalaldehyde
147
3.1.d.
B r i e f I n t r o d u c t i o n i n t o the Photochemistry of Benzaldehyde
148
3.1. e.
O r i g i n a l Ideas
151
3.2.
The Photochemistry of Tere- and Iso-phthalaldehyde
3.2.a.
Results
152
152
- x Page
3.2. b.
3.3.
D i s c u s s i o n i n the L i g h t of Recent Knowledge
The Benzaldehyde Photoproduct
155
156
3.3.a.
Recent Preparation and S p e c t r a l C h a r a c t e r i s t i c s
156
3.3.b.
Experimental
157
3.3.b.i.
P u r i f i c a t i o n of Benzaldehyde
157
3.3.b.ii.
Irradiations
158
3.3.b.iii.
P u r i f i c a t i o n of Product
159
3.3.b.iv.
Attempted C h a r a c t e r i z a t i o n of the 'Photopolymer'
160
of Benzaldehyde
3.3.c.
Conclusion
CHAPTER 4:
and Suggestions f o r Further Work
STUDIES ON THE
164
CYCLOADDITION OF PERFLUOROGLUTARYL-
FLUORIDE TO SOME PERFLUOROOLEFINS
4.1.
The Paterno-Buchi Reaction
168
4.1.a.
Introduction
168
4.1.b.
Mechanism
169
4.1. e.
Limitations
171
4.2.
A p p l i c a t i o n of the Paterno-Buchi Reaction to Polymer
173
Synthesis
4.3.
A p p l i c a t i o n s of the Paterno-Buchi Reaction to Poly-
176
f l u o r i n a t e d and P e r f l u o r o Systems
4.4.
The P h o t o l y s i s of A c y l F l u o r i d e s
183
4.5.
O r i g i n a l Idea
186
4.6.
Experimental
188
4.6.a.
Starting Materials
188
4.6.b.
Irradiations
190
4.6. c.
Results
191
4.7.
Discussion
191
4.8.
Conclusions
196
No.
- xi -
Appendices and References
Appendix A - Apparatus, Instruments and General Techniques
Appendix B - I n f r a r e d Spectra
Appendix C - L e c t u r e s , C o l l o q u i a , Seminars and Conferences Attended
CHAPTER 1
General I n t r o d u c t i o n and Background
The term photopolymerization i s commonly understood to mean the i n i t i a t i o n
by l i g h t of a chain polymerization process, although more g e n e r a l l y i t i m p l i e s
the i n c r e a s e i n molecular weight caused by l i g h t and therefore i n c l u d e s the
1 2
p h o t o c r o s s l i n k i n g o f macromolecules. '
The l i n k between these two aspects of
photopolymerization i s the use o f l i g h t as energy source and polymeric
materials
as the o b j e c t of i n t e r e s t .
P h o t o i n i t i a t e d v i n y l polymerization has been the o b j e c t o f r e s e a r c h
3
i n t e r e s t s i n c e the t u r n o f the century
and a l a r g e volume of s c i e n t i f i c and
4-8
t e c h n o l o g i c a l information has been published.
The area remains one o f
i n t e n s e a c t i v i t y both i n academic and i n d u s t r i a l l a b o r a t o r i e s and i s a l s o of
considerable commercial importance i n the s u r f a c e coatings, e l e c t r o n i c s ,
9-12
p r i n t i n g and r e l a t e d i n d u s t r i e s .
The use o f p h o t o c r o s s l i n k i n g o f polymeric m a t e r i a l s has been t r a c e d back
13
to the Babylonians,
although the development o f t h e area r e a l l y begins with
the work o f Minsk on the s y n t h e s i s o f p o l y ( v i n y l c i n n a m a t e ) .
He a l s o showed
how the i n c o r p o r a t i o n o f dyes i n t o coatings containing the polymer provided a
14 15
means o f p h o t o s e n s i t i z i n g the c r o s s l i n k i n g r e a c t i o n .
'
This deliberate
p h o t o c r o s s l i n k i n g i s , l i k e p h o t o i n i t i a t e d v i n y l polymerization, an area o f
intense c u r r e n t a c t i v i t y and a t o p i c with considerable commercial
,
.
11,12,16
importance.
C r o s s l i n k i n g i s commonly observed as a process competing with degradation
i n polymers exposed to l i g h t .
I n general terms such c r o s s l i n k i n g i s l a r g e l y
due to r e a c t i o n s o f secondary polymer r a d i c a l s formed by cleavage o f groups
or atoms from the main polymer c h a i n .
A c t u a l c r o s s l i n k i n g may occur by r a d i c a l
combinations or by additions to unsaturated
s i t e s i n other c h a i n s .
A number of
examples o f photochemical c r o s s l i n k i n g of polymers and the r e l a t e d photochemical
13 17 18
g r a f t i n g o f one monomer to a polymer may be found i n the l i t e r a t u r e .
' '
- 2 -
The preceding paragraphs very b r i e f l y d e s c r i b e r e a c t i o n s long c l a s s i f i e d
under the general heading o f photopolymerization.
Over the l a s t few y e a r s ,
however, there have been s e v e r a l r e p o r t s o f polymer syntheses of the s t e p growth type i n which photochemical r e a c t i o n s a r e used i n forming the bonds o f
a l i n e a r polymer c h a i n i n each propagation s t e p .
pointed out the need to re-examine
De Schryver and Smets have
the concept o f photopolymerization.
They
have suggested t h a t the term be reserved s p e c i f i c a l l y f o r polymerization
processes i n which every chain propagation s t e p i n v o l v e s a photochemical
19
reaction,
and i n t h i s sense photopolymerization i s d i s t i n c t from photo-
i n i t i a t e d polymerization.
De Schryver and Smets have pointed out t h a t photo-
polymerizations can be d i v i d e d i n t o three c l a s s e s according t o the nature of
the s p e c i e s involved i n the propagation step, which may be a s i n g l e t e x c i t e d
s t a t e , a t r i p l e t e x c i t e d s t a t e , o r a r e a c t i v e ground s t a t e r e s u l t i n g from a
20
photochemical r e a c t i o n .
1.2.
Photopolymerization V i a the S i n g l e t Manifold.
The d i m e r i z a t i o n of anthracene a t the 9,10 p o s i t i o n s i s a w e l l e s t a b l i s h e d
21
photochemical r e a c t i o n proceeding v i a the s i n g l e t s t a t e .
When b i s -
anthracenes a r e i r r a d i a t e d polymers can be obtained and i t has been
demonstrated
t h a t t h i s r e a c t i o n proceeds v i a the s i n g l e t manifold, and g i v e s the head t o t a i l
22 23
product, a s shown i n F i g u r e 1.1.
'
Two p o i n t s a r e p a r t i c u l a r l y worthy o f
note, i n the f i r s t p l a c e the r e a c t i o n proceeds i n the d i r e c t i o n o f polymer
formation when the i r r a d i a t i o n i s c a r r i e d out a t 350 nm and depolymerization
at below 300 nm wavelength;
t h i s s e r v e s to i l l u s t r a t e the importance o f
s e l e c t i n g the appropriate energy range f o r any p a r t i c u l a r photopolymerization
process.
Secondly, the degree o f polymerization (d.p.) a t t a i n a b l e i n t h i s
r e a c t i o n appears to depend on the nature o f the group l i n k i n g the two
anthracene u n i t s i n the monomer, thus f o r monomers o f s t r u c t u r e I s i g n i f i c a n t l y
lower d.p.'s were obtained on i r r a d i a t i o n than f o r monomers o f s t r u c t u r e I I
22 21
(Figure 1.2).
' *
-
3
-
/
OIOIO
009)
hy
Dioro
F i g u r e 1.1
I
I I
F i g u r e 1.2
The e x p l a n a t i o n o f the discrepancy l i e s i n t h e p o s s i b i l i t y o f a c h a i n growth
terminating s i d e r e a c t i o n f o r s t r u c t u r e I which does not e x i s t f o r s t r u c t u r e
I I , namely a 1,5-sigmatropic hydrogen s h i f t from t h e methylene attached t o
C-9 to C-10.
T h i s o b s e r v a t i o n s e r v e s to i l l u s t r a t e the Importance o f understanding a l l
the d e t a i l s o f the p h o t o r e a c t i o n s o f monomers s e l e c t e d f o r use i n step-growth
photopolymerization.
- 4 -
1.3.
Photopolymerlzatlon V i a the T r i p l e t Manifold.
Populating the e x c i t e d s t a t e by way o f energy t r a n s f e r from an appropriate
s e n s i t i z e r ensures r e a c t i o n on the t r i p l e t manifold and excludes I n t e r v e n t i o n
of s i n g l e t s t a t e s o f the monomer.
One o f the e a r l i e s t examples o f s o l u t i o n
phase step-growth photopolymerization was the benzophenone s e n s i t i z e d
polymerization o f tetrachloroblsmaleimldes (Figure 1.3, I I I , X = C l ,
19 24
R = -fCHg)^) • '
A
d e t a i l e d study o f the photochemistry o f the blchromophorlc
system I I I by De Schryver and co-workers u n d e r l i n e s the p o i n t , made I n r e l a t i o n
to the photopolymerlzatlon o f blsanthracenes, t h a t a l l p o s s i b l e a s p e c t s o f the
r e a c t i o n and the p r o p e r t i e s o f the r e a c t a n t s and products must be considered i n
*
X X
P
a
6
m
IV
tr
V
F i g u r e 1.3
designing step-growth photopolymerization p r o c e s s e s .
Thus, although f o r
tetrachlorobismaleimides ( I I I , X = C l , R = -fCH.)- ) where n = 7, 9 o r 11
z n
i r r a d i a t i o n o f a s o l u t i o n o f monomer and benzophenone i n methylene c h l o r i d e
leads to genuine l i n e a r high polymers o f s t r u c t u r e I V , monomers where an even
number o f methylenes
separate the malelmide u n i t s f a i l t o reach high molecular
- 5 -
weight s i n c e the products p r e c i p i t a t e from s o l u t i o n a t a r e l a t i v e l y low degree
o f polymerization.
T h i s i s not the only r e s t r i c t i o n on the g e n e r a l i t y of the
s y n t h e s i s o f polymers I V from monomers I I I . When the monomers having uns u b s t i t u t e d maleimi.de double bonds ( I I I , X = H) a r e i r r a d i a t e d i n s o l u b l e
products a r e formed, presumably accounted f o r by c r o s s l i n k i n g v i a v i n y l
polymerization
a t the double bonds.
F o r some lengths of methylene sequence R
monomeric cyclomers V a r e formed (Figure 1.3);
the r e l a t i v e proportions o f
l i n e a r polymer ( I V ) , cyclomer (V), and i n s o l u b l e c r o s s l i n k e d product depend
on the nature o f the v i n y l s u b s t i t u e n t s X, the l i n k i n g group R, and t h e
r e a c t i o n conditions such a s the monomer concentration.
A f u r t h e r f a c t o r which
24
was
emphasized by these authors
was how c r i t i c a l l y important very high
reagent p u r i t y can be i n r e a c t i o n s of t h i s kind;
thus, although no detectable
d i f f e r e n c e was e s t a b l i s h e d between samples o f tetrachlorobismaleimides p u r i f i e d
by s l i g h t l y d i f f e r e n t techniques one sample polymerized to genuine high polymer
on i r r a d i a t i o n i n the presence o f benzophenone whereas another sample was
recovered as unchanged monomer a f t e r i d e n t i c a l treatment;
presumably t r a c e s o f
an e f f e c t i v e t r i p l e t quencher c o n s t i t u t e d the d i f f e r e n c e between samples.
Other examples o f photopolymerization v i a the t r i p l e t manifold i n c l u d e
25
the i r r a d i a t i o n o f biscoumarins i n the presence o f benzophenone s e n s i t i z e r
and the s y n t h e s i s o f polyoxetanes by i r r a d i a t i o n o f bisbenzophenones i n the
26 27
presence o f equimolar amounts o f the d i o l e f i n s , t e t r a m e t h y l a l l e n e o r furan. '
The u n s e n s i t i z e d p h o t o l y s i s of biscoumarins with s h o r t c h a i n length (n < 8)
28
y i e l d s e x c l u s i v e l y endo cyclomers a r i s i n g from the e x c i t e d s i n g l e t manifold
(Figure 1.4, VI) while benzophenone s e n s i t i z e d r e a c t i o n leads to high molecular
weight polymers.
The predominant exo head t o head s t r u c t u r e was e s t a b l i s h e d by
nmr spectroscopy (Figure 1.4, V I I ) .
The case of photochemical r e a c t i o n between benzophenone and tetramethyla l l e n e has been s t u d i e d i n d e t a i l and i n a d d i t i o n to the oxetane s t r u c t u r e s
- 6 -
n
hv
0*
o
VI
9CO
9
12
«3
Q
OC(CH„LC
ii 212
c©6
hy
H3
0
H
VII
Figure
1.4
a r i s i n g from c y c l o a d d i t i o n there are three t e r t i a r y a l c o h o l s formed v i a
i n i t i a l a b s t r a c t i o n of hydrogens from the methyl groups of
tetramethylallene
by t r i p l e t benzophenone followed by coupling of the k e t y l and a l l y l r a d i c a l s
29
(Figure 1.5).
mass balance.
Products i n Figure 1.5
account f o r over 98% of the o v e r a l l
Approximately 90% of benzophenone molecules r e a c t by c y c l o -
a d d i t i o n , the r e s i d u a l 10% r e a c t i n g by i n i t i a l a b s t r a c t i o n of hydrogen from
29
tetramethylallene.
of bisketones
I n the l i g h t of t h i s evidence one would expect i r r a d i a t i o n
i n the presence of equimolar amounts o f t e t r a m e t h y l a l l e n e
y i e l d copolymers of s t r u c t u r e V I I I ,
structures).
Figure 1.6
(together with
isomeric
to
H
©
<0>O
0
tHA
3'2
n
3'2
H
( C H
©
H
O
3^
tHJ3'2
Figure
1.5
©
(CH,)
3'2
Ar'
Ar'
QK3
H
H
CH
tHJ.
©
VIII
Figure
1.6
m
- 8 -
Such copolymers were r e c e n t l y reported
26
I n which c a . 90% of the polymer chain
l i n k s are oxetanes.
The use of furan as the r e a c t i n g diene system
( i n s t e a d of t e t r a m e t h y l -
a l l e n e ) presented s p e c i a l problems due to i t s v o l a t i l i t y which were s u c c e s s f u l l y
27
overcome i n the end r e s u l t i n g i n the s y n t h e s i s of l i n e a r polymers.
A more d e t a i l e d examination
o f these cases confirms the r e s t r i c t i o n s on
g e n e r a l i t y and the p r a c t i c a l d i f f i c u l t i e s which apply to t h i s area of polymer
synthesis.
1.4.
Photopolymerizatlon V i a a R e a c t i v e Ground S t a t e Species Formed i n an
I n i t i a l Photochemical Reaction.
The photochemical p o l y a d d i t i o n of dibenzaldiimines i s an example o f t h i s
class
(Figure 1.7, I X ) . The r e a c t i o n i s benzophenone s e n s i t i z e d and proceeds
v i a coupling of Ar-CH-NH-R type r a d i c a l s . " '
0
Another example reported i s the photopolymerization o f b i s a z i d e s , the
propagation
s t e p of which i s b e l i e v e d to proceed through a r e a c t i v e n i t r e n e
31-34
intermediate"
(Figure 1.7,
X).
f
R
Ar—CH—N+CHsWI—CH—Ar - ™ s P
• - -CH—NH4<H,-H*KH—
*
(OijljCHOH
*
2
2
340 nm
IX
Figure
1.7
n
- 9 -
Stevens and co-workers
maleimide to benzene
(Figure 1.8) .
37
'
made use of the photocycloadclition of
and a l k y l benzenes
38 39
'
to s y n t h e s i z e l i n e a r polyimides
Reaction i s thought to i n v o l v e 2+2 c y c l o a d d i t i o n o f photo-
e x c i t e d maleimide
to the aromatic r i n g followed by ground s t a t e D i e l s - A l d e r
a d d i t i o n w i t h a second maleimide
unit.
"0 6-^0^0=6^
o
N—R
N
n
Figure
1.8
Another i n t e r e s t i n g example o f t h i s type of photopolymerization i s the
40
r e d u c t i v e coupling of aromatic diketones which a f f o r d s polybenzopinacols.
Photoreductive polymerization w i l l be d e a l t w i t h i n d e t a i l i n Chapter 2 of t h i s
thesis.
1.5.
Step-Growth Photopolymerization i n the S o l i d S t a t e .
41-44
T h i s f i e l d was i n i t i a t e d by Hasegawa and co-workers.
The photo-
c y c l o d i m e r i z a t i o n of o l e f i n s to cyclobutane d e r i v a t i v e s was a p p l i e d to the
s o l i d s t a t e photocycloaddition p o l y m e r i z a t i o n of 2 , 5 - d i s t y r y l p y r a z i n e and
- 10 -
r e l a t e d s t r u c t u r e s (Figure 1.9, X I ) . The s o l i d s t a t e photopolymerlzation was
found to be topochemically c o n t r o l l e d .
The double bonds should be a p p r o p r i a t e l y
l o c a t e d one beside the other f o r the d l m e r l z a t l o n to take p l a c e .
For I n s t a n c e ,
only one c r y s t a l l i n e form of o,a'-bis(4-acetoxy-3-methoxybenzylidene)-pb e n z e n e d l a c e t o n l t r l l e was found to polymerize i n the s o l i d s t a t e (Figure
XII)
1.9,
45
©CH^HQCH-<H0
hv
X
n
9
N
N
hv
N
N
H
XI
_n
Figure
1.6.
1.9
O r i g i n s of Current Work.
The s u c c e s s f u l photoreductive coupling o f aromatic bisketones and the
s y n t h e s i s o f polyoxetane copolymers
from equimolar mixtures of diketones and
- 11 -
d i o l e f i n s are c h a r a c t e r i s t i c examples of the step-growth photopolymerizatlon of
carbonyl compounds.
The work to be d e s c r i b e d i n t h i s t h e s i s was intended as
an attempt to extend the number of known examples i n t h i s a r e a .
To t h i s end, a
number of mono- and di-carbonyl compounds were s y n t h e s i z e d and c h a r a c t e r i z e d ;
t h e i r p h o t o r e a c t i v i t i e s under a v a r i e t y of d i f f e r e n t c o n d i t i o n s were examined,
and r e a c t i o n products were i d e n t i f i e d wherever
possible.
The main reasons f o r undertaking t h i s study were:
(1)
the d e s i r e to explore the r e l a t i v e l y new area of
photopolymerization f o r i t s own
(ii)
step-growth
sake;
the p o s s i b i l i t y of preparing novel polymeric s t r u c t u r e s which might
have i n t e r e s t i n g p h y s i c a l o r chemical p r o p e r t i e s .
The o r i g i n a l o b j e c t i v e was to attempt e s t a b l i s h i n g the range of
46
a p p l i c a b i l i t y of the polymer syntheses formulated i n F i g u r e 1.10.
rr
hy
n
1
•
C
|
C
!
r? n
hy
n
Figure
1.10
I t was intended t h a t X and Y would be e i t h e r f l u o r i n e o r h i g h l y f l u o r i n a t e d
groups but i n p r i n c i p l e a wide v a r i e t y of s t r u c t u r e s could be used.
The
experimental work c a r r i e d out on t h i s i n i t i a l p r o j e c t i n v o l v e d the study of a
model r e a c t i o n between a p e r f l u o r o d i c a r b o n y l compound (namely hexafluorog l u t a r y l f l u o r i d e ) and two d i f f e r e n t perfluoromonoolefins (namely perfluorohept-
- 12 -
1-ene and p e r f l u o r o c y c l o h e x e n e ) . The aim was to determine the conditions under
which the model r e a c t i o n could g i v e a high y i e l d o f 1:1 o r 2:1 adducts, and then
to attempt the a c t u a l polymer forming r e a c t i o n ( d i a c i d f l u o r i d e i n the presence
of a d i o l e f i n ) under the appropriate conditions (Figure 1.11).
F
cr-v
F
hv
hv
^C(CF)
0
2:1
2--1
OF
|C(CF
2)4
h
2
:1
1:1
F i g u r e 1.11
T h i s work was l a r g e l y u n s u c c e s s f u l and the r e s u l t s obtained w i l l be
d i s c u s s e d i n Chapter 4 o f t h i s t h e s i s .
The main body o f work to be described i s concerned with an examination o f
some a s p e c t s o f the photopolymerization o f aromatic carbonyl compounds.
As a
f i r s t aim the photochemistry o f t e r e - and iso-phthalaldehyde was examined both
i n the s o l i d s t a t e and i n the presence o f hydrogen donors.
No r e a c t i o n was
detected i n the f i r s t case, whereas the l a t t e r experiments afforded i n s o l u b l e
branched m a t e r i a l s o f a s y e t u n i d e n t i f i e d s t r u c t u r e s .
I r r a d i a t i o n o f the mono-
- 13 -
f u n c t i o n a l compound, benzaldehyde, e i t h e r neat o r i n the presence o f hydrobenzoin
y i e l d e d a telomer with i n t e r e s t i n g p h y s i c a l p r o p e r t i e s .
Attempts to c h a r a c t e r i z e
t h i s m a t e r i a l w i l l be d e s c r i b e d i n Chapter 3.
F u r t h e r attempts to extend the w e l l known photochemical s y n t h e s i s o f
40
polybenzopinacols
t o polymers with more than two a d j a c e n t C-H_-C-0H u n i t s i n
D 5
the r e p e a t i n g block (polypentaphenylglycerols and higher analogues) (Figure 1.12)
d i d not give p o s i t i v e r e s u l t s .
Model monomer r e a c t i o n s were attempted f o r t h i s
purpose and, as a r e s u l t , i n t e r e s t i n g p r o p e r t i e s o f c e r t a i n aromatic a l c o h o l s
were e s t a b l i s h e d .
9
o
where m > 3
m
J nn
F i g u r e 1.12
F i n a l l y , extension to polymer s y n t h e s i s o f a w e l l e s t a b l i s h e d r e a c t i o n ,
namely the photoreductive coupling o f t h e benzophenone-diphenylmethane system,
afforded polymeric m a t e r i a l s o f r e l a t i v e l y low d.p. S p e c t r o s c o p i c and chemical
13
evidence and e s p e c i a l l y the use o f comparative
C nmr s t u d i e s have been
s u c c e s s f u l l y employed f o r the assignment o f product s t r u c t u r e s .
A detailed
account of t h i s work appears i n Chapter 2. Most o f the chemistry involved i n
these s t u d i e s i s based on a s p e c t s o f the photochemistry o f the carbonyl group.
1.7.
B r i e f I n t r o d u c t i o n i n t o the Photochemistry o f Carbonyl Compounds.
The absorption o f l i g h t i n non-conjugated o r g a n i c molecules u s u a l l y
i n v o l v e s the promotion o f a s i n g l e e l e c t r o n from a a, v
o r n o r b i t a l i n the
ground s t a t e to a p r e v i o u s l y vacant n* o r o* antibonding o r b i t a l .
Molecular
- 14 -
o r b i t a l s , appropriate energy l e v e l s and e l e c t r o n i c t r a n s i t i o n s f o r the s i m p l e s t
example of a molecule containing the carbonyl chromophore, formaldehyde, a r e
47
available.
With simple ketones, the t r a n s i t i o n of lowest energy i s the weak
n •*• I T * t r a n s i t i o n g e n e r a l l y r e s p o n s i b l e f o r the longest wavelength ( c a . 290 ran)
absorption and fundamental i n most photochemical
processes i n v o l v i n g s a t u r a t e d
ketone p h o t o l y s i s . A very i n t e n s e absorption around 150 nm corresponds to a
n -+• ir* e x c i t a t i o n .
Conjugation s h i f t s both the n •*•
wavelengths.
TT* and IT -> I T * absorption bands to longer
The lone p a i r o r b i t a l s a r e r e l a t i v e l y u n a f f e c t e d w h i l s t the h i g h e s t
ir o r b i t a l i n the ground s t a t e i s r a i s e d i n energy, r e l a t i v e to a non-conjugated
carbonyl ir o r b i t a l , and the lowest ir* o r b i t a l lowered i n energy.
I n appropriately
s u b s t i t u t e d unsaturated ketones the ir ir* c o n f i g u r a t i o n may become the lowest
47
r
t r i p l e t s t a t e , the n -»• ir* s h i f t being l a r g e compared to the n •+ ir* s h i f t .
Most of the carbonyl photochemistry
occurs v i a the t r i p l e t e x c i t e d manifold,
indeed v i a the n,ir* t r i p l e t , which r e s u l t s from the t r a n s i t i o n of one e l e c t r o n
from the oxygen n o r b i t a l to the ir* o r b i t a l , followed by a s p i n f l i p
system c r o s s i n g ) .
Figure
(inter-
A common p i c t u r e of the carbonyl n,ir* t r i p l e t i s shown i n
1.13.
t
mm
Figure
1.13
For most carbonyl compounds intersystem c r o s s i n g from the e x c i t e d s i n g l e t
29
t o the t r i p l e t s t a t e i s a v e r y e f f i c i e n t p r o c e s s .
The quantum y i e l d f o r
- 15 -
intersystem
c r o s s i n g of benzophenone i s 1.00.
With some carbonyl compounds
however, the r e l a t i v e energies of the e x c i t e d s t a t e s may
intersystem c r o s s i n g .
be unfavourable f o r
For example 2-naphthaldehyde, 9-anthraldehyde and
9-
48
tetracenealdehyde a l l f l u o r e s c e on i r r a d i a t i o n i n ethanol
intersystem c r o s s i n g .
indicating inefficient
I n non-polar s o l v e n t s the n -»• ir* t r a n s i t i o n i s s h i f t e d to
longer wavelengths and the v •*• it* t r a n s i t i o n to s h o r t e r wavelengths, and i n
heptane s o l v e n t 2-napthaldehyde and s i m i l a r aromatic aldehydes become
f l u o r e s c e n t with e f f i c i e n t intersystem
non-
crossing.
The commonly accepted p i c t u r e of the n, I T * e x c i t e d s t a t e of carbonyl
compounds, i n v o l v i n g promotion of an 'n' e l e c t r o n to an antibonding ir* o r b i t a l ,
29
r e s u l t s i n a lone e l e c t r o n l o c a l i z e d on the oxygen.
analogous to an ordinary alkoxy r a d i c a l .
reactions;
The s t a t e i s thus formally
T h i s analogy extends to observed
thus, alkoxy r a d i c a l s are known to a b s t r a c t hydrogen and add
to
o l e f i n s , r e a c t i o n s which f i n d t h e i r counterparts i n photoreduction and photo29 49 50
c y c l o a d d i t i o n r e a c t i o n s of carbonyl compounds.
'
'
The m a j o r i t y of known photochemical r e a c t i o n s of alkanones have been
1
c l a s s i f i e d under one of three r e a c t i o n t y p e s r ^
R
R
R
\
hu
( i ) cleavage o f the bond to the carbonyl
- Norrish type I cleavage:
+ group
R"
f
0
(ii)
intramolecular
(Norrish type I I ) or i n t e r m o l e c u l a r a b s t r a c t i o n of a
hydrogen atom by the carbonyl oxygen atom:
R
R'-H
+
L
H
H
•R-
\ /
c
!
J
/\
R
i
R
/
K
- 16 -
(ill)
cycle-addition to an unsaturated carbon-carbon l i n k a g e :
n
hu
An oxetane
c—o
R
3
\/
4
An oxetene
(unstable)
V
An o, B-unsaturated
compound
Aldehydes and aromatic ketones undergo r e l a t e d r e a c t i o n s and unsaturated
carbonyl compounds (conjugated and non-conjugated) undergo a wide v a r i e t y o f
cleavage, a b s t r a c t i o n , rearrangement and c y c l o a d d i t i o n r e a c t i o n s . The v a r y i n g
52 53 54
r e a c t i o n s a r e d i s c u s s e d i n standard t e x t s ,
r e l a t i n g t o carbonyl compound photochemistry
those by Swenton and Turro e t a l . ^
'
and t o p i c s s p e c i f i c a l l y
may be found i n reviews such a s
5
The types o f r e a c t i o n d i r e c t l y r e l e v a n t to these s t u d i e s a r e type 2
i n t e r m o l e c u l a r (photoreduction o f carbonyl) and type 3 (oxetane and p o l y oxetane formation).
chapters.
They w i l l be d i s c u s s e d i n more d e t a i l i n the appropriate
CHAPTER 2
Photoreductlve polymerization of aromatic bisketones
- 17 -
2.1.
Introduction
2.1.a.
H i s t o r i c a l background
The photoreductive coupling of benzophenone i n ethanol
i s a w e l l e s t a b l i s h e d r e a c t i o n (Figure 2.1) .
56
o r isopropanol
57
Reaction occurs by n,ir*
99
hv
isopropanol
i
i
OH
OH
F i g u r e 2.1
e x c i t a t i o n of benzophenone carbonyl followed by reduction and coupling of the
resultant ketyl radicals.
With benzophenone and isopropanol the y i e l d has
58
been reported to be q u a n t i t a t i v e
and the r e a c t i o n s shown i n F i g u r e 2.2 have
hv
ii
OH
CH,
I
3
+ H—C
+
OH
3
I
OH
I
CH,
r
>®-f-®
OH
OH
OH
H„C
3 \'X
C
C
OH
C
H
3
^
II
F i g u r e 2.2
^cT
^
^
^
-
- 18 -
been used to account f o r the observed p r o c e s s .
A more d e t a i l e d d i s c u s s i o n of
t h i s photoreduction w i l l be given i n 2.1.b.
At the beginning of t h i s decade the r e a c t i o n was a p p l i e d to the s y n t h e s i s
of polybenzopinacols from benzophenone-type aromatic diketones, according to
59—62
the scheme shown i n F i g u r e 2.3.
Higgins and co-workers i n 1970;
0
0
II
II
n Ar.C.Ar.C.Ar
The f i r s t r e s u l t s were p u b l i s h e d by
they attempted the photoreductive p o l y m e r i z a t i o n
OH
OH
I
—
•c
*
isopropanol/
cosolvent
Figure
Ar
I
Ar
- cAr
2.3
of m- and p-dibenzoylbenzene and 4,4<-dibenzoyldiphenylether ( p r e p a r a t i v e
method A, Table 2.1).
I n the same i s s u e of the same j o u r n a l Pearson and
59
Thiemann
d e s c r i b e d a s i m i l a r i n v e s t i g a t i o n of
(preparative methods D-F, Table 2.1).
weight oligomers.
p-dibenzoylbenzene
Both groups obtained only low molecular
Modifications introduced by Higgins' group (preparative
methods B, C) using an open system under a stream of nitrogen r a t h e r than a
c l o s e d v e s s e l under a nitrogen atmosphere and s h o r t e r i r r a d i a t i o n times gave
a s i g n i f i c a n t l y higher molecular weight polymer from 4,4'-dibenzoyldiphenylether.
Polymers from 4,4'-dlbenzoyldiphenylsulphide
/
4,4*-dibenzoyldiphenyl-methane
and -ethane were a l s o obtained by the modified procedures B,C, but m- and
p-dibenzoylbenzene
and 4,4'-dibenzoyldiphenyl f a i l e d to give polymers.
Higgins claimed t h a t use of a 450 watt lamp with Pyrex f i l t e r i n s t e a d of
a 100 watt long wavelength lamp allowed much s h o r t e r i r r a d i a t i o n times but
61
produced polymers of lower inherent v i s c o s i t y .
He suggested t h a t the lower
molecular weight polymers may have been a r e s u l t of cleavage of C-C bonds by
- 19 -
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- 22 -
6 1
the higher i n t e n s i t y i r r a d i a t i o n ; *
explanation may
t h i s seems u n l i k e l y and a more p l a u s i b l e
l i e i n the g r e a t e r heat output of the 450
watt lamp.
The
1
reported f a i l u r e of m- and p-dibenzoylbenzenes and 4,4 -dibenzoyldiphenyl to
form high polymers was attributed '" to a bathochromic s h i f t of the ir -»• I T *
6-
absorption i n going from benzophenone to these diketones, r e s u l t i n g i n overlap
I T * absorptions and l a c k of e f f i c i e n t hydrogen a b s t r a c t i o n from the
with the n
low-lying ir,ir* t r i p l e t .
Although l a t e r work v a l i d a t e s t h i s explanation i n the
26
case of 4,4'-dibenzoyldiphenyl i t seems l e s s p l a u s i b l e f o r the other monomers.
The higher molecular weight polymers produced by H i g g i n s
1
group, showed no
carbonyl absorptions ( c a . 1650 cm "S i n t h e i r i n f r a r e d s p e c t r a but low molecular
weight p o l y p i n a c o l s showed considerable r e s i d u a l carbonyl s t r e t c h , which was
60
attributed
to unreacted monomer or to such s t r u c t u r e s as the one shown i n
F i g u r e 2.4. , Strong bands around 3500 cm ^ were c h a r a c t e r i s t i c of the t e r t i a r y
OH
OH
OH
I
0
-
c
—
A
r
—
C
C
Ar
I
C-
6.
1-2
Figure
-OH
2.4
groups i n the p o l y p i n a c o l s . The i n f r a r e d s p e c t r a of the polymers were
compared with those of model p i n a c o l s obtained by photocoupling pbenzoyldiphenylether and p-benzoyldiphenylethane, and by coupling
p-benzoyldiphenylmethane with magnesium and i o d i n e .
I n f r a r e d s p e c t r a of the
model p i n a c o l s and the polymers were q u a l i t a t i v e l y s i m i l a r .
Likewise, infrared
s p e c t r a of oligomers from m- and p-dibenzoylbenzene were q u a l i t a t i v e l y s i m i l a r
to the i n f r a r e d spectrum of benzopinacol.
N.m.r. s p e c t r a of the oligomers from m- and p-dibenzoylbenzenes
4,4'-dibenzoyldiphenylether
60
and
showed a s m a l l peak a t S 5.3 assigned to
- 23 -
benzhydryl protons;
the higher molecular weight samples showed no benzhydryl
hydrogen i n t h e i r n.m.r. s p e c t r a .
Higgins^
1
has suggested t h a t i n p r e p a r a t i v e
methods B,C t h i s may be a r e s u l t o f i n c r e a s e d monomer c o n c e n t r a t i o n compared
to method A, and t h a t weaker reducing s o l v e n t s may a l s o y i e l d higher molecular
weight polymer.^
0
Pearson and Thiemann s t u d i e d the i r r a d i a t i o n o f p-dibenzoylbenzene i n
59
isopropanol i n some d e t a i l .
Under 'normal' i r r a d i a t i o n c o n d i t i o n s
(preparative method D, Table 2.1) a polymer comprising c a . 5 coupled monomer
u n i t s was obtained.
The n.m.r. spectrum o f t h i s polymer was assigned as
f o l l o w s : fi 1.3 ( s i n g l e t CH >, 6 2.4 (broad s i n g l e t OH), 6 3.0 (broad s i n g l e t
3
OH),
6 5.8 (very weak benzhydryl hydrogen), 6 7.8 ( m u l t i p l e t , aromatic hydrogens
The i n t e n s i t y o f the s i g n a l a t 6 5.8 i n d i c a t e d t h a t a t l e a s t h a l f the polymer
ends were capped with benzhydryl hydrogen (Figure 2.5, X = H)
OH
OH
F i g u r e 2.5
The r e l a t i v e i n t e n s i t i e s o f the s i g n a l s a t 6 5.8 and 6 1.3 suggested t h a t a
few polymer c h a i n s terminated w i t h i s o p r o p y l a l c o h o l groups (Figure 2.5,
X = (CH^)2
C0H
c y c l i c form.
) w h i l s t the remainder o f the polymer was designated t o be i n
When the r e a c t i o n was c a r r i e d out a t a higher temperature
(100°
p r e p a r a t i v e method E , Table 2.1) the product obtained was s a i d t o be capped
almost e x c l u s i v e l y with hydrogen, the n.m.r. s i g n a l a t 6 5.8 being much stronger
whereas t h e product obtained a t 25° ( p r e p a r a t i v e method F , Table 2.1) was
assigned a c y c l i c s t r u c t u r e s i n c e only aromatic (6 7-7.5) and OH (6 3.0) proton
- 24 -
n.m.r. s i g n a l s were observed.
I n these cases i n f r a r e d s p e c t r a o f the products
59
from p-dibenzoylbenzene showed the absence o f carbonyl groups.
59-61
Elemental analyses o f p o l y p i n a c o l s , where reported,
were sometimes
i n only f a i r agreement with the c a l c u l a t e d v a l u e s .
59
During i r r a d i a t i o n s o f m- and p-dibenzoylbenzenes
a y e l l o w colour has
59
been observed.
Pearson
has suggested t h a t t h i s i s due t o the intermediate
shown i n Figure 2.6 ( i n the case o f p-dibenzoylbenzene), the evidence on which
t h i s assignment was based being a long wavelength
OH
absorption a t 416.4 nm, the
OH
F i g u r e 2.6
n o n - r a d i c a l nature o f the intermediate (which showed no e . s . r . s i g n a l s ) and
its stability.
However m-dibenzoylbenzene could not form an analogous
quinone-dimethide s t r u c t u r e , which c a s t s doubt on t h i s r a t i o n a l i z a t i o n .
62
De Schryver and co-workers
reported t h a t s i g n i f i c a n t l y higher molecular
weight polybenzopinacols could be obtained by i r r a d i a t i o n o f degassed
i s o p r o p a n o l - d i c h l o r o m e t h a n e s o l u t i o n s o f bisbenzophenone a t 350 nm
(preparative method G, Table 2.1) .
No benzhydryl hydrogen s i g n a l appeared
62
i n the n.m.r. s p e c t r a o f the products,
d.p.'s ranging from 23 t o 70.
The r e s u l t s o f the work reviewed above a r e summarised i n Table 2.1.
The e f f e c t of s o l v e n t composition on the r e a c t i o n was examined by v a r i o u s
60,61,62
workers.
De Schryver reported t h a t the r a t e o f disappearance o f the
62
carbonyl f u n c t i o n a l i t y depends on the nature of the cosolvent;
f o r 0.05M
s o l u t i o n s o f 4,4'-dibenzoyldiphenylmethane a t 32°C, r e l a t i v e r a t e s f o r a 1:5
molar r a t i o o f isopropanol:-
c o s o l v e n t were, CHC1_ 1, C H_CH, 2.5 and benzene 4.
C
- 25 -
Higgins claimed t h a t a 50:50 mixture was most s a t i s f a c t o r y f o r the benzeneisopropanol s o l v e n t system, arguing t h a t i n c r e a s i n g the proportion of
isopropanol reduced monomer s o l u b i l i t y w h i l s t decreasing the proportion o f
isopropanol n e c e s s i t a t e d longer i r r a d i a t i o n t i m e s . ^
He reported t h a t f o r
p o l y p i n a c o l s prepared by method A (Table 2.1) i t made no d e t e c t a b l e d i f f e r e n c e
whether the s o l v e n t was neat isopropanol or 50:50 mixtures of THF
isopropanol, or benzene and ethanol, or benzene and
and
isopropanolthese
r e s u l t s are s u r p r i s i n g i n the l i g h t of the work reported by the B e l g i a n group.
As can be seen from the above review of the e a r l y p u b l i c a t i o n s i n t h i s
f i e l d there was some confusion and disagreement
between the v a r i o u s groups.
64
Work c a r r i e d out i n t h i s department
ambiguities.
was r e l e v a n t i n r e s o l v i n g some of the
The e s s e n t i a l f e a t u r e s of t h i s work are summarized i n Table
2.2.
Aromatic diketones were prepared by F r i e d e l - C r a f t s s y n t h e s i s and r i g o r o u s l y
purified.
Monomers were d i s s o l v e d i n mixtures of isopropanol and benzene
and oxygen was excluded from the s o l u t i o n s by bubbling nitrogen through f o r
about 30 mins.
I r r a d i a t i o n s were c a r r i e d out using a Rayonet
photochemical
r e a c t o r i n c o r p o r a t i n g RUL-3500 lamps which emit between 320o8 and 4000A*
with the g r e a t e s t i n t e n s i t y a t 3660A*.
T h i s work was c a r r i e d out s o l e l y to
check the p h o t o r e a c t i v i t y of the monomers and consequently a d e t a i l e d optimiz a t i o n of conditions was not undertaken,
however a number of u s e f u l p o i n t s
emerge from a c o n s i d e r a t i o n of the data presented i n Table 2.2.
the r e a c t i o n s c a r r i e d out using 1:1 benzene-isopropanol
Considering
mixtures, i t i s c l e a r
t h a t i n s e v e r a l cases s i g n i f i c a n t l y higher d.p.'s were obtained by Andrews
than those p r e v i o u s l y reported;
an improvement from d.p.
for example, i n the case of m-dibenzoylbenzene
3 to d.p.
17 was observed.
Since these r e a c t i o n s were
c a r r i e d out under apparently i d e n t i c a l c o n d i t i o n s the most l i k e l y cause o f
the observed d i f f e r e n c e must be the p u r i t i e s of monomer and/or s o l v e n t s and
the explanation advanced p r e v i o u s l y f o r the l a c k of r e a c t i v i t y of
- 26 -
s
id
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id
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G Oi
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Polypinacol
Code
Irradiation in
1:1 benzene:isopropanol
8
•
t
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CM
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CN
CM
in
rn
rH
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in
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Irradiation in
3 to 4:1 benzene:isopropanol
1
- 27 -
•0
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r»
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rH
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a
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- 28 -
m-dlbenzoylbenzene (namely, a bathochromlc s h i f t of the IT •* it* absorption and
i n e f f i c i e n t hydrogen a b s t r a c t i o n by the l o w - l y i n g
TT,TT*
t r i p l e t ) must be i n v a l i d .
T h i s i n t e r p r e t a t i o n i s confirmed by c o n s i d e r a t i o n of the u l t r a v i o l e t s p e c t r a
of aromatic diketones shown i n F i g u r e 2 . 7 . ^
v
L
\t
9
C O T
•5
X
o
i
230
,
250
1
270
J
0
1
290
Figure
r
310
1
330
1
350
1
370
M
n m
)
2.7
For the m a j o r i t y of diketones examined by Andrews the p o l y p i n a c o l s
p r e c i p i t a t e d from s o l u t i o n when a 1:1 benzene-isopropanol mixture was
whereas when a higher proportion of benzene was used the polymers
used
remained
i n s o l u t i o n and consequently a higher d.p. was g e n e r a l l y a t t a i n e d .
The b e s t r e s u l t s i n t h i s f i e l d have been achieved however by De Schryver
40
and co-workers
who adopted a new approach to the s u b j e c t .
They considered
how the photoreductive coupling of d i a r y l ketones was i n f l u e n c e d by the
d e t a i l e d mechanism f o r the photoreduction of benzophenone put forward by
- 29 -
Weiner i n 1971.
The cage r e a c t i o n reported by Welner, t h a t i s t h e combination
of a (C H ) COH and a (CH^COH r a d i c a l t o give the mixed p i n a c o l o f s t r u c t u r e
g
5
2
(CgHg) C(OH)C(OH)(CH ) , c o n s t i t u t e s a c h a i n terminating step i n t h i s context.
2
3
2
Such a complication could be e l i m i n a t e d i f a bisbenzhydrol (Figure 2.8) was
used as both a hydrogen donor and a monomer i n the polymerization, one would then
9^ 9
H— C - - @ — A r — C
OH
—H
OH
F i g u r e 2.8
expect higher molecular wieght polymers t o be obtained.
Further t h i s
approach allows the preparation o f a l t e r n a t i n g copolymers or homopolymers
by choice o f appropriate monomer p a i r s whereas one would expect t h a t the
i r r a d i a t i o n o f a binary mixture of bisketones i n the presence o f isopropanol
40
would l e a d t o s t a t i s t i c a l c o p o l y p i n a c o l s .
De Schryver and co-workers
prepared a number o f aromatic bisketonos and b i s k e t o t r i a z o l e s by w e l l
established routes.
bisbenzhydrols.
Reduction o f some of the diketones afforded the corresponding
I r r a d i a t i o n o f equimolar s o l u t i o n s (benzene solvent) o f b i s k e t o n e s /
bisbenzhydrols a t 350 nm y i e l d e d as expected high molecular weight p o l y p i n a c o l s .
Before i r r a d i a t i o n , oxygen was excluded from the s o l u t i o n s by degassing on a
vacuum l i n e .
R e s u l t s a r e summarized i n Table 2.3. I t can be seen t h a t the
bisketone/bisbenzhydrol system provides the most v a l u a b l e method f o r obtaining
good y i e l d s o f high molecular weight m a t e r i a l s .
I n some cases d.p.'s as high
as 430 were obtained.
On the other hand, the p h o t o l y s i s o f some binary mixtures o f aromatic
bisketones i n the presence o f isopropanol y i e l d e d s t a t i s t i c a l c o p o l y p i n a c o l s .
I n some favourable c a s e s , the n.m.r. spectrum o f the copolymers obtained
- 30 -
Table 2.3
40
Photopolymerizatlon of B i 9 a r y l k e t o n e - Bisbenzhydrol System
0
0
OH
Concentration
OH
b
d.p.
Cnl
430
0.36
Ketone
Hydrol
Ar
Ar'
(mole/litre )
time
A
A
0.300
4 days
1
1
0.170
5 days
A
10
0.013
4 days
A
E
0.170
5 days
0.21
A
P
0.100
4 days
0.08
K5
A
0.170
4 hrs
141,000
362
0.43
K6
A
0.170
5 hrs
140,000
354
0.43
Footnotes:
a
Irradiation
M
—n
174,000
0.18
93,000
102
0.33
a:
combined ketone/hydrol c o n c e n t r a t i o n
b:
measured on the high molecular weight f r a c t i o n obtained
by p r e c i p i t a t i o n
A:
Ar
1:
Ar =
10:
Ar
E:
Ar =
P:
Ar =
CH,
31
Table 2.3 contd.
N
K5
N
Ar
V
N
(CH„)
N
/
CH
CH
N ****
N
K6
Ar
N~(CH_)
CH
N
/
N
N
N
CH
- 32 -
showed three d i s t i n c t l i n k a g e s and from the i n f r a r e d spectrum
intensities
the copolymer's
composition and the number average length of the sequences could
be determined.
De Schryver's work provided two very important c o n c l u s i o n s :
i)
the photopolymerization o f b i s a r y I k e t o n e s i s h i g h l y a f f e c t e d
by every aspect o f the photoreduction o f the model ketones,
ii)
the bisarylketone/bisbenzhydrol system provides a means o f
overcoming the 'cage' r e a c t i o n which i s a c h a i n terminating r e a c t i o n ;
i t i s c l e a r l y the b e s t method f o r the s y n t h e s i s o f high molecular
weight p o l y p i n a c o l s .
2.1.b.
Some a s p e c t s o f r e l e v a n t photochemistry
2.1.b.i.
I n t r o d u c t o r y survey
The photoreduction o f carbonyl compounds i n s u i t a b l e hydrogen donating
67
s o l v e n t s has been widely i n v e s t i g a t e d f o r w e l l over h a l f a century
56
Ciamician and S i l b e r began r e s e a r c h i n the f i e l d .
since
Photoreductive coupling
has already been d i s c u s s e d b r i e f l y i n 2.1.a w i t h r e f e r e n c e t o the p r e p a r a t i o n
o f polybenzopinacols and a simple mechanism f o r the photoreduction o f
benzophenone i n isopropanol was given (see F i g u r e 2.2).
I n the presence o f a l k a l i , however, i t was d i s c o v e r e d t h a t benzhydrol
68
was formed,
and i n a s e r i e s o f photoreductions o f benzophenone and s u b s t i t u t e d
68
benzophenones containing a s m a l l amount o f sodium-2-propanolate, Bachmann
showed t h a t benzhydols could be obtained i n high y i e l d .
He proposed t h a t as
A
f a s t as the p i n a c o l was formed i t decomposed to benzhydrol ( i n the case o f
benzopinacol). However, the proposed mechanisms f o r the formation o f benzhydrol
69
from benzophenone have subsequently been questioned.
The most i n t e n s i v e l y s t u d i e d r e a c t i o n i s t h e a c t u a l photoreductive coupling
r e a c t i o n y i e l d i n g 1,2-ethane d i o l s .
Aldehydes
and ketones undergo the r e a c t i o n ,
ketones having r e c e i v e d by f a r the most a t t e n t i o n .
that yield
Some examples o f ketones
p i n a c o l s on a p r e p a r a t i v e s c a l e i n c l u d e , a p a r t from benzophenone,
6
- 33 -
4,4'-dimethoxybenzophenone,
acetophenone,
72
70
4,4'-dichlorobenzophenone,
2-, 3-, and 4 - a c e t y l p y r i d i n e s ,
73
70
3-benzoylpyridine,
74
and a - t e t r a l o n e .
Benzophenone i s the most thoroughly s t u d i e d ketone, y i e l d i n g
in quantitative y i e l d .
benzopinacol
The quantum y i e l d f o r the formation o f acetone i n
the photoreduction o f benzophenone i n isopropanol i s n e a r l y constant using
75
i r r a d i a t i o n a t s e v e r a l d i f f e r e n t wavelengths between 366 and 254 nm,
suggesting t h a t both n -*• I T * e x c i t a t i o n and TT -*• v* e x c i t a t i o n (of the benzene
29
chromophore) may u l t i m a t e l y b r i n g about r e a c t i o n .
Various s o l v e n t s have been used as hydrogen donors, i n p a r t i c u l a r
a l c o h o l s and alkylbenzenes.
76 77
'
Many comparisons o f s o l v e n t s have been made
with benzophenone as r e a c t i n g ketone.
Some quantum y i e l d s o f benzophenone
78
disappearance i n v a r i o u s s o l v e n t s a r e shown i n Table 2.4.
Table 2.4
Quantum Y i e l d s o f Benzophenone Disappearance
Solvent
Molar Concentration o f
Benzophenone
i n Hydrogen Donor Solvents
Quantum Y i e l d
of Disappearance
Water
lO"
4
0.02
Benzene
icf
2
0.05
Toluene
lo"
2
0.45
Hexane
ID"
2
- ID"
4
1.00
Ethanol
lo"
4
- icf
1
1.00
Isopropanol
io"
5
- ID"
1
0.80
Where the quantum y i e l d s o f benzophenone disappearance
t o 2.00
a r e almost zero
(water and benzene), bond energies with r e s p e c t t o hydrogen a b s t r a c t i o n a r e
high enough (> 100 k c a l mole "S to prevent hydrogen atom a b s t r a c t i o n by the
t r i p l e t with anything other than very low c o l l i s i o n a l e f f i c i e n c y .
77
In
71
- 34 -
hexane, toluene and ethanol, quantum y i e l d s are l e s s than or equal to u n i t y
77
and concentration Independent.
I t I s suggested t h a t a l l benzophenone
t r i p l e t s a b s t r a c t a hydrogen atom, the appropriate C-H bond energies i n
hexane and toluene being approximately 85 and 80 k c a l mole'
1
respectively.
The o v e r a l l quantum y i e l d s then depend on the thermal r e a c t i o n s o f the r a d i c a l
1
R formed on a b s t r a c t i o n from the s o l v e n t RH.
Reversion o f the primary
hydrogen a b s t r a c t i o n r e a c t i o n ( i . e . Ph &0H + R*
2
an o v e r a l l quantum y i e l d o f l e s s than u n i t y .
y i e l d s tend to a l i m i t i n g value of 2, R* [ i . e .
» PhjCO + RH) r e s u l t s i n
I n isopropanol where quantum
(CH^) C0H] t r a n s f e r s hydrogen
2
to benzophenone with the production of acetone and more Ph C0H.
2
Such a
t r a n s f e r i s e n e r g e t i c a l l y improbable i n the benzyl or hexyl r a d i c a l s from
toluene o r hexane.
Where ketones are not photoreduced
i n alcoholic solvents,
a more powerful hydrogen donor such as t r i - n - b u t y l s t a n n a n e may
79
photoreduction, as i n the case of 2-acetonaphthone.
66
A r e c u r r i n g problem
allow
i n mechanistic s t u d i e s o f benzophenone photoreduction
i n isopropanol was the f a i l u r e to d e t e c t the mixed p i n a c o l 2-methyl-l,1diphenyl-1,2-propanediol (Figure 2.9), whereas analogous cross-coupled
76
products were obtained f o r benzophenone photoreduction i n toluene and cumene,
0
T f
OH
3
OH
Figure
2.9
80
and primary a l c o h o l s o l u t i o n s .
Weiner has shown t h a t t h i s mixed p i n a c o l
i s i n f a c t produced i n the photoreduction of benzophenone i n isopropanol, and
under conditions where a l l f r e e k e t y l r a d i c a l s are s c a v e n g e d . ^
Thus, the
mixed p i n a c o l r e s u l t s from a cage r e a c t i o n and the o v e r a l l r e a c t i o n i s explained
- 35 -
by the modified sequence shown i n F i g u r e 2.10. The s i g n i f i c a n t f r a c t i o n o f cage
reaction
(0.11) r e q u i r e s t h a t , i n the p a i r o f r a d i c a l s comprising A
OH
+ (CH ) CHOH
3
0
O".^©
^
2
+
<
C a
)
3 2
(A)
CH.
^
C—CH
OH
3
OH
H
HC
CH
3
3
0
(CH ) COH +
3
2
OH
H,C
,CH.
3
(CH > COH +
3
3
c
2
*
OH
OH
OH
66
OH
OH
HC
3
OH
(B)
F i g u r e 2.10
& H
(where
- 36 -
the e l e c t r o n s p i n s are i n i t i a l l y p a r a l l e l ) , s p i n f l i p p i n g must occur i n some
r a d i c a l p a i r s p r i o r to d i f f u s i o n out of the s o l v e n t cage.
t h a t there has been much controversy
It. must be noted
over the nature o f intermediates
81
photoreduction o f benzophenones i n isopropanol.
t h a t the observed yellow intermediate
i n the
81 82
Filipescu
'
has proposed
has the s t r u c t u r e B (shown i n F i g u r e 2.10)
i n the case o f benzophenone and 4 - a l k y l s u b s t i t u t e d benzophenone photoreductions
81
i n isopropanol.
F o r benzophenone, F i l i p e s c u
suggested a r e a c t i o n scheme
shown i n Figure 2.11.
*
OH
+
^ <Q>~C-<g) +(CH ) 60H
(CH ) CHOH
3
3
2
2
>
B
(R=H)
l
B
+
QH
OH
Figure
OE
2.11
I t was proposed t h a t B y i e l d e d products v i a t h e dark r e a c t i o n shown
i n Figure 2.12.
OH
66
However, Weiner
s t a t e d t h a t the q u a n t i t a t i v e formation
C
"3 V/-3_.
„
j . ^ ^ X ^ S / ^ N
Ph-r-Cf*=V X.
0—H
J
0
r
0
c
§
d a r
/
\
Figure
*
>
reaction
2.12
Products
- 37 -
o f B from the p a i r Ph C(OH) + (CH ) COH i s i n c o n s i s t e n t w i t h the d e t e c t i o n
2
3
2
of the mixed p i n a c o l i n t h e product mixture.
W h i l s t observed yellow
c o l o u r a t i o n i n t h e r e a c t i o n may be due t o the presence o f B, W e i n e r ^
concluded t h a t the yellow intermediate cannot be transformed i n t o products
a t a r a t e c o n s i s t e n t with h i s e a r l i e r s t u d i e s .
The low e f f i c i e n c y o f photoreduction i n benzene has r e s u l t e d i n the
s o l v e n t being used i n many s e n s i t i z a t i o n experiments.
However, there i s a
low quantum y i e l d of reduction even with benzene s o l v e n t and observations
concerning the a c t u a l behaviour of benzophenone t r i p l e t s i n benzene s o l v e n t s
83
are confusing.
The value given f o r the quantum y i e l d o f disappearance o f
benzophenone i n Table 2.4 i s 0.05 and i s the upper l i m i t as determined by
Beckett and P o r t e r .
7 7
B e l l and L i n s c h i t z
8 4
estimated a quantum y i e l d o f 0.1
f o r formation o f the primary k e t y l r a d i c a l PhjCOH compared to 0.022 +_ 0.0O6
85
found by Buettner and Dedinas.
D e a c t i v a t i o n o f t r i p l e t s i n benzene has
86 87
'
to occur v i a formation o f b i r a d i c a l intermediates o f the
87
type shown i n F i g u r e 2.13 ( f o r benzophenone). Schuster and B r i z z o l a r a
have
been suggested
H
F i g u r e 2.13
pointed out t h a t t h i s provides a path f o r formation o f biphenyl according
t o the scheme i n F i g u r e 2.14.
3
The major products from i r r a d i a t i o n o f benzophenone i n benzene (6 x 10*" M
14
s o l u t i o n ) a t 290 nm a r e biphenyl and benzopinacol and
C s t u d i e s have
83
r e c e n t l y shown t h a t the biphenyl i s e s s e n t i a l l y s o l v e n t d e r i v e d .
Schuster
38
C
x2
C—O
6
H
H
2
H
H
OH0>
C
OH
F i g u r e 2.14
88
suggested
t h a t the quenching o f benzophenone t r i p l e t s i n aromatic s o l v e n t s
i n v o l v e s an i n t e r a c t i o n
i n c o r p o r a t i n g a t l e a s t p a r t i a l charge t r a n s f e r
from
ketone t r i p l e t as donor towards aromatic a s acceptor.
2.1.b.ii.
Spin f l i p p i n g and r e a c t i o n s w i t h i n the s o l v e n t cage
The photoreduction o f benzophenone by toluene and cumene i s known
76,89
to y i e l d t e r t i a r y a l c o h o l s ,
c r o s s coupling products r e s u l t i n g from the
combination o f the benzophenone k e t y l r a d i c a l and s u b s t r a t e r a d i c a l s
(Figure 2.15).
As a l r e a d y mentioned, most workers denied the e x i s t e n c e o f
such a product f o r the benzophenone/isopropanol system u n t i l Weiner^
i d e n t i f i e d the mixed p i n a c o l by a n a l y t i c a l g . l . c .
6
The 2-methyl-l,1-diphenyl-
1,2-propanediol has been obtained i n 18% y i e l d i n the e l e c t r o c h e m i c a l reduction
90
of benzophenone i n acetone-water mixture.
I r r a d i a t i o n o f benzophenone i n
methanol r e s u l t s i n the formation o f the mixed p i n a c o l and Mauser obtained
BO 91.
the 1,1-diphenylglycol (Ph C(0H)-C(0H)H ) i n 5% y i e l d . '
I n isopropanol,
2
the c r o s s p i n a c o l was estimated t o be p r e s e n t i n the product to the extent o f
92
11% by Weiner and l e s s than 4% by Gotzmer.
When camphorquinone was used to
- 39 -
OP
f
©O
S
o
OH
0
0 "«>
OH
OH
„ H
CH.
CH,
(trace)
(24%)
©4—r@
n
JO
0
9
CH
W
CH
3
Figure
(24%)
OH
^
CH
OH
3
CH
( 5 2 % )
3
2.15
scavenge a l l the f r e e k e t y l r a d i c a l s which d i f f u s e out of the s o l v e n t cage,
i r r a d i a t i o n of benzophenone i n isopropanol
with benzhydrol.
be 0.8.
y i e l d e d the c r o s s p i n a c o l along
The r a t i o of benzhydrol to the c r o s s p i n a c o l was
found to
T h i s i s good evidence t h a t the mixed p i n a c o l r e s u l t s , a t l e a s t i n
*
p a r t*, from
a cage r e a c t i o n .66,92
fcJ
The i r r a d i a t i o n of benzhydrol i n acetone generated the same r a d i c a l s as
the benzophenone-isopropanol system.
However, a g r e a t e r amount o f the mixed
p i n a c o l i s found among the products of the former r e a c t i o n , p o s s i b l y because
of d i f f e r e n c e s i n the s o l v e n t s forming the cage.
Both systems show the same
81
l i g h t - a b s o r b i n g intermediate.
Complete reduction of the carbonyl group occurs when a benzophenone
k e t y l r a d i c a l a b s t r a c t s a hydrogen atom from an acetone k e t y l r a d i c a l .
A b s t r a c t i o n of a hydrogen atom from a benzophenone k e t y l r a d i c a l by
acetone k e t y l r a d i c a l i s estimated
an
to be n e g l i g i b l e s i n c e the quantum y i e l d
f o r benzophenone disappearance i s high (up to 2 ) ;
a l s o the e n e r g e t i c s of the
process agree with t h i s conclusion s i n c e the 0-H bond s t r e n g t h i n benzophenone
- 40 -
k e t y l r a d i c a l i s 35 k c a l mole
whereas the bond strength i n an acetone k e t y l
1
r a d i c a l i s only 20 k c a l mole .
The f a c t t h a t i n the i r r a d i a t i o n o f benzophenone
93
in
(-)2-butanol
the recovered s o l v e n t i s not racemized could be considered
as evidence i n favour of t h e above hypothesis.
Unlike benzophenone which undergoes a one e l e c t r o n reduction process t o
y i e l d p i n a c o l , photolyses o f d i ( 2 - p y r i d y l ) k e t o n e , d i ( 4 - p y r i d y l ) k e t o n e and
4-pyridyl-phenylketone i n isopropanol l e a d to the formation o f the corresponding
dipyridylmethanols and 4 - p y r i d y l p h e n y l c a r b i n o l a s t h e only products i n each
94 95
case.
'
I t has been shown t h a t the lowest n,ir* t r i p l e t s t a t e o f these
ketones i s involved i n the hydrogen a b s t r a c t i o n r e a c t i o n . The complete
reduction o f the carbonyl chromophore i n the h e t e r o c y c l i c ketones may be
r a t i o n a l i z e d by the d i f f e r e n c e i n e l e c t r o n e g a t i v i t y between nitrogen and
carbon.
Since there i s a higher p r o b a b i l i t y o f f i n d i n g the e l e c t r o n o f the
k e t y l r a d i c a l on nitrogen, the t r a n s f e r of a hydrogen atom from the acetone
k e t y l r a d i c a l y i e l d s the conjugated enol which r e v e r t s t o the c a r b i n o l by
prototropism (Figure 2.16) .
OH
Ph— C — < — >
Thus i t can be seen t h a t the r e d u c i b i l i t y o f
OH
Ph—
C
=
GH
^ )
N
+ Me C0H — ^ P h — C
2
a =
OH
^ ^ N H + Me C0-> P h — C —
2
F i g u r e 2.16
carbonyl compounds depends on the nature o f the carbonyl double bond and i t s
s u b s t i t u e n t s , and i s s e n s i t i v e t o s t r u c t u r e m o d i f i c a t i o n s which a f f e c t the
e l e c t r o n d i s t r i b u t i o n , p a r t i c u l a r l y the u - e l e c t r o n d e r e a l i z a t i o n .
Similarly,
aromatic ketones whose t r i p l e t s t a t e s possess pronounced ir,ir* c h a r c t e r a r e
- 41 -
more s u s c e p t i b l e to complete reduction.
I n the case of the photoreductive
coupling of blsbenzophenones, t h i s imposes some l i m i t s on polymer formation.
2.1.b.iii.
The yellow Intermediate observed I n the photoreduction of
aromatic ketones
As has been pointed out already the formation of a yellow intermediate
a y QC
i s a c h a r a c t e r i s t i c f e a t u r e of the photoreduction of benzophenone i n a l c o h o l .
S e v e r a l explanations have been put forward to account f o r t h i s intermediate,
and these were reviewed by F i l i p e s c u who
concluded, mainly on the b a s i s of
s p e c t r o s c o p i c evidence t h a t the most l i k e l y s t r u c t u r e was the conjugated
81
enol d i s c u s s e d e a r l i e r (Figure 2.10).
Nevertheless a d e f i n i t i v e proof of
the s t r u c t u r e of t h i s frequently observed intermediate has eluded the many
i n v e s t i g a t o r s who have worked on the problem.
I n the photoreduction o f heteroaromatic ketones intermediates have a l s o
been detected s p e c t r o s c o p i c a l l y , f o r example d i ( 4 - p y r i d y l ) k e t o n e g i v e s an
94
i n t e n s e l y absorbing s p e c i e s on photoreduction i n isopropanol.
However, the
d e t e c t i o n of intermediates during photoreduction i s by no means u n i v e r s a l ,
f o r example no intermediate could be detected during the photoreduction o f
94
di(2-pyridyl)ketone
and the yellow colour a s s o c i a t e d w i t h the photoreduction
97
of benzophenone i n isopropanol i s not observed when benzhydrol i s the donor.
Despite the d i f f i c u l t y i n unequivocally i d e n t i f y i n g the i n t e r m e d i a t e ( s )
involved i n photoreduction the s t r u c t u r e proposed by F i l i p e s c u seems a
reasonable candidate s i n c e there i s a body of information i n the l i t e r a t u r e
which can be r a t i o n a l i z e d i n terms of i n i t i a l coupling between the r a d i c a l
derived from the hydrogen donor and the benzophenone k e t y l r a d i c a l , such
coupling o c c u r r i n g a t the ortho or para p o s i t i o n s of a phenyl r i n g . Decafluoro98
photoreduced i n isopropanol e x c l u s i v e l y to decaf luorobenzhydrol (<j> = 0 . 6 ) .
benzophenone provides a good example; t h i s ketone, u n l i k e benzophenone i s
Although the primary photochemical step should be a hydrogen a b s t r a c t i o n by
- 42 -
the n,ir* t r i p l e t s t a t e s i n c e t h i s ketone shows the same p r o p e r t i e s as
benzophenone ( s i m i l a r absorprion spectrum, i d e n t i c a l n,ir* lowest t r i p l e t
energy, and e f f i c i e n t i n t e r s y s t e m c r o s s i n g ) .
The f a i l u r e to i s o l a t e the
p i n a c o l may a r i s e from t h e i n s t a b i l i t y o f t h e p e r f l u o r o p i n a c o l i t s e l f .
99
Dedinas
reported t h a t t h e photoreduction o f decafluorobenzophenone i n
cyclohexane y i e l d s , i n a d d i t i o n to the c r o s s coupling product, ortho and para
s u b s t i t u t e d nonafluorobenzophenones.
The formation o f these products was
r a t i o n a l i z e d as shown i n F i g u r e 2.17.
F
(C F ) CO
6
5
2
+
C H
6
1 2
-^^ ) pC
5
2
6 H l i n
OH
—
F
0
F 4-^-F
5
C H,,
n
'6 ll
+ C f i
F
/
C
5
V
C
F
F
F
H
hv
<c F ) co q
6
5
2
+
'
( C
F
C
OH
OH
OH
H
6 5»^" 6 11
OH
C.H
6 11
C.H
6 11
°
I
H
6 l l - ^ . r F C — ( 0 ) - 6H11
H
6^
C
C
H
F
F
+ HF
Figure 2.17
I r r a d i a t i o n o f acetophenone i n a mixture o f e t h e r and cyclohexane g i v e s
acetophenone p i n a c o l s i n good y i e l d , together with 2-butanol d e r i v a t i v e s and
100
a p - s u b s t i t u t e d acetophenone
(Figure 2.18).
The acetophenone k e t y l r a d i c a l
and ether r a d i c a l combine t o y i e l d the 2-butanol d e r i v a t i v e s i n a manner
analogous t o the formation o f 1,1,2-triphenylethanol i n the photoreduction
o f benzophenone i n toluene.
The formation o f the p - s u b s t i t u t e d acetophenone
can be r a t i o n a l i z e d by p o s t u l a t i n g t h a t the d e l o c a l i z e d k e t y l r a d i c a l i s
attacked a t the para p o s i t i o n by t h e ethoxy e t h y l r a d i c a l t o give t h e e n o l i c
intermediate which would be expected t o be o x i d i z e d by a i r t o y i e l d the observed
product.
- 43 -
1
\
CH
7 ._ . .
/>~A" 3
n
v„.
hv
CH,
CH,
^
CH
I
I 3
CH,
CHCH
CH,
, 3 , 3
OH
nil
OH
JQ
j—
O
OH
u
H
°
r>
O
(12%)
H,C
\
V
OH
HO
3
'
CH
H
3
/
HC
3
(3%)
OEt
/
+ H C~CH-OEf
E t
OEt
H C
H
3""~<0)~|
CH.
3
Figure 2.18
The reduction o f benzophenone i n water I s a l s o c o n s i s t e n t
with t h i s p a t t e r n
101,102
of r e a c t i o n .
I n the absence of oxygen benzopinacol i s obtained whereas
i n aerated s o l u t i o n hydroxybenzophenones are formed (<}> = 0.02) , and a t r a n s i e n t
assigned as a hydroxy1 r a d i c a l adduct o f benzophenone was observed.
2.1.b.iv.
Complex formation between k e t y l r a d i c a l and ketone
The f a t e o f the benzophenone k e t y l r a d i c a l and the acetone k e t y l
radical
which d i f f u s e out of the s o l v e n t cage has been explained i n terms of two
reactions.
Hydrogen atom t r a n s f e r from the acetone k e t y l r a d i c a l to a ground
s t a t e benzophenone molecule r e s u l t s i n the formation o f a new benzophenone
ketyl radical.
Benzopinacol i s then formed from the d i m e r i z a t i o n o f two
benzophenone k e t y l r a d i c a l s .
T h i s mechanism appears p l a u s i b l e
k e t y l r a d i c a l has a high p r o b a b i l i t y
which i s i n e x c e s s .
s i n c e the acetone
of encountering a benzophenone molecule
The disappearance o f the benzophenone k e t y l
i s found from e l e c t r o n
second order k i n e t i c s .
radical
spin resonance and f l a s h p h o t o l y s i s s t u d i e s to follow
Accumulating evidence shows t h a t the photoreduction o f
- 44 -
benzophenone i n benzhydrol does not always proceed through a d i r e c t combination
of the two primary r a d i c a l s ;
i n the photochemical r e a c t i o n between an excess
of deuterated benzophenone and non-deuterated benzhydrol, perdeuterated,
h a l f - d e u t e r a t e d and non-deuterated benzopinacols were not obtained i n the
1 0
expected s t a t i s t i c a l d i s t r i b u t i o n ; " ^
pinacol
obtained.
i n p r a c t i c e l a r g e amounts o f benzo-
small q u a n t i t i e s of mixed p i n a c o l d ^
Q
and p i n a c o l d
Q
were
The r e s u l t can be r a t i o n a l i z e d by a r e v e r s i b l e hydrogen atom
exchange o c c u r r i n g i n a benzophenone-ketyl r a d i c a l complex (Figure 2.19).
J3>
H—0—C 9
JO
»;c—OH
o
>0
F i g u r e 2.19
S i n c e deuterated benzophenone was used i n e x c e s s , the e q u i l i b r i u m was
d r i v e n towards the d i r e c t i o n o f the deuterated k e t y l r a d i c a l , r e s u l t i n g i n a
g r e a t e r amount of benzopinacol
being formed.
103
Schenck
reported t h a t the i r r a d i a t i o n o f a s o l u t i o n o f benzophenone-d^
( i n excess) and benzopinacol-d
Q
i n benzene r e s u l t e d i n the formation o f
benzopinacol-djQ e x c l u s i v e l y (Figure 2.20).
T h i s r e a c t i o n appears somewhat
curious s i n c e benzopinacol i s known to be i n e r t to benzophenone n,ir* t r i p l e t
104
s t a t e a t the u s u a l wavelength
(350 nm) employed i n the photoreduction.
10
The wavelength s e l e c t e d by Schenck was not s p e c i f i e d ; " * i t i s , however,
probable t h a t s h o r t wavelength u l t r a v i o l e t l i g h t was used, s i n c e the C-C
bond i n the p i n a c o l can be c l e a v e d by i r r a d i a t i o n a t 240 nm, or t h e r m a l l y .
One way o f i n t e r p r e t i n g the r e s u l t s i s i n terms of the e q u i l i b r i a
0
- 45 -
6
K
99
o-h-o
^
or
OH
OH
Figure
shown i n F i g u r e
OH
OH
2.20
2.21.
240 nm
OH
OH
OH
C—0-H— 0=C
H-0
Se5
D
fe 5
D
C
C
6
D
5 - ^
OH
Figure
F u r t h e r reports by F r a n z e n
1 0 5
6°5 — C I
OH
C D
,6 5
:
D
6 5
OH
2.21
tend to i n d i c a t e
t h a t the p i n a c o l does not
form from a d i r e c t combination o f the primary k e t y l r a d i c a l s .
The photoreduction
o f benzophenone i n the presence o f benzhydrol y i e l d s two i d e n t i c a l
radicals
14
which however can be d i s t i n g u i s h e d by
C labelling.
Franzen i r r a d i a t e d a
- 46 -
benzene s o l u t i o n containing benzophenone
C and benzhydrol
C;
a mixture
o f benzophenone and benzopinacol as shown i n F i g u r e 2.22 was obtained.
+ H — r 14
-
C—O
c==o *
14
12
c
a of
OH
OH
OH
Ti2
I 12
i;
c-
OH
OH
-c
Figure
The
^0>
2.22
experimental r e s u l t s are c o n s i s t e n t with a redox r e a c t i o n between benzophenone
and diphenylhydroxymethyl
radical.
The r a d i o a c t i v i t i e s o f the p i n a c o l s
formed were found to be l e s s than h a l f the a c t i v i t i e s of the i n i t i a l
benzhydrols.
Also, the r a d i o a c t i v i t y of the p i n a c o l s was found to decrease
12
with i n c r e a s i n g benzophenone
or
O
+
14
H-c
OH
OH
9
Oh
- r
OH
or
OH
T 12
l
^0>
C-
OH
OH
12
-=
C—0—H
Figure
12
OH
I 12
12
r=0---- H—0 — O
9 9.
99.
14
C=0
C concentration (Figure 2.23).
2.23
Po
14
C
14
OH
- 47 -
Furthermore, the e x i s t e n c e of the hydrogen atom exchange between
benzophenone and a k e t y l r a d i c a l has been e s t a b l i s h e d by e l e c t r o n s p i n
resonance s t u d i e s .
form a
1 0 3
The acetone k e t y l r a d i c a l would a l s o be expected to
hydrogen bridge w i t h a b a s i c oxygen atom.
I n t h i s sense, a k e t y l
r a d i c a l / k e t o n e complex should be envisaged to r a t i o n a l i z e the hydrogen atom
t r a n s f e r i n the photoreduction of benzophenone i n i s o p r o p a n o l
a.
C=0-
/
CH
/
C— 0- H—- 0 = C
H-0-C*
\
or
Of
CH
Figure
2.1.b.v.
1 0 3
(Figure 2.24).
CH 3
CH
2.24
E f f e c t o f s t r u c t u r e on photoreduction of aromatic ketones
Not a l l ketones are photoreduced
to g i v e p i n a c o l s .
The r e a c t i v i t y of
aromatic ketones has been r a t i o n a l i z e d i n r e l a t i o n to the lowest l y i n g
t r i p l e t l e v e l s of the k e t o n e .
1 0 6
When the lowest l y i n g t r i p l e t l e v e l has
n,w* c h a r a c t e r , ketones are g e n e r a l l y r e a d i l y r e d u c i b l e with quantum y i e l d s
f r e q u e n t l y approaching u n i t y .
Ketones which possess a T T , T T * c o n f i g u r a t i o n f o r
the lowest t r i p l e t s t a t e , however, are much l e s s disposed towards
an example being p-phenyl benzophenone.
photoreduction,
I t i s suggested t h a t the higher
e f f i c i e n c y i n photoreduction processes of the n,ir* s t a t e may
a r i s e from the
h i g h l y l o c a l i s e d n e l e c t r o n of the oxygen, whereas i n the ir,ir* t r i p l e t
state
the unpaired e l e c t r o n s are more d e l o c a l i z e d and hydrogen a b s t r a c t i o n i s thus
5 5
more e n d o t h e r m i c . '
1 0 7
(Figure 2.25.)
A t h i r d type of p o s s i b l e lowest l y i n g t r i p l e t s t a t e i s a charge t r a n s f e r
106
state.
I n p-aminobenzophenone represented by the formula DRA,
where D i s
48
Odd e l e c t r o n s
delocalized
over ir system
Highly r e a c t i v e
centre i n
hydrogen a b s t r a c t i o n
F i g u r e 2.25
the electron-donating amino group, R i s the aromatic r i n g , and A i s the
e l e c t r o n - a c c e p t i n g carbonyl group, three important c h a r g e - t r a n s f e r s t a t e s
+
may be considered.
These a r e DR A~ corresponding
+
o f benzophenone, D R A corresponding
t o the c h a r g e - t r a n s f e r s t a t e
t o the c h a r g e - t r a n s f e r s t a t e o f a n i l i n e
+
and D RA . The three s t a t e s i n t e r a c t with one another t o give a new low energy
c h a r g e - t r a n s f e r (C-T) s t a t e not present i n benzophenone o r a n i l i n e .
The
negative charge on the oxygen i n t h i s C-T s t a t e r e s u l t s i n v i r t u a l l y zero
r e a c t i v i t y towards hydrogen atom a b s t r a c t i o n .
P o l a r s o l v e n t s such as
isopropanol should enhance i n t r a m o l e c u l a r c h a r g e - t r a n s f e r from the e l e c t r o n
donating group t o the carbonyl group, thus helping t o decrease the energy o f
such c h a r g e - t r a n s f e r s t a t e s below t h a t o f the n,ir* s t a t e .
Thus i n isopropanol
where the C-T s t a t e o f p-aminobenzophenone i s the lowest l y i n g t r i p l e t
the quantum y i e l d o f p i n a c o l i z a t i o n i s zero.
cyclohexane,
state,
I n a l e s s p o l a r s o l v e n t such as
where the c h a r g e - t r a n s f e r t r i p l e t i s no longer the lowest l y i n g
t r i p l e t , p h o t o p i n a c o l i z a t i o n o f p-aminobenzophenone has been shown t o occur
108
q u i t e r e a d i l y with a quantum y i e l d o f 0.2.
p-Hydroxybenzophenone has been
- 49 -
reported t o behave i n a s i m i l a r manner, the molecule r e a c t i n g i n the b a s i c
form i n the e x c i t e d s t a t e where the pK o f i t s protonation e q u i l i b r i u m i s much
lower than i n the ground s t a t e .
I n accord with t h i s theory aminobenzophenones
can be reduced i n isopropanol when converted t o t h e i r onium s a l t s .
However,
1 0
many o f these r e s u l t s have r e c e n t l y been questioned and a r e now s u s p e c t . ^ '
1 1 0
Thus i n r e l a t i o n t o s o l v e n t e f f e c t s on the s u b s t i t u t e d benzophenones,
although the ketones are u n r e a c t i v e i n isopropanol, but r e a c t i n cyclohexane,
the p r o c e s s , i n f a c t does not appear t o i n v o l v e hydrogen atom a b s t r a c t i o n leading
109
to p i n a c o l s .
Pitts
s t a t e s t h a t no p i n a c o l i s formed on i r r a d i a t i o n o f
p-aminobenzophenone i n cyclohexane.
He emphasizes t h a t spectrophotometric
methods o f a n a l y s i s have f r e q u e n t l y been employed i n studying benzophenones
and t h a t these methods i n v o l v e disappearance o f r e a c t a n t r a t h e r than
o f product.
appearance
Thus a l t e r a t i o n s i n r e a c t i o n paths a r i s i n g from u n c o n t r o l l e d
environmental changes and l e a d i n g t o products other than p i n a c o l s may not be
observed.
P i t t ' s contention i s underlined i n s t u d i e s reported by C o h e n
1 1 0
of s o l v e n t e f f e c t s on t h e i s o m e r i z a t i o n of t r a n s - s t i l b e n e i n the presence of
benzophenone and aminobenzophenones, he suggested t h a t t h e f a i l u r e o f paminobenzophenone t o photoreduce
i n p o l a r s o l v e n t s r e s u l t s from e s s e n t i a l l y
the complete absence o f t r i p l e t s r a t h e r than the c h a r g e - t r a n s f e r s t a t e i t s e l f
being u n r e a c t i v e .
P i n a c o l s may only be i s o l a t e d f o l l o w i n g photochemical reduction o f a r y l
ketones i n isopropanol, i f the p i n a c o l s a r e themselves s t a b l e i n i r r a d i a t e d
67
acetone s o l u t i o n s .
Thus 9,9'-dihydroxy-9,9'-bixanthene i s converted i n t o
70
xanthen-9-one i n s u n l i g h t ,
and correspondingly xanthen-9-one i s not
converted t o the p i n a c o l on i r r a d i a t i o n i n isopropanol (Figure 2.26).
Ortho s u b s t i t u t e d aromatic ketones, o r those with other s u b s t i t u e n t s
which can form a six-membered r i n g , hydrogen bonded to the carbonyl oxygen,
may tautomerize i n an i n t r a m o l e c u l a r hydrogen a b s t r a c t i o n r e a c t i o n .
Thus
- 50 -
CH
OT l O
H
HO
HO
H.C
\/
CH
C
II
H.C
00®
3
CH
\CH/
OH
Figure 2.26
2-methylbenzophenone forms an enol under the i n f l u e n c e o f u l t r a v i o l e t l i g h t ,
111
to the complete e x c l u s i o n o f photoreduction. "
2.1.b.vi.
S t e r i c e f f e c t s on photoreduction
The e x c i t e d ketone molecule must come i n t o c l o s e contact with the a l c o h o l
molecule i n order f o r the a b s t r a c t i o n o f the a-hydrogen t o take p l a c e , and
any bulky s u b s t i t u e n t s i n the aromatic ketone o r a l c o h o l which are c l o s e t o
the r e a c t i o n centre could hinder the i n t e r a c t i o n o f the r e a c t a n t s and lower
the r a t e o f hydrogen a b s t r a c t i o n .
The p h o t o l y s i s o f a l k y l p h e n y l ketone i n isopropanol-benzene, y i e l d s a
mixture o f acetone, d l and meso p i n a c o l s and the corresponding hydrols
with
112
•acetone
=
•pinacol
+
•hydrol*
^
*
u a n t u o
v
i
e
l
d
f
o
r
h
v
d
r
o
1
formation i s
found t o i n c r e a s e while t h a t o f p i n a c o l formation and the r a t e constant f o r
hydrogen a b s t r a c t i o n decrease w i t h a - s u b s t i t u t i o n becoming b u l k i e r (Table
2.5).
- 51 -
112
^
Table 2.5
Comparative photolyses o f some a l k y l p h e n y l ketones
0
OH
OH
OH
Rate constant
6,
R
pinacol
Rate constant I n
I n isopropanol
*
*hydrol
k M
r
- 1
sec"
2,4-dimethyl-
1
3-heptanol
k M
_ 1
r
-CH
3
-CH_CH,
2 3
-CH(CH )
3
-C(CH )
3
2
3
-0
sec"
0.34
0.007
7.5 x 1 0
5
2.8 x 1 0
5
0.19
0.033
4.4 x 1 0
5
2.5 x 1 0
5
0.07
0.049
1.3 x 1 0
5
0.5 x 1 0
5
0.00
0
0.20
unknown
1
c
1.0 x 10
The I d e n t i c a l r a t e constant f o r t r i p l e t decay k ( = 3 x 10
d
sec
) found f o r the
ketones i n Table 2.5 suggests t h a t I n c r e a s e d s t e r l c hindrance makes hydrogen
a b s t r a c t i o n more d i f f i c u l t .
i t y i e l d s benzaldehyde
abstraction.
t-Butylphenylketone does not undergo photoreduction,
i n s t e a d by an a-cleavage followed by hydrogen
Ortho s u b s t i t u t e d benzophenones a l s o f a i l to p i n a c o l i z e ;
although orthomethylbenzophenone i s photostable prolonged i r r a d i a t i o n o f
2,4,6-trimethylbenzophenone i n isopropanol l e a d s to 2,4,6-trimethylbenzhydrol
„ „j
* - 113,114
as the reduction product.
The s o l v e n t can a l s o c o n t r i b u t e to s t e r i c hindrance.
The lower r a t e
constant f o r hydrogen a b s t r a c t i o n i n 2,4-dimethyl-3-heptanol (Table 2.5)
52 -
r e l a t i v e to isopropanol, r e f l e c t s a s u b s t a n t i a l decrease i n r e a c t i v i t y .
The
decreasing r a t e o f benzophenone photoreduction i n going from isopropanol
( r e l a t i v e r e a c t i v i t y 1.0), through m e t h y l - t - b u t y l c a r b i n o l (0.90), methyli s o b u t y l c a r b i n o l (0.39) to methylneopentylcarbinol (0.18), has been a t t r i b u t e d
to s t e r i c hindrance as s o l v e n t chain branching
2.1.b.vii.
increases.
1 1 5
'
1 2 6
The temperature e f f e c t on photoreduction
For aromatic ketones p o s s e s s i n g n e a r l y degenerate n,ir* and I T , i r *
triplet
s t a t e s , the r e l a t i v e populations of these s t a t e s a t thermal e q u i l i b r i u m are
given by the Boltzmann d i s t r i b u t i o n
N(n,ir*)
N(ir,ir*)
AE
T
_
e
- ^T
RT
being the energy gap s e p a r a t i n g the two s t a t e s .
i n t e n s i t y o f a non-conjugated
The
phosphorescence
bichromophoric system such as the e s t e r shown
i n F i g u r e 2.27 i s approximately the sum of the phosphorescence
w
w
II
of benzophenone
II
E
Figure
T
= 2 kcal
mol"
1
2.27
and t r i p h e n y l e n e i n a r a t i o l J l g = 1-5 ut 77K.
At room temperature the r a t i o
T
86
I :I
T
B
= 0.20.
The r e l a t i v e population of benzophenone t r i p l e t i n c r e a s e s
v i a thermal a c t i v a t i o n and the emission occurs more r a p i d l y from the s h o r t lived n,IT* t r i p l e t .
I t i s t h e r e f o r e expected t h a t f o r aromatic ketones
e x h i b i t i n g a lowest n,ir* t r i p l e t with a nearby n i r * t r i p l e t , the r e a c t i v i t y
f
towards hydrogen a b s t r a c t i o n w i l l i n c r e a s e w i t h i n c r e a s i n g temperature.
The
- 53 -
i n c r e a s e i n the r a t e o f hydrogen a b s t r a c t i o n with temperature when
2-acetonaphthone i s i r r a d i a t e d i n ethanol could be due to a s i g n i f i c a n t
i n c r e a s e of the n,ir* t r i p l e t p o p u l a t i o n .
1 1 7
On the other hand, the use of high temperatures may have a dramatic
e f f e c t on the f i n a l products.
I r r a d i a t i o n o f benzophenone i n isopropanol a t
s u f f i c i e n t l y high temperatures produces i n c r e a s i n g amounts o f benzhydrol;
a t 150°C, benzhydrol becomes n e a r l y the e x c l u s i v e product, r e s u l t i n g from the
118
d i s p r o p o r t i o n a t i o n of two benzophenone k e t y l r a d i c a l s .
2.1.b.viii.
Photoreductlve a d d i t i o n o f ketones to methylene groups
Carbonyl compounds may undergo photoaddition to methylene groups adjacent
to double bonds or aromatic systems.
Benzophenone has been reported to r e a c t
119
with diphenylmethane i n s u n l i g h t to form 1,1,2,2-tetraphenylethanol
whereas
i r r a d i a t i o n of benzophenone with bis-(4-methoxyphenyl)methane g i v e s the
c a r b i n o l and symmetrical dimers of the r a d i c a l s i n v o l v e d i n the r e a c t i o n
Figure 2.28).
9 9H0>
C3 CO
9H0>
< \ P . .
!H-C
!—«"•-_
C
O
H
OH
+ B CO-^-CB -^-OCH3—»
3
2
9
@ - C
OH
H.CO
OCH
99
+
H
H—C
OH
H,CO
OCH
Figure
OH
2.28
H
f-Q-oca
3
D
OCH
1 2 0
- 54 -
Transannular i n t e r a c t i o n between the e x c i t e d carbonyl group of c y c l o dodecanone and one of the n e a r e s t methylene groups, with i n t r a m o l e c u l a r
121
c y c l i z a t i o n , yields a t e r t i a r y alcohol
(Figure 2.29).
Many other examples
OH
h\>
Figure
CO
2.29
122
of such photoadditions may be found i n the l i t e r a t u r e .
Photoreductive
a d d i t i o n of benzophenone to diphenyl methane w i l l be d e a l t with i n more d e t a i l
i n S e c t i o n 2.2 of t h i s t h e s i s .
2.I.e.
O b j e c t i v e s o f the study
The photoreductive polymerization of aromatic bisketones has been
thoroughly i n v e s t i g a t e d and high molecular weight polybenzopinacols have been
s u c c e s s f u l l y prepared.
The following s e c t i o n s d e s c r i b e attempts to extend
t h i s area of s y n t h e t i c organic photochemistry.
Section 2.2 i s concerned with an i n v e s t i g a t i o n of the p o s s i b i l i t y of
preparing poly(pentaphenylglycerols) and, e v e n t u a l l y , higher
analogues
(see s e c t i o n 1.6) by photoreductive p o l y a d d i t i o n o f bisbenzophenones to
s u i t a b l e hydrogen donors as i l l u s t r a t e d i n F i g u r e 2.30.
For such a process to
occur the requirements would be:
i)
i n i t i a l e x c i t a t i o n o f the carbonyl chromophore by 350 nm u l t r a v i o l e t
light,
ii)
a b s t r a c t i o n of a t e r t i a r y hydrogen by the photoexcited carbonyl
r e s u l t i n g i n the formation of the two primary r a d i c a l s shown i n
F i g u r e 2.31, and
- 55 -
c—
I
I
OH
OH
- c--Ar"
I
C—Ar—(
OH
OH
m
•cI
hv
solvent
-Ar'-f— C—f- H
-C—
-Ar
m
Ar'-
-C-
I
I
OH
L OHJm OH
• C-
I
OH
m
OH
m
where m > 2
F i g u r e 2.30
111)
combination o f the two primary r a d i c a l s to y i e l d the c r o s s coupled
product.
The f i r s t o b j e c t i v e of t h i s e x e r c i s e was therefore the c a r e f u l examination
— A r —COH
where m > 1
F i g u r e 2.31
o f the model r e a c t i o n (Figure 2.32) i n order to e s t a b l i s h whether processes
o c c u r r i n g on photochemical e x c i t a t i o n o f benzophenone i n the presence of
t r i p h e n y l g l y c o l (Figure 2.32, m = 1) would j u s t i f y f u r t h e r attempts to extend
- 56 -
t h i s r e a c t i o n to polymer s y n t h e s i s .
OXQ
hv
H—C
solvent
I
OH
OH
m
where m
Figure
2.32
Section 2.3 i s concerned with some i n v e s t i g a t i o n s on the p o s s i b i l i t y of
extending a r e a c t i o n already mentioned i n 2 . 1 . b . v i i i , namely the photoreductive
119
a d d i t i o n of benzophenone to diphenylmethane
to polymer s y n t h e s i s .
This
would i n i t i a l l y r e q u i r e a re-examination o f the model r e a c t i o n , s i n c e l i t e r a t u r e
r e p o r t s on the formation and y i e l d of photoproducts are somewhat confusing
l a t e r , s e c t i o n 2.3).
(see
Extention of the r e a c t i o n t o polymer formation would
i n v o l v e the i r r a d i a t i o n , under conditions optimized during the model compound
s t u d i e s of a bisbenzophenone i n the presence of a d i f u n c t i o n a l analogue o f
diphenylmethane, f o r i n s t a n c e a bisbenzylbenzene.
One
obtaining
f u r t h e r reason f o r attempting t h i s r e a c t i o n was
the p o s s i b i l i t y of
t e c h n o l o g i c a l l y i n t e r e s t i n g m a t e r i a l s by s t r u c t u r a l modification
the r e s u l t i n g polymer.
I t was
of
thought t h a t dehydration of the f i r s t formed .
poly(1,1,2,2-tetraphenylethanol) under mild conditions
conjugated system (Figure 2.33).
interesting e l e c t r i c a l properties.
could a f f o r d a t o t a l l y
Such polyconjugated systems might possess
Attempts to s y n t h e s i z e w e l l c h a r a c t e r i z e d
m a t e r i a l s of t h i s general type have appeared frequently i n the l i t e r a t u r e i n
123
recent
years.
57
A
?
9
OH
HO
c=c
H
9
Figure
2.2.
\
2.33
Attempts to s y n t h e s i z e poly(pentaphenylglycerols) and higher
2.2.a.
analogues
I n t r o d u c t i o n to the i d e a
As b r i e f l y mentioned i n 2.I.e., the o r i g i n a l i d e a was the s y n t h e s i s of
perphenylated polymers with more than two adjacent C H COH groups i n the
6 i|
c
repeat u n i t .
One conceivable way of e f f e c t i n g such a s y n t h e s i s could i n
p r i n c i p l e be the photoreductive p o l y a d d i t i o n of an aromatic bisketone to a
s u i t a b l e hydrogen donor, as i l l u s t r a t e d i n F i g u r e 2.30.
On the b a s i s of
l i t e r a t u r e information regarding the behaviour of photoexcited carbonyl
groups of the benzophenone type i n the presence of hydrogen donors i t might
be expected t h a t i r r a d i a t i o n of such a mixture a t the appropriate wavelength would
r e s u l t i n the formation of the two primary r a d i c a l s shown i n Figure 2.31.
question to be answered was whether the cage r e a c t i o n between the two
would take p l a c e , and i f so to what extent;
The
radicals
f u r t h e r i t was e s s e n t i a l to
know what other p r o c e s s e s , i f any, would occur.
P o s s i b l e r e a c t i o n paths f o r
the two primary r a d i c a l s considered beforehand are i l l u s t r a t e d i n F i g u r e
2.34.
I t can be seen t h a t the cage r e a c t i o n i s the only process which would b r i n g
about formation of a homopolymer.
D i f f u s i o n out of the cage and d i m e r i z a t i o n
o f r a d i c a l K would r e s u l t i n the formation of a s t r u c t u r e with a p i n a c o l
u n i t i n i t ; a s i m i l a r path f o r r a d i c a l L would give a s t r u c t u r e with
58
Q
Ar
9
Ar
I
OH
K)
OH
OH
(L
m
x21
x2
IT
QUO
Ar
Ar
OH
Ar
OH
Ar
OH
Cage
ID
OH
OH
OH
m
reaction
Y
Ar - C — HH
Ar*
Ar
OH
OH
a .
r
9
C — Ar
II
OH
OH
OH
m
(M)
N
Figure 2.34
2m+2 CgHgCX)H u n i t s .
A hydrogen atom t r a n s f e r from r a d i c a l L to r a d i c a l K
would r e s u l t i n complete reduction of the bisbenzophenone to the benzhydrolended product (M) and o x i d a t i o n of the a l c o h o l i c reagent t o s t r u c t u r e N.
Formation of end groups o f the type M need not n e c e s s a r i l y be chain terminating
for polymer growth s i n c e they can i n t e r a c t with aromatic ketones o f the benzophenone type to give p i n a c o l l i n k s .
End groups o f type N however might c r e a t e
more of a problem s i n c e they might be expected to undergo photochemical cleavage
to give r a d i c a l s ;
polymerization.
benzoins are widely used as p h o t o i n i t i a t o r s f o r r a d i c a l
A l l the other steps i n d i c a t e d i n Figure 2.34 are chain
- 59 -
propagating,
although i f a l l three r a d i c a l combination
processes shown i n
the Figure occurred the r e s u l t i n g p o l y o l would be a copolymer containing
repeating u n i t s with varying numbers o f adjacent CgHgCOH groups, 2, m + 2,
2m + 2.
I t was decided t o proceed with t h i s i d e a i n the hope t h a t a t l e a s t
some information on the photochemical
behaviour o f these systems would be
obtained; the r e a c t i o n shown i n F i g u r e 2.35 was chosen as an i n i t i a l o b j e c t i v e
for t h i s i n v e s t i g a t i o n .
OJlQ
yO
350 nm
polyol ?
H
+ H
solvent
I
OH
OH
OH
OH
Figure 2.35
The study o f the model r e a c t i o n i s an e s s e n t i a l p r e l i m i n a r y step i n the
i n v e s t i g a t i o n o f any p o t e n t i a l step-growth
polymerization.
I t was i n t h i s
context t h a t the photoreaction between benzophenone and t r i p h e n y l g l y c o l was
undertaken,
the product(s) of t h i s r e a c t i o n being appropriate model(s) f o r t h e
repeat u n i t ( s ) o f the a n t i c i p a t e d p o l y o l (Figure 2.35).
2.2.b.
How one event
l e d t o another
Appropriate s t a r t i n g m a t e r i a l s a r e e s s e n t i a l f o r chemical r e a c t i o n s . I n
the case o f the i n v e s t i g a t i o n proposed i n the preceding paragraph, one o f the
s t a r t i n g m a t e r i a l s , benzophenone, was r e a d i l y a v a i l a b l e . T r i p h e n y l g l y c o l ,
however, had to be s y n t h e s i z e d from simpler chemicals.
67
One o f the standard t e x t s o f organic photochemistry
r e a c t i o n shown i n Figure 2.36. No mention o f by-products
conditions appeared i n the t e x t .
reported the
or reaction
A reference was made t o an o l d paper by
- 60 -
0OJCQ
9
hv
^*C^
+
H
H
C— H
OH
I
I
OH
OH
Figure 2.36
124
Ciamician and S i l b e r .
When the r e a c t i o n reported was attempted on a small
s c a l e (nitrogen streamed benzene s o l u t i o n , 350 nm u l t r a v i o l e t l i g h t ) a white
s o l i d was obtained a t n e a r l y q u a n t i t a t i v e y i e l d , which, a f t e r r e c r y s t a l l i z a t i o n
and drying
was found t o be benzopinacol.
R e p e t i t i o n o f the r e a c t i o n a t v a r i o u s
concentrations and f o r d i f f e r e n t i r r a d i a t i o n times y i e l d e d c o n s t a n t l y the same
product, benzopinacol,
unequivocally
i d e n t i f i e d by melting p o i n t
elemental analyses and s p e c t r o s c o p i c examinations.
determination,
Even v a r i a t i o n o f the benzo-
phenone-benzylalcohol molar r a t i o seemed t o produce no a l t e r a t i o n s i n the nature
or y i e l d o f t h e f i n a l product.
Examination o f the s o l v e n t a f t e r i r r a d i a t i o n
by t . l . c . on s i l i c a revealed the presence o f t r a c e s o f benzopinacol and s e v e r a l
124
6V
other products.
Consultation o f the reference
i n d i c a t e d i n the t e x t
r e v e a l e d t h a t Ciamician and S i l b e r themselves appeared not t o be d e f i n i t e about
the formation o f t r i p h e n y l g l y c o l from the benzophenone-benzylalcohol mixture
on exposure t o s u n l i g h t .
I n the same paper, however, r e f e r e n c e s were made t o
e a r l i e r work by Ciamician and S i l b e r , and a l s o by the r i v a l group, headed by
Paternb;
view.
these r e f e r e n c e s appeared t o be i n t e r e s t i n g from s e v e r a l p o i n t s o f
These very e a r l y , almost p r e h i s t o r i c a l s t u d i e s (by modern standards) o f
the 'actions o f s u n l i g h t
1
on organic substances, however p r i m i t i v e and crude,
have s i g n i f i c a n t l y contributed t o the development o f modern organic photochemistry
- 61 -
so as to deserve a b r i e f mention i n t h i s t h e s i s .
2.2.C.
The 'pre-history' o f s y n t h e t i c o r g a n i c photochemistry - the nature
of a dispute
S y n t h e t i c s t u d i e s on the photochemistry of carbonyl compounds go back to
1886 when Ciamician and S i l b e r t r i e d to ' e s t a b l i s h the p r i n c i p a l p r o c e s s e s
125
determined or, b e t t e r say, a c c e l e r a t e d by the s o l a r r a y s ' .
A few y e a r s
l a t e r , Loew t r i e d the f i r s t s y s t e m a t i c c l a s s i f i c a t i o n o f the 'actions of l i g h t '
on organic substances.
126
I n subsequent papers
56 127
'
Ciamician and S i l b e r
examined the photochemistry of v a r i o u s carbonyl compounds and e s t a b l i s h e d the
f a c t that i n s o l a t i o n of the ketone
(or aldehyde)/alcohol system r e s u l t s i n the
'oxidation of the a l c o h o l to aldehyde whereas the ketones
(or aldehydes) transform
127
themselves i n t o the corresponding p i n a c o l s ' .
Thus, benzophenone and
acetophenone y i e l d e d on i n s o l a t i o n i n ethanol benzopinacol and
'acetophenopinacol
127
respectively;
acetaldehyde was produced as w e l l .
The p h o t o r e a c t i v i t y of benzophenone i n aromatic a l c o h o l s was a l s o examined
128
by Ciamician and S i l b e r
but the r e a c t i o n was found to be 'a l o t more
complicated than i n the previous case, because more products are formed i n t h i s
1
reaction .
Copious amounts of benzopinacol were i s o l a t e d from the r e a c t i o n of
benzophenone with b e n z y l a l c o h o l on exposure to s u n l i g h t , together with some
hydrobenzoin, (CgHgCHOH)^
The i n t e r e s t i n g f e a t u r e of t h i s r e a c t i o n was the
i s o l a t i o n of a substance melting a t 168° and g i v i n g the f o l l o w i n g elemental
analyses:
I
C
82.95%
H
6.44%
C
B
The v a l u e s c a l c u l a t e d f o r 2g ie°2 ^
(CgH ) CO + C H CH OH) were:
5
2
g
5
2
II
82.77%
6.44%
t h e
'
a
d
d
i
t
i
o
n
C 82.76%, H 6.21%.
P
r o d u c t
'
o
f
t
n
e
t
w
o
reagents,
On the b a s i s of t h i s evidence
Ciamician and S i l b e r assigned to the product the s t r u c t u r e of t r i p h e n y l g l y c o l
1
- 62 -
(Figure 2.36) , a compound a l r e a d y known a t t h a t time to have a melting p o i n t
of 1 6 4 ° .
1 2 9
Subsequently another group of I t a l i a n workers i n v e s t i g a t i n g the a c t i o n of
s u n l i g h t on organic substances, Paternb and h i s c o l l a b o r a t o r s of the U n i v e r s i t y
of Rome, began p u b l i s h i n g t h e i r r e s u l t s .
I n a paper published i n 1909 they
d e s c r i b e d the p h o t o r e a c t i v i t y of benzophenone with v a r i o u s a l i p h a t i c
119
hydrocarbons.
They confirmed what Ciamician and S i l b e r had claimed p r e v i o u s l y ,
namely t h a t i n a l l cases examined about two t h i r d s of the we! ght of benzophenone used was transformed i n t o benzopinacol.
They a l s o reported the i s o l a t i o n
of some 'addition products' formed i n the r e a c t i o n s examined.
In the same paper Paterno and C h i e f f i a l s o described the behaviour of
benzophenone on i n s o l a t i o n i n the presence of aromatic hydrocarbons,
namely
benzene, toluene, ethylbenzene, p-xylene e t c . They acknowledged C i a m i c i a n and
128
S i l b e r ' s work i n t h i s f i e l d
but they pointed out t h a t the formation of
benzopinacol i n the r e a c t i o n between benzophenone and cumene reported by
their
128
rivals
was
'an i s o l a t e d observation i n which the authors d i d not study what
change d i d cumene undergo during the r e a c t i o n ' .
Furthermore, Paternb and C h i e f f i
reported the i s o l a t i o n of the a d d i t i o n product from the benzophenone/toluene
i n s o l a t i o n ( ( C ^ H J _C(0H)CH„C^H,_) i n modest y i e l d ,
b
b
i
2 b
5
I t should a l s o be mentioned here t h a t i t was i n t h i s important paper
t h a t the process now
famous as the Paterno-Buchi r e a c t i o n and the photoreductive
addition of benzophenone to diphenylmethane were f i r s t reported.
F u r t h e r work by Paterno appeared i n the l i t e r a t u r e on the photoreactions
of acids, e t h e r s ^
0
and b e n z y l a c e t a t e ^ " ^ with benzophenone.
Paterno and h i s
team a l s o i n v e s t i g a t e d the behaviour of benzophenone on i n s o l a t i o n i n the presence
132
of various a l k a l o i d s .
I n most of these s t u d i e s , benzopinacol was
isolated
i n s i g n i f i c a n t q u a n t i t i e s , o c c a s i o n a l l y s m a l l amounts of the 'addition products'
were obtained.
Paterno and C h i e f f i s t a t e d t h a t a d d i t i o n of benzophenone to
- 63
molecules was only p o s s i b l e when the methylene group, -CH ~, was p r e s e n t .
2
S i m i l a r behaviour was observed when benzophenone was i n s o l a t e d i n the presence
1
1
of b e n z y l p h e n o l . ^ " ^
I n 1914, Paterno published h i s 11th paper on the 'Synthesis i n Organic
134
Chemistry by Means of L i g h t ' .
I n i t he summarized work a l r e a d y done by him
and coworkers and b i t t e r l y c r i t i c i z e d Ciamician and S i l b e r f o r 'not having
c l e a r l y understood the concepts o f the r e a c t i o n s they were attempting' and f o r
d e l i b e r a t e l y 'presenting Paternb's work under f a l s e l i g h t * .
Furthermore Paterno
128
pointed out t h a t the evidence presented by Ciamician and S i l b e r
f o r the
formation o f t r i p h e n y l g l y c o l from benzophenone and b e n z y l a l c o h o l was
insufficient,
t h e r e f o r e , Paterno i n s i s t e d , no c o n c l u s i o n could be drawn as to whether the
compound was a c t u a l l y formed i n the r e a c t i o n o r not.
135
Ciamician and S i l b e r r e p l i e d
by saying t h a t a t the time o f
128
publication
they, too, had t h e i r r e s e r v a t i o n s regarding the formation of
triphenylglycol;
they could not however, accept the charges o f d e l i b e r a t e l y
stating false results.
%
134
Paterno a l s o attempted
an e a r l y c l a s s i f i c a t i o n of the photoreactions
of carbonyl compounds as f o l l o w s :
i)
' t r i m e t h y l e n i c condensation'
C
II
c
+
c
— ^
I
o
ii)
— —c
I
—
I
c
— o—c
/ \
I I
'doubling o f the carbon chain'
C
||
O
H
C
=»»
H
C
C
H
- 64 iii)
' e n o l i c condensation'
\ /
c
h
_I
>
+H—
S 1
0
iv)
_l_l_
T~"i
OH
OH
H
'dehydrogenation of alkanes'
C
C H
II
+
^
n 2n+l
0
-
C
C—+
|
|
OH
OH
C H.
n 2n
A comprehensive review of examples f o r each o f the above! c l a s s e s appears
i n the paper.
I t i s indeed hard to overestimate the importance o f these e a r l y workers'
e f f o r t s on the development o f modern o r g a n i c photochemistry.
Despite the l a c k
of h e l p f u l t h e o r e t i c a l concepts and s p e c t r o s c o p i c and chromatographic t o o l s
to analyse observed r e a c t i o n s , they p a t i e n t l y c o l l e c t e d data which l a t e r on
served t h e i r purpose.
Speaking a t the V I I Congress o f Applied Chemistry i n
London i n 1909, Paternb t r i e d to a t t r a c t the a t t e n t i o n o f the young chemists
of the time to the impressive r e s u l t s obtained i n the f i e l d o f photochemical
synthesis.
'For us', he concluded, 'a much more modest f i e l d i s r e s e r v e d , the
c o l l e c t i o n and p r e p a r a t i o n o f the m a t e r i a l which should serve i n the c o n s t r u c t i o n
136
of the m a j e s t i c e d i f i c e ' .
A p o i n t , however, which was made c l e a r from the above information i s t h a t
the
two f a t h e r f i g u r e s o f organic photochemistry never r e a l l y agreed on whether
t r i p h e n y l g l y c o l i s produced on i r r a d i a t i n g benzophenone i n b e n z y l a l c o h o l o r
not.
2.2.d.
The r e s o l u t i o n o f the dispute
121
I n the o r i g i n a l paper proposing the formation o f t r i p h e n y l g l y c o l ,
C i a m i c i a n and S i l b e r d e s c r i b e d t h r e e separate i n s o l a t i o n s of benzophenone
- 65 -
w
d i s s o l v e d i n neat benzylalcohol (1:2 / ) f o r periods from 4 to 5 months.
w
main product i s o l a t e d by them was benzopinacol.
hydrobenzoin,
The
Other products reported were
t r i p h e n y l g l y c o l and a r e s i n , which the authors a t t r i b u t e d to the
a c t i o n of l i g h t on benzaldehyde, i t s e l f a p o s s i b l e r e a c t i o n product a r i s i n g
from the o x i d a t i o n of b e n z y l a l c o h o l .
them.
Benzaldehyde
however was not i s o l a t e d by
The scheme shown i n F i g u r e 2.37 was proposed by the authors f o r the
C
+ H
9
9
Oh
C —
-c
OH
c- a
OH
OH
H
2
C
+ H
C- H
OH
OH
OH
eDJ> D
9
C
+ H
C-
H
H
II
0
OH
Figure
OH
OB
2.37
benzophenone/benzylalcoho1 i n s o l a t i o n .
The r e a c t i o n was r e - i n v e s t i g a t e d by us.
w
A 1:2 /
w
s o l u t i o n of benzophenone
i n b e n z y l a l c o h o l (25g:50g) was t r a n s f e r r e d i n t o a Pyrex tube, n i t r o g e n streamed
for
20 mins, the tube was q u i c k l y stoppered and the s o l u t i o n was
for
18 h r s a t 350 run.
irradiated
At the end o f the i r r a d i a t i o n p e r i o d the s o l u t i o n was
yellow and the i n s i d e s u r f a c e of the tube was covered with a l a y e r of white
crystals.
Examination of the tube contents by t . l . c . on s i l i c a
(benzene,
chloroform) and i . r . spectroscopy r e v e a l e d the presence o f unreacted s t a r t i n g
m a t e r i a l s , benzopinacol and s m a l l amounts of benzaldehyde.
No
triphenylglycol
was i s o l a t e d or detected by t . l . c . on s i l i c a ; concentrations g r e a t e r than 1%
would have r e a d i l y been detected.
I r r a d i a t i o n time to 89 h r s .
The r e a c t i o n was repeated i n c r e a s i n g the
Again as i n the previous case the s o l u t i o n was
yellow and the i n s i d e s u r f a c e of the tube was covered with white c r y s t a l s .
- 66 -
Benzopinacol and benzaldehyde were e a s i l y i d e n t i f i e d by t . l . c . on s i l i c a
(benzene, chloroform) and i . r . spectroscopy, along with unreacted s t a r t i n g
m a t e r i a l s and hydrobenzoin.
The i n t e r e s t i n g f e a t u r e o f t h i s experiment
the d e t e c t i o n by t . l . c . on s i l i c a of t r i p h e n y l g l y c o l .
was
Attempts to i s o l a t e
the product by f r a c t i o n a l p r e c i p i t a t i o n (ethanol s o l v e n t ) were, however,
u n s u c c e s s f u l , probably due to the s m a l l amounts of m a t e r i a l p r e s e n t .
A t h i r d i n v e s t i g a t i o n was undertaken under the same c o n d i t i o n s .
This
time, however, c o l o u r l e s s c r y s t a l s which formed on the i n s i d e w a l l of the r e a c t i o n
tube were p e r i o d i c a l l y broken by means of a long s p a t u l a i n order to allow the
u l t r a v i o l e t - l i g h t to penetrate the s o l u t i o n .
A f t e r 180 h r s of i r r a d i a t i o n a
crop o f c r y s t a l s and a v i s c o u s b r i g h t yellow s o l u t i o n had formed i n s i d e the
tube.
The c r y s t a l s were separated by f i l t r a t i o n and the y e l l o w o i l recovered
was nitrogen streamed and r e - i r r a d i a t e d for a f u r t h e r 120 h r s .
The
crystals
separated were found to c o n s i s t of a mixture of unreacted benzophenone,
benzopinacol, hydrobenzoin
chloroform).
and t r i p h e n y l g l y c o l by t . l . c . on s i l i c a
(benzene,
The yellow o i l a l s o deposited a f r e s h crop of c r y s t a l s during
the 120 h r s i r r a d i a t i o n p e r i o d .
Examination of these c r y s t a l s ( c a . 1.5g)
by
i . r . spectroscopy showed the m a t e r i a l to be t r i p h e n y l g l y c o l by comparison
w i t h the i . r . spectrum o f t r i p h e n y l g l y c o l obtained by ground s t a t e s y n t h e s i s
(see
2.2.e).
The yellow o i l was found to c o n s i s t of benzaldehyde,
hydrobenzoin
and t r a c e s o f benzopinacol, b e n z y l a l c o h o l and unreacted benzophenone.
Attempts
to o b t a i n a pure sample of t r i p h e n y l g l y c o l by repeated r e c r y s t a l l i z a t i o n s from
v a r i o u s s o l v e n t s were l a r g e l y u n s u c c e s s f u l , s i n c e a very f a i n t spot corresponding
to benzopinacol was always p r e s e n t on the t . l . c . p l a t e s
(benzene).
These experiments c e r t a i n l y confirmed the c o r r e c t n e s s of Ciamician's
observations.
I t would a l s o appear t h a t the formation of t r i p h e n y l g l y c o l from
benzophenone/benzylalcohol
was a l s o confirmed.
i s time dependent.
The formation of benzaldehyde
F i n a l l y , i r r a d i a t i o n of an 1:1 molar mixture of benzophenone
- 67 -
and b e n z y l a l c o h o l i n benzene s o l u t i o n (0.0035 t o t a l concentration) f o r 160 h r s
(350 run) afforded t r i p h e n y l g l y c o l i n c a . 8% y i e l d .
2.2.e.
Ground s t a t e syntheses o f t r i p h e n y l g l y c o l
The f i r s t attempt t o s y n t h e s i z e the above mentioned compound (method A)
137
was based on an e s t a b l i s h e d router
namely the a c t i o n o f benzoin on an
excess o f phenylmagnesiumbromide.
The e x e r c i s e afforded 60% o f n e a r l y pure
triphenylglycol.
Repeated r e c r y s t a l l i z a t i o n s gave 45% o f a white
s o l i d which on examination
crystalline
by t . l . c . on s i l i c a was found to be a s i n g l e compound
(Figure 2.38).
0
OH
OH
(method A)
Figure 2.38
T r i p h e n y l g l y c o l was a l s o prepared
corresponding
(method B) by reduction o f the
carbonyl compound, a-phenylbenzoin
(2,2-diphenyl-2-
hydroxyacetophenone), i t s e l f prepared by the a c t i o n o f one mole o f b e n z i l on one
mole o f phenylmagnesiumbromide (Figure 2.39).
Pure t r i p h e n y l g l y c o l (85%) was obtained from t h i s preparation, M.pts
and s p e c t r o s c o p i c data f o r the products obtained by the two methods were
identical.
Elemental analyses were s a t i s f a c t o r y .
Preparation and p u r i f i c a t i o n
procedures w i l l be d e s c r i b e d i n more d e t a i l i n 2 . 2 . j . i i i .
2.2.f.
The benzophenone/triphenylglycol
photoreactlon
Following p r e p a r a t i o n , c h a r a c t e r i z a t i o n and rigorous p u r i f i c a t i o n o f
t r i p h e n y l g l y c o l , i t was decided to proceed with the i r r a d i a t i o n o f a 1:1 molar
9
68
Et_0
OH
EtOH
NaBH
(method B )
H
OH
OH
Figure 2.39
r a t i o o f t h i s compound and benzophenone f o r reasons s t a t e d i n 2.2.a.
Benzene
was chosen a s an appropriate s o l v e n t .
I n the f i r s t experiment t r i p h e n y l g l y c o l (2.90g, 0.01 mole) prepared by
method A and benzophenone (1.82g, 0.01 mole) were d i s s o l v e d i n benzene (350 mis)
i n a long Pyrex tube.
The c l e a r , c o l o u r l e s s s o l u t i o n was nitrogen streamed,
the tube was q u i c k l y stoppered and i r r a d i a t e d f o r 18.4 h r s a t 350 nm;
This
experiment y i e l d e d unchanged s t a r t i n g m a t e r i a l s , as i n d i c a t e d by t . l . c . on
silica
(benzene, chloroform, ethanol) and i . r . s p e c t r a l examination.
R e p e t i t i o n o f e x a c t l y the same r e a c t i o n using t r i p h e n y l g l y c o l prepared by
method B y i e l d e d i d e n t i c a l r e s u l t s .
I n a subsequent experiment, benzophenone (0.273g, 0.0015 mole) and
t r i p h e n y l g l y c o l (0.435g, 0.0015 mole) prepared by method B were d i s s o l v e d i n
benzene (50 mis) i n a Pyrex tube.
The s o l u t i o n was degassed by s e v e r a l f r e e z e -3
pump-thaw c y c l e s and tube was s e a l e d under reduced pressure
(10
mmBg).
I r r a d i a t i o n f o r 94 h r s a t 350 nm afforded q u a n t i t a t i v e recovery o f s t a r t i n g
materials.
During t h i s experiment a p a r a l l e l photoreaction between benzophenone
- 69 -
and benzhydrol
(1:1 molar r a t i o ) was c a r r i e d out i n order to t e s t the
e f f i c i e n c y of the u l t r a v i o l e t lamps:
benzopinacol was q u a n t i t a t i v e l y obtained
a f t e r 3 h r s of i r r a d i a t i o n .
R e p e t i t i o n of t h i s r e a c t i o n using t r i p h e n y l g l y c o l prepared by method A
gave the same r e s u l t .
On the b a s i s of the l i t e r a t u r e information a v a i l a b l e on the
o f benzophenone with a l c o h o l i c hydrogen donors, one would
photoreactions
expect some i f not
a l l the processes shown i n F i g u r e 2.40 to occur upon i r r a d i a t i o n of the
benzophenone/triphenylglycol
system.
materials i s a surprising r e s u l t .
The q u a n t i t a t i v e recovery of s t a r t i n g
I t seemed remarkable and
l e d to a considerable
e f f o r t i n p u r i f y i n g the t r i p h e n y l g l y c o l and seeking evidence f o r the
presence
o f an impurity which could a c t as an e f f i c i e n t quencher o f t r i p l e t benzophenone.
Benzene s o l v e n t and benzophenone were a l s o e x h a u s t i v e l y searched f o r
impurities.
R e p e t i t i o n s of the i r r a d i a t i o n s using more r i g o r o u s l y p u r i f i e d
m a t e r i a l s made no d i f f e r e n c e to the r e s u l t .
One hypothesis considered was t h a t the hydrogen atom t r a n s f e r i l l u s t r a t e d
i n Figure 2;40 d i d i n f a c t occur i n low y i e l d and t h a t the a-phenylbenzoin
formed acted as a quencher i n very low c o n c e n t r a t i o n s .
The hypothesis seemed
worth i n v e s t i g a t i n g s i n c e one could p o s t u l a t e a degenerate i s o m e r i z a t i o n
pathway i n v o l v i n g a photoenolization and phenyl migration which might have
accounted f o r the p o s t u l a t e d quenching (Figure 2.41).
The
photochemistry
o f a-phenylbenzoin i s not d i s c u s s e d i n the l i t e r a t u r e , depitc: the very
138
e x t e n s i v e i n v e s t i g a t i o n s reported on benzoins i n g e n e r a l .
When i r r a d i a t e d
under the conditions d e s c r i b e d p r e v i o u s l y , a-phenylbenzoin proved to be
p a r t i c u l a r l y p h o t o l a b i l e , both on i t s own
amounts o f
and i n the presence of equimolar
benzhydrol.
F i n a l l y , the 'quencher theory' was excluded by the i r r a d i a t i o n of a nitrogen
streamed benzene s o l u t i o n containing a 1:1:1
molar mixture of benzophenone,
70
Q
Q
hv
»
II
99
OH
OH
a ca
x2
OH
OH
OH
OH
OH
REACT!
H ATOM
TRANSFER
OH
OH
OH
hv
9\9
V \
OH
OH
«
hv
F i g u r e 2.40
OH
- 71 -
Figure 2.41
benzhydrol and t r i p h e n y l g l y c o l
12 h r s (Figure 2.42).
(0.0035H t o t a l concentration) a t 350 nm f o r
An 1:1 molar mixture of t r i p h e n y l g l y c o l and benzopinacol
was obtained, benzophenone and benzhydrol having completely disappeared.
0
<§H-
i i
9
©4OH
1 mole
OH
OH
1 mole
CH
0.0035M
12 h r s
1 mole
99
OH
OH
350 runs
OH
Figure 2.42
T h i s r e a c t i o n confirmed the observations t h a t the t e r t i a r y hydrogen i n
- 72 -
t r i p h e n y l g l y c o l i s i n e r t towards a b s t r a c t i o n by t r i p l e t benzophenone.
2.2.g.
The p h o t o r e a c t i v i t y of
1,2,2,2-tetraphenylethanol
The observations described above concerning the photochemical
behaviour
of t r i p h e n y l g l y c o l c e r t a i n l y put an end to the hopes of o b t a i n i n g poly(pentaphenylglycerol)s by the photoreductive p o l y a d d i t i o n of bisketones to
polyphenylated a l c o h o l i c hydrogen donors o f the type d i s c u s s e d .
The
new
question which arose was whether the p h o t o s t a b i l i t y of t r i p h e n y l g l y c o l was due to
the presence o f two adjacent CgH^COH u n i t s next to the t e r t i a r y hydrogen, which
was expected to be a b s t r a c t a b l e .
I n order to t e s t t h i s hypothesis i t was
decided to s u b s t i t u t e the 2-hydroxy group i n t r i p h e n y l g l y c o l with a group of
a t o t a l l y d i f f e r e n t nature, f o r i n s t a n c e an aromatic r i n g , and i n v e s t i g a t e the
photochemical
behaviour of the r e s u l t i n g system.
To t h i s end 1,2,2,2-
tetraphenylethanol (Figure 2.43) was s y n t h e s i z e d by reducing
<0H
D
6
benzopinacolone
H
EtOH
Figure
6
OH
2.43
and subsequently i r r a d i a t e d with benzophenone (1:1 molar r a t i o ) i n benzene
s o l u t i o n (0.0056M t o t a l concentration) f o r 12 hrs a t 350 nm.
s p e c t r o s c o p i c examination and t . l . c . on s i l i c a
Infrared
(benzene, chloroform, ethanol)
e s t a b l i s h e d t h a t no d e t e c t a b l e r e a c t i o n had taken p l a c e ; s t a r t i n g m a t e r i a l s
were q u a n t i t a t i v e l y recovered.
- 73 -
As i n the case o f t r i p h e n y l g l y c o l , i r r a d i a t i o n o f a benzene s o l u t i o n
containing an 1:1:1 molar mixture o f benzophenone, benzhydrol and 1,2,2,2tetraphenylethanol (0.0035H t o t a l concentration) a t 350 nm f o r 24 h r s r e s u l t e d
i n the formation of an 1:1 molar mixture o f benzopinacol and 1,2,2,2tetraphenylethanol.
No other products were detected by t . l . c . on s i l i c a ,
benzophenone and benzhydrol having disappeared completely.
2.2.h.
Some r e l e v a n t photoreactions
I t was so f a r e s t a b l i s h e d t h a t the t e r t i a r y hydrogen i n the s t r u c t u r e
shown i n F i g u r e 2.44 i s a b s t r a c t a b l e when X = H o r CJA- but non-abstractable
b 5
when X = ( C H J _C0H and (C-H..) ,C.
6 5 2
6 5 3
C
9
o
H
c
X
OH
Figure 2.44
In an attempt to examine the p o s s i b i l i t y o f other v e r s i o n s o f the system
shown being i n e r t to hydrogen a b s t r a c t i o n by benzophenone t r i p l e t , hydrobenzoin
(X = (CgHjXH(OH)) and 1-phenylethanol (X = CH^)) were i r r a d i a t e d i n the presence
of e i t h e r benzophenone o r i t s d i f u n c t i o n a l analogue, m-dibenzoylbenzene.
I r r a d i a t i o n o f a 1:1 molar s o l u t i o n o f benzophenone and 1-phenylethanol
i n benzene (350 nm) r e s u l t e d i n 100% disappearance o f both s t a r t i n g m a t e r i a l s
a f t e r 140 h r s o f i r r a d i a t i o n .
Benzopinacol and acetaldehyde were among the
r e a c t i o n products immediately recognized.
i d e n t i f i e d by t . l . c . on s i l i c a (benzene).
At l e a s t three more products were
- 74 -
I r r a d i a t i o n of a 1:1 molar mixture of m-dibenzoylbenzene and
hydrobenzoin
i n benzene presented s p e c i a l problems due to the low s o l u b i l i t y of the d i o l .
However the p o r t i o n o f i t t h a t d i d d i s s o l v e i n benzene a t 0.0035M t o t a l
concentration r e a c t e d r e a d i l y with the photoexcited benzophenone-type carbonyl
of m-dibenzoylbenzene y i e l d i n g hydroxy1 containing m a t e r i a l s (350 run, 160 h r s ) .
Again a b r i g h t yellow colour developed s h o r t l y a f t e r the lamps were turned on.
The i r r a d i a t i o n was repeated using methylene c h l o r i d e s o l v e n t i n order to
ensure complete s o l u b i l i t y of both s t a r t i n g m a t e r i a l s .
A f t e r only 38 h r s
of i r r a d i a t i o n s o l u t i o n was again b r i g h t yellow and s l i g h t l y t u r b i d .
Examination
o f the tube contents r e v e a l e d t h a t some s t a r t i n g m a t e r i a l s had been l e f t
unchanged but most of them had r e a c t e d to g i v e s e v e r a l products as shown by
t . l . c . on s i l i c a
(benzene).
The products from the above r e a c t i o n s were not r i g o r o u s l y examined, the
main o b j e c t i v e of the e x e r c i s e being to e s t a b l i s h whether photoreaction with
benzophenone occurred or not.
2.2.1.
Attempts to prepare pentaphenylglycerol v i a ground s t a t e chemistry
I n v e s t i g a t i o n s so f a r r e v e a l e d t h a t the model r e a c t i o n f o r the polymer
s y n t h e s i s formulated i n F i g u r e 2.30 does not occur due to a r a t h e r s u r p r i s i n g
i n e r t n e s s of t r i p h e n y l g l y c o l towards benzophenone t r i p l e t s .
f u r t h e r i n v e s t i g a t e t h i s behaviour
e x h i b i t i n g the same remarkable
Attempts to
l e d to the discovery of another
molecule
inertness.
At the same time, the p r e p a r a t i o n of the expected product,
pentaphenyl-
g l y c e r o l was undertaken v i a ground s t a t e s y n t h e s i s i n order to examine i t s
s t a b i l i t y , determine i t s p r o p e r t i e s and provide a r e f e r e n c e f o r comparison.
139
The compound i s reported i n the l i t e r a t u r e
and the r e c i p e f o r i t s p r e p a r a t i o n
given i n the o r i g i n a l paper was followed i n every d e t a i l
(see F i g u r e 2.45).
The o r i g i n a l worker reported t h a t pentaphenylglycerol was obtained as a white
c r y s t a l l i n e s o l i d a f t e r a number o f r e c r y s t a l l i z a t i o n s (m.pt. 163°), and t h a t
- 75 -
C H —O
2
5
OH
|
v
,0
C,H
c—c—c
II
I II
0
OH
* ©-?—f—=—©>
Et 0
v=/
2
|
OH
0
|
OH
|
OH
F i g u r e 2.45
139
i t s elemental a n a l y s i s was s a t i s f a c t o r y .
I n our hands, t h i s r e a c t i o n gave a white c r y s t a l l i n e s o l i d (5g),
m.pt. 162°, which, a f t e r repeated r e c r y s t a l l i z a t i o n s from methanol and
drying under vacuum over P ° 5 analysed as f o l l o w s :
C 87.54, H 5.64.
2
^2^2^^
C a l c u l a t e d f i g u r e s f o r pentaphenylglycerol
a r e :
C
83,33
H
'
5
T h i s m a t e r i a l was found t o be a s i n g l e component by t . l . c . on s i l i c a
ethanol, methanol, a c e t o n i t r i l e ) .
and drying under vacuum over P ° 5
I t melted a t 164°.
f
o
r
4
8
n
r
s
g
a
2
which analysed a s f o l l o w s :
C 87.44, H 5.87.
v
e
a
97
* ' *
(benzene,
Further r e c r y s t a l l i z a t i o n s
m a t e r i a l melting a t 164°
Sublimation
(120°, 0.005 mmHg),
gave a m a t e r i a l i d e n t i c a l t o the one obtained a f t e r r e c r y s t a l l i z a t i o n s ( i . r .
s p e c t r a were superimposable), melting a t 164.5°, which analysed:
H 6.04.
The h i g h e s t m/e peak observed i n the mass spectrum o f our
was 260 (molecular weight o f pentaphenylglycerol = 472);
to fragmentation i n the mass spectrometer source.
C 87.15,
product
t h i s was a t t r i b u t e d
The *H n.m.r. spectrum
showed two peaks, one i n the aromatic hydrogen region (6 7.30)
and another
a t 6 2.73 which disappeared on a d d i t i o n o f D^O. The i n t e g r a t e d i n t e n s i t i e s
were i n a r a t i o o f 15:1, f o r pentaphenylglycerol the c a l c u l a t e d r a t i o i s 8.33:1.
The s o l i d s t a t e i n f r a r e d spectrum o f the m a t e r i a l (KBr d i s c ) showed a r a t h e r
- 76 -
broad OH band a t 3465 cm
3080 cm
, a m u l t i p l e t i n the C-H
aromatic region
(3020 cm
-
and peaks i n the f i n g e r p r i n t region are g e n e r a l l y c o n s i s t e n t with
139
the product s t r u c t u r e proposed i n the paper.
However, the s o l u t i o n phase
(CCl^ solvent) of the m a t e r i a l showed only one peak a t j u s t over 3600 cm~^.
Comparative i . r . s t u d i e s on some phenylated d i o l s and monoalcohols (see
Table 2.6)
one
showed t h a t 1,2-diols g e n e r a l l y d i s p l a y two peaks i n d i l u t e s o l u t i o n s ,
above and one below 3600 cm
the former being assigned
s t r e t c h i n g and the l a t t e r to the i n t r a m o l e c u l a r l y bonded OH
to the f r e e
OH
(Figure 2.46).
I1
c
H
c
I
H
H
Figure
2.46
The s i n g l e OH peak i n the s o l u t i o n phase i . r . spectrum i n d i c a t i n g the
absence of intramolecular hydrogen bonding i n the product from the a c t i o n of
p h e n y l l i t h i u m on d i e t h y l mesoxalate seemed r a t h e r s u r p r i s i n g and
with the formula of pentaphenylglycerol.
inconsistent
Furthermore, elemental a n a l y s i s data
and n.m.r. i n t e g r a t e d i n t e n s i t y r a t i o s suggested t h a t the product obtained
139
i n our hands was
not the one claimed i n the paper.
T h i s thought l e a d to a
systematic search f o r a compound which could be formed from the above r e a c t i o n
i n good y i e l d and be c o n s i s t e n t with the data obtained;
(CgHg)^COH looked a promising candidate.
164°-165°;^°
I t s melting point i s reported
i t s mass spectrum extends to m/e
a n a l y s i s f i g u r e s (C, 87.65;
H, 6.19)
triphenylcarbinol,
to be
260 and c a l c u l a t e d elemental
agree w e l l w i t h those obtained i n t h i s
- 77 -
Table 2.6
Comparative
s o l u t i o n phaae l . r . s p e c t r a of some phenylated 1,2-dlols
and monoalcohols
(OH s t r e t c h i n g region, CCl^ s o l u t i o n , 3mm
Concentration range:
10
-3
M-8
KBr c e l l )
x 10
-4
M
Absorptions
S t r u c t u r a l formula
Name
3900
^Q
Hydrobenzoin
H-
•C
C
H
I
I
OH
OH
Triphenylglycol
•C—H
OH
OH
Benzopinacol
< f - 0
OH
Benzylalcohol
H
OH
C—H
I
OH
?
Benzhydrol
CH
Product obtained
from the r e a c t i o n :
C H Li
+
C H — O - C — C — C — OC,H_
2 5
|, , ,
2 5
6
O
5
OH O
Proposed
139
formula:
T IT
Q-c—c-c-Q
OH
3300
J
OH
OH
L
- 78 -
work.
F u r t h e r the p.m.r. and i . r . s p e c t r o s c o p i c r e s u l t s a r e i n complete
accord with the product being t r i p h e n y l c a r b i n o l .
T h i s hypothesis was
confirmed
139
by comparison with an a u t h e n t i c specimen.
I n the o r i g i n a l paper,
following colour t e s t f o r 'pentaphenylglycerol' was suggested:
'The
the
product
from pentaphenylglycerol + a c e t y l c h l o r i d e + d i m e t h y l a n i l i n e i n c o l d f o r
5 mins was t r e a t e d with a s o l u t i o n of hydroxylamine and the mixture made
a l k a l i n e with a l c o h o l i c KOH, heated and cooled.
A reddish-wine
produced on a c i d i f i c a t i o n and a d d i t i o n of FeCl-j s o l u t i o n ' .
colour
The t e s t
was
was
c a r r i e d out twice on a sample of the r e a c t i o n product and on a sample of pure
triphenylcarbinol.
I n both cases the same reddish-wine
colour was produced.
The author has been unable to a s c e r t a i n the s i g n i f i c a n c e attached by the o r i g i n a l
worker to the colour t e s t , although c l e a r l y i t i s not c h a r a c t e r i s t i c of
pentaphenylglycerol.
results.
C a r e f u l r e p e t i t i o n of the o r i g i n a l r e c i p e gave i d e n t i c a l
- 79 -
2.2.j.
Experimental
2.2.j.i.
Readily a v a i l a b l e m a t e r i a l s
Benzylalcohol ( t e c h n i c a l grade) was purchased from Hopkin & Williams L t d . ,
and s t o r e d over 4A molecular s i e v e s ; p r i o r t o use i t was twice f r a c t i o n a l l y
distilled
(15 cm x 4 cm d i a . , g l a s s h e l i c e s ) ; the f r a c t i o n d i s t i l l i n g
205° and 206° was c o l l e c t e d ( l i t .
s i n g l e spot on t . l . c . on s i l i c a
1 4 0
between
205.03°/760 mmHg). The product gave a
(chloroform, ethanol, benzene).
Benzhydrol was obtained from departmental stock, r e c r y s t a l l i z e d twice
from ethanol/water (70:30) and sublimed twice (95°/0.005 mmHg);
had a melting p o i n t o f 69° ( l i t .
silica
1 4 0
the product
69°) and gave a s i n g l e spot on t . l . c . on
(ethanol, benzene, chloroform, toluene, a c e t o n i t r i l e ) .
Benzophenone ( t e c h n i c a l grade) was purchased from Hopkin & W i l l i a m s L t d .
and r e c r y s t a l l i z e d t w i c e from ethanol/water (70:30) and once from cyclohexane,
melting a t 48.5° ( l i t .
1 4 0
49°).
I t gave a s i n g l e spot on t . l . c . on s i l i c a
(benzene, ethanol, chloroform, a c e t o n i t r i l e , toluene, e t h y l a c e t a t e ,
t e t r a c h l o r i d e , acetone/water
carbon
50:50).
1-Phenyl ethanol ( t e c h n i c a l grade) was purchased from BDH Laboratory
Reagents and s t o r e d over 4A molecular sieves,-
p r i o r to use i t was d i s t i l l e d
twice under reduced p r e s s u r e (15 cm x 4 cm d i a . , g l a s s h e l i c e s , 98°-100°/20 mmHg
lit.
(col.
1
4
0
,
98°-99°/20 mmHg). The product gave a s i n g l e peak on a n a l y t i c a l g . l . c .
,
A /140°).
Diethyl ketomalonate (C H OCOCOOC H,.) was purchased from A l d r i c h
2
5
2
and used as obtained without p u r i f i c a t i o n .
Chemicals,
I t s m.s. and i . r . spectrum were
c o n s i s t e n t with the assigned s t r u c t u r e .
Benzoin, b e n z i l and benzopinacolone were a l l obtained from departmental
stock, r e c r y s t a l l i z e d twice from appropriate s o l v e n t s , d r i e d under vacuum and
i d e n t i f i e d by i n f r a r e d spectroscopy (KBr d i s c s ) and melting point, determinations
P u r i t i e s were checked by t . l . c . on s i l i c a (benzene).
- 80 -
Sodium borohydride was purchased from BDH
Laboratory Reagents and used
as obtained.
2.2.j.ii.
Solvents
Benzene ( a n a l y t i c a l grade) was purchased from Hopkln & Williams L t d . ,
twice f r a c t i o n a l l y d i s t i l l e d
sodium, wire f o r two weeks.
i n t o a dry f l a s k .
(15 cm x 4 cm d i a . , Dixon gauzes) and s t o r e d over
P r i o r to use i t was r e d i s t i l l e d under nitrogen
A n a l y t i c a l g . l . c . i n d i c a t e d a s i n g l e component ( c o l . 'A'/60°).
Methylene c h l o r i d e ( t e c h n i c a l grade) was obtained from departmental stock,
f r a c t i o n a t e d twice (40°-42°) and s t o r e d over anhydrous magnesium sulphate f o r
two days.
I t was r e d i s t i l l e d under nitrogen (41°) before use.
Ethanol and 1,4-dioxane were obtained from departmental stock and used
without p u r i f i c a t i o n .
2.2.j.iii.
M a t e r i a l s s y n t h e s i z e d from simpler chemicals
S y n t h e s i s o f hydrobenzoin from benzoin
Sodium borohydride
s o l u t i o n of benzoin
(2.7g, 0.072 mole) i n water (50 mis) was added to a
(15.Og, 0.072 mole) i n 1,4-dioxane (200 mis) contained
i n a c o n i c a l f l a s k and the mixture was b o i l e d (20 mins).
Following d e s t r u c t i o n
of unreacted NaBH^ with d i l u t e CH^COOH and evaporation of the s o l u t i o n , a white
s o l i d was obtained which was washed with water and r e c r y s t a l l i z e d twice ( e t h a n o l /
water 60:40) to give hydrobenzoin
(12.lg, 8 0 % ) , m.pt. 147°-148° ( l i t .
150°), i d e n t i f i e d by mass spectrometry
( c o r r e c t molecular ion a t m/e
expected fragment ions) and i n f r a r e d spectroscopy.
1 4 0
214
149°and
The substance was
r e c r y s t a l l i z e d t h r e e more times from the same s o l v e n t and f i n a l l y from a l a r g e
volume of ethanol/water (80:20); m.pt.
on
147.5° (big p l a t e s , s i n g l e spot on
t.l.c.
silica).
S y n t h e s i s of m-dibenzoylbenzene
m-Dibenzoylbenzene was i n i t i a l l y prepared according to the published route.
- 81 -
To a s t i r r e d s o l u t i o n of i s o p h t h a l o y l c h l o r i d e
benzene (400 m i s ) ,
i n small portions
(50g, 0.246 mole) i n dry
anhydrous aluminium c h l o r i d e (80g, 0.60
(ca. 60 mine).
The s o l u t i o n was
mole) was
added
r e f l u x e d f o r 2 h r s , cooled
and hydrolysed by pouring i n t o 10% HCl/ice water s o l u t i o n (3 l i t r e s ) .
evaporation of benzene, the r e s u l t i n g crude m a t e r i a l was
After
recovered by
filtration
and washed s u c c e s s i v e l y with a 5% aqueous s o l u t i o n of sodium carbonate, a 5%
aqueous s o l u t i o n of HC1
and water p r i o r to r e c r y s t a l l i z a t i o n from cyclohexane.
Repeated r e c r y s t a l l i z a t i o n
(20 to 25 times) afforded
spot on t . l . c . on s i l i c a (acetone,
methanol, t o l u e n e ) .
103°-104° ( l i t .
6 0
chloroform, benzene, ethanol,
The y i e l d of pure m a t e r i a l was
109°-110°).
a material giving a single
acetonitrile,
j u s t under 21%;
m.pt.
The product had the c o r r e c t m.s. and i . r .
spectrum.
The u n s a t i s f a c t o r y y i e l d obtained by the above procedure to a more
d e t a i l e d i n v e s t i g a t i o n of t h i s r e a c t i o n .
by t . l . c .
A n a l y s i s of the r e a c t i o n by-products
(benzene, chloroform) revealed the presence of low mobility
substances
( p o s s i b l e polymeric m a t e r i a l s ) , some u n i d e n t i f i e d products, and i s o p h t h a l i c
acid.
The l a t t e r must have r e s u l t e d from the h y d r o l y s i s o f unreacted
isophthaloyl chloride.
I n one preparation
using the procedure given above i t
was p o s s i b l e to i s o l a t e c a . lOg of i s o p h t h a l i c a c i d from the r e a c t i o n l i q u o r s by
treatment with aqueous potassium carbonate and subsequent a c i d i f i c a t i o n o f the
aqueous l a y e r .
I n an attempt to improve the y i e l d of the r e a c t i o n , the following modified
procedure was
used:
doubly d i s t i l l e d i s o p h t h a l o y l c h l o r i d e (200g) were d i s s o l v e d
i n sodium d r i e d benzene (2O0O mis) with vigorous s t i r r i n g .
anhydrous aluminium c h l o r i d e
(400g) was
added i n smaller portions than i n the
previous method over a longer period of time ( c a . 6 h r s ) ;
was
complete, the mixture was
r e f l u x e d for another 6 h r s .
F i n e l y ground
when the
addition
s t i r r e d a t room temperature f o r 6 hrs and
Following
h y d r o l y s i s of the mixture,
then
organic
- 82 -
m a t e r i a l s were e x t r a c t e d with benzene (2 x 1000 mis) and the e x t r a c t s b o i l e d
three times with a c t i v a t e d animal c h a r c o a l .
The c o l o u r l e s s s o l u t i o n obtained
was evaporated and the recovered white s o l i d was r e c r y s t a l l i z e d three times
from cyclohexane to give pure m-dibenzoylbenzene (196g, 70%) as shown by t . l . c .
on s i l i c a using a v a r i e t y of e l u e n t s .
T h i s product had the c o r r e c t m.s. and
i . r . spectrum, m.pt. 103°-104°, and elemental a n a l y s i s (found C, 83.68;
5.29;
calculated for
C
H
2 0
0
1 4
c
2 '
8 3
9
- °/'
H
H,
» 4.93).
A small sample of the p u r i f i e d m-dibenzoylbenzene
was d i s s o l v e d i n a
l a r g e volume of b o i l i n g cyclohexane, and the s o l u t i o n was l e f t to cool slowly
over a p e r i o d of s e v e r a l days.
Large prisms of m a t e r i a l , some o f them n e a r l y
2.5 cm long were obtained, having a very sharp melting p o i n t o f 103.8°.
Preparation o f 1,2,2,2-tetraphenylethanol
To a s o l u t i o n of benzopinacolone (3.48g, 0.01 mole) i n ethanol (100 mis)
a s o l u t i o n o f sodium borohydride
(0.38g, 0.01 mole) i n water was s l o w l y added.
A f t e r f r o t h i n g had subsided, the mixture was r e f l u x e d f o r 2 h r s .
Addition of 2
l i t r e s of water caused the p r e c i p i t a t i o n of a white powdery m a t e r i a l which
recovered by f i l t r a t i o n ,
was
washed with copious amounts of water, r e c r y s t a l l i z e d from
50:50 methanol/water and d r i e d under vacuum to give 1,2,2,2-tetraphenylethanol
(2.8g, 8 0 % ) , m.pt.
for
C H 0:
2 g
2 2
150°
C, 89.14;
(lit.
1 4 0
H, 6.29.
151°);
found C, 88.89;
H, 6.20;
calculated
The m a t e r i a l gave a s i n g l e spot on
on s i l i c a (benzene, chloroform, ethanol, methanol).
no molecular ion, the h i g h e s t peak being a t m/e
t.l.c.
The mass spectrum showed
332 (molecular i o n - 1 8 ) ;
other main peaks were a t 224, 243, 182, 167, 165, 152, 105, 77.
the
The
infrared
spectrum of the r e c r y s t a l l i z e d product (nujol mull) showed a t r i p l e t
of peaks
i n the OH s t r e t c h i n g region, 3600 (strong-sharp), 3540 (weak-sharp), c a .
1
3450 (broad-very weak) cm .
The product was r e - p u r i f i e d by sublimation a t
140°/0.005 mmHg; the i n f r a r e d spectrum of t h i s product
(m.pt. 151.5°) showed
a q u a r t e t o f peaks i n the OH stretching region a t 3590 (strong-sharp),
- 83 -
3560 (weak-sharp),
3540 (medium-sharp), 3450 (medium-broad) cm
to peaks a t v
3080, 3050, 3020, 2960, 2920, 1590, 1490, 1445, 1045,
7o5 cm
max
:
(spectrum recorded as KBr disc) .
, i n addition
1030,
I n an attempt t o ensure the complete
dryness o f the product, a benzene s o l u t i o n o f a sample o f the sublimed
1,2,2,2-tetraphenylethanol was r e f l u x e d i n a Dean-Stark apparatus;
there
was no change i n the i n f r a r e d spectrum or the m.pt. of the recovered sample.
A f u r t h e r s u r p r i s i n g r e s u l t was obtained when the s o l u t i o n phase i n f r a r e d
spectrum of the substance was examined under the conditions s p e c i f i e d i n
Table 2.6.
A doublet o f peaks was obtained, s i m i l a r t o the ones obtained
f o r 1,2-diols i n the OH s t r e t c h i n g region, possibly i n d i c a t i n g the existance
of some degree o f intermolecular hydrogen bonding i n an associated dimer.
Preparation o f g-phenylbenzoin
A saturated s o l u t i o n o f b e n z i l (16g) i n ether was slowly added (30 mins)
t o a s t i r r e d ether s o l u t i o n (200 mis) o f phenylmagnesiumbromide (from 15g
bromobenzene) a t 0°.
The r e s u l t i n g s o l u t i o n was r e f l u x e d f o r 30 mins, then
hydrolysed by pouring i n t o 1 l i t r e 10% HCl/ice water mixture.
A brown viscous
mass was obtained which was t r e a t e d several times w i t h ethanol t o give a
w h i t i s h powder (65%);
t h i s was r e c r y s t a l l i z e d several times from ethanol/water
(70:30) g i v i n g a-phenylbenzoin (50%), a white c r y s t a l l i n e s o l i d m.pt.
(lit.
1 4 0
C, 83.31;
88°);
found:
H, 5.59.
C, 83.89;
H, 5.95;
c a l c u l a t e d f o r C_H,^0„:
20 16 2
This m a t e r i a l gave a s i n g l e spot on t . l . c . on s i l i c a
(benzene, chloroform, ethanol, acetone/water, a c e t o n i t r i l e ) .
f u r t h e r p u r i f i e d by sublimation (90°/0.005 mmHg);
melted a t 88.8°.
being m/e
87°
The product
was
the sublimed m a t e r i a l
The mass spectrum showed no molecular i o n the highest peak
184 w i t h prominent peaks at m/e
i s extensive fragmentation i n the source.
183, 151, 106, 105, 77;
c l e a r l y there
The u.v. spectrum i n cyclohexane
revealed three peaks a t 350 ( 3 8 ) , 347 (84), and 317 (258) nm (c) i n a d d i t i o n
to strong aromatic bands.
The i . r . spectrum (KBr disc) showed v
: 3500,
- 84 -
3050, 3040, 1675, 1600, 1580, 1500, 1450, 1350, 1250, 1185, 1030, 850, 700
1
(doublet) cm .
The n.m.r. spectrum showed a m u l t i p l e t I n the aromatic proton
region a t 6 7.7(15) and a s i n g l e t a t 6 4.91(1) which disappeared on a d d i t i o n
of D2O assigned t o the hydroxy1 group.
Preparation o f T r i p h e n y l g l y c o l
137
Method A;
Finely ground benzoin (21.2g, 0.1 mole) was slowly added
to a vigorously s t i r r e d ether s o l u t i o n o f phenylmagnesiumbromide (from 55g
bromobenzene).
Addition, over a period o f 1 h r , was c a r r i e d out a t 20°, the
r e s u l t i n g mixture was s t i r r e d f o r 5 hrs a t room temperature and then gently
refluxed f o r 6 h r s ;
mixture.
i t was then hydrolysed by pouring i n t o 5% HCl/ice water
A powdery product was obtained i n 60% y i e l d which, a f t e r repeated
r e c r y s t a l l i z a t i o n s from ethanol yielded pure t r i p h e n y l g l y c o l (45%) , m.pt.
icc° tn- 128,129 ...-o . , . 0 ,
165
(lit.
168 , 164 ) .
Method B:
A s o l u t i o n o f sodium borohydride (0.01 mole) i n water was
slowly added t o a s t i r r e d s o l u t i o n o f a-phenylbenzoin (0.01 mole) i n ethanol
(150 mis).
A f t e r i n i t i a l vigorous f r o t h i n g had subsided, the mixture was
refluxed f o r 3 hrs.
water;
A white m a t e r i a l p r e c i p i t a t e d on a d d i t i o n o f 1 l i t r e o f
i t was recovered by f i l t r a t i o n , washed w i t h water, r e c r y s t a l l i z e d
from ethanol/water (70:30) and d r i e d under vacuum t o give t r i p h e n y l g l y c o l
(85%) , m.pt. 166°.
Materials obtained by both methods gave, a f t e r repeated r e c r y s t a l l i zations from ethanol/water (70:30), single spots on t . l . c . on s i l i c a
(benzene, toluene, chloroform, a c e t o n i t r i l e , methanol,
acetone/water,
ethanol, carbon t e t r a c h l o r i d e , ethylacetate, chloroform/carbon t e t r a chloride).
Elemental analyses were as f o l l o w s :
H, 5.94; method B:
C, 82.73;
method A:
C, 82.91;
H, 6.25; calculated f o r C H 0 : C, 82.38;
20 18 Z
0
H, 6.44. Both samples displayed the same s p e c t r a l c h a r a c t e r i s t i c s .
i n f r a r e d spectrum (KBr disc) showed v
The
: 3570, 3470, 3090, 3070, 3040,
2940, 1500, 1450, 1190, 1065, 1045, 1030, 900, 760, 750, 700, 620 (doublet).
- 85 -
The
H n.m.r. spectrum (CDCl /CD.jC0CD , TMS e x t . r e f . ) showed a
3
6 7.7(15), doublets at 6
a s i n g l e t at 6 3.88(1);
5.59
raultiplet
3
(J = 4 Hz, 1) and 6 4.04
the signals at 6 4.04
at
(J = 4 Hz, 1 ) , and
and 3.88 disappeared
on
a d d i t i o n of D^O allowing t h e i r assignment as hydroxyl protons attached t o
the secondary and t e r t i a r y carbons r e s p e c t i v e l y .
Sublimation o f t r i p h e n y l g l y c o l (130°/0.005 mmHg) afforded a m a t e r i a l
(m.pt. 166.8°) whose i . r . spectrum i n the s o l i d s t a t e (KBr disc) displayed
1
3 peaks i n the OH s t r e t c h i n g region (v
:
max
i n the C-H a l i p h a t i c s t r e t c h i n g region (v
3560, 3520, 3460 cm" )
:
1
2930, 2890 cm" ).
and 2 peaks
There were
DlclX
also some minor differences i n the f i n g e r p r i n t region o f the spectrum.
Elemental
1
analysis f i g u r e s , and H n.m.r. spectrum o f the sublimed were not d i f f e r e n t
from those o f the r e c r y s t a l l i z e d m a t e r i a l .
The substance gave a s i n g l e spot
on t . l . c . on s i l i c a (benzene, chloroform, ethanol, a c e t o n i t r i l e ) .
The
solution
phase i n f r a r e d spectrum o f the sublimed m a t e r i a l i n the OH s t r e t c h i n g region
(CCl solvent - see Table 2.6) was the same as the one f o r the r e c r y s t a l l i z e d
4
material.
2.2.k.
Discussion and
Conclusions
The basic question asked i n t h i s Section, as already set out i n 2.2.a was:
'Can poly(pentaphenylglycerols) and higher analogues o f s t r u c t u r e shown i n
Figure 2.30 be prepared by the photoreductive a d d i t i o n o f aromatic bisketones
to s u i t a b l e a l c o h o l i c hydrogen donors?'.
This question was answered i n 2.2.f.
where i t was established t h a t the model r e a c t i o n i l l u s t r a t e d i n Figure
2.47
i s l i m i t e d t o the case where m = 1, benzopinacol being q u a n t i t a t i v e l y obtained;
when m = 2 r e a c t i o n does not a f f o r d any detectable products.
Cases where m > 2
have not been examined, p a r t l y i n view o f the absence o f reports
on such
compounds i n the l i t e r a t u r e and p a r t l y due t o the doubts on the p o s s i b i l i t y
o f t h e i r existence a r i s i n g from the f a i l u r e t o i s o l a t e pentaphenylglycerol from
the r e a c t i o n described i n 2.2.1.
- 86 -
9
+
H
350 nms
solvent
C_
OH
_m=l or 2
Figure 2.47
The f a i l u r e o f the model r e a c t i o n (Figure 2.47, m = 2) t o proceed leads
to the conclusion that the photoreductive polymerization o f bisketones cannot be extended beyond the polybenzopinacol
stage, i n other words t h i s type
o f polymerization cannot be applied t o the synthesis o f s t r u c t u r e s o f the k i n d
shown i n Figure 1.12.
Although the question regarding the synthesis o f poly(pentaphenylglycerols)
and higher analogues was answered, some new questions have been uncovered:
a)
The o l d dispute between Ciamician and Paterno regarding the formation
o f t r i p h e n y l g l y c o l was resolved i n favour o f Ciamician
(2.2.d).
However,
when the reaction was repeated by us a b r i g h t yellow colour was observed a f t e r
a few hours o f u l t r a v i o l e t i r r a d i a t i o n , i n d i c a t i n g the formation o f an
intermediate.
By analogy t o the benzophenone/isopropanol and benzophenone/
ethanol photoreductions
(see 2.1.b) i t seems probable t h a t t h i s i s a species
o f the type shown i n Figure 2.48.
Such a species might act as an i n t e r n a l
l i g h t f i l t e r and t h i s would account f o r the slow r e a c t i o n r a t e observed and the
f a i l u r e o f the r e a c t i o n t o go i n t o completion even a f t e r 300 hrs o f i r r a d i a t i o n
(see 2.2.d).
A l t e r n a t i v e l y , one could a t t r i b u t e the b r i g h t yellow colour t o
the photolysis o f benzaldehyde, i t s e l f a product o f the benzylalcohol/
benzophenone photoreaction;
p h o t o l y s i s o f neat colourless benzaldehyde was
87
99
-C
OH
Ok
*C
CH
C
H
=
_9
\ _ / —
HO
H
C
~
OH
Figure 2.48
found t o y i e l d yellow coloured materials (see Chapter 3 ) .
A b r i g h t yellow colour was also observed i n the photoreactions o f
m-dibenzoylbenzene/hydrobenzoin mixtures and benzophenone/l-phenylethanol
mixtures (2.2.g).
Again, one could postulate the formation o f s i m i l a r coloured
intermediates as shown i n Figure 2.49. However, the o r i g i n o f the yellow
CH
HO
OH
c
II
0
c= (
)—c
/
c-
I
HO
OH
H
I
OH
Figure 2.49
colour has not been r i g o r o u s l y examined and the nature o f the intermediates
involved i s open t o question.
- 88 -
3)
The inertness o f t r i p h e n y l g l y c o l and 1,2,2,2-tetraphenylethanol
towards benzophenone t r i p l e t i s another question not easy t o deal w i t h .
In
2.1.b.vi the s t e r i c e f f e c t on photoreduction was examined and some examples
were given showing t h a t s t e r i c hindrance can be important.
Comparative
molecular model studies o f the compounds examined here have shown t h a t f o r
both structures the t e r t i a r y hydrogen, which was expected t o be a b s t r a c t a b l e ,
appears t o be only marginally more hindered than the t e r t i a r y hydrogen
i n benzhydrol or hydrobenzoin.
I n our view, i t seems u n l i k e l y t h a t the complete
lack o f r e a c t i v i t y e x h i b i t e d by these compounds can be accounted f o r by s t e r i c
hindrance;
on the other hand, the C-C
a bond separating the (OH)HC(CgH )
5
group from the (CgHg)COH group ( i n t r i p h e n y l g l y c o l ) and the (CgH,.) 3C group
2
( i n 1,2,2,2-tetraphenylethanol) should r u l e out any e l e c t r o n i c i n t e r a c t i o n s
between the groups, at l e a s t o f the type known and understood by us.
the
Finally,
'quencher theory* having been r u l e d out (see 2 . 2 . f ) , we are l e f t w i t h no
explanation t o suggest f o r these observations.
Other authors have commented on the unexpected s e l e c t i v i t y of the
benzophenone t r i p l e t i n hydrogen a b s t r a c t i o n r e a c t i o n s . Thus, although i t i s
w e l l established t h a t hydrogen a b s t r a c t i o n occurs r e a d i l y from toluene and
diphenylmethane i t has been reported t h a t the t e r t i a r y hydrogen o f t r i p h e n y l 97
methane i s not abstractable.
I n the case o f these three hydrocarbons i t
i s not d i f f i c u l t t o construct a r a t i o n a l i z a t i o n o f these observations i n terms
of s t e r i c hindrance.
On the other hand i f s t e r i c e f f e c t s are c o n t r o l l i n g the
a b s t r a c t a b i l i t y o f the t e r t i a r y hydrogens i n benzhydrol, hydrobenzoin, t r i p h e n y l g l y c o l and tetraphenylethanol the e f f e c t s depend on rather s u b t l e d i f f e r e n c e s
which are not r e a d i l y detected by examination o f space f i l l i n g molecular models.
y)
The f a i l u r e t o i s o l a t e pentaphenylglycerol or detect high molecular
weight products from the r e a c t i o n between d i e t h y l mesoxalate and excess o f
p h e n y l l i t h i u m i s another problem which arose during the course o f these
- 89 -
investigations.
Evidence presented i n s e c t i o n 2.2.1 tends to suggest t h a t
139
the o r i g i n a l claim to have s y n t h e s i z e d pentaphenylglycerol
was
erroneous.
The o r i g i n a l author's only evidence, apart from the 'colour t e s t ' which.has
been shown to be meaningless, i s the good agreement found and c a l c u l a t e d
analytical figures.
However, the o c c l u s i o n of methanol s o l v e n t i n the
molecule due to inadequate drying might have lowered elemental a n a l y s i s
f i g u r e s , leading to the wrong c o n c l u s i o n s .
The formation of t r i p h e n y l c a r b i n o l from the r e a c t i o n of a l a r g e excess
of p h e n y l l i t h i u m with d i e t h y l ketomalonate i s not i n h e r e n t l y unreasonable
and
i t i s i n t e r e s t i n g to note t h a t the product y i e l d obtained i n t h i s work and
by the o r i g i n a l author corresponds to the formation of a t h i r d of a mole of
c a r b i n o l f o r each d i e t h y l ketomalonate
r e a c t i o n was not undertaken;
consumed.
A d e t a i l e d study of t h i s
however i f i t i s assumed t h a t the i n i t i a l a t t a c k
of p h e n y l l i t h i u m takes p l a c e a t the c e n t r a l ketogroup and i s followed by
e l i m i n a t i o n of carbon monoxide and ethoxide anion, the beginnings of a p o s s i b l e
r a t i o n a l i z a t i o n can be c o n s t r u c t e d .
Although i t may be t h a t pentaphenyl-
g l y c e r o l i s i n h e r e n t l y unstable and fragmented
as f a s t as i t i s formed;
this
would be s u r p r i s i n g s i n c e examination of space f i l l i n g models would not l e a d
one to suspect t h a t the compound i s s i g n i f i c a n t l y more s t e r i c a l l y hindered
than, say, benzopinacol.
However, the observation t h a t benzopinacol g i v e s
118
r a d i c a l s by C-C bond homolysis under mild c o n d i t i o n s
may be quoted i n
support of the p o s t u l a t e d i n s t a b i l i t y of p e n t a p h e n y l g l y c e r o l .
6)
F i n a l l y the d i f f e r e n c e i n the s o l i d s t a t e i n f r a r e d spectrum between
r e c r y s t a l l i z e d and sublimed t r i p h e n y l g l y c o l , and the unexpected
of
exhibition
a doublet of peaks i n the OH s t r e t c h i n g region by 1,2,2,2-tetraphenylethanol
i n CC1 s o l u t i o n (see 2 . 2 . j . i i i ) are f u r t h e r questions which remain unanswered.
2.3. Use of the diphenylmethane-benzophenone r e a c t i o n as the polymer
b u i l d i n g step
4
- 90 -
2.3.a.
D e t a i l s of model reactions
2.3.a.l.
Discussion o f l i t e r a t u r e
The diphenylmethane-benzophenone photoreaction was f i r s t i n v e s t i g a t e d by
11
Paternb and C h i e f f i almost 60 years a g o . ^
Their experiment consisted o f
i n s o l a t i n g 20g (0.109 mole) o f benzophenone and 25g
methane i n a sealed tube.
temperature,
(0.148 mole) of diphenyl-
Such a mixture c o n s t i t u t e s a l i q u i d mass a t ambient
so the authors found i t more convenient not to use a solvent.
Hard c r y s t a l s were observed forming on the i n s i d e w a l l o f the tube a f t e r
only two days o f i n s o l a t i o n ;
they were separated a f t e r ten days and the
remaining s o l u t i o n was i n s o l a t e d again u n t i l r e a c t i o n was complete.
The s o l i d m a t e r i a l obtained was dissolved i n b o i l i n g benzene and an
'almost pure' novel compound c r y s t a l l i z e d on cooling.
Examination o f the
r e c r y s t a l l i z a t i o n solvent revealed the presence o f traces o f the novel compound
and the excess o f dlphenylmethane.
No other materials were i d e n t i f i e d .
I n order t o make sure t h a t the s o l i d m a t e r i a l obtained from the i n s o l a t i o n
was i n f a c t pure, the authors t r e a t e d i t successively w i t h the f o l l o w i n g hot
solvents:
1
ethanol, 'acetic e t h e r , 'acetic a c i d ' , 'acetic ether' again
and
f i n a l l y benzene, s t i l l leaving an i n s o l u b l e p o r t i o n ['acetic ether' i s the
l i t e r a l t r a n s l a t i o n , we t h i n k t h i s was probably e t h y l a c e t a t e ] . A l l the samples
thus obtained melted a t 212°-214°. The novel compound was found t o be only
s l i g h t l y soluble i n the above solvents ( i n cold) and also i n d i e t h y l e t h e r ,
chloroform, carbon d i s u l p h i d e , p-xylene, fused phenol, fused thymol etc. I t
was found t o be soluble i n hot solvents g i v i n g l a r g e , w e l l defined needles on
cooling.
The r e s u l t s o f elemental analysis and e b u l l i o s c o p i c molecular
weight determination i n ethanol and benzene were i n good agreement w i t h the
values calculated f o r C ^ I ^ O . t h e 1:1 a d d i t i o n product.
Q
Treatment o f the product w i t h ?2 5
^
n
1
XY -
6 1 1 6
afforded tetraphenylethylene,
i d e n t i f i e d by means of elemental analysis and m.pt.
determination.
Treatment
w i t h phosphorous and iodine afforded tetraphenylethane s i m i l a r l y i d e n t i f i e d .
- 91 -
On the b a s i s o f the above evidence the authors assigned to the product
119
the s t r u c t u r e of 1,1,2,2-tetraphenylethanol.
141
The compound was f u r t h e r studied by Bergmann and Engel
who
isolated
two forms of i t , one melting a t 235° (a) and another melting a t 216°
($) ,
the l a t t e r prepared by the i n s o l a t i o n o f the benzophenone-diphenylmethane
mixture.
They a t t r i b u t e d t h i s phenomenon to isomerism of 1,1,2,2-tetraphenyl-
ethanol, r e s u l t i n g from i n a b i l i t y of the (CgH,.) C0H and (CgHg) CH groups
141
2
2
present i n the molecule to r o t a t e f r e e l y about the ethane C-C bond.
142
Wegler
r e - i n v e s t i g a t e d the i n s o l a t i o n experiment and obtained a product
which, a f t e r three r e c r y s t a l l i z a t i o n s from acetone melted a t 215°-217°.
Attempts to r e p l a c e the OH group by c h l o r i n e never gave halogenated d e r i v a t i v e s ,
and only a f t e r repeated r e c r y s t a l l i z a t i o n s was a homogeneous product obtained,
i d e n t i f i e d as tetraphenylethylene.
By repeating the r e c r y s t a l l i z a t i o n o f the
photochemically prepared 1,1,2,2-tetraphenylethanol f i f t e e n times, i t s m.pt.
was r a i s e d to 229°.
The same r e s u l t was obtained when treatment with the
s o l v e n t was c a r r i e d out i n c o l d , so the author concluded t h a t h i s r e s u l t s
could not be i n t e r p r e t e d as the B-form being rearranged to the a-form.
When
the $-form was heated f o r s e v e r a l hours i n p y r i d i n e a t 135°, i t s melting
p o i n t was lowered somewhat and r e c r y s t a l l i z a t i o n of the product y i e l d e d the
a-form.
Wegler concluded t h a t the 3-form was impure a and t h a t heating w i t h
p y r i d i n e changed the i m p u r i t i e s to m a t e r i a l s r e a d i l y removed by
recrystallization.
subsequent
The author considerad the reported cases of benzophenone
photoreduction i n the presence of a l i p h a t i c and aromatic hydrocarbons, where
benzopinacol and the dimerized hydrocarbons are formed and concluded t h a t
i m p u r i t i e s i n the B-form were probably benzopinacol and tetraphenylethane.
He then prepared an a r t i f i c i a l mixture of a and 20% benzopinacol and t e t r a phenyl ethane and claimed t h a t i t behaved e x a c t l y l i k e the s o - c a l l e d B-form.
He a t t r i b u t e d the easy p u r i f i c a t i o n o f the B-form by b o i l i n g i t i n p y r i d i n e
to the decomposition o f benzopinacol present i n t o benzophenone and benzhydrol
- 92 -
which could then be e a s i l y removed by r e c r y s t a l l i z a t i o n .
When the cx-form
was t r e a t e d w i t h sodium i n benzene, CH (CgH,-) , (CgHg^CO, (CgH,.) CHOH,
2
2
2
CgHgCOOH and predominantly (CgH > C = C(CgH ) were obtained, whereas
5
2
5
2
treatment o f the 0-forra w i t h b o i l i n g benzene i n the presence o f sodium gave
142
an intense blue-green colour a t t r i b u t e d by the author
t o the presence o f
benzopinacol.
I n the same year t h a t Wegler published h i s r e s u l t s , 1,1,2,2-tetraphenylethanol was independently prepared by Richard v i a ground s t a t e synthesis and
i t s melting p o i n t was determined t o be 2 3 6 . 5 ° . T h r e e years e a r l i e r the
same compound was prepared by the action o f phenylmagnesiumbromide ono, ao
o 144
diphenylacetophenone and the reported melting p o i n t was 232 -233 .
In
1937, a s i m i l a r r e a c t i o n , namely the action o f phenylmagnesiumbromide on
o
o 145
CgHgCHClCOCl afforded 1,1,2,2-tetraphenylethanol melting at 232.5 -233 .
1,1,2,2-Tetraphenylethanol was also obtained i n low y i e l d by b o i l i n g
benzopinacol i n cyclohexanone;
1
t h i s sample had a m.pt. o f 232°-233°. ^^
The
f o l l o w i n g year the same author reported the r e p e t i t i o n o f the benzophenonediphenylmethane i n s o l a t i o n experiment i n i t i a l l y performed by Paterno and
119
Chieffi;
he obtained a product which, a f t e r r e c r y s t a l l i z a t i o n s , melted
a t 217°-218° on a copper block whereas m.pt. determination using a Kofler
apparatus caused sublimation t o minute needles which became opaque a t 230°-232°
and melted sharply a t 243°-244°
Further studies o f the photochemical
1
reaction by B a n c h e t t i ^ y i e l d e d a product which melted at 206°-210°;
treatment
of the product w i t h a large volume o f acetone yielded a compound m e l t i n g a t
217°-218°.
Considerable reduction i n the volume o f acetone yielded small
amounts o f benzopinacol, i d e n t i f i e d oil the basis of i t s 'behaviour under the
147
microscope'.
Further r e c r y s t a l l i z a t i o n of 1,1,2,2-tetraphenylethanol from
acetic acid caused a r i s e i n the melting p o i n t t o 223°-224° whereas
r e c r y s t a l l i z a t i o n from acetic anhydride yielded a m a t e r i a l melting at 227°228°.
F i n a l l y , b o i l i n g the m a t e r i a l i n cyclohexanol f o r one hour and
- 93 -
r e c r y s t a l l i z a t i o n o f the nearly pure material thus obtained from chloroform147
acetone and then chloroform-ethanol yielded a product melting a t 244 .
Having s a t i s f i e d himself on the question o f the p u r i t y o f 1,1,2,2-tetraphenylethanol thus obtained, and having established the formation o f benzopinacol
from the photochemical experiment, Banchetti d i d not i n v e s t i g a t e the possible
147
formation o f any other by-products.
He concluded
t h a t the best way t o
obtain 1,1,2,2-tetraphenylethanol i n high y i e l d was the i n s o l a t i o n o f the
benzophenone-diphenylmethane mixture; p u r i f i c a t i o n o f the m a t e r i a l from the
l a s t traces o f benzopinacol ( i t s e l f a low y i e l d by-product o f the photoreaction)
necessitated however heating the ethanol w i t h a high b o i l i n g solvent preferably cyclohexanol - followed by r e c r y s t a l l i z a t i o n .
This method afforded
o 147
a non-specified high y i e l d o f pure m a t e r i a l melting at 244 .
148
Another preparation o f the ethanol appeared i n the l i t e r a t u r e i n 1956:
treatment o f 0.01 mole o f the ketoester C H C(0)-CH(CgH )-0-C(0)CH i n d i e t h y l g
5
5
3
ether w i t h 0.01 mole phenylmagnesiumbromide, r e f l u x i n g f o r 30 mins, c o o l i n g ,
adding another 0.05 mole phenylmagnesiumbromide during 40 mins and
refluxing
f o r 15 mins gave a f t e r evaporation of d i e t h y l e t h e r solvent and p u r i f i c a t i o n
from chloroform 38% pure 1,1,2,2-tetraphenylethanol.
The melting p o i n t o f
the compound was however reported t o be 231°-232.5°.^^
A few years l a t e r a
group o f American workers obtained 1,1,2,2-tetraphenylethanol by the a d d i t i o n
reaction o f sodium diphenylmethide w i t h benzophenone i n l i q u i d ammonia solvent
followed by r e c r y s t a l l i z a t i o n from methylene c h l o r i d e ;
o
o 149
were obtained, melting a t 243 -244 .
86% o f pure compound
The l i t e r a t u r e i n t h i s area already presents a r a t h e r confused p i c t u r e ,
i t was therefore necessary t o re-examine the photoreaction of benzophenone
w i t h diphenylmethane before proceeding t o the proposed polymerization o f
bifunctional
monomers.
Results o f t h i s re-examination are presented i n the
next section and the l i t e r a t u r e claims reviewed t h e r e a f t e r .
- 94 -
2.3.a.ii.
a)
Experimental
Results
I r r a d i a t i o n s without solvent
A 1:1 molar mixture o f benzophenone and diphenylmethane ( s t a r t i n g w i t h
15g benzophenone) forming a homogeneous l i q u i d mass was t r a n s f e r r e d i n t o a
c y l i n d r i c a l Pyrex tube and nitrogen streamed f o r % n r . The tube was q u i c k l y
stoppered and i r r a d i a t e d a t 350 nm (ca. 40°). A f t e r 30 hrs o f i r r a d i a t i o n
the inside w a l l s o f the tube were covered w i t h a t h i c k layer o f colourless
c r y s t a l s and remaining s o l u t i o n was b r i g h t yellow.
The tube was opened,
c r y s t a l s were broken by means o f a long spatula and l e f t as a s o l i d
p r e c i p i t a t e a t the bottom o f the tube.
The s o l u t i o n was nitrogen streamed
again f o r h hr and r e - i r r a d i a t e d f o r another 60 h r s .
c r y s t a l s had formed i n the i n s i d e w a l l o f the tube.
Again colourless
Following opening o f
the tube, d e s t r u c t i o n o f the c r y s t a l l i n e l a y e r , n i t r o g e n streaming and
stoppering, s o l u t i o n was r e - i r r a d i a t e d f o r a f u r t h e r 14 hr period;
a new
layer o f c r y s t a l s had formed and yellow colour appeared somewhat more intense.
At t h a t stage the tube was opened, the c r y s t a l s were f i l t e r e d o f f and the
b r i g h t yellow s o l u t i o n obtained was nitrogen streamed and r e - i r r a d i a t e d f o r
29 hrs y i e l d i n g another layer o f hard colourless c r y s t a l s .
At t h a t p o i n t the
reaction was stopped, the c r y s t a l s were f i l t e r e d o f f , combined w i t h the crop
obtained from the previous f i l t r a t i o n and dissolved i n b o i l i n g benzene.
Slow
cooling o f the benzene s o l u t i o n y i e l d e d 17.3g (ca. 60%) o f a white c r y s t a l l i n e
material i n w e l l defined needles.
Examination o f the needles by t . l . c . on
s i l i c a (benzene) revealed the presence o f one component only, whereas
examination o f the yellow s o l u t i o n revealed the presence o f the same
m a t e r i a l and also benzophenone and diphenylmethane.
Examination o f the
r e c r y s t a l l i z a t i o n solvent by the same method revealed the presence o f the
c r y s t a l l i n e m a t e r i a l , benzophenone and diphenylmethane.
was detected.
No benzopinacol
Melting p o i n t o f the c r y s t a l s obtained was found t o be
- 95 -
o
o
228 -229 . Subsequent r e c r y s t a l l i z a t i o n s from chloroform caused only a very
small r i s e i n the melting p o i n t , not exceeding 2°.
The same r e a c t i o n was attempted using a 20% excess o f diphenylmethane.
This time however colourless c r y s t a l s formed i n the inside w a l l o f the tube
were not broken but were l e f t t o accumulate.
A f t e r 130 hrs o r i r r a d i a t i o n
a b r i g h t yellow colour was observed i n s i d e the tube.
Working-up the r e a c t i o n
products as before afforded ca. 40% o f the white c r y s t a l l i n e s o l i d which,
a f t e r r e c r y s t a l l i z a t i o n s from benzene and chloroform was found t o melt a t
229°-230°. Examination o f the white s o l i d , yellow s o l u t i o n and r e c r y s t a l l i z a t i o n solvents by t . l . c . on s i l i c a (benzene, chloroform) f a i l e d again t o
reveal the presence o f benzopinacol or other by-products.
B o i l i n g the white
c r y s t a l l i n e m a t e r i a l i n p y r i d i n e f o r 1.5 h r s , p r e c i p i t a t i o n w i t h water and
r e c r y s t a l l i z a t i o n o f the product thus obtained from benzene large c r y s t a l s
(70%), m.pt. 231°.
0)
Photoreactions i n benzene solvent
An 1:1 molar mixture o f benzophenone and diphenylmethane
(starting
w i t h lOg benzophenone) was dissolved i n benzene (0.01M w i t h respect t o both
reagents) i n a c y l i n d r i c a l Pyrex tube.
The c l e a r , colourless s o l u t i o n was
nitrogen streamed f o r 1 h r , tube was q u i c k l y stoppered and i r r a d i a t e d a t 350 :
f o r 110 h r s .
A white p r e c i p i t a t e had formed a t the end o f the i r r a d i a t i o n
p e r i o d , the s o l u t i o n being again b r i g h t yellow.
was recovered by f i l t r a t i o n , m.pt. 230°-231°.
showed v
The c r y s t a l l i n e m a t e r i a l
I . r . spectroscopy (KBr disc)
: 3540, 3080, 3060, 3020, 2920, 1600, 1580, 1480, 1445, 1340,
UlcLX
1160, 1075 (doublet), 1050, 1030, 740, 700, 650 (doublet), 620 ( t r i p l e t ) ,
580, 560 cm and was c l e a r l y d i s t i n c t from the i . r . spectrum o f benzopinacol
1
(KBr disc) v
max
:
3568-3540 ( c h a r c t e r i s t i c doublet i n the 0-H s t r e t c h i n g
r e g i o n ) , 3080, 3060, 3020, 1600, 1580, 1495, 1445, 1340, 1320, 1160, 1030,
1
760, 740, 700, 650 (doublet), 610 cm" .
Analysis o f the c r y s t a l l i n e m a t e r i a l
- 96 -
by t . l . c . on s i l i c a (benzene, chloroform) r e v e a l e d the presence o f one r e a c t i o n
product only, together with two very f a i n t spots corresponding with s t a r t i n g
materials.
R e c r y s t a l l i z a t i o n o f the product from chloroform d i d not cause
a s i g n i f i c a n t a l t e r a t i o n i n the melting point (231°-232°), or the s o l i d
s t a t e i . r . spectrum
(KBr d i s c ) .
The h i g h e s t peak i n the mass spectrum
occurred a t m/e = 332 (parent i o n (350)-18, most probably l o s s o f w a t e r ) ,
with major peaks a t 343, 342, 339, 183, 182, 177, 152, 105, 77. The m a t e r i a l
was r e c r y s t a l l i z e d once more from benzene and d r i e d under vacuum f o r 24 h r s
(m.pt. 232°).
14
Treatment o f t h e m a t e r i a l according t o B a n c h e t t i ' s p r o c e d u r e ^
resulted i n p a r t i a l
(20%) l o s s o f m a t e r i a l but no s i g n i f i c a n t i n c r e a s e i n
the melting p o i n t was observed
C, 88.86;
(m.pt. 232°-233°).
Elemental a n a l y s i s gave:
H, 6.60; c a l c u l a t e d f o r C H 0 , C, 88.70;
o c
0 0
H, 6.75. The
F.T. n.m.r. spectrum o f the m a t e r i a l i n CDCl^/CD-jCOCD-j ( e x t . TMS r e f . )
showed a s i n g l e t a t 6 7.13 (aromatic H) and four s i n g l e t s a t 6 5.23(A),
6 4.73(B), 6 3.02(C) and 6 2.81(D);
of D 0;
2
1:1.
peaks (C) and (D) disappeared on a d d i t i o n
the i n t e g r a t e d i n t e n s i t i e s were i n the r a t i o (A) + (B):(C) + (D) =
On the b a s i s o f the above evidence peaks (A) and (B) were assigned
to the t e r t i a r y hydrogen i n 1,1,2,2-tetraphenylethanol and peaks (C) and (D)
to the hydroxyl hydrogen.
I n a l a t e r experiment,
diphenylmethane (2.l0g, 0.0125 mole) and benzo-
phenone (2.275g, 0.0125 mole) were d i s s o l v e d i n benzene (50 mis, 0.5M w i t h
r e s p e c t to both r e a g e n t s ) . The c l e a r s o l u t i o n was nitrogen streamed f o r 1 h r ,
the Pyrex tube was q u i c k l y stoppered and the s o l u t i o n i r r a d i a t e d a t 350 run
for
309.2 h r s .
The s o l u t i o n became b r i g h t yellow and a white p r e c i p i t a t e
was formed a t the bottom o f the tube.
The p r e c i p i t a t e was separated by
f i l t r a t i o n , washed with a l i t t l e c o l d benzene and d r i e d under vacuum.
Both
the white p r e c i p i t a t e and the yellow s o l u t i o n were examined by t . l . c . on
silica
(benzene, chloroform, e t h a n o l ) .
I n both s o l v e n t and p r e c i p i t a t e
- 97 -
1,1,2,2-tetraphenylethanol was i d e n t i f i e d .
S t a r t i n g m a t e r i a l were not present,
i n d i c a t i n g t h a t r e a c t i o n had gone t o completion.
Analysis o f the solvent,
however, revealed the presence o f spots corresponding t o 1,1,2,2tetraphenylethane and biphenyl (CgHg-CgH,-). A very f a i n t spot corresponding
to benzopinacol was also observed.
Analysis of the q u a n t i t a t i v e l y recovered
p r e c i p i t a t e , m.pt. 216°-218° showed the presence o f some benzopinacol
spot).
(faint
R e c r y s t a l l i z a t i o n o f the product from chloroform y i e l d e d pure
1,1,2,2-tetraphenylethanol, m.pt.
230°-231°.
I s o l a t i o n o f pure benzopinacol
from the r e c r y s t a l l i z a t i o n l i q u o r s was not possible, probably due t o small
amounts o f m a t e r i a l present.
Over 95% o f pure tetraphenylethanol was
obtained from the r e c r y s t a l l i z a t i o n .
2.3.a.iii.
Comments on l i t e r a t u r e claims i n the l i g h t o f present r e s u l t s
Results from present experiments lead t o the f o l l o w i n g conclusions:
a)
the diphenylmethane-benzophenone photoreaction a t 350 nm i s a slow
one, both i n benzene solvent and without the use o f solvent.
3)
I r r a d i a t i o n o f a neat benzophenone-diphenylmethane mixture i s
d i f f i c u l t t o study because o f the hard c r y s t a l s which keep forming on the
i n s i d e w a l l s o f the c y l i n d r i c a l Pyrex i r r a d i a t i o n tube.
These c r y s t a l s
considerably diminish the amount o f l i g h t reaching the i n t e r i o r o f the
tube, i t follows t h a t i r r a d i a t i o n times reported should be t r e a t e d w i t h
caution.
Also e s p e c i a l l y i n the study o f the 1:1 molar mixture, frequent
opening of the tube, could have r e s u l t e d i n the upsetting of the precise
1:1 molar r a t i o .
Y)
I r r a d i a t i o n of neat reagents f o r up t o ca. 150 hrs ( j u s t over 6 days)
under the above mentioned conditions r e s u l t e d i n only p a r t i a l . r e a c t i o n , w i t h
1,1,2,2-tetraphenylethanol as the only detectable product.
pinacol nor 1,1,2,2-tetraphenylethane
6)
Neither benzo-
were detected by t . l . c . on s i l i c a .
During a l l i r r a d i a t i o n s a b r i g h t yellow colour has been observed.
On the basis o f e a r l i e r r a t i o n a l i z a t i o n s (see 2.1.b, also 2.2.k) one could
- 98 -
a t t r i b u t e the yellow colour t o the formation o f structures such as those
shown i n Figure 2.50.
Formation o f a s i m i l a r s t r u c t u r e from the combination
99. JK
OH
. ^ Q
H
HO
c
H
and/or
H
Figure
H
2.50
of two benzophenone k e t y l r a d i c a l s can be excluded since i n the photoreduction
of benzophenone i n benzhydrol where two such primary r a d i c a l s are i n i t i a l l y
formed, no yellow colour i s observed (see 2 . 1 . b . i i i ) .
Again, as i n the
case o f the benzophenone-benzylalcohol photoreaction examined i n 2.2.d
such
coloured species could act as i n t e r n a l l i g h t f i l t e r s and could account f o r
the
low reaction r a t e .
c)
I r r a d i a t i o n o f a d i l u t e benzene s o l u t i o n (0.01M t o t a l concentration)
of benzophenone-diphenylmethane f o r 110 hrs resulted i n incomplete r e a c t i o n ,
y i e l d i n g 1,1,2,2-tetraphenylethanol as the only detectable product.
On the
other hand, the reaction went t o completion a f t e r 309.2 hrs o f i r r a d i a t i o n o f
a more concentrated s o l u t i o n (0.5M);
the l a t t e r experiment however afforded
benzopinacol, 1,1,2,2-tetraphenylethane and biphenyl, a l l i n minute amounts.
These r e s u l t s suggest t h a t the formation of benzopinacol and t e t r a p h e n y l ethane occurs only under f a i r l y r e s t r i c t e d conditions;
thus n e i t h e r are found
i n any o f the i r r a d i a t i o n s o f mixtures o f benzophenone and diphenylmethane
e i t h e r neat or i n d i l u t e s o l u t i o n (0.01M) whereas at higher concentration
(0.5M) these out-of-cage products were formed i n detectable q u a n t i t i e s .
- 99 -
C l e a r l y the f a c t o r s which c o n t r o l whether the in-cage product
(1,1,2,2-
tetraphenylethanol) or the out-of-cage products are formed must be
subtle.
A d e t a i l e d i n v e s t i g a t i o n of the e f f e c t s of concentration
fairly
and
duration of i r r a d i a t i o n have not been undertaken s i n c e i t i s e s t a b l i s h e d
t h a t under a wide range of conditions the r e q u i r e d product, t e t r a p h e n y l ethanol i s formed i n > 95% y i e l d ;
t h i s would allow polymers of d.p.
> 20
to be obtained from i r r a d i a t i o n of s u i t a b l e b i f u n c t i o n a l analogues.
Never-
t h e l e s s i t i s p o s s i b l e to speculate about the explanation of these
observations.
I n the f i r s t i n s t a n c e i t may
be t h a t the r e l a t i v e proportions of in-cage
and out-of-cage r e a c t i o n are c o n t r o l l e d by the d e t a i l s of the medium's
composition.
A l t e r n a t i v e l y i t may be t h a t the out-of-cage products
from a r e a c t i o n of an intermediate
(such as A, F i g u r e 2.50)
arise
with ground
s t a t e benzophenone, t h a t i s by a process somewhat analogous to t h a t
suggested
81
p r e v i o u s l y by F i l i p e s c u ,
and shown i n F i g u r e
2.51.
Such a r e a c t i o n could only occur when the concentration of (A) becomes
high enough and t h e r e f o r e the p r o b a b i l i t y of i t coming i n contact with a
9 j®
6
H-C
0
r
J L . I - . ==(
n
0
X
x2
x2
H—C
Figure
2.51
C
H
HO
6o
C—C
OH
- loo -
benzophenone molecule becomes s i g n i f i c a n t .
I n c r e a s i n g the c o n c e n t r a t i o n o f
the s o l u t i o n would a l s o make the r e a c t i o n more probable by i n c r e a s i n g the
chance of intermediate (A) coming i n contact with a ground s t a t e benzophenone
molecule.
I r r a d i a t i o n o f the neat benzophenone/diphenylmethane system.may
not l e a d to the formation o f intermediate A i n s u f f i c i e n t l y high c o n c e n t r a t i o n
because of the f i l t e r e f f e c t o f the p r e c i p i t a t i n g t e t r a p h e n y l e t h a n o l . Thus
the coloured s t r u c t u r e (A) p o s t u l a t e d i n F i g u r e 2.50 could be important i n
the r a t i o n a l i z a t i o n o f the observed slow r e a c t i o n r a t e , the appearance o f the
yellow colour and the minute amounts o f benzopinacol and 1,1,2,2-tetraphenylethane obtained under some c o n d i t i o n s . I t could not however e x p l a i n the
formation o f b i p h e n y l , which i s most probably due t o the prolonged
of benzophenone i n benzene s o l u t i o n .
77 84—88
'
irradiation
Such a r e a c t i o n i s known to
83 88
y i e l d benzopinacol and biphenyl as the main products,
'
and by i t s e l f
would account f o r the formation o f both products mentioned above, would not
however e x p l a i n the formation o f 1,1,2,2-tetraphenylethane.
The almost e x c l u s i v e formation o f 1,1,2,2-tetraphenylethanol i n these
r e a c t i o n s i s a marked exception t o the normal behaviour o f t r i p l e t benzophenone
i n the presence o f hydrogen donors, where benzopinacol formation i s the main
process.
Even with aromatic hydrocarbon hydrogen donors which a r e s t r u c t u r a l l y
f a i r l y c l o s e l y r e l a t e d t o diphenylmethane the in-cage d i m e r i z a t i o n o f the
primary r a d i c a l s formed from i n i t i a l hydrogen a b s t r a c t i o n appears t o be a
r e l a t i v e l y low y i e l d process.
As a l r e a d y mentioned toluene and cumene y i e l d
only ca. 50% o f the corresponding cage products when i r r a d i a t e d i n the presence
7
6»89
of benzophenone.
On the other hand, the cage r e a c t i o n product o f the benzophenonediphenylmethane r e a c t i o n i s a p e c u l i a r compound i n i t s e l f , being i n s o l u b l e
or only s l i g h t l y s o l u b l e i n a very wide range o f laboratory s o l v e n t s i n the
c o l d , t h i s being a property not shared by c l o s e l y r e l a t e d s t r u c t u r e s such as
benzopinacol, 1,2,2,2-tetraphenylethanol, t r i p h e n y l g l y c o l e t c .
1
The H F.T.
- 101 -
n.m.r. spectrum o f the m a t e r i a l d i s p l a y s two d i s t i n c t t e r t i a r y hydrogens and
two hydroxy1 hydrogen resonances.
T h i s could be a t t r i b u t e d t o the e x l s t a n c e
of two s t a b l e conformational isomers o f the m a t e r i a l , as shown i n F i g u r e 2.52,
although i t i s worth noting t h a t the r e l a t e d s t r u c t u r e s l i s t e d above do not
show t h i s e f f e c t .
Due t o the low s o l u b i l i t y o f the m a t e r i a l i n most c o l d
0
II
H
OH
OH
Figure 2.52
s o l v e n t s i t was not p o s s i b l e to i n v e s t i g a t e i t s s o l u t i o n phase i . r .
spectrum
or examine i t s p h o t o r e a c t i v i t y with benzophenone i n benzene s o l u t i o n a t
concentrations comparable t o those o f previous
experiments.
Deciding whether the experimental r e s u l t s obtained i n our hands a r e i n
agreement with e a r l i e r r e p o r t s i s a r a t h e r d i f f i c u l t t a s k .
p a p e r s * " ^ r e c o r d e d
Earlier
l i m i t e d experimental d e t a i l s ;
the i r r a d i a t i o n
source was the sun r a t h e r than a lamp of defined output, the temperature
was not recorded and may w e l l have been s i g n i f i c a n t
(ground temperatures i n
the North A f r i c a n d e s e r t may reach 70°C) and almost a l l these e a r l y papers
are devoid o f q u a n t i t a t i v e information.
S p e c t r a l and chromatographic
evidence not being a v a i l a b l e t o these e a r l y workers, the melting p o i n t o f
the product acquired a c e n t r a l r o l e i n the determination of p u r i t y .
Ways
of drying o f 1,1,2,2-tetraphenylethanol however were r a r e l y s p e c i f i e d and
o c c l u s i o n o f t r a c e s o f s o l v e n t can be c r i t i c a l i n melting p o i n t determinations.
Once these p o i n t s a r e taken i n t o account, an i d e a o f the d i f f i c u l t i e s
arising
- 102 -
i n a s s e s s i n g previous r e s u l t s becomes c l e a r .
142
Wegler's claim
t h a t as much as 20% benzopinacol and hydrocarbon can
be present as the by-products o f the i n s o l a t i o n experiment seems t o be
g r o s s l y exagerated.
Wegler must have expected t o observe t h e formation of
benzopinacol i n view o f the reported behaviour o f benzophenone on i n s o l a t i o n
i n the presence o f v a r i o u s hydrogen donors;
i t i s however s u r p r i s i n g t h a t
Paterno c a t e g o r i c a l l y excluded the formation o f benzopinacol or any other
119
by-products i n t h i s case
benzopinacol formation.
s i n c e he had reported so many examples o f
A p o s s i b l e explanation could be t h a t any benzopinacol
or tetraphenylethane formed i n Paterno's experiments was destroyed by b o i l i n g
the r e a c t i o n product i n benzene before examination.
I n our hands, b o i l i n g
a toluene s o l u t i o n containing an 1:1 molar mixture o f benzopinacol and
1,1,2,2-tetraphenylethane f o r 3 h r s r e s u l t e d i n the t o t a l disappearance o f
s t a r t i n g m a t e r i a l s and formation of 1,1,2,2-tetraphenylethanol with t r a c e s
of benzophenone and benzhydrol as by-products.
147
Banchetti
claimed to have i s o l a t e d benzopinacol out o f h i s own
i n s o l a t i o n experiment, by c o n s i d e r a b l y reducing the volume o f the mother
l i q u o r s o f r e c r y s t a l l i z a t i o n o f the crude 1,1,2,2-tetraphenylethanol.
147
d i d not however s p e c i f y t h e percentage o f benzopinacol i s o l a t e d .
He
On the
other hand, the evidence f o r the p i n a c o l formation (behaviour under the
microscope) i s open to question.
147
Banchetti'a p u r i f i c a t i o n technique
should a l s o be considered with
great c a u t i o n s i n c e 1,1,2,2-tetraphenylethanol i t s e l f i s not very s t a b l e a t
150
high temperatures, decomposing by cleavage o f the ethane C-C bond.
The
reported by-products, benzopinacol and 1,1,2,2,-tetraphenylethane are very
s o l u b l e i n s o l v e n t s l i k e acetone and chloroform even a t room temperature;
i t should t h e r e f o r e be adequate t o wash and then r e c r y s t a l l i z e the product
from one o f these s o l v e n t s .
I n our hands, p u r i f i c a t i o n o f an 1,1,2,2-
tetraphenylethanol sample (already r e c r y s t a l l i z e d from chloroform and benzene)
using B a n c h e t t i ' s method ( b o i l i n g with cyclohexanol) d i d not s i g n i f i c a n t l y
- 103 -
a f f e c t the m.pt. or the l . r . spectrum of the m a t e r i a l recovered.
however I n t e r e s t i n g to n o t i c e t r a c e s of (CgHg) 2
C 0
C
H
I t was
^ 6 5^ 2 ^ 2 P
r e s e n t
*
n
cyclohexanol ( t . l . c . on s i l i c a , benzene) probably r e s u l t e d from p a r t i a l
thermal decomposition
temperatures.
of the tetraphenylethanol a t r e l a t i v e l y high
I n one of our i n i t i a l i r r a d i a t i o n s o f neat benzophenone and
diphenylmethane, crude product obtained was r e c r y s t a l l i z e d from benzene and
chloroform only;
t . l . c . on s i l i c a ,
13
C F.T. n.m.r. and
evidence however showed the product to be pure.
1
H F.T. n.m.r.
No benzopinacol or 1,1,2,2-
tetraphenylethane were detected which d i r e c t l y c o n t r a d i c t s B a n c h e t t i ' s
assertions.
The long arguments concerning melting p o i n t s demonstrate the
shortcomings
of t h i s p a r t i c u l a r c r i t e r i o n of p u r i t y ;
i t i s worth noting t h a t
1,1,2,2-tetraphenylethanol prepared v i a ground s t a t e chemistry has a l s o given
•
,. .
. .
n-,,-0
varying melting p o i n t s , 235 ,
232°-233°,
144
231°-232.5°,
148
141 „,„o _-,-,o 146 -...o . . o 149
_o 143
232 -233 ,
243 -244 ,
236.5 ,
n
232.5°-233°.
145
I t seems q u i t e l i k e l y t h a t
the compound e x i s t s i n two isomeric forms, p o s s i b l y c i s o i d and t r a n s o i d
conformational isomers, having d i f f e r e n t m.pts.;
supports t h i s p r o p o s i t i o n .
F.T. n.m.r. evidence
The v a r y i n g m.pts. recorded could thus r e s u l t
from v a r y i n g proportions of the two i s o m e r i c forms.
On the b a s i s of the r e s u l t s obtained from the model r e a c t i o n , one would
expect the i r r a d i a t i o n of an aromatic bisketone i n the presence of an
equimolar amount of a bisbenzylbenzene to y i e l d a l i n e a r polymer containing
at l e a s t 95% tetraphenylethanol u n i t s i n the backbone.
By analogy with the
model r e a c t i o n the polymer formation would be expected to be slow and the
product would be expected to contain a s m a l l percentage of benzopinacol
tetraphenylethane u n i t s .
and
The formation of these two types of u n i t would be
chain propagating r a t h e r than chain terminating and indeed no r e a c t i o n s which
would be chain terminating were observed i n t h i s study of the model r e a c t i o n ,
apart from the formation of t r a c e s of biphenyl which presumably arose from
- 104 -
r e a c t i o n o f benzophenone with the s o l v e n t .
F i n a l l y , c r o s s l i n k i n g and/or
branching might occur v i a the t e r t i a r y hydrogen i n the tetraphenylethanol
and tetraphenylethane types of u n i t of the proposed polymer.
o
For the a c t u a l polymer forming r e a c t i o n , m-dibenzylbenzene and mA
and p-dibenzylbenzenes were s e l e c t e d as appropriate monomers.
Benzene was
chosen as the s o l v e n t .
2.3.b.
2.3.b.i.
S y n t h e s i s of monomers
D i s c u s s i o n of p o s s i b l e routes
The preparation, p u r i f i c a t i o n and c h a r a c t e r i z a t i o n of m-dibenzoylbenzene
has already been described i n s e c t i o n 2 . 2 . j . i l l .
The preparation of a r y l a l k y l a t e d aromatic hydrocarbons has been the
s u b j e c t o f many r e p o r t s .
Zincke obtained 1,4-,
1,2-dibenzylbenzene and
diphenylmethane by the a c t i o n o f m e t a l l i c z i n c on a mixture of b e n z y l c h l o r i d e
and b e n z e n e . S i m i l a r
r e s u l t s were obtained by T h i e l e and Balhom, who
152
reacted benzene with formaldehyde i n the presence of s u l p h u r i c a c i d .
Huston and Friedmann showed t h a t the aluminium c h l o r i d e c a t a l y s e d r e a c t i o n
of b e n z y l c h l o r i d e with benzene gave a complex mixture from which they i s o l a t e d
diphenylmethane, anthracene, anthraquinone, a l i t t l e 1,2-dibenzylbenzene and
1,4-dibenzylbenzene, m.pt. 85°-86° ( a l c o h o l ) .
Japanese workers reported the s y n t h e s i s of p-phenylenedibenzyl i n a
very impure s t a t e (melting point range:
20°) by s t i r r i n g a mixture of benzene
and b e n z y l c h l o r i d e i n t e t r a c h l o r o e t h a n e with z i n c powder under n i t r o g e n ;
154
the impure m a t e r i a l was found to be photoconductive.
Profft, Drechsler
and Oberender,^^ obtained low y i e l d s of 1,4-dibenzylbenzene (m.pt. 86.5°)
from the r e a c t i o n of tetrachlorodurene with benzene under F r i e d e l - C r a f t s
conditions.
- 105 -
Pure 1,4-dibenzylbenzene, m.pt. 84°-85° (acetone) was prepared by the
one-step h y d r o l y s i s and decarboxylation of C g H g - O ^ - p - ( C H - C H ( C C l ) C g H ) ;
g
4
3
156
5
the same compound was a l s o obtained from the a c t i o n of N^/KOH a t over
190°
156
on 1,4-(p-bromobenzoyl)benzene.
P o s s i b l e routes f o r alkane preparation from the corresponding
carbonyl
157
compound i n c l u d e the Clemensen reduction and the Wolff-Kishner r e d u c t i o n .
The Clemensen reduction i n v o l v e s t r e a t i n g the carbonyl compound with
amalgamated z i n c and concentrated HC1, y i e l d i n g hydrocarbon as the main
product, but a l s o v a r i a b l e q u a n t i t i e s of the secondary
case of ketones) and unsaturated substances.
do not give s a t i s f a c t o r y r e s u l t s ;
a l c o h o l s ( i n the
P u r e l y aromatic ketones however
p i n a c o l s and resinous products o f t e n
157
predominate.
The Wolff-Kishner reduction a f f o r d s hydrocarbons upon heating
the corresponding hydrazone or semicarbazone of the carbonyl compound with
157 158
potassium hydroxide or with sodium ethoxide i n a s e a l e d tube.
'
The
Huang-Minion modification of the r e a c t i o n (formation and decomposition
hydrazone i n one r e a c t i o n v e s s e l ) i s experimentally more convenient
of the
and
reported to proceed i n b e t t e r y i e l d .
F i n a l l y a r y l a l k a n e s may
a l s o be s y n t h e s i z e d by reduction of the
158
corresponding a r y l a l k y l h a l i d e s or a r y l a l k y l t o s y l e s t e r s .
This synthetic
route would i n v o l v e reduction of the corresponding carbonyl compound to the
a l c o h o l , c o n v e r s i o n of the a l c o h o l to the a r y l a l k y l h a l i d e or to the t o s y l
e s t e r , and f i n a l l y reduction with an e f f i c i e n t reducing agent, such as
LiAlH .
1 5 8
4
2.3.b.ii.
S e l e c t i o n of routes
I n our hands, attempts to prepare m-dibenzylbenzene by reducing the
corresponding dicarbonyl compound, m-dibenzoylbenzene v i a e i t h e r the
Wolff-Kishner reduction (Huang-Minion m o d i f i c a t i o n ) , or the Clemensen reduction
gave u n s a t i s f a c t o r y r e s u l t s .
A mixture of products was obtained i n the l a t t e r
- 106 -
case which was found d i f f i c u l t t o separate, whereas the former route r e s u l t e d
i n the formation o f dark i n t r a c t a b l e t a r s .
154
R e p e t i t i o n o f the Japanese workers' experiment
yielded a small quantity
of a mixture comprising a t l e a s t 10 components ( t . l . c . on s i l i c a ,
benzene).
The f a i l u r e t o obtain the arylalky.Lated hydrocarbons by the above
d e s c r i b e d routes l e d to the i n v e s t i g a t i o n o f a l t e r n a t i v e syntheses o f 1,4and 1,3-dibenzylbenzene, shown s c h e m a t i c a l l y i n Figure 2.53. I n a d d i t i o n to
these routes once could a l s o attempt the p r e p a r a t i o n o f the dibromide
d e r i v a t i v e of the bisbenzhydrol by t r e a t i n g i t w i t h constant b o i l i n g HBr
followed by reduction using an e f f i c i e n t H
source i n an appropriate s o l v e n t .
Another a t t r a c t i v e i d e a would be t o u t i l i s e a r e a c t i o n reported by
G r i n t e r and Mason;
they obtained triphenylmethane by r e f l u x i n g t r i p h e n y l 159
c a r b i n o l i n formic a c i d .
of benzhydrol
I f t h i s process could be extended t o the conversion
t o diphenylmethane, an easy s y n t h e s i s o f the r e q u i r e d monomers
might be a v a i l a b l e from bisbenzhydrols
(Figure 2.54).
The experimental d e t a i l s o f these v a r i o u s attempts to s y n t h e s i z e the
r e q u i r e d monomers a r e given below.
i n Figure 2.53.
The steps r e f e r r e d t o a r e those i n d i c a t e d
- 107 -
H
^
H
H
II
B
OH
CI
OH
F/vi
CI
(
C
iii
V
0
O
0 = S = 0O
00== SS =
=0
—<0H
H
H
H
MgCl
6 6o
H
MgCl
v IE
CH
CH
iv
H
H
-?-©-r
H
vii)
>
H
H
H
H
B
II
OH
OH
/ / v iv i)
iii
E v).
H
H
H
MgBr
S0C1
Key
i
solvent
(v)-
H 2
°°
r
""2™"
^
^
(ii)
^
iii)
^
(g)
chloride
O
R
A Q
LiAlH
Mg
solvent
(iv)
H a B H
f v i n
. OH"
Figure 2.53
4
solvent
5 > (v)
108
Q
Q
H
II
HCOOH
^
OH
H
H
Figure 2.54
Q
- 109 -
Experimental
Step A;
Magnesium turnings (48.60g) i n a 3 necked round bottom f l a s k f i t t e d
with a mechanical s t i r r e r , p r e s s u r e e q u a l i z i n g dropping f u n n e l , double s u r f a c e
r e f l u x condenser, nitrogen gas i n l e t rjid thermometer w e l l were covered with
1.8 l i t r e s f r e s h l y d i s t i l l e d THF.
The: dropping funnel was f i l l e d with dry
bromobenzene (314.00g) and a few drops were added with e f f i c i e n t s t i r r i n g .
The r e a c t i o n s t a r t e d smoothly a f t e r about 5 mins, without the use of c a t a l y s t .
Addition of bromobenzene was r e g u l a t e d by monitoring the pot
which was maintained between 70°-8o°.
temperature
The s o l u t i o n got p r o g r e s s i v e l y darker
and was dark brown a f t e r about 2h h r s when most of the magnesium had been
consumed.
A f t e r a d d i t i o n of bromobenzene had f i n i s h e d , pot contents were
s t i r r e d f o r a f u r t h e r 1 hr period, a t the end of which temperature
to 30°.
Slow a d d i t i o n of terephthalaldehyde
(67.Og) on 0.7
l i t r e THF was
s t a r t e d with e f f i c i e n t s t i r r i n g , taking care to maintain the pot
below 40°.
dropped
then
temperature
A f t e r a l l the terephthalaldehyde s o l u t i o n had been added, the
pot contents were dark red.
The mixture was b o i l e d under r e f l u x f o r 2 h r s ,
cooled to room temperature,
and c a r e f u l l y poured i n t o ice/water (2.5 l i t r e s )
a c i d i f i e d with HC1 and s t i r r e d f o r 1 hr.
The organic l a y e r was separated and
the water l a y e r was e x t r a c t e d twice with benzene (2 x 300 m i s ) .
The
combined THF/benzene s o l u t i o n s were d r i e d over anhydrous magnesium sulphate and
f i n a l l y v o l a t i l e s o l v e n t s were removed under vacuum to give l l 6 g of crude
product
(80%).
R e c r y s t a l l i z a t i o n s from ethanol/water (75:25) afforded 70%
o f pure product
(lit.
V
max
: )
1 6 0
171°)
3 2 7 0
1280, 1240
'
( t . l . c . on s i l i c a , benzene, chloroform), m.pt.
169°-170°
d i s p l a y i n g the f o l l o w i n g i n f r a r e d absorptions (KBr d i s c ,
3 0 8 0
'
3 0 4 0
'
3 o 2 0
'
2 9 0 0
'
1 6 0 0
'
1 5 L 0
'
(doublet), 1200, 1185, 1155, 1120,
870, 830, 790, 740, 700, 635, 570, 495
1
cm" .
1 4 9 0
'
L 4 5 0
'
1 4 2
°'
1 3 4 0
'
1080, 1030, 1020, 1010,
920,
- 110 -
The r e a c t i o n d i d not proceed i n ether s o l v e n t due to the low
solubility
of terephthalaldehyde i n t h a t medium.
Step B;
p-Bisbenzhydrol (40g) obtained from step A and f r e s h l y d i s t i l l e d
t h i o n y l c h l o r i d e (180 mis) were heated under r e f l u x f o r 2 h r s .
The excess
o f t h i o n y l c h l o r i d e was d i s t i l l e d o f f under reduced p r e s s u r e and 100 mis
of
a c e t i c a c i d p l u s 2 drops of concentrated h y d r o c h l o r i c a c i d were added.
The
white s o l i d which p r e c i p i t a t e d was f i l t e r e d o f f and t r e a t e d again with 60 mis
of g l a c i a l a c e t i c a c i d p l u s two drops of concentrated h y d r o c h l o r i c a c i d .
The s o l u t i o n was b o i l e d with d e c o l o u r i z i n g c h a r c o a l , f i l t e r e d hot and the
c o l o u r l e s s f i l t r a t e allowed to c o o l .
Cooling caused the p r e c i p i t a t i o n of the
c o l o u r l e s s d i c h l o r i d e which was f i l t e r e d and d r i e d by pumping under vacuum
for 48 hrs a t 60°.
m.pt. 190°
1600,
(lit.
1 6 1
White needles were obtained from chloroform/hexane,
197°-198°), \ >
max
(KBr d i s c ) :
3080, 3060, 3035, 2960,
1585, 1510, 1500, 1450, 1425, 1345, 1260, 1225, 1120,
1080,
1030,
1
1020, 1000, 835, 785, 735, 700, 635, 615, 495 cm" .
Steps C,E:
p-Bisbenzhydrylchloride (lO.Og) obtained from step B were slowly
added under nitrogen to 200 mis f r e s h l y d i s t i l l e d THF and magnesium turnings
(5.0g) with e f f i c i e n t s t i r r i n g .
Reaction was allowed to proceed f o r 1 hr and
then h a l f of the r e s u l t i n g s o l u t i o n was s t i r r e d with 100 mis isopropanol f o r
8 h r s , whereas the other h a l f was poured i n t o 500 mis of i c e / w a t e r mixture
and s t i r r e d f o r 5 h r s .
Both r e a c t i o n s gave l a r g e l y p-bisbenzhydrol, unreacted
p-bisbenzhydrylchloride and a few other minor products but no p-bisbenzylbenzene
was
isolated.
Step F:
p-Bisbenzhydrol (lO.Og) obtained from step A was d i s s o l v e d i n
f r e s h l y d i s t i l l e d p y r i d i n e (300 mis) and toluene p-sulphonylchloride (10.Og)
was slowly added.
A f t e r 3 hrs of s t i r r i n g under nitrogen, s o l u t i o n
heated to 60° f o r 1 hr and then cooled to room temperature.
was
Addition of
0.5 l i t r e s of water caused the p r e c i p i t a t i o n of a yellow o i l which was
- Ill -
separated and pumped under vacuum f o r 48 h r s .
was
Resulted resinous m a t e r i a l
found to be a mixture o f a t l e a s t 8 components by t . l . c . on s i l i c a
(benzene).
Most of i t d i s s o l v e d i n hot water and stayed i n s o l u t i o n even
on cooling t o 5°.
P r e p a r a t i o n o f p-bisbenzhydrylbromide:
p-Bisbenzhydrol (20g) obtained
from step A was slowly added t o constant b o i l i n g HBr (400 mis) and the
r e s u l t a n t brown s o l u t i o n was b o i l e d under r e f l u x f o r 3 h r s .
Most o f the
water was taken o f f by d i s t i l l a t i o n under reduced p r e s s u r e , the residue
was d i s s o l v e d i n 500 mis o f benzene and b o i l e d using a Dean-Stark
apparatus.
When n e a r l y a l l the water had come o f f , benzene s o l u t i o n was d r i e d over
anhydrous magnesium sulphate and then volume o f benzene was reduced to 100 mis.
Addition o f 600 mis o f hexane caused the p r e c i p i t a t i o n o f a m a t e r i a l which
was
f i l t e r e d and d r i e d by pumping under reduced pressure f o r 24 h r s .
(85%) thus obtained, m.pt. 105°-108° ( l i t .
bromine by Lassaigne's t e s t ;
1490,
775
^
m a x
1 6 0
The s o l i d
112.5°), was found t o contain
(nujol mull):
3080, 3040, 3020, 1510,
1420, 1300, 1250, 1200, 1165, 1120, 1075, 1030, 1020, 1000, 830,
1
(doublet), 730, 700, 675, 605, 495 (doublet) cm" .
m a t e r i a l by t . l . c . on s i l i c a
Examination o f the
(benzene) revealed the presence o f one component
only.
Attempted reduction of the p-bisbenzhydrylbromide:
from the previous preparation
NaAlH (OCH CH OCH )
2
2
2
3
2
The bromide obtained
(15.0g) was d i s s o l v e d i n dry benzene (200 m i s ) ;
( V i t r i d e ) i n benzene (10% excess) was added and the
mixture was r e f l u x e d f o r 2 h r s .
A f t e r cooling and d e s t r u c t i o n o f t h e
excess V i t r i d e with water, the benzene l a y e r was separated, d r i e d over
anhydrous magnesium sulphate and the s o l v e n t was removed under reduced
p r e s s u r e t o y i e l d a w h i t i s h powder (13.Og), m.pt. 185°-194° which was found
to be i n s o l u b l e i n hot ethanol o r c o l d hexane.
I t was d i s s o l v e d i n toluene
and p r e c i p i t a t e d by slow a d d i t i o n o f 60°-80° petroleum e t h e r .
The product
- 112 -
thus obtained was d r i e d by pumping under vacuum f o r 24 hrs a t 40
examined by i . r . spectroscopy (Nujol m u l l ,
v
:
m
a
x
and
3080, 3060, 3025, 1600,
1580, 1510, 1490, 1450, 1420, 1375, 1160, 1110, 1075, 1030, 1020, 790,
700, 625 cm ^) .
form;
730,
I t was not p o s s i b l e to obtain the product i n a c r y s t a l l i n e
i t appeared to be a r e l a t i v e l y high molecular weight m a t e r i a l .
Attempted reduction of the p-bisbenzhydrol i n formic a c i d :
p-Bisbenzhydrol
(35,Og) obtained from step A was added to a l a r g e volume (2 l i t r e s ) of 98%
formic a c i d a t 60°.
A f t e r each a d d i t i o n vigorous e f f e r v e s c e n c e was
and the evolved gases gave a white p r e c i p i t a t e with lime water.
observed
A f t e r the
o
a d d i t i o n was complete, the r e s u l t a n t brown s o l u t i o n was heated a t 60
for
6 h r s with s t i r r i n g and product was p r e c i p i t a t e d a f t e r c o o l i n g by pouring
the s o l u t i o n i n t o 5 l i t r e s of water.
A yellow o i l (22.Og) was
obtained
which was separated, d r i e d by pumping under reduced p r e s s u r e a t 60° f o r
24 h r s and examined by i . r . spectroscopy
(contact f i l m , v
2920, 1740, 1510, 1490, 1450, 1370, 1160, 1080, 1030
-1
850, 815, 760, 730, 700, 630 c m .
m a x
: 3060, 3040,
( d o u b l e t ) , 945,
920,
T h i s yellow o i l was d i s t i l l e d under
vacuum (15-20 mmHg, 90°-260°) to y i e l d a y e l l o w i s h o i l which c r y s t a l l i z e d
slowly on standing i n a sample b o t t l e .
The i . r . spectrum was
the same as the one of the yellow o i l before d i s t i l l a t i o n .
essentially
The high b o i l i n g
f r a c t i o n which remained i n the d i s t i l l a t i o n pot was e x t r a c t e d with chloroform
and p r e c i p i t a t e d with 60°-80° petroleum ether to y i e l d a w h i t i s h powder.
Neither the yellow nor the white m a t e r i a l appeared to be the d e s i r e d product.
Step G:
To m-dibenzoylbenzene (lOOg) (obtained as d e s c r i b e d i n 2 . 2 . j . i i i )
i n 2000 mis ethanol i n a 5 l i t r e round bottom f l a s k f i t t e d w i t h r e f l u x
condenser was slowly added a s o l u t i o n of NaBH^ (45g) i n water
(300 m i s ) .
The r e s u l t a n t s o l u t i o n was r e f l u x e d f o r 5 h r s and cooled to room temperature.
Following the d e s t r u c t i o n of unreacted borohydride with 5% a c e t i c a c i d
s o l u t i o n , the volume of s o l v e n t was reduced to 200 mis.
Addition of a l a r g e
- 113 -
volume of water caused the p r e c i p i t a t i o n of a white m a t e r i a l which was
c o l l e c t e d on a f i l t e r , washed s u c c e s s i v e l y with water, 5% HC1
solution
and 5% aqueous sodium carbonate s o l u t i o n , and then b o i l e d with a c t i v a t e d
animal c h a r c o a l i n ethanol s o l u t i o n .
The white s o l i d obtained a f t e r
r e c r y s t a l l i z a t i o n s from ethanol/water (70:30)
spectroscopy (KBr d i s c , v
:
(80%) was examined by i . r .
3300, 3060, 3020, 2880, 1600, 1490,
1475,
max
1450, 1335, 1270, 1235, 1195, 1070, 1030, 1020, 950, 920
1
800, 780, 760, 740, 700 ( d o u b l e t ) , 600, 545 cm" ,
Step B':
( d o u b l e t ) , 830,
m.pt.
151°-153°.
was c a r r i e d out i n e x a c t l y the same way as s t e p B.
A dark o i l
was obtained i n 90% y i e l d which was examined by L a s s a i g n e ' s method and
found to contain c h l o r i n e .
obtained f o r step D*.
film, v
m
:
T h i s product was not p u r i f i e d but was used as
The i n f r a r e d spectrum of the o i l was recorded (contact
3080, 3060, 3020, 2940, 1600, 1590, 1490, 1450, 1210,
1075, 1030, 1000, 830, 790, 760, 730, 700, 625, 580
Step D:
LiAlH
4
was
1150,
1
cm" .
(lOg, 0.26 mole) i n a 2 l i t r e 3 necked round bottom f l a s k
f i t t e d with a mechanical s t i r r e r , p r e s s u r e e q u a l i z i n g dropping
n i t r o g e n gas i n l e t and double s u r f a c e r e f l u x condenser
s u l p h u r i c a c i d bubbler
was
funnel,
l e a d i n g to a concentrated
covered w i t h 1 l i t r e sodium d r i e d e t h e r ;
the
mixture was s t i r r e d v i g o r o u s l y f o r 30 mins and then cooled to 0° by means of
an i c e / w a t e r / s a l t bath.
p-Bisbenzhydrylchloride (32.7g, 0.1 mole) obtained
from step B was shaken with e t h e r (0.5 l i t r e s ) and the r e s u l t e d s l u r r y
s l o w l y added to the mixture i n the f l a s k with vigorous s t i r r i n g .
of the mixture changed e v e n t u a l l y from grey to l i g h t green.
was complete, the mixture was gently r e f l u x e d f o r 12 h r s .
was
The colour
After addition
The excess
l i t h i u m aluminium hydride was destroyed by s u c c e s s i v e slow a d d i t i o n s of
162
water
(lOg), 10% NaOH (15g) and water
(30g),
r e s u l t i n g i n the formation
o f a granular p r e c i p i t a t e which was f i l t e r e d o f f , washed with two 200 mis
p o r t i o n s o f benzene and destroyed by slowly adding i t i n t o a l a r g e volume of
- 114 -
6N HC1 u n t i l a c l e a r s o l u t i o n was formed.
The combined e t h e r e a l and
benzene s o l u t i o n s were d r i e d over anhydrous magnesium sulphate and
finally
the s o l v e n t s were removed under reduced p r e s s u r e .
was
A whitish solid
obtained which was r e c r y s t a l l i z e d s e v e r a l times from hot ethanol, b o i l e d
with a c t i v a t e d animal c h a r c o a l and then r e c r y s t a l l i z e d s e v e r a l times from
methanol and ethanol to give a y e l l o w i s h c r y s t a l l i n e m a t e r i a l impure
b i s b e n z y l b e n z e n e (30%) , melting a t 83°-85° ( l i t .
1 4 0
1,4-
86°).
Step D'; was c a r r i e d out i n the same way as step D apart from the a d d i t i o n
of the m-bisbenzhydrylchloride which was e a s i e r than i n D, s i n c e the
compound i s s o l u b l e i n e t h e r .
Reaction afforded a brown o i l which was
d i s t i l l e d from a short column, b o i l e d with a c t i v a t e d animal c h a r c o a l i n
benzene and d i s t i l l e d again to y i e l d a yellow o i l ;
the o i l was e s t a b l i s h e d by Lassaigne's t e s t .
absence of c h l o r i n e from
Finally a yellowish o i l
was obtained by d i s t i l l a t i o n a t 220°-239°/14 mmHg ( l i t .
1 4 0
229°-231°/14 mmHg
226°-227°/19 mmHg).
2.3.b.ill.
Reasons f o r f a i l u r e
The r e s u l t s obtained i n 2 . 3 . b . i i i n d i c a t e t h a t the only s u c c e s s f u l step
out of those shown i n F i g u r e 2.53 are A, G, B, and B', D and D'.
Treatment of 1,4-bisbenzhydrol with constant b o i l i n g HBr d i d i n f a c t
give a bromide, but reduction of the bromide with V i t r i d e
(NaAlH (OCH CH OCH
2
2
2
i n benzene s o l u t i o n a t 80° r e s u l t e d i n the formation of polymeric m a t e r i a l s .
On the other hand reduction of the corresponding d i c h l o r i d e with l i t h i u m
aluminium hydride i n ether a t 0°-37° r e s u l t e d i n the formation of d i b e n z y l benzene.
Both V i t r i d e and l i t h i u m aluminium hydride are e x c e l l e n t sources
of hydride anion.
The two s t a r t i n g m a t e r i a l s though bear d i f f e r e n t h a l i d e
s u b s t i t u e n t s , bromine being b u l k i e r and not as s t r o n g l y attached to the
carbon atom as c h l o r i n e .
One could t h e r e f o r e r a t i o n a l i z e the d i f f e r e n c e i n
behaviour between the two b e n z y l h a l i d e s by p o s t u l a t i n g p a r t i a l i o n i z a t i o n o f
- 115 -
the p-bisbenzhydrylbromide y i e l d i n g a s t a b l e carbenium ion which could then
i n i t i a t e polymerization, by e l e c t r o p h i l i c a t t a c k on phenyl r i n g s .
Alternatively
the polymerization may have occurred during the formation o f the bromide;
again a carbenium intermediate i s i n v o l v e d and t h i s might have attacked an
aromatic r i n g o r been quenched by a hydroxy1 group.
The treatment o f p-bisbenzhydrol with a l a r g e excess o f formic a c i d
would appear t o have y i e l d e d the formate e s t e r and polymeric m a t e r i a l s ,
p o s s i b l y v i a the route shown i n Figure 2.55.
The reasons why t r i p h e n y l c a r b i n o l
i s converted t o triphenylmethane, whereas benzhydryl hydroxyl i s not r e p l a c e d
9
o
HCOOH
H
H
OH
^
H
OH
H + H„0 + HCOO
OH
HCOO
H
H
OH
®
OH
formate e s t e r
9
H
H
OH
polyether
H
6D
OH
H
Figure 2.55
- 116 -
by hydrogen under the same conditions probably l i e I n a combination of
s t e r l c and e l e c t r o n i c e f f e c t s .
2.3.b.vi.
P u r i f i c a t i o n and proof o f s t r u c t u r e
1,4-dlbenzylbenzene was p u r i f i e d by two more r e c r y s t a l l l z a t l o n s from
absolute ethanol, b o i l i n g with a c t i v a t e d animal c h a r c o a l I n benzene,
sublimation a t 106°/0.01 mmHg, another r e c r y s t a l l i z a t i o n from ethanol and
washing with the same s o l v e n t (10°).
I t was then pumped under reduced
p r e s s u r e (0.01 mmHg) a t 40° f o r 48 h r s .
product, m.pt.
T h i s procedure gave 20% of pure
85.8° (lit.^° 86°) i n b i g p l a t e s a n a l y z i n g as f o l l o w s :
C 92.56, H 7.12;
calculated for C
2 o
H
1 8
C 92.98, H 7.02.
was found t o give a s i n g l e spot on t . l . c . on s i l i c a
v
max
(KBr d i s c ) :
The substance
(benzene, chloroform);
3070,. 3060, 3020, 2900 (doublet), 2430, 1950, 1915, 1600,
1595, 1510, 1490, 1450, 1430, 1415, 1335, 1320, 1210, 1175, 1160, 1105,
1
1030, 930, 855, 760, 725, 700, 600, 485, 460 cm" .
to m/e = 258 corresponding to the parent i o n ;
121, 120, 90, 77.
1070,
The mass spectrum extended
main peaks a t 192, 167, 150,
Lassaigne's t e s t on the sample showed the absence of chlorine,
as d i d the mass spectrum.
1
The H n.m.r. spectrum i n CDCl^ ( i n t . TMS r e f . )
showed two peaks i n the aromatic hydrogen region (6 7.10, 6 6.96) and a
s i n g l e t a t 6 3.80.
1,3-Dibenzylbenzene was p u r i f i e d by f u r t h e r d i s t i l l a t i o n s between
220°-235°/15 mmHg and f i n a l l y by a d i s t i l l a t i o n a t 140°/3 mmHg under nitrogen.
A c o l o u r l e s s o i l was obtained, a n a l y z i n g as f o l l o w s :
(calculated for C
2 Q
H
1 Q
C 92.88, H 7.02);
chloroform) gave a s i n g l e spot;
v
max
C 92.73, H 7.23
t . l . c . on s i l i c a
(contact f i l m ) :
(benzene,
3100, 3080,
3020, 2900, 2840, 1940, 1870, 1800, 1600, 1490 (doublet), 1445
3040,
(doublet),
1
1090, 1075, 1030, 1000, 770, 750, 730, 700, 600, 550, 460, 430 cm" .
L a s s a i g n e ' s t e s t on the product showed the absence of c h l o r i n e .
spectrum extended to m/e = 258, corresponding to the parent i o n ;
The mass
main
- 117 -
peaks a t 181, 180, 168, 166, 153, 91,
2.3.c.
77.
Polymerization runs
2.3.C.I.
A preliminary Investigation
1,4-Dlbenzylbenzene (1.2918g, 0.005 mole) and 1,3-dlbenzoylbenzene
(1.4316g, 0.005 mole) were d i s s o l v e d i n benzene (50 mis, 0.2M
to both reagents) i n a c y l i n d r i c a l Pyrex v e s s e l .
with r e s p e c t
The c l e a r , c o l o u r l e s s
s o l u t i o n was nitrogen streamed f o r 30 mins, the tube was q u i c k l y stoppered
and i r r a d i a t e d a t 350 nm f o r 24 h r s .
A b r i g h t yellow colour developed a t
an e a r l y stage during the i r r a d i a t i o n and a t r a c e of a white p r e c i p i t a t e
appeared a t the bottom of the tube.
Benzene s o l v e n t was removed by f r e e z e -
d r y i n g and a yellow m a t e r i a l was q u a n t i t a t i v e l y recovered showing both
hydroxyl and benzophenone-type carbonyl bands i n the i . r . region.
The
presence of the strong carbonyl band was a t t r i b u t e d to e i t h e r unreacted
monomer or to low molecular weight m a t e r i a l formed (telomer of poly(1,1,2,2-tetraphenylethanol));
thus the e a r l i e r expectation t h a t the
polymerization r e a c t i o n might be a slow one was confirmed.
On the other
hand, the presence of the hydroxy1 band i n d i c a t e d t h a t , as expected, hydrogen
a b s t r a c t i o n was t a k i n g p l a c e and t h a t the benzophenone-type k e t y l r a d i c a l
of m-dibenzoylbenzene was i n f a c t y i e l d i n g products e i t h e r by d i f f u s i o n out
of the cage and d i m e r i z a t i o n or by in-cage combination with the r a d i c a l
r e s u l t i n g from p-bisbenzylbenzene.
The i . r . spectrum of the y e l l o w i s h
powder d i s p l a y e d the f o l l o w i n g absorptions
(KBr d i s c , v
c a . 3400 (broad), 3080, 3050, 3020 ( s t r o n g ) , 2900, 1655,
1480,
1445,
1420,
1320,
1275,
1160,
1
(doublet), 700, 640, 620, 555 cm .
polybenzopinacol
1090,
1030,
1000,
:)
3540, 3520 -
1600,
1580,
845, 830,
780,
1510,
740
Comparison with the i . r . spectrum of
M (prepared by i r r a d i a t i o n of m-dibenzoylbenzene i n
isopropanol/benzene, see Table
2.2), s y n t h e s i z e d by Andrews and
64
Feast
(KBr d i s c , v
:
max
3560, 3500 - c a . 3400 (broad), 3060, 3020 (weak),
- 118 -
2960 ( p o s s i b l y occluded s o l v e n t o r Incorporated iaopropanol m o i e t i e s ) , 1600,
1560, 1495, 1450, 1420, 1330, 1265, 1155, 1100, 1030, 920, 790, 765, 750,
1
700, 645, 615 cm ) r e v e a l e d t h a t the two s p e c t r a d i f f e r i n many regions;
d i f f e r e n c e s i n the r e l a t i v e i n t e n s i t i e s o f t h e 0-H and aromatic C-H
absorptions were evident, t h e yellow m a t e r i a l having a much stronger C-H
aromatic group o f peaks.
were a l s o observed.
D i f f e r e n c e s i n the f i n g e r p r i n t region o f t h e spectrum •
Washing the m a t e r i a l obtained w i t h c o l d hexane i n
order t o e l i m i n a t e any unreacted bisbenzylbenzene, followed by drying under
vacuum, d i d not a l t e r the colour, weight or the s o l i d s t a t e i . r . spectrum."*
2.3.c.ii.
Examination of the e f f e c t of concentration
The i r r a d i a t i o n s shown i n Table 2.7 were c a r r i e d out i n the same way as
i n the previous experiment ( c y l i n d r i c a l Pyrex tubes, nitrogen streaming
followed by s t o p p e r i n g , i r r a d i a t i o n a t 350 nm).
I n a l l c a s e s , s o l u t i o n went
b r i g h t yellow and a t r a c e o f a white p r e c i p i t a t e was observed a t the bottom
of the tube;
i t was separated from the yellow s o l u t i o n by f i l t r a t i o n ,
washed with a few drops o f c o l d benzene, d r i e d under vacuum and weighed;
i n a l l cases i t amounted t o c a . 5% o f the t o t a l weight o f the two r e a c t a n t s
used, and was i n s o l u b l e i n a wide range o f l a b o r a t o r y s o l v e n t s .
Benzene s o l v e n t was removed from yellow s o l u t i o n s by f r e e z e - d r y i n g and
yellow s o l i d s were obtained which were d r i e d by pumping under reduced p r e s s u r e
and examined by i . r . spectroscopy
experiments
(KBr d i s c s ) .
The s p e c t r a obtained from
A, B and C were very s i m i l a r and comparable t o the i . r . spectrum
of t h e yellow product obtained .from the 24 h r s i r r a d i a t i o n
( 2 . 3 . c . i . ) , but
the benzophenone-type carbonyl band was much weaker, i n d i c a t i n g t h a t longer
i r r a d i a t i o n times r e s u l t e d i n i n c r e a s e d comsumption o f a t l e a s t one o f the
monomers (m-dibenzoylbenzene).
The r e l a t i v e i n t e n s i t i e s o f the carbonyl
band i n the s p e c t r a o f the t h r e e products was roughly the same, i n d i c a t i n g
t h a t i n the concentration range 0.1M-1M r e a c t i o n r a t e (as monitored by
- 119 -
Table 2.7
I r r a d i a t i o n s o f egulmolar s o l u t i o n s of m-dlbenzoylbenzene/m- and pdibenzylbenzene of v a r y i n g concentrations
Expt.
Bisketone
Alkane
Solvent
Total
concn.
Irradiation
time
A
m-dibenzoylbenzene
0.7158g
0.0025 mole
p-bisbenzyl
benzene
0.6459g
0.0025 mole
benzene
50 mis
0.1M
240 h r s
B
m-dibenzoylbenzene
0.7158g
0.0025 mole
p-bisbenzyl
benzene
0.6459g
0.0025 mole
benzene
25 mis
0.2M
240 h r s
C
m-dibenzoylbenzene
0.7158g
0.0025 mole
p-bisbenzyl
benzene
0.6459g
0.0025 mole
benzene
12.5 mis
0.4M
240 h r s
D
m-dibenzoylbenzene
2.860g
0.01 mole
m-bisbenzyl
benzene
2.580g
0.01 mole
benzene
20 mis
1M
240 h r s
carbonyl consumption) was not d r a m a t i c a l l y changing.
A t y p i c a l i . r . spectrum of the white i n s o l u b l e p r e c i p i t a t e obtained
from experiments A, B and C d i s p l a y e d the f o l l o w i n g absorptions (KBr d i s c ,
V
max
:)
3550 (very s t r o n g ) , 3090, 3060, 3020, 2960, 1660, 1600, 1580, 1495,
1475, 1445, 1420, 1340-1270 (broad), 1260, 1175, 1160, 1100, 1035, 1020,
960, 925, 910, 845, 805, 775, 745, 710, 700, 680, 645, 635, 610, 570,
540, 470
1
cm" .
The i . r . spectrum of the white i n s o l u b l e p r e c i p i t a t e obtained from
experiment D was not d i f f e r e n t from the one d e s c r i b e d i n the preceding
paragraph.
The benzene-soluble m a t e r i a l was d r i e d by pumping under reduced
pressure following removal of s o l v e n t ;
a p o r t i o n of i t was p r e c i p i t a t e d from
benzene/60°-80° petroleum ether and a white powder was thus obtained a n a l y z i n g
- 120 -
as f o l l o w s : C 85.98, H 5.92.
recorded (KBr d i s c , v
):
The l . r . spectrum of the white powder was
3550, 3520 - ca. 3400 (broad), 3080, 3040,
max
3020, 2920-2845 (possibly occluded petroleum e t h e r ) , 1655
(strong),
1600,
1580, 1495, 1445, 1420, 1320, 1275, 1175, 1160, 1140, 1045, 1030, 1000,
1
845, 815, 750, 700, 640, 620 cm .
920,
The carbonyl peak appeared c o n s i d e r a b l y
stronger than i n the i . r . s p e c t r a of the yellow products obtained from
experiments A, B and C, i n d i c a t i n g t h a t consumption of carbonyl i n the r e a c t i o n
between the two meta isomers was q u a l i t a t i v e l y slower than i n the r e a c t i o n
between m-dibenzoylbenzene and p-dibenzylbenzene.
Another p o r t i o n (2.0g) of the crude yellow product i s o l a t e d from
experiment D was d i s s o l v e d i n benzene (10 m i s ) , nitrogen streamed,
i r r a d i a t e d a t 350 nm f o r 435 h r s .
and
Again, a white s o l i d p r e c i p i t a t e d during
i r r a d i a t i o n (ca. 6 % ) , which d i s p l a y e d an i . r . spectrum s i m i l a r to those
already d e s c r i b e d f o r the white p r e c i p i t a t e s p r e v i o u s l y obtained.
The
yellow benzene s o l u t i o n was separated, and the s o l v e n t was removed by f r e e z e drying y i e l d i n g a yellow s o l i d which was p r e c i p i t a t e d from benzene/60°-80°
petroleum e t h e r .
The white powder obtained from p r e c i p i t a t i o n was examined
by i . r . spectroscopy;
a very s m a l l absorption a t c a . 1660 cm * was
i n d i c a t i n g t h a t most of the m-dibenzoylbenzene had been consumed.
phase i . r . spectrum of t h i s product
c e l l ) showed a s i n g l e t a t 3560 cm
1
observed
The
solution
(CCl^ s o l v e n t , s a t u r a t e d s o l u t i o n , 0.1
mm
(0-H) , a doublet a t 3060-3020 cm
(aromatic C-H), and a broad s i n g l e t a t 2920 cm
1
( a l i p h a t i c C-H);
the
r e l a t i v e i n t e n s i t i e s of the 0-H and aromatic C-H peaks were roughly the same
(aromatic C-H
s l i g h t l y stronger).
The s o l u t i o n phase i . r . spectrum of
64
polybenzopinacol M
(see Table 2.2).examined under the same c o n d i t i o n s showed
-
a s i n g l e t a t 3560 cm * and a shoulder a t 3600 cm * (0-H), a very broad
absorption between 3500-3400 cm * (hydrogen bonded 0-H), two s i n g l e t s a t
3060-3030 cm
1
(aromatic C-H), and a strong s i n g l e t a t 2960 cm
1
(aliphatic
- 121 -
C-H, p o s s i b l y due to occluded s o l v e n t ) .
stronger than the two aromatic C-H
The 0-H peak was c o n s i d e r a b l y
peaks.
The above p r e l i m i n a r y i n v e s t i g a t i o n s l e d to the c o n c l u s i o n t h a t the
product obtained from the m-dibenzoylbenzene/m-dibenzylbenzene r e a c t i o n was
not a polybenzopinacol (by comparative s o l i d s t a t e and s o l u t i o n phase i . r .
evidence).
T h i s was an encouraging r e s u l t and gave the i n c e n t i v e f o r a
more thorough examination o f the p o l y a d d i t i o n r e a c t i o n .
2.3.c.iii.
a)
Large s c a l e experiments
m-Dibenzoylbenzene/p-dlbenzylbenzene
m-Dibenzoylbenzene (28.631g, 0.1 mole) and p-dibenzylbenzene
0.1 mole) were d i s s o l v e d i n sodium-dried benzene (500 mis, 0.4M
to both r e a g e n t s ) .
(25.834g,
with r e s p e c t
The s o l u t i o n was nitrogen streamed f o r 30 mins, the
c y l i n d r i c a l Pyrex tube was q u i c k l y stoppered and i r r a d i a t e d a t 350 nm f o r
263 h r s .
During i r r a d i a t i o n a white m a t e r i a l p r e c i p i t a t e d ,
remaining s o l u t i o n became b r i g h t yellow.
whereas
The white m a t e r i a l (A) was
recovered by f i l t r a t i o n , washed with a l i t t l e c o l d benzene, d r i e d by pumping
under reduced p r e s s u r e , weighed
(KBr
disc);
(2.482g) and examined by i . r . spectroscopy
spectrum obtained was e s s e n t i a l l y the same as the ones recorded
for p r e v i o u s l y obtained white p r e c i p i t a t e s , already d e s c r i b e d i n 2 . 3 . c . i i i .
The yellow s o l u t i o n separated y i e l d e d , following removal of s o l v e n t by
f r e e z e - d r y i n g and pumping under reduced p r e s s u r e , a yellow m a t e r i a l (B)
(51.980g) which was s p e c t r o s c o p i c a l l y examined ( i . r . , KBr d i s c ) ;
i t was
then r e d i s s o l v e d i n benzene (500 mis) and r e - i r r a d i a t e d f o r a f u r t h e r 144 h r s
p e r i o d , y i e l d i n g another white p r e c i p i t a t e (C) (0.832g) and a yellow s o l i d
(D) (51.140g).
S o l i d (D) was then d i v i d e d i n t o 2 x 25g p o r t i o n s .
were made:
Two benzene s o l u t i o n s
- 122-
25g o f s o l i d (D) I n 100 mis benzene
25g of s o l i d
(D) I n 250 mis benzene
The two s o l u t i o n s were r e - i r r a d l a t e d f o r 118 h r s , y i e l d i n g only s l i g h t
white p r e c i p i t a t e s ( c a . 1% o f the weight o f s o l i d (D) used) and yellow
s o l i d s (E) (from 25g (D)/100 mis CgH ) and (F) (from 25g (D)/250 mis C Hg).
g
$)
g
m-Dibenzoylbenzene/m-dlbenzylbenzene
m-Dibenzoylbenzene (28.631g, 0.1 mole) and m-dibenzylbenzene (25.834g,
0.1 mole) were d i s s o l v e d i n sodium d r i e d benzene (500 mis, 0.4M with r e s p e c t
to both r e a g e n t s ) .
The s o l u t i o n was nitrogen streamed f o r 30 mins, the
c y l i n d i c a l Pyrex tube was q u i c k l y stoppered and i r r a d i a t e d a t 350 nm f o r
263 h r s . During i r r a d i a t i o n a white m a t e r i a l p r e c i p i t a t e d , whereas
remaining s o l u t i o n became b r i g h t yellow.
The white m a t e r i a l (G) was
recovered by f i l t r a t i o n , washed with a l i t t l e c o l d benzene, d r i e d by pumping
under reduced p r e s s u r e , weighed (2.482g) and examined by i . r . spectroscopy
(KBr d i s c ) ;
spectrum obtained was the same as the ones recorded f o r p r e v i o u s l y
obtained white p r e c i p i t a t e s , described i n 2 . 3 . c . i i i .
The yellow s o l u t i o n
separated y i e l d e d , following removal of s o l v e n t by freeze-drying and
pumping under reduced p r e s s u r e , a yellow m a t e r i a l (H) (51.980g) which was
s p e c t r o s c o p i c a l l y examined ( i . r . , KBr d i s c ) ;
i t was then red!ssolved i n
benzene (500 mis) and r e - i r r a d i a t e d f o r a f u r t h e r 144 h r s period, y i e l d i n g
another white p r e c i p i t a t e ( I ) (1.044g) and a yellow s o l i d (J) (50.920g).
S o l i d (J) was then d i v i d e d i n t o 2 x 25g p o r t i o n s .
Two benzene s o l u t i o n s
were made:
25g o f s o l i d
(J) i n 100 mis benzene
25g of s o l i d (J) i n 250 mis benzene
The two s o l u t i o n s were r e - i r r a d i a t e d f o r 118 h r s , y i e l d i n g only s l i g h t
white p r e c i p i t a t e s , and yellow s o l i d s (K) (from 25g (J)/ICO mis CgHg) and
(L) (from 25g (J)/250 mis CJH ).
fi
Following s p e c t r a l examinations, s o l i d s
- 123 -
(K) and
(L) were combined, d i s s o l v e d i n 250 mis of benzene and r e - i r r a d i a t e d
(350 ran) f o r 171 h r s , y i e l d i n g again very s l i g h t white p r e c i p i t a t e s (< 1% of
the combined (K) + (L) weight) and a yellow benzene-soluble s o l i d
(M)
(48.932g).
2.3.d.
C h a r a c t e r i z a t i o n of products
A l l products obtained from experiments d e s c r i b e d i n 2 . 3 . c . i l l were
d r i e d by pumping under reduced p r e s s u r e before
examination.
I . r . s p e c t r a (KBr d i s c s ) were the! same as the ones obtained for
corresponding products d e s c r i b e d i n 2 . 3 . c . i and 2 . 3 . c . i i ;
(D), ( E ) ,
spectra of (B),
( F ) , (H), ( J ) , ( K ) , ( K ) , ( L ) , (M), a l l d i s p l a y e d absorptions a t
1660 cm *, i n d i c a t i n g the presence of benzophenone-type carbonyl groups
a t t r i b u t a b l e to e i t h e r unreacted monomer or low molecular weight polymer
chains capped with aromatic carbonyl ends.
Products
(E) and (F) were combined, d i s s o l v e d i n benzene and the
b r i g h t yellow s o l u t i o n s thus obtained were added dropwise
excess of 60°-80° petroleum e t h e r with e f f i c i e n t s t i r r i n g .
to a 10-fold
A white s o l i d
(N) was obtained i n 89% y i e l d , which was c o l l e c t e d and d r i e d under vacuum.
(N) was r e d i s s o l v e d i n benzene forming a b r i g h t yellow s o l u t i o n .
Second
p r e c i p i t a t i o n from 60°-80° petroleum e t h e r afforded a white s o l i d
(0) (80%)
which was d r i e d by pumping under vacuum f o r 6 days at 40°;
follows:
C 86.54, H 7.18
i n the i . r . spectrum.
(CB^Clg s o l v e n t ) .
i t analyzed as
(0) s t i l l d i s p l a y e d a weak absorption a t 1660 cm
1
I t d i d not form f i l m s on c a s t i n g on a c l e a n Hg s u r f a c e
Small, b r i t t l e f i b r e s were drawn out of the melt;
it
became tacky between 188°-207° and melted between 207°-220°.
S i m i l a r l y , product
(M) was p r e c i p i t a t e d from benzene/60°-80° petroleum
e t h e r y i e l d i n g a powder (P) (80%) which was d r i e d i n the same way
as ( 0 ) .
No f i l m s were obtained, but s m a l l , b r i t t l e f i b r e s were drawn out of the melt.
(P) became tacky between 165°-177° and melted between 177°-192°.
- 124 -
The number average molecular weights o f the samples were determined by
the
i s o p i e s t i c method i n chloroform and are recorded below:
n
Total I r r
time (hrs)
Sample
n
M
n
Sample
Total I r r
time (hrs)
M
n
(B)
263
2780
(H)
263
2030
(D)
407
3560
(J)
407
2130
(E)
525
3590
(K)
525
3320
(F)
525
3530
(D
525
3410
(0)
525
3690
(M)
525
3510
(P)
696
3670
Polymer c h a r a c t e r i z a t i o n was attempted by F.T.
H n.m.r. spectroscopy (see
Table 2.8).
S p e c t r a o f samples
(0) and (P) were run i n CDCl-j s o l v e n t ( e x t . TMS
64
reference) and compared to the s p e c t r a o f p-bisbenzylbenzene, p o l y p i n a c o l M,
1,1,2,2-tetraphenylethanol, benzopinacol and 1,1,2,2-tetraphenylethane.
The f i r s t observation was the group o f peaks between 6 1.48 - 6 0.60
i n d i c a t i n g the presence of occluded s o l v e n t containing a l i p h a t i c C-H bonds,
apparently petroleum ether.
Polybenzopinacol M showed s i m i l a r peaks a t 6 1.61,
6 1.28. T h i s observation was somewhat s u r p r i s i n g s i n c e both
(0) and (P) were
pumped under reduced p r e s s u r e f o r a long time before the s p e c t r a were run, and
t h a t should
ether.
for
have e l i m i n a t e d any occluded v o l a t i l e m a t e r i a l s such as petroleum
Evaporation o f a l a r g e volume o f the same batch o f petroleum e t h e r used
p r e c i p i t a t i o n o f (0) and ( P ) , d i d not y i e l d any high b o i l i n g r e s i d u e s .
Both
(0) and (P) d i s p l a y e d peaks a t S 3.81 - 6 3.82 a s s i g n e d t o the methyl
protons i n the -C H -CH -C H group, and peaks a t 6 4.80 - 6 4.81, assigned
6
4
2
g
5
to the t e r t i a r y hydrogen i n a 1,1,2,2-tetraphenylethane type o f u n i t .
peaks a t 6 4.38 - 6 4.39 however could not be unequivocally
Broad
assigned t o any
- 125 -
Table 2.8
Comparative F.T. H n.m.r. s p e c t r a o f some phenylated substances
(CDC1 s o l u t i o n s , e x t . TMS r e f . ) .
3
705
«.J9 3*2
Product (P)
'I
2
o**
A^A_/VJA_
T-o2
Product (O)
TOM
3 55 i-foi i-ag
Polybenzopinacol M
64
6 96
p-Bisbenzylbenzene
A
3-80
1
706
U-9o
A
1,1,2,2-Tetraphenylethane
115
1A U_
1,1,2,2-Tetraphenylethanol
f
I
f
f
t
i
M
PPm s c a l e
i
- 126 -
s t r u c t u r e s i n c e the t e r t i a r y proton resonance i n 1,1,2,2-tetraphenylethanol
occurs a t & 5.23 and <5 4.73.
13
Comparative F.T.
C n.m.r. spectroscopy proved a more u s e f u l technique
for the c h a r a c t e r i z a t i o n o f the m a t e r i a l s (see Table 2.9).
The t r i p l e t s
observed i n the 6 77 t o 78 region i n some o f the s p e c t r a a r e due t o the
s o l v e n t CDClj.
They a r e not seen where i t was p o s s i b l e t o prepare very
concentrated s o l u t i o n s .
Spectrum o f (0) showed a group o f peaks between 6 144.25 - 8 128.65
assigned t o the carbon atoms o f the aromatic r i n g s , and peaks a t 6 83.95,
6 81.35, 6 61.08, 6 57.44 and <S 42.44. Peaks a t 6 57.44 and 6 42.44 were
3
assigned by the sp h y b r i d i z e d carbons i n u n i t s analogous to 1,1,2,2tetraphenylethane and bisbenzylbenzene r e s p e c t i v e l y . The peak a t 6 83.95
3
was assigned t o the sp
h y b r i d i z e d carbon of polybenzopinacol and peak a t
6 61.08 t o the carbon bonded to hydrogen i n the 1,1,2,2-tetraphenylethanol
type o f u n i t present i n the polymeric m a t e r i a l . There remained the peak a t
6 81.35 which should correspond t o the carbon bonded t o the OH group i n the
1,1,2,2-tetraphenylethanol type o f u n i t , although i t has to be acknowledged
t h a t such a peak i s not v i s i b l e i n the spectrum o f the model compound
1,1,2,2-tetraphenylethanol.
T h i s may be a consequence o f the very low
s o l u b i l i t y of the model compound and i n p r a c t i c e i t was only with considerable
p e r s i s t a n c e i n the face o f d i f f i c u l t y t h a t a *^C spectrum was recorded.
1
13
Thus, combined
H and
C n.m.r. evidence would suggest t h a t , as
p r e d i c t e d , the polymeric m a t e r i a l contains three major types o f groups as
shown i n F i g u r e 2.56 and a l s o t h a t some polymer ends are capped with
benzophenone-type aromatic carbonyl (CgHg-C(O)-) and benzyl (CgHg-C^-) groups.
I n view o f t h i s conclusion i t i s r a t h e r s u r p r i s i n g t h a t prolonged
did not r e s u l t i n the formation o f higher molecular weight
irradiation
products.
- 127 -
Table 2.9
13
Comparative F.T.
C n.m.r. s p e c t r a of some phenylated substances
(CDClj s o l u t i o n s , e x t . TMS r e f . ) .
flU6
urns
8395
Product (P)
CDC1-
Polybenzoplnacol M
aA.
64
CDC1U0O8
[iM-56
ittJM
^275
M'« «
p-Bisbenzylbenzene
J.
|iX8'»
IOT-35
12410
1,1,2,2-Tetraphenylethanol
CDC1.
S6-6?
(16
06
JL
1,1,2,2-Tetraphenylethane
n.<9
Benzopinacol
CDCl.
150
140
I
I
130 120
I
I
110 100
I
I
90
80
70
60
50
I
I
I
I
I
ppra s c a l e
40
I
- 128 -
OH
H
H
OH
ra- or p
OH
OH
H
Figure
2.3.e.
DJ CQ
H
2.56
Reactions of the polymers
2.3.e.i.
Depolymerization
A sample o f the polymeric m a t e r i a l (O) was introduced i n t o a 3 necked
round
bottom f l a s k f i t t e d with water condenser, thermometer pocket and n i t r o g e n gas
inlet.
The f l a s k was s l o w l y heated by means o f a f r e e flame u n t i l the polymer
had melted and then temperature was r a i s e d up to 350° and maintained t h e r e
f o r 5 mins.
A b l a c k t a r was formed which was l e f t to c o o l under n i t r o g e n .
Examination o f the black t a r by i . r . spectroscopy gave the f o l l o w i n g r e s u l t s
(contact f i l m , v
1510, 1495, 1450
max
:) 3080, 3040, 3020, 2900, 2840, 1660
( s t r o n g ) , 1600,
(doublet), 1430, 1420, 1320, 1300, 1280, 1255, 1205,
1580,
1180,
1170, 1120, 1075, 1030, 1000, 985, 910, 850, 830, 800, 780, 720, 710, 700,
620, 600, 485 cm \
Examination of the black t a r by t . l . c . on s i l i c a
r e v e a l e d the presence of m-dibenzoylbenzene,
640,
(benzene)
p-bisbenzylbenzene, diphenylmethane
and benzophenone amongst the p y r o l y s i s products.
A s i m i l a r treatment of polybenzopinacol M (see Tables M (see T a b l e s 2.4
64
2.6) prepared by Andrews and F e a s t
spectrum
(contact f i l m , v
2920, 1660
gave a black t a r with a d i f f e r e n t
i.r.
:) c a . 3480 (broadband), 3299, 3060, 3020,
max
( s t r o n g ) , 1660, 1580, 1495, 1445, 1340, 1290, 1270, 1170, 1120,
and
- 129 -
1075, 1020, 1000, 985, 970, 950, 930, 910, 820, 780, 760, 700, 650, 640 can
.
m-Dibenzoylbenzene, m-bisbenzhydrol, benzophenone and benzhydrol were i d e n t i f i e d
amongst the p y r o l y s i s products by t . l . c . on s i l i c a (benzene).
These r e s u l t s are c o n s i s t e n t with the s t r u c t u r e s a s s i g n e d to these
materials.
2.3.e.ii.
Treatment w i t h dehydrating agents.
The following experiments were performed w i t h product (0)
a)
The polymeric m a t e r i a l (20.Og) was d i s s o l v e d i n dry benzene
(0.5 l i t r e s )
i n a 2 l i t r e 3 necked round bottom f l a s k f i t t e d w i t h gas i n l e t , r e f l u x
condenser and thermometer pocket.
Dry HC1 was bubbled through the straw-yellow
s o l u t i o n a t room temperature (26°).
A f t e r c a . 10 mins the temperature rose t o
28° and s o l u t i o n went r e d d i s h , p r o g r e s s i v e l y darkening t o brown-red;
temperature
o
stayed constant a t 28
a f t e r 3 h r s of bubbling.
S o l u t i o n was subsequently
r e f l u x e d f o r a f u r t h e r 3 h r s period under an atmosphere of HC1.
A f t e r cooling
to room temperature, a s m a l l p o r t i o n of the s o l u t i o n was taken out, benzene
s o l v e n t was removed under vacuum and the s o l i d obtained was examined by i . r .
spectroscopy (KBr d i s c ) .
No change was observed, the spectrum being super-
imposable w i t h t h a t of product ( 0 ) .
HC1 was bubbled through the benzene s o l u t i o n f o r a f u r t h e r 30 hr period
a t room temperature.
the
of
the
E x p u l s i o n o f HC1 by p a s s i n g a stream of nitrogen through
s o l u t i o n , removal o f the s o l v e n t under reduced p r e s s u r e and p r e c i p i t a t i o n
the s o l i d obtained from benzene/60°-80° petroleum t h e r y i e l d e d a m a t e r i a l w i t h
same i . r . spectrum (KBr d i s c ) and melting p o i n t as ( 0 ) .
3)
The polymeric m a t e r i a l (2.00g) was d i s s o l v e d i n dry benzene
(70 mis)
i n a 250 ml 2 necked round bottom f l a s k f i t t e d with a Dean-Starke apparatus
and a r e f l u x condenser.
80 mis of g l a c i a l a c e t i c a c i d and a few drops of
concentrated s u l p h u r i c a c i d were added and the s o l u t i o n was r e f l u x e d f o r 4 h r s .
A f t e r cooling the pot contents down t o room temperature, a drop of the s o l u t i o n
- 130 -
was p l a c e d on a NaCl p l a t e ;
pumping under reduced pressure f o r s e v e r a l hours
r e s u l t e d I n the removal o f v o l a t i l e m a t e r i a l s and the d e p o s i t i o n of a t r a n s p a r e n t
f i l m on the p l a t e , v ^ ^ :
3080, 3060, 3030, 2970, 2920-2850 (strong, assigned
to t r a c e s of apiezon grease e x t r a c t e d by r e f l u x i n g benzene from the ground g l a s s
j o i n t s ) , 1680 (strong), 1600, 1580, 1505, 1495, 1480, 1455, 1445, 1410, 1220,
1
1180, 1160, 1075, 1035, 1020, 1000, 915, 850, 790, 760, 740, 700, 680, 620 cm" .
The bulk of the s o l u t i o n was washed with 5% aqueous potassium carbonate,
then plenty o f water;
benzene l a y e r was separated, d r i e d over anhydrous
magnesium sulphate and v o l a t i l e m a t e r i a l s were removed under reduced p r e s s u r e .
A grey powder was obtained (1.85g) which was pumped under reduced p r e s s u r e f o r
6 h r s a t 40°.
The s o l i d s t a t e i . r . spectrum of the m a t e r i a l (KBr d i s c ) was the
same as the i . r . of the c o l o u r l e s s f i l m described above.
o
y)
The polymeric m a t e r i a l (4.00g) was heated a t 250
excess of ortho-phosphoric a c i d .
f o r 30 mins with an
A f t e r cooling to room temperature, polymeric
m a t e r i a l was e x t r a c t e d with benzene.
Following washing of the benzene l a y e r with
aqueous potassium carbonate, then plenty o f water and drying over anhydrous
magnesium sulphate, a drop o f the benzene s o l u t i o n was p l a c e d on a NaCl p l a t e ;
the t h i n f i l m deposited a f t e r evaporation of s o l v e n t under reduced p r e s s u r e
was examined by i . r . spectroscopy;
v
:
3080, 3060, 3030, 2910, 1660 (strong)
IDclX
1600, 1575, 1510, 1490, 1470, 1445, 1430, 1340, 1280, 1250, 1170, 1155, 1110,
1075, 1030, 1020,'1000, 980, 915, 850, 790, 765, 730, 710, 700, 680, 640, 620,
555, 490
6)
1
cm" .
Product (0) (3.00g) was d i s s o l v e d i n 80 mis o f dry benzene;
90 mis
o f g l a c i a l a c e t i c a c i d and a small c r y s t a l of iodine was added and the s o l u t i o n
was t r e a t e d s u c c e s s i v e l y with an excess o f water, d i l u t e aqueous potassium
carbonate, water again, 5% t h i o s u l p h a t e s o l u t i o n , and f u r t h e r water.
The yellow
benzene l a y e r was d r i e d over anhydrous magnesium sulphate, then v o l a t i l e
m a t e r i a l s were removed by pumping under reduced p r e s s u r e and a y e l l o w i s h powder
- 131 -
was obtained (3.85g) which was p r e c i p i t a t e d from benzene/60°-80° petroleum
ether (white powder, 8 0 % ) .
I . r . examination (KBr d i s c ) showed the presence
o f a weak 0-H band and a weak band a t 1680
-1
cm .
Refluxing the same s o l u t i o n f o r 4.5 h r s followed by e x a c t l y the same
treatment y i e l d e d 80% of a w h i t i s h powder with the following i . r . absorptions
(KBr d i s c , v
nicix
):
3080, 3060, 3030, 2920, 1680 ( s t r o n g ) , 1600, 1580, 1505,
1495, 1480, 1445, 1410, 1220, 1180, 1160, 1075, 1035, 1020, 1005, 915, 860, 840,
790, 765, 740, 700, 680, 620 cm ^.
T h i s i . r . spectrum was found to be very n e a r l y
superimposable to the one obtained from experiment B.
c)
The polymeric m a t e r i a l (1.20g) was d i s s o l v e d i n dry benzene (100 m i s ) ;
toluene p-sulphonic a c i d (0.80g) was added and the s o l u t i o n was r e f l u x e d f o r
30 mins.
A f t e r cooling, benzene was washed with aqueous potassium carbonate
( 5 % ) , then water and d r i e d over anhydrous magnesium s u l p h a t e .
Removal of the
s o l v e n t under reduced pressure y i e l d e d 1.09g o f a m a t e r i a l whose i . r .
spectrum
was found to be superimposable with the one obtained f o r products from experiments
0 and 6.
The same r e s u l t was obtained when the experiment was c a r r i e d out
s t i r r i n g the polymer/toluene p-sulphonic a c i d s o l u t i o n a t room temperature f o r
4 hrs.
F i n a l l y , heating the polymer with an excess o f cone, s u l p h u r i c a c i d f o r
P
30 mins.gave water s o l u b l e t a r s , whereas r e f l u x i n g with 2 ° 5 *
n
xylene f o r 2 h r s
gave a m a t e r i a l d i s p l a y i n g v a r i o u s types of carbonyl bands i n the i n f r a r e d ,
i n c l u d i n g one a t 1660 cm ^.
2.3.e.iii.
a)
P a r a l l e l model compound s t u d i e s
1,1,2,2-tetraphenylethanol (2.00g, 0.0057 mole) i n hot g l a c i a l a c e t i c
a c i d (150 mis) was b o i l e d under r e f l u x f o r 1 h r i n the presence o f a c r y s t a l
of iodine.
0.1M
A f t e r cooling, s o l u t i o n was t r e a t e d s u c c e s s i v e l y with water (50 m i s ) ,
aqueous potassium carbonate (50 m i s ) , d i l u t e aqueous t h i o s u l p h a t e (30 mis)
and water (50 m i s ) .
A y e l l o w i s h p r e c i p i t a t e was obtained which was d i s s o l v e d
- 132 -
i n benzene (100 mis) and kept over anhydrous magnesium sulphate overnight.
Following removal of benzene s o l v e n t and drying under reduced p r e s s u r e , the
y e l l o w i s h m a t e r i a l (1.82g) was examined by i . r . spectroscopy (KBr d i s c , v»
):
nicLx
3075, 3060, 3020, 1680, 1600, 1580, 1490, 1445, 1340, 1320, 1280, 1185,
1175,
1160, 1075, 1030, 1015, 1000, 980, 945, 925, 840, 780, 760, 745, 700, 655, 635,
1
629, 620, 610, 575, 470 cm .
Examination of the product by t . l . c . on s i l i c a
(benzene) showed the presence of tetraphenylethylene, benzopinacolone
1,1,2,2-tetraphenylethane.
and
R e c r y s t a l l i z a t i o n s of the product from chloroform/
methanol afforded a y e l l o w i s h m a t e r i a l i n the form o f elongated p l a t e s , s i n g l e
spot on t . l . c . on s i l i c a (benzene), m.pt. 220°-221°, having the f o l l o w i n g i . r .
spectrum
(KBr d i s c , v
) : 3079, 3065, 3020 (doublet), 1600, 1575, 1490,
1190, 1160, 1080, 1035, 1005, 985, 920 ( t r i p l e t ) ,
1
575, 470, 450 cm .
1445,
780, 765, 750, 700, 630,
620,
R e c r y s t a l l i z a t i o n o f the product from benzene/ethanol gave
1.5g o f a white c r y s t a l l i n e s o l i d , m.pt.
222°-223°.
The i . r . spectrum of the
c r y s t a l l i n e s o l i d was found to be superimposable with the one recorded f o r the
product obtained from s i m i l a r treatment of 1,1,2,2-tetraphenylethanol, and i s
t h e r e f o r e tetraphenylethylene, m.pt.
3)
223°-224° (benzene/ethanol)
1,1,2,2-tetraphenylethanol (lO.OOg, 0.028 mole) i n hot benzene (200 mis)
was b o i l e d under r e f l u x f o r 3 h r s i n the presence of
P
p
2
cooling, benzene s o l u t i o n was f i l t e r e d and excess 2 ° 5
a d d i t i o n of water.
°5
(20.00g).
w
destroyed by c a r e f u l
a
s
After
Evaporation of the benzene s o l v e n t y i e l d e d a white m a t e r i a l
(9.0g) d i s p l a y i n g no 0-H band but C-H a l i p h a t i c and benzopinacolone-type
carbonyl bands im the i . r . region (KBr d i s c ) .
R e c r y s t a l l i z a t i o n s of the
white m a t e r i a l from chloroform/methanol and benzene/ethanol y i e l d e d c a . 7g of
pure tetraphenylethylene, m.pt.
223°-224°, i d e n t i f i e d by s o l i d s t a t e i . r .
spectroscopy (KBr d i s c ) and mass spectrometry (m/e extended to 332 corresponding
to the parent i o n .
The mother l i q u o r s from r e c r y s t a l l i z a t i o n s were found by
t . l . c . on s i l i c a (benzene) to contain benzopinacolone and 1,1,2,2tetraphenylethane .
- 133 -
1,1,2,2-tetraphenylethanol was recovered unchanged a f t e r being b o i l e d
under r e f l u x (1 hr) i n e i t h e r benzene or toluene (0.028M).
T r a c e s of benzo-
phenone and diphenylmethane were observed on t . l . c . on s i l i c a
r e s u l t i n g probably from p a r t i a l thermal decomposition
(benzene),
of the ethanol.
Refluxing an equimolar toluene s o l u t i o n of benzopinacol and 1,1,2,2tetraphenylethane (0.1M with r e s p e c t to both reagents) f o r 3 h r s r e s u l t e d i n
t o t a l consumption of both s t a r t i n g m a t e r i a l s and formation of 1,1,2,2"
tetraphenylethanol, i d e n t i f i e d by t . l . c . on s i l i c a
spectroscopy
(KBr d i s c ) .
(benzene) and i . r .
Traces of benzophenone, diphenylmethane and
benzhydrol were a l s o observed on the t . l . c . p l a t e s .
F i n a l l y , heating 1,1,2,2-tetraphenylethanol under nitrogen a t 350° f o r
5 mins (round bottom f l a s k , f r e e flame) r e s u l t e d i n t o t a l decomposition
of the
m a t e r i a l and q u a n t i t a t i v e formation of benzophenone and diphenylmethane,
i d e n t i f i e d by t . l . c . on s i l i c a (benzene) and i . r . spectroscopy
(contact f i l m ) .
- 134 -
2.3.f.
Experimental
2.3.£.l.
Readily available materials
The o r i g i n and p u r i f i c a t i o n procedure (where appropriate) f o r benzophenone,
m-dibenzoylbenzene and NaBH^ used i n thisi have a l r e a d y been d e s c r i b e d i n 2 . 2 . j .
Vitride
(NaAlH (OCH CH OCH )
2
2
2
3
2
70% benzene s o l u t i o n ) was purcahsed from
A l d r i c h Chemical8 L t d . and used as obtained.
Diphenylmethane was purchased from BDH Laboratory Reagents.
I t was
d i s t i l l e d t w i c e from a s h o r t column and then f r a c t i o n a t e d under n i t r o g e n
o
o
(760 mmHg, 264 -266 ) .
I n a second f r a c t i o n a t i o n under an atmosphere o f
nitrogen a t 760 mmHg, product d i s t i l l i n g a t 266° was c o l l e c t e d i n a dry f l a s k
(lit.^^
silica
265.6°/760 mmHg). The m a t e r i a l was a s i n g l e component by t . l . c on
(benzene, ethanol, a c e t o n i t r i l e , carbon t e t r a c h l o r i d e ) ;
the i . r .
spectrum
was recorded (contact f i l m , v
) : 3080, 3060, 3020, 2900, 2840, 1600, 1580,
max
1490, 1450, 1430, 1380, 1320, 1200, 1180, 1155, 1110, 1075, 1030, 940, 920,
890, 845, 810, 785, 700, 610, 550, 460, 445 cm
The pure compound c r y s t a l l i z e d
slowly on standing forming b i g c o l o u r l e s s prisms, m.pt.
26°-27° ( l i t . * " ^
26°-27°).
Benzhydrylchloride v:as obtained from departmental s t o c k .
twice under n i t r o g e n before use;
I t was
distilled
the f r a c t i o n d i s t i l l i n g between 170°-176°/
20 mmHg was c o l l e c t e d ( b . p t . ^ ^ 173°/19 mmHg) .
Terephthalaldehyde was purchased from Koch-Light L a b o r a t o r i e s L t d . and
r e c r y s t a l l i s e d twice from methanol/water 70:30.
a s i n g l e spot on t . l . c . on s i l i c a
(lit.^^
116°).
parent i o n ;
2.3.f.ii.
White needles obtained gave
o
(benzene, chloroform) and melted a t 117
The mass spectrum extended to m/e = 134 corresponding t o the
main peaks a t 133, 105, 84, 77, 57, 51.
Solvents
Benzene was p u r i f i e d as d e s c r i b e d i n 2 . 2 . j . i i ;
THF ( f r e s h l y d i s t i l l e d )
was obtained from departmental stock and used immediately;
p y r i d i n e and
- 135 -
toluene ( A n a l y t i c a l grades) were obtained from BDH Laboratory Reagents and used
without f u r t h e r p u r i f i c a t i o n ;
isopropanol ( t e c h n i c a l grade) was obtained
from F i s o n s Laboratory Reagents L t d . ;
i t was p u r i f i e d by f r a c t i o n a l
d i s t i l l a t i o n p r i o r to use.
2.3.f.iii.
M a t e r i a l s s y n t h e s i z e d from s i m p l e r chemicals
1,1,2,2-tetraphenylethane was prepared by the Wurtz coupling o f a l k y l . ...
157,158
halides:
R e - d i s t i l l e d benzhydrylchloride (10.125g, 0.05 mole) was d i s s o l v e d i n
sodium-dried d i e t h y l e t h e r (500 mis) i n an 1 l i t r e round bottom f l a s k
with nitrogen i n l e t , double s u r f a c e r e f l u x condenser
equipped
(leading to a concentrated
s u l p h u r i c a c i d b u b b l e r ) , and mechanical s t i r r e r .
T h i n l y s l i c e d sodium (4.6g, 0.2 mole) was added and f l a s k contents were
s t i r r e d a t room temperature f o r 24 h r s under an atmosphere of n i t r o g e n , and
then r e f l u x e d f o r a f u r t h e r 12 hr p e r i o d .
A f t e r c o o l i n g , the e t h e r e a l s o l u t i o n
was f i l t e r e d and excess sodium was c a r e f u l l y destroyed using isopropanol. E t h e r
was removed under reduced p r e s s u r e and a white s o l i d was obtained c o n s i s t i n g
of
1,1,2,2-tetraphenylethane, diphenylmethane
benzene).
and benzhydrol
( t . l . c . on
A f t e r s e v e r a l r e c r y s t a l l i z a t i o n s from ethanol and a c e t i c a c i d ,
1,1,2,2-tetraphenylethane was i s o l a t e d i n a pure s t a t e as shown by t . l . c .
silica
silica,
(benzene, chloroform, ethanol) i n 85% y i e l d , m.pt. 213°
on
1
( l i t . * ' * 212.5°).
Lassaigne's t e s t on the product showed t h a t c h l o r i n e was absent.
2.3.g.
D i s c u s s i o n and Conclusions
The bisbensophenone/bisbenzylbenzene photopolymerization was found to be
s i m i l a r to the model r e a c t i o n i n some r e s p e c t s , e.g. the slow r e a c t i o n r a t e ,
the
e a r l y appearance o f the yellow colour during i r r a d i a t i o n s and the formation
of products c o n t a i n i n g three main types of u n i t as shown i n F i g u r e 2.56.
- 136 -
However some new questions have a r i s e n :
a)
the o r i g i n and s t r u c t u r e of the white I n s o l u b l e p r e c i p i t a t e s obtained
i n a l l photoreaction,
$)
the f a i l u r e of the polymer forming r e a c t i o n to proceed to completion
even a t prolonged i r r a d i a t i o n s , c o n t r a r y to the behaviour of the benzophenone/
diphenylmethane system and d e s p i t e the presence of unreacted -C_H -CH„-C,H_
o 4
2 b 5
and -CgH ~C(0)-CgHg r e s i d u e s i n the polymeric m a t e r i a l s , detected by n.m.r.
4
and i . r . spectroscopy.
y)
the slower r a t e o f molecular weight i n c r e a s e observed f o r the
m-dibenzoylbenzene/m-dibenzylbenzene system, r e l a t i v e to the corresponding
m-/p- one, although both systems gave m a t e r i a l s of rougly the same molecular
weight a f t e r 525 h r s o f i r r a d i a t i o n (see p. 124).
A t y p i c a l i . r . spectrum of the white p r e c i p i t a t e from the above photor e a c t i o n s has already been described i n 2 . 3 . c . i i .
Attempts to measure M
r
of
such m a t e r i a l s i n s o l u t i o n f a i l e d due to extremely low s o l u b i l i t y i n a wide
v a r i e t y of solvents.
S i m i l a r l y , low s o l u b i l i t y i n deuterated s o l v e n t s prevented
examination by n.m.r. spectroscopy.
I t i s p o s s i b l e t h a t white p r e c i p i t a t e s
might be e i t h e r branched or c r o s s l i n k e d m a t e r i a l s , formed by the i n t e r a c t i o n of
a photoexcited bisbenzophenone carbonyl and t e r t i a r y hydrogen i n e i t h e r a
1,1,2,2-tetraphenylethanol type of u n i t or a
u n i t , as shown i n Figure 2.57
1,1,2,2-tetraphenylethane type
( i n the case of b r a n c h i n g ) .
The f a i l u r e of the polymerization r e a c t i o n to proceed to completion i s a
d i f f i c u l t question to deal with.
I n p a r t i c u l a r the e s t a b l i s h e d presence of
both benzoyl and benzyl groups i n the r e a c t i o n products r u l e s out the p o s s i b i l i t y
of one type o f f u n c t i o n a l group being t o t a l l y consumed by some k i n d of s i d e
r e a c t i o n , thus l e a v i n g the other i n excess.
One could a t t r i b u t e t h i s phenomenon
to the formation of e i t h e r an e f f i c i e n t t r i p l e t quencher or a strong l i g h t
absorbing intermediate which does e f f e c t i v e l y stop the r e a c t i o n a t a p a r t i c u l a r
stage.
- 137 -
Q
X
H
5
H or OH
n
/
n
OHO
Q
n
OH
Figure
I
2.57
The o r i g i n of the yellow colour observed during i r r a d i a t i o n s i s d i f f i c u l t
to account f o r .
P r e c i p i t a t i o n of the yellow crude polymeric m a t e r i a l s from
benzene/60°-80° petroleum ether afforded white powders whose i . r . s p e c t r a and
M
n
were not d i f f e r e n t from those of the crude m a t e r i a l s . Treatment of the
white powders w i t h benzene a t room temperature
b r i g h t yellow s o l u t i o n s .
r e s u l t e d i n the formation of
Evaporation of benzene s o l v e n t gave yellow m a t e r i a l s ,
whereas a d d i t i o n of excess 60°-80° petroleum ether to the yellow benzene
s o l u t i o n s caused the p r e c i p i t a t i o n of white m a t e r i a l s ; the i . r . s p e c t r a of
these products were superimposable.
I t was f i r s t thought t h a t some k i n d of
a s s o c i a t i o n between benzene s o l v e n t and the product occurs which g i v e s r i s e to
- 138 -
the coloured s p e c i e s .
However the same c y c l e of c o l o u r l e s s to yellow changes
can be e f f e c t e d using chloroform, which excludes such an e x p l a n a t i o n .
Treatment o f the polymeric m a t e r i a l s with dehydrating agents e l i m i n a t e d
the hydroxy1 peak i n the i . r . region and gave r i s e to a new peak a t 1680 cm
a t t r i b u t e d to a benzopinacolone-type carbonyl group.
1
T h i s was observed both
i n r e a c t i o n s c a r r i e d out a t high temperature and room temperature, and i s
c o n s i s t e n t w i t h the expected r e a c t i o n scheme shown i n Figure 2.58.
The
OJQ
I
OH
H
H
OH
OH
I
OH
H
H
11
0
Figure
o
2.58
1,1,2,2-tetraphenylethanol type of u n i t would be expected to loose HOH
giving
a conjugated s t r u c t u r e ; the benzopinacol type of u n i t would be expected to
rearrange to a benzopinacolone one^"* and the 1,1,2,2-tetraphenylethane
s t r u c t u r e would be expected to be u n r e a c t i v e .
The model compound 1,1,2,2-tetraphenylethanol appears to be p a r t i a l l y
d i s s o c i a t i n g a t temperatures of c a . 80° or over y i e l d i n g r a d i c a l s by rupture
o f the ethane C-C a bond.
I n the absence o f dehydrating agents these r a d i c a l s
appear to recombine forming the i n i t i a l product, or d i f f u s e out o f the cage
- 139 -
and diraerize y i e l d i n g benzopinacol and 1,1,2,2-tetraphenylethane, a l l the
steps are r e v e r s i b l e and s i n c e the ethanol d e r i v a t i v e i s very i n s o l u b l e , i t
i s normally the predominant product.
Addition of dehydrating agent a t high
temperatures causes the rearrangement
of the benzopinacol component of t h i s
system to benzopinacolone
(Figure 2.59).
99
OH
T h i s hypothesis would e x p l a i n
A
•^2
inert
solvent
H
0
<0H= r<0>
!
w
OH
//
9 J®
— c
OH
Figure
OH
2.59
the observed behaviour of the ethanol and i t s formation from benzopinacol and
tetraphenylethane.
At room temperature 1,1,2,2-tetraphenylethanol i s known
to dehydrate q u a n t i t a t i v e l y to tetraphenylethylene ( p e r c h l o r i c a c i d /
166
methylenechloride s o l v e n t ) , no by-products were reported.
I t can be concluded t h a t the photoreductive a d d i t i o n of m-dibenzoylbenzene
to p- or m-dibenzylbenzene a t 350 run leads to the formation of low molecular
weight m a t e r i a l s (M ca. 3500) c o n t a i n i n g u n i t s analogous to 1,1,2,2n
tetraphenylethanol, benzopinacol and 1,1,2,2-tetraphenylethane.
In contrast
to the model r e a c t i o n , polymerization does not proceed to completion even a t
prolonged
(over 700 h r s ) i r r a d i a t i o n s .
The products obtained decompose
- 140 -
thermally a t high temperatures to y i e l d s t a r t i n g m a t e r i a l s together with t r a c e s
of diphenylmethane and benzophenone.
Treatment with dehydrating agents r e s u l t s
i n the e l i m i n a t i o n of water and the occurrence of rearrangements,both r e s u l t s
being e n t i r e l y c o n s i s t e n t with the s t r u c t u r e s assigned to the
polymers.
I t would seem on the b a s i s of the r e s u l t s obtained i n t h i s work t h a t
t r u l y s u c c e s s f u l photoreductive polymerization i s l i k e l y to be l i m i t e d to the
case of benzopinacols, although the h i s t o r y of the a r e a suggests t h a t i t would
be f o o l i s h to make dogmatic statements to t h i s e f f e c t .
CHAPTER 3
The products of i r r a d i a t i o n of benzaldehyde and i t s d i f u n c t l o n a l
analogues
- 141 -
3.1.
Introduction
3.1.a.
E a r l y photochemical
investigations
I n v e s t i g a t i o n s i n t o the nature of the products formed on
benzaldehyde,
exposing
e i t h e r neat or i n the presence of other substances to a c t i n i c
r a d i a t i o n go back to the beginning of the century,
i n 1901, C i a m i c i a n and
127
S i l b e r i n s o l a t e d a mixture of benzaldehyde and ethanol i n a s e a l e d g l a s s tube;
they obtained acetaldehyde, a r e s i n , and an u n s p e c i f i e d q u a n t i t y of hydrobenzoin.
Steam d i s t i l l a t i o n of the r e s i n gave q u a n t i t i e s of m a t e r i a l s
described as 'benzoic ether', 'isohydrobenzoin' (the two forms of
reported may
hydrobenzoin
have been the d l - and meso-diastereomers), and a 'yellow, hard and
f r a g i l e m a t e r i a l ' which was separated, d r i e d and p r e c i p i t a t e d from benzene/
petroleum e t h e r .
A white powder was thus obtained melting a t 100° - 101°;
was found to have the same composition as hydrobenzoin
four times as high.
but a molecular
it
weight
On the b a s i s of these f i n d i n g s the authors assigned to the
white powder the formula 4(C,„H,.0„).
14 14 2
S i m i l a r r e s u l t s were obtained on
127
i n s o l a t i o n of an e t h e r e a l s o l u t i o n of benzaldehyde.
F i v e y e a r s l a t e r the same workers reported r e s u l t s from the i n s o l a t i o n of
128
neat benzaldehyde i n a sealed g l a s s tube f o r a period of over 8 months.
The r e a c t i o n product was described as a t r a n s l u c e n t mass s i m i l a r to
p i t c h ' which i s a deep red v a r n i s h ;
observed on the w a l l s of the tube.
'greek
a few c r y s t a l s of benzoic a c i d were
The t r a n s l u c e n t mass was e x t r a c t e d with ether
and steam d i s t i l l e d to y i e l d a l i t t l e unreacted benzaldehyde and a yellow r e s i n
which, a f t e r repeated treatments with b o i l i n g water and drying, gave a
material'.
'fragile
Following treatment of an e t h e r e a l s o l u t i o n of the r e s i n with aqueous
carbonate and r e p r e c i p i t a t i o n from benzene/petroleum ether a white powder was
obtained which was found to become tacky a t 120° and melt between 125° -
130°.
Elemental a n a l y s e s and molecular weight determinations i n benzene gave r e s u l t s
pointing to the formula 9C_H 0. C i a m i c i a n and S i l b e r suggested t h a t the r e s i n
7 6
obtained from the i n s o l a t i o n of neat benzaldehyde might i n f a c t be i d e n t i c a l to
- 142
-
t h e one o b t a i n e d from t h e I n s o l a t i o n o f t h e b e n z a l d e h y d e / e t h a n o l
d i f f e r e n c e i n the e m p i r i c a l formulae, they proposed,
mixture;
m i g h t j u s t be due
the
to
128
difficulties
i n h e r e n t i n t h e a n a l y s i s o f amorphous s u b s t a n c e s .
I n s o l a t i o n of a benzaldehyde/benzylalcohol mixture
5 months a f f o r d e d s m a l l q u a n t i t i e s o f h y d r o b e n z o i n
4.4g
W
( l O g , 1:1 /w) f o r
and i s o h y d r o b e n z o i n
o f a r e s i n a p p a r e n t l y t h e same a s t h a t a l r e a d y d e s c r i b e d . O n
w
hand, i n s o l a t i o n o f a benzaldehyde/benzophenone m i x t u r e
r e s u l t e d i n t h e f o r m a t i o n o f a r e s i n and
m a t e r i a l which,
(15g, 2:1
and
the other
/w,
small q u a n t i t i e s of a white
3 months)
crystalline
f o l l o w i n g e x t r a c t i o n and p u r i f i c a t i o n from a c e t i c a c i d
melted
a t 236° - 237° and a n a l y s e d a s f o l l o w s :
C, 81.02; H, 5.65 ( c a l c u l a t e d f o r
41 34°5
'
' 5 . 6 1 ) . On t h e b a s i s o f t h e s e r e s u l t s t h e a u t h o r s
128
C
H
:
C
8
1
,
1
8
;
H
C
H
assigned to the c r y s t a l l i n e product the formula 4 ^ 3 4 ° 5 '
an a d d u c t between f o u r m o l e c u l e s o f b e n z a l d e h y d e
corresponding to
and one o f benzophenone.
C i a m i c i a n and S i l b e r a l s o i n v e s t i g a t e d t h e p r o d u c t s formed on i n s o l a t i n g a
167
benzaldehyde/nitrobenzene mixture.
Two compounds were i s o l a t e d a s s i g n e d t h e
0
Figure
3.1
o
s t r u c t u r e s shown i n F i g u r e 3.1 a l o n g w i t h some r e s i n m e l t i n g a t 125
o
- 130
.
I n an a t t e m p t t o p r e p a r e n o v e l compounds c o n t a i n i n g n i t r o g e n - i o d i n e
bonds, M a s c a r e l l i i n s o l a t e d a b e n z a l d e h y d e / i o d o x y b e n z e n e
(CgHglOg) m i x t u r e
(250g, 5:1
w
/w,
10 months, s e a l e d t u b e ) .
168
The y e l l o w - b r o w n
w i t h e t h e r , l e a v i n g a w h i t i s h r e s i d u e ( c a . 2g, m.pt.
p r o d u c t was
240° - 245°) w h i c h
treated
was
r e c r y s t a l l i z e d from a c e t i c a c i d t o g i v e w e l l d e f i n e d w h i t e c r y s t a l s m e l t i n g a t
250°.
T h i s p r o d u c t was
s l i g h t l y s o l u b l e i n most o r d i n a r y s o l v e n t s and was
found
- 143 -
to have the same composition as benzaldehyde and a molecular weight three times
as high.
The author described t h i s new compound as a 'trimer of benzaldehyde'
without f u r t h e r examining
i t s p r o p e r t i e s . Other products i s o l a t e d and
c h a r a c t e r i z e d were benzoic a c i d , s t i l b e n e , iodobenzene, t r a c e s of i o d i n e and the
usual r e s i n melting between 125° - 130°;
obtained which were not i d e n t i f i e d .
s e v e r a l high b o i l i n g l i q u i d s were a l s o
The i n t e r e s t i n g f e a t u r e of t h i s
experiment
167
i n the author's view
1
was the formation of the r e s i n and the c r y s t a l l i n e
t r i m e r ' on i n s o l a t i o n of benzaldehyde i n the presence of an o x i d i z i n g agent
(C H I0 ).
6
5
2
Three years l a t e r , Ciamician and S i l b e r r e i n v e s t i g a t e d the i n s o l a t i o n of
169
neat benzaldehyde
i n order to e s t a b l i s h whether the •trimer' d e s c r i b e d by
168
Mascarelli
did i n f a c t form i n the absence of iodinated compounds or not.
Neat benzaldehyde (lOOg) was i n s o l a t e d i n a sealed tube f o r over 29 months so
that the r e a c t i o n could proceed to completion.
At the end of the i r r a d i a t i o n
period an almost s o l i d red-brown m a t e r i a l had formed i n s i d e the tube, together
with a few drops of water.
T h i s experiment afforded 0.8g of the
1
trimer
1
described by M a s c a r e l l i (m.pt. 245° - 246° ( a c e t i c a c i d ) ) separated by v i r t u e
of i t s i n s o l u b i l i t y i n d i e t h y l e t h e r , c a . 12g of an o i l ( b o i l i n g between 177°
200°) composed mainly of benzaldehyde,
hydrobenzoin,
'
s m a l l q u a n t i t i e s of benzoic a c i d and
and 82.5g of the r e s i n a l r e a d y described i n previous e x p e r i -
127 128 131
ments.
-
'
167
'
The r e s i n was r e d i s s o l v e d i n ether, t r e a t e d with aqueous
sodium carbonate, then the e t h e r e a l l a y e r was separated and d r i e d over calcium
chloride.
P r e c i p i t a t i o n from petroleum ether y i e l d e d a y e l l o w i s h amorphous
material;
a portion of i t was p r e c i p i t a t e d s e v e r a l times from benzene/40° - 70°
petroleum ether u n t i l a white powder was obtained which, a f t e r d r y i n g a t
melted between 160° - 170°.
100°
T h i s m a t e r i a l was found to have the same elemental
composition as benzaldehyde and molecular weight determination i n a c e t i c a c i d
i n d i c a t e d a tetramer.
T h i s 'tetramer' of benzaldehyde was r e a c t i v e towards
phenylhydrazine and s e m i c a r b a z i d e hydrochloride;
treatment with semicarbazide
- 144 -
hydrochloride i n a c e t i c a c i d afforded a compound with an elemental composition
C
H
N
corresponding to the formula 9 2 7 ° 4 3
m e l t i n
a
9
2
t
2 3 2
° which the authors
assigned to the semicarbazone of the tetramer 4C_H 0.
7 6
On the b a s i s of t h i s
evidence they proposed the s t r u c t u r a l formula shown i n Figure 3.2 f o r the
photoproduct of benzaldehyde.
H
0
H
0
Ok i i
C
C—
H
0
1
C —
C—H
o
Figure 3.2
The i n s o l a t i o n of benzaldehyde i n the presence of a l i p h a t i c hydrocarbons
119
v
was examined by Paterno and C h i e f f i .
They reported obtaining the r e s i n o u s
product a l r e a d y described by Ciamician and S i l b e r i n a d d i t i o n to the 'trimer'
described by M a s c a r e l l i .
Heating the ' t r i m e r
1
i n sealed tubes a t 300° r e s u l t e d
i n the formation of benzaldehyde whereas the amorphous r e s i n gave under i d e n t i c a l
treatment a tarry l i q u i d ;
no inflammable gases or v o l a t i l e l i q u i d s were observed.
D i s t i l l a t i o n of the tarry l i q u i d afforded benzaldehyde and a high b o i l i n g f r a c t i o n
which c r y s t a l l i z e d on standing and was i d e n t i f i e d as hydrobenzoin by melting
point determination.
I n 1914, Ciamician and S i l b e r repeated the i n s o l a t i o n of a benzaldehyde/
benzophenone mixture and i s o l a t e d a compound melting a t 245° whose elemental
a n a l y s i s and molecular weight determinaticn suggested t h a t i t could be the
'addition product' of the two reagents (
C
H
2
0
7 2 2 3 ^ ' t h a t i s an adduct of two
molecules of benzaldehyde with one of benzophenone.
The r e p o r t s on these e a r l y i n v e s t i g a t i o n s a r e confusing. Paterno d i d not
miss the chance to indulge i n s c o r n f u l c r i t i c i s m of Ciamician and h i s team f o r
what he considered to be t h e i r i n a c c u r a t e and i n c o n s i s t e n t r e p o r t s on the
resinous product formed on i n s o l a t i o n of benzaldehyde, 'which melted i n i t i a l l y
- 145 -
a t 100° - 101° then a t 125° - 130° and now melts a t 160° - 170° and which was
i n i t i a l l y an octamer or nonamer of benzaldehyde and i t i s now recognized as a
tetramer ..
1
3
4
However confusing they might be, these e a r l y experiments r e p r e s e n t the only
reported attempts to i n v e s t i g a t e the s t r u c t u r e of t h i s ' r e s i n ' formed on
i r r a d i a t i o n of benzaldehyde.
I n subsequent y e a r s the p r e p a r a t i v e photochemistry
of benzaldehyde i n the presence of a wide v a r i e t y o f substances was examined by
v a r i o u s workers;
i t was found to photooxidize y i e l d i n g benzoic a c i d , add to
unsaturated l i n k a g e s , quinones or methylene groups, a b s t r a c t hydrogen from
s u i t a b l e donors e t c . A comprehensive review of these processes may be found i n
167
standard t e x t s such as the one by Schonberg.
The r e a c t i o n s a r e g e n e r a l l y
c o n s i s t e n t with the expected behaviour of a t r i p l e t e x c i t e d carbonyl group l i n k e d
to an aromatic r i n g .
F i n a l l y , the ' r e s i n ' reported by the e a r l y workers was
r e c e n t l y prepared by the gas phase i r r a d i a t i o n of benzaldehyde a t X > 300nm
and was found to possess i n t e r e s t i n g photophysical p r o p e r t i e s ;
171
e l u c i d a t e i t s s t r u c t u r e were however reported.
3.1.b.
no attempts to
Ground s t a t e polymerization of benzaldehyde and i t s d i f u n c t i o n a l analogues
Benzaldehyde was found not to polymerize under the a c t i o n of y - i r r a d i a t i o n
172
or by treatment i n s o l u t i o n or i n bulk with a wide range of c a t i o n i c
initiators.
However, when benzaldehyde was heated with b o r o n t r i f l u o r i d e etherate a t 150° i n
the absence of s o l v e n t a polymeric product was formed i n low y i e l d
(1.4%) . I t
was r e l a t i v e l y non-polar and f l u o r e s c e n t softening a t 79° and melting a t 88°.
Compression moulding a t 90° gave a g l o s s y , b r i t t l e d i s c .
n e i t h e r boron nor f l u o r i n e ;
The product contained
e b u l l i o m e t r i c determinations both i n carbon t e t r a -
c h l o r i d e and i n benzene i n d i c a t e d a polymer of d.p. 133.
The polymer was
i d e n t i f i e d as polybenzyl on the b a s i s of elemental a n a l y s i s and i n f r a r e d
172
o
spectroscopy.
Mixtures of benzaldehyde and styrene t r e a t e d a t 0 with boront r i f l u o r i d e etherate copolymerized through the carbonyl group of benzaldehyde to
y i e l d a product i s o s t e r i c with polystyrene but which may not have a d e f i n i t e
- 146 -
repeat u n i t .
Elemental a n a l y s i s of the copolymer produced from a 50:50 mixture
of monomers i n d i c a t e d a product i n c o r p o r a t i n g approximately 80% styrene and 20%
benzaldehyde,
and having a molecular weight of 14,600.
Both i s o - and tere-phthalaldehyde have been polymerized under a v a r i e t y o f
conditions to give benzoin copolymers,
173 174
'
which are claimed to be very u s e f u l
as coatings which can be c r o s s - l i n k e d t o form binders f o r g l a s s - f a b r i c laminates.
The copolymers were s a i d to possess e x c e l l e n t thermal s t a b i l i t i e s and t e a r
174
strength.
Terephthalaldehyde has a l s o been polymerized i n the presence o f
175
176
ketene and b o r o n t r i f l u o r i d e e t h e r a t e ,
a pale yellow powder o f d.p.
and DMSO.
The l a t t e r method y i e l d e d
< 9, s o l u b l e i n DMSO, DMF and ethylene carbonate,
i d e n t i f i e d by i . r . spectroscopy as polybenzoin
(Figure 3.3,1);
autooxidation i n
176
DMSO s o l u t i o n gave the high-melting and i n s o l u b l e p o l y b e n z i l (Figure 3.3,11).
Reduction of terephthalaldehyde i n dioxane with Zn and Ct^(SO^)^ afforded
polymer
with HNO^ r e s u l t e d i n the formation
o f 3.3,111).
poly(p-phenylenedicarbonyl),
poly(p-phenylenebis(hydroxymethylene))
(Figure
Treatment o f t h i s
177
Condensing the polycarbonyl with o-phenylenediamine and/or
i.e. polybenzil
H
~€H-irOH
" © - s - s -
In
II
I
OH
I
OH
III
Figure 3.3
- 147 -
3,3",4,4'-tetraminobiphenyl y i e l d s heat r e s i s t a n t r e s i n o u s p o l y q u i n a x o l i n e s
u s e f u l i n the preparation of p r o t e c t i v e c o a t i n g s and laminated r e s i n s having
177
heat s t a b i l i t y , s o l v e n t r e s i s t a n c e , f l e x i b i l i t y and low s o f t e n i n g p o i n t s .
178
Copolymers of terephthalaldehyde with v a r i o u s substances l i k e ferrocene,
179
180
poly(vinylalcohol)
and polyamide a c i d s
have been reported. F a i r l y
r e c e n t l y , s e l e c t i v e chemical r e a c t i o n s on one aldehydic group o f t e r e - and i s o 181
phthalaldehyde were made p o s s i b l e by use o f polymer supports.
3.I.e.
The photochemistry
of phthalaldehyde
Schttnberg and Mustafa reported t h a t a benzene s o l u t i o n o f phthalaldehyde
exposed to s u n l i g h t f o r 1 day deposited c o l o u r l e s s c r y s t a l s of a dimer, m.pt.
o
ca. 184 (decomposition)
,?
182
(Figure 3.4).
H
i
H
OH
i
H
C-H
hu
7"
» ©C°
11
»a/or
»
o
Figure 3.4
Kagan i r r a d i a t e d phthalaldehyde
(200 mg) i n carbon t e t r a c h l o r i d e (50 mis)
for 1 h r . under nitrogen and reported obtaining c r y s t a l l i n e p h t h a l i d e , i . e . the
lactone of 2-hydroxymethylbenzoic a c i d , m.pt. 70° i n c a . 80% y i e l d . H e
obtained s i m i l a r r e s u l t s a t d i f f e r e n t concentrations, i n the presence of a i r ,
and with i r r a d i a t i o n a t e i t h e r 253.7nm or 350nm.
t h a t i r r a d i a t i o n of phthalaldehyde
On the other hand, he showed
(0.727g) i n pentane (250 mis) a t 350nm f o r
1 hr. (Nj atmosphere) y i e l d e d 67% o f the pure photodimer shown i n F i g u r e 3.5; and
F i g u r e 3.5
- 148 -
i r r a d i a t i o n of neat phthalaldehyde (N^ atmosphere) a t 350nm f o r 3 h r s . y i e l d e d
phthalide (15%), the photodimer
(55%), and 30% of unchanged
F i n a l l y , i r r a d i a t i o n of phthalaldehyde (0.172g) i n benzene
under
starting material.
(50 mis) a t 350nm
atmosphere gave phthalide (45%) the dimer (51%) and unchanged
starting
183
material (4%).
The l a c k of dimer formation i n c h l o r i n a t e d s o l v e n t s was
a t t r i b u t e d by Kagan to e f f i c i e n t quenching of the d i m e r i z a t i o n s t e p i n the
proposed mechanism by C I * r a d i c a l s from the s o l v e n t .
T h i s was the f i r s t
example
of a photochemical Canizzaro r e a c t i o n i n which both photo-oxidation and
-reduction was shown to occur simultaneously on i r r a d i a t i o n of an aldehyde.
Cohen and co-workers showed t h a t the d i m e r i z a t i o n of phthalaldehyde i s
s t e r e o s p e c i f i c i n c o n t r a s t to the d i m e r i z a t i o n of o-phthalaldehydic a c i d
(2-formylbenzoic acid) which i s n o n - s t e r e o s p e c i f i c ;
184
two quite d i f f e r e n t paths.
185
Further work by Kagan
the r e a c t i o n s proceed v i a
on the p h o t o l y s i s of phthalaldehyde a t 77K pointed
to the conclusion t h a t a benzoyl r a d i c a l intermediate was involved i n the
r e a c t i o n which was assumed to proceed from a short l i v e d phthalaldehyde e x c i t e d
s t a t e to form phthalide and/or the photodimer.
3.1.d. B r i e f i n t r o d u c t i o n i n t o the photochemistry of benzaldehyde
Benzaldehyde, one of the few molecules which e x h i b i t phosphorescence i n the
186 187
gas phase
'
has been e x t e n s i v e l y used as a t r i p l e t energy donor both i n the
gas phase^*^ and i n s o l u t i o n . T h e
molecule has been the o b j e c t of
numerous t h e o r e t i c a l and spectroscopic s t u d i e s and a s u b s t a n t i a l amount of data
appear i n the l i t e r a t u r e .
D i r e c t photolyses of gaseous benzaldehyde reported upto the e a r l y s e v e n t i e s
192-195
have only been p r e l i m i n a r y i n nature.
I t was e s t a b l i s h e d t h a t n •* I T *
e x c i t a t i o n i n the gas phase r e s u l t e d i n polymer formation on the c e l l w a l l and
t h a t a t elevated temperatures the quantum y i e l d of benzaldehyde consumption
195
as high as 40.
I t was a l s o reported t h a t a t X < 270nm benzaldehyde
was
- 149 -
decomposed to benzene and carbon monoxide.
B l a c e t and Vanselow
claimed
that hydrogen gas, b e n z i l , benzophenone and diphenyl were formed i n a d d i t i o n to
benzene and carbon monoxide upon i r r a d i a t i o n of benzaldehyde a t 313nm.
I n an attempt to obtain absolute quantum y i e l d s f o r the primary photop h y s i c a l and photochemical processes and to study the e f f e c t o f wavelength on
the system, S t e e l and coworkers c a r r i e d out a d e t a i l e d examination of the photo196
chemistry of benzaldehyde.
The quantum y i e l d s of benzene and carbon monoxide
formation, benzaldehyde consumption and phosphorescence emission were studied.
These data, together with information from following the phorphorescence l i f e time over a range o f pressure and e x c i t a t i o n wavelengths, and t r i p l e t
transfer
studies allowed a p i c t u r e of the primary photophysical processes to be b u i l t up
(Figure 3.6) and r a t e constants f o r these processes to be determined.
authors i n t e r p r e t e d
t h e i r data as i n d i c a t i n g t h a t with 276nm l i g h t , S
The
Q
>
e x c i t a t i o n , r e s u l t e d i n the population of the higher v i b r a t i o n a l l e v e l s of two
different t r i p l e t states
(T^ and D .
At low p r e s s u r e s , d i s s o c i a t i o n occurs from
both these v i b r a t i o n a l l y e x c i t e d t r i p l e t s y i e l d i n g benzene and carbon monoxide.
c H,. + CO
C-H_
40
v
decomposition
o
30
cm
x 10
20
365nm
hu
10
276nm
0
O'
F i g u r e 3.6
- 150 -
C o l l i s i o n a l d e a c t i v a t i o n of these s t a t e s feeds the lower v i b r a t i o n a l l e v e l s of
the
lowest t r i p l e t ;
from here there are no chemical decay channels and phos-
phorescence can be observed.
S
Q
>
S
1
I n c o n t r a s t to S
excitation,
Q
e x c i t a t i o n (X i> 365nm) r e s u l t s i n e f f e c t i v e l y zero benzene or
carbon monoxide formation, s i n c e only the lower v i b r a t i o n a l l e v e l s of one
t r i p l e t were populated, and the phosphorescence y i e l d s were i n s e n s i t i v e to
pressure.
There was however a s i g n i f i c a n t quantum y i e l d of benzaldehyde
consumption and polymer formation could be observed.
The products of i r r a d i a t i o n of benzaldehyde i n s o l u t i o n have r e c e n t l y been
197
examined by Bradshaw and coworkers.
When i r r a d i a t e d i n benzene s o l u t i o n f o r
r e l a t i v e l y s h o r t periods, benzaldehyde y i e l d e d almost equal amounts of benzoin,
deoxybenzoin and hydrobenzoin;
i n ethanol s o l u t i o n the main product was
benzoin with only a t r a c e of benzoin p r e s e n t .
A more d e t a i l e d
hydro-
investigation
showed that benzoin was the major i n i t i a l product of the r e a c t i o n i n d i l u t e
benzene s o l u t i o n and t h a t i t was slowly consumed on prolonged i r r a d i a t i o n .
The
p i c t u r e i s complicated by the observation t h a t i r r a d i a t i o n of benzoin i n benzene
apparently g i v e s f i r s t benzaldehyde and then deoxybenzoin and hydrobenzoin a t
197
longer i r r a d i a t i o n times.
Other workers showed by means of c h e m i c a l l y induced dynamic n u c l e a r s p i n
p o l a r i z a t i o n (CIDNP) t h a t on i r r a d i a t i o n of benzaldehyde i n s o l u t i o n a t r i p l e t
benzaldehyde a b s t r a c t e d a hydrogen atom from a ground s t a t e benzaldehyde molecul
198
to give a r a d i c a l p a i r which c o l l a p s e d to form benzoin.
The r e a c t i o n was
r e v e r s i b l e as shown by the f a c t t h a t benzoin on i r r a d i a t i o n formed the same
radical pair.
No products were however i s o l a t e d from these s t u d i e s .
The photochemistry of benzoin has r e c e n t l y been i n v e s t i g a t e d i n more d e t a i l
I t was found t h a t i r r a d i a t i o n of the compound (3.18g) i n benzene s o l u t i o n
(300 mis) f o r 6 h r s . r e s u l t e d i n only 28% conversion. V.p.c. showed benzaldehyd
and benzoin benzoate were the only v o l a t i l e products formed.
Column chromato-
graphy on s i l i c a g e l afforded unreacted benzoin (2.1g, 66%) and benzoin benzoate
- 151 -
(0.21g, 1 3 % ) .
I r r a d i a t i o n of benzoin i n benzene i n the presence of dodecanethiol
(an e f f i c i e n t scavenger of benzoyl r a d i c a l s ) r e s u l t e d i n an i n c r e a s e d y i e l d of
199
benzaldehyde
and t o t a l supression of benzoin benzoate
200
Kornis and De Mayo
formation.
a t t r i b u t e d the e f f i c i e n t formation o f benzaldehyde
from benzoin to hydrogen t r a n s f e r from the hydroxybenzyl r a d i c a l to the benzoyl
r a d i c a l (Figure 3.7), although benzaldehyde
could a l s o be formed v i a an i n t r a -
molecular H a b s t r a c t i o n such a s t h a t postulated by P i t t s and coworkers f o r the
F i g u r e 3.7
201
formation o f acetaldehyde i n the vapour phase p h o t o l y s i s of a c e t o i n .
p i c t u r e i s by no means c l e a r ;
The
thus although both the benzoyl and hydroxybenzyl
r a d i c a l have been trapped by i r r a d i a t i n g benzoin i n the presence of N-oxides and
138
n i t r o s o compounds,
the i n c r e a s e i n benzaldehyde
quantum y i e l d with added
t h i o l i s c o n s i s t e n t with H-transfer p r i o r to or a t the same time as a-cleavage.
I t has been shown t h a t b e n z i l i s formed by combination of two benzoyl
r a d i c a l s ; a n d
i t i s known t h a t b e n z i l y i e l d s benzoin benzoate as the
major product of i r r a d i a t i o n i n cumene s o l u t i o n , t h a t i s i n the presence o f a
hydrogen donor.
3.I.e.
O r i g i n a l ideas
The photoreductive polymerization of aromatic diketones i s w e l l documented
(see Chapter 2 ) .
However, there have been no r e p o r t s on the i r r a d i a t i o n s o f
- 152 -
aromatic dialdehydes i n the presence of hydrogen donors.
I t was t h e r e f o r e
decided to i n v e s t i g a t e the behaviour of two of these dialdehydes, namely t e r e and iso-phthalaldehyde, on exposure to u l t r a v i o l e t l i g h t both i n the s o l i d s t a t e
and i n s o l u t i o n i n the presence of hydrogen donors.
I t was a l s o decided to
attempt a c l o s e r examination of the 'photopolymer* formed on i r r a d i a t i o n of neat
benzaldehyde i n the l i q u i d phase i n the hope of obtaining some information on
the s t r u c t u r e of t h i s m a t e r i a l which has been the s u b j e c t of s e v e r a l previous
investigations.
3.2.
The photochemistry of t e r e - and iso-phthalaldehyde
3.2.a.
Results
A summary of experimental procedures and r e s u l t s obtained may
Table
be found i n
3.1.
I r r a d i a t i o n s were c a r r i e d out i n s e a l e d tubes under reduced p r e s s u r e i n
order to exclude oxygen from the system, s i n c e terephthalaldehyde i s known to
204
y i e l d t e r e p h t h a l i c a c i d on i r r a d i a t i o n i n the presence of oxygen.
D i s t i l l e d water and perfluoro(methylcyclohexane) were used as the
suspending
agents f o r the s o l i d s t a t e i r r a d i a t i o n s s i n c e the dialdehydes were not d e t e c t a b l y
soluble i n e i t h e r of these media a t 25°.
I n both c a s e s e f f i c i e n t s t i r r i n g
mixing was provided by means of an e x t e r n a l mechanical
and
stirrer.
Whereas i r r a d i a t i o n s i n the s o l i d s t a t e afforded q u a n t i t a t i v e recovery of
s t a r t i n g m a t e r i a l s , i r r a d i a t i o n s i n the presence of a hydrogen donor afforded
i n i t i a l l y i n s o l u b l e products which showed both carbonyl and hydroxyl
absorptions i n the i . r . region.
modifications:
I r r a d i a t i o n s were repeated under the following
(a) the s o l u t i o n s were made as concentrated as p o s s i b l e , (b) H-
donor and s o l v e n t were very c a r e f u l l y p u r i f i e d before use, (c) s o l u t i o n s were
c a r e f u l l y degassed on a g r e a s e - f r e e , Hg-free vacuum l i n e and tubes were s e a l e d
under lower p r e s s u r e ( c a . 10 ^ mm Hg),
(d) 350nm r a d i a n t source was used i n s t e a d
of the HANOVIA 450-W Hg lamp i n an attempt to e f f e c t g r e a t e r o v e r l a p between
ft
3
H Donor
Medium i
<
ro
<
<
<
O
&
a
CN
®
o
n
u
rH
o
B
CM
m
*r
O
&
i
CJ
ro
a
ro
u
ro
a
© ®
u
u
a
o
a
a
§
o
1
f
g
h
Not characterised
Not characterised
Not characterised
1:4 v/v
1:4 v/v
j
1:4 v/v
in
O
rH
ro
ro
61.5
in
Not characterised
<
1
01
ro
ro
a
8
u
a
a
o
s
4J
in
0.351
1
1:3 v/v
<
1
1
1
f Comments
98% starting materials j
back
Products
•o
0.448
i
Solvent
Ratio
H-donor
o
0.0369
m
1
26.5
rH
0.0486
u —
ro
Suspension
c
u
CHO
r^^j quantitatively
recovered
CHO
1
Temp. Method
u
Suspension
j
(Hrs.) j
.9
Carbonyl
: Compound
• Starting Materials
- 153 -
<
m
PQ
in
^>
m
m
M<
m
n
©>
Q
a
?
a
?
ro
a
a
o
ro
a
u
i
ro
u
a
a
S
a
@
o
a
ro
- 154 -
Table 3.1 (cont.)
Footnotes:
a. LAMP A:
LAMP B:
b.
HANOVIA 450-W Hg Lamp.
RUL-350 mm Photochemical
Reactor.
METHOD A: I r r a d i a t i o n s c a r r i e d out i n pyrex tubes;
solutions
degassed by s e v e r a l freeze-pump-thaw c y c l e s on
conventional vacuum l i n e s and sealed under reduced
pressure ( r e s i d u a l p r e s s u r e i n tube ^ 0.005 mm Hg).
METHOD B: I r r a d i a t i o n s c a r r i e d out i n pyrex tubes;
solutions
degassed by s e v e r a l freeze-pump-thaw c y c l e s on high
vacuum grease-free/mercury f r e e vacuum l i n e and
s e a l e d under reduced p r e s s u r e ( r e s i d u a l p r e s s u r e i n
tubes 10~5 mm Hg).
METHOD C: I r r a d i a t i o n c a r r i e d out i n 1L f l o r e n t i n e f l a s k ;
s o l u t i o n nitrogen streamed f o r 1 h r . and q u i c k l y
stoppered.
c.
I d e n t i f i e d by i . r . spectroscopy/recovered m a t e r i a l gave one
major spot corresponding t o therephthalaldehyde on s i l i c a t . l . c .
examination (CHCl^ e l u e n t ) .
d.
2% o f a yellow m a t e r i a l was a l s o obtained (soluble i n a c e t o n e ) .
(u
: 3450, 2930, 2860, 2740, 1700, 1605 c m . ) .
max
- 1
e.
Product e x t r a c t e d by f r e e z e - d r y i n g (112.5% of the t e r e p h t h a l aldehyde used, r e a c t i o n with donor and/or s o l v e n t ( ? ) ) .
B r i t t l e f i b r e s drawn out o f the melt. Displayed c o n s i d e r a b l e
thermal s t a b i l i t y (no change i n i . r . a f t e r strong h e a t i n g on
bunsen flame). Soluble i n DMF, NMP, P y r i d i n e , e t h a n e d i o l ,
ethylmethylketone.
R e p r e c i p i t a t i o n from DMF ( s o l v e n t ) / C C 1
55% o f a yellow m a t e r i a l .
f.
4
(nonsolvent) afforded
Product e x t r a c t e d by f r e e z e - d r y i n g (116.4% o f the i s o p h t h a l aldehyde u s e d ) . B r i t t l e f i b r e s drawn out of the melt. Soluble
i n DMF, NMP, P y r i d i n e , ethylmethylketone.
R e p r e c i p i t a t i o n from DMF ( s o l v e n t ) / C C 1
61% o f a yellow m a t e r i a l .
4
(nonsolvent) afforded
g.
i . r . spectrum o f product obtained superimposable with i . r .
of product obtained from expt. 3 - s i m i l a r p h y s i c a l p r o p e r t i e s .
h.
i . r . spectrum o f product obtained superimposable with i . r .
of product obtained from expt. 4 - s i m i l a r p h y s i c a l p r o p e r t i e s .
- 155 -
the lamp emission and the carbonyl n
length p h o t o l y s i s e f f e c t s ,
modified, the use of DMF
v*
absorption and to exclude s h o r t wave-
(e) work-up of the s o l u t i o n s a f t e r i r r a d i a t i o n
was
or any other high b o i l i n g s o l v e n t being avoided.
The
products however were the same as those obtained i n the previous experiments.
Treatment of the products w i t h DMF
a t room temperature f o r 7 days r e s u l t e d
i n s u b s t a n t i a l degradation and i n c o r p o r a t i o n of DMF
by both i . r . spectroscopy and mass spectrometry.
i n t o the products, as shown
Heating of the DMF-treated
products under high vacuum (100°) for 1 day r e s u l t e d i n p a r t i a l e l i m i n a t i o n of
the DMF
peaks from the i . r . spectrum.
stability
The products showed c o n s i d e r a b l e thermal
(no change i n the i . r . spectrum a f t e r heating a t 250° f o r 10 mins.).
B r i t t l e f i b r e s could be drawn from the melt.
Comparison of the i . r .
spectra
of the products with that of polybenzoin prepared according to e s t a b l i s h e d
173
route
revealed considerable d i f f e r e n c e i n the p o s i t i o n s and i n t e n s i t i e s of
the main bands.
Both photoproducts were found to be s o l u b l e i n (CH^^SO g i v i n g
b r i g h t yellow s o l u t i o n s .
However, i n c o n t r a s t with the behaviour of poly-
173
benzoin
no autooxidation was detected, the s o l u t i o n s being s t i l l c l e a r a f t e r
2 months of standing whereas polybenzoin s o l u t i o n s p r e c i p i t a t e p o l y b e n z i l ;
i n t r o d u c t i o n of oxygen gas i n the s o l u t i o n s a f f e c t e d no change;
of the photoproducts
a f t e r 3 months of standing using water as the non-solvent
y i e l d e d unchanged photoproducts,
3.2.b.
precipitation
as shown by i . r . spectroscopy.
D i s c u s s i o n i n the l i g h t of r e c e n t knowledge
The n o n - r e a c t i v i t y of the dialdehydes i n the s o l i d s t a t e should not be
considered as a s u r p r i s i n g r e s u l t , s i n c e the most l i k e l y i n i t i a l product (a
138
benzoin-type s t r u c t u r e ) would be expected to c l e a v e r a p i d l y ,
s t a r t i n g m a t e r i a l as the main product.
The s m a l l y i e l d
y i e l d i n g the
( c a . 2%) of a coloured
m a t e r i a l obtained from the r e l a t i v e l y longer i r r a d i a t i o n of isophthalaldehyde
i n perfluoro(methylcyclohexane) non-solvent could be the r e s u l t of an out of
cage d i f f u s i o n and d i m e r i z a t i o n of the r a d i c a l s r e s u l t e d from cleavage of the
- 156 -
initially
formed benzoin s t r u c t u r e ;
such a process would give p i n a c o l and
b e n z i l - t y p e s t r u c t u r e s which could f u r t h e r r e a c t to form the coloured m a t e r i a l ( s ) .
The behaviour of the dialdehydes on i r r a d i a t i o n i n the presence of a H-donor i s
vastly different.
S t a r t i n g m a t e r i a l s disappear completely and new products are
formed, the p h y s i c a l c h a r a c t e r i s t i c s and s p e c t r a l parameters of which were
c o n s i s t e n t with t h e i r being branched low molecular weight p i n a c o l s .
The
branching occurs p o s s i b l y v i a the t e r t i a r y benzhydryl hydrogen i n the polymer
backbone which would be expected to be more e a s i l y a b s t r a c t a b l e than the t e r t i a r y
hydrogen i n isopropanol.
3.3.
The benzaldehyde
3.3.a.
photoproduct
Recent preparation and s p e c t r a l c h a r a c t e r i s t i c s
Benzaldehyde was r e c e n t l y i r r a d i a t e d i n the gas phase r e s u l t i n g i n the
171
formation of a polymeric f i l m with i n t e r e s t i n g p r o p e r t i e s .
The r e a c t i o n
v e s s e l c o n s i s t e d of a c y l i n d r i c a l Pyrex (or quartz) sleeve placed c o n c e n t r i c a l l y
around a medium pressure mercury vapour lamp ( P h i l i p s p h i l o r a HPK 125).
experiments were performed a t 50.0 +_ 0.2°.
The
The lamp (protected by a quartz tube)
and the r e a c t i o n c e l l were immersed i n 1M CuSO. which served as t h e r m o s t a t i c
4
f l u i d and a l s o , i n a l a y e r 0.5 cm t h i c k between the lamp and the c e l l , as a
f i l t e r to cut o f f a l l l i g h t with wavelengths
< 300nm.
T h i s s e l e c t i o n was
necessary to minimize benzaldehyde decomposition to benzene and carbon monoxide.
I n every p h o t o l y s i s , the p r e s s u r e drop observed corresponded to a t l e a s t 70%
of
the benzaldehyde polymerizing. The gas chromatographic a n a l y s e s of the
r e s i d u a l gases showed peaks with the same r e t e n t i o n time as benzene and benzaldehyde, the l a t t e r being present i n t r a c e q u a n t i t i e s .
F r e e z i n g down of the
r e s i d u a l gases showed the presence of an important f r a c t i o n t h a t was
non-
condensable a t -196° assigned by the authors^"^ as carbon monoxide formed by
secondary p h o t o l y s i s of the photopolymer.
The product was removed from the c e l l s
mechanically or by d i s s o l u t i o n i n v a r i o u s s o l v e n t s .
I t was found to d i s s o l v e
- 157 -
very slowly i n tetrahydrofuran, dioxane and methanol a t room temperature,
q u i c k l y i n benzene a t 20° and methanol a t 60°.
and
The u l t r a v i o l e t absorption
spectrum of the polymer i n methanol s o l u t i o n showed a maximum a t 234nm, a
0
shoulder a t 248nm (corresponding to the absorption maximum of benzoin^ ^) and a
s t r u c t u r e l e s s t a i l out to a t l e a s t 450nm.
a l s o recorded
The i . r . spectrum of the polymer was
(KBr d i s c ) and was shown to be d i f f e r e n t from t h a t of benzoin.
Two absorption bands a t 1685 and 1723 cm * were i n d i c a t i v e of two d i f f e r e n t
carbonyl environments.
Luminescence e x c i t a t i o n s p e c t r a of the product
s o l u t i o n , room temperature)
(benzene
taken with 366, 406, and 436nm e x c i t a t i o n were
c o n s i s t e n t with the presence of two a c t i v e chromophores i n the s t r u c t u r e .
polymer f i l m on the c e l l w a l l was found to s e n s i t i z e c i s _
The
, trans isomerization
of 1,3-pentadienes and to be a c t i v e even a f t e r long periods of s e r v i c e .
Its
a c t i v i t y decreased by a f a c t o r of 15 a f t e r 3 h r s . of i r r a d i a t i o n i n the presence
of 50.7 t o r r of oxygen;
t h i s treatment a l s o caused the disappearance of the
171
y e l l o w i s h c o l o u r a t i o n of the polymer.
established;
3.3.b.
3.3.b.i.
The s t r u c t u r e of the polymer was
the aim of t h i s work was to f i l l t h a t
not
gap.
Experimental
P u r i f i c a t i o n of benzaldehyde
300 mis. portions of t e c h n i c a l grade benzaldehyde (BDH Chemicals Ltd.)
K
C
were washed w i t h f i v e 200 mis. p o r t i o n s of 1M 2 ° 3
(aqueous s o l u t i o n ) .
The
m a t e r i a l thus obtained was l e f t to stand over lOOg anhydrous MgSO^ f o r 5 h r s .
I t was then t r a n s f e r r e d through a s i n t e r i n t o a 500 mis 3-necked f l a s k (operation
c a r r i e d out under a nitrogen b l a n k e t ) . T h i s product was f r a c t i o n a l l y d i s t i l l e d
(vacuum j a c k e t e d column, 3' x 1", packed with g l a s s h e l i c e s ) .
The
apparatus
used i n the f r a c t i o n a l d i s t i l l a t i o n was d r i e d i n the oven before assembly
purged with dry nitrogen f o r s e v e r a l hours before the f r a c t i o n a t i o n was
and
started;
a nitrogen atmosphere was maintained throughout by means of a nitrogen l i n e .
E q u i l i b r a t i o n of the column took about 24 h r s . (pot temp. 178°, column temp.
- 158 -
210 , head temp. 170
178°.
- 178 ) ;
head temperature was f i n a l l y e q u i l i b r a t e d a t
Take o f f r a t e was kept a t approximately 1 : 120;
the f i r s t 30 and
last
50 mis were d i s c a r d e d . Benzaldehyde thus p u r i f i e d was stored under dry nitrogen
No s i g n s of benzoic a c i d were noticed a t the neck of the f l a s k .
a n a l y s i s f i g u r e s , mass spectrum and i . r . spectrum
were i n d i c a t i v e of pure benzaldehyde.
by t . I . e . on s i l i c a
(recorded as a l i q u i d f i l m )
A s i n g l e spot was obtained on examination
(benzene, chloroform, e t h y l a c e t a t e , acetone/water, carbon
t e t r a c h l o r i d e , propanol);
one peak only.
Elemental
analytical g.l.c.
( C o l . A, 150°, C o l . 0, 110°) showed
The u l t r a v i o l e t spectrum showed the following a b s o r p t i o n s :
370 ( 2 ) , 353 (8.4), 338.7 (10.4), 327.5 (10.4), 317 (9.4), 306 (7.3), 288
285 (318.4), 278.5 (412), 248 (2906), 241
3.3.b.ii.
(360),
(3618) nm (e) (cyclohexane).
Irradiations
Benzaldehyde was t r a n s f e r r e d i n t o dry c y l i n d r i c a l Pyrex v e s s e l s under
nitrogen, degassed by s e v e r a l freeze-pump-thaw c y c l e s on a conventional vacuum
-3
l i n e , and s e a l e d under reduced p r e s s u r e (10
mm Hg).
I n some i r r a d i a t i o n s a
Hg-free, g r e a s e - f r e e vacuum l i n e was used and the tubes were s e a l e d under lower
pressure ( c a . 10 ^ mm Hg).
350nm lamps.
A l l i r r a d i a t i o n s were c a r r i e d out a t c a . 40° using
The r e a c t i o n was found to be very slow.
A yellow colour u s u a l l y
developed a f t e r 50 h r s . of i r r a d i a t i o n and the i n i t i a l l y water white mobile
l i q u i d turned i n t o a brown v i s c o u s mass a f t e r 200 h r s . of i r r a d i a t i o n .
Benzaldehyde was i n i t i a l l y i r r a d i a t e d f o r periods of 250 -*360 h r s .
In a
l a t e r experiment four p o r t i o n s of the pure m a t e r i a l were i r r a d i a t e d f o r 100,
128
660 and 1110 h r s .
Contrary to previous r e p o r t s
observed on the w a l l s of the tube.
350
no c r y s t a l l i n e m a t e r i a l s were
The v i s c o u s mass formed appeared homo-
geneous and no signs of water or other immiscible l i q u i d s were detected which
c a s t s doubts on the v a l i d i t y of e a r l i e r
arguments.
The tubes were frozen i n l i q u i d a i r before the s e a l was broken and the open
end was immediately connected to a concentrated s u l p h u r i c a c i d bubbler.
pressure was noticed on opening the tubes, even a f t e r prolonged
No
irradiations,
- 159 -
I n d i c a t i n g the absence of non-condensable gases.
3.3.b.ii.
P u r i f i c a t i o n of product
The crude products appeared as very v i s c o u s masses containing s u b s t a n t i a l
amounts of unreacted benzaldehyde.
They were g e n e r a l l y p u r i f i e d by repeated
p r e c i p i t a t i o n s from benzene/60° - 80° petroleum e t h e r .
The r e s u l t a n t yellow
powders were d i s s o l v e d i n d i e t h y l e t h e r , washed with d i l u t e aqueous carbonate,
then with water and p r e c i p i t a t e d again using petroleum ether as the non-solvent.
Some samples were a l s o p r e c i p i t a t e d from ethanol/water.
127 128
previous r e p o r t s
'
169
'
i t was not p o s s i b l e to obtain white powders even
a f t e r a g r e a t number of p r e c i p i t a t i o n s .
a f f o r d any c r y s t a l l i n e compounds.
Concentration of mother l i q u o r s d i d not
I n some e a r l y experiments, steam d i s t i l l a t i o n
was used as a p u r i f i c a t i o n technique;
benzaldehyde was the only d e t e c t a b l e
s t e a m - v o l a t i l e m a t e r i a l ( t . l . c . on s i l i c a
100°,
I n c o n t r a s t with
(benzene, chloroform), C o l . A,
150°,
60°).
The products were found to be s o l u b l e i n carbon t e t r a c h l o r i d e ,
methylenechloride, toluene, acetone
chloroform,
( i n cold) and i n hot a l c o h o l i c s o l v e n t s ;
they were i n s o l u b l e i n a l i p h a t i c hydrocarbons,
methanol/water/potassium carbonate mixtures.
aqueous potassium carbonate or
On slow c o o l i n g of hot concentrated
or d i l u t e a l c o h o l i c s o l u t i o n s , yellow amorphous powders were obtained.
long (sometimes over 100 cm.)
f i b r e s were drawn out of the melt;
Fairly
they were
however very b r i t t l e .
T . l . c . a n a l y s i s of the p r e c i p i t a t e d products
(benzene/petroleum
ether,
ethanol/water) showed the presence of one component only, sometimes with a small
f a i n t t a i l which i s however not uncommon f o r polymeric m a t e r i a l s (benzene,
chloroform, carbon t e t r a c h l o r i d e / c h l o r o f o r m 50:50, ethanol/chloroform 50:50,
chloroform/methanol/carbon t e t r a c h l o r i d e , acetone/methanol/ethanol, e t h a n o l /
acetone 50:50, benzene/chloroform,
ethanol/acetone/water).
D e c o l o u r i z a t i o n of the amorphous m a t e r i a l was attempted using a c t i v a t e d
animal c h a r c o a l i n hot methanol s o l u t i o n .
Repeated treatments gave an o f f white
- IbO -
material
(60%) which could not be f u r t h e r decolourized by t h i s method;
the same s p e c t r a l c h a r a c t e r i s t i c s as the y e l l o w i s h
i t had
powder obtained from the
precipitations.
A l l products melted between 130° - 140° and elemental a n a l y s i s
correponded to those c a l c u l a t e d f o r benzaldehyde.
figures
Photopolymer y i e l d s ( a f t e r
p r e c i p i t a t i o n and drying) were found to vary with i r r a d i a t i o n time as
follows:
32% (100 h r s . ) , 48% (350 h r s . ) , 59% (660 h r s . ) , 68% (1110 h r s . ) .
3.3.b.iv.
Attempted c h a r a c t e r i z a t i o n of the 'photopolymer' of benzaldehyde
The s o l i d s t a t e i . r . spectra
(KBr d i s c s ) and the u l t r a v i o l e t spectra
(methanol) of the photoproducts obtained from i r r a d i a t i o n s v a r y i n g i n d u r a t i o n
from lOO to 1100 h r s . were i d e n t i c a l and the same as those reported p r e v i o u s l y
The ^"H n.m.r. spectrum (CDCl^, i n t . TMS
(6 7.3).
r e f . ) displayed o n l y one broad peak
The "^C n.m.r. spectrum showed a peak a t 6 198.9
1
( p o s s i b l y carbonyl
carbon), a s i n g l e t a t 6 128.3
(aromatic r i n g carbons) and a s i n g l e t a t 6 42.38
which i s d i f f i c u l t to assign;
i t s value i s however c l o s e to the one recorded
for the sp"' hybridised
carbon i n 1,4-dibenzylbenzene (see Chapter 2 ) .
spectrum of the m a t e r i a l
The mass
m
extended to / e 930 (d.p. of c a . 9) with prominent
peaks a t i r r e g u l a r i n t e r v a l s , namely a t 8lO, 722, 706, 690, 616, 600, 583, 569,
553, 511, 493, 477, 465, 405, 389, 375, 361, 351, 339, 315, 301, 283, 271, 252,
239, 221, 210, 208, 180, 168, 152, 122, 105, 90, 77 (spectrum recorded a t 70 eV).
Determinations of molecular weights i n chloroform s o l u t i o n
gave d.p.'s i n the range 9 - 1 1
( i s o p i e s t i c method)
f o r p u r i f i e d samples, independent of i r r a d i a t i o n
time.
The s o l u t i o n phase i . r . spectrum of the photoproduct
saturated
s o l u t i o n ) was recorded i n the region 4000 to 2500 cm.
Appendix B ) .
indicated
(carbon t e t r a c h l o r i d e ,
1
(Spectrum 39,
The spectrum showed some a l t e r a t i o n on s u c c e s s i v e d i l u t i o n and
the presence of f r e e hydroxyl (3620 cm. ^, sharp),
hydrogen bonded hydroxyl (3200 - 3500 cm. \
internally
broad and s t r u c t u r e l e s s ) and
- 161 -
aromatic carbon - hydrogen s t r e t c h i n g (3030 - 3090 cm.
) .
The shoulder
v i s i b l e a t higher concentrations (D, Spectrum 39, Appendix B) might a r i s e from
intermolecular hydrogen bonding and the band i n the region 2800 - 3000 cm. ^
d i s p l a y s s t r u c t u r e which a l s o a l t e r s somewhat on d i l u t i o n ;
t h i s band would
be expected to a r i s e from a l i p h a t i c carbon - hydrogen s t r e t c h i n g modes, however
the band shape a l t e r a t i o n on d i l u t i o n i s p u z z l i n g .
of the benzaldehyde
The s o l i d s t a t e i . r .
spectrum
'photopolymer' (No. 31, Appendix B) d i s p l a y s two
absorptions i n the carbonyl r e g i o n , 1685 and 1723 cm. *;
the carbonyl
frequencies observed f o r benzoin benzoate, one of the reported benzaldehyde
photoproducts, were 1712 cm. ^ ( e s t e r carbonyl) and 1698 cm. * (keto group);
i t seems u n l i k e l y therefore t h a t the benzoin benzoate u n i t i s a p a r t of the
photopolymer s t r u c t u r e , although i t must be admitted t h a t t h i s i s not a
p a r t i c u l a r l y rigorous argument.
I r r a d i a t i o n of the m a t e r i a l (3.0g) i n benzene (20 mis) (nitrogen streamed
s o l u t i o n , 24 h r s . , 300nm) e f f e c t e d no change i n e i t h e r the molecular weight or
the s p e c t r a l c h a r a c t e r i s t i c s .
These usual p h y s i c a l approaches to s t r u c t u r e e l u c i d a t i o n d i d not y i e l d a
convincing s t r u c t u r a l hypothesis although i t i s c l e a r t h a t the product contains
hydroxyl, carbonyl and phenyl groups.
I n view of t h i s f a c t i t was decided to
attempt some i n v e s t i g a t i o n s o f chemical r e a c t i o n s on the benzaldehyde
'photo-
polymer' i n the hope t h a t t h i s ' c l a s s i c a l ' approach might y i e l d some
s t r u c t u r a l evidence.
An account o f these preliminary s t u d i e s i s given below.
Attempted photoreduction of the 'photopolymer' (3.0g, benzene/isopropanol
2:3
(50 m i s ) , nitrogen streamed s o l u t i o n , 24 h r s . , 300nm) y i e l d e d unchanged
s t a r t i n g m a t e r i a l as evidenced by i . r . and n.m.r. spectroscopy.
Attempts to obtain c r y s t a l l i n e d e r i v a t i v e s of the *photopolymer' v i a the
carbonyl groups by r e a c t i n g small portions of i t with 2,4-dinitrophenylhydrazine i n ethanol or hydroxylamine hydrochloride i n the presence o f e i t h e r
p y r i d i n e o r sodium a c e t a t e gave i n c o n c l u s i v e r e s u l t s .
The l a t t e r
experiment
- 162
-
a f f o r d e d r e c o v e r y o f s t a r t i n g m a t e r i a l w h e r e a s t h e former r e s u l t e d
formation
o f a m a t e r i a l w h i c h was
u n s t a b l e and
c o u l d n o t be
T r e a t m e n t o f t h e p h o t o p r o d u c t w i t h bromine i n c a r b o n
s o l u t i o n a t room t e m p e r a t u r e
as evidenced
purified.
tetrachloride
e f f e c t e d no change i n t h e s t r u c t u r e o f t h e m a t e r i a l
by i . r . s p e c t r o s c o p y .
s l o w a b s o r p t i o n o f bromine was
However on h e a t i n g t h e s o l u t i o n a t 50°
observed
with simultaneous
e v o l u t i o n o f an
g a s , p o s s i b l y r e s u l t i n g from s u b s t i t u t i o n o r o x i d a t i o n r e a c t i o n s .
the photoproduct
did
i n the
(2.0g) w i t h bromine ( l . O g ) i n a c e t i c a c i d
a
acid
Refluxing
(20 m i s ) f o r 2 h r s .
n o t e f f e c t i n c o r p o r a t i o n o f bromine i n t o t h e o r i g i n a l s t r u c t u r e a s shown by
Lassaigne's test.
The
operation resulted
t h e i . r . s p e c t r u m a t 1770
h y d r o x y l band was
for
cm.
observed;
i n t h e a p p e a r a n c e o f a new
peak i n
^ b u t no change i n t h e shape o r i n t e n s i t y o f
the
t h e s e l a t e r r e s u l t s f a v o u r an o x i d a t i o n p r o c e s s
the r e a c t i o n s w i t h bromine.
R e f l u x i n g the
'photopolymer
1
(5.0g) w i t h a c e t y l c h l o r i d e (100 m i s ) f o r 3 h r s .
under a n i t r o g e n b l a n k e t a f f o r d e d a m a t e r i a l whose i . r . s p e c t r u m showed a
c o n s i d e r a b l y d i m i n i s h e d h y d r o x y l band i n t e n s i t y and
cm.
p r e s u m a b l y due
to acetate group(s).
i n t e n s i t y o f the a l i p h a t i c carbon
R e f l u x i n g the
in
n e u t r a l acetone
1
photopolymer
1
No
a new
absorption a t
1740
s u b s t a n t i a l i n c r e a s e i n the
- hydrogen a b s o r p t i o n was
(5.0g) w i t h p o t a s s i u m
however
apparent.
permanganate
(750 m i s ) f o r 3 h r s . y i e l d e d a p r o d u c t
(lO.Og)
whose i . r .
spectrum
showed no m a j o r change from t h a t o f t h e o r i g i n a l m a t e r i a l .
P y r o l y t i c decomposition
aldehyde
tar.
The
i n an i n e r t atmosphere y i e l d e d p r i m a r i l y b e n z -
( o v e r 90% y i e l d ) a l o n g w i t h s e v e r a l minor p r o d u c t s
an
intractable
v e r y h i g h y i e l d o f b e n z a l d e h y d e from t h i s p y r o l y s i s s u g g e s t s
u n i t i s n o t s u b s t a n t i a l l y changed on
i n c o r p o r a t i o n i n t o the polymer.
examination
o f t h e n o n - v o l a t i l e r e s i d u e s by t . l . c .
chloroform,
acetone,
carbon
on s i l i c a
t h a t the
Attempted
(benzene,
t e t r a c h l o r i d e ) d i d not y i e l d d e f i n i t i v e
s i n c e t h e r e were many o v e r l a p p i n g components.
i t was
and
ethanol,
results
Contrary to previous r e p o r t s
n o t p o s s i b l e t o i s o l a t e h y d r o b e n z o i n from t h i s
experiment.
119
- 163
Reduction
-
w i t h a n e x c e s s o f sodium b o r o h y d r i d e
i n 1,4-dioxane s o l u t i o n
(40 h r s . a t r e f l u x ) r e s u l t e d i n a l m o s t c o m p l e t e e l i m i n a t i o n o f t h e c a r b o n y l
f u n c t i o n ( s ) and
spectrum
(No.
i n c r e a s e i n t h e i n t e n s i t y o f t h e h y d r o x y l bands i n t h e i . r .
32, Appendix B ) .
m o l e c u l a r w e i g h t may
Mass s p e c t r a l a n a l y s i s i n d i c a t e d t h a t
h a v e been s i g n i f i c a n t l y r e d u c e d .
r e d u c t i o n w i t h e x c e s s V i t r i d e i n benzene s o l u t i o n
On
the
t h e o t h e r hand,
( n i t r o g e n b l a n k e t , 18 h r s . a t
r e f l u x ) r*f.ar&i(i an a l m o s t q u a n t i t a t i v e r e c o v e r y o f a m a t e r i a l whose i . r .
spectrum
(No.
33, Appendix B) was
s i g n i f i c a n t l y d i f f e r e n t from t h e one
from t h e r e d u c t i o n w i t h sodium b o r o h y d r i d e
a b s o r p t i o n s were t o t a l l y e l i m i n a t e d .
rationalized
i f the
1
does
r e f l u x i n g of the
and a s i g n i f i c a n t change
spectrum
this reaction
Such a d i f f e r e n c e i n b e h a v i o u r
(No.
(Found:
i n t h e i n t e n s i t y and
i n t h e number and
38, Appendix B ) .
C,
5.70%) was
be
reduces
'photopolymer' w i t h aqueous s u l p h u r i c a c i d
84.94;
H,
shape o f the h y d r o x y l
(6N)
bands
i n t e n s i t i e s o f t h e c a r b o n y l bands i n
Elemental a n a l y s i s of the product
5.07%;
C a l c u l a t e d f o r (C_H.O) :
/ b
H,
might
not.
r e s u l t e d i n a marginal c h a n g e
the i . r .
i n t h i s case the carbonyl
photopolymer• c o n t a i n e d e s t e r groups s i n c e V i t r i d e
them w h e r e a s b o r o h y d r i d e
Prolonged
and
obtained
C,
from
79.22?
n
c o n s i s t e n t w i t h t h e o v e r a l l change b e i n g r e p r e s e n t e d a s : -
+
(C.H.0)
7 6 n
T h a t i s an a p p a r e n t
l o s s o f one
r e s i d u e s i n the polymer.
" »
molecule
The p r o d u c t
(C-H_0, )
7 5 h n
of water
of t h i s r e a c t i o n although
extremely nauseous s m e l l which p r e c l u d e d f u r t h e r
Treatment of the
dichromate
f o r e v e r y two
a s o l i d had
(80 m i s ) ) w i t h
(10 m i s ) ) and c o n c e n t r a t e d s u l p h u r i c a c i d
potassium
(15 m i s )
f o r 40 h r s . a t r e f l u x , r e s u l t e d i n a c o n s i d e r a b l e d e c r e a s e i n t h e i n t e n s i t y
the bands i n the i . r .
spectrum
of
a s s o c i a t e d w i t h h y d r o x y l and an i n c r e a s e i n t h e
i n t e n s i t y and number o f bands i n t h e c a r b o n y l r e g i o n .
s i g n i f i c a n t a l t e r a t i o n i n t h e p o s i t i o n and
a l i p h a t i c carbon
an
examination.
'photopolymer' (3.0g i n benzene
(20.Og i n w a t e r
benzaldehyde
T h e r e was
also
a
i n t e n s i t y o f t h e bands i n t h e
- hydrogen s t r e t c h i n g r e g i o n .
Elemental a n a l y s i s of
the
- 164
product
(Found:
being represented
C, 64.98;
H,
-
4.56%) was
c o n s i s t e n t w i t h the o v e r a l l
as:2- , +
/H
Cr 0
(C H O)
»
(C,H,0_
7 6 n
T h a t i s , an a p p a r e n t
7 6 2.5 n
'photopolymer'.
p a r t i c u l a r l y r e p r o d u c i b l e and a t t e m p t s
solvents
(6.27%).
_)
i n c o r p o r a t i o n o f t h r e e oxygen atoms f o r e a c h p a i r
benzaldehyde r e s i d u e s i n the
product
change
T h i s experiment,
to prepare
of
however, was
larger q u a n t i t i e s of
not
the
r e s u l t e d i n t h e i s o l a t i o n o f a g r e e n i s h powder, s o l u b l e i n o r g a n i c
( e t h a n o l , benzene, chloroform)
w h i c h was
found t o c o n t a i n chromium
T r e a t m e n t o f t h i s m a t e r i a l w i t h d i e t h y l e t h e r a f f o r d e d an
s o l u b l e m a t e r i a l which contained
1.28%
chromium.
ether-
Treatment of both m a t e r i a l s
w i t h d i l u t e s u l p h u r i c a c i d i n e t h e r s o l u t i o n d i d n o t e f f e c t r e m o v a l o f chromium;
t h e s e m a t e r i a l s were p r o b a b l y
The
chromium c o m p l e x e s o f t h e
r e s u l t s of the r e a c t i o n s o f the
'photopolymer'.
*photopolymer' w i t h a c i d and o x i d i z i n g
a g e n t s u n d e r a c i d c o n d i t i o n s a r e n o t amenable t o a s i m p l e e x p l a n a t i o n .
hydroxyl d i m i n i s h i n g / c a r b o n y l i n c r e a s i n g e f f e c t of the a c i d
reminiscent of a pinacol - pinacolone
molecule
obvious
of water
t y p e o f r e a c t i o n and
The
treatment i s
the l o s s of a
i s , of course, a l s o c o n s i s t e n t w i t h such a sequence.
An
c a n d i d a t e f o r t h e o x i d a t i o n r e a c t i o n w h i c h r e s u l t s i n an i n c r e a s e i n t h e
oxygen c o n t e n t b u t no change i n t h e c a r b o n / h y d r o g e n r a t i o would be o x i d a t i o n o f
aldehyde to c a r b o x y l i c a c i d u n i t s ;
Appendix B) d o e s n o t s u p p o r t
u n f o r t u n a t e l y the i n f r a r e d spectrum
s u c h a r a t i o n a l i z a t i o n and
p r o c e s s i s a c c o m p a n i e d by a marked d e c r e a s e
p r o d u c t ' and
3.3.c.
The
35,
i n f a c t the o x i d a t i o n
i n the hydroxyl
intensity.
I t has not proved p o s s i b l e , a t the time o f w r i t i n g to r a t i o n a l i z e
r e s u l t s d e s c r i b e d above;
(No.
the p o s s i b l e nature of the benzaldehyde
the
'photo-
s u g g e s t i o n s f o r e l u c i d a t i o n o f i t s s t r u c t u r e a r e d i s c u s s e d below.
C o n c l u s i o n s and s u g g e s t i o n s f o r f u r t h e r work
p r e s e n t e x p e r i m e n t a l work adds t o t h e f a c t s known a b o u t t h e b e n z a l d e h y d e
'photopolymer• w i t h o u t
s o l v i n g the problem o f i t s s t r u c t u r e .
I t i s perhaps
- 165
-
s u r p r i s i n g t h a t i n t h e l i g h t o f a v a i l a b l e knowledge and
remains unsolved
techniques
t h e problem
d e s p i t e the i n t e r m i t t e n t a t t e n t i o n s of d i f f e r e n t workers
a period of seventy y e a r s .
I n attempting
t o s e t up h y p o t h e s e s
for test i t
becomes c l e a r t h a t an enormous v a r i e t y o f s t r u c t u r e s c o u l d r e a s o n a b l y
be
d e r i v e d by
of
'paper c h e m i s t r y ' f o r t h e p r o d u c t
benzaldehyde;
In
Chapter
this point i s i l l u s t r a t e d
the photochemistry
photochemical
below.
the combination
process.
I f we
o f r a d i c a l p a i r s p r o d u c e d from
c o n s i d e r the primary
known t o be formed on i r r a d i a t i o n o f b e n z a l d e h y d e we
o f p o s s i b i l i t i e s c a n be g e n e r a t e d
in
F i g u r e 3.8.
p r o c e s s e s , and
o f one
The
i t may
products.
products.
be
t h a t the
I f , on
these are
illustrated
'photopolymer
1
a r i s e s from f u r t h e r r e a c t i o n s
t h e o t h e r hand, t h e r a d i c a l - r a d i c a l r e or other o f the phenyl
I I drawn i n t h e l o w e r h a l f o f t h e F i g u r e would be
rings
the
Both t h e s e s p e c i e s c o u l d l e a d t o a v a r i e t y o f f u r t h e r
However t h e s e a r e by no means t h e o n l y p l a u s i b l e i n i t i a l
r a d i c a l - r a d i c a l combination,
p o s i t i o n s of phenyl
radicals.
radicals
s e e t h a t a v e r y l a r g e number
from t h e i r c o m b i n a t i o n ;
o c c u r r e d a t t h e p a r a - p o s i t i o n s o f one
t h e s t r u c t u r e s I and
initial
pair of
top p a r t o f t h e F i g u r e s u m m a r i z e s some o f t h e e s t a b l i s h e d
of these m a t e r i a l s .
combination
irradiation
o f a r o m a t i c c a r b o n y l compounds, d i s c u s s e d i n
2, a p r e v a l e n t theme was
an i n i t i a l
of prolonged
over
products
of
which could e q u a l l y reasonably occur a t ortho
r i n g s (generating conjugated
d i e n e s ) and between
C l e a r l y t h e s t r u c t u r e s w h i c h c o u l d be drawn a r e a l m o s t
identical
endless,
t h i s a p p r o a c h t o a s t r u c t u r a l h y p o t h e s i s i s u n l i k e l y t o be v e r y h e l p f u l a t
and
this
stage.
It
The
i s p e r h a p s w o r t h d i s c u s s i n g p o s s i b l e ways around t h e p r e s e n t
t e c h n i q u e s a v a i l a b l e i n t h e p r e s e n t work s u g g e s t
p o l y m e r o f b e n z a l d e h y d e , and
a s i n g l e component ( t . l . c . on
t h a t i t h a s a d.p.
silica)
be r e g e n e r a t e d on p y r o l y s i s a l t h o u g h
in
the polymer.
Probably
and
t h a t the product
i n the range 9 - 1 1 ,
difficulties.
i s a homothat i t i s
t h a t the b a s i c benzaldehyde u n i t s
there are several d i f f e r e n t s t r u c t u r a l
the f i r s t p o i n t to e s t a b l i s h
i n any
t h i s i n v e s t i g a t i o n would be t h e homogeneity o f t h e m a t e r i a l ;
can
units
continuation of
t h i s might
be
- 166 -
H
H
//
IOH
O
II
hu
C
OH
H
i
c
O
hu
c
C
C-
i
//
o
o
/
OH
C
/
H
Vc
H
HO
4
KETONIZATION
6o
F i g u r e 3.8.
H
I
I l l u s t r a t i o n o f some p o s s i b l e modes o f c o m b i n a t i o n
o f t h e p r i m a r y r a d i c a l p a i r formed on
of
irradiation
benzaldehyde.
t e s t e d u s i n g high p r e s s u r e l i q u i d chromatography.
Assuming t h e p r o d u c t i s shown
t o be homogeneous, t h e l i n e s o f s t r u c t u r a l i n v e s t i g a t i o n r e p o r t e d h e r e a r e
probably capable of f u r t h e r e x p l o i t a t i o n .
the p o s s i b i l i t i e s .
Two examples w i l l
serve to i l l u s t r a t e
The p r o d u c t o f r e d u c t i o n w i t h V i t r i d e w i l l be a t l e a s t a
two component m i x t u r e i f t h e 'photopolymer' backbone c o n t a i n s e s t e r
links;
- 167 -
the
components m i g h t be s e p a r a b l e by h i g h p r e s s u r e l i q u i d c h r o m a t o g r a p h y and
amenable t o c h a r a c t e r i z a t i o n .
The p y r o l y t i c f r a g m e n a t i o n o f t h e p r o d u c t s
o b t a i n e d by t r e a t i n g t h e 'photopolymer' w i t h s u l p h u r i c a c i d and
a g e n t s may
the
oxidizing
y i e l d products other than benzaldehyde which might provide c l u e s to
overall
structure.
The above s u g g e s t i o n s a r e i l l u s t r a t i v e o f t h e c h e m i c a l a p p r o a c h , and i t i s
still
p o s s i b l e t h a t s p e c t r o s c o p i c t e c h n i q u e s m i g h t y i e l d more d e t a i l e d
information.
the
even
n.m.r. s p e c t r a m i g h t p r o v e much more i n f o r m a t i v e i f a s a m p l e o f
benzaldehyde
if
T h u s , improved "^C n.m.r. f a c i l i t i e s may w e l l be u s e f u l ;
'photopolymer' d e r i v e d from CgD^CHO were t o be p r e p a r e d .
Finally,
a s y s t e m a t i c s t u d y o f p o s s i b l e model compounds were c a r r i e d o u t t h e r e c e n t
r e s o l u t i o n improvements i n t h e ESCA t e c h n i q u e m i g h t a l l o w u s e f u l
i n f o r m a t i o n t o be deduced.
structural
CHAPTER 4
S t u d i e s on t h e c y c l o a d d i t i o n o f p e r f l u o r o g l u t a r y l f l u o r i d e t o some
perfluoroolefins
- 168 -
4.1.
The P a t e r n o - B u c h i
4.1.a.
reaction
Introduction
The
p h o t o c y c l o a d d i t i o n o f c a r b o n y l compounds t o o l e f i n s l e a d i n g
formation o f oxetanes
( F i g u r e 4.1) was f i r s t
to the
r e p o r t e d by P a t e r n o and C h i e f f i
119
at
the beginning o f the century.
u
\
R
/
c
C
the reaction i n
R
\
^
Bttchi r e i n v e s t i g a t e d
R
C
C
<
hu
R'
Figure
4.1
1954^°^ and a s a r e s u l t o f h i s work t h e c y c l i c f o u r member e t h e r
t h e r e a c t i o n p r o d u c t was v e r i f i e d .
However, i t was n o t u n t i l
structure for
fourteen
l a t e r t h a t t h e f i r s t a t t e m p t t o d e m o n s t r a t e t h e s c o p e and u s e f u l n e s s
of the
29
r e a c t i o n was made.
years
^
The r e a c t i o n
i s frequently
referred to as the Paterno-
B u c h i r e a c t i o n and i t i s r e c o g n i s e d a s t h e most u s e f u l method f o r t h e s y n t h e s i s
o f c y c l i c f o u r membered e t h e r
(carbonyl
Both s t a r t i n g
materials
compounds and o l e f i n s ) a r e r e a d i l y a v a i l a b l e e i t h e r c o m m e r c i a l l y o r
through w e l l e s t a b l i s h e d
nearly
compounds ( o x e t a n e s ) .
quantitative,
laboratory
syntheses.
Y i e l d s v a r y from v e r y low t o
depending on a v a r i e t y o f f a c t o r s , t h e number and n a t u r e
o f s i d e r e a c t i o n s b e i n g one o f them.
Comprehensive r e v i e w s o f t h e P a t e r n o -
29 207
Btlchi r e a c t i o n a r e a v a i l a b l e .
In
'
t h e o r i g i n a l e x p e r i m e n t , P a t e r n o and C h i e f f i r e p o r t e d t h a t
insolation
o f benzophenone i n a p e t r o l e u m m i x t u r e r i c h i n 2 - m e t h y l - 2 - b u t e n e r e s u l t e d i n
the
f o r m a t i o n o f a n o x e t a n e i n good y i e l d
(Figure 4.2).
Btichi's assignment o f
o x e t a n e s t r u c t u r e s t o t h e p r o d u c t s o b t a i n e d by i r r a d i a t i o n o f a c e t o p h e n o n e ,
b e n z a l d e h y d e and b u t a n a l i n t h e p r e s e n c e o f p u r e 2 - m e t h y l - 2 - b u t e n e was b a s e d
on
t h e i d e n t i f i c a t i o n o f c a r b o n y l compounds formed from a c i d c a t a l y s e d
cleavage
- 169 -
H_C
9
CH
f
c
9
H
CH
cu 3<0)-
sunliqht
C
H
H
CH
CH
H
CH
CH
F i g u r e 4.2
of these products.
A c o m p r e h e n s i v e t a b l e o f o x e t a n e s p r e p a r e d by t h e
v
29
P a t e r n o - B u c h i r e a c t i o n h a s been p r o d u c e d by A r n o l d .
s u c c e s s f u l l y undergoing
C a r b o n y l compounds
p h o t o c y c l o a d d i t i o n i n c l u d e a l i p h a t i c and a r o m a t i c
a l d e h y d e s and k e t o n e s , fluorocompounds, p - q u i n o n e s a s w e l l a s compounds
c o n t a i n i n g f u n c t i o n a l groups i n a d d i t i o n t o t h e c a r b o n y l g r o u p .
embrace l i n e a r and c y c l i c s y s t e m s , i n c l u d i n g f l u o r o o l e f i n s .
used
I n a d d i t i o n to
o l e f i n s o t h e r u n s a t u r a t e d s y s t e m s have been employed i n c l u d i n g
a c e t y l e n e s and k e t e n i m i n e s .
Olefins
allenes,
The c y c l o a d d i t i o n may be i n t r a m o l e c u l a r o r i n t e r -
molecular.
4.1.b.
Mechanism
P h o t o r e d u c t i o n and c y c l o a d d i t i o n r e a c t i o n s a r e c h a r a c t e r i s t i c o f t h e
29
carbonyl n
ir* s t a t e
and c a r b o n y l compounds u n d e r g o i n g
208
g e n e r a l l y undergo p h o t o r e d u c t i o n i n i s o p r o p a n o l .
photocycloaddition
The i m p o r t a n t s t e p s i n t h e
r e a c t i o n f o r e l e c t r o n r i c h o l e f i n s may f r e q u e n t l y be r e p r e s e n t e d by t h e scheme
shown i n F i g u r e 4.3.
R e a c t i o n may be b r o u g h t
about by i r r a d i a t i o n i n r e g i o n s
where o n l y t h e c a r b o n y l compounds a b s o r b ;
thus i n i t i a l
c a r b o n y l chromophore c a n be d e m o n s t r a t e d .
Deactivation of the excited
without oxetane
e x c i t a t i o n of the
state
f o r m a t i o n may o c c u r by a v a r i e t y o f c o m p e t i n g p r o c e s s e s , t h e
-5
85
n,ir* t r i p l e t e x i s t i n g i n f l u i d
s o l u t i o n f o r approximately
10
sec.
o f c y c l o a d d i t i o n must be r a p i d enough t o o c c u r b e f o r e t h e e x c i t e d
compound r e t u r n s t o t h e ground s t a t e by, f o r example, r a d i a t i v e
The r a t e
carbonyl
deactivation.
S i n g l e t and t r i p l e t e x c i t e d s t a t e s may be quenched b y i n t e r a c t i o n w i t h some
- 170 -
hi)
i)
Excitation
ii)
RCOR
•
Intersystem Crossing
RCOR*
(singlet)
RCOR* ( s i n g l e t )
*
RCOR*
(triplet)
radiative or non-radiative
iii)
D e a c t i v a t i o n RCOR*
with or without
with molecular
iv)
>
RCOR
(ground
state)
quenchers
rearrangement
Reaction
1
-R
O
•R'
RCOR*
R— •
R'
K"
R
F i g u r e 4.3:
Reaction
•R'
— R'
R'
R
scheme f o r o x e t a n e
other molecule such a s an unsaturated
system
29
R'
formation
The
actual photocycloaddition
g e n e r a l l y i n v o l v e s a t t a c k on t h e ground s t a t e o l e f i n by t h e n,ir*
triplet
29
excited carbonyl
compound.
The r e a c t i o n s e q u e n c e i n F i g u r e 4.3 i n v o l v e s
a d d i t i o n o f t h e l o n e e l e c t r o n o f t h e oxygen atom t o a n u n s a t u r a t e d
giving a 1,4-biradical intermediate
oxetane.
which subsequently
With unsymmetrical u n s a t u r a t e d
system
r i n g c l o s e s t o form t h e
o l e f i n s two i s o m e r s
may be formed;
t h e s t e r e o c h e m i s t r y o f t h e m a j o r a d d u c t c a n be p r e d i c t e d from a c o n s i d e r a t i o n
of t h e r e l a t i v e s t a b i l i t y
of the possible b i r a d i c a l intermediates.
n,rt* t r i p l e t
s p i n i n v e r s i o n must o c c u r
i s involved,
T h e r e i s good e v i d e n c e
f o r the formation
before
I f the
209
bonding.
of the b i r a d i c a l
intermediate
29
during
the reaction,
and a s i g n i f i c a n t number o f c y c l o a d d i t i o n p r o d u c t s c a n
be r a t i o n a l i z e d by t h e b i r a d i c a l mechanism.
T h e r e a r e however a l t e r n a t i v e
mechanisms p r o p o s e d w h i c h i n c l u d e c h a r g e - t r a n s f e r complex f o r m a t i o n , a n d
211 212
e x c i p l e x formation.
'
F o r i n s t a n c e i n t r a m o l e c u l a r c y c l o a d d i t i o n i n 5213
hept-2-one i s t h o u g h t t o p r o c e e d v i a s i n g l e t e x c i p l e x f o r m a t i o n .
I t has
b u t a d i e n e p r o c e e d s by a d d i t i o n o f d i e n e t r i p l e t t o ground s t a t e benzophenone.
a l s o been s u g g e s t e d t h a t c y c l o a d d i t i o n o f benzophenone t o 2 , 3 - d i m e t h y l - l , 3 -
214
- 171
Other r e p o r t s
-
o f o x e t a n e f o r m a t i o n from e x c i t e d o l e f i n s and
ground s t a t e
•
i
, ,
, 215,216,217
c a r b o n y l compounnf. h.wo a p p e a r e d .
4.I.e.
Limitations
A m a j o r r e s t r i c t i o n on
extent
s u c c e s s f u l high y i e l d photocycloaddition
is
the n a t u r e and
of competing p r o c e s s e s ,
by
t h e e x c i t e d c a r b o n y l from t h e o l e f i n ,
m a i n l y hydrogen
The
c a s e may
cyclohexene
be
exemplified
(Figure 4.4),
by
where t h r e e p r o d u c t s i n a d d i t i o n
ho
H
H
3 6
01'
X2
99
*9
H
H
OH
abstraction.
to t h e o x e t a n e
9 6
H
H
&
itself;
the r e a c t i o n of p h o t o e x c i t e d benzaldehyde w i t h
isolated.
H
abstraction
s o l v e n t , o r even t h e o x e t a n e
t h e hydrogen a t o e t h e r oxygen b e i n g p a r t i c u l a r l y s u s c e p t i b l e t o
reactions
OH
Figure
H
H
OH
4.4
H
are
- 172
Cyclobutane
f o r m a t i o n may
-
be an a l t e r n a t i v e r e a c t i o n t o o x e t a n e
formation,
218
a s w i t h 1,4-quinones s u c h a s c h l o r a n i l
(Figure 4.5).
and
o
R
hu
J*
Figure
t y p e I I p r o c e s s e s may
N o r r i s h type I
4.5
compete w i t h o x e t a n e f o r m a t i o n .
N o r r i s h type I rupture
o f a c y l - h a l i d e bonds o f p e r f l u o r o a c y l c h l o r i d e s and b r o m i d e s competes w i t h
219
oxetane formation
Products
from t h e s e c a r b o n y l compounds.
must be
s t a b l e to the i r r a d i a t i o n c o n d i t i o n s used.
a r e t r a n s p a r e n t i n t h e l o n g w a v e l e n g t h r e g i o n b u t may
220
at short
Oxetanes
r i n g open on
irradiation
wavelengths.
P h o t o c h e m i c a l l y a c t i v e chromophores p r e s e n t i n a d d i t i o n t o t h e
group o f t h e c a r b o n y l compound may
l e a d t o c o m p l i c a t i o n s , f o r example i n
f u r t h e r r e a c t i o n beyond o x e t a n e f o r m a t i o n
29 221
tetramethylallene (Figure 4.6).
'
(CH ) C=C=C(CH )
3
2
carbonyl
3
as with i r r a d i a t i o n of fluorenone
2
Figure
4.6
and
- 173
-
O x e t a n e p r o d u c t s though d e t e c t a b l e and
n.m.r. s p e c t r o s c o p y
may
be
c h a r a c t e r l z a b l e by
Infrared
and
too u n s t a b l e f o r p u r i f i c a t i o n , an example b e i n g
o x e t a n e from 4,4'-dimethyoxybenzophenone and
i s o b u t y l e n e which fragments i n t o
29
formaldehyde and d i a r y l e t h y l e n e
the
(Figure 4.7).
208
'
OCH.
I—T
V2
hu
CH =C(CH )
2
3
2
l(4-CH.,0(C6 H 4'2
0
(4-CH OC H ) C=(CH )
3
Figure
4.2.
6
4
2
3
+ HCHO
2
4.7
A p p l i c a t i o n o f t h e P a t e r n o - B u c h i r e a c t i o n t o polymer s y n t h e s i s
The
p h o t o c h e m i c a l r e a c t i o n o f a c a r b o n y l group w i t h an o l e f i n y i e l d i n g
an o x e t a n e h a s been u s e d f o r c r o s s l i n k i n g , c h a i n e x t e n s i o n and
modification of p o l y m e r s . ^
I n p r i n c i p l e , t h e r e a r e two
structural
p o s s i b l e ways i n
w h i c h the r e a c t i o n c a n be u s e d i n t h e s y n t h e s i s o f l i n e a r p o l y m e r s w i t h
u n i t s i n the p o l y m e r c h a i n ;
they a r e r e p r e s e n t e d
by e q u a t i o n s
( i ) and ( i i )
26
i n F i g u r e 4.8.
The
l o w e r r o u t e was
examined by Andrews and
oxetane
Feast;
h»
27
'
(i)
\
0
c
c
— c-
\
+ c
Li
Figure
4.8
i_L
c
c — y
(ii)
a v a r i e t y of aromatic bisketones
m e t h y l a l l e n e and
- 174
-
and
two
d i f f e r e n t d i o l e f i n i c systems,
f u r a n were used a s monomers.
several c r i t e r i a :
T h e i r c h o i c e was
based
the model r e a c t i o n s w i t h m o n o f u n c t i o n a l r e a g e n t s
tetraon
were
29
thoroughly
s t u d i e d and u n d e r s t o o d ;
photostable
solvents;
monomers and
p o l y m e r s were s o l u b l e i n
r e a c t i o n s p r o c e e d e d i n h i g h y i e l d and
conversion
without
c h a i n t e r m i n a t i n g s i d e r e a c t i o n s and b o t h r e a c t a n t s and p r o d u c t s
were s t a b l e t o
r a d i a t i o n i n t h e e n e r g y iung<= r e q u i r e d f o r p h o t o p o l y m e r i z a t i o n .
These
r e s t r i c t i o n s eliminated a large proportion
reactions as candidates
o f t h e documented P a t e r n o - B t i c h i
f o r photopolymerization
studies.
I n the case of the b i s k e t o n e - t e t r a m e t h y l a l l e n e photopolymerizations,
i n v e s t i g a t i o n s c a r r i e d out e s t a b l i s h e d t h a t under a p p r o p r i a t e c o n d i t i o n s
p o l y m e r s i n w h i c h c a . 90% o f the polymer c h a i n l i n k s a r e o x e t a n e s c a n
prepared
by
i r r a d i a t i o n of equimolar s o l u t i o n s of aromatic
26
methylallene
i n benzene.
k e t o n e s seem t o be
I n t h i s r e s p e c t , the behaviour
i n l i n e with the behaviour
of t h e i r
raonofunctional
co-
be
d i k e t o n e s and
of aromatic
the
tetra-
bisanalogue,
benzophenone, w h i c h a f f o r d s c a . 90% o x e t a n e s upon i r r a d i a t i o n i n t e t r a m e t h y l a l l e n e , and
10% h y d r o x y l - c o n t a i n i n g
formed i n an i n i t i a l
products,
a r i s i n g p r e s u m a b l y from
hydrogen a b s t r a c t i o n r e a c t i o n by
the
radicals
photoexcited
29
carbonyl
( s e e C h a p t e r 1, S e c t i o n 1 . 3 ) .
The r e a c t i o n between benzophenone and f u r a n h a s been t h e s u b j e c t o f
222-229
numerous i n v e s t i g a t i o n s .
I n 1963 i t was r e p o r t e d t h a t i r r a d i a t i o n
benzophenone i n e x c e s s o f f u r a n g i v e s t h e 1:1
adduct,
of
6,6-diphenyl-2,7-dioxa-
222,223,224
bicyclo[3.2.0Jhept-3-ene
the f o r m a t i o n
o f 2:1
i n near q u a n t i t a t i v e y i e l d .
Subsequently
a d d u c t s from t h e p h o t o c y c l o a d d i t i o n
o f two
molecules
of
225
benzophenone t o one
o f f u r a n was
reported,
and a d d u c t s i s o l a t e d were a s s i g n e d
the s t r u c t u r e s shown i n t h e upper p a r t o f F i g u r e 4.9.
chemical behaviour
By a n a l o g y t o t h e p h o t o -
o f the b i s k e t o n e - t e t r a m e t h y l a l l e n e system, i r r a d i a t i o n
e q u i m o l a r amounts o f b i s k e t o n e s and
f u r a n i n benzene were e x p e c t e d
p o l y m e r s o f t h e s t r u c t u r e shown i n t h e l o w e r
p a r t o f F i g u r e 4.9.
to
of
yield
Several
- 175
O
II
-
Q
H
it
II
Q
o
H
H
5
H
Q
O.
Ar
i
3:
3
Ar
Ar
n
Q
Figure
n
4.9
a t t e m p t s to e f f e c t t h e e x p e c t e d r e a c t i o n were l a r g e l y u n s u c c e s s f u l , y i e l d i n g
o n l y low m o l e c u l a r w e i g h t m a t e r i a l s s u g g e s t i n g t h a t t h e p r o b l e m s i n h e r e n t i n
t h e q u a n t i t a t i v e m a n i p u l a t i o n o f f u r a n (b.p. 32°C) were p r e v e n t i n g
p r e p a r a t i o n o f p r e c i s e l y equimolar s o l u t i o n s .
the
Finally this difficulty
was
overcome by p r e p a r i n g 2:1 a d d u c t s between t h e d i k e t o n e s and f u r a n a c c o r d i n q t o
the e q u a t i o n i n F i g u r e 4.10.
These
a d d u c t s b e i n g s o l i d s c o u l d be
quantitatively
Q
\
ho
Ar
Figure
manipulated
Ar
without d i f f i c u l t y ,
s o l u t i o n s o f 2:1
4.10
and s u b s e q u e n t
i r r a d i a t i o n of
equimolar
f u r a n - d i k e t o n e a d d u c t s and d i k e t o n e s i n b e n z e n e gave r i s e
27
l i n e a r polymers
o f d.p.'s upto 23.
m a t e r i a l s r e v e a l e d both oxetane
Spectroscopic examinations
of these
and h y d r o x y l bands i n t h e i n f r a r e d r e g i o n .
to
- 176 -
P r e v i o u s s t u d i e s o f t h e r e a c t i o n between benzophenone and f u r a n had n o t
revealed
any t e n d e n c y f o r hydrogen a b s t r a c t i o n
from f u r a n by benzophenone
222-229
triplets;
i n d e e d i n t h e r e a c t i o n s o f benzophenone w i t h m e t h y l f u r a n s ,
where a b s t r a c t i o n from t h e a l l y l i c C - H bonds m i g h t be e x p e c t e d t o be
favourable,
228
t h e a u t h o r s s p e c i f i c a l l y s t a t e t h a t o x e t a n e s were t h e o n l y p r o d u c t s .
since the experimental d e t a i l s o f the polymerizations
r e a c t i o n s were d i f f e r e n t i n s e v e r a l r e s p e c t s
relatively
could
slow oxetane formation),
be p o s t u l a t e d .
For instance
be
and t h o s e o f t h e model
(due t o low monomer s o l u b i l i t y and
p o s s i b l e s o u r c e s o f t h e h y d r o x y l hydrogen
s l o w p h o t o r e a c t i o n o f benzophenone w i t h
77 83—87
benzene i s known t o y i e l d b e n z o p i n a c o l and d i p h e n y l ;
contain
However,
'
a l s o , a l l polymers
a C - H bond a t o two e t h e r o x y g e n s and s u c h h y d r o g e n s a r e known t o
p a r t i c u l a r l y s u s c e p t i b l e to a b s t r a c t i o n .
232
Such a b s t r a c t i o n s
could
lead to
c r o s s l i n k i n g and p r e c i p i t a t i o n .
It
i s thus apparent t h a t a p p l i c a t i o n o f the Paterno-Btichi r e a c t i o n to
polymer s y n t h e s i s i n t h e s y s t e m s i n v e s t i g a t e d was o n l y p a r t l y s u c c e s s f u l , m a i n l y
due
t o competing p r o c e s s e s
( e s p e c i a l l y hydrogen a b s t r a c t i o n and c r o s s l i n k i n g ) ,
r e l a t i v e l y low monomer s o l u b i l i t y and p r o l o n g e d i r r a d i a t i o n t i m e s .
4.3.
Applications
perfluoro
o f t h e P a t e r n o - B u c h l r e a c t i o n t o p o l y f l u o r i n a t e d and
systems
C y c l i c ethers
a s a c l a s s have b e e n known f o r a l o n g t i m e and h a v e been
w e l l recognized as useful organic
Generally
ethers,
preparation
and p l a s t i c i z e r s .
because o f
I n 1961 however, a new c l a s s o f f o u r membered
f l u o r o s u b s t i t u t e d o x e t a n e s , appeared i n t h e l i t e r a t u r e and t h e i r
from f l u o r o o l e f i n s and f l u o r o a l d e h y d e s v i a t h e P a t e r n o - B t i c h i
r e a c t i o n was d e s c r i b e d .
ethers
and a s s o l v e n t s
s u c h e t h e r s have been l i m i t e d i n t h e i r u s e f u l n e s s
r e l a t i v e l y low s t a b i l i t y .
cyclic
intermediates
More s p e c i f i c a l l y t h i s new c l a s s o f p o l y f l u o r o c y c l i e
c a r r i e d one h y d r o g e n atom on t h e r i n g c a r b o n a d j a c e n t
to ether
oxygen;
t h e i r o u t s t a n d i n g c h e m i c a l and p h y s i c a l s t a b i l i t y was e m p h a s i z e d by t h e
233
author.
- 177 -
The new 2 - h y d r o p o l y f l u o r o o x e t a n e s r e p o r t e d r a n g e d
l i q u i d s t o low m e l t i n g s o l i d s , depending
carbons i n the molecule.
from c l e a r ,
colourless
g e n e r a l l y on t h e t o t a l number o f
T h o s e c o n t a i n i n g l e s s t h a n about
were c l e a r , c o l o u r l e s s l i q u i d s b o i l i n g from 100° - 300°C.
eighteen carbons
They e x h i b i t e d
high
h y d r o l y t i c s t a b i l i t y , b o t h under aqueous a c i d and aqueous b a s e c o n d i t i o n s .
They
were s o l u b l e i n a l k a n o l s , e t h e r s a n d v a r i o u s p e r f l u o r o c a r b o n s o l v e n t s b u t
i n s o l u b l e i n w a t e r and s o l u t i o n s c o n t a i n i n g h i g h p e r c e n t a g e o f w a t e r .
They were
n o n - i n f l a m m a b l e and e x h i b i t e d o u t s t a n d i n g r e s i s t a n c e a g a i n s t t h e r m a l and
oxidative degradation.
T h e s e p r o p e r t i e s made t h e new compounds u s e f u l a s
' s t a b l e l i q u i d ' m a t e r i a l s , f o r example, a s t r a n s f o r m e r f l u i d s ,
f l u i d s for high
t e m p e r a t u r e power t r a n s m i s s i o n s , o r h y d r a u l i c s y s t e m s , o r l i q u i d
mechanical d r i v e s .
coupled
V i g o r o u s c h l o r i n a t i o n c o u l d s u b s t i t u t e t h e 2-hydrogen
w i t h c h l o r i n e , and t h e 2 - c h l o r i n e c o u l d be r e a d i l y c o n v e r t e d t o o t h e r
i n t e r e s t i n g c h e m i c a l i n t e r m e d i a t e s by c o n v e n t i o n a l methods o f r e p l a c e m e n t and
modification of the r e l a t i v e l y reactive ring
chlorine substituent using
s t a n d a r d methods employed i n s y n t h e t i c o r g a n i c c h e m i s t r y .
T h e s e p o l y f l u o r o - 2 - h y d r o o x e t a n e s were g e n e r a l l y p r e p a r e d by d i r e c t
i r r a d i a t i o n o f t h e two r e a c t a n t s i n c y l i n d r i c a l q u a r t z r e a c t o r s
approximately
f o u r d i a m e t e r s l o n g , m a i n t a i n e d a t a t m o s p h e r i c p r e s s u r e and u n d e r r e f l u x
a s o l i d carbon dioxide/acetone cooled condenser.
r e a c t a n t s were u s e d .
mercury
resonance
No s o l v e n t s f o r t h e two
U l t r a v i o l e t l i g h t from a l o w - p r e s s u r e , 10 w a t t , q u a r t z ,
lamp f i t t e d
the source o f energy.
from
i n a s p i r a l around
I r r a d i a t i o n t i m e s ranged
t h e r e a c t o r was employed a s
from t h r e e d a y s
(chlorotri-
fluoroethylene/w-hydroperfluorovaleraldehyde) t o twelve days (hexafluoropropene-l/perfluoro-n-butyraldehyde).
Y i e l d s ranged
from 27% t o 6 6 % o f t h e o r y .
233
No mention o f b y - p r o d u c t s
Oxetanes
o r s i d e r e a c t i o n s was made by t h e a u t h o r .
s u c c e s s f u l l y s y n t h e s i z e d by t h i s method a r e i l l u s t r a t e d i n
F i g u r e 4.11 and i n c l u d e 3 , 4 , 4 - t r i f l u o r o - 3 - t r i f l u o r o m e t h y l - 2 - p e r f l u o r o - n propyloxetane
(I),
3,4,4-trifluoro-2,3-bis(trifluoromethyl)oxetane
(II),
- 178
-
2-(4H-octafluoro-n-butyl)-3,4,4-trifluoro-3-trifluoromethyloxetane
Vapour p h a s e chromatography and
(III).
n.m.r. s t u d i e s r e v e a l e d t h e p r e s e n c e
CF
CF
3
of
two
C,F
3 6
3
CF„
CF II
II
2
Figure
isomers
f o r the o x e t a n e s o b t a i n e d ,
products.
I I I
4.11
the s t r u c t u r e s g i v e n a r e f o r the m a j o r
S i m i l a r p o l y f l u o r i n a t e d o x e t a n e s were r e p o r t e d
i n the
following
233,235,236
years.
236
I t was
(450 w a t t
r e p o r t e d by Cook and
Hanovia h i g h - p r e s s u r e
Landrum
t h a t under a c t i n i c
m e r c u r y lamp) h e x a f l u o r o a c e t o n e gave good
y i e l d s of o x e t a n e s w i t h e t h y l e n e , v i n y l
f l u o r i d e and
With v i n y l and v i n y l i d e n e f l u o r i d e i t was
p o s s i b l e a d d u c t s and
irradiation
vinylidene fluoride.
p o s s i b l e t o i s o l a t e and
a l s o determine the isomer
identify
distribution.
Free r a d i c a l addition of a l i p h a t i c aldehydes to f l u o r i n a t e d o l e f i n s
been shown t o y i e l d k e t o n e s d e r i v e d
t e r m i n a l c a r b o n o f t h e d o u b l e bond.
under c e r t a i n circumstances
from a d d i t i o n o f an a c y l r a d i c a l t o
237,238
k e t o n e s and
both
B i s s e l l and
o x e t a n e s can be
has
the
F i e l d s have shown t h a t
produced
239
simultaneously.
phase of mixtures
formation
They r e p o r t e d
of acetaldehyde
o f complex m i x t u r e s
that u l t r a v i o l e t irradiation
and
a fluorinated ethylene
i n the
gas
r e s u l t e d i n the
from w h i c h t h e k e t o n e d e r i v e d from a d d i t i o n
an a c e t y l r a d i c a l to t h e CF^ group o f the o l e f i n and
c y c l o a d d i t i o n of the aldehyde to the o l e f i n could
the oxetane d e r i v e d
be o b t a i n e d .
Four
tetrafluoroethylene, chlorotrifluoroethylene, bromotrifluoroethylene
l , l - d i c h l o r o - 2 , 2 - d i f l u o r o e t h y l e n e were s t u d i e d .
The
of
from
olefins,
and
major product i n each
case
- 179
was
the ketone.
The
r e a c t o r c o n s i s t e d of a 5 l i t r e
c o o l e d q u a r t z w e l l was
was
-
i n s e r t e d , a 100
f l a s k i n t o which a water-
w a t t h i g h - p r e s s u r e m e r c u r y v a p o u r lamp
suspended i n t h e w e l l a t t h e c e n t r e
of
the f l a s k .
i n t r o d u c e d t h r o u g h a vacuum m a n i f o l d a t t a c h e d
Gaseous r e a c t a n t s
t o a s i d e arm
The
r e a c t a n t s were i n t r o d u c e d from s u p p l y c y l i n d e r s u n t i l
was
obtained.
The
m i x t u r e was
h a l f i t s i n i t i a l value;
component, b u t
t'niis d i d n o t
represent
telomerlc materials
extended f u r t h e r .
reactor.
the d e s i r e d
i r r a d i a t e d u n t i l the pressure
t h e y i e l d s o f b o t h k e t o n e and
i r r a d i a t i o n t i m e was
of the
had
were
pressure
fallen
to
complete consumption of
either
oxetane a c t u a l l y decreased i f the
S i z e a b l e q u a n t i t i e s of high b o i l i n g
a c c u m u l a t e d i n t h e bottom o f
the r e a c t o r .
Perfluorinated
o x e t a n e s , i n o t h e r words o x e t a n e s w i t h e i t h e r f l u o r i n e o r p e r f l u o r i n a t e d
attached
to t h e r i n g c a r b o n s were p h o t o c h e m i c a l l y s y n t h e s i z e d
f o r the
groups
first
time
240
by
H a r r i s and
Coffman i n 1961.
B e f o r e t h e p u b l i c a t i o n o f t h e i r work
o n l y known example o f t h i s c l a s s was
hexafluorooxetane i t s e l f ,
the
p r e p a r e d by
the
241
electrolytic
c a r r i e d out
f l u o r i n a t i o n o f t h e p a r e n t compound, o x e t a n e .
e i t h e r a t atmospheric pressure
the b.p.'s o f t h e r e a c t a n t s .
o r i n g l a s s ampoules d e p e n d i n g
I n the c a s e o f a t m o s p h e r i c p r e s s u r e
the r e a c t o r c o n s i s t e d o f a v e r t i c a l q u a r t z tube
magnetic s t i r r e r ,
a gas
i n l e t a d a p t o r and
( 2 " x 10")
the
e x i t o f w h i c h was
stream of n i t r o g e n
h e l i x shaped
passed.
reactions,
carbon
acetone/solid
carbon
u l t r a v i o l e t r a d i a t i o n source consisted
pressure
m e r c u r y lamp w h i c h was
filled
of the r e a c t i o n mixture.
w i t h the
s h a k e n , t h e ampoule and
p r o d u c t s were s e p a r a t e d
attached
to a s h a k e r .
i t s c o n t e n t s were i r r a d i a t e d w i t h two
H - 85 C - 3 lamps p l a c e d
techniques.
A l t e r n a t i v e l y , a g l a s s ampoule was
f l u o r o c a r b o n y l compound and
as c l o s e to the b o t t l e as p o s s i b l e .
c h r o m a t o g r a p h i c a l l y and
examined by
of
f i t t e d around
q u a r t z r e a c t i o n t u b e so t h a t i t s r a d i a t i o n impinged p r i m a r i l y upon t h e
portion
dioxide
f i t t e d w i t h a T - t u b e through w h i c h a s l o w
The
(4" x 2*1") low
on
f i t t e d with a
a large acetone/solid
c o o l e d c o n d e n s e r v e n t e d through a t r a p , a l s o c o o l e d by
dioxide,
S y n t h e s e s were
a
the
liquid
partially
While being
General
I n both
Electric
cases,
spectroscopic
- 180 -
Some p o r f l u o r o o x e t a n e s p r e p a r e d by t h e methods d e s c r i b e d
listed
i n T a b l e 4.1.
of oxetanes
cases
prepared
I t : c a n be s e e n from t h i s
from a c i d o r d i a c i d
a s h i g h a s 9 1 % . No b y - p r o d u c t s
above a r e
table that percentage y i e l d s
f l u o r i d e s a r e v e r y h i g h , i n some
from t h e s e r e a c t i o n s were r e p o r t e d by
240
the a u t h o r s .
I n c o n t r a s t to t h i s behaviour,
i r r a d i a t i o n o f sym-di-
c h l o r o t e t r a f l u o r o a c e t o n e and h e x a f l u o r o p r o p e n e f o r two d a y s
lead t o the formation o f t h e corresponding oxetane
i n an ampoule
(12%) , two u n i d e n t i f i e d i n 240
v o l a t i l e compounds, CF2CI2 ( 1 % ) , CO, CO^ and S i F In a following publication, Harris investigated
4
the photoreactions of
219
a c y l f l u o r i d e s i n the presence of f l u o r o o l e f i n s ;
that
he s t a t e d c a t e g o r i c a l l y
' i r r a d i a t i o n o f m i x t u r e s o f p o l y f l u o r o a c y l f l u o r i d e s and f l u o r o o l e f i n s
leads p r i m a r i l y to the formation o f oxetanes;
f l u o r i d e and h e x a f l u o r o p r o p y l e n e g i v e
f o r example, p e r f l u o r o b u t a n o y l
t h e c i s and t r a n s i s o m e r s o f 2 - p e r f l u o r o -
n-propyl-3-trifluoromethyltetrafluorooxetane
(Figure 4.12).
V i r t u a l l y no
C
n-C F COF +
3
7
CF =CFCF
2
F
" 3 7~
hu
n
3
-CF.
F
F
F i g u r e 4.12
o t h e r products a r e formed.
1
When t h e p h o t o r e a c t i o n o f h e x a f l u o r o p r o p y l e n e w i t h
was
perfluoroacylchlorides
examined however, a v a r i e t y o f p r o d u c t s was formed. . T h u s p e r f l u o r o -
b u t a n o y l c h l o r i d e and h e x a f l u o r o p r o p y l e n e y i e l d e d a t l e a s t t e n p r o d u c t s
240
(Figure 4.13).
terminal
In contrast to the reactions of fluoroacyl fluorides with
fluoroolefins
( i n which
1:1 a d d u c t s were v i r t u a l l y
p r o d u c t s ) o n l y s m a l l y i e l d s o f 1:1 a d d u c t s were f o u n d .
the exclusive
T h e r e were a l s o
- 181 -
240
T a b l e 4.1.
U l t r a v i o l e t c y c l e - a d d i t i o n s o f p e r f l u o r o c a r h o n y l compounds t o
perfluoroolefins
C a r b o n y l compound
Olefin
Period of
irradiation
(days)
Oxetane
(% y i e l d )
(CF )
3
CF =CFCF
CF^COCF^
39g
2
(0.235m)
43g
CF =CFCF
C F C0C F
CF =CFCF
3
7
45g
3
7
3
7
45g
3
7
40g
C F
(0.123m)
2
45g
( C
3
(0.233m)
2
(0.131m)
C F COC F
2
35g
(50)
CF,
(0.286m)
C F COC F
2 5
2 6
43g (0.162m)
0—,(C F )
3
F
5 11
(0.129m)
2
17g
(62)
0 —
12
(C F )
3
l c
F,|
,1
7
2
( 3 2 )
F
'
5 11
3
F
CT
(33,
2
CF.
(0.133m)
CF =CFCF
56g
95g
2
(0.483m)
CF =CFCF
35g
68g
7
2
(0.162m)
C O F
7 15
40g (O.H3m)
F I
3
2
(38)
|-CF
F
° - f
(0.453m)
2
hCF
3
3
CF =CFCF
50g
O
3
(0.633m)
C F C0F
F
2
2
3
C
7
.CF.
(0.233m)
CF COF
3
(46)
3
CF =CFCF
2
}
.CF„
2
35g
F
2 5 2
(0.267m)
= C F C
2
3
L
i ^
C
F
3
F
3
7
(7 3)
3
15
13
(0.333m)
2
(91)
|-CF
;
r ~ 3
F
F
F0C(CF ) C0F
CF =CFCF
26g
60g
2
3
(0.107m)
2
(CF ) COF
2
3
3
(34)
(0.40m)
CF.
F
F
(CF ):
2
and
1(31)
IF
- 182
n-C,F_COCl
37
+
C F =CFCF,
2 3
h
" >
CF
CF
3
n-C F (CF -CF)Cl
3
7
-
n-C,F_Cl
37
(trace)
n-C,.F,
+
6 14
21%
A
3
O
CI
C F -n
3
C
O
?
+
2
+
F
h i 7
- n
and/or
CF
32%
3
g
%
2
C 1 [ C F CF C F ( C F ) ]C1
+
n-C.F C F ( C F _ ) C _ F -n
38%
+
CF,CFC1CF„C1
11%
Figure
trace
4.13
r e l a t i v e l y s m a l l amounts o f t h e p r o d u c t s o b t a i n e d from t h e p h o t o l y s i s o f
acyl chloride i t s e l f .
sequences
The b u l k o f t h e p r o d u c t s was
thought to a r i s e
beginning w i t h a d d i t i o n s of the a c y l c h l o r i d e p h o t o l y s i s
from
fragments
240
(i.e.
t h e c h l o r i n e atom and
A s i m i l a r behaviour
the p e r f l u o r o a l k y l r a d i c a l )
was
observed
b u t a n o y l b r o m i d e and p e r f l u o r o p r o p y l e n e
n-C F CBr
3
n
-
C
+
?
F
4 9
C
F
(
C
F
3
CF =CFCF
2
)
C
F
3 7
C F . CF_
, 3 | 3
BrCF -C
CFCF Br
2
2.
_
n
+
+
h
"
3
n
-
c
»
F
3
7
c
(Figure 4.14).
BrCCF^F(CF > I C ^
3
2
+
3
+
+
2
C. „ F „
12 26
Figure
The
olefin.
i n t h e p h o t o r e a c t i o n between p e r f l u o r o -
CCF CF(CF )] Br
n-C F.
6 14
to the
(?)
+
n-C.F_Br
3 7
4.14
a c y l h a l i d e / h e x a f l u o r o p r o p y l e n e r e a c t i o n s were a l l c a r r i e d o u t i n t h e
same manner.
The
r e a c t o r c o n s i s t e d o f a v e r t i c a l q u a r t z tube
f i t t e d with a magnetic s t i r r e r ,
a l a r g e acetone-dry
(2 x l O i n . )
i c e cooled condenser
through
a d r y i c e c o o l e d t r a p , t h e e x i t o f w h i c h was
f i t t e d w i t h a T-tube
through
w h i c h a slow s t r e a m o f n i t r o g e n p a s s e d .
ultraviolet
s o u r c e c o n s i s t e d o f a h e l i x shaped
resonance
(4 x 2.5
The
vented
radiation
i n . ) low p r e s s u r e m e r c u r y
lamp w h i c h f i t t e d around t h e q u a r t z r e a c t o r so t h a t i t s r a d i a t i o n
- 183 -
impinged p r i m a r i l y upon t h e l i q u i d p o r t i o n
4.4.
The p h o t o l y s i s o f a c y l
of the reaction
mixture.
fluorides
A knowledge o f t h e band p o s i t i o n s and i n t e n s i t i e s forms t h e s t a r t i n g
point
f o r any photochemical i n v e s t i g a t i o n .
I n the u l t r a v i o l e t spectra o f
p e r f l u o r o a c y l h a l i d e s a marked b a t h o c h r o m i c s h i f t o f t h e maximum o f t h e
n
tr* t r a n s i t i o n i s o b s e r v e d on p a s s i n g
from t h e f l u o r i d e s t h r o u g h
chlorides
219
to t h e b r o m i d e s .
The s p e c t r a l c h a r a c t e r i s t i c s o f t h e p e r f l u o r o b u t a n o y l
h a l i d e s a r e r e c o r d e d i n T a b l e 4.2 a s an example.
As
e a r l y a s 1959, H a s z e l d i n e and Nyman d e m o n s t r a t e d t h a t i r r a d i a t i o n o f
c h l o r o d i f l u o r o a c e t y l f l u o r i d e gave m a i n l y 1 , 2 - d i c h l o r o t e t r a f l u o r o e t h a n e and
d i c h l o r o d i f l u o r o m e t h a n e w i t h s m a l l amounts o f s e v e r a l o t h e r
materials
T a b l e 4.2
A b s o r p t i o n bands o f p e r f l u o r o b u t y r y l h a l i d e s i n t h e u.v. r e g i o n
n-C^COX
Gaseous p h a s e
Cyclohexane
X
A
(nm) (e)
max
A
F
215 (66)
CI
258
fluoride
(nm) ( e )
-
( 3 8 ) ; 266 (37)
Br
including
max
259
(46.5);
217
(692);
266 (46)
273 (56)
c a r b o n y l f l u o r i d e , c a r b o n y l c h l o r i d e f l u o r i d e , and s i l i c o n
(Figure
C1CF
tetra-
4.15).
COF
h
"
»
C1CF C F C I
+
C I CF
+
C0FC1
+
COF
+
SiF
F i g u r e 4.15
More d e t a i l e d p h o t o l y t i c
s t u d i e s o f p o l y f l u o r o a c y l f l u o r i d e s were
reported
219
by
Harris;
t h e e x p e r i m e n t a l p r o c e d u r e was t h e same a s i n t h e a c y l h a l i d e /
p e r f l u o r o p r o p e n e i r r a d i a t i o n s (see S e c t i o n
4.3).
P o l y f l u o r o a l k a n e s were the
- 184
main p r o d u c t s
obtained
-
from t h e s e p h o t o l y s e s ;
f o r example, from t h e
of p e r f l u o r o b u t a n o y l f l u o r i d e , the major product
hexane.
was
i s o l a t e d was
I n a d d i t i o n a h i g h e r b o i l i n g f r a c t i o n was
i s o l a t e d having
perfluoro-n-
obtained
from w h i c h an
ether
t h e s t r u c t u r e (n-C^F^)^CFOC^F^-n.
A n a l y s i s o f the i n f r a r e d s p e c t r a o f t h e e f f l u e n t g a s e s
c o n s i s t e d o f 5 - 15% C C ^ , t r a c e s o f S i F
and CO^.
irradiation
and
4
C
3
F
I J
and
7
indicated that
t h e r e m a i n d e r was
they
CO
T h e s e r e s u l t s wore c o n s i s t e n t w i t h the scheme p r o p o s e d by H a r r i s
(Figure 4.16).
I n t h i s scheme t h e p h o t o e x c i t e d
C F COF
3
C F d!bF
?
3
C F COF
3
2
?
• C F *
?
3
C P 3
a c y l f l u o r i d e molecule c l e a v e s
+
7
*COF
>
7
C
C F *
3
+
7
F
3 7°v
C F COF
3
XT'
?
C F
T 7
C F "
3
7
C F C^
+
3
7
CF"
•
C F OCF(C F )
3
7
3
7
2
C F
T 7
2 'COF
F i g u r e 4.16:
•
Scheme a c c o u n t i n g
COF
+
2
CO
for r e s u l t s of i r r a d i a t i n g p e r f l u o r o -
butanoy1fluoride
t o g i v e a p e r f l u o r o p r o p y l r a d i c a l and
p e r f l u o r o p r o p a n e was
observed
a fluoroformyl r a d i c a l .
Since
no
among t h e r e a c t i o n p r o d u c t s , i t f o l l o w s t h a t
t h e p e r f l u o r o p r o p y l r a d i c a l does n o t a b s t r a c t a f l u o r i n e atom from the
fluoride.
acyl-
I t i s a l s o p r o b a b l e t h a t t h e a l t e r n a t i v e mode o f c l e a v a g e o f
the
*
e x c i t e d a c y l f l u o r i d e molecule ( i . e . C F C O F
3
occur.
C F CO"
7
3
+
7
F") does
not
To a m a j o r e x t e n t t h e p e r f l u o r o p r o p y l r a d i c a l r e a c t s w i t h a n o t h e r
r a d i c a l to give perfluorohexane;
however i t c a n a l s o a t t a c k a m o l e c u l e o f
a c y l f l u o r i d e a t t h e oxygen t o g i v e t h e r a d i c a l C F O C F C F
3
combines w i t h a n o t h e r
such
7
3
7
the
which e v e n t u a l l y
p e r f l u o r o p r o p y l r a d i c a l t o g i v e an e t h e r .
The
f a t e of
- 105 -
the
"COF r a d i c a l produced i n t h e p h o t o l y s i s was i n d i c a t e d by t h e d e t e c t i o n o f
C02» CO and COF2 i n t h e e f f l u e n t g a s e s .
T h e r a d i c a l may
d i r e c t l y t o COF2 and CO a s i n d i c a t e d i n F i g u r e
disproportionate
4.16 o r p o s s i b l y
to g i v e o x a l y l f l u o r i d e which then undergoes d i s p r o p o r t i o n a t i o n .
and
i t dimerizes
The CO2
S i F ^ p r e s u m a b l y a r i s e by r e a c t i o n o f COF2, o x a l y l f l u o r i d e o r t h e "COF
r a d i c a l with the w a l l s o f the r e a c t i o n v e s s e l .
From t h e i r r a d i a t i o n o f a
m i x t u r e o f p e r f l u o r o b u t a n o y l f l u o r i d e and p e r f l u o r o o c t a n o y l f l u o r i d e ,
perfluoro-
n-hexane, -decane, and - t e t r a d e c a n e were i s o l a t e d a s e x p e c t e d on t h e b a s i s o f
t h e r e a c t i o n scheme g i v e n abovei
I r r a d i a t i o n o f a d i a c y l f l u o r i d e , p e r f l u o r o g l u t a r y l f l u o r i d e was c a r r i e d
out
under t h e same e x p e r i m e n t a l c o n d i t i o n s
f o r four days.
t i m e , t h e r e a c t i o n m i x t u r e was c o m p l e t e l y s o l i d .
evident:
i ) hard b r i t t l e m a t e r i a l
stuck
A t t h e end o f t h i s
Two k i n d s o f w h i t e s o l i d
t o t h e s i d e s o f t h e r e a c t o r and
ii)
somewhat 'mushy' s o l i d from t h e c e n t r e p o r t i o n
The
t o t a l y i e l d o f r e c o v e r e d s o l i d was r o u g h l y 4 5 % on a w e i g h t b a s i s .
solids reacted
190°
not
with moist a i r to give,
of the reaction v e s s e l .
Both
a f t e r s e v e r a l days, products melting a t
- 300° and 100° - 195° r e s p e c t i v e l y .
extensively
were
The n a t u r e o f t h e s e m a t e r i a l s was
i n v e s t i g a t e d by t h e a u t h o r , who assumed t h a t t h e y were l a r g e l y
l o n g - c h a i n d i c a r b o x y l i c a c i d f l u o r i d e s o f s t r u c t u r e FOC ( C F 2 ) n C O F .
3
I n c o n t r a s t t o t h e b e h a v i o u r o f p e r f l u o r o a c y l f l u o r i d e s , the. i r r a d i a t i o n
of a p e r f l u o r o a c y l c h l o r i d e leads
to decarbonylation r e s u l t i n g p r i m a r i l y i n the
240
formation o f a p o l y f l u o r o a l k y l c h l o r i d e .
C l e a v a g e o f t h e C - C I bond seems
t o o c c u r w i t h t h e f o r m a t i o n o f R-CO* and C I " r a d i c a l s .
hexafluoroglutarylchloride
The p h o t o l y s i s o f
a p p a r e n t l y p r o c e e d s i n a manner a n a l o g o u s t o t h a t
of monofunctional a c i d c h l o r i d e s y i e l d i n g 1,3-dichloro-hexafluoropropane a s
t h e m a j o r p r o d u c t a l o n g w i t h some 1 , 6 - d i c h l o r o p e r f l u o r o h e x a n e .
The r e l a t i v e
p r o p o r t i o n o f t h e p r o d u c t r e s u l t i n g from d i m e r i z a t i o n o f r a d i c a l s i s
s i g n i f i c a n t l y l a r g e r than f o r monofunctional a c y l c h l o r i d e s .
No p r o d u c t s w i t h
240
more t h a n s i x c a r b o n s were i s o l a t e d and no p e r f l u o r o c y c l o p r o p a n e was f o u n d .
- 186
-
From t h e p h o t o l y s e s o f p o l y f l u o r o a c y l b r o m i d e s o n l y t h e d e c a r b o n y l a t i o n
p r o d u c t s , p e r f l u o r o a l k y l b r o m i d e s were i s o l a t e d .
F o r example, from 5 H - o c t a -
fluorovalerylbromide, 4H-octafluorobutylbromide
(93%) and CO were o b t a i n e d .
The
d i f f e r e n c e s i n behaviour
e x h i b i t e d by t h e t h r e e t y p e s o f
240
acyl
h a l i d e s upon i r r a d i a t i o n can be r e l a t e d t o t h e r e l a t i v e s t r e n g t h s o f t h e C - X
bonds i n t h e compounds.
I n the p h o t o l y s i s o f the a c y l f l u o r i d e s ,
i n which
t h i s bond i s t h e s t r o n g e s t , no p r o d u c t s a r e found whose f o r m a t i o n would demand
i t s r u p t u r e t o y i e l d a f l u o r i n e atom.
4.5.
Original
idea
A p p l i c a t i o n o f t h e P a t e r n o - B u c h i r e a c t i o n t o polymer s y n t h e s e s i n t h e
a r o m a t i c d i k e t o n e / d i o l e f i n s e r i e s was
d i s c u s s e d i n S e c t i o n 4.2.
behaviour
On
only p a r t l y successful for reasons
t h e o t h e r hand, l i t e r a t u r e i n f o r m a t i o n on
the
o f t h e p e r f l u o r o a c y l f l u o r i d e / p e r f l u o r o o l e f i n s y s t e m on e x p o s u r e
ultraviolet irradiation
a t t r a c t i v e one
( S e c t i o n s 4.3
and
4.4)
made t h i s s y s t e m
f o r u s e i n l i n e a r polymer s y n t h e s i s .
appear
Thus, the use o f
an
liquid
p e r f l u o r o r e a c t a n t s would e l i m i n a t e t h e c o m p l i c a t i o n s i n t r o d u c e d by u s e
solvents.
I r r a d i a t i o n s of p r e c i s e l y equimolar
f l u o r i d e s / p e r f l u o r o d i o l e f i n s would be e x p e c t e d
weight
mixtures of
to
of
perfluorodiacid-
to y i e l d l i n e a r high
molecular
p e r f l u o r o p o l y o x e t a n e s s i n c e no s i d e r e a c t i o n s seem t o compete w i t h
240
oxetane
formation.
Such p r e c i s e l y m e t e r e d m i x t u r e s would be e x p e c t e d
be e a s i l y formed and
l i n e techniques.
t h e n be e x c l u d e d
transferred
to
i n t o q u a r t z v e s s e l s u s i n g c o n v e n t i o n a l vacuum
Oxygen, w h i c h d i s s o l v e s v e r y r e a d i l y i n f l u o r o c a r b o n s ,
could
from t h e m i x t u r e by s u c c e s s i v e f r e e z e - pump - thaw c y c l e s .
P r o d u c t s would be e x p e c t e d
photopolymerization.
t o be t r a n s p a r e n t i n t h e e n e r g y
The main a d v a n t a g e o f t h e
p e r f l u o r o o l e f i n s y s t e m however, l i e s
perfluorodiacidfluoride/
i n the absence
a b s t r a c t i o n r e a c t i o n s by t h e p h o t o e x c i t e d c a r b o n y l .
c o u l d i n t e r f e r e w i t h polymer formation
range r e q u i r e d f o r
of competing hydrogen
The o n l y r e a c t i o n
i s the t e l o m e r i z a t i o n of the
which
acid
- 187 -
fluoride,
'
w h i c h would d e s t r o y t h e r e q u i r e d
o l e f i n and a c y l f l u o r i d e g r o u p s .
d.p.
would be l i m i t e d ;
As
reaction.^
however t h e r e was a c a t e g o r i c a l s t a t e m e n t i n t h e
o x e t a n e f o r m a t i o n was t h e
0
b r i e f l y mentioned i n S e c t i o n
compounds i s complex, i t f.n a l s c
therefore
of the
I f t h i s reaction occurred the attainable
l i t e r a t u r e t h a t under a p p r o p r i a t e c o n d i t i o n s
exclusive
1:1 s t o i c h i o m e t r y
1.7 t h e p h o t o c h e m i s t r y o f c a r b o n y l
an a r e a
n e c e s s a r y f o r workers using
of considerable
a c t i v i t y and i t i s
carbonyl photochemistry as a s y n t h e t i c
method t o be r e a d y t o modify p r o c e d u r e s i n t h e l i g h t o f new i n f o r m a t i o n .
is
f o r example, e s t a b l i s h e d
reaction
that the d e t a i l e d course o f a photochemical
i s dependent on t h e n a t u r e o f i n c i d e n t l i g h t
c h r o m a t i c ! t y ) and t h e p h y s i c a l c o n d i t i o n s
solution,
nature of solvent,
I t
( w a v e l e n g t h and mono-
of the reagents
(gas,
solid,
presence of s e n s i t i z e r s or quenchers).
T h u s an
approach to t h e i n v e s t i g a t i o n o f step-growth p h o t o p o l y m e r i z a t i o n s l e a d i n g t o
perfluoro
or highly
f l u o r i n a t e d p o l y o x e i t a n e s would i n v o l v e
a compromise between
choosing systems which could y i e l d i n t e r e s t i n g polymers i f a p p r o p r i a t e
reaction conditions
c o u l d be found and c h o o s i n g s y s t e m s known t o p r o c e e d i n
h i g h y i e l d and c o n v e r s i o n and would t h e r e f o r e
within
a reasonable
The
be more l i k e l y t o y i e l d p o l y m e r s
time.
f i r s t o b j e c t i v e o f t h e e x e r c i s e was t h e r e f o r e
the photochemical
e x a m i n a t i o n o f s i m p l e s y s t e m s , by i r r a d i a t i n g a w e l l - c h a r a c t e r i z e d
and
vigorously
As
p u r i f i e d d i a c i d f l u o r i d e i n t h e presence o f an o l e f i n .
mentioned i n S e c t i o n
1.6, p e r f l u o r o g l u t a r y l f l u o r i d e was c h o s e n , p a r t l y b e c a u s e
o f t h e f a c t t h a t i t s p h o t o c h e m i s t r y h a s been documented and t h e r e
no
already
r e a s o n s w h i c h would e x c l u d e i t a s a c a n d i d a t e f o r p o s s i b l e
seem t o be
photo-
240
polymerization attempts,
in i t s preparation
and p a r t l y b e c a u s e o f t h e c o n s i d e r a b l e
a v a i l a b l e i n t h i s Department.
Two d i f f e r e n t
o l e f i n s were a l s o u s e d , a c y c l i c one and a s t r a i g h t c h a i n
Results
o b t a i n e d w i l l be d i s c u s s e d
i n Section
4.6.
expertise
perfluoro-
terminal
one.
- 188 -
4.6.
Experimental
4.6.a.
Starting materials
P e r f l u o r o g l u t a r y l f l u o r i d e was p r e p a r e d by t h e r o u t e o u t l i n e d i n
F i g u r e 4.17.
Typical r e s u l t s f o r the various stages i n t h i s synthesis are as
Cl./AlCl.
STAGE 1
STAGE 2
STAGE 3
F
KMn0 /acetone
4
KF/CH..CN
3
4
F
F
STAGE 5
STAGE 4
F i g u r e 4.17
follows:Stage
1.
trichloride
mechanical
initially
P e r c h l o r o c y c l o p e n t a d i e n e (780g, 2.85 m o l e s ) and a l u m i n i u m
(121g, 0.92 m o l e s ) were mixed i n a 1 1. R.B. f l a s k u s i n g a
stirrer.
C h l o r i n e was p a s s e d i n t o t h e m i x t u r e ;
h e a t was a p p l i e d
t o s t a r t t h e r e a c t i o n and t h e r e a f t e r c h l o r i n e was p a s s e d a t s u c h
o
a r a t e t h a t t h e temperature
o f t h e m i x t u r e was m a i n t a i n e d a t ^ 45 C by t h e
exothermicity of the reaction.
r e a c t i o n temperature
The f l o w o f c h l o r i n e was s t o p p e d when t h e
f e l l below 30°C.
The b l a c k s o l i d o b t a i n e d was t r e a t e d
with l a r g e e x c e s s o f water u n t i l a y e l l o w o i l appeared.
Recrystallization
o f t h i s o i l from e t h a n o l g a v e 649g o f o c t a c h l o r o c y c l o p e n t e n e ( 6 6 % ) i d e n t i f i e d
by
i.r.
spectroscopy
(u
1620, 1200, 770 cm.
.
max
Stage
potassium
2.
Octachlorocyclopentene
f l u o r i d e were mixed w i t h 2.5 l i t r e s o f s u l p h o l a n e i n a 5 1. R.B.
f l a s k using a mechanical
180°
(350g, 1.02 m o l e s ) and 942g o f d r y
stirrer.
- 185° f o r a b o u t l * j d a y s .
and c o l l e c t e d
T e m p e r a t u r e was r a i s e d and m a i n t a i n e d a t
P r o d u c t formed was c a r r i e d v i a n i t r o g e n s t r e a m
i n liquid a i r traps.
F r a c t i o n a l d i s t i l l a t i o n o f the crude
- 189
p r o d u c t gave 129g
spectroscopy
(u
S t a g e 3.
-
of octafluorocyclopentene
1780,
max
1720,
1410,
1340,
(60%) i d e n t i f i e d by
1310,
300g o f p o t a s s i u m permanganate
1235,
1180,
(1.90 m o l e s )
lOOO, 9 0 0 ) .
were added i n
small p o r t i o n s to a s t i r r e d s o l u t i o n of octafluorocyclopentene
0.47
moles)
i n 2 l i t r e s of dry acetone.
Temperature
was
and
then r e f l u x f o r 2 hours.
m i x t u r e was
w i t h SO2 i n a p o l y t h e n e bag.
I t was
then f i l t e r e d ,
a c i d i f i e d with d i l .
An e t h e r e a l s o l u t i o n was
c o n t i n u o u s e x t r a c t i o n o v e r n i g h t , d r i e d o v e r MgSO^ and
r e m o v a l o f e t h e r , m a t e r i a l was
S
H2 °4
a n (
lOOg were k e p t f o r t h e n e x t s t a g e .
s p e c t r o s c o p y (u
the
acetone
was
* decolourised
then obtained
filtered.
o b t a i n e d by vacuum d i s t i l l a t i o n
by
After
(0.01
mm.
Perfluoroglutaric acid
3500, 1780,
1180
cm.
1
of
temperature
2 l i t r e s o f w a t e r were t h e n added and
removed, t h e aqueous s u s p e n s i o n was
i d e n t i f i e d by i . r .
On c o m p l e t i o n
a l l o w e d t o warm up t o room
allowed to stand o v e r n i g h t .
Hg/140°C).
(lOOg,
l o w e r e d by means
o f an a c e t o n e / d r i c o l d b a t h and m a i n t a i n e d a t below -20°C.
the p'sriranganate a d d i t i o n , s o l u t i o n was
i.r.
was
).
max
S t a g e 4.
350g
140g
(1.79 m o l e s )
flask
(0.73 moles)
o f p e r f l u o r o g l u t a r i c a c i d were mixed w i t h
o f p r e v i o u s l y d i s t i l l e d b e n z o t r i c h l o r i d e i n a 1 1.
f i t t e d w i t h a water c o n d e n s e r / a c e t o n e - d r i c o l d c o l d f i n g e r
connected
H
to a 2
S 0
6 1
4 bubbl -
Temperature
was
system
r a i s e d up t o 212° u s i n g a
l i s s a p o l nx b a t h w h i l e s t i r r i n g was p r o v i d e d by means o f a m a g n e t i c
A f t e r about
5 h r s . of b o i l i n g ,
distillation
78° - 160°
g.l.c.
was
f r a c t i o n was r e t a i n e d and
i d e n t i f i e d by i . r .
S t a g e 5.
(3 f o o t c o l u m n / g l a s s h e l i c e s ) .
found
t o c o n t a i n m a i n l y one
P e r f l u o r o g l u t a r y l c h l o r i d e thus obtained
spectroscopy ( u
m a x
Perfluoroglutarylchloride
1810,
1200,
(258g, 1.14
lllO,
moles)
to a s o l u t i o n o f 1 Kg. o f d r y p o t a s s i u m f l u o r i d e i n 2.5
nitrile
stirrer.
( f r a c t i o n a t e d from P ° 5 ^ i n a 5 1. R.B.
2
On
stirrer.
t h e a p p a r a t u s was m o d i f i e d f o r f r a c t i o n a l
and m i x t u r e was d i s t i l l e d
( C o l . A/100°C).
R.B.
990,
was
The
component by
(144g,
890,
90%)
805
cm."
s l o w l y added
l i t r e s of dry aceto-
f l a s k using a mechanical
a d d i t i o n of the a c i d c h l o r i d e , the pot temperature r o s e ;
the
- 190 -
r e a c t i o n was assumed t o have f i n i s h e d when, a f t e r a d d i n g
c h l o r i d e t h e p o t temperature
a l l the acid
went down t o room t e m p e r a t u r e .
then m o d i f i e d f o r f r a c t i o n a t i o n
(3 f o o t c o l u m n / g l a s s
T h e a p p a r a t u s was
helices);
t h e 45° - 48°
f r a c t i o n was found t o c o n t a i n m a i n l y a c i d f l u o r i d e and some a c e t o n i t r i l e by
g.l.c.
( C o l . A/room t e m p e r a t u r e ) .
I n f r a r e d a n a l y s i s of t h e product
obtained
(156g, 6 9 % ) r e v e a l e d t h e p r e s e n c e o f some a c i d c h l o r i d e - peak a t 1810 cm.
(u
max
:
1
1
11B0, 1200, 1135, 3.010, 900 c m . " ) ,
P e r f l u o r o h e p t - l - e n e was s y n t h e s i z e d by p y r o l y s i n g t h e c o r r e s p o n d i n g
244
perfluorocarboxylic acid
salt:
CF., ( C F J , C 0 0 H
3
2 6
N
S
- °
H
» CF„ ( C F j COONa
3
2 6
CF (CF ) CF=CF
3
Perfluoro-octanoic acid
o f NaOH i n 100 m i s o f w a t e r .
8 hrs.
Product obtained
about 1 h r .
4
2
(lOOg, 0.24 m o l e s ) was n e u t r a l i s e d u s i n g 9.66g
S a l t was d r i e d b y pumping under vacuum f o r
(103g, 9 9 % ) was p y r o l y s e d (40O°C/760 mm Hg)
R e s u l t i n g c o l o u r l e s s l i q u i d was washed w i t h a q . l^CO^,
P
and vacuum t r a n s f e r r e d from 2 ° 5 '
t h e p r o d u c t t o be p u r e .
i.r.
2
spectroscopy
(u
c
9-1- -
a
t
room t e m p e r a t u r e
for
degassed
( C o l . A) showed
T e r m i n a l o l e f i n t h u s o b t a i n e d was i d e n t i f i e d b y
:
1
1780, 1370, 1320, 1200, 1070, 940 c m . " ) .
Yield
nicix
after purification:
71g ( 8 6 % ) .
P e r f l u o r o c y c l o h e x e n e was p r o v i d e d .
f l u o r i n a t i o n of undecafluorocyclohexane.
( C o l . A/70°C) and c h a r a c t e r i z e d b y i . r .
I t was o b t a i n e d from t h e d e h y d r o I t was found t o be p u r e b y g . l . c .
spectroscopy
(u
:
1740, 1370,
nicix
1300,
1260, 1190, 1150, 1110, 1010,
4.6.b.
1
980 c m . " ) .
Irradiations
General
Procedure
S t a r t i n g m a t e r i a l s were a c c u r a t e l y weighed s o a s t o g i v e a 2:1 o l e f i n /
P
a c i d f l u o r i d e m o l a r r a t i o and were i n t r o d u c e d i n t o a f l a s k c o n t a i n i n g 2 ° 5 "
- 191
They were d e g a s s e d
-
by means o f 4 - 5 f r e e z e - pump - thaw c y c l e s on
c o n v e n t i o n a l vacuum l i n e and t h e n vacuum t r a n s f e r r e d
a
into c y l i n d r i c a l
v e s s e l s and s e a l e d under r e d u c e d p r e s s u r e (10 ^ t o r r ) .
quartz
After irradiations,
t u b e s were f r o z e n i n l i q u i d a i r , h o t s p o t t e d , opened and c o n n e c t e d
through
t r a p s t o a c o n v e n t i o n a l vacuum l i n e .
to the
vessel in series,
b a t h ) and
4.7.
two
t r a p s were c o n n e c t e d
t h e one n e a r e s t t o i t b e i n g a t -78°C
t h e o t h e r one a e i n g a t -178°C
s e p a r a t e d by
4.6.c.
The
two
(acetone/dricold
(liquid a i r ) .
P r o d u c t s were t h u s
volatility.
R e s u l t s (see Table
4.3)
Discussion
The
r e s u l t s o b t a i n e d i n d i c a t e t h a t d e s p i t e l i t e r a t u r e r e p o r t s on
4= i
*i
, *i
*
4-v.
219,233,234,235,236,240
s u c c e s s f u l p e r f l u o r o and p o l y f l u o r o o x e t a n e s y n t h e s e s
o f t e n i n h i g h y i e l d s , none o f t h e r e a c t i o n s a t t e m p t e d
amount o f o x e t a n e .
v e r y low y i e l d ,
h e r e gave a d e t e c t a b l e
I n most c a s e s telomeirs o f a c i d f l u o r i d e were o b t a i n e d i n
i n a d d i t i o n t o low v o l a t i l i t y
products.
I r r a d i a t i o n o f p e r f l u o r o h e p t - l - e n e by i t s e l f u s i n g t h e 5-w
Hanovia
low p r e s s u r e lamp which d e f i n i t e l y h a s an o u t p u t a t 185nm where t h e
m i g h t be e x p e c t e d
to absorb
to a product which,
seemed l i k e l y
( E x p t . 9, T a b l e 4.3)
r e s u l t e d i n a 26%
on t h e b a s i s o f g . l . c . a n a l y s i s and
t o be a m i x t u r e o f i s o m e r s and
infrared
olefin
conversion
spectroscopy
telomers of the s t a r t i n g
olefin.
I s o m e r i z a t i o n o f f l u o r o o l e f i n s v i a f l u o r i n e atom s h i f t s h a s b e e n r e p o r t e d
r e c e n t l y by H a s z e l d i n e f o r t h e i r r a d i a t i o n o f
perfluoro-2,3-dimethylbut-
245
2-ene.
The
low t e m p e r a t u r e
some e a r l i e r a t t e m p t s had
reaction
( E x p e r i m e n t 5) was
that
almost a l l examples r e p o r t e d i n the l i t e r a t u r e o c c u r r e d a t t e m p e r a t u r e s
well
route to oxetane
o x e t a n e was
I t seemed p o s s i b l e t h a t i n o u r e x p e r i m e n t s
f o r m a t i o n may
formed i t may
i t was
(after
noted
below a m b i e n t .
f a i l e d to g i v e oxetanes) because
c a r r i e d out
t h e d i r a d i c a l on
have e i t h e r r e v e r t e d t o monomers o r i f t h e
have been i n a h i g h v i b r a t i o n a l e n e r g y
state
and
th
- 192 -
II
Dl
II
u
*>
1)
o
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o
• I
in
t;
-i
•
o
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-rl .11
>
in
rH
HI
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•ft
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•u
o
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<d
3
c
C-i fl
.c:
w -I
•rl
x;
c
S
•H
in
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o o
•iH
in
n»
o
nl
!H
(V
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r-l
•
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El
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ID D<
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id
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4J
in at K
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or -
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IF
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fu
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fc.
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- 193 -
Table 4.3 ( c o n t . )
Footnotes:
a.
Olefin/acid fluoride r a t i o :
b.
Lamp
Lamp
Lamp
Lamp
c.
Using r e f r i g e r a t e d methanol b a t h .
d.
As % o f t o t a l w e i g h t o f s t a r t i n g m a t e r i a l s
e.
Plus isomers by i . r . evidence (peak a t 1720 cm. ^
A
B
C
D
F
HANOVIA
RAYONET
HANOVIA
HANOVIA
450-W Hg Lamp
RPR-2O0 253.7nm
PCR 1L/5W Low P Hg Lamp
125W medium P Hg Lamp
F
\
/
C=C
/
R
f.
2:1.
f
) .
\
R
f
Gc/MS examination o f t h e 8 component m i x t u r e r e v e a l e d t h e
presence o f a substance (m/e = 469) which c o u l d be e i t h e r
OFC(CF-) CFO o r t h e 1:1 adduct. I . r . evidence ( s t r o n g - COF
-1
a b s o r p t i o n 1880 cm. ) seems t o f a v o u r OFC(CF_)-CFO.
6
g.
I . r . spectrum o f o i l showed s t r o n g -COF a b s o r p t i o n
s t r o n g R--C00H a b s o r p t i o n
Hi
lOOO cm.
h.
(1880 cm. ^)
(1780 cm. ^) and s t r o n g bands around
, c h a r a c t e r i s t i c o f oxetanes.
Waxy s o l i d o b t a i n e d by t r e a t i n g i n v o l a t i l e m a t e r i a l s w i t h
CCl^. I . r . spectrum f a i l e d t o r e v e a l s t r o n g -COF band.
M a t e r i a l s l i g h t l y s o l u b l e i n H-0 g i v i n g s t r o n g l y a c i d s o l u t i o n
(pH = 1 -»• 2) .
k.
Gc t r a c e ( C o l . A/30°).
starting materials.
I . r . spectrum s i m i l a r t o t h a t o f
1.
Orange wax s o l u b l e i n h o t H^O ( s t r o n g l y a c i d i c s o l u t i o n ) , i n
acetone, i n s o l u b l e i n Et^O, CCl^.
I . r . spectrum shows t h e
presence o f s t r o n g -COF a b s o r p t i o n
(1880 cm.
.
m. Low v o l a t i l i t y m a t e r i a l s heated a t 200°/0.01 mm Hg t o y i e l d a
y e l l o w o i l and a r e m a i n i n g r e d brown v i s c o u s l i q u i d . I . r .
s p e c t r a o f b o t h m a t e r i a l s appeared v e r y s i m i l a r . No -COF
a b s o r p t i o n around 1880 cm. ^, s t r o n g band a t 1720 cm. ^.
Probably t e l o m e r and/or isomers o f p e r f l u o r o o l e f i n .
n.
I . r . e x a m i n a t i o n o f low v o l a t i l i t y f r a c t i o n showed a much s t r o n g e r
peak a t 1720 cm. * and a s m a l l e r peak a t 1880"* ( t e r m i n a l
perfluoroolefin).
F r a c t i o n heated a t 280°/0.01 mm Hg f o r 2 h r s . t o y i e l d a
c o l o u r l e s s f a i r l y m o b i l e l i q u i d and a y e l l o w i s h o i l d i s p l a y i n g
s i m i l a r i . r . and n.m.r. s p e c t r a . Gc t r a c e s ( C o l . 0^ a t
-
165°) show 4 and 7 components r e s p e c t i v e l y - p r o b a b l y
telomers o f t h e p e r f l u o r o o l e f i n .
different
- 194 -
o
i t s e l f have c l e a v e d .
was formed.
However, even a t -20
no d e t e c t a b l e amount o f oxetane
The I n t e r e s t i n g f i n d i n g was t h a t a t low t e m p e r a t u r e s no o l e f i n
i s o m e r i z a t i o n was observed e i t h e r
(Experiment 10, Table 4 . 3 ) .
Since l i t e r a t u r e r e p o r t s o r i g i n a t e f r o m r e p u t a b l e e s t a b l i s h m e n t s , a r e
w e l l documented and have been r e p e a t e d and extended by s e v e r a l o t h e r w o r k e r s ,
the
p o s s i b i l i t y o f u n r e l i a b l e r e p o r t s can be d i s m i s s e d , and t h e reasons f o r
our f a i l u r e r e q u i r e c a r e f v l a n a l y s i s .
An o b v i o u s q u e s t i o n i s whether lamps
used had s u f f i c i e n t o u t p u t a t t h e r e q u i r e d wavelengths and t h i s i s n o t easy t o
deal w i t h .
The f a c t t h a t t e l o m e r i z a t i o n r e a c t i o n s o f b o t h a c i d f l u o r i d e and
o l e f i n components have been observed can be t a k e n as good evidence t h a t
was absorbed by monomers t o some e x t e n t .
light
N e v e r t h e l e s s , i t would be more
s a t i s f a c t o r y i f a h i g h i n t e n s i t y l i g h t source i n c o r p o r a t i n g a broad band
monochromator were a v a i l a b l e f o r p r e p a r a t i v e work which r e q u i r e s wavelengths
s h o r t e r t h a n t h e 254nm band o f t h e mercury lamp;
equipment.
we were unable t o o b t a i n such
The a b s o r p t i o n o f p e r f l u o r o a c y l f l u o r i d e s i s r e p o r t e d as X
215nm
219
(e - 6 6 ) ,
whereas t h e s h o r t w a v e l e n g t h end o f t h e spectrum o f a mercury
lamp c o n s i s t s p r e d o m i n a n t l y o f l i n e s a t 185, 238, 248 and 254nm.
between t h e e m i s s i o n o f t h e lamp and t h e COF
Overlap
a b s o r p t i o n w i l l t h e r e f o r e be poor,
which p o s s i b l y accounts f o r t h e l o n g ( s e v e r a l days) i r r a d i a t i o n p e r i o d s r e p o r t e d
for
s u c c e s s f u l p e r f l u o r o - o x e t a n e syntheses d e s p i t e t h e use o f h i g h powered
219,233,234,235,240 „ . '
_
_
.
lamps.
On b a l a n c e , i t seems t h a t s i n c e o t h e r s have
J4
t
s u c c e s s f u l l y used mercury lamps, o v e r l a p between lamp e m i s s i o n and
COF
a b s o r p t i o n was n o t t h e main cause o f t h e f a i l u r e t o s y n t h e s i z e o x e t a n e s , however
a more r e a d i l y r e g u l a t e d system would o f f e r advantages t o any f u t u r e worker i n
this
field.
Having c o n s i d e r e d q u e s t i o n s r e l a t e d t o t h e ' F i r s t Law o f P h o t o c h e m i s t r y ' ,
doubts about t h e p u r i t y o f r e a c t a n t s need a t t e n t i o n .
was i d e n t i f i e d by i . r . , m.s.,
r e l i a b l y pure.
and n.m.r. s p e c t r o s c o p y .
Perfluorohept-l-ene
G.l.c. showed i t t o be
P e r f l u o r o c y c l o h e x e n e was a l s o found t o be p u r e by g . l . c .
- 195 -
As f a r as t h e p u r i t y o f a c i d f l u o r i d e i s concerned, i t was known from t h e
beginning t o contain traces o f a c e t o n i t r i l e
( g . l . c . e v i d e n c e ) , which appears
29
n o t t o quench t h e c a r b o n y l t r i p l e t .
Careful fractionation
under U
(using
a 3 f o o t column packed w i t h 'Dixon gauzes') b e f o r e use, a f f o r d e d m a t e r i a l , which,
on g . l . c . e x a m i n a t i o n , appeared t o be f r e e from a c i d c h l o r i d e c o n t a m i n a t i o n .
However, s i n c e p u r i f i c a t i o n o f a c i d f l u o r i d e prepared by exchange f l u o r i n a t i o n
i s a ver> i i f t i c u l t t a s k :.i.i£inly flue t o t h e f o r m a t i o n o f a c i d h a l i d e azeotropes
t h e p o s s i b i l i t y o f a c i d c h l o r i d e t r a c e s b e i n g p r e s e n t can n o t be e x c l u d e d .
I f t h i s were t h e case, i t would be expected
t h a t R.C0C1 (A
258nm, e ^
r
max
219
40)
would o v e r l a p s t r o n g l y w i t h t h e i n t e n s e 254nm band o f t h e mercury lamp;
consequently
a c y l c h l o r i d e s o r t h e i r p h o t o l y s i s p r o d u c t s c o u l d be a c t i n g as
quenchers f o r t h e e x c i t e d s t a t e r e q u i r e d f o r oxetane f o r m a t i o n , o r i n t e r f e r i n g
w i t h oxetane f o r m a t i o n a t some o t h e r
stage.
I n most cases, a c i d f l u o r i d e s used f o r s u c c e s s f u l oxetane syntheses were
219
prepared e i t h e r from a c i d s u s i n g SF^ o r by e l e c t r o c h e m i c a l f l u o r i n a t i o n .
One case o f a s u c c e s s f u l use o f an a c i d f l u o r i d e o r i g i n a t i n g from an a c i d
219
c h l o r i d e has been r e p o r t e d .
However m a t e r i a l was subsequently
d i s t i l l a t i o n t h r o u g h a spinning-band
still,
p u r i f i e d by
as opposed t o t h e f r a c t i o n a l
d i s t i l l a t i o n procedure used by u s .
Quartz g l a s s used f o r t h e p r e p a r a t i o n o f t h e i r r a d i a t i o n tubes was examined
by u l t r a v i o l e t spectroscopy.
I t was found t o be t r a n s p a r e n t i n t h e r e g i o n
220 - 300nm and v i r t u a l l y t r a n s p a r e n t i n t h e r e g i o n below 220nm;
some s l i g h t
a b s o r p t i o n was observed a t 215nm (A = 0.13) where t h e COF group i s r e p o r t e d t o
219
absorb.
T h i s however should n o t be s i g n i f i c a n t f o r t h e r a t i o n a l i z a t i o n o f
the f a i l u r e t o o b t a i n t h e d e s i r e d
adducts.
F i n a l l y , a sample o f p e r f l u o r o g l u t a r y l f l u o r i d e used f o r i r r a d i a t i o n s was
examined f o r C I c o n t e n t by shaking i t i n a sealed tube w i t h aqueous s i l v e r
nitrate.
them.
S i l v e r s a l t s o b t a i n e d a f t e r t r e a t m e n t d i d n o t c o n t a i n AgCl amongst
I t should be k e p t i n mind however t h a t an e f f i c i e n t quencher can t o t a l l y
24
i n h i b i t r e a c t i o n a t e x t r e m e l y low c o n c e n t r a t i o n s indeed,
as t h e bismaleiraide
,
- 196 -
p h o t o p o l y m e r i z a t i o n experiments by De S c h r y v e r , Feast and Smets have shown
(Section 1.3).
4.8.
Conclusions
The p r e l i m i n a r y i n v e s t i g a t i o n s c a r r i e d o u t on t h e c y c l o a d d i t i o n o f
p e r f l u o r o g l u t a r y l f l u o r i d e t o t h e two p e r f l u o r o o l e f i n s under a v a r i e t y o f
e x p e r i m e n t a l c o n d i t i o n s have served t o i l l u s t r a t e
s y n t h e t i c o r g a n i c c h e m i s t r y can be.
how d i f f i c u l t t h i s area o f
The i s o l a t i o n o f h i g h p u r i t y FOC (CF2) . j
C
O
F
f o l l o w i n g i t s p r e p a r a t i o n from t h e c o r r e s p o n d i n g a c i d c h l o r i d e i n CH^CN s o l v e n t
appears t o be a s e r i o u s problem n o t easy t o d e a l w i t h by u s i n g s t r a i g h t f o r w a r d
fractional distillation
techniques.
High temperature i r r a d i a t i o n s seem t o
promote o l e f i n t e l o m e r i z a t i o n , whereas low temperature i r r a d i a t i o n s seem t o
l e a v e t h e o l e f i n unchanged.
of
I t i s d i f f i c u l t t o be d e f i n i t e about t h e causes
f a i l u r e t o o b t a i n t h e oxetanes.
High p u r i t y s t a r t i n g m a t e r i a l s a r e
r e q u i r e d f o r t h e s e r i o u s i n v e s t i g a t i o n o f any chemical r e a c t i o n .
This
c o n d i t i o n i s i m p e r a t i v e i n t h e case o f photochemical i n v e s t i g a t i o n s .
Bearing
t h i s i n mind, and g i v e n t h e suspect p u r i t y o f p e r f l u o r o g l u t a r y l f l u o r i d e any
f u t u r e examiner o f t h e proposed syntheses r e p o r t e d i n t h i s c h a p t e r m i g h t do
w e l l t o s y n t h e s i z e p e r f l u o r o g l u t a r y l f l u o r i d e by an a l t e r n a t i v e r o u t e so as t o
exclude t h e p o s s i b i l i t y o f c h l o r i d e contamination.
APPENDICES
AND REFERENCES
APPENDIX
A
APPARATUS, INSTRUMENTS AND GENERAL TECHNIQUES
Vacuum system
Freeze d r y i n g , p y r o l y s e s , freeze-pump-thaw c y c l e s , s u b l i m a t i o n s and
v a c u u m d i s t i l l a t i o n s r e q u i r i n g p r e s s u r e s o f t h e o r d e r o f 10
mm Hg were
undertaken w i t h a c o n v e n t i o n a l vacuum system i n c o r p o r a t i n g a r o t a r y o i l pump
and a mercury d i f f u s i o n pump.
Pressures as low as 10 ^ mm Hg were a c h i e v e d
(where r e q u i r e d ) by means o f a grease f r e e , m e r c u r y - f r e e vacuum l i n e
i n c o r p o r a t i n g a r o t a r y o i l pump, an Edwards vapour pump, e l e c t r o n i c p r e s s u r e
measuring d e v i c e s and ' t e f l o n ' t a p s .
I n f r a r e d s p e c t r a - see Appendix B.
Mass s p e c t r a were measured w i t h an A.E.I. MS9 s p e c t r o m e t e r .
U l t r a v i o l e t s p e c t r a were r e c o r d e d on a Unicam SP800 s p e c t r o p h o t o m e t e r .
N.m.r. s p e c t r a were recorded on a Bruker S p e c t r o s p i n HX 90E High R e s o l u t i o n
NMR s p e c t r o m e t e r o p e r a t i n g a t 90MHz f o r *H and 22.635MHz f o r ^ C
(ambient
temperature).
M o l e c u l a r w e i g h t s were r e c o r d e d on a Perkin-Elmer 115 M o l e c u l a r Weight Apparatus
u t i l i z i n g t h e vapour p r e s s u r e ( i s o p i e s t i c ) method o f d e t e r m i n i n g t h e number
average m o l e c u l a r w e i g h t o f a s o l u t e i n s o l u t i o n .
i n chloroform solution;
A l l measurements were made
b e n z i l was used as s t a n d a r d f o r t h e d e t e r m i n a t i o n
of the instrument constant.
An o p e r a t i n g temperature o f 37° was employed.
M o l e c u l a r w e i g h t s c o u l d be measured w i t h + 2% s t a n d a r d d e v i a t i o n .
A n a l y t i c a l vapour phase chromatography
A Perkin-Elmer 452 Gas Chromatograph was used w i t h a column o f d i - n d e c y l p h t h a l a t e / C e l i t e (2.2m x 7mm d i a . ) , hydrogen as c a r r i e r gas and a h o t
wire detector.
Carbon and hydrogen a n a l y s e s were c a r r i e d o u t w i t h a Perkin-Elmer 240 E l e m e n t a l
Analyser.
Chromium a n a l y s i s was c a r r i e d o u t on a Perkin-Elmer 403 Atomic
Absorption
Spectrophotometer.
T h i n l a y e r chromatography was c a r r i e d o u t u s i n g Merck 60F-254 s i l i c a g e l p l a t e s
and c a r e f u l l y p u r i f i e d s o l v e n t s a t room t e m p e r a t u r e .
M e l t i n g p o i n t s were r e c o r d e d u s i n g a R e i c h e r t m e l t i n g p o i n t microscope and a r e
uncorrected.
Irradiations.
Unless o t h e r w i s e
i n d i c a t e d , i r r a d i a t i o n s were c a r r i e d o u t w i t h Rayonet
Type RS P r e p a r a t i v e Photochemical Reactors (Models RPR-204 o r RPR-208).
sources were e i t h e r RUL-3500& lamps o r RUL-3000A*.
Temperatures were ca. 30°.
R e a c t i o n v e s s e l s were g e n e r a l l y c y l i n d r i c a l i n shape and
7 diameters long.
Light
approximately
APPENDIX B
INFRARED SPECTRA
I n f r a r e d s p e c t r a were r e c o r d e d on a P e r k i n - E l m e r 457
I n f r a r e d Spectrophotometer (PE457) o r a P e r k i n - E l m e r
Spectrophotometer
(PE577).
conditions designated
Spectrum
No.
S p e c t r a were r u n u s i n g KBr
Grating
Infrared
c e l l s under t h e
by:
(A)
KBr
(B)
Nujol
(C)
Thin contact f i l m
disc
mull
Instrument
PE457
577
Grating
Discussed
on page;
66
Material
Conditions
triphenylglycol
isolated
from i r r a d i a t i o n o f
Ph CO + PhgCHOH
2
PE457
84
triphenylglycol
obtained
v i a ground s t a t e
syntheses
(recrystallized)
PE577
85
triphenylglycol
obtained
v i a ground s t a t e
syntheses
(sublimed)
PE577
74
crude product
from
n
±zr
of m-dibenzoylbenzene +
hydrobenzoin
5.
PE577
76
product
i n CU^Cl^
from d i e t h y l -
mesoxalate + PhLi
PE457
84
a-phenylbenzoin
7.
PE457
69
p r o d u c t from i r rn o f a-phenylb e n z o i n i n benzene s o l u t i o n
8.
PE457
69
p r o d u c t f r o m i r rn o f a-phenylb e n z o i n + b e n z h y d r o l i n benzene
PE457
82
1,2,2,2-tetraphenylethanol
B
vi-ecrystallized)
10.
PE457
83
1,2,2,2-tetraphenylethanol
(sublimed)
11.
PE457
82
12.
PE577
113
m-bisbenzhydrylbenzene
13.
PE457
109
p-bisbenzhydrylbenzene
14
PE457
112
m-dibenzoylbenzene
o i l d i s t i l l e d from products
o f p-bisbenzhydrylbenzene + HCOOH
15
PE457
111
(PhCBrH)„C-H. p a r a isomer
2 6 4
B
16.
PE457
112
p o l y m e r i c m a t e r i a l formed on
B
C
H
t r e a t m e n t o f (PhCBrH) 6 4» P
a r a
2
isomer, w i t h V i t r i d e i n benzene
17.
PE577
110
(PhCClH) „C,.H . p a r a isomer
Z b H
18.
PE457
113
(PhCClH)„C.H. meta isomer
19.
PE457
116
1,4-dibenzylbenzene
20.
PE457
116
1,3-dibenzylbenzene
21.
PE577
95
^ 6 4
1,1,2,2-tetraphenylethanol
I r r a d i a t i o n s o f equlmolar amounts o f m-dlbenzoylbenzene (DBB) and
e i t h e r p-dibenzylbenzene (p-dbb) o r m-dibenzylbenzene (m-dbb).
22.
PE457
117
DBB/p-dbb:
yellow product
from
preliminary investigation
(24 h r s . i r r a d i a t i o n )
23.
PE457
119
DBB/p-dbb:
t y p i c a l spectrum o f
white p r e c i p i t a t e
24.
PE457
119
DBB/m-dbb:
t y p i c a l spectrum o f
white p r e c i p i t a t e
25.
PE457
121
DBB/p-dbb:
t y p i c a l spectrum o f
yellow polymeric m a t e r i a l
(578 h r s . i r r a d i a t i o n )
26.
PE457
122
DBB/m-dbb:
t y p i c a l spectrum o f
yellow polymeric m a t e r i a l
(578 h r s . i r r a d i a t i o n )
27
PE457
128
b l a c k t a r o b t a i n e d from p y r o l y s i s
of yellow polymeric m a t e r i a l
from DBB/p-dbb (sample 0)
28.
PE457
131
p r o d u c t from t r e a t m e n t o f sample
(0) w i t h a c e t i c a c i d / i o d i n e i n
benzene
B
Photoreduction o f dlaldehydes
29.
PE457
155
p r o d u c t from i r r
1 1
o f tere-
phthalaldehyde i n isopropanol/
benzene
30.
PE457
155
product from i r r
1 1
of iso-
phthalaldehyde i n isopropanol/
benzene
The benzaldehyde p h o t o p r o d u c t
31.
PE457
160
T y p i c a l spectrum o f t h e
benzaldehyde p h o t o p r o d u c t (BPP)
NaBH,
32.
PE457
163
p r o d u c t from BPP
dioxane
33.
PE457
163
^ ^
„„„
p r o d u c t f r o m BPP
34.
PE457
162
p r o d u c t f r o m BPP
ffif^v-j—*
chloride
35.
PE577
163
j
A. B
„„„
p r o d u c t f r o m BPP
dichromate
• • •>
H
c
Vitride _
>
Benzene
v
(no Cr found)
36.
PE457
164
p r o d u c t f r o m BPP
d
l
c
h
r
°
H
m
a
t
e
l
c
h
r
°
H
m
a
t
e
^
(Cr c o n t e n t 6.27%)
37.
PE457
164
p r o d u c t from BPP
d
)
B
(Cr c o n t e n t 1.28%)
6N H SO.
-—2-»
38.
PE457
163
p r o d u c t f r o m BPP
39.
PE457
160
BPP i n CC1. s o l u t i o n
4
Pure CCl.
4
75% Pure CCl /25% s a t u r a t e d s o l n . o f BPP i n C C l
4
4
50% Pure CCl^/50% s a t u r a t e d s o l n . o f BPP i n CCl^
s a t u r a t e d s o l u t i o n o f BPP i n CC1.
I
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a DO
2yo
2000
an
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am
mn
m
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nm
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ion
am I' 600
am
too 250
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25)0
20X)
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1210
KB
803
600
q p 250
r
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25P
nVM:...JMI
ayo
tfa
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UP
an
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600
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r*T T T
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APPENDIX C
The Board o f Studies i n Chemistry r e q u i r e s t h a t each postgraduate r e s e a r c h
t h e s i s contain an appendix
(a)
listing
a l l research c o l l o q u i a , research seminars and l e c t u r e s (by e x t e r n a l
speakers) arranged by the Department o f Chemistry s i n c e 1 October 1976;
and
(b)
a l l research conferences attended by the w r i t e r of the t h e s i s ,
during the p e r i o d when the research f o r the t h e s i s was c a r r i e d out.
1.
Research C o l l o q u i a , Seminars and L e c t u r e s
1.1.
1976-77
a)
U n i v e r s i t y o f Durham Chemistry C o l l o q u i a
Wednesday, 20th October
P r o f e s s o r J.B. Hyne ( U n i v e r s i t y o f C a l g a r y ) , "New Research on an
Old Element - Sulphur".
Wednesday, 10th November
Dr. J.S. Ogden (Southampton U n i v e r s i t y ) , "The C h a r a c t e r i z a t i o n o f
High Temperature
Species by Matrix I s o l a t i o n " .
Wednesday, 17th November
Dr. B.E.F. Fender
( U n i v e r s i t y o f Oxford), " F a m i l i a r but Remarkable
Inorganic S o l i d s " .
Wednesday, 24th November
Dr. M.I. Page (Huddersfield P o l y t e c h n i c ) , "Large and Small Rate
Enhancements o f I n t r a m o l e c u l a r C a t a l y s e d R e a c t i o n s " .
Wednesday, 8th December
P r o f e s s o r A.J. Leadbetter ( U n i v e r s i t y o f E x e t e r ) , " L i q u i d
Crystals".
Wednesday, 26th January
Dr. A. Davis (ERDR), "The Weathering o f Polymeric M a t e r i a l s " .
Wednesday/ 2nd February
Dr. M. F a l k , (NRC Canada), " S t r u c t u r a l Deductions from the
V i b r a t i o n a l Spectrum o f Water i n Condensed Phases".
Wednesday, 9th February
P r o f e s s o r R.O.C. Norman ( U n i v e r s i t y o f Y o r k ) , " R a d i c a l C a t i o n s ;
Intermediates i n Organic R e a c t i o n s " .
Wednesday, 23rd February
Dr. G. H a r r i s ( U n i v e r s i t y o f S t . Andrews), "Halogen Adducts o f
Phosphines and A r s i n e s " .
F r i d a y , 25th February
P r o f e s s o r H.T. Dieck (Frankfurt U n i v e r s i t y ) , "Diazadienes - New
Powerful Low-Valent Metal Liganda".
Wednesday, 2nd March
Dr. F. Hibbert (Birkbeck College, London), " F a s t Reaction S t u d i e s
of Slow Proton T r a n s f e r s I n v o l v i n g Nitrogen and Oxygen A c i d s " .
F r i d a y , 4 t h March
Dr. G. B r i n k (Rhodes U n i v e r s i t y , R.S.A.), " D i e l e c t r i c S t u d i e s
of Hydrogen Bonding i n A l c o h o l s " .
Wednesday, 9 t h March
Dr. 1.0. Sutherland ( S h e f f i e l d U n i v e r s i t y ) , "The Stevans*
Rearrangement O r b i t a l Symmetry and R a d i c a l P a i r s " .
F r i d a y , 18th March
P r o f e s s o r Hans Bock (Frankfurt U n i v e r s i t y ) , "Photoelectron S p e c t r a
and Molecular P r o p e r t i e s :
A Vademecum f o r the Chemist".
Wednesday, 30th March
Dr. J.R. MacCallum ( U n i v e r s i t y o f S t . Andrews),
of Polymers".
"Photooxidation
Wednesday, 20th A p r i l
Dr. D.M.J. L i l l e y
(G.D. S e a r l e , Research D i v . ) , " T a i l s o f
Chromatin S t r u c t u r e - Progress towards a Working Model".
Wednesday, 27th A p r i l
Dr. M.P. Stevens ( U n i v e r s i t y o f H a r t f o r d ) , "Photocycloaddition
Polymerisation".
Wednesday, 4th May
Dr. G.C. T a b i s z ( U n i v e r s i t y o f Manitoba), " C o l l i s i o n Induced
L i g h t S c a t t e r i n g by Compressed Molecular Gases".
Wednesday, 11th May
Dr. R.E. Banks (UMIST), "The Reaction o f Hexafluoropropene
with
H e t e r o c y c l i c N-Oxides".
Wednesday, 18th May
Dr. J . Atwood ( U n i v e r s i t y o f Alabama),
"Novel S o l u t i o n Behaviour
o f Anionic Organoaluminium Compounds:
the Formation o f L i q u i d
Clathrates".
Wednesday, 25th May
P r o f e s s o r M.M.
Kreevoy ( U n i v e r s i t y o f Minnesota), "The Dynamics
of Proton T r a n s f e r i n S o l u t i o n " .
Wednesday, 1 s t June
Dr. J . McCleverty
( U n i v e r s i t y o f S h e f f i e l d ) , "Consequences of
Deprivation and Overcrowding
and
on the Chemistry o f Molybdenum
Tungsten".
Wednesday, 6th J u l y
P r o f e s s o r J . Passmore ( U n i v e r s i t y o f Brunswick), "Adducts Between
+
Group V Pentahalides and a P o s t s c r i p t on S _ I " .
b)
Durham U n i v e r s i t y Chemical S o c i e t y
Tuesday, 19th October
Dr. J.A. Salthouse ( U n i v e r s i t y o f Manchester), "Chemistry and
Energy".
Tuesday, 26th October
Dr. R.E. Richards ( U n i v e r s i t y o f Oxford), "NMR
Measurements on
Intact Biological Tissue".
Tuesday, 2nd November
Dr. B. S u t c l i f f e ( U n i v e r s i t y of Y o r k ) , "The Chemical Bond as a
Figment of the Imagination".
Tuesday, 16th November
Mr. R. F i c k e n (Rohm & Haas), "The Graduate i n I n d u s t r y " .
Tuesday, 30th November
Dr. R.J. Donovan ( U n i v e r s i t y of Edinburgh), "The Chemistry of
the
Atmosphere".
Tuesday, 18th January
Professor I . F e l l s
( U n i v e r s i t y of Newcastle), "Energy Storage:
the Chemists' Contribution to the Problem".
Tuesday, 8th February
Dr. M.J. C l e a r e (Johnson Matthey Research C e n t r e ) , "Platinum
Group Metal Compounds as Anti-Cancer Agents".
Tuesday, 1 s t March
Professor J.A.S. Smith (Q.E. C o l l e g e , London), "Double Resonance".
Tuesday, 8th March
P r o f e s s o r C. Eabom ( U n i v e r s i t y of S u s s e x ) , " S t r u c t u r e and
Reactivity".
1.2.
1977-78
a)
U n i v e r s i t y of Durham Chemistry C o l l o q u i a
Tuesday, 27th September
Dr. T . J . Broxton (La Trobe U n i v e r s i t y , A u s t r a l i a ) , " I n t e r a c t i o n
of Aryldiazonium S a l t s and A r y l a z o a l k y l E t h e r s i n B a s i c
Alcoholic
Solvents".
Wednesday, 19th October
Dr. B. Heyn ( U n i v e r s i t y o f Jena, D.D.R.), "o-Organo-Molybdenum
Complexes as Alkene Polymerisation C a t a l y s t s " .
Thursday, 27th October
Professor
R.A. F i l l e r
( I l l i n o i s I n s t , o f Technology, U.S.A.),
"Reactions o f Organic Compounds with Xenon F l u o r i d e s " .
Wednesday, 2nd November
Dr. N. Boden ( U n i v e r s i t y o f Leeds),
"NMR
Spin-Echo Experiments
f o r Studying S t r u c t u r e and Dynamical P r o p e r t i e s
of M a t e r i a l s
1
Containing I n t e r a c t i n g Spin- ! P a i r s " .
Wednesday, 9th November
Dr. A.R. B u t l e r
( U n i v e r s i t y of S t . Andrews), "Why I l o s t F a i t h
i n L i n e a r Free Energy
Relationships".
Wednesday, 7th December
Dr. P.A. Madden ( U n i v e r s i t y of Cambridge), "Raman Studies o f
Molecular Motions i n L i q u i d s " .
Wednesday, 14th December
Dr. R.O. Gould ( U n i v e r s i t y o f Edinburgh), "Crystallography t o the
Rescue i n Ruthenium Chemistry".
Wednesday, 25th January
Dr. G. Richards ( U n i v e r s i t y o f Oxford), "Quantum Pharmacology".
Wednesday, 1 s t February
Professor
K.J. I v i n
Metathesis Reaction:
of Cycloalkenes".
(Queen U n i v e r s i t y , B e l f a s t ) , "The O l e f i n
Mechanism o f Ring-Opening Polymerisation
F r i d a y , 3rd February
Dr. A. Hartog (Free U n i v e r s i t y , Amsterdam, Holland), " S u r p r i s i n g
Recent Studies i n Organo-Magnesium
Chemistry".
Wednesday, 22nd February
Professor J.D. B i r c h a l l (Mond D i v i s i o n , I . C . I . L t d . ) , " S i l i c o n
i n the Biosphere".
Wednesday, 1 s t March
Dr. A. Williams
( U n i v e r s i t y of K e n t ) , "Acyl Group T r a n s f e r
Reactions".
F r i d a y , 3rd March
Dr. G. van Koten ( U n i v e r s i t y o f Amsterdam, H o l l a n d ) , " S t r u c t u r e
and R e a c t i v i t y of Arylcopper C l u s t e r Compounds".
Wednesday, 22nd March
P r o f e s s o r H. Vahrenkamp ( U n i v e r s i t y of F r e i b u r g , Germany),
"Metal-Metal Bonds i n Organometallic Complexes".
Wednesday/ 19th A p r i l
Dr. M. Barber
(UMIST), "Secondary Ion Mass S p e c t r a of Surfaces
and Absorbed S p e c i e s " .
Tuesday, 16th May
Dr. P. Ferguson (C.N.R.S., Grenoble), "Surface Plasma Waves and
Absorbed Species on Metals".
Thursday, 18th May
P r o f e s s o r M. Gordon ( U n i v e r s i t y of E s s e x ) , "Three C r i t i c a l P o i n t s
i n Polymer S c i e n c e " .
Monday, 22nd May
P r o f e s s o r D. Tuck ( U n i v e r s i t y of Windsor, O n t a r i o ) , " E l e c t r o chemical S y n t h e s i s of I n o r g a n i c and Organometallic Compounds".
Wednesday - Thursday 24th, 25th May
P r o f e s s o r P. von R. S c h l e y e r ( U n i v e r s i t y of E r l a n g e n , Nllrnberg),
I.
"Planar Tetra-coordinate Methanes, P e r p e n d i c u l a r
E t h y l e n e s , and P l a n a r A l l e n e s " .
II.
Ill.
"Aromaticity i n Three Dimensions".
" N o n - c l a s s i c a l Carbocations".
Wednesday, 2 1 s t June
Dr. S.K. T y r l i k (Academy o f Science, Warsaw), "Dimethylglyoximec o b a l t Complexes - C a t a l y t i c Black Boxes".
F r i d a y , 23rd June
P r o f e s s o r W.B.
Pearson ( U n i v e r s i t y o f F l o r i d a ) , "Diode L a s e r
Spectroscopy a t 16 pm".
F r i d a y , 30th June
P r o f e s s o r G. Mateescu
(Case Western Reserve U n i v e r s i t y ) ,
"A Concerted Spectroscopy Approach t o the C h a r a c t e r i z a t i o n o f
Ions and Ion P a i r s :
b)
F a c t s , P l a n s , and Dreams".
Durham U n i v e r s i t y Chemical S o c i e t y
Thursday, 13th October
Dr. J.C. Young, Mr. A.J.S. Williams ( U n i v e r s i t y o f Aberystwyth) ,
"Experiments and Considerations Touching Colour".
Thursday, 20th October
Dr. R.L. Williams (Metropolitan P o l i c e F o r e n s i c Science Dept.),
"Science and Crime".
Thursday, 3rd November
Dr. G.W.
Gray ( U n i v e r s i t y o f H u l l ) , " L i q u i d C r y s t a l s - T h e i r
O r i g i n s and A p p l i c a t i o n s " .
Thursday, 24th November
Mr. G. R u s s e l l (Alcan), "Designing f o r S o c i a l A c c e p t a b i l i t y " .
Thursday, l e t December
Dr. B.F.G. Johnson
( U n i v e r s i t y of Cambridge), "Chemistry of
Binary Metal Carbonyls".
Thursday, 2nd February
P r o f e s s o r R.A. Raphael ( U n i v e r s i t y o f Cambridge), " B i z a r r e
Reactions of A c e t y l e n i c Compounds".
Thursday, 16th February
P r o f e s s o r G.W.A. Fowles ( U n i v e r s i t y of Reading), "Home Winemaking".
Thursday, 2nd March
P r o f e s s o r M.W.
Roberts ( U n i v e r s i t y of B r a d f o r d ) , "The Discovery
of Molecular Events a t S o l i d S u r f a c e s " .
Thursday, 9th March
P r o f e s s o r H. Suschitzky ( U n i v e r s i t y of S a l f o r d ) , " F r u i t f u l
F i s s i o n s o f Benzofuroxans".
Thursday, 4th May
P r o f e s s o r J . Chatt ( U n i v e r s i t y of S u s s e x ) , "Reactions of Coordinated
Dinitrogen".
Tuesday, 9th May
P r o f e s s o r G.A. Olah (Case Western Reserve U n i v e r s i t y , C l e v e l a n d ,
Ohio), " E l e c t r o p h i l i c Reactions o f Hydrocarbons".
2.
Conferences Attended
Photopolymerization and Polymer Photodegradation, Southampton, September 1976.
1 s t Polymer Surfaces Symposium, Durham, March 1977.
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