Studies in Organic Chemistry 42
SIMILARITY HÖDELS
IV O R G A N I C C H E M I S T R Y ,
R I O C H E M I S T R Y AND
RELATED FIELDS
Edited by
Romuald I . Zalewski
Institute of Commodity Science, Academy of Economics, Poznan, Poland
Tadeusz M . K r y g o w s k i
Department of Chemistry, University of Warsaw, Warsaw, Poland
and
John Shorter
School of Chemistry, University of Hull, Hull, England
ELSEVIER
Amsterdam — Oxford — New York — Tokyo
1991
XIII
CONTENTS
1.
S i m i l a r i t y models: s t a t i s t i c a l t o o l s and problems
in using t h e m
by Τ . M . Krygowski and K . Wozniak
2.
I
S u b s t i t u e n t e f f e c t p a r a m e t e r s and models applied in organic
chemistry
by 3 . Shorter
3.
77
The t r a n s m i s s i o n of s u b s t i t u e n t e f f e c t s in organic systems
by M . Godfrey
4.
149
P r o p e r t i e s of h y d r o g e n as a s u b s t i t u e n t in planar organic
pi-systems
by G . Hafelinger
5.
177
S i m i l a r i t y models in IR and UV spectroscopy
by C . L a u r e n c e
6.
231
D e s c r i p t i o n of p r o p e r t i e s of b i n a r y solvent m i x t u r e s
by H . Langhals
7.
283
A d d i t i v i t y rules and c o r r e l a t i o n methods in gas c h r o m a t o g r a p h y
by 3. O s z c z a p o w i c z
8.
343
S i m i l a r i t y models in organic e l e c t r o c h e m i s t r y
by 3. S. 3aworski and Μ. K . Kalinowski
9.
387
P r i n c i p a l c o m p o n e n t analysis as a t o o l in organic c h e m i s t r y
and food c h e m i s t r y
by R . I . Z a l e w s k i
10.
455
Q u a n t i t a t i v e s t r u c t u r e - a c t i v i t y relationships
by D . 3- Livingstone
11.
The q u a n t i t a t i v e d e s c r i p t i o n of s t e r i c
by M . C h a r ton
Index
557
effects
629
689
R.I. Zalewski, T . M . Krygowski and J. Shorter (Eds), Similarity
Biochemistry and Related Fields
Studies in Organic Chemistry, Vol. 42
© 1991 Elsevier Science Publishers B.V., Amsterdam
CHAPTER
Models in Organic Chemistry,
6
DESCRIPTION O F PROPERTIES O F BINARY SOLVENT
Heinz
283
MIXTURES
Langhals
I n s t i t u t für Organische C h e m i e der U n i v e r s i t ä t
K a r l s t r a s s e 23, D-8000 M ü n c h e n 2, Germany
München,
TABLE OF CONTENTS
1.
introduction
284
2.
Binary Liquid Mixtures
3.
The P a r a m e t e r s o f Equation
286
4.
Further
P o l a r i t y Scales
290
5.
Special
Binary Mixtures
298
6.
Solutions o f E l e c t r o l y t e s
303
6.1
L i t h i u m P e r c h l o r a t e in A c e t i c A c i d
303
6.2
L i t h i u m P e r c h l o r a t e in Ether
304
6.3
The P o l a r i t y of A l c o h o l i c E l e c t r o l y t e Solutions
306
3
288
7.
Solid Solutions
8.
Regions of L i m i t e d M i s c i b i l i t y
308
9.
Slow and Fast Processes
310
10.
307
A p p l i c a t i o n s of Equations 3 and 6
Determination
10.2.
Analysis of Binary Mixtures
318
10.3.
Examination
318
10.4.
of Water
313
10.1.
of Unusual
in W a t e r - C o n t a i n i n g
P o l a r i t y Scales
P e r y l e n e Dyes as P o l a r i t y Probes
318
10.3.2
S e x t e t R e a r r a n g e m e n t s as P o l a r i t y Probes
323
Calculation of Molar Concentration
Studies o f R e a c t i o n
10.5.1
10.5.2
10.6
313
10.3.1
from
Weight
Percentages
10.5.
Solvents
Further
11.
Outlook - Further
12.
References
328
Mechanisms
330
Solvolysis o f t e r t - B u t y l C h l o r i d e in
Ethanol-Water
330
N o n - l i n e a r W i n s t e i n Relationships
334
Applications
337
Extensions
337
338
284
1. I N T R O D U C T I O N
Similarity
models
experimental
The
polar
reactions.
powers
can
data
are
properties
The e f f e c t
of
ten
be
and
in
of
used
for
important
media
the
the
a
key
part
play
o f solvents
reaction
predictions
for
on c h e m i c a l
rate
and
the
This
has
known
stimulated
the
development
p o l a r i t y scales are
(3), defined in equation
of
the
in
basis
chemical
reactions
choice
c o n t r o l the f o r m a t i o n o f r e a c t i o n products;
on
of
of
and
may be as high as
the
solvent
may
empirical
p o l a r i t y scales
g i v e n here as examples:
see
(1). The
and
[1]
1
[2]
as a basis the
r a t e constant
t e r t - b u t y l chloride, with
hand,
is
well-
1:
T
which
two
W i n s t e i n Y scale
E ( 3 0 ) = 28590 [kcal · ^of ]/^^
other
several
completely
for a r e v i e w see (1-2).
Q
of
few
effects.
biochemical
Y = lg ( k / k )
has
only
i n v e s t i g a t i o n of solvent
the
E^(30)
given
in
k of a chemical
the
scale
equation
reference
of
Dimroth
2,
is
solvent
and
derived
reaction;
80%
Reichardt
from
namely,
the
ethanol/water
a
(4-7),
solvolysis
( k ) . On
Q
the
the
definition
of
effect:
the
spectroscopic
s o l v a t o c h r o m i s m (the peak s h i f t λ
in the u v / v i s absorption) of dye 1. E~(30) is
max
1
the m o l a r energy o f e x c i t a t i o n o f the dye in the corresponding solvent.
The e m p i r i c a l p o l a r i t y scales are w e l l established
i m p o r t a n t tools for m e c h a n i s t i c any c h e m i c a l
reactions
are
and p r e p a r a t i v e - o r i e n t e d
carried
m a t e r i a l is dissolved in a solvent
m i x t u r e even
at
reaction
products
this,
the
the
impurities,
the
solvents
the
are
out
usually
most c o m m o n
of
and
sample.
chemists.
starting
reaction
as
technical
important
phases.
However, hardly
to run a c h e m i c a l r e a c t i o n , and thus the
be considered
liquid
are
Normally a
when a sensitive p o l a r i t y scale, e.g.
p o l a r i t y of a solvent
in pure
beginning is binary or has
can
for pure o r g a n i c solvents and
even m o r e components.
further
grade and
components,
contain
and,
other
o f these being w a t e r .
During
as
the
well
as
substances
as
This is obvious
the E-p(30) scale, is used to the d e t e r m i n e
the
1
286
2. B I N A R Y L I Q U I D M I X T U R E S
The
necessity
polarity
of
are
well
to
binary
serious
established
mixtures.
problem.
obtained
scale
to develop
a binary
between
and
the
correlation
included
For
pure
solvents
polarity
applies
Moreover
(1)
pure
the
solvents
obvious.
the next
generally
for
the
useful
example
this
linear
Surprisingly,
mixtures
their
has
and
to
be
correlations
the
solvent
as
the
Y
linear
mixtures
a
a
are
Winstein
however,
measured
the
scales
extension
proved
between
d e t e r i o r a t e s when
of
composition
Empirical polarity
a i m should be
literature,
mentioned.
polarities
t h e i r c o m p o s i t i o n in vol % or m o l e
be
the
scales,
already
to
to
- so
j u d g i n g by
different
scale
relation between
thus
for pure solvents
However,
E^(30)
which
(1,8,9).
a quantitative
m i x t u r e seems
function
are
of
% g i v e c o m p l e x curves (4,8,10), in some cases
even w i t h m a x i m a and m i n i m a (11,12).
F i g . l : P l o t o f the E^(30) values against c
t e r t - b u t y If o r m a m i d e / b e n z e n e .
for the binary m i x t u r e N -
287
Fig.2: a) Plot o f the E ( 3 0 ) values against
T
N-tert-butylformamide/benzene
(c / c * + l ) a c c o r d i n g to e q u a t i o n
In c
p
for the b i n a r y m i x t u r e
- b) p l o t o f E^OO) against In
3.
288
Several
for
attempts
example
E^(30)
have been
(13,14,15),
values
for
the
a
made
typical
mixture
to find
a general
s o l u t i o n to
this p r o b l e m ,
see
example
of which
is g i v e n by
f i g . 1, where
the
N-tert-butylformamide/benzene
are
plotted
against
c , the m o l a r c o n c e n t r a t i o n o f the m o r e polar c o m p o n e n t ( N - t e r t - b u t y l f o r m a m i d e ) .
But a s o l u t i o n o f the p r o b l e m f i r s t c a m e about w i t h
the
E^(30)
values
polar c o m p o n e n t
against
the
of a binary
logarithm of
the
m i x t u r e gave
the o b s e r v a t i o n
molar
t h a t a plot of
concentration
a straight
line at
of
high
the
more
concentrations
(16,17) as shown in F i g . 2a.
At
low c o n c e n t r a t i o n s
tends
to
E^(30)°,
concentration
the
the
plot deviates
Ε^(30)
range the
value
from
of
two-parameter
the
a straight
less-polar
equation
line and
as
component.
c^ —> 0, it
For
3 c o u l d be developed,
the e n t i r e c u r v e , i n c l u d i n g the c u r v e d s e c t i o n , can be described
the
whole
with
which
in closed f o r m
(16-
17):
E (30) = E
T
In ( c / c * + 1) + Ε ( 3 0 ) °
D
p
E^(30), E ^ ( 3 0 ) ° ,
the
equation.
computer
coefficient
The
and c^ w e r e d e f i n e d above,
These
program
which
o f equation
(c / c * + l )
which
is shown
covers
the
latter
can
be
varies
3 can
the
be
and E ^ and c* are
determined
graphically
parameter
o f the p l o t o f E^(30) against
validity
from
[3]
χ
c*
and
the
(16)
parameters of
or
takes
by
the
concentration
straight
line
are
demonstrated
range
statistical
a
In (c / c * + l ) as a test f o r l i n e a r i t y .
by
a
plot of
E^(30)
is g i v e n in f i g . 2b for the d a t a o f f i g . 1. The s t r a i g h t
a
using
correlation
of
in
three
orders
nature
and
of
magnitude.
correspond
to
against
In
line which
Deviations
experimental
error.
3. T H E P A R A M E T E R S O F E Q U A T I O N 3
The
parameter
sensitivity
has
the
component
becomes
of
E^
the
has
E^(30)
dimensions
above
important
of
the
dimensions
of
energy
and
is
a
measure
scale t o w a r d s
r e l a t i v e changes o f c . The
concentration
and
which
the
interaction
for
the
polarity
of
is
the
between
the
concentration
the
two
mixture.
c*
the
parameter
of
solvent
Thus
of
the
c*
polar
components
divides
the
289
concentration
region
into
two
parts.
This
is
best
illustrated
by
the
limiting
one may o b t a i n
equation
behaviour of f u n c t i o n 3.
E (30)
T
= E
In
D
(c
/c*
c
E (30)
Τ
T
= —
c
Ρ
+
< <c
1)
+
[3]
E (30
T
51
c
Ρ
> > c*
(
+ E ,(30)
I
T
ρ
[4]
Ε (30)
= Ejyln
χ
c
+
p
(Ε
0
χ
( 30 ) - Ε ^ · 1 η
c*)
[5]
For low c o n c e n t r a t i o n s
4
by
applying
concentration
a
o f the polar component,
Taylor
range,
type
the
series
c^
<< c*,
expansion
contributions
of
to
both
equation
3.
Thus
components
to
in
this
polarity
are
c u m u l a t i v e (see b e l o w ) .
F o r high c o n c e n t r a t i o n , c^
and equation
>> c*,
3 can be s i m p l i f i e d
we have a linear
the q u o t i e n t c^/c* becomes large c o m p a r e d
to o b t a i n equation
dependence o f E^(30)
on
5. In this c o n c e n t r a t i o n
In c . T h i s corresponds
to
to 1,
region
the
linear
part in f i g . 2a.
The
experimentally
component,
c
accessible
= 0,
to
the
range
pure,
of
c
extends
more-polar
from
the
component,
c
Ρ
p a r a m e t e r c*
o f equation
3 for
the
m i x t u r e under
test
is large,
postulated
less-polar
x
.
Ρ
c*
if
p-|
>> c^
r e g i o n . In this case
p o l a r i t y and
the
of a m i x t u r e s , see
r e v i e w s (1,9-10,12,18), is s a t i s f i e d .
I f , however,
c* is s m a l l ,
<0.06
correlation
the
relationship between
a
the
mol/1,
linear
m
c
Ρ
linear r e l a t i o n s h i p is o b t a i n e d over the w h o l e c o n c e n t r a t i o n
frequently
pure,
=
between
polarity
and
c
is
non-linear
the
, a
the
composition
over
say
the
290
e x p e r i m e n t a l l y relevant
c o n c e n t r a t i o n range.
This is d e m o n s t r a t e d
in f i g . 1 for
binary m i x t u r e N-tert-butylformamide/benzene,
for w h i c h c* is low.
There
from
equation
the
polarity
is
relation
still
another
between
important
the
result
concentration
and
3 due
of
a
to
the
binary
the
logarithmic
mixture:
the
a d d i t i o n of a s m a l l amount of a polar solvent to a solvent w i t h a low p o l a r i t y w i l l
markedly
increase the p o l a r i t y o f the
a l i t t l e solvent w i t h
decrease
in
polarity.
chromatography
From
equation
decreasing
c*
This corresponds
is
in a
noticeable
for example,
o f a d d i t i v e s on r e a c t i o n r a t e s o f c h e m i c a l
obvious
The e x p e r i m e n t a l v a l i d i t y
other
t o p r a c t i c a l experience,
the a d d i t i o n of
that
the
magnitude
of
the
effect
with
reactions.
increases
with
values.
4. F U R T H E R P O L A R I T Y
for
hand,
low p o l a r i t y to a p o l a r solvent w i l l not result
or the e f f e c t
3 it
m e d i u m . On the o t h e r
SCALES
of equation
3 f o r the
E^(30) scale has
p o l a r i t y scales (18-21) and can be expressed in general
also
form
been
found
by e q u a t i o n
6.
E
In
D
In ( c / c * + 1) + P °
[6]
p
equation
6 Ρ
is
the
polarity of
a
binary
p o l a r i t y scale. P ° is the p o l a r i t y o f the pure,
have the
same meaning
as
in e q u a t i o n
3.
l i m i t i n g behaviour when e x t r e m e values are
mixture
measured
less polar c o m p o n e n t .
Essentially
both
(No.
empirical
show s i m i l a r
considered.
1, are based on
such as π —> π * absorption (Nos. 1,4-7), c h a r g e - t r a n s f e r
3), fluorescence
an
E ^ , c*, and c
equations
E m p i r i c a l p o l a r i t y scales, a s e l e c t i o n of w h i c h is shown in T a b l e
various e f f e c t s ,
by
(Nos. 8,9) and solvolysis (No. 2). The Ej(\)
absorption
scale (No. 5)
responds not only t o the p o l a r i t y of t h e m e d i u m , but also shows sensitive response
to
its h y d r o g e n - b o n d i n g donor
character.
In t e r m s of the c r i t e r i a used in a l l p o l a r i t y scales s t u d i e d to date,
e q u a t i o n 6 is a
v a l i d d e s c r i p t i o n of polar behaviour o f b i n a r y l i q u i d m i x t u r e s as a f u n c t i o n of t h e i r
c o m p o s i t i o n (17,19). T h e linear r e l a t i o n s h i p b e t w e e n Ρ or Ρ - P ° , r e s p e c t i v e l y ,
In (c / c * + 1), for some p o l a r i t y scales m e n t i o n e d in T a b l e 1 is i l l u s t r a t e d in
f i g u r e 3.
and
291
Table 1: E m p i r i c a l solvent p o l a r i t y scales; see (1,17).
No.
polarity
solvent
scale
probe
process
1
E (30)
1
π -> π * absorption
2
Y
2
solvolysis
3
Ζ
3
CT-absorption
4
π -> Ή * absorption
5
π -> π * absorption
T
4
5
V
E (1)
6
MOED
T
7
X
8
S
9
S
R
π -> π * absorption
7
π -> π * absorption
R«CH
fluorescence
3
9, R = H
2
reaction
6
8,
l
dependent
fluorescence
ln(c /c* + ι]
P
Fig.3:
L i n e a r r e l a t i o n s h i p b e t w e e n Ρ and In ( c ^ / c * + 1) for various
p o l a r i t y scales (equation 3): •
•
E^(30) e t h a n o l - 1-decanol,
Y w a t e r - m e t h a n o l , χ = 2; Η Ζ m e t h a n o l - a c e t o n e ,
e t h a n o l - n-heptane, χ = 1, o r d i n a t e Ρ - Ρ
5.8
χ = 1;
χ = 2; Τ π *
292
Table 2: The p a r a m e t e r s E ^ and c* from
and various solvent
No.
equation
6 for b i n a r y solvent
mixtures
p o l a r i t y scales G.
a)
components'
Ε
D
kcal/mol
mol/l
"k
mol/l
kcal/mol
G
1
1.99
butanol
0.14
42.2
2
2.27
ethanol
0.14
acetone
3
2.53
methanol
0.10
acetone
4
N-tert-butylformamide
1.87
0.27
acetone
5
3.59
water
0.664
acetone
242
(water
1000
c)
1.83
ethanol
0.10
acetonitrile
7
1.08
1-hexanol
0.08
acetonitrile
8
1.83
methanol
0.06
acetonitrile
9
2.70
water
0.293
acetonitrile
132
(water
acetonitrile
10
0.9994
1
28
42.2
0.9997
1
29
46.0
0.9995
1
31
42.2
0.9994
1
11
48.9
0.9956
1000
c)
9)
46.0
0.9997
1
30
46.0
0.9988
1
29
46.0
0.9988
1
31
45.7
0.9992
1
11
53.3
0.9921
b)
N-tert-butylformamide
benzene
42.2
1
acetone
6
0.9995
31
acetone
8)
2.27
0.01
34.5
0.9985
1
31
12
293
No.
components
^
kcal/mol
c*
mol/l
kcal/mol
r
c^
η
mol/l
G
11
water
1.33
1.98
1-butanol
(water
33.8
l-butanol
12
10~
4
b )
water tert-butyl-
water
1.42
0.340
2.82
1.01
t e r t - b u t y l alcohol
14
water N - t e r t - b u t y l -
4.90
28.2
formamide
15
1-butanol
2.42
0.03
carbon disulphide
16
1-octanol
2.83
0.06
carbon disulphide
17
pinacolone
9.30
7.89
carbon disulphide
18
water
3.00
0.301
dimethoxyethane
19
water
5.19
5.28
dimethylacetamide
20
water
9.49
d
DMEU '
21
11.0
e )
i-butanol
3.20
1.64
DMF
22
ethanol
DMF
0.9981
1
22
-384
0.9901
1
hydroperoxide
13
49.8
2.78
0.607
6)
49.7
0.9984
1
10
43.3
0.9967
1
26
50.4
0.9965
1
21
32.6
0.9991
1
30
32.6
0.9968
1
30
32.6
0.9946
1
16
38.2
0.9996
1
12
43.0
0.9984
1
13
42.5
0.9992
1
20
43.8
0.9994
1
30
43.8
0.9979
1
30
8
4
8
14
294
No.
components
a)
Ε
D
kcal/mol
Ρ
c*
mol/l
"k
mol/l
kcal/mol
G
23
3.55
methanol
0.696
DMF
24
9.56
water
11.52
DMF
25
4.93
1-butanol
4.29
DMSO
26
3.95
ethanol
2.69
DMSO
27
24.0
water
53.8
DMSO
28
acetonitrile
3.23
0.77
43.8
0.9975
1
31
43.7
0.9979
1
18
43.8
0.9953
1
30
45.0
0.9979
1
30
45.1
0.9997
1
20
36.0
0.9991
29
1,4-dioxan
29
5.39
1-butanol
0.90
1,4-dioxan
30
ethanol
4.99
0.72
1,4-dioxan
31
4.55
methanol
0.35
36.0
0.9997
1
30
36.0
0.9993
1
30
36.0
0.9992
30
1,4-dioxan
32
nitromethane
3.49
1.01
1,4-dioxan
33
propionitrile
3.33
1.41
1,4-dioxan
34
water
4.33
0.512
1,4-dioxan
(water
1,4-dioxan
368
b)
1000
c )
36.0
0.9993
1
31
36.0
0.9983
1
30
36.0
0.9993
1
27
43.8
0.9969
1
8)
39
14
295
No.
Ε
components
D
kcal/mol
mol/l
kcal/mol
mol/l
G
35
36
10.5
water
DMPU
12.8
e,f)
water
6.29
38.1
42.1
0.9996
1
18
52.0
0.9987
(water
14.3
10
-4
-126
ethano ,b)
37
water
5.58
34.3
water
563
ioo<r
55.9
0.9962
1
10
40.9
0.9989
H M P A g)
39
water
17.9
(water
150
9.13
10"
55.4
0.9300
1
25
-57.9
0.9920
1
methanol^
water
1.80
12.4
52.2
271
(water
1000^
48.4
m e t h o x y e t h a n o l, b")
1
water
1-butanol
12.3
17.4
1.43
0.06
nitromethane
43
ethanol
1.41
methanol
nitromethane
0.9802
0.9982
42.2
0.9996
I
18
46.3
0.9991
1
31
0.03
0.9970
46.3
nitromethane
44
8)
6)
N-methylpyrrolidone
42
37
10
methoxyethanol
41
39
6
methanol
40
0.9980
9)
formamide
38
34
12
ethanol
1.66
30
0.9995
0.01
46.3
29
10
296
No.
45
components
a)
Ε
D
kcal/mol
4130
water
c*
mol/l
1000
c)
kcal/mol
46.3
1.69
water
4.22
1-propanol
23.5
(water
10
-4
b
ι
i )
1-propanol
47
3.09
0.502
4.01
acetone
32.1
pyridine
49
2.90
1-dodecanol
0.89
pyridine
50
9.64
ethanol
12.8
pyridine
51
2.90
1-hexanol
1.11
pyridine
52
6.92
methanol
5.84
pyridine
53
0.9956
1
25
-126
0.9952
nitromethane
46.0
1
propylene carbonate
48
50.5
1
water
6.46
13.6
tert-pentyl
water
pyridine
0.9990
9
0.9871
1
28
40.2
0.9990
1
30
40.2
0.9955
1
31
40.2
0.9976
1
30
40.2
0.9981
1
31
40.2
0.9938
30
alcohol
1.02
0.95
pyridine
55
11)
40.2
pyridine
54
0.9997
3
nitromethane
46
mol/l
7.09
5.48
40.2
0.9934
1
29
40.2
0.9960
1
29
297
No.
56
components'
ι)
water
D
kcal/mol
mol/l
4.03
0.449
G
kcal/mol
37.4
302
tetrahydrofuran
57
1-butanol
TMU
58
1000^
b)
3.56
0.91
3.51
0.81
TMU
59
5.82
water
TMU
b
TMU '
60
4.02
h )
300
(water
1000
c)
methanol
water
water
2.25
0.31
ethanol
2.04
5.47
-1.71
3.08
31
41.0
0.9993
1
31
41.0
0.9986
1
14
45.9
0.9989
ethanol
methanol
acetone
49.3
55.9
72.9
4
-3.19
3.05
78.7
4
2.15
0.48
acetonitrile
65
0.9994
6
n-heptane
64
20)
1
6
ethanol
63
0.9690
5)
ethanol
62
"k
moi/l
0.9997
41.0
h )
acetone
61
45.1
1
h )
ethanol
η
20
tetrahydrofuran
(water
1
72.1
3
4.66
0.65
66.3
3
0.9995
30
0.9917
30
24
-0.9985
31
-0.9977
31
0.9987
47
0.9999
31
30
298
a)
κ ι
No.
Ε
components
*
c*
^
kcal/mol
ο
Ρ^.
mol/l
kcal/mol
r
c^.
η
mol/l
G
66
methanol
8.52
2.66
63.7
0.9938
3
31
1,4-dioxan
67
water
6.67
49.7
35.2
ethanol
a) The
polar
0.9974
5
more
polar
component
component
(c
imidazolidinone
(70).
> c^).
e)
is m e n t i o n e d
-
c)
Substitute
More
for
first.
than
HMPA.
25
34
- b) For high c o n c e n t r a t i o n s
1000
f)
mol/l.
-
d)
of
l,3-Dimethyl-2-
1,3-Dimethyl-3,4,5,6-tetrahydro-
2 ( l H ) - p y r i m i d i n o n e . - g) C a u t i o n (71,72) - h i g h l y t o x i c ! - h) T e t r a m e t h y l u r e a .
T a b l e 2 gives an impression o f the range o f v a l i d i t y o f e q u a t i o n 6, and shows
the
result
the
of
applying it
components
aromatic
used
to
various
- polar
solvents
-
p o l a r i t y scales.
The
number
protic, dipolar aprotic,
and
non-polar
lead
to
the
conclusion
that
equation
6
and
variety
solvents,
provides
of
including
a
general
d e s c r i p t i o n o f the p o l a r i t y o f b i n a r y m i x t u r e s and is not c o n f i n e d to c e r t a i n
(22) of solvent.
has
a
strong
Us v a l i d i t y
tendency
polarity effects
for scale 5 and
to
form
mixture ethanol/water
bonds,
is
particularly
types
(19),
which
notable.
Thus
caused by hydrogen bonding are also described by e q u a t i o n 6.
5. S P E C I A L B I N A R Y
MIXTURES
Special
observed
features
postulated
hydrogen
the
are
in another
context
with
that
the
solvent
1,4-dioxan
mixture water/1,4-dioxan.
acts as
a
It
was
"solvent-structure-breaker"
(23). This special p r o p e r t y o f the solvent can be i n v e s t i g a t e d using e q u a t i o n 3.
Normal
behaviour
a water content
concentration
c^,
a c c o r d i n g to e q u a t i o n 3 is observed
o f ca.
50%\ this is seen in the l e f t
however,
the
steeper r e l a t i o n s h i p w i t h o t h e r E
with
the
E^(30) scale up to
region o f F i g . 4 . A t a c e r t a i n
l i n e a r r e l a t i o n s h i p a b r u p t l y gives w a y t o a
n
and c* values (19).
second
299
In
the
following
designated
discussion,
region
I and
the
region
concentration
I I . For
change at c^ ( d i s c o n t i n u i t y in the
p l o t t e d against
In c ,
p
the
ranges
c^ < c^
and
c
p
mixture water/1,4-dioxan,
1st d e r i v a t i v e ) can even be d e t e c t e d
i.e. w i t h o u t i n t r o d u c i n g f u r t h e r
> c^
the
are
sudden
i f E^(30) is
parameters.
60
50
40
, c
In
2
4
p
Fig.4: D o u b l e line for the m i x t u r e w a t e r / 1 , 4 - d i o x a n - E^(30) versus In c
a c c o r d i n g to e q u a t i o n 3 (see
The existence
o f t w o regions o f v a l i d i t y
c^ c o u l d be i n t e r p r e t e d by assuming
the water
hydrogen
with
the
that
for e q u a t i o n
structure
postulated
of water
action
of
3 with
in region I , at
m o l e c u l e s r e m a i n i s o l a t e d and t h a t
bonded
p
text).
occurs
1,4-dioxan
a critical
low w a t e r
the f o r m a t i o n of a
in region
as
a
change
at
concentrations,
three-dimensional
I I . T h i s model
is
consistent
"solvent-structure-breaker"
(see
above).
In F i g . 4 , t h e line of r e g i o n I can be e x t r a p o l a t e d
r
n
a
x
for c
= c
ρ
ρ
is s m a l l e r than
i n t o r e g i o n I I (broken line). Thus,
a v i r t u a l p o l a r i t y value is o b t a i n e d
r
the a c t u a l
j
for w a t e r E^(30) = 56, w h i c h
1
ν
is t h e p o l a r i t y w i t h
p o l a r i t y value o f 63.1 (6). E ( 3 0 )
T
300
which
water,
as
the
more
polar
component,
affects
1,4-dioxan
within
region I .
Since the e f f e c t i v e p o l a r i t y of w a t e r is s u b s t a n t i a l l y l o w e r at high d i l u t i o n ,
concentrated
solutions,
water molecules
water,
rather
the
t o conclude
in m o l e c u l a r associates is responsible
o f a second, steeper
mixture water/1,4-dioxan,
especially w i t h
with
might venture
than the c h a r a c t e r i s i c s
The o c c u r r e n c e
to
one
but
those i n c l u d i n g w a t e r ,
water/1,4-dioxan.
The
mixture
studies of r e a c t i o n mechanisms,
scales (19). A l l scales s t u d i e d
that
can
also
molecule.
to e q u a t i o n
be
observed
a l t h o u g h the e f f e c t
water/ethanol,
3 is not
with
other
which
is
very
as
for
has been s t u d i e d e x t e n s i v e l y using several p o l a r i t y
produced
double
w a t e r / e t h a n o l : · Υ, χ = 2, y = 1; •
straight
lines
(three
examples
Ε ( 1 ) , χ = 1, y = 4; A
τ
, χ = 1, y =4, o r d i n a t e : Ρ - P ° + 7.7 (x and y are s c a l i n g
fig.5).
mixtures,
important
F i g . 5 : Double lines a c c o r d i n g t o e q u a t i o n 6 for the m i x t u r e
factors for
confined
is not as pronounced
shown in F i g . 5).
πj
than in
i n t e r a c t i o n of
for the high p o l a r i t y o f pure
o f the i s o l a t e d w a t e r
line a c c o r d i n g
specific
are
301
Ε (30)
τ
50
46
10
0
Fig.6: E^(30) values of 1 - b u t a n o l / n i t r o m e t h a n e
concentration
of
as a f u n c t i o n of the m o l a r
1-butanol.
a)
b)
/
UJ
50-
/
ln(cp/c**1)
ln(c /c**l)
u
Fig.7: a) R e l a t i o n s h i p b e t w e e n
between
E^(30) and In {c^fc*
+ 1), b) r e l a t i o n s h i p
E^(30) and In ( c / c * + 1). B o t h for the m i x t u r e 1-
butanol/nitromethane.
u
302
It
is r e m a r k a b l e
within
the
different
that
limits
the various p o l a r i t y scales produce c^
of
abscissae
experimental
since
double line phenomenon
characteristic
only
for
an
of
indicator
the
c*
values
the
binary
for
the
between
in
Fig.5
vary
for
the
each
values
break
which
points
coincide
appear
at
Thus,
the
p o l a r i t y scale.
is not p e c u l i a r to the E^(30) scale, but must be taken as a
mixture water/ethanol.
change in solvent
the change in solvent s t r u c t u r e
reaction
error;
U(IV) and
The
structure.
solvent
p o l a r i t y scale
A further
striking
evidence
is the the dependence o f r a t e constant
U(V1) (24)
as
a
function
of
the
is
for
the
of
an
of
1-
composition
ethanol/water mixture.
Even
more
butanol
interesting
and
represent a f u r t h e r
increases
and
polarity
a
at C p
examples
m a x i m u m at
decreases
m a x
This phenomenon
the
mentioned
nitromethane., and
above
of ethanol
type of b i n a r y m i x t u r e (21). Here
reaches
again
component
than
a c e t o n i t r i l e or
and
attains
the
p o l a r i t y value
mixtures
nitromethane,
p o l a r i t y o f the
c, . A s c
increases
k
ρ
the
are
and
of
further,
the
which
mixture
however,
pure,
more
the
polar
. This is i l l u s t r a t e d in F i g . 6 .
is k n o w n for alcohols as " e l e v a t e d
p o l a r i t y " (21) and
for m i x t u r e s
w i t h c h l o r o f o r m as " s y n e r g e t i c p o l a r i t y e f f e c t " (11).
Equation 3 holds even
is
observed
(see
in this case. W i t h i n
Fig.7a).
However,
region I , c
within
region
substance is less polar, acts w i t h
1-butanol
in
relationship
this
where
region
c
is
u
there
the
is
a
molar
linear
concentration
of
polar c o m p o n e n t
1-butanol.
and n o r m a l
behaviour
which
as
pure
l i k e a m o r e polar a d d i t i v e . A c c o r d i n g l y
between
the
E^(30)
less p o l a r
Fig.7b). By analogy to the previous examples,
the
< c^,
p
II nitromethane,
and
In ( c / c * + 1),
u
component
1-butanol
(see
a v i r t u a l p o l a r i t y can be d e f i n e d
C o n t r a r y to previous cases, however,
it is
for
greater
than the a c t u a l p o l a r i t y of the a l c o h o l .
Here,
also,
negative
bond
two
slope
straight
donor-acceptor
donor:
the
polarity,
mixture
other
model
component
promotes
remarkable
lines
unlike in the
the
are
observed.
previous cases.
with
the
in each
formation of
The
second
This can
line,
alcohol
or
chloroform
case as
an
additive, which
a
solvent
polar
however,
be e x p l a i n e d by a
as
structure.
a
hydrogen
itself
This
has
a
hydrogen
has
bond
a low
behaviour
is
in so far as i t c o n t r a d i c t s the usual v i e w t h a t the p o l a r i t y o f a solvent
lies
within
the
solvents can be enhanced
limits
of
its
components;
by adding less polar
furthermore
components.
the
polarity
of
303
6. S O L U T I O N S O F E L E C T R O L Y T E S
The
influence
of the a d d i t i o n o f e l e c t r o l y t e s on the p o l a r i t y o f an organic
is an i n t e r e s t i n g p r o b l e m , but has
separation
manner.
of
On
the
the
self-solvation
ions
other
which
electrolytes
on
mechanistic
studies
could
hand,
in media
causes
reaction
and
received
influence
a
lower
rates
has
is
l i t t l e a t t e n t i o n (25-28). The full
the
solvent
with
structure
with
attributed
as
to
is the
The
aggregation
the
of
dyes
is w e l l - k n o w n
as
and
H-
and
occurs
the use o f this scale.
In
order
overcome
the
pyridiniumphenolate betaine
forms
the
calculated
basis
from
of
^
m
Even dye 8 f o r m s
will
a
of
effect"
(10,29)
in
interaction
of
is the
problems
(30)
electrolytes
with
different
a bathochromic
for
the
solvatochromic
fluorescent
polarity
scale
o f the fluorescence
from
was
types
shift
dye c h r o m o p h o r e s
basis
with
ions.
to these media (25).
of
of
the
as s m a l l
as
t h e ?Tj* p o l a r i t y scale
dye
aggregation
dye 8 can
(the
(32-34)
S
-
be used, and
the
S
values
Η-aggregates,
pointed
solvatochromism
of
electrolyte.
dependence
isolated
out
dye
of
this
being
a c c o r d i n g t o e q u a t i o n 2.
Η - a g g r e g a t e s in e l e c t r o l y t e s o l u t i o n (25). H o w e v e r ,
as
The
by
effect
The
1 o f the E^(30) scale aggregates too, as i n d i c a t e d by a
Zelinskii's
x
not be o b t a i n e d
equilibrium,
the
formed
"salt
direct
or
even w i t h
(4) (25), w h i c h
and excludes
change in line shape)
are
charge
profound
examined.
J-aggregates
(31)
to
very
solvent.
dyes added
cause a h y p s o c h r o m i c
u v / v i s - a b s o r p t i o n . This a g g r e g a t i o n
p-diethylaminonitrobenzene
a
i n v e s t i g a t i o n o f the p o l a r i t y o f solutions o f
o f p o l a r i t y probes, for e x a m p l e
aggregation
stacking
the
the
H o w e v e r , the i n f l u e n c e on solvent p o l a r i t y should be
One m a i n p r o b l e m in the
in
low p o l a r i t y , i o n - p a i r s
interaction
well-known
been
solvent
but
by
the
Förster
molecules
solvent
from
can
polarity
given by e q u a t i o n 3 or 6, w h i c h hold even
non-aggregated
(30).
be
on
Because
studied
the
fluorescence
molecules in
of
in solutions
concentration
this,
the
containing
of
salt
is
for e l e c t r o l y t e solutions.
6.1 Lithium P e r c h l o r a t e in A c e t i c A c i d
The special
postulation
salt
of
effect
the
of LiClO^
solvent
in a c e t i c
separated
ion-pair
a c i d is t h e e x p e r i m e n t a l basis f o r
(35). H o w e v e r ,
little
is k n o w n
the i n f l u e n c e o f the salt c o n c e n t r a t i o n on s o l v e n t p o l a r i t y . This can be
by
the S scale m e n t i o n e d above.
The linear relation between
a c c o r d i n g t o e q u a t i o n 6 is shown in F i g . 8.
the
about
investigated
S and In (c / c * + 1)
Ρ
304
63 η
Fig.8: L i n e a r r e l a t i o n s h i p b e t w e e n S and In (c / c * + 1) for L i C l O ^ in
Ρ
ο
a c e t i c a c i d a c c o r d i n g to e q u a t i o n 7:
= -0.724 and S
=62.1
k c a l / m o l , c o r r e l a t i o n c o e f f i c i e n t r = -0.9987 w i t h
16 points, c
Ρ
and c* in m o l / l
A 2 molar solution of L i C l O ^
in a c e t i c
a c i d increases the p o l a r i t y o f solvent
S = 61.1 to S = 59.8. This corresponds to 2 units on the
is n o t i c e a b l e ,
The
but not high enough
to e x p l a i n the special salt
linear c o r r e l a t i o n o f F i g . 8 can
the c o n c e n t r a t i o n
were
a
liquid.
be used t o e x t r a p o l a t e
o f pure L i C l O ^ . This w o u l d
A n S value
of
E^(30) scale. The
from
effect
effect.
the s t r a i g h t
line up
to
then be the p o l a r i t y of L i C l O ^ i f i t
58.1 is o b t a i n e d
which
characterizes
i t as
a
polar
a d d i t i v e , but i t is not as polar as w a t e r (S = 47.2).
6.2 Lithium P e r c h l o r a t e in E t h e r
Lithium
Perchlorate
can
obtained
be
highly
is v e r y
(36,37).
concentrated
soluble
in d i e t h y l e t h e r
A c c o r d i n g to
solutions
of
LiClO.
Pocker
and
in e t h e r
and solutions up t o 6 Μ s a l t
Buchholz
can
be
(38)
regarded
(see
as
also
(39))
fused
salts
305
with
small
solutions
solvent
-
amounts
of
see
example
for
(44)
who
functional
line
by
complex
line can
per cent
values
the
added.
(40-43).
p o l a r i t y of this m i x t u r e . The
coworkers
by
solvents
applied
plotting
Unusual
first
the
Berson
weight
per
be analysed
reactivities
S u r p r i s i n g l y only
Ω scale
cent
(45).
LiClO^
They
1
6 (see
to m o l - l .
b e l o w ) . A p l o t o f the
in
known
about
the
made by Sauer
and
obtained
against
by the a p p l i c a t i o n of e q u a t i o n
observed
is
measurements were
o f L i C l O ^ have to be c o n v e r t e d
a p p l i c a t i o n o f equation
are
little
the
Ω
Ω values
curved
values.
6. F i r s t l y ,
This can
a
these
This
the w e i g h t
also be done
against
the
m o l a r c o n c e n t r a t i o n of L i C l O . is shown in F i g . 9.
Fig.9: The p o l a r i t y o f L i C l O ^ / e t h e r m i x t u r e s (44) by Ω scale as a
function
o f the m o l a r c o n c e n t r a t i o n
function
p l o t t e d is c a l c u l a t e d by the a p p l i c a t i o n o f e q u a t i o n 6
(E
D
The corresponding
= 0.047, c* = 0.0015 m o l / l , Ω
f u n c t i o n 6 is p l o t t e d as
a
0
(see below) o f L i C l O ^ . - The
= 0.499, r = 0.973, η = 13).
line in F i g . 9 . I t
the c* v a l u e of the m i x t u r e is v e r y low, and one can conclude
is r e m a r k a b l e
from
this that
that
the
306
interaction
of
the
concentrations.
On
solvated
the
salt
other
starts
hand,
to
only
e q u a t i o n 6 is observed - no double s t r a i g h t
is u n i f o r m
take
one
place
single
even
at
relationship
lines. T h e r e f o r e ,
the
very
low
according
solvent
to
structure
up to a salt c o n c e n t r a t i o n o f 40% by w e i g h t .
6.3 T h e Polarity of A l c o h o l i c E l e c t r o l y t e Solutions
T h e p o s s i b i l i t y of e x t e n d i n g e q u a t i o n
pointed
out
by
Rezende
and
6 even
coworkers
to solutions o f e l e c t r o l y t e s
(26). T h e y
used
the
equation
was
to
first
give a
q u a n t i t a t i v e d e s c r i p t i o n o f the i n f l u e n c e o f salts on various c h e m i c a l r e a c t i o n s
(27)
known
was
in
the
literature.
In
further
studies
(28)
the
E^,(30)
polarity
scale
a p p l i e d to the p o l a r i t y o f e l e c t r o l y t e solutions in the alcohols m e t h a n o l , e t h a n o l , 1propanol,
Nal,
1-butanol,
KI, LiC10 ,
4
and
2-butanol.
NaCl0
and
4
The
the
alkali
alkali
metal
earth
salts
salts
LiCl,
LiBr,
Ca(C10 ) ,
4
L i l , NaBr.
Sr(C10 ) ,
2
4
and
2
B a ( C 1 0 ) 2 w e r e i n v e s t i g a t e d - e q u a t i o n 3 holds in a l l cases.
4
T h e p a r a m e t e r s E ^ and c* of e q u a t i o n 3 v a r y c o n s i d e r a b l y both w i t h the n a t u r e of
the salt
and the a l c o h o l (28). T h e p a r a m e t e r
of
the a l c o h o l . This r e s u l t is consistent
of
salt
at w h i c h
polarity
of
interaction
c*
value
With
the
i n t e r a c t i o n must
alcohol,
the
becomes
varies
divalent
with
t h e salt
essential,
only
lower
for
little with
cations
the
This is consistent
with
s o l v a t i o n demand.
With the
c*
c* decreases w i t h decreasing
is
the
be
the
fact
taken
t h a t c* is t h e
i n t o account
concentration
the s o l v a t i o n o f the
the
value
nature
o f the
decreases
t h e increasing surface
salt
markedly
concentration
- the
salt
lower
the
is g e t t i n g worse.
The
with
at
i t is
monovalent.
decreasing
ion
o f the ions and the
is v e r y s i m i l a r - t h e r e
is v e r y
in the series; c h l o r i d e , b r o m i d e and i o d i d e anions g i v e s i m i l a r c*
O n l y the
Perchlorate
l o w e r c*
values.
The
linear c o r r e l a t i o n s a c c o r d i n g
has
a very
low p o l a r i z a b i l i t y ,
to e q u a t i o n
3 were
s a l t - s o l u t i o n s up to the c o n c e n t r a t i o n o f the pure
m o l e c u l a r w e i g h t . One
might naively expect
the
results
extrapolated
size.
increasing
variation
ion, w h i c h
the
which
c a t i o n when
charge
anions the e f f e c t
of
polarity
little
values.
in m a r k e d l y
for the a l c o h o l -
salts g i v e n by t h e i r d e n s i t y
same p o l a r i t y for
the
and
same
salt
regardless o f a l c o h o l , but this was not found - the c a l c u l a t e d p o l a r i t y o f the
pure
salt
with
depends on the
decreasing
solvent
a l c o h o l used
polarity of
structure
the
as second
a l c o h o l . This
(double s t r a i g h t
component,
might
lines) w h i c h
the c o n c e n t r a t i o n of salt c o n t i n u o u s l y from
be
would
due
i t decreases s l i g h t l y
to
occur
a
possible
i f one
change
could
in
increase
the pure solvent up to the pure salt. In
307
other
words,
structure
a
from
Nevertheless
were
pure
pure
molten
salt
might
have
a
completely
different
"solvent"
a d i l u t e d salt s o l u t i o n in some a l c o h o l .
one
can
liquids at
roughly c a l c u l a t e
room
the p o l a r i t y o f the salts m e n t i o n e d
temperature.
o r d e r of m a g n i t u d e of the value for
The
calculated
E^,(30) values
i f they
are
of
the
water.
7. S O L I D S O L U T I O N S
T h e solvent
polarity
p o l a r i t y is p r i m a r i l y d e f i n e d
for c r y s t a l l i n e solids;
and a p o l a r i t y probe
in c o m m o n w i t h
Organic
glasses,
liquids, for e x a m p l e
for
example
purpose because o f the
that
things
are usually i s o t r o p i c .
methacrylate),
can
be
examined
The use o f the E^,(30) p o l a r i t y scale is d i f f i c u l t
low s o l u b i l i t y o f dye
a
properties
H o w e v e r , glasses have many
their properties
poly(methyl
to define
these solids have a n i s o t r o p i c
becomes a l a t t i c e d e f e c t .
e m p i r i c a l p o l a r i t y probes.
fact
for liquids and i t is d i f f i c u l t
for e x a m p l e ,
1 in the
for this
polymeric medium
a good o p t i c a l q u a l i t y o f the solid sample is r e q u i r e d for the
with
and
the
absorption
measurement.
Solvatochromic
fluorescent
because fluorescent
dyes are
t o be
l i g h t can be d e t e c t e d
of
the sample being e x a m i n e d is a l i g h t
a
detector.
There
Z e l i n s k i i ' s S scale
are
no
(32) w i t h
problems
fluorescent
the
E,p(30) value o f about
latter
can
be
w i t h high s e n s i t i v i t y and the
fluorescence
dye
optical
8 as
a
inhomogeneities.
p o l a r i t y probe
onto
Therefore
is useful
for
the S scale and the E^(30) scale (E^(30) =
calculated
37 is o b t a i n e d
for the e x a m i n a t i o n o f solids,
source w h i c h can easily be focussed
with
solids. By the linear c o r r e l a t i o n b e t w e e n
-1.93-S + 160.4)
preferred
for
(46), w h i c h
poly(methyI methacrylate)
is s i m i l a r to t h a t
of
-
an
tetrahydro-
furan.
The
polarity of polymers
is increased
by polar a d d i t i v e s . B o t h the i n f l u e n c e o f low
m o l e c u l a r w e i g h t a d d i t i v e s and c o p o l y m e r i s a t i o n are q u a n t i t a t i v e l y described
(46) by
e q u a t i o n 6. F i g . 10 is g i v e n as an e x a m p l e
methyl
methacrylate
and the polar c o m p o n e n t
for the c o p o l y m e r i z a t i o n b e t w e e n
2-hydroxyethyl methacrylate.
T h e v a l i d i t y o f m e a s u r e m e n t s o f the p o l a r i t y o f p o l y m e r s is f u r t h e r established
the
application of equation
reorientation
in
the
solid
6. Solvent
or
the
orientation of
reorientation
of
liquids is r e p l a c e d
the
low
molecular
by
by
chain
weight
308
a d d i t i v e s . In this way the e m p i r i c a l l y d e f i n e d p o l a r i t y o f media is meaningful
for
even
solids.
67
65
63
61
59
In
( C p / 0 . 704
+
1)
Fig. 10: P o l a r i t y o f the b i n a r y c o p o l y m e r o f m e t h y l m e t h a c r y l a t e
and
2 - h y d r o x y e t h y l m e t h a c r y l a t e using the p o l a r i t y scale S. c
p
is the
m o l a r c o n c e n t r a t i o n of the unit 2 - h y d r o x y e t h y l m e t h a c r y l a t e
(E
D
= -3.193, c* = 0.704 m o l / l , S ° = 66.5, r = -0.9995, η = 17).
8. R E G I O N S O F L I M I T E D M I S C I B I L I T Y
The phenomenon
o f double s t r a i g h t lines (see section 5) is r e l a t e d t o the f o r m a t i o n
of
solvent
two
distinct
structures.
For
binary
mixtures
between
η-alcohols
and
w a t e r the i n f l u e n c e o f chain l e n g t h o f the alcohols on the p o l a r i t y o f the m i x t u r e s
can be
i n v e s t i g a t e d (47). Double s t r a i g h t lines are o b t a i n e d even w i t h m e t h a n o l
shown in F i g . 11.
as
309
0
χ ln(c / c * + l )
Ρ
2
F i g . 11: E^,(30) values o f b i n a r y m i x t u r e s b e t w e e n
n-alkanols and w a t e r
a f u n c t i o n o f I n i c ^ / c * + 1) a c c o r d i n g to equation
Water/methanoi
(X = 0.157); some values are taken
T: W a t e r / e t h a n o l
as
1. - H :
from
(X = 0.318); some values are taken
(4). -
from
(4). -
W a t e r / 1 - p r o p a n o l (X = 1.349). - · : W a t e r / l - b u t a n o l (X =
1.705)
With
not
methanol
very
alcohols.
as
The
but
longer
solvent s t r u c t u r e
are
a component
different,
this
the
to t h a t
with
l o w e r p o l a r i t y the
difference
chain
length
of water
and
increases
of
the
finally
with
slope
the
alcohols,
with
o f the
chain
the
1-butanol
less
t w o lines
is
length
of
the
similar
is
the
two different
phases
formed.
It can t h e r e f o r e
function
formation
between
water
to
be c o n c l u d e d t h a t the f o r m a t i o n o f t w o solvent s t r u c t u r e s
of limited
of
the
get
two
miscibility
separate
t w o solvent
two
and occurs
phases
structures
phases,
but
is
even
with
determined
l o w e r alcohols.
only
by
the
- this is too s m a l l b e t w e e n
high
enough
with
higher
is not a
However,
surface
tension
l o w e r alcohols
alcohols.
This
the
may
and
be
310
a d d i t i o n a l l y i n f l u e n c e d by the fact
that
the t w o solvent s t r u c t u r e s
in the case of l o w e r alcohols than w i t h higher
This behaviour
is not
described
for b i n a r y m i x t u r e s o f c o m p o n e n t s
r e s t r i c t e d to w a t e r as polar c o m p o n e n t .
octylbenzene
or D M F w i t h c y c l o h e x a n e
9. S L O W A N D F A S T
are m o r e s i m i l a r
alcohols.
with
limited
have essentially
E.p(30) scales,
scales
as
PROCESSES
far
as
components
form
typically
an
pure
analysis
with
solvents
(22,49)
exception,
occurs
with
the same behaviour (48).
The m a j o r i t y of p o l a r i t y scales show m u t u a l linear c o r r e l a t i o n and w i t h
principal
miscibility
Binary mixtures of acetonitrile
but
are
and
these
weakly
concerned.
by
also
polar
This
fact
multi-parameter
mutually
Y and
is c o n f i r m e d
analysis
correlate.
merocyanines
the
(31). A
This
which
by
few
behaviour
have
positive
s o l v a t o c h r o m i s m (10,50). One o f the first cases t o be studied was B r o o k e r ' s (51) χ,-^
scale, w h i c h
be
is based on the s o l v a t o c h r o m i s m o f dye 7. P o l a r i t y scales l i k e x
discussed
extensively
here,
particularly
their
applications
to
binary
R
will
solvent
mixtures.
Studies
of the s o l v a t o c h r o m i s m
o f the
phthalimide d e r i v a t i v e 8 indicates
exhibits strongly positive solvatochromism
proposed
as
for
influence
the
phenomena, and
the basis for the S p o l a r i t y scale by Z e l i n s k i i
solvatochromic
fluorescence,
(see
in fluorescence
of
(21).
oxygen
A
see
linear
(34).
The
relationship
but a linear r e l a t i o n s h i p w i t h
F i g . 12).
Thus,
dye
m e n t i o n e d exceptions,
8
since
is
the χ ^
especially
i t supplies
the
by
is
also
exists
for
this
E.^.(30)
for
was
(32-33);
dye
scale
scale is observed
suitable
this
this
and colleagues
absorption
with
that
for
clarifying
the
absorption
previously
a c o m m o n basis for both groups o f p o l a r i t y
scales.
It
is
known
however,
The
that
the
behaviour
of
states
with
that
reorientation
solvated
of
weakly
transitions
takes place
ground
state
( S ) of
q
8
has
only
a
small
dipole
moment;
first e l e c t r o n i c a l l y e x c i t e d s t a t e (Sj), has a large dipole m o m e n t
different
assuming
the
polar
by
applies
in such
in
absorption
large
dipole
solvents,
this
to
8
the
whereas
effect:
the
a short
states
with
Franck-Condon
period of t i m e
molecules.
emission
moments
s o l v a t i n g shell o f
by r e o r i e n t a t i o n o f the solvent
and
a dye
that
are
can
be
strongly
small
dipole
principle
(52). The
(18).
explained
by
solvated
by
moments
are
for
electronic
the s o l v a t i o n is unable
electronic
transition
to
follow
311
F i g . 12: L i n e a r c o r r e l a t i o n b e t w e e n a) the fluorescence
E^,(30) and b) the absorption w i t h
ordinates
F i g . 13: S c h e m a t i c
o f dye 8 and
χ ^ for pure solvents.
The
are c a l c u l a t e d a c c o r d i n g to e q u a t i o n 2.
representation
dye 8 in polar solvents.
of a b s o r p t i o n and emission processes of
312
Consequently
the
orientation of
s t a t e o f an e l e c t r o n i c
the
s o l v a t i n g shell of the
effects.
Absorption
these w i l l
only influence
t r a n s i t i o n , but not the
and
initial
state,
fluorescence
and
of
final
can
8
solvation
s t a t e . The
in
the
latter will
initial
s t i l l bear
be s t a b i l i z e d o n l y by p o l a r i z a t i o n
proceed
as
given
in
the
scheme
in
F i g . 13.
The i n i t i a l s t a t e , S , is l i t t l e
Sj,
has
a large
s t a t e . Thus
the
X
solvent
scale.
p
i n f l u e n c e d by the
dipole moment,
polarization effects
Excitation
is
are
followed
favorable
molecules.
described
for
conserved
transition
reaction
phenomena
of
the
of
from
of
(53,54,55-56).
fluorescence,
state
orientation
The
the
excited
of
fluorescence
electronic
the
is
of
8 correlates
with
is
in
fully
the
E^(30)
the
which
the
from
Sj
is
1
by
scale.
The
of o t h e r
combination
the
absorption
orientation
effects
other,
interact.
but
results
in
to
measuring
the
be
times,
reorientation
Thus,
it
1
is observed.
with
made
o f the
is reasonable
dye
concept
solvent,
that
7,
and
such
E^(30)
7
(x
a
furthermore,
however,
the
that
c f . the
or
These,
Frequently,
correlation
conclusion
of
R
proposed
the
are
not
scale)
is
a
to
S
1
polarity
is
occurs
solvent
by
orientation
of the
reasonable
initial
that
of
of
dye
the
1 is
polarization
independent
a r e l a t i v e l y slow process,
of
indicator
is o f c r u c i a l
described
by
as
and
each
p r e v a i l and
(57). In o r g a n i c
correctly
dye
energy
considerations
by Bakhshiev
processes are
the
excitation
effects
These
the
dyes is by no means
orientation
scale.
to
shell;
to p e r m i t a
absorption
extreme
Q
m o d i f i c a t i o n (M) as
dipole moment
therefore
s i m i l a r (1). H o w e v e r , in most cases the behaviour
as
state,
- by analogy
solvating
sourrounding
to
influenced
It
excited
s is long enough
because the
large.
the
molecules
transition
which
transition
10
corresponds
states
(besides p o l a r i z a t i o n e f f e c t s )
this
to
solvent
to S^'
Finally
energy
relaxation of
-8
-9
10
the
Sj
The
by the s o l v a t i n g shell o f the S
c r u c i a l for a b s o r p t i o n
by
l i f e t i m e of the e x c i t e d s t a t e (Sj) o f ca.
more
polar solvents.
but is surrounded
this
allow
for
the
short
chemistry
influence.
the
E.p(30)
scale.
E q u a t i o n 6 c h a r a c t e r i z e s the polar behaviour
o f b i n a r y liquid m i x t u r e s a c c o r d i n g
the Xp scale or to an absorption scale using dye 8 as a r e f e r e n c e .
concluded
mixtures
that
in
equation
fast
the c o n c e n t r a t i o n
information
6 will
processes.
o f the
also describe
Equation
polar solvent
on solvent s t r u c t u r e
the
6 cannot,
on t h e
polar
behaviour
therefore,
surface
is p r o v i d e d by c o m p a r i n g
in solvent m i x t u r e s for absorption and emission (21).
be
of the
the
Thus i t can
of binary
solely
dye
solvent
attributed
(58-59).
c* values
to
be
to
Further
o f dye
8
313
10. A P P L I C A T I O N S O F E Q U A T I O N S 3 A N D 6
The v a l i d i t y o f e q u a t i o n
different
6 is w e l l established
p o l a r i t y scales. On
for the
this basis
for b i n a r y solvent
the e q u a t i o n
itself
m i x t u r e s and v e r y
can
be used
as
a
tool
i n t e r p o l a t i o n o f E^(30) values (60) or d i f f e r e n t o t h e r purposes, for example,
for m e c h a n i s t i c
studies.
10.1. Determination of Water in Water-Containing Solvents
The
residual
reactions,
content
of
water
metallorganic
products,
and
reactions
over a l k a l i
solvents
dimethyl
such
neat
content
as
or over
of
these solvents
titration
occur
in
A
simple
and
water
p o l a r i t y scale)
can
Dimroth
markedly
and
presence
relation between
calibration
although
plots.
the
This
Generally
for
especially
when
of v e r y
ethanol
preparative
the
have
work
samples
are
hygroscopic
the
are
to
be
water
old.
The
determination of water,
but
(dead-stop
method)
and " k n o w - h o w " . F u r t h e r
of
systems.
So
water
can
be
the
method
with
the
redox
with preparative
for
the
most
determination
a
handicap
curves
shift
has
have
the
small
solvent.
This
has
been
used
by
the
peak
shift
of
water
prevented
been
of
even
d e t e r m i n a t i o n of
and
not
So
to t h e w a t e r c o n t e n t
peak
this
work.
solvents.
polarity of
(62) for the
calibration
number
reaction
which
t h a t w a t e r has a v e r y high solvent p o l a r i t y (e.g. w i t h
increase
the
a great
like ether
is
dye 1, w h i c h is v e r y sensitive
the
chemical
titration
procedure
compared
Reichardt
many
may d e t e r m i n e yields,
for solvents
m e t h o d for the
equipment
uncomplicated
developed using the f a c t
E^,(30)
is u n k n o w n ,
the
c a r r i e d out as a standard
for
d i m e t h y l f o r m a m i d e , or
sieves.
(61) is a useful
needs special
complications
however,
sulphoxide,
is i m p o r t a n t
and
is no p r o b l e m
metals;
molecular
Karl-Fischer titration
the
for example,
s e l e c t i v i t i e s . There
commonly stored
stored
in d r i e d solvents
water
by
amounts
o f a solvent sample.
content
gives
general
use
the
measured
for
some
very
of
of
However,
non-linear
the
binary
method,
mixtures
(4,8,62-63).
The p r o b l e m w i t h
the non-linear plots can be solved by t h e a p p l i c a t i o n o f e q u a t i o n
3 (64-68). T h i s gives
a further,
determinating
For
water.
and essential,
p r a c t i c a l applications,
to equation 7 w i t h E ^ = 28590
[kcal-nm]/E .
n
simplification
equation
for
2 and
the
3 are
procedure
of
transformed
314
ff
c = c
• exp ( Ε ^ / λ
K
max
- Ε^/λ°
ff
max
) - c
[71
c in equation 7 is the c o n c e n t r a t i o n of w a t e r
Η
dimension of c . c
in g/1 or m o l / l c o r r e s p o n d i n g t o
the
Ή
is the c* value in the dimensions o f c. λ
w a v e l e n g t h of the p y r i d i n i u m p h e n o l a t e betaine 1 in the
Q
and λ
is the λ
value o f the pure d r y solvent.
max
»
~ max
K
p a r a m e t e r s Ε , c , and
λ
m
Q
x
are
J
g i v e n in T a b l e
used solvents f o r the p y r i d i n i u m p h e n o l a t e b e t a i n e
is the a b s o r p t i o n
max
water-containing
Ε
Η
3 for a n u m b e r
E*
mol/l
1.
λ°
Ε^/λ°
max
nm
max
nm
7960
677.5
11.7
10600
625.5
16.9
21500
574.1
37.4
10100
660.3
15.3
5830
567.3
10.3
20100
575.3
34.9
9530
748.4
12.7
5510
664.9
8.29
(g/D
acetone
0.664
(12.0)
acetonitrile
0.293
(5.28)
1-butanol
1.98
(35.7)
t e r t - b u t y l alcohol
1.01
(18.2)
N-tert-butyl­
28.2
formamide
(508)
tert-butylhydro-
0.340
p e r o x i d e (69)
(6.13)
dimethoxyethane
0.301
(5.42)
Ν,Ν'-dimethylacetamide
5.28
(95.1)
The
of frequently
Table 3: P a r a m e t e r s of equation 7 and dye 1 for f r e q u e n t l y used solvents at
solvent
solvent
is g i v e n above.
20°C.
315
ff
solvent
c
ff
E
ff
X°
E
I\°
max
mol/l
max
nm
nm
3010
672.7
4.47
6600
794.2
8.31
2990
654.2
4.57
2714
679.5
3.99
1190
633.9
1.88
4550
549.8
8.28
5120
511.4
10.0
50.8
699.0
0.0727
1600
516.1
3.10
15900
547.7
29.0
2320
677.5
3.42
6.92
617.5
0.0112
566.1
29.9
(g/D
a
DMEU '
b )
11.0
(198)
1,4-dioxan
0.512
(9.22)
DMF
11.52
(208)
b
DMPU '
c )
12.8
(230)
DMSO
53.8
(969)
ethanol
38.1
(686)
formamide
34.3
(618)
HMPA
d )
1000
(18020)
methanol
150
(2700)
2-methoxyethanol
12.4
(223)
N-methylpyrrob
lidone ^
17.4
(313)
1000
nitromethane
(18020)
4.22
1-propanol
(76.0)
31.6
solvent
ff
J
E
ff
X°
E / \°
max
mol/l
max
nm
nm
9264
621.5
14.9
4030
711.2
5.67
7090
764.4
9.28
4910
697.3
7.04
(g/D
propylene carbonate
0.502
(9.04)
pyridine
5.48
(98.7)
THF
0.449
(8.09)
TMU
e )
4.02
(72.4)
a) l , 3 - d i m e t h y l - 2 - i m i d a z o l i d i n o n e
(70).
3,4,5,6-tetrahydro-2(lH)-pyrimidinone
b) s u b s t i t u t e
of
HMPA.
-
d) c a u t i o n
(71,72)
easily
be c a r r i e d
out.
-
c) 1 , 3 - d i m e t h y l -
highly
toxic!
-
e)
tetramethylurea.
The
determination
solvatochromic
that
the
1.0.
λ
of water
can
pyridiniumphenolate
e x t i n c t i o n of
is
max
equation 7 and
the
determined
the
betaine
long w a v e l e n g t h λ
and
the
content
p a r a m e t e r s of Table
- A small
is dissolved
3.
m
Q
of
x
in
of dye
water
is
the
amount
solvent
1 lies
between
calculated
The accuracy
of
the
of
the
sample
by
J
0.7
so
and
means o f
method
depends
Ή
only on the precision o f the s p e c t r o m e t e r
of
the o r d e r o f 5% at
resolution.
The
a water
sensitivity of
content
the
and the m a g n i t u d e of c
o f 10 g / I w i t h
determination
and is t y p i c a l l y
s p e c t r o m e t e r s having 1 nm
of water
in a c e t o n i t r i l e
which
is
value
is
Η
obtained
with
such
a
spectrometer
is
for
example
0.2
i m p o r t a n t for the e r r o r o f the d e t e r m i n a t i o n . For c < c
concentration
constant;
determination
is constant,
whereas
for a more d e t a i l e d discussion see
for c
(64-66).
g/1.
ϋ
The
the absolute
> c
the
c
e r r o r in the
relative error
is
317
For
high precision
measured w i t h
water
determinations
high a c c u r a c y .
d e r i v a t i v e of the u v / v i s s p e c t r u m .
signal to noise
in
the
ratio of
determination
Mathias'
rule
the
maximum wavelength
However,
spectrometer
method.
(74), w h i c h
the
T h i s c o u l d be done by the
c o n n e c t s the
this w o u l d result
(73) and
Therefore,
better
half-radii
would
a
x
)
g i v e higher
secants a c c o r d i n g
M a t h i a s ' rule d i r e c t l y before
the
be
first
the
uncertainties
of
the
must
the
in a decrease of
are
should be done w i t h
F i g . 14: The precise l o c a l i s a t i o n o f A
m
results
14. A c a l i b r a t i o n o f the s p e c t r o m e t e r
and a f t e r
U
calculation of
obtained
by
applying
to F i g .
h o l m i u m glass (75) and
determination.
m
a
o f a broad absorption band by
x
the use o f M a t h i a s ' r u l e - the lines should be d r a w n in the
region of 10 t o 15 % f r o m
^
F o r a rough r o u t i n e test f o r the w a t e r
colour
of
the
sufficient
and
when
dye
the
dye
can
solution
give
with
a
is
not
a
x
-
content
colour
the w a v e l e n g t h
concentration
m
t o an
very
o f a solvent,
scale
high
of
accuracy
and
the
a comparison
absorption
of between
person
of
wavelengths
5 and
doing
the
the
is
10 nm
test
is
318
experienced
in c o l o u r c o m p a r i s o n .
are given, for e x a m p l e ,
Colour scales,
absorption
wavelength
and colour,
in (76-77).
The p a r a m e t e r s o f equation
7 for
f r e q u e n t l y used solvents
T a b l e 3. The p a r a m e t e r s for f u r t h e r solvents
and dye
1 are
given in
can be easily measured in the known
manner.
The
validity
therefore
of
the
equation
The
versus
polarity.
advantage
determinations.
of
dye
Therefore
Problems
for e x a m p l e
of
max
the
spectrometer
for
other
refraction
established
1 is
dye
come
turbid
1
high
when
of
be
the
used
p o l a r i t y scales;
these o t h e r p o l a r i t y
of
the
for
solvatochromism
all
samples do not
1 should be r e p l a c e d
can
easily
be
determined
by a s i m p l e t h r e e - p o i n t - m e t h o d
effects.
(65). W i t h
number
routine
water
have good o p t i c a l
in these cases by
the
dye 8 (66).
fluorescence
physical
a
sensitivity
should
about
for
be c a r r i e d out w i t h
the
liquids; dye
s o l v a t o c h r o m i c fluorescent
λ
is w e l l
d e t e r m i n a t i o n o f w a t e r can
probes.
quality,
3
T h i s has
been
without
(66). E q u a t i o n
done
gases a c o n c e n t r a t i o n
even
for
the
7 can
density
determination
with
a
also be
and
an
fluorescence
the
applied
index o f
accuracy
of
10
ppm is possible by a simple pressure m e a s u r e m e n t (66).
10.2. A n a l y s i s of Binary Mixtures
The v a l i d i t y
can
be
more
o f equation
7 is not
applied generally
sensitive,
the
higher
A p p l i c a t i o n s include,
limited
t o solvent
to b i n a r y solvent
the
polarity difference
for example,
continuous chromatography
the
mixtures
mixtures
involving water,
(65-66). The
between
determination
the
o f solvent
but
determination
two
is
components.
composition during
or c o l u m n d i s t i l l a t i o n .
10.3. Examination of Unusual Polarity Scales
10.3.1 P e r y l e n e
With
the
the
rate
increasing
Dyes as P o l a r i t y Probes
E^(30) p o l a r i t y scale the
enhancement
polarity of
of
the
a
medium.
negative
solvatochromism,
solvolysis r e a c t i o n ,
There
is
no
is taken
doubt
for i t corresponds e x a c t l y to c h e m i c a l e x p e r i e n c e
ability
of
reorientation
which
are
solvent
to
(17). H o w e v e r ,
sensitive
towards
stabilize
this
polar
is not
other
structures
of
or w i t h
the
i n d i c a t o r for
the
the
direction of
the
and is a measure o f
the
a
substrate
by
so
obvious
when
p o l a r i t y scales
solvent
effects.
This
is
scale o f B r o o k e r (51), the s o l v a t o c h r o m i s m
o f dye
Y scale
an
about
effect,
the
as
7, w h i c h
the
case
is m o r e
for
solvent
are
the
used
x
R
a measure o f
319
the
polarizability
of
the
solvent
than
for
the
solvation
effect
by
solvent
r e o r i e n t a t i o n (17).
<
>
This
effect
10
is even
more
pronounced
with
the
p o l a r i t y probe
hexylheptyl)-perylene-3,4:9,10-tetracarboxylic-bisimide
d i p o l e of the c h r o m o p h o r e
the
special
structure
measurements
are
of
(78)),
BHPD
dye
10,
(bis-N,N'-(l-
which
by the
possible
dye,
the
solubility
is
in a w i d e v a r i e t y o f
are
polar
energy
of
coefficient
possible
versus
a precise s p e c t r o m e t e r .
investigation of
for
this
as
low
is
so
high
solvents,
that
as
simple,
E^,(30)
-0.046!,
15
by a p p l i c a t i o n o f equation
a
linear
from
media
results
for
as
to w h a t
no
linear
there
is
values,
as
is
shown
points).
A
solution
3. A p l o t o f the
o f these
in
of
kind
of
solvents
of
the
(correlation
problem
(79)
the
concentration
was
c of
the
with
the
the c o n c e n t r a t i o n o f the component
measurements
be
checked
correlation
15
very
but can
can be
Fig.
the
with
e x c i t a t i o n energy ( E ^ ( B H P D ) )
r e l a t i o n only when
is used, but not w i t h
p o l a r i t y . The
A decision
to
solvatochromism
M o r e o v e r the solvent e f f e c t
fluorescence.
not
with
In ( c / c * +1) gives
polar c o m p o n e n t
lower
the
dye
excitation
no
because of the p o i n t s y m m e t r y o f the m o l e c u l e . Due
the
high to v e r y low p o l a r i t y . The s o l v a t o c h r o m i s m is not v e r y pronounced,
measured w i t h
has
are
g i v e n in T a b l e 4 for
pure
solvents and in T a b l e 5 for b i n a r y m i x t u r e s .
The
solvatochromism
solvent
values
the
(79),
can
be
but
not
used as
scale. The
of
BHPD
very
is v e r y
sensitive
to
sensitive
dipole
a novel p o l a r i t y scale
latter reflects
to
polarizability effects
effects.
Therefore,
for these e f f e c t s
mainly polarizability effects
but is s t i l l s l i g h t l y i n f l u e n c e d by solvent d i p o l e
effects.
and
the
of
the
E^(BHPD)
might
(17) o f the
replace
solvent,
320
Table 4: B H P D (dye 10) as a p o l a r i t y
solvent
probe for pure
max
[nm]
solvents
E (BHPD)
b )
E (30)
T
[kcal/mol]
T
[kcal/m
cyclohexane
516.6
55.34
39.9
diethyl
517.4
55.26
34.5
ether
acetone
519.2
55.07
42.2
acetonitrile
520.2
54.96
46.0
tetrahydrofuran
521.48
54.83
37.4
methanol
521.54
54.82
55.4
ethanol
521.81
54.79
51.9
1-propanol
523.25
54.64
50.7
1-butanol
523.5
54.61
50.2
1,2-dichIoroethane
524.3
54.53
41.9
methylene chloride
524.3
54.53
40.7
dimethylformamide
525.5
54.41
43.8
chloroform
526.4
54.31
39.1
toluene
526.57
54.30
33.9
d i m e t h y l sulphoxide
528.45
54.10
45.1
1-methylnaphthalene
541.15
52.83
35.3
a) M a x i m u m o f the long w a v e l e n g t h a b s o r p t i o n . - b) C a l c u l a t e d
a c c o r d i n g to e q u a t i o n 2. - c) See (1,4-6).
from
(
321
Table 5: B H P D (dye 10) as a p o l a r i t y probe for binary m i x t u r e s - a p p l i c a t i o n of
e q u a t i o n 6 w i t h Ρ = E - J B H P D ) at
solvents
3 1
20°C.
E
Q
[kcal/mol]
DMSO
-0.085
c*
E^(BHPD)
[m o l / l ] [ k c a l / m o l ]
0.103
54.37
toluene
DMSO
-1.413
24.06
54,79
-0.503
10.91
54.53
c )
-0.9974
c
d )
k
[mol/l]
8.45
-0.9963
-1.974
23.30
55.06
acetone
DMSO
-9.743
463
54.40
-13.3
328
54.81
-24.46
480
54.85
-2.16
7.30
54.29
-0.99996
22
-3.861
10.14
54.84
THF
1-methylnaphthalene
-0.9945
31
toluene
1-methylnaphthalene
-0.9974
20
methanol
1-methylnaphthalene
-0.9980
23
ethanol
DMSO
-0.9988
21
DMF
DMSO
0.9994
25
2
DMSO
DMSO
n
b )
21
DMSO
2
r
23
THF
CH C1
0
-0.9994
21
-0.499
0.534
54.12
-0.9989
21
8.45
322
a)
c*
[kcal/mol]
1-methylnaphthalene
E (BHPD)°
r
T
[mol/l] [kcal/mol]
n
b )
c
c )
d)
R
[r
-1.295
0.558
54.80
0.9995
1.06
1.032
0.296
54.83
0.9991
0.63
ethanol
1-methylnaphthalene
21
methanol
a) The f i r s t c o m p o n e n t is the m o r e p o l a r / p o l a r i z a b l e c o n c e r n i n g the E ^ ( B H P D )
scale. - b) C o r r e l a t i o n c o e f f i c i e n t .
- c) N u m b e r o f p o i n t s , d) C r i t i c a l c o n c e n t r a t i o n
for change in solvent s t r u c t u r e .
55
Ω
X
CQ
54
30
40
50
60
E (30)
T
F i g . 15: L a c k o f c o r r e l a t i o n b e t w e e n E ^ ( B H P D ) and E^(30) for the
s o l v e n t s o f T a b l e 4.
323
10.3.2 Sextet
R e a r r a n g e m e n t s as P o l a r i t y Probes
N e w p o l a r i t y scales can
solvent
effects
be developed
on m i c r o s c o p i c
on the basis ot* r e a c t i o n k i n e t i c s to measure
processes. The
and G r u n w a l d (3) on the basis of the
been
a
very
important
tool,
p r a c t i c a l applications; see
both
Y solvent
p o l a r i t y scale o f W i n s t e i n
solvolysis r e a c t i o n
for
the
for e x a m p l e
study
of
of t e r t - b u t y l chloride
reaction
mechanisms and
(1,10). L a t e r on it t u r n e d out that
problems with
this p o l a r i t y scale, for i t is l i m i t e d to very polar solvents.
there
mechanistic
were
intermediates,
nascent ions, see
for e x a m p l e
of spectroscopic
on
the
basis
polarity
because
a
is
aggregation
Berson
Ω scale
bimolecular
phenomena
different
and
are
Moreover
ion-pairs
specific
favoured. A generally
reaction
would
(45),
Diels-Alder Reaction,
a
by
steps,
for
there
acting
as
solvation of
the
(29). T h e r e f o r e secondary p o l a r i t y scales on the basis
chemical
The
of
it
a
caused
elementary
m e a s u r e m e n t s were
of
scales.
dependence
problems
r e v e r s i b i l i t y o f the
has
a good
which
is
reaction
(26).
be
and
Moreover
takes
only
a p p l i c a b l e p o l a r i t y scale
supplement
as
a
measure
p a r t i a l l y useful
therefore
there
is
to
for
principally
no
the
other
the
solvent
this
pupose,
sensitive
ionization
in
the
to
rate-
d e t e r m i n i n g step.
On
the
other
strongly
hand,
solvent
Beckmann
the
rate
dependent.
rearrangement,
t h o r o u g h l y studied
the
(82-88). The
w h i c h can easily be p r e p a r e d
CH -C=N
—
3
constant
The
CH -C=N
the
of
Beckmann
the
rearrangement
Chapman-variant
ketoxime
reaction
of
reaction
pathway
for a n t i - m e t h y l k e t o x i m e
(84-88), is g i v e n by equation
-
picrates,
of
has
is
the
been
picrates,
8.
CH -C=N-R — CH -C-N-R
3
^
(80)
(81)
thermal
CH -CEN-R
3
ox
of
mechanism
3
3
ox
ο χ
k
X = 2,4,6-Trinitrophenyl
The r a t e - d e t e r m i n i n g step o f the r e a c t i o n is the m i g r a t i o n o f R w i t h the f o r m a t i o n
of
a
nitrilium
ion
(89).
The
reaction
is
followed
by
two
fast
steps
-
the
r e c o m b i n a t i o n of the ion-pairs and the final
f o r m a t i o n o f the N - p i c r y l a c e t a m i d e s .
The
of
be
rate
constant
especially
Fischer
of
useful
the
as
Chapman-variant
a
solvent
the
p o l a r i t y probe
(90) for the i n v e s t i g a t i o n o f solvent e f f e c t s .
Beckmann
and
has
rearrangement
been
used
might
already
It is i m p o r t a n t t h e r e f o r e
by
that
324
the
rate-determining
strongly negative
of
about
30
step,
the
kcal/mol
for
the
endothermic
step d u r i n g the
that
transition
in
the
ionisation,
is
an
irreversible
reaction
(80)
alkyl
m i g r a t i o n are
r e a c t i o n should not
state
of
the
reaction
additional
indications
that
there
is
a
separation
between
which
is m a i n l y c o n c e n t r a t e d
in the
(88),
and
charge
on
this averages solvent
and
makes
coefficient
the
negative
specific
solvent
the
l e a v i n g group;
effects
less
an
be a l l o w e d . A n o t h e r advantage is
p o s i t i v e p a r t i a l charge,
the
-
r e a c t i o n e n t h a l p y o f -80 k c a l / m o l (91) and an a c t i v a t i o n e n t h a l p y
probable.
m i g r a t i n g alkyl
Finally
the
of e x t i n c t i o n a l l o w s r e a c t i o n k i n e t i c m e a s u r e m e n t s at
the
group
effects
large
molar
high d i l u t i o n
and
so the solvent is only l i t t l e p e r t u r b e d by the p o l a r i t y probe.
Alkyl
should
and
be
aryl
subsituents
chosen
systems. To e x c l u d e
effect
to have a
possible
the
possible
as
m i g r a t i n g groups.
substituents
test
for specfic
12
alkyl
solvent
effect
13
migration
with
aromatic
s o l v a t i o n of the m i g r a t i n g group
w h i c h e x c l u d e such an a t t a c k
on bridgehead d e r i v a t i v e s of v e r y d i f f e r e n t
11
The
formation of π - c o m p l e x e s
f u r t h e r any possible backside
one can use bridgehead
In o r d e r
are
to e x c l u d e
one
can
of a nucleophile.
compare
the
solvent
structures.
14
The r a t e c o n s t a n t s for the m i g r a t i o n of the o x i m e p i c r a t e s w i t h
these groups (92)
i n v e r y d i f f e r e n t solvents are given in T a b l e 6.
It can
easily be seen t h a t
11 ... 13 is about constant
the r a t i o o f the
migration aptitude
o f the
for d i f f e r e n t solvents. This is d e m o n s t r a t e d
substituents
by F i g . 16.
325
7 -I,
T a b l e 6: Solvent dependence of the r a t e constants (k· 10 [s ]) of m e t h y l k e t o x i m e
r
picrates
subst.
R:
1 -bicyclo-
25°C
1 -bicyclo-
[2.2.2]octyl
[3.2.l)octyl
(11)
(12)
solvent
methanol
at
35.2
(1)
1 -ada m a n l y 1 1 - b i c y c l o [3.2.2jnonyl
(13)
88.8
338.3
396.7
180.0
133.3
(2)
13.41
28.3
180.0
1 - b u t a n o l (3)
9.03
17.5
107.8
ethanol
DMSO
(4)
DMF
CH C1
2
CHC1
2
3
THF
lg
125.7
321.7
(14)
1833
2083
(5)
65.3
128.3
750.0
876.7
(6)
1 1.85
24.7
336.7
313.3
(7)
4.67
10.01
116.7
120.3
(δ)
4.05
5.15
29.5
36.8
k
F i g . 16: L i n e a r c o r r e l a t i o n b e t w e e n
for d i f f e r e n t pure solvents
lg k of 13 and lg k o f 11, 12, and
(see Table 6).
14
326
F i g . 17: L i n e a r c o r r e l a t i o n b e t w e e n
of
13 and t h e X
R
lg k of the B e c k m a n n
rearrangement
values of B r o o k e r (51).
/
lg
k
6G
50
E O0)
T
F i g . 18: L i n e a r c o r r e l a t i o n b e t w e e n
of
lg k of the B e c k m a n n
rearrangement
13 and the E ( 3 0 ) values of D i m r o t h and R e i c h a r d t (6) - • :
T
alcohols (lg k = 0 . 0 9 · Ε ( 3 0 ) - 9.4; r = 0.994), · : o t h e r
Τ
(lg k = 0 . 2 1 · Ε ( 3 0 ) - 13.3; r = 0.990).
Τ
solvents
327
So specific solvent
other
hand,
Table
6).
large
the
It was
shown
microscopic
X^-solvent
this
polarity
scale
are
in e a r l i e r
and
is
of
the substrates are essentially
fast
work
not
another
Brooker
given
important
However,
alcohols
with
is v e r y
in D M F and
that
these
p o l a r i z a b i l i t y (17,21). A useful
p o l a r i t y scale
phenomena
F i g . 18.
interactions
rearrangement
a
in
too;
F i g . 17.
this
single
one
-
the
On
reasonably
the
other
correlation
other
solvents.
the E ( 3 0 ) scale w i t h
T
solvents
act
measure o f
is d e m o n s t r a t e d
linear
for the
good linear c o r r e l a t i o n of
(51)
mainly
these
good
hand,
by
is
excluded. On
DMSO (nr. (4) and
the
solvent
but
This is in c o n t r a s t
orientation
two:
one
to the
the Y scale o f the S ^ l
by the fact t h a t w i t h the solvolysis r e a c t i o n the c h a r g e separation
is
l o c a l i z e d on o n l y a
few
atoms;
see
(93)
s o l v a t i o n of the educt.
This can be e f f i c i e n t l y
solvent,
by polar solvent
and
structure
especially
o f alcohols.
c h a r g e separation
see
equation
by
the
polar
hydrogen
So
values
lg k and
of
linear
also
for
for
other
rate
the
not
with
as
the
steep.
the
not
The
so
Beckmann-Chapman
scale
for
o f D M S O are added
p o s s i b i l i t y should
be
efficient
as
for
with
straight
the
the
the
number
S^2
reactions,
is observed
that
the
of
-
and
solvolysis
is of
lower
greater
therefore,
c o u l d be
and
the
atoms,
molecules
S^l-type
solvent
This result
could
the
important
explain
in some cases, when
high
the
bond
rearrangement
charge
to polar p r o t i c solvents,
excluded
of
line of F i g . 18, at
spread
is o b t a i n e d .
(94) w h i c h
discussion
a large
polarizability of
example
effect
is given
in the t r a n s i t i o n
o r i e n t a t i o n o f solvent
the second
of
further
for
solvolysis
l i k e the 0 - - - H - 0 - hydrogen
is spread over
stabilization
the
reactions,
is
one obtains
solvent
enhancement
s m a l l amounts
Finally,
bonding
for alcohols
correlation
strong
with
transition state
a
the
even
for e x a m p l e
to w a t e r .
reaction
of
rate
the
Beckmann rearrangement
in DMSO or D M F is not due to c o m p l e x a t i o n . This can
done
of
by
the
application
rearrangement
of
equation
13 is measured
3.
in the
To
this
binary
end,
the
rate
constant
mixture methylene
as a f u n c t i o n of the c o m p o s i t i o n . E q u a t i o n 3 is t r a n s f o r m e d
of
single
s o l v a t e d by the r e o r i e n t a t i o n o f
structures
8. In this case s o l v a t i o n by the
reactions.
importance
In c o n t r a s t ,
in the
for
the
with
correlations
r e a c t i o n of t e r t - b u t y l c h l o r i d e . A possible e x p l a n a t i o n for these d i f f e r e n c e s
state
their
is
correlation
linear
obtained,
by
effects
the
(5) of
of
be
the
chloride/DMSO
t o e q u a t i o n 9.
k
[9)
k°
U
p
328
k
is the
rate
component
equation
constant
with
for
lower
the
rearrangement
polarity
have been defined
(methylene
previously.
in the
chloride).
With
equation
m i x t u r e and
The
other
k
in the
symbols
9 a linear
relation
pure
of
the
between
lg k / k ° and In (c / c * + 1) is obtained.
-0. 1 ί
1
G
1
0. 2
1
•. 4
1
In
1
0. a
0. 6
(Cp/9.
1
1-1)
Fig. 19: Linear c o r r e l a t i o n between lg k / k ° and in ( c ^ / c * + 1) a c c o r d i n g
t o equation
The
linear
correlation
correlation
DMSO.
coefficient
The
component
9 for the m i x t u r e C h ^ C ^ / D M S O (oxime p i c r a t e
c*
value
ranges
in
0.991
as
from
an
Fig.19
for
(E^ =
14 points)
indicator
medium
0.863 k c a l - m o l Κ
to
indicates
for
large,
the
see
a
normal
interaction
(17), just
c* =
as
9.73
solvent
with
the
for
13).
mol-l
effect
more
a normal
\
by
polar
solvent
effect.
10.4. C a l c u l a t i o n of Molar Concentration from Weight Percentages
Concentrations
For many
in binary
mixtures
purposes, for example
are
often
given in the
literature
for the a p p l i c a t i o n of equation
in w e i g h t
3 or 6, the
%.
molar
329
concentration
density
of
of one component
the
mixture.
c o n c e n t r a t i o n s are
is r e q u i r e d
However,
in
and
many
this can
cases
the
be
densities
of
binary
LiClO^/Ether,
in
which
measurements
(see
from
at
from
only
the
a
few
known.
T h e problem can be solved by the a p p l i c a t i o n of equation
the
calculated
densities
mixtures
the
above).
The
(37) and p l o t t e d against
(67).
This
concentrations
densities
is
of
for
6, w h i c h
demonstrated
LiCIO^
nine salt
were
holds also
for
the
needed
concentrations
for
for
example
polarity
were
taken
In (c / c * + 1) as in F i g . 20.
1.3-1
RHO
In
(Cp/14. 08
Fig.20: D e n s i t i e s of solutions of L i C l O ^ in ether
+
1)
(37) as a f u n c t i o n of
In (c / c * + 1) w i t h c as the m o l a r c o n c e n t r a t i o n of L i C l O .
Ρ
Ρ
4
(E
= 1.414293, c* = 14.08 m o l / l , p ° = 0.706135, r = 0.99996,
D
η = 9).
W i t h the linear c o r r e l a t i o n o f F i g . 15 the density o f a s o l u t i o n o f L i C l O ^ in ether
can
be
calculated directly
high p r e c i s i o n .
and
from
t h i s the
content
in w e i g h t
% is
found
with
330
The converse c a l c u l a t i o n of the c o n c e n t r a t i o n
Therefore
equation
6a
has
to
be
transformed
m o l e c u l a r w e i g h t of L i C l O ^ and G the c o n t e n t
ρ
c
= E
Ρ
6
In
D
(c /c*
- M W / G = EL.- I n
D
=
E
D
'
l
+
p
n
(c
1)
p
(c /c*
+
p
from
to
weight
% is m o r e c o m p l i c a t e d .
equation
10
MW as
+ p°
/c*
1)
+
1)
+ p°
[10]
+
p°
-
c 'IvW/G
[ I I ]
p
10 c a n n o t be solved d i r e c t l y t o g i v e the c o n c e n t r a t i o n
by
transformation
to
the
[6a|
Equation
the
with
by w e i g h t .
equation
11
the
concentration
in closed f o r m ,
can
be
but
iteratively
d e t e r m i n e d using a c o m p u t e r p r o g r a m w h i c h m i n i m i z e s the residue δ .
10.5. Studies of R e a c t i o n Mechanisms
10.5.1 Solvolysis of t e r t - B u t y l C h l o r i d e in E t h a n o l - W a t e r
The discovery
o f the
W i n s t e i n r e l a t i o n s h i p (3), w h i c h
is based on the solvolysis o f
t e r t - b u t y l c h l o r i d e , p l a y e d a key r o l e in the d e v e l o p m e n t
o f the e m p i r i c a l p o l a r i t y
concept.
of
Subsequently
Winstein
studied
the
influence
solvolysis o f t e r t - b u t y l c h l o r i d e in e t h a n o l / w a t e r
activation,
AG^, of this r e a c t i o n
curvature,
as the w a t e r c o n t e n t o f the m i x t u r e is increased:
AS^, however,
This unusual
and surprising behaviour led to numerous
the A G ^ value,
functional
increases as a m o n o t o n i c f u n c t i o n ,
which
course,
Since
is composed
whilst
the
speculations
without
strong
the
(10,23,93,96-101)
been g i v e n in (17). It seems to c o n t r a d i c t
the
of enthalpy
apparently
solvolysis
e q u a t i o n 6 appears a p p r o p r i a t e .
of
the
the course of Δ H ^ a n d
of
and
entropy
experience
terms,
s i m p l e r q u a n t i t i e s Δ Η ^ and
tert-butyl
chloride
is
changes in the m e d i u m , an analysis o f W i n s t e i n and Fainberg's
AG^gg
on
energy o f
is more c o m p l e x and m a x i m a and m i n i m a o c c u r (see Fig.21).
and an e x p l a n a t i o n has
complicated.
temperature
m i x t u r e s (95). The free
has
a
A S ^ appear
sensitive
to
that
simple
so
polarity
measurements using
As shown in F i g . 2 2 , the free e n t h a l p y o f a c t i v a t i o n
solvolysis o f t e r t - b u t y l c h l o r i d e in e t h a n o l / w a t e r
m i x t u r e s and
the
331
correspondingly
by equation
proportional quantities
In l ^ g g
o
r
^
c
a
n
^
e
described
quantitatively
6 as a f u n c t i o n of c o m p o s i t i o n .
Fig.21: T h e r m o d y n a m i c data for the solvolysis of t e r t - b u t y l c h l o r i d e in
ethanol-water
An
interesting
point
is,
(95).
as
with
other
polarity
regions of v a l i d i t y of e q u a t i o n 6 are observed
*
25
mol/l
anomalous.
(double
lines).
Thus
the
free
scales
(see
section
5),
that
two
w i t h a c r i t i c a l t r a n s i t i o n point at
enthalpy
of
activation
shows
c^
nothing
The high precision o f W i n s t e i n ' s k i n e t i c m e a s u r e m e n t s must be stressed;
t h i s is expressed by the c o n f o r m i t y o f the e x p e r i m e n t a l
points to the
lines in F i g .
22.
The
activation enthalpy ΔΗ
calculated
from
0°
and
and
the
the r a t e c o n s t a n t s at
t o 45 v o l . % w a t e r
at
1
25°C.
at
It
activation entropy Δ S ' o f
only t w o temperatures
2 5 ° and 5 0 ° C and in the range o f 50 t o
can
be
shown
that
equation
6
holds
the
reaction
(95); in the
were
range 0
100 v o l . % w a t e r
for
the
series
of
332
measurements
at
0°C
slightly different
from
and
50°C
(see
Table
the measurements at
7);
their
and
c*
values
are
only
25°C.
AS'
In (c /c*+ 1)
D
Fig.22: A n a l y s i s of solvolysis d a t a o f t e r t - b u t y l c h l o r i d e in
according
to equation
T a b l e 7: A p p l i c a t i o n of equation
Range
b)
c)
ethanol-water
6.
6 to the W i n s t e i n scale.
c*
d)
yO
e)
25
I
2.9
11.6
-1.79
0.9991
50
I
2.4
9.7
-0.52
0.9998
7
0
II
2.6
0.001
(-26.9)
0.9845
12
0.001
(-26.1)
0.9935
10
0.9996
6
II
25
+
(AH )
b )
a) T e m p e r a t u r e
value
2.7
I
for
1
-0.944 *
in
ethanol.
°C
.
b) See
f) C o r r e l a t i o n
energy, i) In k c a l / m o l .
0.26
text,
(26.1)
c) In Y
coefficient,
h , i )
units,
d) m o l / l .
g) N u m b e r
of
9
e) e x t r a p o l a t e d
points,
Y
h) A c t i v a t i o n
333
The change of t e m p e r a t u r e
data
was
conducted
temperature
with
the
was
value
in
25°C
from
0 ° to 5 0 ° C
water
for the
concentrations
in a l l cases). By chance
o f c,
corresponding
to the
c a l c u l a t i o n o f the a c t i v a t i o n
of
ca.
25
mol/l
(the
this value coincides
intersection
second
approximately
p o i n t o f the
t w o lines in
+
1
F i g . 22. Based on this the course of the f u n c t i o n a l c u r v e of Δ Η
in F i g . 21 can
be
characterized.
For c
< c^ (region I , Δ Η ^ ~ In 1^98 - In ^ 3 2 3 ) ' A H ^ is a m o n o t o n i c f u n c t i o n o f
Ρ
ο
the w a t e r c o n t e n t . The E^ and c* values of In k are only s l i g h t l y d i f f e r e n t at 25
and 50 C. Thus even
the solvent dependence o f Δ Η '
is a p p r o x i m a t e l y described
e q u a t i o n 6 ( t a b l e 7). In this c o r r e l a t i o n the expansion
i n t o account,
since
temperature
In
the
at
a given c o n c e n t r a t i o n
o f the l i q u i d must
in vol % t h e m o l a r w a t e r
be
by
taken
content
is
dependent.
region c
dependence
composition
* c^
p
on
a number
concentration.
and
the
of factors
Going
temperature
cause Δ Η ^ t o have a r a t h e r
beyond
change
measurements for d e t e r m i n i n g Δ Η ^ are
c^,
the
temperature
have
the
effect
complex
dependence
that
the
of
individual
made p a r t l y in region I and region I I . This
+
results in the unusual
Finally,
values
in
on
the
region
the
m a x i m u m at
solvent
A S ^ (Figs.
difference
c
> c,
ρ
κ
(region
composition
is
v e r y high w a t e r c o n t e n t
not be discussed
of
1
f u n c t i o n a l course of Δ Η .
here;
22
this is d e a l t
and
23),
can
II) a
monotonic
observed,
as
in
region
of
I . The
the
with
be
in (96,102). T h e c o n c e n t r a t i o n
explained
in
an
analogous
ΔΗ^
additional
may be a result o f m i x i n g problems and
will
dependence
manner
to
the
b e t w e e n A H ^ and A C J .
The solvolysis o f t e r t - b u t y l c h l o r i d e in e t h a n o l - w a t e r ,
characteristic
w h i c h can
studies
dependence
of o t h e r solvolysis r e a c t i o n s
be t r e a t e d
in
them.
ethanol/water,
mixtures
here at
present
the
reference
problems
i f the
point
of
temperature
the
length, is
(23,101-102,103-104),
in a s i m i l a r way, and is also g e n e r a l l y t y p i c a l of
Furthermore
may
in solvent
discussed
Y
mechanistic
scale,
80
vol %
differs substantially
from
25°C.
Another
result
of
influenced
by
should,
least
since
at
the
the
previous
polarity of
in solvent
the
analysis
is
medium,
mixtures,
be
of
the
general
free
a simpler
these always c o n t a i n c o n t r i b u t i o n s f r o m
the
interest:
energy
parameter
of
for
reactions
activation, AG^,
than Δ Η ^ and Δ S^,
t h e r m a l expansion
o f the
liquid
334
which
are
not
reaction-specific.
Special
attention
is
therefore
required
when
a
solvent m i x t u r e e x h i b i t s t w o regions o f v a l i d i t y o f e q u a t i o n 6 (cf. also s e c t i o n 5.).
10.5.2 N o n - l i n e a r W i n s t e i n R e l a t i o n s h i p s
The
results
studies:
as
just m e n t i o n e d
a
mechanistic
criterion,
r e l a t i o n s h i p s , e.g.
straight
line,
see
a p p l i c a t i o n s o f e q u a t i o n 4 to
by
mechanistic
the W i n s t e i n r e l a t i o n s h i p is o f t e n
analogy
to
(3,105-108). In the f i r s t
other
place
linear
free
energy
t o solvent
polarity effects
leading
range
of
mechanism
(LFE)
polarity
different
measurements,
is
solvents.
reactions
are
used
In
as
order
usually studied
studied
to increase or decrease o f
to the t r a n s i t i o n s t a t e . F u r t h e r m o r e ,
solvent
in
and is o f t e n r e l a t e d
an
to
used
the value m , the slope o f the
is i n t e r p r e t e d as a measure o f the s e n s i t i v i t y o f the r e a c t i o n
separation
large
lead to o t h e r
linear c o r r e l a t i o n o f a process w i t h
charge
a linear c o r r e l a t i o n over a
indication
obtain
a
using solvent
of
uniform
sufficient
reaction
number
mixtures, often
of
ethanol-
water.
As
the
p o l a r i t y o f these m i x t u r e s is governed
t o redefine
by e q u a t i o n
the previously m e n t i o n e d m e c h a n i s t i c
6, i t seems
worthwhile
c r i t e r i a on the basis o f equation
6.
From
equation
6,
the
slope
m
of
a
relationship
processes P j and P 2 is described by e q u a t i o n
dP.
η
=
d
A
E
( c
- ^ - 2
n
=
P
E
2
good
D2
linear
+ c*
|
(
c
2
+
p
C
12 is independent
must be
fulfilled:
1.
c*
The
values
equation
12
independent.
of
in
polarity-dependent
[12]
V
between
Pj
and
P2
requires
of c , and hence one of
both
brackets
The
two
)
—
relationship
equation
between
12.
processes
are
very
logarithmic term
are
the
similar
similar
following
(c*j
and
in e q u a t i o n
that
the
6 has
Ä
c
*2^-
slope
the
slope
three
^he
is
are
t
e
r
p
m
s
o
f
concentration
an a p p r o x i m a t e l y equal
Pj
and
l i n e a r l y dependent.
2. The c* values
(c*
in
conditions
n u m e r i c a l value in both cases for a g i v e n value o f c . Consequently,
P2
m
c*
9
are d i f f e r e n t in both cases, but considerably larger t h a n
>> c
m
a
x
) . The c
values
in e q u a t i o n
12 become
small
3
c^™ *
compared
335
to the c* values
for any e x p e r i m e n t a l l y possible c o n c e n t r a t i o n
becomes c o n c e n t r a t i o n
and P 2 as a T a y l o r series, w h i c h
between
3.
The
Ρ and c
c*
relevant
c* values
of
one
are
these
there
is
both
concentrations.
very
Equation
found, e.g.
with
is
the
often
occurs
fulfilled.
W i n s t e i n scale,
in m e c h a n i s m ,
t o another
or even
upon
However,
if
medium,
Even
more
c o m p l i c a t e d is
when
mixtures
observed
binary
with
critical
p a r t i c u l a r l y when
mixtures
such
as
transition
solvolysis
and
Brown
good
tosylates
higher
water
regular
contents,
break
participation
in
with
the
a change
are
the
The
to
deviations
in r e a c t i o n
?
a
non-linear
necessarily
cf.
follow
transition
also
from
(109). This
lines)
are
out
and
used.
in
These
c
p
are
frequently-used
ethanol-water
is described
(see
here.
the solvolysis o f i s o p r o p y l , c y c l o h e x y l ,
Y scale up
relationship,
by
its dependence on
carried
free
are
Fig.
energies
a water
1
mechanism
of
content
observed,
in
(110).
was
be c o n t r a d i c t e d by the behaviour o f isopropyl t o s y l a t e
shielded and easily accessible to n u c l e o p h i l i c a t t a c k ,
These were
and
1,4-dioxan-water
(110) studied
substantial
LFE
(double
reactions
in e t h a n o l - w a t e r .
linear c o r r e l a t i o n w i t h
solvent
for the m i x t u r e e t h a n o l - w a t e r
and c o w o r k e r s
2-adamantyl
points
acetone-water,
T a b l e 2) (19,65). A n e x a m p l e
Bentley,
o f the
0
simplified
a continuous
v a r y i n g the
P .
with
In each case Ρ
p
P .
is only o b t a i n e d by e s t i m a t i n g the c* values.
influence
can
of c .
it does not
that
and
compared
and
information
the
12
also P .
Pj
A linear relationship
small
and m becomes independent
conditions
is a change
mechanism
but
slope
both for
and l i k e w i s e a linear r e l a t i o n b e t w e e n P .
l i n e a r l y dependent and t h e r e f o r e
three
and the
be expanded
as usual is t r u n c a t e d .
different,
n e g l e c t i n g the
relationship
that
are
experimentally
and In c
One
results,
values
E q u a t i o n 6 can
independent.
activation
o f ca.
which
represent
Nucleophilic
discussed.
show
50%. A t
a
solvent
This appears
to
, w h i c h , because it is hardly
shows the smallest
deviations.
f i n a l l y a t t r i b u t e d to a s p e c i f i c s o l v a t i o n o f the l e a v i n g anion, since
the
c o r r e s p o n d i n g mesylates
show linear r e l a t i o n s h i p s w i t h
T h e solvolysis data can
be analysed
r e l a t i o n s h i p is observed
at a w a t e r c o n t e n t o f ca. 50% and can be i n t e r p r e t e d as a
critical
t r a n s i t i o n point (see
section
on the basis o f e q u a t i o n
5). Since
s o l v o l y s i s of t e r t - b u t y l c h l o r i d e (Y scale)
the
E
n
values
according
to e q u a t i o n
the Y scale.
6 . The break
s i m i l a r c* values
are
and the various tosylates,
12 is s u f f i c i e n t . For
in L F E
found for
the
a discussion o f
t e r t - b u t y l chloride
and
336
cyclohexyl
equal
mesylate
(Table 8, Nos.
1 and 2), the r a t i o of the
in region I and 11. Thus an a p p r o x i m a t e
entire
water
concentration
range.
The
relatively
explains the s l i g h t d e v i a t i o n s at high w a t e r
low
E
c
DI
b)
value
of
No.
k
Ε
m
c)
c*
c
a)
t e r t - B u t y l chloride
6.7
11.6
-16.1
6.3
0.001
Cyclohexyl
4.7
10.8
-17.3
4.6
(0.001)
3
2-Adamantyl
4.7
8.3
-21.6
9.9
0.001
4
2-Propyl
3.2
12.9
-14.7
5.0
(0.001)
5
Cyclohexyl
8.3
32.8
-16.8
7.7
0.001
tosylate
tosylate
a) In In k2^g u n i t s , b) In m o l / l . c) Value for pure a l c o h o l e x t r a p o l a t e d
e q u a t i o n 6. d) E s t i m a t e d , since
The
tosylates,
however,
t w i c e as
must
exist
Nos.
1 and
at
large
behave
c^,
as
quite
differently
-7.16
-
d)
-11.7
-
d)
-9.1
from
(Table 8,
coincides
with
Nos.
1,3,
and
4).
value
that
of
breaks in the
of cyclohexyl tosylate
No. I .
is not s u f f i c i e n t . D e t a i l e d analysis,
however,
(Table
A p p r o p r i a t e l y the
shows,
the same way as Nos. 3 and 4. The solvolysis r e a c t i o n
can be analysed
in an e x a c t l y analogous
that
Here,
also,
linear,
with
two
mechanism
and
the
straight
lines.
to
This
E^
No. 5 behaves in
mixtures
manner.
L F E relationship w i t h
transition
8,
resulting
in a c e t o n e - w a t e r
Sridharan and V i t u l l o (108) studied the solvolysis o f g e m i n a l dihalides in
water.
are
relationships
L F E r e l a t i o n s h i p is c o n s i d e r a b l y worse. In this case a s i m p l e c o m p a r i s o n o f the
values
The
in L F E r e l a t i o n s h i p s whose slopes
those in region I . T h e r e f o r e ,
F i g . 1 in (110). The c*
5) no longer
,
too few points are a v a i l a b l e for c a l c u l a t i o n .
much higher values of E ^ in region II result
almost
0 1
c)
b)
1
tosylate
even
In k
II
2
mesylate
2
the
Region 11
In
*l
a)
E^
for
25°C.
Region I
Substrate
is almost
contents.
T a b l e 8: Solvolysis (95,110) in solvent m i x t u r e at
No.
values
L F E r e l a t i o n s h i p is observed
was
the
Y scale
attributed
n u c l e o p h i l i c solvent
to
turned
a
out
change
p a r t i c i p a t i o n . I t can
1,4-dioxanto be
of
be
non­
reaction
shown,
337
however,
with
that
the
critical
transition
point
of
1,4-dioxan-water
mixtures
coincides
the point of i n t e r s e c t i o n o f the t w o lines.
The last
examples show
mechanistic
Therefore,
that
the e x i s t e n c e o f an L F E r e l a t i o n s h i p is only a l i m i t e d
c r i t e r i o n for s t u d y i n g solvent
when
e x a m i n i n g such
dependent
processes,
binary
processes in solvent
mixtures
should
mixtures.
be checked
for
c r i t i c a l t r a n s i t i o n points.
10.6 Further Applications
By means of equation
3 or 6 the
p o l a r i t y o f a m e d i u m can
a problem, when r e a c t i o n mechanisms are d i f f e r e n t
example
in
is the
non-polar
polar
media,
media,
generation
thermolysis
of percarboxylic
generally
however,
in polar
proceeds
heterolyis
media
esters,
according
other
cases,
where
the
addition
of
a
the
small
small
amount
extent
(the
of
polar
relationship
additive,
c
is
roughly
should
of
formation;
in
mechanism.
If
the
polarity of
polar
additive
should
p
<
> c* this is t r u e only to a
logarithmic).
In
be
adjusted
to
in c h r o m a t o g r a p h i c
methods,
where
p
Criegee
(53), c* plays a key r o l e . I f c
p o l a r i t y is s t r o n g l y dependent on c , but i f c
minimum
(111), w h i c h ,
radical
the
to
media. A n
prevails.
enhance the solvent p o l a r i t y as m u c h as possible
c*,
to
i t is advantageous to adjust
the m e d i u m t o a point at w h i c h homolysis just
In
for a r e v i e w see
homolytically with
occurs
is desired,
be e x a c t l y adjusted
in polar or non-polar
order
approximately
to
employ
a
( i f c*
is
c*
small).
Other
applications
are
a d d i t i v e increase the p o l a r i t y o f a solvent
markedly,
where
the
one
can
get
more
i n f o r m a t i o n about
the a p p l i c a t i o n o f the k n o w l e d g e about
11. O U T L O O K - F U R T H E R
A p a r t from
in
many
chemistry,
which
equation
of copolymerisates,
Another
field
is the
mixtures. Initial
amounts o f
in p o l y m e r
polar
chemistry
p a r a m e t e r s o f c o p o l y m e r i z a t i o n by
binary mixtures.
EXTENSIONS
the previously described
others
small
or are
can
6 might
only
areas o f c h e m i s t r y ,
be
mentioned
be v e r y useful,
e.g
for the
a d d i t i v e s of p o l y m e r s and p o l y m e r
extension
experimental
though t h e r e are c o m p e n s a t i n g
o f the e q u a t i o n
(112).
here.
6 can
For
planning and
be
the
utilized
polymer
investigation
blends.
to t e r n a r y
results d e m o n s t r a t e t h a t
effects
equation
briefly
and
even
more
this is in p r i n c i p l e
complex
possible
338
Finally,
pure
the
equation
substance.
(113).
The
This
latter
might
has
can
be
be e x t e n d e d
been
even
demonstrated
thought
to
be
to e x p l a i n the
for
pure
polarity of a
gases
(66)
a binary m i x t u r e of
the
single
and
n-alkanols
polar
OH-group
w i t h the h y d r o c a r b o n residue.
I f one c a l c u l a t e s the m o l a r c o n c e n t r a t i o n o f the O H -
groups
m o l e c u l a r w e i g h t and density
in pure alcohols
from
the
w i t h a binary m i x t u r e o f alcohols and a l i p h a t i c hydrocarbons
One
m i g h t expect
increments
of
its
to
be able
polar
to c a l c u l a t e
f u n c t i o n a l groups.
the
same behaviour
(113) is found.
p o l a r i t y o f a pure
These
as
calculations,
substance
however,
from
are
non-
2nd.
ed.,
linear.
12.
REFERENCES
1. C . R e i c h a r d t ,
Solvents
and
Solvent
Effects
in O r g a n i c
Chemistry,
V e r l a g C h e m i e , W e i n h e i m , 1988.
2. E . D . A m i s and J . F . H i n t o n , Solvent E f f e c t s on C h e m i c a l Phenomena,
Press, New Y o r k ,
1973.
3. E . G r u n w a l d and S.Winstein, J . A m . C h e m . S o c ,
4. K . D i m r o t h , C . R e i c h a r d t ,
(1963)
Academic
70 (1948) 846-846.
T.Siepmann and F . B o h l m a n n , L i e b i g s A n n . C h e m . , 661
1-37.
5. C . R e i c h a r d t ,
Angew.Chem.,
91
(1979)
119-131; A n g e w . C h e m . I n t . E d . E n g l . , 18
(1979) 98-110.
6. C . R e i c h a r d t ,
Liebigs A n n . C h e m . , (1983) 721-743.
7. C . R e i c h a r d t , M.Eschner and G . S c h ä f e r ,
8. K . D i m r o t h and C . R e i c h a r d t ,
T o p . C u r r . C h e m . , 11 (1968)
9. A . S t r e i t w i e s e r Jr., C h e m . R e v . ,
10. K . S c h w e t l i c k ,
1-73.
56 (1956) 620-725.
Kinetische
aktionsmechanismen,
L i e b i g s A n n . C h e m . , (1990) 5 7 - 6 1 .
Methoden
zur
Untersuchung
D e u t s c h e r V e r l a g der Wissenschaften,
11. Z . B . M a k s i m o v i c , C . R e i c h a r d t
and
A.Spiric,
von
Re-
Berlin,
1971.
Z . A n a l y t . C h e m . , 270
(1974)
Theorie
Reaktionen,
100-
104.
12. V . A . P a l m ,
Grundlagen
der
quantitativen
organischer
A k a d e m i e - V e r l a g , B e r l i n , 1971.
13. A . H . F a i n b e r g and S.Winstein, J . A m . C h e m . S o c ,
78 (1956) 2770-2771.
14. H.Elias, G.Gumbel, S.Neizel and H . V o l z , Z . A n a l y t . C h e m . , 306 (1981) 240-244.
15. T . M . K r y g o w s k i ,
P.K.Wrona,
(1985) 4519-4527.
U.Zielowska
and
C.Reichardt,
Tetrahedron,
41
339
16. H.Langhals, N o u v . J . C h i m . , 5 (1981) 97-99.
17. H.Langhals,
Angew.Chem.,
94
(1982)
739-749;
A r . g e w . C h e m . I n t . E d . E n g l . , 21
(1982) 724-733.
18. I . A . K o p p e l
and V . A . P a l m
i n : N . B . C h a p m a n and J.Shorter, Advances
in Linear
Free Energy Relationships, Plenum Press, London, 1973, pp. 203-280 .
19. H.Langhals, C h e m . B e r . ,
114 (1981) 2907-2913.
20. H.Langhals, Z . P h y s . C h e m .
21.
(Wiesbaden),
127 (1981) 45-53.
H.Langhals, N o u v . J o u r n . C h i m . , 5 (1981) 511-514.
22. M . C h a s t r e t t e , T e t r a h e d r o n ,
35 (1979)
1441-1448.
23. M . J . B l a n d a m e r and J.Burgess, Chem.Soc.Rev.,
4 (1975) 55-75.
24. D . M . M a t t h e w s , J . D . H e f l e y and E.S.Amis, J.Phys.Chem., 63 (1959)
25. H.Langhals, T e t r a h e d r o n , 43 (1987)
1236-1247.
1771-1774.
26. M.C.Rezende,
D . Z a n e t t e and C . Z u c c o , T e t r a h e d r o n L e t t . ,
27. M . C . R e z e n d e ,
C . Z u c c o and D . Z a n e t t e , T e t r a h e d r o n , 41 (1985) 87-92.
28. M.C.Rezende,
T e t r a h e d r o n , 44 (1988) 3513-3522.
29. R . W . H o f f m a n n ,
Aufklärung
Thieme Verlag, Stuttgart,
von
Reaktionsmechanismen,
1st.
ed.,
Georg
1976.
30. T h . F ö r s t e r , N a t u r w i s s e n s c h a f t e n ,
33 (1946) 166-175.
31.
R.W.Taft,
M.J.Kamlet,
(1984) 3423-3424.
J.L.M.Abboud
and
Progr.Phys.Org.Chem.,
13
(1981)
485-630.
32. I . A . Z h m y r e v a ,
V.V.Zelinskii,
Dokl.Akad.Nauk.S.S.S.R.,
129
V.P.Kolobkov
(1959)
1089-1092;
and
N.D.Krasnitskaya,
Chem.Abstr.,
55
(1961)
26658L
33. V . V . Z e l i n s k i i ,
V.P.Kolobkov
and L . G . P i k u l i k ,
Opt.Spectrosk.
1 (1956)
161-167;
C h e m . A b s t r . , 51 (1957) 4148b.
34. T.V.Veselova,
I.I.Reznikova,
A.S.Cherkasov,
V.I.Shirokov,
Opt.Spectrosk.,
25
(1968) 98-103; C h e m . A b s t r . , 96 (1968) 72593t.
35. S.Winstein, P . E . K l i n e d i n s t , Jr.
and
C.G.Robinson,
J.Am.Chem.Soc,
83
885-895.
36. H . H . W i l l a r d and G . F . S m i t h , J . A m . C h e m . S o c ,
37. L . G . S i l e n and K . E k e l i n , A c t a Chem.Scand.,
45 (1923) 286-297.
7 (1953) 987-1000.
38. Y . P o c k e r and R . F . B u c h h o l z , J . A m . C h e m . S o c ,
39. C . A . K r a u s and L . E . S t r o n g , J . A m . C h e m . S o c ,
92 (1970) 2075-2084.
72 (1950) 166-171.
40. Y . P o c k e r and R . F . B u c h h o l z , J . A m . C h e m . S o c ,
92 (1970) 4033-4038.
41.
99 (1977) 2284-2293.
Y . P o c k e r and D . L . E l l s w o r t h , J . A m . C h e m . S o c ,
42. B.R.Sundheim, Fused Salts,
M c G r a w - H i l l Book C o . J n c , N e w Y o r k ,
1964.
(1961)
340
43. Μ . B l a n d e r , M o l t e n Salt C h e m i s t r y ,
44. R . B r a u n and J.Sauer, C h e m . B e r . ,
45. J . A . B e r s o n ,
Interscience
119 (1986)
Z . H a m l e t and W . A . M u e l l e r ,
46. H.Langhals,
Angew.Chem.,
94
Publishers,
452-453;
(1982) 432-433; H.Langhals, A n g e w . C h e m . S u p p l . ,
47. H.Langhals, T e t r a h e d r o n
48. H.Langhals,
49. S.Wold,
Z.Phys.Chem.
Kem.Tidskr.,
[J.Shorter,
reference
Lett.,
multiple
84 (1962)
297-304.
Angew.Chem.Int.Ed.Engl.,
1982,
21
1138-1144.
339-342.
( L e i p z i g ) , 268 (1987) 91-96.
84
Correlation
to
(1986)
1964.
1269-1275.
J.Am.Chem.Soc,
(1982)
New York,
(1972)
Analysis
34-37;
of
regression,
Chem.Abstr.
Organic
77
Reactivity,
Research Studies Press,
(1972)
with
3961 l q
particular
Wiley,
Chichester,
1982].
50. J . A . H o w a r d and K . U . I n g o l d , C a n . J . C h e m . ,
51. L.G.S.Brooker,
G.H.Keyes
and
42 (1964)
D.W.Heseltine,
1044-1056.
J.Am.Chem.Soc,
73
(1951)
5350-5358.
52. E . L i p p e r t ,
W.Lüder,
F.Moll,
W.Nägele,
H.Boos,
H.Prigge
and
I.Seibold-
B l a n k e n s t e i n , A n g e w . C h e m . , 73 (1961) 695-706 and r e f e r e n c e s c i t e d
53. H.Langhals,
Nachr.Chem.Tech.Lab.,
28 (1980) 716-718; C h e m . A b s t r . ,
therein.
95 (1985)
R9816q.
54. K . F r i t z s c h e and H.Langhals,
Chem.Ber.,
55. H.Langhals and S.Pust, C h e m . B e r . ,
56. T . P o t r a w a
and H.Langhals,
57. N.G.Bakhshiev,
16
2275-2286.
118 (1985) 4 6 7 4 - 4 6 8 1 .
Chem.Ber.,
Opt.Spectrosk.
117 (1984)
120 (1987)
(1964)
1075-1078.
821-832;
Chem.Abstr.
61
(1964)
9043g.
58. H.Langhals,
N o u v . J o u r n . C h i m . , 6 (1982)
285-286.
59. P.Suppan, N o u v . J o u r n . C h i m . , 6 (1982) 285.
60. J.G.Dawber,
(1988)
61. A.I.Vogel,
London,
J.Ward
and
R.A.Williams,
J.Chem.Soc,
Faraday
Trans. 1,
84
713-727.
A Textbook
of Q u a n t i t a t i v e
Inorganic Analysis, 4 t h . ed.,
Longman,
1978, p. 668.
62. K . D i m r o t h and C . R e i c h a r d t ,
63. B.P.Johnson,
Anal.Lett.,
B.Gabrielsen,
Z . A n a l y t . C h e m . , 215 (1966) 344-350.
M.Matulenko,
19 (1986) 939-962; C h e m . A b s t r . ,
J.G.Dorsey
105 (1986)
64. H.Langhals,
Z . A n a l y t . C h e m . , 305 (1981) 26-28.
65. H.Langhals,
Z . A n a l y t . C h e m . , 308 (1981)
441-444.
66. H.Langhals,
Z . A n a l y t . C h e m . , 310 (1982)
427-428.
67. H.Langhals, Z . A n a l y t . C h e m . , 319 (1984)
293-295.
and
164184a.
C.Reichardt,
341
68.
H.Langhals, A n a l . L e t t . , 20 (1987)
1595-1610.
69. H.Langhals, E . F r i t z and I . M e r g e l s b e r g , Chem.Ber.,
113 (1980)
3662-3665.
70. T.Mukhopadhyay and D.Seebach, H e l v . C h i m . A c t a , 39 (1982) 3 8 5 - 3 9 1 .
71. J.F.Schmutz, Chem.Eng.News,
72.
16th Jan.
(1978) 3 9 - 4 1 .
H.Spencer, C h e m . I n d . , (1979) 728-733.
73. D.Ziessow,
Berlin,
On-line
Rechner
in
der
Chemie,
1st.
ed.,
Walter
de
Gruyter,
1973.
74. R . B r d i c k a ,
Grundlagen
der
Physikalischen
Chemie,
10th.
ed.,
VEB,
Berlin,
1972, p. 252, 503.
75. J.M.Vandenbelt,
J.Opt.Soc.Am.,
51
(1961)
802-803;
Chem.Abstr.
55
(1961)
193601.
76. H.Beyer and W . W a l t e r , L e h r b u c h der Organischen
Verlag, S t u t t g a r t ,
Chemie,
20th. ed., S . H i r z e l
1984, p. 555.
77. M.Klessinger, C h e m i e in uns. Z e i t , 12 (1978) 1-11.
78. S . D e m m i g and H.Langhals, C h e m . B e r . ,
121 (1988) 225-230.
79. H.Langhals and K . H a d i z a m a n i , to be published.
80. L . G . D o n a r u m a and W . Z . H e l d , O r g . R e a c t i o n s ,
11 (1960) 1-156.
8 1 . A . W . C h a p m a n and F . A . F i e d l e r , J . C h e m . S o o , (1936) 448-453.
82. R.Huisgen, J . W i t t e and I . U g i , C h e m . B e r . ,
90 (1957)
83. R.Huisgen, J . W i t t e and W . J i r a , Chem.Ber.,
84. R.Huisgen,
I.Ugi,
M.T.Assemi
and
1844-1850.
90 (1957)
J.Witte,
Liebigs
1850-1856.
Ann.Chem.,
602
(1957)
127-134.
85. R.Huisgen,
J.Witte,
H.Walz and
W . J i r a , L i e b i g s A n n . C h e m . , 604
(1957)
191-
202.
86. H.P.Fischer
and F . F u n k - K r e t s c h m a r ,
H e l v . C h i m . A c t a , 52 (1969) 913-933.
87. H.Langhals, G.Range, E.Wistuba and C . R ü c h a r d t ,
Chem.Ber.,
114 (1981) 3813-
3830.
88. H.Langhals and C . R ü c h a r d t ,
89. G.Fodor and S.Nagubandi,
90. H.P.Fischer,
91. J.D.Mc
Tetrahedron
Cullough,
Chem.Ber.,
Tetrahedron,
114 (1981) 3831-3854.
36 (1980)
1279-1300.
L e t t . , (1968) 285-290.
D.Y.Curtin
and
I.C.Paul,
J.Am.Chem.Soc,
94
(1972)
874-
882.
92. H.Langhals and K . H a d i z a m a n i , C h e m . B e r . ,
93. E . M . A r n e t t , P . M c C . D u g g l e b y and
J.J.Burke,
123 (1990) 407-409.
J.Am.Chem.Soc,
85 (1963)
1352.
94. E . T o m m i l a and M . L . M u r t o , A c t a Chem.Scand.,
17 (1963)
1947-1956.
1350-
342
95. S.Winstein and A . M . Fainberg,
96. E . M . A r n e t t , W.G.Bentrude,
87 (1965)
J.Am.Chem.Soc,
J.J.Burke
and
79 (1957)
5937-5950.
P . M c C . Duggleby,
J.Am.Chem.Soc,
1541-1552.
97. E . M . A r n e t t , W . G . B e n t r u d e
and
P.McC.
Duggleby,
J.Am.Chem.Soc,
87
(1965)
2048-2050.
98. M . H . A b r a h a m , J . C h e m . S o c , P e r k i n T r a n s , II, (1977) 1028-1031.
99. L . M e n n i n g a and J . F . B . N . E n g b e r t s ,
J.Org.Chem.,
100. W.Good, D.B.Ingham and J.Stone, T e t r a h e d r o n ,
101.
L. P.Ham m e t t ,
Physikalische
Organische
41 (1976)
3101-3106.
31 (1975) 257-265.
Chemie,
1973; Physical O r g a n i c C h e m i s t r y , M c G r a w - H i l l ,
Verlag
Chemie,
New Y o r k ,
Weinheim,
1970.
102. R . H u q , J . C h e m . S o c , Faraday Trans. I , (1973) 1195-1201.
103. H . A . J . H o l t e r m a n n and J . B . F . N . E n g b e r t s ,
104. E . M . D i e f a l l a h ,
(Frankfurt
M.A.Moussa,
am M a i n ) ,
J.Phys.Chem.,
M.A.Ashy
and
J.Org.Chem.,
107. A . D . A l l e n ,
108. S.Sridharan
K.M.Koshy,
N.N.Mangru
T.T.Tidwell,
99 (1977) 8093-8095.
H.Langhals and C . R i i c h a r d t , C h e m . B e r . ,
110. T . W . B e n t l e y , C . T . B o w e n , H . C . B r o w n and F.J.Chloupek,
38-42.
111. C . R i i c h a r d t , T o p . C u r r . C h e m . , 6 (1966) 251-300.
112. H.Langhals,
and
104 (1982) 207.
and V . P . V i t u l l o , J . A m . C h e m . S o c ,
109. 1.Mergeisberg,
(1981) 83-84.
46 (1981) 412-415.
M.P.Jansen,
J.Am.Chem.Soc,
Z.Phys.Chem.
115 (1979) 89-98.
105. D . N . K e v i l l and A . W a n g , J . C h e m . S o c , C h e m . C o m m u n . ,
106. J.S.Lomas,
83 (1979) 443-446.
S.A.Ghonaim,
to be published.
113. H.Langhals, N o u v . J o u r n . C h i m . , 6 (1982) 265-267.
113 (1980)
2424-2429.
J.Org.Chem.,
46 (1981)