AN ABSTRACT OF THE THESIS OF
MICHAEL PAUL FLEMING
for the
(Degree)
(Name of student)
in
CHEMISTRY
MASTER OF SCIENCE
presented on
(Major)
in( <
/973
(Date)
Title: PYROLYSIS OF DITERMINALLY UNSATURATED,
EIGHT-MEMBER CHAINS
Abstract approved:
Redacted for privacy
Elliot N. Marvell
A novel reaction has been proposed, and several systems
which have the potential to undergo the corresponding reverse reaction have been studied. This process may be presented in general
form by the reaction of 1, 5-hexadiene and ethene to form 1, 7-octadiene, Pyrolysis of 1, 7-octadiene at 500° -650°C in a flow system
failed to give encouraging evidence for the reverse reaction,
A more facile reaction is expected for the oxygen homolog,
allyl 3-butenyl ether, due to a more favorable enthalpy term. Neither
1, 5-hexadiene nor formaldehyde, the sought-for products, were con-
firmed to result from the pyrolysis of this ether at 300* -450°C.
Evidence supporting the reverse of our proposed reaction was
obtained when 1, 5-hexadiene and acetone were isolated in ca. 13%
yield from the pyrolysis of allyl 1, 1,dimethy1-3,butenyl ether at
500° C,
Concerted and biradical mechanisms have been suggested.
Intramolecular ene reactions were reviewed as were the pyrolysis of vinyl and ally], ethers, Products resulting from ene reactions
were present in the pyrolysis of the previously mentioned diterminally,
unsaturated eight-member chains, The interesting formation of
7- methyl -6- octenal from allyl 1, 1-dimethy1-3-butenyl ether is pro-
posed to occur via a series of intramolecular ene and retro ene
reactions,
APPROVED:
Redacted for privacy
Professor of Chemistry
in charge of major
Redacted for privacy
Chairman of Department of Chemistry
Redacted for privacy
Dean of Graduate School.
Date thesis is presented
/973
Typed by Opal Grossuicklaus for Michael Paul Fleming
Pyrolysis of Diterminally Unsaturated,
Eight-Member Chains
by
Michael Paul Fleming
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
June 1974
ACKNOWLEDGEMENTS
The author would like to express his sincere
appreciation to Dr. Elliot N. Marvell for his encouragement and guidance.
TABLE OF CONTENTS
INTRODUCTION
1
HISTORICAL
Introduction
Intramolecular Ene Reactions
Vinyl Ethers
Allyl Ethers
DISCUSSION
Pyrolysis of 1, 7-Octadiene
Pyrolysis of Allyl 3-Butenyl Ether
Pyrolysis of Allyl 1, 1-Dimethyl-3-butenyl Ether
2
6
21
23
26
26
28
31
CONCLUSIONS
34
EXPERIMENTAL
35
BIBLIOGRAPHY
47
APPENDIX
53
LIST OF TABLES
Page
Table
1.
Pyrolytic runs of 1, 7-octadiene.
27
2.
Pyrolytic runs of allyl 3-butenyl ether,
29
3.
Pyrolytic runs of allyl 1, 1-dirnethy1-3-butenyl
ether.
32
PYROLYSIS OF DITERMINALLY UNSATURATED,
EIGHT-MEMBER CHAINS
INTRODUCTION
The theory of orbital symmetry control of concerted reactions
as put forth in a series of papers by Woodward and Hoffmann nearly
eight years ago kindled a new interest in thermal reactions. A novel
process based on the Woodward-Hoffmann suggestions was conceived
in 1969 by Dr. Marvell, and several unsuccessful attempts have been
made in these laboratories to find examples of this new reaction.
The proposed reaction involved the sigmaddition of 1, 5-hexadiene
to an olefin. Although the enthalpy change is favorable for the reac-
tion as shown, failure to find examples could be attributed to the
possibility that the unfavorable entropy term dominates at the required high temperatures. Consequently, we decided to look for the
reverse reaction and some attempts to do that are presented in this
thesis.
HISTORICAL
General
Chemists, like astronomers, frequently attempt to set their
sights on a distant goal only to observe some other phenomena rival-
ing the original objective in interest. Thus, our attempts to explore
the reversal of the proposed reaction have led us to look at an old
reaction, the ene reaction, in a, new light. Since they have assumed
some importance in our work, the intramolecula,r ene reaction and the
retro-ene process will be reviewed here along with the pyrolysis of
vinyl and allyl ethers.
A brief, general characterization of the ene reaction will be
presented before its intramolecular examples are studied. The
ene reaction [see Scheme 1) is basically simple, but because of
X
HvX
Y
Scheme 1
this inherent simplicity, it has many variations, some of them wellknown under other names (e. g., olefin formation by ester pyrolysis,
decarboxylation of r3,1ceto acids]. The broad scope of the ene reaction
began to receive attention with the publication of a paper in 1943 by
Alder (1) who applied the "ene" label by considering the reaction as
the "indirect substituting addition" of a compound with a double bond
[enophile] to an olefin possessing an allylic hydrogen [ene]. Rising
interest during the last three decades in this frequently overlooked
reaction is reflected in the publication of several surveys (2-4).
The mechanistic questions arising from the ene reaction have
not been fully resolved, but several general traits have been noted.
The usual inability of free-radical inhibitors markedly to alter the
rate of ene processes have led to arguments against chain-mechanisms (5,
The observation that solvent polarity changes have little
6).
effect on the rate (7) and the absence of products resulting from rearrangement of ionic intermediates are evidence against an ionic
route (13).
Naturally-occurring p-pinene 1 is especially reactive in the
ene reaction and has been employed with a number of enophiles (8-12).
The complete retention of the pinane skeleton in the isolated products
argues against the formation of either the carbonium ion 2 or radical
3.
Optically active 4 adds to maleic anhydride in an ene manner to
yield the optically active adduct 5 in support of a concerted transition
0
0
Ph_
rCH3
Ph
CH
3
0
5
state rather than an ionic process which would undergo either a
4
hydride or methyl shift to form the more stable benzylic ion 6 [not
0
ED
Ph
H
observed] (14). It has been noted by Berson (15) that the preservation
of asymmetry in the ene product is a necessary but insufficient condi-
tion for a concerted mechanism since it also is compatible with a
route in which a carbon-carbon bond is formed first. The concerted
X
)
X
eX
y
y
Y
7
9
8
mechanism utilizes a six-centered transition state 7 as originally
proposed by Koch ( l 6) and Arnold and Dowell. (17).
Complete migra-
tion of the double bond of propene-l-C14 in the reaction with maleic
anhydride (18) also is consistent with concertedness in the transition
O
0
CH -CH-=...CH
3
2
CH
+
/I 0
*
2
0
2
\(\.)
state. Unfortunately the formation of intermediate biradical 8 or
zwitterion 9 is not definitely ruled out (15, 17, 20, 21), since these
transient species may prefer to transfer hydrogen to form the ene
product rather than rearrange.
5
Either a syn, syn 10 or an anti, anti 11 arrangement [corresponding to a cis- or trans-addition respectively, to the enophile] in
the concerted transition state is thermally allowed. Mode 10 is pre-
10
11
ferred both for steric reasons and maximization of allylic resonance by
positioning the axis of the breaking carbon-hydrogen bond parallel to
the p-orbitals of the adjacent double bond. Preference for cis-addi-
tion to the enophile has recently been shown by Friedrich and coworkers (19) when the deuterated olefin 12 reacted with maleic
0
CD
IL 2
(CH3)3 C --e---CD3 +
0
200°
CD2
(CH3 )3C - C -CD
2
D
H
12
13
anhydride to form 13. Allowing for a limit of detectability of the
trans isomer of 30%, the addition is at least 70% cis and may even
be stereospecific, Besides the syn, syn pathway, the cis-addition is
also consistent with a biradical or zwitterion intermediate in which
the transfer of the cis-hydrogen is kinetically preferred.
As the above discussion indicates, there still are mechanistic
questions posed by this seemingly simple reaction, In summary, the
ene reaction is believed to prefer a concerted route, but an intermediate biradical may be present if stabilized or, more importantly,
6
if the optimum transition state geometry is nonattainable.
Intramolecular Ene Reactions
1, 3-and 1, 4-Dienes
The well-known 1, 5-hydrogen shift undergone by conjugated
dienes has been extensively reviewed (2, 22, 23) and needs no further
150-2000
discussion here. Deconjugation of a 1, 3 -diene system by a single
methylene group produces a system which can undergo an intra-
molecular ene reaction to form a vinyl cyclopropane [(3) and sources
therein]. Cis-1, 4-hexadiene 14 equilibrates with its ene-product
isomer 15 and upon heating to 4000 C forms product 16 irreversibly
400°
CI-13
14
15
16
probably thru a competing ene reaction within 14.
The retro-ene opening of a 3-membered ring to a 1, 4-diene
was originally discovered in the bicyclo systems 17 and 18 by Doering
3100
17
18
and Roth (25). Eight-carbon rings can adopt the proposed "saddle"
7
conformation 19 more easily than rings of seven carbons which in
turn are more favorable than the six-carbon ring (22).
19
1, 5-Dienes
The Cope rearrangement normally predominates exclusively
over the ene reaction for 1, 5-dienes. Thus, 1, 5-hexadiene 20 re-
arranges to itself rather than the ene-product, cyclohexene 21, which
O
A
20
21
A \
\
2
H
2
22
in turn fails to open up to 1, 5-hexadiene in retro-ene fashion but does
undergo a retro-Diels-Alder reaction to 1, 3-butadiene and ethene (26).
The ene-reaction is neither expected nor found (27-29) in 1, 5-diyne
systems.
Ene-products 25 and 26 are formed when the 1-en-5-yne systems
23a-23c are heated to 340° C (30). A rapid equilibrium is believed
R1
CR1
C= CH2
23
a) R1=R2=1-1
b) Ry=CH3,R2=1-1
R2=CH3
c)
CH2
CH2.
C
340°
1
_+
R
R2
2
24
25
26
8
to exist between 23 and 24 [Cope rearrangement] followed by an
irreversible cyclization of 24 to biradical 27. A hydrogen shift
27
then produces 25 or 26.
1, 6-Dienes
Five-membered rather than seven-membered rings appear to
be favored when 1, 6-dienes undergo intramolecular ene reactions.
Ring opening within pinane 28 to. form 29 has been explained by an
500°
//k
29
30
579'
31
199'
13%
intermediate biradical 32 (31, 32) which is analogous to the proposed
33
32
thermal cleavage of the a- and 13-pinene skeletons (33). Originally
(31, 32) a free-radical mechanism was believed responsible for the
transformation of 29 into 30 and 31 as it was for a similar rearrangement of 6, 6-dimethylnorpinane 33 (34). The negligible effect of
free-radical initiators or inhibitors on the pinane rearrangement,
and its first-order kinetics prompted Huntsman and Curry (35) to
propose the familiar concerted, six-centered ene transition state 34
OH
650°C,.
36
35
34
for the process, which is consistent with the experimental AS of
-18 e. u. Linalool 35 undergoes an intramolecular ene reaction to
form all four possible diasteromeric plinols 36.
On the basis of the general observation (3) that a hydrogen from
a primary carbon rather than a secondary carbon is preferentially
transferred in the ene mechanism, 1, 6-octadiene 37 should cyclize
faster than 1, 6-heptadiene.
A mixture of cis- and trans-1, 6-
octadiene cyclizes at 457°C [contact time of 56 seconds] to produce
457°
/)
H
37
350/0
38
solely 1-methyl-cis-2-vinylcyclopentane 38, but 1, 6-heptadiene fails
to cyclize when heated to 500° C (36). At a substantially higher
temperature 1, 6-heptadiene 39 yields a variety of products.
800°
39
10
Pyrolysis of vinylcyclopentane gave the same product distribution
[details of mechanism will be discussed later].
A concerted ene mechanism is not geometrically feasible for
trans, trans-1, 6-cyclodecadiene 40. An equilibrium between two
biradical intermediates has been discussed by Roth (2) to explain the
product distribution which includes the ene product 41 as the major
a:0
2494
4%
cc>
40
72%
41
product. The rigidly-fixed pi-systems of 42 are at a favorable dis-
tance apart [-N-2 A] and relative position to form pentacyclo 43 at
a moderate rate at room temperature (41).
42
43
The more facile ene reaction of trans-6-octen-1 -yne 44, compared to 1, 6-octadiene, is probably due to the lower energy required
HC =C
44
45
to break the pi-bond in the alkyne moiety (37).
Kimel and co-workers (38) have pyrolyzed a large number of
11
acetates 46 to form pstudoionone derivatiVes 51 and 10-31% of a
cyclic isomer 52.
49
52
51
One of the mechanisms which describes the formation of 52 involves
rearrangement of 46 to the intermediate propargyl vinyl ether 49
which then undergoes a Claisen rearrangement to the allene ketone
50 (39). An intramolecular ene reaction in which the allene acts as
the enophile converts 50 to 52.
Several intermolecular ene reactions which involve a nitroso
compound as the enophile and an olefin as the ene component are
/\
known, but only recently has an intramolecular case been described.
53
54
Motherwell and Roberts have heated the nitroso-olefin 53 to form a
12
cyclic hydroxylamine 55 via a proposed pseudo-bicyclo [3. 3. 1] transition state 54 (80).
7-Dienes
At 320°C 1, 7-octadiene 56 equilibrates with its isomer, ciscyclooctene 57 thru an ene mechanism. The equilibrium shift to the
320°
H
57
56
diene at higher temperatures is probably caused by the dominant
entropy factor. Trans- cyclooctene opens to 1, 7-octadiene at a lower
temperature [250°C] than 57 due primarily to increased ring strain
(2).
At much higher temperatures in a flow system 56 produces a
pyrolysate consisting mainly of 1, 5-hexadiene.
720°
35%
57
56
trace
58
trace
Cis -cyclooctene at the same temperature and conditions rearranged
720°
57
3%
mainly to the retro-ene product 56 (40). Vinylcyclohexane 58 was
eliminated as a precursor to 1, 5-hexadiene and 1, 7-octadiene.
Ring closure of 8- methyl -1, 7-nonadiene _51 solely to
13
1-methyl-2-isopropenylcyclohexane 60 occurs at 490° C, but no
reaction was observed at 440°C. A -CO 2 CH3 group on C 1 in 59
490°
25 %
60
59
lowers the required temperature to 400° C (42) by making the enophilic
C1 -C2 double bond more electron deficient, in agreement with Hoff-
mann's general observations (3). Incorporation of one of the double
bonds into a cyclohexane ring causes the failure of either 61 or
61
62 to cyclize at temperatures up to 500' C. Steric interference
from quasi-axial hydrogens is the suggested cause for this failure
(42).
1, 8-Dienes
At 720°C 1, 8-nonadiene 63 undergoes 65% conversion to
1, 5-hexadiene in addition to traces of cis-cyclononene 64 and vinylcycloheptane 65 (4Q),
Lambert and Napoli (43) have very recently
720°
63
64
65
pyrolyzed a 1,6- and a 1, 8-diene in which the unsaturated chain ends
14
are somewhat constrained due to incorporation of a benzene ring into
the chain. The gas-phase pyrolysis of 4-o allylphenyl-l-butene 66
for 24 hours gave a 1:1 ratio of 67 and 68 in nearly quantitative yield.
350°
66
67
350°
68
Both ene products are thought to arise from a concerted reaction.
Unlike those in compound 66, the terminal double bonds in o-allyl-
styrene 69 cannot easily achieve the optimum geometry for the six-
centered transition state, which leads to 73, but apparently react
via the diradical 70. Ring-closure or hydrogen shift then forms 71
or 72, respectively.
330°
13 hr,
69
72
71
90-95%
8-5%
70
73
1%
15
Blomquist and Taussig have reported that the thermolysis of
cyclononanol 74a or of cyclononyl acetate 74b in a flow system at
500°C produces a mixture of 1, 8-nonadiene 63 and both geometric
isomers of cyclononene (44, 45). Under similar conditions it was
500°
74
64
63
75
a) RAH
b) RCOCI-13
noted that 20% of cis-cyclononene 64 was converted to 63 while transcyclononene gave 85% 63, and almost 15% 64. The larger conversion
for the trans isomer is partly due to the proximity of C1 to C5 in the
trans isomer (46).
75
Another report (40) indicates that vinylcycloheptane and 1, 8-nonadiene
are produced almost quantitatively when either cis or trans-cyclononene is heated at 520° -720°C. At 520°C the diene to vinylcyclo-
alkane ratio is --24 and decreases to 4 at 720°C, which is similar
to the trend reported by Roth (2) for the eight-carbon system.
The cyclic allene 76 undergoes ring opening to 1-nonen-8-yne
77 (47) by a retro-ene reaction. A second retro-ene pathway leads to
16
720°
77
76
79
78
76
78 which reacts further by an intramolecular Die ls-Alder reaction
to give 79, which is one of the observed products.
1, 9 -Dienes
Several years ago Rienacker (48) reported the rearrangement
of cis-cyclodecene 80 at 580°C to 80% 1, 9-decadiene 81 and 5%
vinylcyclooctane 82. The role of cyclodecene as a precursor to
580°
80
81
1, 9-decadiene had been indicated earlier when Blomquist (45) heated
cyclodecyl acetate to 500° C and isolated 20% of 1, 9-decadiene.
1, 11-Dienes
At 720°C 1, 11-dodecadiene 83 fails to undergo ring closure to
cyclododecene but does eliminate propene to yield 1, 8-nonadiene
63
17
as the sole product.
83
63
Under the same conditions both cis- and trans-cyclododecene, 84a
and 84b, gave identical product distributions. It was also noted
+ 84a +84b
84
a) cis-
63
83
85
5
34
3
20
:
b) trans-
that pyrolysis of 85 at 720 ° C produced 63, 83 84a and 84b in the
same ratio as the pyrolysis of 84a or 84b (40).
On the basis of their pyrolyses of cycloheptene, cyclooctene,
cyclononene and cyclododecene, Crandall and Watkins (40) have
proposed an elaborate set of equilibria, Scheme Z. Competitive
(CH
2)n
CH3
(CH
)
2 n
(CH2)n
>
(CH2)n
(CH2)n
(CH2)n
(CH )
2n
Scheme 2
pathways explain the temperature dependence of the diene/vinyl-
cycloalkane ratio experienced in the nine-carbon system. The
32
18
scheme also shows the concerted-biradical nature of the ene reaction.
The loss of ethylene by 56 has been rationalized as
arising from either of the following biradicals:
P-Hydroxy Olefin Cleavage
An ene reaction involving a ketone or aldehyde as the enophile
and an olefin as the ene results in a p-hydroxy olefin.
Conversely,
the reverse reaction, a p-hydroxy olefin cleavage, constitutes a
retro-ene process. Intramolecular p-hydroxy cleavage results in a
rearrangement such as 87 reverting to 86, Marvell and Whalley (49)
205°
86
87
have recently reviewed this subject and also the closely related
"enolene" rearrangement. This latter reaction is generally thought
to proceed thru an ene process in which the hydrogen transferred
is that of the enol. Conia and his co-workers have studied the
(CH 2)x
enolene behavior of numerous compounds and their earlier work has
19
been reviewed by Conia (56). More recently, a series of papers
(51-55) describing some of their later studies has appeared. Upon
pyrolysis in a static system, cyclohexanones 88 and 89 are reported
to yield ene products (51).
350
100%
90
88
91
92
17%
17%
0
89
93
70%
94
30%
Epimerization between 90 and 91 occurs under the experimental
conditions. Studies in which the positions of the carbonyl function
and olefin were varied also led to hydrindane skeletons (52-54).
0
CHO
CHO
320q,
H
epimerization
20
A mixture of 1-decalones and 7-hydrindanones resulted from the
pyrolysis of 95 due to two competing enolene rearrangements and
subsequent epimerization (55).
Spiro compounds have been reported (56, 57) to result from
enolene processes. Thus, (+)-2-(1-isopropeny1-4-penteny1)-5methyl cyclohexanone 96 rearranges under sustained heating to 4 iso-
meric accranic ketones, one of which is 97. After six hours of
H
2200
36 hr.
'NIBHEN
1100
96
97
il
+ 3 other
acoranic
ketones
heating at 365°C, 98 rearranges to 99 probably by two successive
enolene rearrangements.
98
21
Vinyl Ethers
The thermal behavior of allyl vinyl ethers has been explored
extensively due primarily to studies of the well-known Claisen
rearrangement (58). The literature contains far fewer reports of
the pyrolytic work with alkyl vinyl ethers. Some time ago Wang and
Winkler (59) suggested that free radicals do not play a major role
in the thermal rearrangement of ethyl vinyl ether to ethene and
0
CH =CH-O-CH
2
\-
2-CH3
CH
2=
\
CH-
`113A
CH3
\ CH 27-CH 2 + CH 3 CHO
100
acetaldehyde which instead proceeded thru transition state 100. The
observation of Blades and Murphy (60) that the entropy of activation
for the above pyrolysis [- 10. 2 e. u.] compared favorably with that of
allyl vinyl ether prompted the suggestion that 101 would be a better
O
530°
101
representation for the transition state than 100.
Product
studies (61-63) have lent evidence in favor of the latter mechanism
[see Scheme 3]. The retro-ene character of the reaction is obvious.
447-521°
Scheme 3
Wilson (64, 65) reports that at 375°C [contact time of 54
22
seconds] 2, 3- dihydrofuran 102 rearranges only to a small extent to
give 103 by a sigmatropic [1,3] shift.
375°
CHO
103
102
An increase in the operating temperature resulted in a decrease of
103 and the formation of crotonaldehyde, carbon monoxide, and
propene until at 550°C the latter two products were the major ones.
Cyclopropanealdehyde 103 under these conditions gives only a small
amount of crotonaldehyde with the major products, carbon monoxide
and propene, being in a 1:1 ratio. An equilibrium between 102 and
103 has been suggested. Similar cyclopropopyl-ring formation
O
CH3 CH =CHCHO
102
>--
CHO
C0+
C0
+
103
is found when compound 106 is pyrolyzed. It is interesting to note
450-475°
0
>--
475-525°
COCH3
CH3CH,---=CHCOCH
3
106
that if 2, 3- dihydrofuran 102 underwent the retro-ene reaction com-
mon to acyclic viny ethers, 104 would be formed, A possible second
step could be the enolene rearrangement of 104 to cis crotonaldehyde
105.
23
o)
o
102
104
The retro-ene reaction of 3, 4-dihydro-2H-pyran 108 to
4-pentenal has not been observed. Isotope-labeling studies of the
pyrolysis of 108 over alumina indicate proton adsorption and de-
adsorption on the agent's surface prior to formation of acrolein and
ethene (67-69). The non-catalytic thermolysis of 108 to acrolein and
ethene as the sole products (73) has been shown to be first order (71,
72) and may follow a concerted mechanism. One of the additional
products that was observed [but not investigated] at temperatures
above 510°C might be the addition product of acrolein and the starting pyran (73).
N..../
)
..A
CI
The thermal behavior of 2, 3, 4, 5-tetrahydrooxepin
300-500°
iNs
,,,
\
+
0
11
109
108
109 has received little attention, but it has been reported not to react
within a contact time of five seconds over CuCO 3
Cu( OH)
2
at 250° C
(74).
Allyl Ethers
Gas-phase pyrolytic studies have been carried out on a great
number of acyclic allyl ethers 110 by Malzahn (75) and Cookson and
Wallis (76). A concerted mechanism is supported by the experimental
24
R
500-600°
50
2
R1
110
data. No evidence for products obviously arising from a free-radical
pathway has been reported, and the transfer of deuterium from the
non-allylic a-position to C 3 of the allyl group was observed. The
reaction rate is rather insensitive to variations in either the allyl
or alkyl branch of the ether. The lowest relative rate (compared
to diphenylmethyl allyl ether] reported by Cookson and Wallis was
0. 17 for ethyl allyl ether and the highest value, 3. 6, was for diphenylmethyl 1- methylallyl ether. Inductive removal of electrons from the
non-allylic a-position enhances the rate. A k H /kD ratio of
1. 1 has
been measured for allyl a- deuteriodiphenylmethyl ether (76), but a
much larger value, 60-75% of the theoretical maximum, has been
noted for deuterio-isopropyl allyl ether (77).
Dehydrogenation of 2, 5-dihydrofuran 111 to furan has been
j
shown to be first-order and to have ,LS
,= -3. 9 e. u. ( 78).
Each
343-409°
iii
methylene group is thought to lose one hydrogen. Likewise, 5, 6-
dihydro-21-I-pyran 112 also fails to give a retro-ene reaction.
25
600°
+ CH2O
112
Pyrolysis gives 1, 3-butadiene and formaldehyde, the expected prod-
ucts of a retro-Diels-Alder reaction (79).
26
DISCUSSION
Reversal of the proposed sigmaddition process involves
cleaving an eight-atom system into six and two carbon fragments
with net conversion of a sigma to a pi bond. Enthalpy and entropy
56
114
113
act in opposing directions for the hydrocarbon system. Conversion
to 1, 7-octadiene 56 is favored by an enthalpy gain of ca. 19 kcal/
mole, while the fragmentation is favored entropically. As a result,
it is expected that higher temperatures and lower pressures will aid
the fragmentation.
1, 7-Octadiene
This diene has been pyrolyzed previously as was reported in
the historical section. Three reactions appear to dominate within
the temperature range of 300° to 800° C. At the lower end of the
57
56
113
58
range an equilibrium exists between 1, 7-octadiene 56 and
27
cis-cyclooctene 57 with the diene favored at higher temperatures (2).
The cleavage to 1, 5-hexadiene 113 and rearrangement to vinylcyclohexane 58 occurs at temperatures above 700°C (40). Although the
observation of 1, 5-hexadiene was exciting, the conditions were not
encouraging for mechanistic studies. We have studied the pyrolysis
in the intermediate range [500° -650°C], and the results are not
particularly promising.
Considerable tar formation was noted when the temperature was
raised or the contact time increased or both [Table 1]. This polymer
formation was accompanied by a marked decrease in the recovery of
condensable material and the appearance of aromatic compounds such
as benzene, toluene, and styrene in the mixture. A peak in the glc
spectrum having the same retention time as 1, 5-hexadiene was ob-
served, but it corresponded only to a minor component of the pyrolysate, and its identity could not be confirmed owing to the complexity
of the mixture. Thus it did not appear to be promising to attempt
studies of the origin of the 1, 5- hexadiene reported by Crandall and
Watkins (40).
Table 1. Pyrolytic runs of 1, 7-octadiene,
Run
T
3
(°C)
500
550
580
4
648
1
2
aPercent
Contact
Time
(sec.
32, 3
30.4
59.8
82.3
)
Recovery
(%)
Reactant
j%)a
cis-Cyclooctene
(%)a
5
69
84
57
51
8
3
13
3
0
75
9
= (component's peak area/total area of glc chromatogram X 100). Data were collected Qn
a 1/4"x 2, 5 meter Carbowax 20M (504 on base-washed firebrick) column.
28
All 1 3,7butenyl Ether
The possibility of the fragmentation process can be enhanced
by replacement of a methylene by an oxygen in an appropriate position.
\10
+
CH2
115
113
The fragmentation of the ether to a carbonyl is favored both enthalpy-
wise and entropically since a C-0 pi bond is stronger than a C-0
sigma bond (81), The retro-sigmaddition process should therefore
be observed, if real, at a lower temperature. Several products
were observed when allyl 3-butenyl ether 115 was pyrolyzed at 400° 450 ° C [Table 2]. At ca. 450 ° C the yield of condensable product
decreased to too low a level to permit further study. The sought-for
O
CH CH== CHCHO +
3
115
116
117
118
a) cis
b) trans
products, 1, 5-hexadiene and formaldehyde, appeared to be present
in small quantities as indicated by gle data, but neither isolation nor
spectral examination proved possible.
29
Table 2. Pyrolytic runs of allyl 3-butenyl ether.
T
(°C)
Run
1
2
3
4
5
6
7
8
9
10
a
Contact
Time
(sec. )
Recovery Reactant
( %)
(%)a
0
0
0
0
0
3
1
0
0
70
.73
13
9
5
89
87
6
4
1
8
3
2
73
77
13
9
5
2
5
16
.35
3
6
2
6
149
55
400
425
450
450
193
13
94.0
(%)a
100
100
96
9.8
18.8
29.0
33.S
62.9
97.8
a
(%)a
6Heptenal
71
54
81
300
350
400
400
400
400
82. 7
Croton3-13utenal aldehyde
71
21
2
2
19
52
67
Percent = (component's peak area (total/area of glc chromatogram X 100). Data for runs 1-6 were
collected on a 1/4" x 8 foot Carbowax 20M (20% on Chromosorb P, 30/60 mesh) column. Data
for runs 7-10 were collected on a 1/4"x 6 foot SE-30 (20% on AW-DMCS Chromosorb G, 45/60
mesh) column.
The products which were formed in reasonable yields merit a
few comments. The four-carbon aldehydes, 116, 117a and 117b,
appear to be formed from an initial retro-ene process, followed by
H
116
115
1L
117b
a 1, 5-hydrogen shift and double bond isomerization (82).
117a
These are
not unexpected or unusual products.
The formation of 6-heptenal is a novel and exciting development,
although not totally unexpected. This aldehyde was isolated and iden-
tified by its spectral properties. Its identity was confirmed via
30
synthesis as illustrated below. Prediction of its formation had been
OH
H20
00H
118
115
made from the known equilibrium between 1, 7-octadiene and ciscyclooctene.
The cyclooctene is symmetrical and ring-opening to
the diene can occur in two ways, proper labeling being the only way
56
57
Or
N--118
115
to differentiate them. The ether furnishes the label and also leads
to a more stable ring-cleavage product thereby making "inversion"
of the eight-atom chain nearly irreversible.
This intriguing process
does not seem to have been noted previously.
Concerted and/or biradical processes may be operative in the
formation of 6-heptenal [Scheme 4]. A similar suggestion has been
made previously for the all-carbon system [Scheme 2].
The con-
certed rearrangement of tetrahydro-2H-oxocin.s 121 and 122 (83, 84)
are analogous to the retro-ene processes undergone by acyclic
vinyl and allyl ethers. At the present time it is uncertain to what
degree, if any, biradicals are involved in the formation of 6-heptenal.
31
/.
0
/
121
123
122
124
O
115
120
Scheme 4
Allyl 1, 1-Dimethy1-3-butenyl Ether
The presence of 1, 5-hexadiene and acetone in the mixture
resulting from the pyrolysis of allyl 1, 1-dimethy1-3-butenyl ether
125 at 400° -500°C [Table 3] is encouraging evidence for our
\
125
400°
113
126
127
proposed fragmentation process. If a concerted ground -state
mechanism is operating several possible routes may be suggested
32
[Scheme 5] (85). From studies of molecular models at least one
2
2
[Tr + Tr +
2
/1A
+
2
o-
2
+ a- +
0
2
conformation appears to be favorable for each route. Formation of
biradical 128 may also lead to the elimination of acetone. It must be
stressed that these routes to six plus two fragmentation are purely
128
speculations. Possible future reactants are 4-pentenyl vinyl ether
and 1, 2-bis (vinyloxy) ethane both of which were synthesized.
Table 3. Pyrolytic runs of ally' 1,1-dirnethy1-3-butenyl ether.
Run
1
2
3
a
T
(°C)
395
450
500
Contact
Time
1,5Recovery Reactant
(sec. )
(%)
45.5
56.3
69
75
53
108
(0/0)a
Hex adiene Acetone
a
(%)a
7- Methyl6 -octenal
(%)a
79
2
2
16
27
12
49
4
13
10
12
63
Percent (component's peak area/total area of glc chromatogram X 100). Data were collected
on a 1/4" x 6 foot SE-30 (20% on AW -DMCS Chromosorb G, 45/60 mesh) column.
33
The presence of 7- methyl -6- octenal 127 in the mixture is
suggested to arise from a series of ene and retro-ene processes
analogous to those presented in Scheme 4. Although no attempts
were made to optimize the aldehyde yield, the yields achieved indi-
cate possible future use in synthesis.
34
CONCLUSIONS
The pyrolysis of allyl 1, 1-dirnethy1-3-butenyl ether has furn-
ished encouraging evidence for the reverse of our proposed sigmaddition reaction. Although several concerted mechanisms have been
suggested, a biradical route cannot be excluded at this time.
The formation of 6-heptenal and 7-methyl-6-octenal from their
acyclic allyl ethers is suggested to proceed via a sequence of ene
and retro-ene processes involving formation of intermediate tetrahydro-2H-oxocins. Future work in these laboratories hopefully will
reveal more details of the mechanisms involved.
35
EXPERIMENTAL
Pyrolytic Studies
The apparatus constructed for the pyrolytic studies is shown
in Figure 1. Both the column and its joints are of "Vycor" glass.
The column has an inside diameter of 22 mm and a heated length of
45 cm. Electrical current to the heating element, which was spiraled
around the column and insulated both from the column and the outside
environment by layers of asbestos, is monitored by a taperingvoltage regulator. The temperature can be determined (±3C°) at
any one of three positions on the column by means of iron-constantan
thermocouples. One thermocouple was placed ca. 5 cm from each
end of the column, and the third one was positioned in the center. A
stainless-steel case surrounds the column with the enclosed space
being filled with an insulating material.
The column was filled with 3/8-inch lengths of 8 mm quartz
tubing. These pieces of quartz had been thoroughly washed for sev-
eral hours in water, acetone and finally ether before being dried at
120° C for several days. The volume of the quartz-filled column was
94 ml.
A definite sequence of steps was followed prior to each pyro-
lytic trial. The column was plugged at the lower end, completely
filled with chloroform and allowed to stand for at least thirty minutes.
36
After draining the column, the cleansing step was repeated. The
column was heated to 150°C for one hour while a stream of nitrogen
[Prepure] was flowing through it. The inlet and collecting systems
were quickly assembled while the column was hot, and the gas flow
was resumed. Teflon tape was used in the joints for the initial runs,
but prevention of leaks was difficult and the tape was later replaced
with silicone grease (Dow-Corning).
The vaporizer was heated in a mineral oil bath to a temperature 10 °-25° C below the boiling point of the reactant.
The tube con,
necting the vaporizer to the column was maintained above the boiling
point of the reactant by means of heating tape. The collection traps
were cooled by immersion in a mixture of chloroform, carbon tetrachloride and dry ice. Following heating of the column to the desired
operating temperature, a soap-bubble flowmeter was attached to the
outlet of the collection system and the flow rate noted. The reactant
was placed in the vaporizer, and heating was continued for about five
minutes after the vaporizer appeared to be empty,
Solvent Preparation
Anhydrous Ethyl Ether
Commercial, U. S. P. ethyl ether was dried for at least 24 hours
over anhydrous calcium chloride. Following filtration, ca.
1
37
meter of 2 mm sodium was pressed directly into a gallon of ether
and allowed to stand for one day. Additional sodium was added if the
original wire was entirely consumed. The ether was distilled from
fresh sodium wire and stored over sodium.
Anhydrous Thiophene-free Benzene
The method of Vogel (86) was followed. Technical grade
benzene was shaken several times with concentrated sulfuric acid
until the acid layer was a very pale yellow in color. After having
been washed with water and saturated sodium carbonate solution,
the benzene was dried over calcium chloride. The benzene was
stored over sodium after distillation.
3 -Buten- 1 -ol
This compound was prepared by the method of Ettlinger and
Hodgkins (87). Reaction was carried out under rigorously anhydrous
conditions in a nitrogen atmosphere. A mixture of 50 g (2. 06 g
atoms) of magnesium turnings [Matheson, Coleman and Bell, Grignard
Reagent Grade] and 2 1 of anhydrous ethyl ether [distilled directly
from lithium aluminum hydride] was placed in the reaction flask and
cooled to 0° -3°C in an ice bath. To this mixture was added over
7 hrs. a solution of 183 ml [2. 25 moles] of allyl chloride in 300 ml
of anhydrous ethyl ether. The mixture was stirred vigorously
38
during addition and for 2 hrs. after the reaction seemed complete.
Paraformaldehyde, dried in a vacuum over phosphorous
pentoxide [106 g, 3. 54 moles as formaldehyde], was depolymerized
at 195° -200°C, and the formaldehyde was carried in a stream of dry
nitrogen into the reaction vessel. During the addition, the slurry of
allyl magnesium chloride was stirred vigorously and the temperature
maintained at 0° -3 ° C. Saturated ammonium chloride solution [600
ml] was added to the mixture at room temperature followed by 20 ml
of concentrated ammonium hydroxide. The ether layer was separated,
dried [MgSO4] and the product isolated by fractional distillation on a
spinning-band column, b. p. 112° -113* C [lit. (87) b. p. 113. 5° C];
nmr [CC14] 8 2, 26 [q, 2H], 3.58 [t, 2H, J = 6 Hz], 4.16 [[, OH],
5.07 [m, 2B], 5. 79 [m, 11-1]; 57.5 g [39 V.
Allyl 3- Butenyl Ether 115
This ether was synthesized by a method derived from those of
Moon and Lodge (88) and of Kirmse and Kapps (89). The reaction
was carried out under nitrogen and rigorously dry conditions. A
solution of 25.7 g (356 mmoles) of 3-buten-1 -ol in 80 ml of anhydrous
benzene [distilled directly from lithium aluminum hydride] was
added with vigorous stirring at ambient temperature to a mixture of
16.9 g [401 mmoles] of sodium hydride [Ventron, 57% mineral oil
dispersion] in 400 ml of dry benzene over a 2 hr. period. The
39
temperature rose slightly during the addition. The mixture was heated
under reflux for 30 min. and allowed to cool to room temperature, In
30 min. a solution of 43.4 g [359 mmoles] of allyl bromide [Matheson,
Coleman and. Bell] in 80 ml of anhydrous benzene was added to the
rapidly stirred suspension which was then heated under reflux for
5. 5 hrs. The mixture was washed with water until neutral and the
benzene layer dried [MgSO4],
The product was isolated by fractional
distillation with a spinning-band column, b. p. 115° -116°C [lit. (88)
112° -113°C]; ir[neat] cm-1 915, 990, 1420, 3080 [=CH2], 1100
[C-O-C], 1470, 2850 [-CH2-], 1640 [C =C]; nmr [CC14] 8 2.30 [q, 2H],
3.41 [t, 2H, J. 6 H ], 3.91 [d, 2H, Jz--- 6 Hz], 5.11 [m, 4H], 5.82
[m, 2H]; 18.54 g [46. 4%].
4 -Penten- 1-ol
This compound was prepared by the method of Karasch and
Fuchs (90). Anhydrous conditions and a nitrogen atmosphere were
used. A mixture of 600 ml of anhydrous ethyl ether [distilled directly
from lithium aluminum hydride] and 24.3 g [1.00 g atom] of mag-
nesium turnings was placed in the reaction flask and cooled to 0°C
in an ice bath. While the mixture was being rapidly stirred, 89. 5 ml
[ 1. 10 moles] of allyl chloride was added over a period of 5. 5 hrs.
The suspension of allyl magnesium chloride was stirred at room
temperature for 45 min., and 60 ml [1. 2 moles] of ethylene oxide
40
was very cautiously added over 2. 5 hrs. Stirring was continued
overnight. The mixture was refluxed for 2 hrs. and then 500 g of
ice was added followed by 700 ml of a 20% acetic acid solution. The
organic layer was extracted with ether, and the extracts were washed
with saturated sodium carbonate and dried [MgSO4]. Fractional distillation with a spinning band column produced 71. 73 g [83. 3%] of the
product, b,p 52° -56*C [44 mm] [lit. (90) b. p. 76. 4*C [60 mm]];
nmr [CC14] S 1.57 [quint. , 2H, J = 7 Hz], 2.08 [q, 2H, J = 7 Hz],
3. 52 [t, 2H, J= 7 Hz], 4. 13 [s, OH], 4.98 [m, 2H], 5.69 [m, 1H].
4-Pentenyl Vinyl Ether
Synthesis of this material was accomplished by the method of
Watanabe and Conlon (91). A mixture of 64. 05 g [744 mmoles] of
4-penten-1 -ol, 490 g [6. 80 moles] of ethyl vinyl ether [Aldrich] and
8. 0 g of mercuric acetate [Baker and Adamsom, Reagent Grade] was
heated under reflux with magnetic stirring. The progress of the
reaction was followed by gas-liquid chromatography on a 1/4"x2. 5
meter Carbowax 20 M [5% on base-washed firebrick] column. The
chromatographic peak corresponding to the starting alcohol had al,
most completely disappeared after 3. 67 hrs. at which time the mixture was cooled to room temperature. The mixture was stirred for
one hour after addition of 7, 0 g [50. 7 mmoles] of anhydrous potas-
sium carbonate, and the product was isolated by fractional distillation
41
with a spinning band column, b. p. 116° -118°C [lit. (92) b. p. 115* 116°C [750 mm]]; it [neat] cm-1 812, 965 [CH=C-0], 1080, 1205
[=C-0-], 1615 [C=C-0], 1640 [C=C], 3065 [=CH2]; nmr [CC14] 5
2H, J=7 Hz], 2. 15 [q, 2H, J = 7 Hz], 3. 63 [t,
2H,
J= 7 Hz], 3.88 [d of d, 1H, J= 2 Hz, J=7 Hz], 4.05 [d of d,
1H,
1. 75 [quint.
,
J= Z Hz, J=14 Hz], 5.01 [m, 2H], 5. 79 [m, 1H], 6.38 [d of d, 1H,
J=7 Hz, J=14 Hz]; 6. 58 g [7.9%].
1, 1-Di (4-pentenoxy)ethane
This compound was formed as a side product in the preceding
synthesis of 4-pentenyl vinyl ether, and was isolated by fractional distillation with a spinning band column. It was identified by its spectra
and its reaction with dilute acid to produce 4-penten-l-ol and acetaldehyde; b. p. 118° -120°C [48 mm]; it [neat] cm-1 745 [-CH-], 910,
390 [=CH-], 1100, 1137 [0-C-0], 1340, 2890 [-C-H], 1380, 2960
[-C1-13], 1640 [C=C], 3050 [ =CH2]; nmr [CC14] 5 1. 21 [d, 3H, J=6 Hz],
1.61 [quint.
,
2H, J=7 Hz], 2. 12 [q, 2H, J=7 Hz], 3.44 [m, 4H], 4. 60
[q, 1H, J=6 Hz], 4.98 [m, 41-1], 5. 79 [m, 21.1]; m/e = 197; 20. 2 g.
2-Methyl-4-penten-2-ol
The alcohol was prepared by the method of Bacon and Farmer
(93).
The reaction was conducted under anhydrous conditions in a
nitrogen atmosphere. A mixture of 48. 6 g [2. 00 g atoms] of
42
magnesium turnings in 450 ml of anhydrous ethyl ether [distilled
directly from lithium aluminum hydride] was placed into the reac-
tion flask and cooled to 0°C in an ice bath. A solution of 77.3 g
[1.01 moles] of allyl chloride in 400 ml of dry ethyl ether was added
over 3. 5 hrs. with vigorous stirring. The suspension of the Grignard
reagent was stirred for 1 hr. at ambient temperature and then cooled
to -10°C in an isopropyl alcohol-dry ice bath. After 58.1 g [1.00
mole] of acetone had been added [ca. 90 min. ], the mixture was
stirred at room temperature for 3 hrs. Very cautious addition of
500 g of ice was followed by addition of 500 ml of 20% acetic acid.
The unreacted magnesium was removed by filtration, and the reaction mixture was extracted with ether. The ether extracts were
washed with saturated sodium carbonate and dried [MgSO4].
The /
product was isolated by fractional distillation with a spinning-band
column, b. p. 118°C [lit. (93) b. p. 117' -119°C [775 mm]]; it [neat]
cm-1 915, 1000 [=CH-], 1380 [-CH3], 1640 [C=C], 3060 [=-CH2],
3200 [-OH]; nmr [CC14] 5 1. 16 [s,
11-1],
2. 19 [d, 21-1, J=7 Hz], 2. 74
[s, OH], 5. 03 [m, 2H], 5. 86 [m, 1H]; 51. 87 g [51. 4%].
Ally' 1, 1-dimethyl-3-butenyl Ether 125
Preparation of this ether was patterned after the synthesis of
allyl 3-butenyl ether. A nitrogen atmosphere and anhydrous conditions were employed. A solution of 49.9 g [498 rnmoles] of
43
2- methyl -4- penten -2 -ol in 50 ml of anhydrous benzene [distilled
directly from lithium aluminum hydride] was added over 2. 5 hrs.
to a well stirred mixture of 23. 2 g [551 mmoles] of sodium hydride
[57% dispersion in mineral oil] in 400 ml of dry benzene.
The mix-
ture was stirred for 30 min. and then heated under reflux for an
additional 30 min. With very vigorous stirring a solution of 60.6 g
[501 mmoles] of allyl bromide in 50 ml of anhydrous benzene was
added to the mixture over 30 min., and the solution was heated under
reflux for 3 hrs. The reaction mixture was washed with water and,
the benzene layer was separated and dried [MgSO4]. Isolation of the
product was by fractional distillation with a spinning-band column,
b. p. 145° C [lit. (94) b. p. 190-193° C, see following compound]; it
[neat] cm--1 917,995 [-CH=C], 1370, 1385 [gem-dimethyl], 1645 [ C=C],
3050 [=CH2]; nmr [CC14] 5 1. 12 [s, OH], 2.21 [d, 2H, J=7 Hz], 3. 86
[m, 2H], 5.08 [m, 4H], 5. 70 [m, 2H]; 32. 5 g [46. 4%].
Anal. Calculated for C H
9
16
0: C, 77. 09; H, 11. 50
Found: C, 76. 87; H, 11.34
2, 4- Dimethyl- 6- hepten -2, 4-diol
This compound was obtained as a by-product in the preparation
of allyl 1, 1-dimethy1-3-butenyl ether. An earlier report (94) has
incorrectly identified it as allyl 1, 1- dimethyl- 3- butenyl ether.
diol was purified by repeated fractional distillations with a
The
44
spinning-band column, b. p. 193° -194° C [760 mm], 96° -98°C
[30 mm]; ir [neat] cm-1 912, 997 [CH=C], 1177, 1370, 1380 [gemdimethyl], 1640 [C=C], 3100 [ =CH2], 3180 [-OH]; nmr [CC14] 5 1. 25
[s, OH], 1, 49 [d,
11-1,
J=15 Hz], 1. 72 [d, 114, J= 15 Hz], 2. 24 [d, 2H,
J=7 Hz], 4.02 [2H, 01-1], 5. 01 [m,
Anal.
21-1],
5. 81 [m, 114]; 5. 22 g.
Calculated for C H1802: C, 68.31; H, 11.47
Found: C, 68.49; H, 11. 54
1, 2-Bis (vinyloxy) ethane
Preparation of this ether was similar to the synthesis of 4-pentenyl vinyl ether. A mixture of 31.2 g [503 mmoles] of ethylene glycol,
245. 6 g [3, 41 moles] of ethyl vinyl ether, and 8. 0 g of mercuric ace-
tate was heated under reflux with stirring for 48 hrs, under nitrogen.
Reaction progress was followed by gas-liquid chromatography using
a 1/4" x 2. 5 meter Carbowax 20 M [5% on base-washed firebrick]
column. When the reaction was complete, 8. 0 g of anhydrous potassium carbonate was added to the reaction mixture and the product was
isolated with a spinning-band column, b. p. 126° -128° C [lit. (95)
b. p. 125° -126.8° C]; ir [neat] cm-1 817, 960 [CH=C-0], 1085, 1200
[ =C-0-C], 1615 [C=C-0], 3070 [ =CH2]; nmr [CC14] 5 3. 81 [s, OH],
3.92 [d of d, 2H, J=2 Hz, J=7 liz],4. 08 [d of d, 2H, 3=2 Hz, J=14 H
6.38 [d of d, 2H, J= 7Hz, J=14 Hz]; 8. 79 g [14.9%1.
45
6-Heptenal 118
A mixture containing 1.0 g of sodium acetate and 59.06 g [322
mmoles as peracetic acid] of a commercial solution of peracetic acid
[41. 5% by titration (96)] was slowly added to a well-stirred solution of
60.9 g [554 mmoles] of 1, 7-octadiene in 150 ml of acetone. Stirring
was continued for 4 hrs. at 23°C, 5 hrs. at 45°C, and 2 hrs. at
65°C. The mixture then gave a negative starch-iodide test. Frac-
tional distillation gave an acetate b. p. 102°C [1, 7 mm]; ir [neat] cm910, 990 [CH=C], 1240 [C-O-C], 1640 [C=C], 1735 [C=0], 3060
[=C1-12], 3230 [-OH]; nmr [CC14] 6 1. 41 [m, 61-1], 2. 07 [m,
51-1],
3, 51
[m, 31-1], 3.97 [m, in], 4.96 [m, 21-1], 5, 77 [m, 1H]; 12.07 g.
The acetate was hydrolyzed by the method of Brasen and
Hauser (9 7). A mixture of 9.3 g [53. 5 mmoles] of acetate, 2.16 g
of sodium hydroxide, 25 ml of water and 25 ml of 95% ethanol
was heated under reflux for 4 hrs.
The solution was extracted
with ether and the combined extracts were washed with saturated
sodium chloride and dried [MgSO4]. A diol was isolated by frac-
tional distillation, b. p. 77° -80°C [0. 1 mm]; ir [neat] cm-1 908,
990 [-CH=C], 1640 [C=C],, 3050 [ =CH 2 ], 3180 [-OH]; nmr [ CC1 4]
5 1.40 [m, 6H], 2. 16 [m, 21-1], 3.48 [m, 31-1],4.58[s, ZH, OH], 4.97
[m, 2H], 5. 78 [m, 1H]; 5. 75 g.
A solution of the 2. 00 g of diol in 50 ml of ethanol was
r
46
heated to 42°C, and a solution containing 3. 2 g of potassium periodate
in 135 ml of IN sulfuric acid was quickly added. The mixture was
stirred for 20 min. and was then extracted with ether. Fractional
distillation produced I, 80 g of product, b. p. 35 ° -38 ° C [5. 0 mm]
which was found to be 75% 6-heptenal [lit. (98) b. p, 88° -89° [80 mm]]
by gas-liquid chromatography; ir [neat] cm-1 910, 995 [-CH=C], 1640
[C=C], 1725 [C=0], 2720 [CHO], 3050 [ =CH2]; nmr [CC14] 8 3. 53
[m, 4H], 2.07 [q, 2H, 3= 7Hz], 3.37 [t, 2H, J=7 Hz], 4.99 [m, 2H],
5. 75 [m, 1H], 9.67 [s,
11-1]; 14%.
7- Methyl -6- octenal 127
This compound was a product of the pyrolysis of allyl 1, 1-dimethy1-3-butenyl ether and was isolated by gas-liquid chromatography on a 1/4" x 6 foot SE-30 [20% on AW-DMCS Chromosorb G,
45/60 mesh] column, b. p. 201° C; ir [neat] cm-1 1375, 1390 [gemdimethyl], 1670 [C=C], 1725 [C=0], 2725 [CHO]; nmr [CC14] 5 1. 50
[m, 10 H], 1. 98 [q, 2H, J = 7Hz], 2. 36 [m, 2H], 5. 07 [m, 1H], 9.68
[t, 1H, J= 7 Hz].
Anal.
Calculated for C9H 16 0: C, 77. 09; H,
11. 50
Found : C, 76.94; H, 11, 41
47
BIBLIOGRAPHY
1.
K. Alder, F. Pascher and A, Schmitz, Chem. Ber, 76, 27
(1943).
2.
W. R. Roth, Chimica, 20 229 (1966).
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H. M, R. Hoffmann, Angew. Chem: Int. Ed. Engl., 8, 556
(1969),
4.
E. C. Keung and H. Alper, J. Chem. Educ., 49, 97 (1972).
5.
W. G. Bickford, G. S. Fisher, L. Kyame and C, E. Swift,
J. Am, Oil Chemists' Soc., 25, 251 (1948).
6.
E. H. Farmer, Trans. Faraday Soc.
7.
R. Huisegen and H. Pohl, Chem. Ber., 93, 527 (1960).
8.
G. I. Birnbaum, Chem. Ind. iLondon), 1116 (1961).
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R. T. Arnold and J. S. Showell, J. Amer. Chem. Soc., 79,
,
38, 340 (1942).
419 (1957).
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J, P. Bain, J. Amer. Chem. Soc., 68 638 (1946).
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APPENDIX
53
ati
I
°Ia
,045
Apr,
IP
I
4,1,
ie
A* I
ti
Li
Figure 1. Pyrolysis apparatus (X 1/4).