Table Of ContentPTROLYSES OF DIHYDROPYRAN DERIVATIVES
DISSERTATION
Presented in Partial Fulfillment of the Requirements
for the Degree Doctor of Philosophy in the
Graduate School of the Ohio State
University
By
MYRON BECKER, B.S.
The Ohio State University
1952
Approved by
Adviser
1
ACKNOWLEDGEMENT
The author wishes to express his deep appreciation
to Dr. Christopher L. Wilson for the suggestion of this
research and for his guidance and encouragement in its
development.
Appreciation to the General Motors Corporation is
also expressed for their fellowship grant in the academic
year 1949-50.
11
TABLE OF CONTENTS
Page
I. HISTORICAL x
II. INTRODUCTION 4
III. EXPERIMENTAL 7
A* Cyclobutanecarboxaldehyde 7
1* Pyrolysis of calcium formate and calcium
cyclobutanecarboxylate 7
(a) Cyclobutanecarboxyllc acid 7
(b) Calcium cyclobutanecarboxylate 9
(cj Cyclobutanecarboxaldehyde 10
(d) Characterization 10
2* Lithium aluminum hydride reduction of
cyclobutanecarbonitrile 11
(a) Cyclobutanecarbonitrile 11
(b) Cyclobutanecarboxaldehyde 14
3* Sodium trimethoxyborohydride reduction of
cyclobutanecarbonyl chloride 16
(a) Cyclobutanecarbonyl chloridd 16
(b) Cyclobutanecarboxaldehyde 17
4. Dehydrogenation of cyclobutanemethanol 16
(a) Cyclobutanemethanol 16
(b) Preparation of the silver-copper
dehydrogenation catalyst 20
(c) Cydobutanecarboxaldehyde 20
ill
TABLE OF CONTENTS (continued)
B. Preparation of 2-phenyl-3,4-dihydro*2H-pyran 22
C. Pyrolysis apparatus 23
1. Furnace and related equipment 23
(a) Dropping Funnel 23
(b) Oaa Flow 23
(c) Furnace 23
(d) Pyrolysis Tube 23
(e) Traps 24
D. Technique of thermal decomposition 23
E. Isolation and estimation of products 26
F. Pyrolyaes of dihydropyran 26
1. At different temperatures 26
2. Dihydropyran at 410° and 350° 31
3* Dihydropyran-toluene solution at 400° 32
G. Pyrolyses of cyclobutanecarboxaldehyde 33
1. At different temperatures 33
H. Pyrolysis of 3»4-dihydro-2H-pyran-2-
carboxaldehyde 34
I. Pyrolysis of 2-phenyl-3»4-dihydro-2H-pyran 35
1. Pyrolysis of cinnamaldehyde 3 5
2. Pyrolysis of 2-phenyl-3,4-dihydro-2H-pyran 37
IV. DISCUSSION 39
A. Preparation of cyclobutanecarboxaldehyde 39
B. 2-Phenyl-3»4-dihydro-2H-pyran 44
!▼
TABLE OF CONTENTS (continued)
C. Pyrolyses of dihydropyran and cyclobutane-
carboxaldahyda 44
D. Pyrolyses of 3,L-dihydro-2H-pyran-2-carbox-
aldehyde and2 -phenyl-3,4-dihydro-2H-pyran 50
E. General 53
V. SUMMARY 55
VI. APPENDIX 57
A. Tables 57
B. Spectra 61
C. Nucleophilic substitution in aromatic
compounds 67
VII. BIBLIOORAPHY 71
VIII.AUTOBIOGRAPHY 7 U
I. HISTORICAL
The dlhydrofurans and -pyrane fall into two groups, ao
far as thair chamical raactlons are concerned. 2,3-Dihydro-
furans and 3,4~dlhydro-2H-pyrans, which have the double
bond in the •position to the oxygen atom, react very
similarly to vinyl ethers, while 2,5-dihydrofurans and
5,6-dihydro-2H-pyrans behave as olefins in which the
activity of the double bond is not affected by the oxygen
atom. This review is concerned primarily with the former
group of compounds.
A reaction characteristic of many vinyl ethers is the
rearrangement which occurs upon heating*. Such a re-
1
arrangement has been observed by Wilson in the pyrolysis
of 2,3-dlhydrofuran which gave mainly cyclopropanecarbox-
aldehyde and crotonaldehyde. At 460°, the yield of the
cyclic aldehyde was 40%, calculated on the dihydrofuran
consumed, but at higher temperatures Increasing proportions
of propylene and carbon monoxide were formed. Cyclopropane-
carboxaldehyde was found to give a small amount of dihydro
furan on pyrolysis at 500°; thus, the decomposition is
reversible.
* A literature review of the vinyl ether rearrangement
2
has been recently presented by Aten •
-l-
A similar sequence of reactions was reported by Aten
in the decomposition (450-525°) of methyl dAhydrofuran to
cyclopropylmethyl ketone and propenylmethyl ketone*
0 0
M I!
The first step, a rlnyl ether rearrangement, was not
measurably reversible*
Several pyrolyses of 3 ,4-dihydro-2H-pyrans have also
3
been studied* Bremner, Jones, and Beaumont have found
that 3,4-dihydro-2H-pyran decomposed at 500-540° to
acrolein (B5Jl) ethylene (66£)* Some carbon monoxide,
hydrogen, and high boiling residues were also formed.
Variations in the material of the pyrolysis tube or its
packing did not seriously alter the yields* Although the
addition of methyl iodide (ljl) to the dihydropyran did not
increase the rate of formation of acrolein, it seemed to
accelerate the acrolein*s decomposition* Nitric oxide had
a similar but less marked effect* The authors, therefore,
concluded that the thermal decomposition of dihydropyran
did not take place by a chain mechanism involving free
radicals*
Acrolein and ethylene have also baan obtainad from
tetrahydrofurfuryl alcohol in ona stage by uaa of an
4,5,6
aluminum silicata catalyst . By analogy to tha
4,5
pyrolysis of 2,3-dihydrofuran, Wilson has suggastad
tha possible existence of a cyclobutanecarboxaldehyde
intermediate in such a sequence of reactions,
r r dehydrating heat
g -CHO
l^J-CHgOH catalyst - o
CH2 = CH-CHO
Several derivatives of 3,4-dlhydro-2H-pyran have been
pyrolymed. Thus, 5-chloro-3,4-dlhydro-2H-pyran, when
passed with nitrogen over pumice at 400-450° yielded
7
* -chloroacroleln and ethylene ; 2-isobutoxy-3,4-dihydro-
2H-pyran, when passed through a steel tube at 400° produced
6
acrolein and vinyl isobutyl ether (96% yield) •
II. INTRODUCTION
A review of the literature thua indicates that cyclo-
propyl intarraadlataa art formad by a vinylic athar rearrange
ment in tha thermal decomposition of 2,3-dihydrofuran der
ivatives. Although postulated, such a rearrangement has as
yet not bean observed in tha pyrolyses of 3,4-dihydro-2H-
pyrans•
Tha purpose of this research was to study tha pyrolyses
of various 3 ,4-dlhydro-2H-pyrans and to determine whether
they rearranged to cyclobutyl intermediates during their
degradations. Absence of such intermediates would denote
that the decompositions probably occurred by a reverse
Diels-Alder type mechanism, as exemplified by the reversion
of cyclohexene to ethylene and 1,3-butadiene •
CHOI
CH2= CH2-h CH2= CH-CHO
ii* -r i
ch2
o
The approach to the problem was twofold. First,
dihydropyran and the postulated intermediate, cyclobutane
carboxaldehyde were thermally decomposed under similar
conditions. A comparison of the results should indicate
qualitatively whether the cyclic aldehyde conformed with
the requisites or s chemical Intermediate; that is, whether
it yielded the same products as\lts postulated precursor
and whether it did so at a sufficiently rapid rate to
account for their formation froralthe precursor.
Secondly, several 3»4-dlhydno-2H-pyrans substituted
in the two position, were pyrolysbd and the products were
carefully isolated. The Intervention of an unsymmetrical
cyclobutyl intermediate in the reaction might be manifested
by the presence of four products rather than by the usual
two formed in the decomposition of a Diels-Alder adduct.
This would result from a dual fission of the four membered
ring.
RCH ■= CH2
CH^CH-CHO
RCH = CH-CHO
ch2= ch2
The occurrence of such scissions in saturated cyclo-
butane rings has been demonstrated by Staudinger and
10
Rheiner who isolated four products from the thermal
decomposition of 1-methyl-2,2,3-trlphenyl cyclobutanol.
heat
l
OH 0
/ ( (C6H;)CH- CH2+ (C6H$)2CH
0
II
2 f(C6H$)CH~ C(C6H5)2 +CH3C - CHj
