Heterogeneous catalytic hydrogenation of aromatic compounds

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Iowa State University Capstones, Theses and
Retrospective Theses and Dissertations
Dissertations
1971
Heterogeneous catalytic hydrogenation of aromatic
compounds: I. Deuteration and hydrogen
exchange of mono- and polyalkylbenzenes, II.
Selectivity in the reduction of diarylalkanes, III.
Competitive hydrogenolysis of arylmethanols
David Herbert Bohlen
Iowa State University
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Recommended Citation
Bohlen, David Herbert, "Heterogeneous catalytic hydrogenation of aromatic compounds: I. Deuteration and hydrogen exchange of
mono- and polyalkylbenzenes, II. Selectivity in the reduction of diarylalkanes, III. Competitive hydrogenolysis of arylmethanols "
(1971).Retrospective Theses and Dissertations. 4944.
https://lib.dr.iastate.edu/rtd/4944
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72-5179
BOHLEN, David Herbert, 1938-
HETEROGENEOUS CATALYTIC HYDROGENATION OF AROMATIC
COMPOUNDS: I. DEUTERATION AND HYDROGEN EXCHANGE
OF MONO- AND POLYALKYLBENZENES, II. SELECTIVITY
IN THE REDUCTION OF DIARYLALKANES, III. COMPETITIVE
HYDROGENOLYSIS OF ARYLMETHANOLS.
Iowa State University, Ph.D., 1971
Chemistry, organic
University Microfilms, A XERQXCompany, Ann Arbor, Michigaui
THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED
Heterogeneous catalytic hydrogénation of aromatic compounds:
I. Deuteration and hydrogen exchange of mono- and
polyalkylbenzenes,
II. Selectivity in the reduction of diaiylalkanea »
III. Competitive hydrogenolysis of arylmethanols
by
David Herbert Bohlen
A Dissertation Submitted to the
Graduate Faculty in Partial Fulfillment of
The Requirements for the Degree of
DOCTOR OF PHILOSOPHY
Major Subject: Organic Chemistry
Approved t
Signature was redacted for privacy.
In Charge of Major Wi
Signature was redacted for privacy.
Signature was redacted for privacy.
Dean of Graduate Cpl
Iowa State University
Of Science and Technology
Amest Iowa
1971
PLEASE NOTE:
Some Pages have indistinct
print. Filmed as received.
UNIVERSITY MICROFILMS
11
TABLE OK CONTENTS
Page
PART I. DEUTERATION AND HYDROGEN EXCHANGE 1
OF MONO- AND POLYALKYLBENZENES
INTRODUCTION 2
LITERATURE REVIEW 5
RESULTS AND DISCUSSION 27
EXPERIMENTAL 63
PART II. SELECTIVITY IN THE REDUCTION OF 78
DIAJRYLALKANES
INTRODUCTION 79
LITERATURE REVIEW 82
RESULTS AND DISCUSSION 93
EXPERIMENTAL 1 ]3
PART III. COMPETITIVE HYDROGENOLYSIS OF 128
ARYLMETHANOLS
INTRODUCTION 129
LITERATURE REVIEW 131
RESULTS AND DISCUSSION 144
EXPERIMENTAL 166
BIBLIOGRAPHY 181
ACKNOWLEDGMENTS 189
1
PART I. DEUTERATION AND HYDROGEN EXCHANGE OF MONO- AND
POLYALKYLBENZENES
2
INTRODUCTION
The study of the deuteration of the mono- and poly-
alkylbenzenes was initiated after the report of the hydro­
gen-deuterium exchange reactions of dimethylcyclopentane
(1). The perdeutero isomer predominates in the reaction
mixture; complete hydrogen-deuterium exchange was achieved
on a palladium catalyst at 60°Co Epimerization of the
trans isomer to the cis isomer was also observedo The
mechanism by which complete exchange occurs and by which
epimerization is achieved is not understood.
It has been shown that the reduction of the benzene
nucleus in acetic acid catalyzed by platinum proceeds
through an adsorbed cyclohexene intermediate (2). The hy­
drogénation in acetic acid is nonstereoselective; the reduc­
tion produces a mixture of cis- and trans-dialkvlcyclo-
hexanes. Various intermediates are proposed to account
for the nonstereoselectivity but none of the intermediates
completely explains the experimental observations accumu­
lated over the years.
The deuteration of the mono- and polyalkylbenzenes
was studied to determine the extent of deuterium incorpo­
ration into the cyclohexane product through deuteration and
hydrogen-deuterium exchange.
The reductions of the alkylbenzenes were carried out to
determine: a) the effectiveness of acetic acid-d^ as a
3
source of deuterium and che possible synthetic utilization
of the acid as a deuterium source, b) the role played by
a carbon alpha to the benzene or cyclohexane nucleus in the
exchange process, and c) the mechanistic implications derived
from information concerning an a-adsorbed complex.
The polyalkylbenzenes were hydrogenated to determine:
a) the role played by the ring carbons in the exchange
process, b) the effect of the extent of alkyl substitution
on the amount of deuterium incorporation, c) the effect of
the alkyl substitution pattern on the amount of deuterium
incorporation, d) the extent of deuterium incorporation into
cis- and trans-dialkylcyclohexanes, and e) the mechanistic
implications derived from information concerning the fomia-
tioii of a-complexes at the ring carbons and the nature of
the intermediate leading to the cis- and trans-dialkylcyclo­
hexanes.
A few half-hydrogénation experiments were performed
and the aromatic and aliphatic hydrocarbons separated and
analyzed for deuterium incorporation. This limited study
was carried out to determine the extent of deuterium
exchange in the aromatic compound prior to hydrogénation.
The study was carried out to gain information about
the mechanism of the hydrogénation and exchange reactions
of aromatic hydrocarbons, the nature of the intermediate
in the reduction, especially the intermediate which leads
4
to cis-trans isomerization of the dialkylcyclohexanes and
the mechanism of cycloalkene isomerization and exchange.
5
LITERATURE REVIEW
Hydrogénations of Alkylbenzenes
Early reports concerning the hydrogénation of benzene
and alkylbenzenes were made by Willstatter and Waldschmidt-
Leitz (3), Skita and Meyer (4), Skita and Schneck (5), and
Adams and Marshall (6). Willstatter and Waldschmidt-Leitz
used platinum black and acetic acid at room temperature
and atmospheric pressure. Skita, Meyer, and Schneck used
colloidal platinum in glacial acetic acid at three atmo­
spheres and 80°C and Adams and Marshall used reduced plat­
inum oxide in acetic acid at three atmospheres and room
temperature#
Kuhn and Winterstem studied the hydrogénation of
1,n-diphenylconjugated polyenes and found acetic acid to be
the solvent of choice when the fully saturated product was
desired (7).
Smith reviewed the catalytic hydrogénation of aromatic
hydrocarbons with an emphasis on kinetics and stereo­
chemistry (8)o In kinetic work considerable attention must
be given to reproducibility of the catalyst, purity of the
aromatic compound, temperature control, and a balance be­
tween catalyst weight and agitation conditions so that equi­
librium conditions are maintained. These conditions are
required so the reaction rate rather than the diffusion
rate is studied.