Progress in Physical Organic Chemistry, Volume 3

392 Pages·1965·12.667 MB·English

Progress in
PHYSICAL
ORGANIC
CHEMISTRY
VOLUME 3
Progress in
PHYSICAL
ORGANIC
CHEMISTRY
VOLUME 3
Editors
SAUL G. COHEN, Department of Chemistry
Brandeis University, Wallhum, Massachusetts
ANDREW STREITWIESER, JR., Department of Chemistry
University of California , Berkeley, California
ROBERT W. TAFT, Department of Chemistry
University of California, Irvine, California
1965
INTERSCIENCE PUBLISHERS
a division of John Wiley Sons New York London Sydney
Copyright @ 1965 by John Wiley & Sons, Iiic.
All rights reserved
Library of Congress Catalog Card Number 63-19364
PRINTED IN THE UNITED STATES OF AMERICA
Introduction to the Series
Physical organic chemistry is a relatively modern field with deep
roots in chemistry. The subject is concerned with investigations of
organic chemistry by quantitative and mathematical methods. The
wedding of physical and organic chemistry has provided a remarkable
source of inspiration for both of these classical areas of chemical
endeavor. Further, the potential for new developments resulting
from this union appears to be still greater. A closening of ties with
all aspects of molecular structure and spectroscopy is clearly antici-
pated. The field provides the proving ground for the development of
basic tools for investigations in the areas of molecular biology and
biophysics. The subject has an inherent association with phenomena
in the condensed phase and thereby with the theories of this state of
matter.
The chief directions of the field are: (a) the effects of structure and
environment on reaction rates and equilibria; (b) mechanism of re-
actions; and (c) applications of statistical and quantum mechanics
to organic compounds and reactions. Taken broadly, of course, much
of chemistry lies within these confines. The dominant theme that
characterizes this field is the emphasis on interpretation and under-
standing which permits the effective practice of organic chemistry.
The field gains its momentum from the application of basic theories
and methods of physical chemistry to the broad areas of knowledge
of organic reactions and organic structural theory. The nearly in-
exhaustible diversity of organic structures permits detailed and syste-
matic investigations which have no peer. The reactions of complex
natural products have contributed to the development of theories of
physical organic chemistry, and, in turn, these theories have ulti-
mately provided great aid in the elucidation of structures of natural
products.
Fundamental advances are offered by the knowledge of energy
states and their electronic distributions in organic compounds and
V
vi INTRODUCTION TO THE SERIES
the relationship of these to reaction mechanisms. The development,
for example, of even an empirical and appr0ximat.e general scheme
for the estimation of activation energies would indeed be most, notable.
The complexity of even the simplest organic compounds in terms of
physical theory well endows the field of physical organic chemistry
with the frustrations of approximations. The quantitative correla-
t,ioris employed in this field vary from purely empirical operational
formulations to the approach of applying physical principles to a
workable model. The most common procedures have involved the
application of approximate theories to approximate models. Critical
assessment of t,he scope and 1iniitat.ionso f these approximate applica-
t,ions of theory leads t)o further development and understanding.
Alt'hough he may wish to be a disclaimer, the physical organic chem-
ist attempts to compensate his lack of physical rigor by the vigor of
his eff0rt.s. There has indeed been recently a great OUtpOuI'ing of
work in t.his field. We believe t,hat a forum for exchange of views and
for critical and authoritative reviews of t,opics is an essent,ial need of
this field. It is our hope that the projected periodical series of volumes
under this tit'le will help serve this need. The general organization
and charact'cr of the scholarly presentat,ions of our series will corre-
spond to that of the several prot,otypes, e.g., Advances in Enzymology,
Advances in Chemical Physics, and Progress in Inorganic Chemistry.
We have encouraged the authors t,o review topics in a style that is
not, only somewhat more speculative in character but which is also
more detailed than presentations normally found in textbooks. Ap-
propriate t,o this quantitative aspect of organic chemistry, authors
have also been encouraged in the cit,atiori of numerical data. It is
intended t.hat' t$ese volumes will find wide use among graduate stu-
dents as well as pract'icing organic chemists who are not necessarily
expert iti the field of these special topics. Aside from these rather
obvious considerations, the emphasis in each chapter is the personal
ideas of the author. We wish to express our gratitude to the authors
for the excellence of their individual presentations.
We greatly welcome comments and suggestions on any aspect of
these volumes.
SAULG . COHEX
ANDREWS TREITWIESJEHR.,
ROBERTW . TAFT
Contributors to Volume
3
G. M. BADGER
University of Adelaide, Adelaide, Australia
E. GRUNWALD
Brandeis University, Waltham, Massachusetts
J. H. HAMMONS
Swarthmore College, Swarthmore, Pennsylvania
E. 31. KOSOWER
Department of Chemistry,S tate University of New York,S tony Brook,
Long Island, New York
C. L. PERRIN
Department of Chemistry, University of California, San Diego,
California
A. STREITWIESER, JR.
Department of Chemistry, University of California, Berkeley,
California
vii
Contents
Pyrolysis of Hydrocarbons
BY G. M. BADGER 1
Acidity of Hydrocarbons
BYA NDREWST REITWIESJERR. ,A ND JAMES H. HAMMOSS 41
Reactions through Charge-Transfer Complexes
BY EDWARMD . KOSOWER 81
Mechanisms of Organic Polarography
BY CHARLELS. PERRIN 165
Ultra-fast Proton-Transfer Reactions
BY ERNESTG RUNWALD 317
Author Index 3J9
Subject Index 3 79
Cumulative Index, Volumes 1-3 387
ix
Progress in Physical Organic Chemistry, Volume 3
Edited by Saul G. Cohen, Andrew Sireitwieser, Jr. Robert W. Taft
Copyright 0 1965 by John Wiley & Sons, Inc.
Pyrolysis of Hydrocarbons
BY G. Al. BADGER
University of Adelaide, Adelaide, Australia
CONTENTS
I. Introduction ................................................... 1
11. Alkanes ....................................................... 5
111. Alkenes.. ...................................... ........ 7
IV. Unsubstituted Aromat,ic
A. Benzene.. .......
B. Naphthalene ............................................. 9
C. Anthraceue ....................
D. Phensnthrene.. ......: . .......
E. Naphthalene and Benzene
F. Phenanthrene and
G. Pyrene and Benzene.. ..................................... 17
V. Alkylbenzenes and Alkenylbenzenes .............................. 17
A. Styrene .................................................. 17
R. Toliiene .................................................. 19
C. Ethylbenzene ............................................ 24
D. Propylbenzene. .............. ......... 27
E. Indene ............. ....................... 28
F. Butylbenzene. ...... ............. 29
G. Tetralin.. ......... ....................... 33
H. a,w-Diphenylalkanes ........
VI. The Influence of Temperature. .................................. 36
References ............................................. : ...... 38
I. Introduction
The thermal degradation or pyrolysis of organic materials has
played an important role in the history and development of organic
chemistry. Benzene was discovered (1) by Faraday in 1825 in the
condensate of a compressed illuminating gas which had been prepared
by the pyrolysis of whale oil. Years later benzene was isolated from
coal tar (2), the by-product formed during the pyrolysis of coal in the
manufacture of coal gas. Still later, in his classical experiments on the
pyrolysis of hydrocarbons, Berthelo t (3) obtained benzene by passing
acetylene through a red hot tube. Many other hydrocarbons and
1
2 M. BADGER
C.
related compounds have similarly been produced by pyrolytic proc-
esses. The pyrolysis of petroleum and of similar materials has at-
tained considerable importance, arid coal tar has remained an im-
portant source of aromatic. compounds.
The first systematic work on the pyrolysis of hydrocarbons was
carried out by Berthelot (3) at a time when analytical techniques other
than distillation and crystallization were unknown. His work has
been repeated and extended by many other workers using improved
techniques. It must be reriienibered, however, that results obtained
before the introduction of techniques such as chromatography, gas-
liquid chroniatography, ultraviolet spectroscopy, and infrared spec-
troscopy, need to be accepted with caution. The purity of the start-
ing materials is often suspect, as are the identities of some of the
products; and the temperature of the pyrolysis was often described
simply as “red heat,” “dull red heat,” or “bright red heat.”
Early speculations on the mechanisms of the reactions involved
were thoroughly reviewed in the monographs by Egloff (4) and
Hurd (5). The free radical reactions involved in the decomposition
of simple hydrocarbons have been summarized by Steacie (6), and
the kinetics of these reactions by Trotman-Dickenson (7). Several
other useful reviews have also been published (8-12). In the present,
review it is proposed to discuss not only the processes of break-down
under conditions of high temperature, but also the mechanisms of re-
synthesis involved in the formation of polycyclic aromatic hydro-
carbons.
Berthclot (3) suggested that the pyrolysis of hydrocarbons involves
a primary degradation to acetylene, and that the polymerization of
this substance leads to benzene and other aromatic hydrocarbons.
A similar view was held by Groll (13), and this hypothesis has also
found support from other workers (14,15).
Benzene and many other aromatic hydrocarbons are certainly
formed by the pyrolysis of acetylene (16). On the other hand, how-
ever, although hydrogen, methane, and ethylene are important prod-
ucts in all hydrocarbon pyrolyses, acetylene has been reported only
very rarely.
It has also been suggested that the pyrolysis of hydrocarbons gives
butadiene as a degradation product, and that this conipound is the
precursor of the aromatic hydrocarbons found in the resulting tar.
This hypothesis originated from the observation (17) that the pyroly-
PYROLYSlS HYDROCARBONS 3
OF
sis of butadiene at 800°C. gave a tar containing 25% benzene and
20% naphthalene. The hypothesis was supported by Jones (18),
and also by Weizmann (19,20). According to the latter, polycyclic
hydrocarbons could be formed by a series of Diels-Alder reactions in-
volving alkenes, or aromatic hydrocarbons, and butadiene. Thus,
phenanthrene and anthracene might be formed by addition of buta-
diene to naphthalene; and triphenylene, chrysene, benzo [clphenan-
threne, and benz [alanthracene might be formed from butadiene and
phenanthrene.
The pyrolysis of butadiene has recently been investigated at 550"
(21) and at 700" (22). At the lower temperature, cyclohexene, cyclo-
hexadiene, and Cs aromatic compounds were formed. At the higher
temperature, complete conversion of the acyclic and alicyclic com-
ponents to aromatic compounds occurred, and benzene, toluene, and
polycyclic compounds were observed among the products. The di-
merization of butadiene is known to yield 3-vinylcyclohexene (23) ,
and pyrolysis of this compound gave products similar to those from
butadiene itself (24,21). Rloreover, ethylene and propylene have
been shown to react with butadiene to yield the Diels-Alder adducts
cyclohexene and 3-methylcyclohexene, respectively ; and with in-
creased contact time there was preferred formation of benzene in the
presence of ethylene, and of toluene in the presence of propylene (25).
There is thus good evidence that a t>ypeo f Diels-Alder reaction can
occur at high temperatures, and it seems likely that this reaction plays
a part in some pyrolyses.
On the other hand, although butadiene is formed from many hydro-
carbons under pyrolytic conditions (26) , recent evidence suggests that
it cannot be an important intermediate in the synthesis of polycyclic
hydrocarbons at high temperatures. For example, the pyrolysis of a
mixture of pyrene and butadiene (22) gave yields of benzopyrenes
only very slightly greater than those obtained by the pyrolysis of
butadiene itself. In any case the relative activation energies for the
diene addition and for radical addition (7) suggest that resynthesis
proceeds by radical rather than molecular addition.
Attention must also be directed to the hypothesis that the pyrolysis
of hydrocarbons can lead to CBf ragments, and that the resynthesis of
aromatic hydrocarbons proceeds from these units (27). It was sug-
gested that thermal abstraction of hydrogen from allene (a product
obtained by Szwarc (28) from the pyrolysis of propylene) would give