Phase-Transfer Catalysis. New Chemistry, Catalysts, and Applications

201 Pages·1987·2.51 MB·English

by  Charles M. Starks (Eds.)

Phase-Transfer Catalysis
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In Phase-Transfer Catalysis; Starks, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
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In Phase-Transfer Catalysis; Starks, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
ACS SYMPOSIUM SERIES 326
Phase-Transfer Catalysis
New Chemistry, Catalysts,
and Applications
Charles M. Starks, EDITOR
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1/b Developed from a symposium sponsored by
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American Chemical Society, Washington, DC 1987
In Phase-Transfer Catalysis; Starks, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Library of Congress Cataloging-in-Publication Data
Phase-transfer catalysis.
(ACS symposium series; 326)
"Developed from a symposium sponsored by the
Division of Petroleum Chemistry, Inc. at the 190th
Meeting of the American Chemical Society, Chicago,
Illinois, September 8-13, 1985."
Bibliography: p.
Includes index.
01 1. Phase-transfer catalysis—Congresses.
w0 2. Phase-transfer catalysts—Congresses.
6.f I. Starks, Charles M. II. American Chemical Society.
2
03 Meeting (190th: 1985: Chicago, Ill.) III. American
7- Chemical Society. Division of Petroleum Chemistry,
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9 Inc. IV. Series.
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bk- QD505.P49 1987 541.3'95 86-25957
1/ ISBN 0-8412-1007-1
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er Copyright © 1987
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m American Chemical Society
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er Roland F. Hirsch Charles S.Tuesday
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In Phase-Transfer Catalysis; Starks, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Foreword
The ACS SYMPOSIUM SERIES was founded in 1974 to provide a
medium for publishing symposia quickly in book form. The
format of the Series parallels that of the continuing ADVANCES
IN CHEMISTRY SERIES except that, in order to save time, the
papers are not typeset but are reproduced as they are submitted
by the authors in camera-ready form. Papers are reviewed under
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0 the supervision of the Editors with the assistance of the Series
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6.f Advisory Board and are selected to maintain the integrity of the
32 symposia; however, verbatim reproductions of previously pub
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7- lished papers are not accepted. Both reviews and reports of
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19 research are acceptable, because symposia may embrace both
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In Phase-Transfer Catalysis; Starks, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Preface
SCIENTIFIC KNOWLEDGE AND INDUSTRIAL APPLICATION of the phase-
transfer catalysis (PTC) technique have expanded greatly during the last 15
years. As its practical simplicity and economic advantages have become
more recognized, this field appears to be growing even more. Growth of
PTC is easily measured (1) by the number of entries indexed by Chemical
Abstracts, (2) by the fact that Chemical Abstracts has decided to form a
separate "C. A. Selects" on PTC, (3) by the increasing number of phase-
01 transfer agents offered for sale by chemical supply companies, (4) by the
0
pr worldwide increase in specialized publications on PTC in a variety of
6.
32 languages, and (5) by the less easily measured but clearly exponential
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7- growth in the use of PTC for industrial chemical processing. I estimate the
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19 volume of phase-transfer catalysts totaled about 40,000 lb of catalysts per
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b year in 1980 but grew to more than 1 million lb of catalyst per year in
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02 1985.
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0. I am grateful to the authors who took the time and effort to prepare
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oi: manuscripts, often on tight deadlines. I also wish to thank the many
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7 | reviewers who helped to bring out points of particular interest, to clarify
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9 ambiguous areas, and to generally improve the quality of already excellent
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9, writing. I am especially grateful to Lisa Butler who single-handedly and
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er cheerfully handled and prepared numerous letters, notices, copies, revisions,
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e reviews, and manuscripts.
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ate: CHARLES M. STARKS
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n Vista Chemical Company
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ati Ponca City, OK 74602
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ix
In Phase-Transfer Catalysis; Starks, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Chapter 1
Phase-Transfer Catalysis: An Overview
Charles M. Starks
Vista Chemical Company, Ponca City, OK 74602
Uniquely interesting, complex and useful activities and phenomena
occur at interfaces: one need only to look at the interfaces between
the land, the atmosphere, and the sea to find this truth. The same
1
00 truth occurs in chemical interfaces, although sometimes it is the
h
c lack of activity that draws our attention. In many chemical
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2 situations where two species cannot collide and therefore cannot
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0 react because they are separated by an interface, the lack of
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8 activity has been overcome by use of the technique of PHASE TRANSFER
9
k-1 CATALYSIS (PTC), which not only allows reaction to occur, but often
b to occur in very selective ways.
1/
2 An early and clear example of PTC(1) demonstrated that the lack
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0.1 of reactivity between a mixture of 1-chlorooctane and aqueous sodium
1 cyanide (without organic solvent) could be overcome by the use of a
oi: phase transfer agent, whose function was to transfer cyanide ion in
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7 | reactive form from its normal aqueous phase into the chlorooctane
98 phase. Use of a small amount of phase transfer agent makes the
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9, system catalytic, since the phase transfer agent can repeatedly
1 transfer active cyanide ions into the organic phase for reaction
ber with 1-chlorooctane. This sequence of steps is represented by
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e equation 1, where Q+ represents a quaternary salt containing
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e sufficiently long alkyl groups or other organic structure as to make
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e: QCN predominantly soluble in the organic phase.
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aqueous Cl" + Q+CN" r CN" + Q+Cl"
phase ^
Other classic examples illustrating the use of quaternary salts as
phase transfer catalysts were published by Makosza(2), and by
Brandstrom(3.) . Subsequent development of crown ethers(4-7) and
cryptands(7-8) as phase transfer catalysts gave PTC an entirely new
dimension since now the inorganic reagent, as sodium cyanide in the
above equation, need no longer be dissolved in water but can be used
0097-6156/87/0326-0001$06.00/0
© 1987 American Chemical Society
In Phase-Transfer Catalysis; Starks, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
2 PHASE-TRANSFER CATALYSIS
as a dry solid. This development gave rise to liquid-solid PTC as a
partner to liquid-liquid PTC.
Since 1971 phase transfer catalysis has emerged as a broadly
useful tool(9-16) . not only in organic chemistry, but also in
inorganic chemistry(17), for new analytical applications(18), in
electrochemistry(27a), photochemistry(27b), and especially in
polymer chemistry.(21.27-31) The substantial number of publications,
patents, reviews, and books (200 to 400 per year since 1980)
concerned with PTC in both scientific and commercial applications
attests to the high level of interest that this technique has
generated.
Commercial usage of PTC techniques has increased markedly
during the last five years not only in the number of applications
(currently estimated to be fifty to seventy-five different
uses(22)), but also in the volume of catalysts consumed (estimated
01 to be about one million pounds per year(22)) and in the volume of
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h products manufactured (estimated to be fifty to one hundred million
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6. pounds per year(22)) in the United States alone. Many indicators
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03 point to additional extensive commercial applications of the PTC
7- technique a ll around the world, and these indicators suggest that
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19 future chemical manufacturing processes will more an more
k- incorporate PTC because of its advantages of simplicity, reduced
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1/ consumption of organic solvents and raw materials, mild reaction
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10 conditions, specificity of reactions catalyzed, and enhanced control
0. over both reaction conditions, reaction rates, and yields. For some
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oi: currently produced polymers PTC provides the only reasonable and
7 | d practical commercial method of manufacture(22).
8 Enormous progress has been made in recent years in a ll aspects
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1 of phase transfer catalysis, and the symposium on which this volume
19, is based(23) was organized to provide a sample of some of the
er advances in three areas: (1) theory and application of the method;
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m (2) design of specific catalysts for increased efficiency and
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ec selectivity; and (3) use of PTC in polymer chemistry. The excellent
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n D which stimulate and delight those of us who have a strong interest
o in PTC.
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The general concept of phase transfer catalysis applies to the
transfer of any species from one phase to another (not just anions
as illustrated above), provided a suitable catalyst can be chosen,
and provided suitable phase compositions and reaction conditions are
used. Most published work using PTC deals only with the transfer of
anionic reactants using either quaternary ammonium or phosphonium
salts, or with crown ethers in liquid-liquid or liquid-solid
systems. Examples of the transfer and reaction of other chemical
species have been reported(24) but clearly some of the most
innovative work in this area has been done by Alper and his
co-workers, as described in Chapter 2. He illustrates that
gas-liquid-liquid transfers with complex catalyst systems provide
methods for catalytic hydrogénations with gaseous hydrogen,
In Phase-Transfer Catalysis; Starks, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
1. STARKS Overview 3
catalytic oxidations with gaseous oxygen, and carbonylation of alkyl
halides, olefins and acetylenes with carbon monoxide.
A portion of substantial theoretical and historical importance
in PTC has centered around the question of 'what is the nature of
the species transferred, and where in the reaction sequence do the
slow steps take place.' These questions prompted much debate during
the early years of PTC when development and understanding of the
reaction sequence and mechanism of PTC was emerging. It generally
came to be recognized that small changes in the complex sequence of
steps of even the simplest phase transfer catalyzed system can
result in differing kinetics, differences in optimal catalyst
structure, and different optimal reaction conditions, even for
similar reactions. Of particular interest in this volume is
Chapter 3 by Liotta and co-workers, who have found that even the
amount of water present in liquid-solid PTC may substantially affect
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0 the site where final reaction occurs. These observations have led
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ch Liotta to postulate a new phase in which reaction may occur.
26. Montanari and co-workers, who have been prolific contributors in
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0 PTC, have also provided (Chapter 6) significant insight into the
87- effect of water on PTC reactions.
9
1 In a series of highly useful applications phase transfer
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b catalysis has given the chemist the ability to conduct reactions
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2 between organic compounds and strong inorganic oxidants such as
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1 permanganate, dichromate, hypochlorite, and hydrogen peroxide(25).
0.
1 Use of these oxidants previously has been limited and experimentally
oi: inconvenient because of the narrow range of stable organic solvents
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7 | which one could use to bring the oxidants and substrate into
98 contact. The power of PTC for permanganate oxidations and the use of
9, 1 PTC to study the mechanism of these oxidations is demonstrated by
1 Lee in Chapter 8.
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Catalyst Improvements
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e: Although quaternary ammonium salts, phosphonium salts, crown ethers,
at and cryptands are generally excellent catalysts for most PTC
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n applications, there are many potential PTC applications where these
atio agents have deficiencies. For example, ordinary tetraalkyl
c quaternary salts decompose at high temperatures (greater than
ubli 120-149°C), or at low temperatures under highly alkaline conditions
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or in the presence of highly nucleophilic anions such as phenoxide.
Crown ethers and cryptands are stable under these conditions but are
much more expensive (100 to 1000 fold cost) than quaternary salts,
and for practical commercial use they must be completely recovered
for re-use. Open-chain polyethers, mainly polyethylene glycols,
catalyze some kinds of two-phase reactions, are stable and are quite
low in cost, but their limited utility substantially restricts their
application to a narrow range of reactions.
The possibility of solving the catalyst recovery problem by
attaching active catalyst centers to insoluble polymeric substrates
was recognized early(26) , as was the possible use of chiral PTC
catalysts to introduce chirality in products(1). Much work in both
these areas has been partially successful(27). However, the results
have not been completely satisfactory in that resin bound catalysts
have shown much lower catalytic activity than soluble catalysts and
they frequently lose their activity with repeated use. Chiral
In Phase-Transfer Catalysis; Starks, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.