Organic Process Research & Development 2000, 4, 88−93
Epoxidation of Styrene to Styrene Oxide: Synergism of Heteropoly Acid and
Phase-Transfer Catalyst under Ishii-Venturello Mechanism
G. D. Yadav* and A. A. Pujari
Chemical Engineering DiVision, UniVersity Department of Chemical Technology (UDCT), UniVersity of Mumbai,
Matunga, Mumbai - 400 019, India
Abstract:
other hand, organic hydroperoxides such as cumene hydro-
peroxide (CHP), tert-butyl hydroperoxide (TBHP), ethyl-
benzene hydroperoxides (EBHP), etc.1,4 possess many ad-
vantages, including relative ease of handling and their higher
reactivities. Acid labile epoxides of such compounds as
styrene, R-methylstyrene, R-pinene, etc. which cannot be
prepared with peroxy acids have been prepared in excellent
yield by using hydroperoxides.
A practical route for direct epoxidation of olefins by
aqueous H2O2 which is environmentally clean and relatively
easy to handle, through the use of a suitable catalyst, is
desirable.5 The synergism of phase-transfer catalysis and
tungstate and phosphate (arsenate) ions under acidic condi-
tions or heteropoly acids for the oxidation of olefins, alcohols,
and diols with dilute H2O2 has been achieved in the
laboratories of Ishii6 and Venturello7,8 who have demon-
strated that olefins can be epoxidized with dilute H2O2
(<10%) with high selectivity to epoxide (80-90%) in short
times under mild conditions. These are now called Ishii-
Venturello epoxidations.
Heteropolyacids (HPA), such as dodecatungstophosphoric
acid and dodecamolybdophosphoric acid are often used not
only for the oxidation of organic substrates but also for many
acid-catalyzed reactions because they possess the dual
characteristics of oxidising ability and strong acidity. The
use of HPA for the oxidation of olefins with H2O2 generally
produces trans glycols because of the subsequent cleavage
of the oxirane ring of the reacting epoxide by eletrophilic
attack of strong acid. However, with the PTC, the epoxides
are easily formed under milder conditions.
Ishii-Venturello Epoxidation. In the context of epoxi-
dation of styrene, it is appropriate to deal briefly with the
Ishii-Venturello chemistry that involves the use of HPA,
H2O2, and PTC, which was useful in the interpretation of
rate data in the present studies.
Epoxidation of olefinic double bonds is of considerable impor-
tance in a variety of industries. Epoxides are raw materials for
a wide variety of chemicals such as glycols, alcohols, carbonyl
compounds, alkanolamines, and polymers such as polyesters,
polyurethanes, and epoxy resins. Epoxidation of styrene with
aqueous H2O2 was carried out by using synergism of heteropoly
acids and phase-transfer catalysis in a biphasic system under
the so-called Ishii-Venturello chemistry. The kinetics of ep-
oxidation of styrene to styrene oxide was studied. Styrene was
converted quantitatively to styrene oxide with 100% selectivity
of the converted styrene in ethylene dichloride as the solvent
at 50 °C. The effects of various parameters were studied on
the rate of reaction. Dodecatungstophosphoric acid (DTPA) and
cetyldimethylbenzylammonium chloride (CDMBAC) were found
to be the best heteropoly acid (HPA) and PTC combination,
respectively, for the epoxidation. The reaction mechanism is
very complex. At higher temperatures, there is a slight
degradation of hydrogen peroxide as well as some thermal
oligomerisation of styrene. The kinetic equation is complex due
to the nature of the epoxidising species. The reaction can be
represented by a pseudo-first-order kinetics where the order
in styrene concentration is unity. An apparent activation energy
of 7.26 kcal/mol was found.
Introduction
Styrene oxide is an important intermediate in organic
process industry, and it can be produced by epoxidation of
styrene amongst other routes. The current work was centered
around the epoxidation of styrene to styrene oxide by using
a synergism of heteropoly acids and phase-transfer catalysts
under the so-called Ishii-Venturello chemistry.
There are several methods of preparation of epoxides,
starting from olefins, R-halocarbonyls, carbonyls, epichloro-
hydrin, and substituted hydroxyl compounds.1-3 Epoxidation
with commercially available peroxyacids such as peroxy-
acetic acid, peroxybenzoic acid, peroxyfluoroacetic acid,
m-chloroperoxybenzoic acid, and m-nitroperoxybenzoic acid
is often a method of choice for laboratory preparation.
However, peroxy acids are hazardous to handle and the yields
obtained by using them in the epoxidation of some industri-
ally relevant compounds such as R-olefins are poor. On the
The highly selective epoxidation of terminal alkenes by
the complex WVI/PV/H2O2/PTC has been extensively inves-
tigated by several groups and was recently commercialised.9
There are contradictory reports about the basic mechanism,
and two schools of thought have emerged. According to the
general concept of PTC, various steps in this system are given
(4) Hiatt, R. R.; Howe, G. R. J. Org. Chem. 1971, 36, 2493-2497.
(5) Matoba, Y., Ishii, Y.; Ogawa, M. Synth. Commun. 1984, 14, 865-873.
(6) Ishii, Y.; Yamawaki, T.; Ura, H.; Yamada, H.; Ogawa, M. J. Org. Chem.
1988, 53, 3587-3593.
(7) Venturello, C.; Alneri, E.; Ricci, M. J. Org. Chem. 1983, 48, 3831-3833.
(8) Venturello, C.; Ricci, M. J. Org. Chem. 1983, 51, 1599-1602.
(9) Duncan, D. C.; Chambers, R. C.; Eric, H.; Hill, L. C. J. Am. Chem. Soc.
1995, 117, 681.
* To whom correspondence should be addressed.
(1) Swern, D. Organic Peroxides; Wiley-Interscience Inc.: New York, 1972;
Vol. II, p 265.
(2) Swern, D. Chem. ReV. 1949, 45, 1.
(3) Wilkinson, S. G. Int. ReV. Sci., Org. Chem. Ser. 2 1975, 2 111.
88
•
Vol. 4, No. 2, 2000 / Organic Process Research & Development
10.1021/op990055p CCC: $19.00 © 2000 American Chemical Society and The Royal Society of Chemistry
Published on Web 01/08/2000