Epoxidation of styrene to styrene oxide: synergism of heteropoly acid and phase-transfer catalyst under Ishii−Venturello mechanism

Abstract

Epoxidation of olefinic double bonds is of considerable importance 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 epoxidation 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.