Epoxidation of cyclic alkenes with hydrogen peroxide and tert-butyl hydroperoxide on Na-containing Tiβ zeolites

Abstract

The liquid-phase epoxidation of a series of cyclic alkenes with H2O2 and TBHP over Na-Tiβ zeolites without undergoing further acid-treatment has been carefully investigated. Many factors such as the time, the conversion, the solvent, the Si/Na ratio, the Si/Ti ratio and the Ti/Na ratio, have been found to take effects on the conversion of cyclohexene and H2O2 as well as the selectivity to epoxide. Lower conversion (about 6.2 mol%) of cyclohexene has shown an improvement for the selectivity to epoxide (about 90%). The solvent having bigger dielectric constant is very helpful to enhance the reactivity of substrate, particularly MeCN is an optimal choice for improving the selectivity to epoxide (up to 59%). The reactivity of cyclic alkenes decreases with increasing carbon number from C6 to C12, the selectivity to corresponding cyclic epoxides is C12 ≈ C8 (100%) > C7 (71%) > C5 (20%) > C6 (1.2%), where the exception of C5 is related to its low dissolubility and steric conformations of reactant and products molecules. Linear alkene shows the higher reactivity and the lower selectivity to epoxide than cyclic alkene with the same carbon number. TBHP as the oxidant significantly retards the reactivity of C6, C7 and C12, and shows more beneficial to the selective production of epoxide than H2O2. © 2001 Elsevier Science B.V. All rights reserved.