Epoxidation of cyclohexene, using transition-metal substituted a-titanium arsenate { alpha-TiMAs, where M=Cu(II), Co(II), Mn(II), Fe(111), Cr(III) and Ru(III)} as a catalyst and dry tert-butyl hydroperoxide as an oxidant, was studied. In the epoxidation reaction, cyclohexene was oxidized to cyclohexene oxide, cyclohexenol and cyclohexenone. It was found that the reactivity of the epoxidation reaction decreased in the order alpha-TiRuAs > alpha-TiMnAs > alpha-TiFeAs > alpha-TiCrAs > alpha-TiCoAs > alpha-TiCuAs. A maximum selectivity for epoxidation of cyclohexene (89.89%) was observed for alpha-TiRuAs/dryTBHP system after 4 h of reaction when concentrations of the catalyst and the substrate were 0.20 and 20 mmol, respectively. The competitive epoxidation of cyclic olefins were studied and the reactivity-order in the relative rates of epoxidation of cyclic olefins was found to decrease in the order norbomene > cyclooctene > cyclohexene > cyclopentene. The mechanism for epoxidation of cyclohexene catalyzed by alpha-TiMAs/dryTBHP system is proposed. (C) 2004 Elsevier B.V. All rights reserved.