Epoxidation of alkenes catalysed by Mn III (Schiff base) complexes

Abstract

The epoxidation of cyclohexene using various MnIII(Schiff base) NCS complexes as catalyst and PhIO as oxidant give cyclohexeneoxide, cyclohexenol and cyclohexenone as the products. The effect of catalyst concentration shows that, on increasing the concentration of catalyst the yield of the epoxide decreases. The relative rate of reaction of cyclic alkenes follows the order; nor-bornene > cyclo-octene > cycloheptene > cyclohexene > cyclopentene. This shows that rigid co-ordination of alkene to oxomanganese(V) catalyst does not take place in the rate-determining step. The effect of various additives viz., pyridine, imidazole, NaHCO3, NaH2PO4, sodium lauryl sulphate, cetyl trimethyl ammonium bromide, and Triton X-100 shows that axial ligation due to pyridine, imidazole etc. increases the yield of epoxide. The surfactants Triton X-100 and sodium lauryl sulphate show that micellar catalysis plays a positive role.