Metal catalysis in oxidation by peroxides part 8 [1] further insight on the mechanism of vanadium(V) catalyzed oxidation of sulphides and alkenes by hydrogen peroxide

The oxidation of p-chlorophenyl methyl sulphide, geraniol and cyclohexene with hydrogen peroxide in the presence of catalytic amounts of bis acetylacetonato oxovanadium(IV) [VaO(acac)2] in dioxane and dioxaneethanol has been studied, p-Chlorophenyl methyl sulphoxide and 2,3-epoxygeraniol are produced in quantitative yield; oxidation of cyclohexene is, on the other hand, much less selective, affording 2-cyclohexen-1-ol, 2-cyclohexen-1-one and cyclohexene oxide as major products. Kinetic studies indicate that the rate of sulphide oxidation, at relatively low hydrogen peroxide concentration, is first-order in sulphide, oxidant and catalyst whereas, at higher [H2O2]o, zero-order dependence on hydrogen peroxide is observed. Autodecomposition of H2O2, which takes place at [VaO(acac)2] much higher than that used in oxidation experiments shows zero-order dependence on [H2O2]o and second-order dependence on [VaO(acac)2]. The equilibrium formation of monoperoxovanadium(V) species as the oxidizing agent is suggested. The relevance of acid-base equilibria, involving vanadium peroxoacid, on its oxidizing efficiency is discussed, also on the ground of potentiometric experiments. The mechanism of geraniol epoxidation, which accounts for the high reactivity and regioselectivity observed, is also discussed. © 1980.