Metal catalysis in oxidation by peroxides part 14. Kinetics and mechanism of titanium-catalyzed oxidation of sulphides with t-butyl hydroperoxide

Abstract

The oxidation of di-n-butylsulphide, p-methylphenylmethylsulphide and p-chlorophenylmethylsulphide with t-butyl hydroperoxide in the presence of catalytic amounts of TiO(acac) 2 and Ti(OPr i) 4 has been studied in toluene. The reaction affords the corresponding sulphoxides in quantitative yield. Kinetic studies indicate that the oxidation rate is first order in the hydroperoxide and catalyst whereas the dependence on substrate initial concentration is rather complex, leading to an apparent positive but fractional order. This behaviour suggests that coordination of the sulphides to Ti(IV) occurs in solution. Two alternative mechanisms, both consistent with the experimental data, the ‘electrophilic’ oxidation of the free substrate by the peroxotitanium species present in the system or the intramolecular oxygen transfer to the coordinated sulphide, are discussed.