Metal Catalysis in Oxidation by Peroxides. Part 13. The Electrophilic Character of Oxygen Transfer from Peroxomolybdenum (VI) to Sulphides

The effect of the addition of HMPT on the oxidation rates of p-chlorophenylmethyl sulphide and of a series of phenyl-substituted arylmethyl sulphides with hydrogen peroxide in the presence of catalytic amounts of MoO2(acac)2 in ethanol at 25 °C was studied. HMPT added at relatively low concentration inhibits the oxidation of p-ClC6H4SCH3, whereas at higher HMPT the oxidation rates become independent of its concentration. Under these conditions the substituent effect on the oxidation rates of the set of arylmethyl sulphides follows the Hammett free-energy relationship (p = -0.7) contrary to the complex behaviour observed previously. These findings, while ruling out the possibility that the oxidation occurs at the complexed sulphide, strongly support the electrophilic mechanism for these oxidation reactions. © 1982.