Oxidations of aromatic sulfides promoted by the phthalimide N-oxyl radical (PINO)

The oxidation of a series of alkyl aryl sulfides promoted by the phthalimide N-oxyl radical (PINO) has been investigated by kinetic and product analysis. Sulfoxides are formed as major reaction products in the oxidation of thioanisoles and benzyl phenyl sulfides. The observation of fragmentation products in the oxidation of 2-phenyl-2-propyl phenyl sulfide and diphenylmethyl phenyl sulfide indicates that the reaction involves an initial electron transfer reaction from the sulfide to PINO with the formation of aryl sulfide radical cations and the anion PINO^-. Combination of the species then leads to a radical adduct precursor of sulfoxides while the rapid C–S cleavage occurs with aryl sulfide radical cations that can form the stable 2-phenyl-2-propyl or diphenylmethyl carbocation.