Benzenesulphenanilidyl radicals. Reactivity of 4′-methoxy- and 4′-methoxy-2-nitro-benzenesulphenanilidyl radicals

Abstract

Oxidation of 4′-methoxybenzenesulphenanilide (1a) with lead dioxide at 30 °C afforded the NN-bis(phenylthio)p-anisidine (7a) and 2,7-dimethoxyphenazine (3a) together with minor amounts of diphenyl disulphide (4a), whereas at 10 °C almost exclusive formation of compound (7a) and the o-benzoquinone di-imine (8a) was observed; compound (8a) was found to be thermally unstable and to give, quantitatively, compounds (4a) and (3a). The reaction products are rationalized by assuming that 4′-methoxybenzenesulphenanilidyl radicals (2a), produced by oxidation of compound (1a), undergo C_ortho–N coupling to give the dimer (9a), which is responsible for the reaction products observed. A comparable trend was observed by producing the radical (2a) from reaction of compound (1a) with t-butoxy-radicals and by thermal decomposition of compound (7a). These findings rule out the nitrene mechanism previously suggested for the formation of compound (3) from oxidation of the reagent (1a). Evidence has been found that C_ortho–N coupling is the main reaction path, exhibited also by 4′-methoxy-2-nitrobenzenesulphenanilidyl radicals (2c) generated from the corresponding anilide (1c) by reaction with t-butoxy-radicals or oxidation with lead dioxide, which thus rejects a previous claim that the radicals (2)(Ar = Ph and Ar = C₆H₄NO₂-o) exhibit different chemical behaviour.