Benzenesulphenanilidyl radicals. Part 2. Substituent and solvent effects on the reactivity of 4′-substituted benzenesulphenanilidyl radicals produced by oxidation with lead dioxide of the corresponding benzenesulphenanilides

Abstract

Oxidation of benzenesulphenanilide (1d) with lead dioxide in benzene affords the p-benzoquinone diimine (5d) together with minor amounts of N,N-bis (phenylthio) aniline (4d) and diphenyl disulphide (7a). The formation of the products is explained in terms of p-C–N coupling of the benzenesulphenanilidyl radicals (2d) and subsequent fragmentation of the resulting dimer. A similar trend is observed in the oxidation of 4′-chloro- and 4′-bromo-benzenesulphenanilides (1e) and (1f), whereas 4′-nitrobenzenesulphenanilide (1g) leads to the o-phenylenediamine (12g), arising from o-C–N coupling of the sulphenanilidyl radical (2g). The oxidation of the sulphenanilides (1e) and (1f) in acetonitrile produces the phenazines (3e) and (3f) and the disulphide (7a), whereas the anilide (1g) and 4′-cyanobenzenesulphenanilide (1h) give azobenzenes (11g) and (11h) and the disulphide (7a); these results are discussed in terms of a possible mechanism involving oxidation of the N–N dimers (14e–h) which are in rapid equilibrium with the corresponding sulphenanilidyl radicals (2e–h). Evidence is also presented that the oxidation of 2-nitrobenzenesulphenanilides leads to products ascribable to intermediate 2-nitrobenzenesulphenanilidyl radicals, in contrast with a previous claim.