Anodic oxidation of sulfonamides. II. Anodic oxidation of 4'-substituted benzenesulfonanilides in acetonitrile.

Abstract

Anodic oxidation of benzenesulfon-p-anisidide (I), benzenesulfon-p-toluidide (II), and N-methylbenzenesulfon-p-anisidide (III) were investigated by cyclic voltammetry and controlled potential electrolysis at a glassy-carbon anode in acetonitrile. I showed a single anodic wave in the absence of pyridine, and three anodic waves in the presence of pyridine. On electrolysis of I in the absence of pyridine, p-benzoquinone and benzenesulfonamide were formed. On electrolysis of I in the presence of pyridine, N, N'-dibenzenesulfonyl-N-(4'-methoxyphenyl)-5-methoxy-o-phenylenediamine (IV) and 1-(2-benzenesulfonamido-5-methoxyphenyl) pyridinium perchlorate (V) were obtained. Anodic oxidation of II in acetonitrile containing excess of pyridine gave N, N'-dibenzenesulfonyl-N-(p-tolyl)-5-methyl-o-phenylenediamine (VI) and N, N'-dibenzenesulfonyl-5, 5'-dimethyl-2, 2'-biphenyldiamine (VII). The formation of VI and VII was interpreted in terms of one-electron transfer followed by dimerizations of the free radical of II. On electrolysis of III in the presence of pyridine, 1-(N-methyl-3-benzenesulfonamido-6-methoxyphenyl) pyridinium perchlorate (VIII) was formed as the main product. The position of pyridination, which was ortho to the methoxy-group, was explained on the basis of steric factors.