Anodic oxidation of carboxamides. IV. Anodic dimerization of 4- and 4'-substituted benzanilides in the presence of a strong base.

Abstract

Anodic oxidation of several 4-and 4'-substituted benzanilides in the presence of a strong base, 1, 8-diazabicyclo [5. 4. 0] undecene-7 (DBU), was investigated by cyclic voltammetry and controlled potential electrolysis at a glassy carbon electrode in acetonitrile. The original voltammetric peak of the anilides shifted to less positive potentials on addition of DBU. The magnitude of the cathodic shift was linearly correlated with the Hammett σ values of the 4'-substituents, and the oxidation process could be explained in terms of a one-electron abstraction from the anilide which exists as a hydrogen-bonded complex with the base. Controlled potential electrolysis of the anilides under basic conditions gave three different types of dimers depending on the nature of the 4'-substituent, X. When X=alkyl group, the 4- (N-benzoyl-N-phenyl) amino-2, 5-cyclohexadienone derivative (2) was obtained. Diphenylamine derivatives (3) and (4) produced through N-2' and N-4' dimerization were the main products when X=hetero atom and X=H, respectively. A sandwich-type approach of the radicals formed by the initial one-electron transfer can account for these results.