Anodic oxidation of Schiff's bases. Part II. Anodic pyridination of N-benzylidene-p-anisidines in acetonitrile

Abstract

Anodic oxidation of N-benzylidene-p-anisidines in acetonitrile containing excess of pyridine results in the formation of a pyridinated Schiff's base in which the pyridinium group is ortho to the azomethine nitrogen atom on the anisidine ring. The pyridination process was investigated by cyclic voltammetry and controlled potential electrolysis at a glassy-carbon electrode. It is suggested that the sequence of pyridination is one-electron transfer from the lone pair of the azomethine nitrogen atom, proton transfer to pyridine from the ortho-position of the anisidine ring to the azomethine linkage, a further one-electron transfer to form a carbonium ion, and attack of pyridine. When pyridine was present in an equimolar amount or in slight excess, the behaviour at the electrode was rather complex; probably anodic acetamidation and/or anodic hydroxylation occured.