Two-electron oxidation of N, N, N′, N′-tetramethyl naphthidine in acetonitrile The reactivity of its dication to aromatic nucleophilic substitution by pyridine

Abstract

The electrochemical oxidation of N, N, N′, N′-tetramethyl-1,1′-naphthidine (TMN), has been studied at the platinum electrode in acetonitrile. Cyclic voltammetry and coulometric studies show that, in neutral acetonitrile, TMN oxidizes to a stable dication (TMN 2+), in a reversible two-electron transfer. The factors that could contribute to this unusual behaviour I the anodic oxidation of aromatic amines are discussed. Electrochemical studies in acetonitrile, but with the addition of acid (anhydrous trifluoroacetic acid) and of bases (pyridine and 2,6-lutidine) were also performed. In acid medium, the anodic oxidation of TMN shows behaviour similar to the one observed for homologous compounds such as benzidines. However, in basic medium and when the base, such as pyridine, can act as a nucleophile, a reaction is observed with TMN 2+. The product is a pyridinium salt, resulting from an aromatic nucleophilic substitution on the naphthalene moiety. The kinetics of this reaction were studied by electrochemical and spectroscopic methods.