Kinetics of oxidation of benzidines in acetonitrile at the rotating platinum disc electrode

Abstract

N,N′-Diphenylbenzidine, N,N′-di- p-anisylbenzidine, N,N′-dimethyl- N,N′-diphenylbenzidine, and N,N,N′,N′-tetraphenylbenzidine were oxidized at a rotating platinum disc electrode in acetonitrile containing 0.1 M LiClO 4. Equilibrium potentials, standard rate constants, transfer coefficients and diffusion coefficients were determined using a method extending the one of Jahn and Vielstich[1]. With each of the benzidines, the standard rate constants for the oxidation to the semiquinoneimine cations are equal to the rate constants for the further oxidation to the diphenoquinonediimine dications. The standard rate constants for the different benzidines grow in the order given above. At positive potentials, the N,N′-di- p-anisyldiphenoquinonediimine dication is oxidized, probably at the methoxy group. The resulting intermediate decomposes in a homogeneous reaction of the first order with the rate constant k 1 = 5.5 s −1, and the second intermediate is further oxidized yielding the yet unknown final product.