CHANNEL ELECTRODE VOLTAMMETRIC AND IN-SITU ELECTROCHEMICAL ESR STUDIES OF COMPROPORTIONATION OF METHYL VIOLOGEN IN ACETONITRILE

Two redox processes of methyl viologen (+2/+, +/0) in acetonitrile wer e investigated by using channel electrode voltammetric and in situ ele ctrochemical ESR methods. Two separated unequal plateau currents of th e first (+2/+) and second (+/0) redox processes of the viologen were o bserved in the channel electrode voltammograms and showed a cube-root depedndence on the electrolyte flow rate, respectively. The simple Lev ich analysis resulted in two different diffusion coefficients of D-+2= 2.2X10(-5) cm(2)/s and D-+=3.0X10(-5) cm(2)/s from the limiting curren ts. In situ electrochemical ESR studies were performed for the monocat ion radicals generated at the potentials of the two plateau currents i n the electrolyte flow range 1.3X10(-1) greater than or equal to v(f) greater than or equal to 2.7X10(-3) cm(3)/s. Backward implicit finite difference method was employed to simulate the electrochemical kinetic problem of two sequential electron transfers (MV(+2) + e reversible a rrow MV(+), MV(+) + e reversible arrow MV(o)) coupled with reversible comproportionation (MV(2+) + MV(o) (kb)reversible arrow(kj)). k(j) was found to be greater than 10(6) M(-1) s(-1).