FORMATION AND DECAY OF N,N,N',N'-TETRAETHYL-P-PHENYLENEDIAMINE RADICAL-CATION IN AQUEOUS-SOLUTION - A KINETIC-STUDY BY STOPPED-FLOW TECHNIQUE

A kinetic study has been carried out on the oxidation of N,N,N',N'-tetraethyl-p-phenylenediamine (TEPD) by metal ion like Ce4+, oxoanions viz., MnO4- and Cr2O7(2-); peroxides such as peroxomonosulphate (PMS), peroxodisulphate (PDS), and H2O2; and halogens namely Cl2, Br2, and I2. The fast kinetics of the formation and decay of the radical cation TEPD.+ have been analyzed at 565 nm by the stopped-flow technique under pseudo-first-order conditions. From the kinetic data, it has been inferred that the reactions were found to be of first-order with respect to [TEPD] and [oxidant] but over all it has been of second-order. The observed second-order rate constants in both the formation and decay of TEPD.+ has been correlated with the oxidation potentials of the various oxidants employed in this study. The effect of pH on the oxidation has been investigated in the formation and decay of TEPD.+ as well as reduction studies have also been carried out using dithionite which has been found to regenerate the TEPD from the TEPD.+ and the corresponding rate constant has also been determined. Besides these, this article also explains how the TEPD, which forms TEPD.+ acts as a better electron relay than TMPD(N,N,N',N'-tetramethyl-p-phenylenediamine) which forms TMPD.+, even though both of them undergo one-electron oxidation and are used in the chemical routes to solar energy conversions. The observed rate constants for electron transfer were correlated theoretically using Marcus theory. The observed and calculated rate constants have good correlation. (C) 1995 John Wiley & Sons, Inc.