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'-tet raethyl-p-phenylenediamine (TEPD) by metal ion like Ce4+, oxoanions vi z., MnO4- and Cr2O7(2-); peroxides such as peroxomonosulphate (PMS), p eroxodisulphate (PDS), and H2O2; and halogens namely Cl2, Br2, and I2. The fast kinetics of the formation and decay of the radical cation TE PD.+ have been analyzed at 565 nm by the stopped-flow technique under pseudo-first-order conditions. From the kinetic data, it has been infe rred that the reactions were found to be of first-order with respect t o [TEPD] and [oxidant] but over all it has been of second-order. The o bserved second-order rate constants in both the formation and decay of TEPD.+ has been correlated with the oxidation potentials of the vario us 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 ha s been found to regenerate the TEPD from the TEPD.+ and the correspond ing rate constant has also been determined. Besides these, this articl e also explains how the TEPD, which forms TEPD.+ acts as a better elec tron relay than TMPD(N,N,N',N'-tetramethyl-p-phenylenediamine) which f orms TMPD.+, even though both of them undergo one-electron oxidation a nd are used in the chemical routes to solar energy conversions. The ob served rate constants for electron transfer were correlated theoretica lly using Marcus theory. The observed and calculated rate constants ha ve good correlation. (C) 1995 John Wiley & Sons, Inc.