KINETIC AND MECHANISTIC STUDIES OF INDIGOCARMINE OXIDATION BY CHLORAMINE-T AND CHLORINE IN ACIDIC BUFFER MEDIA

Oxidations of indigocarmine (IC) by chloramine-T (CAT) and aqueous chl orine (HOCl) in acidic buffer media, pH 2-6, have been kinetically stu died at 30 degrees C using spectrophotometry. The CAT reaction rate sh ows a first-order dependence on [IC](o) and an inverse fractional orde r on [p-toluenesulfonamide]. The effect of [CAT] on the rate is strong ly pH dependent with a variable order of 1-2 on [CAT]o in the pH range 6-2. The chlorine reaction rate follows first-order in [IC](o) and [H OCl](o) each in the pH range 6-2. Addition of halide ions and variatio n of ionic strength of the medium have no influence on the reaction ra te. There is a negative effect of dielectric constant of the solvent. The kinetics of the IC oxidation with CAT at pH 6 and of that with HOC l at pHs 2-6 are similar suggesting similarity in their rate determini ng steps. A two-pathway mechanism for the CAT reaction and a one-pathw ay mechanism for the HOCl reaction, consistent with the kinetic data, have been proposed. Activation parameters have been calculated using t he Arrhenius and frying plots. (C) 1995 John Wiley and Sons, Inc.