Kinetic and Mechanistic Studies of Indigocarmine Oxidation by Chloramine-T and Chlorine in Acidic Buffer Media

Article abstract of DOI:10.1002/kin.550270706

Oxidations of indigocarmine (IC) by chloramine-T (CAT) and aqueous chlorine (HOCl) in acidic buffer media, pH 2-6, have been kinetically studied at 30 deg C using spectrophotometry.The CAT reaction rate shows a first-order dependence on ₀ and an inverse fractional order on .The effect of on the rate is strongly pH dependent with a variable order of 1-2 on ₀ in the pH range 6-2.The chlorine reaction rate follows first-order in ₀ and ₀ each in the pH range 6-2.Addition of halide ions and variation of ionic strength of the medium have no influence on the reaction rate.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 HOCl at pHs 2-6 are similar suggesting similarity in their rate determining steps.A two-pathway mechanism for the CAT reaction and a one-pathway mechanism for the HOCl reaction, consistent with the kinetic data, have been proposed.Activation parameters have been calculated using the Arrhenius and Erying plots.