Oxidative decolorisation of indigocarmine dye by chloramine-t in acidic buffer (ph= 5.8) medium catalysed by nitrite ion: a kinetic and mechanistic study

Kinetics of oxidative decolorisation of indigocarmine(IC) dye by CAT in pH 5.8 buffer medium catalyzed by nitrite ion has been studied at 300K spectrophotometrically at λmax= 610 nm. The reaction is first order with respect to [IC], [Nitrite ion] and second order with respect to [CAT]. It also shows an inverse first order on p-toluenesulphonamide concentration [TSA] and inverse fractional order on [H+]. The additions of the reaction product p-toluenesulphonamide and halide ions have no significant effect on the rate of the reaction. The variation of ionic strength of the medium did not affect the rate indicating that non ionic species are involved in the rate determining step. The dielectric effect is positive. The reaction was studied at different temperatures and the activation parameters have been deduced. Oxidation products were characterized. Test for free radicals was found to be negative. The derived rate law based on the proposed mechanism is in complete agreement with the observed kinetic data.