Effect of Cetyltrimethylammonium Bromide and Sodium Dodecyl Sulphate on Oxidation of Indigo Carmine with Potassium Peroxy Diphosphate: A Kinetic and Mechanistic Study

Abstract

The oxidative kinetic study of Indigo carmine (IC) with potassium peroxydiphosphate (PDP) in absence and presence of cationic cetyl-trimethylammonium bromide (CTAB) and anionic sodium dodecyl sulphate (SDS) micelles was studied in an aqueous sulphuric acid medium by maintaining the ionic strength at 3.0 mol dm-3 using sodium sulphate. The pseudo-zero-order constant was determined from the linear plots of absorbance versus time under the conditions [IC] < [PDP]. The reaction obeys zero-order kinetics with respect to varying [IC], first order kinetics with respect to varying [H+] and [PDP] in the absence and in presence of micelles. The reaction rate was accelerated with varying [CTAB] and [SDS] and reached a limiting value. The [surfactant] rate profile has limited nature since the reaction is unimolecular on the micelle surface. The binding constant of peroxy diphosphate was also determined with CTAB and SDS micelles by applying Berezin equation for the kinetic pattern.