Kinetic study of oxidation of paracetamol by water-soluble colloidal MnO2 in the presence of an anionic surfactant

The kinetics of the oxidation of paracetamol [PCM] by water-soluble colloidal MnO2 was investigated spectrophotometrically at 298 K in the absence and presence of an anionic surfactant, sodium dodecyl sulphate (SDS), in aqueous solution. The reaction was first order with respect to [MnO2], [PCM] and [H2SO4]. The effects of [Mn(II)], [salt], dielectric constant and ionic strength of the medium on the kinetics of the reaction have also been examined. Micelles of SDS in aqueous solution accelerated the reaction rate, and partitioning of MnO2 in favour of the micellar pseudophase was remarkable. The catalytic effect of SDS in aqueous solutions has been treated by well-defined mathematical (Tuncay), Menger and Portnoy, and Piszkiewicz models. The binding constant (7.59 x 10(-2) mol(-1) dm(3)), dissociation constant (32.43), rate constant in the micellar phase (5.15 x 10(4) s(-1)), cooperativity index (1.98) and various thermodynamic activation parameters have been evaluated, and on the basis of the observed kinetic data, possible reaction mechanism and rate law have been proposed.