Oxidation of aspartic acid by water soluble colloidal MnO₂ in absence and presence of ionic and nonionic surfactants

Abstract

The kinetics of the oxidation of aspartic acid by water-soluble form of colloidal manganese dioxide has been studied in acidic perchlorate media. Monitoring the disappearance of the colloidal MnO₂ spectrophotometrically at 390 nm has been used to follow the kinetics. The reaction is first-order in both [MnO₂] and [aspartic acid] but fractional-order in [HClO₄]. The results suggest formation of an adsorption complex between aspartic acid and MnO₂. The complex decomposes in a rate-determining step, leading to the formation of a free radical, which again reacts with the colloidal MnO₂ in a subsequent fast step to yield the product. The anionic micelles of sodium dodecyl sulfate have no effect on the oxidation rate whereas the rate constant increased with increase in [TX-100] which has been explained in terms of mathematical model proposed by Tuncay et al. A mechanism in agreement with the observed kinetic results is proposed and discussed. Freundlich isotherm is used to explain the adsorption of aspartic acid on colloidal MnO₂. Different activation parameters (Ea, ΔH#, ΔS#) have been evaluated and discussed.