Abstract
Aqueous solution of water soluble colloidal MnO2 was prepared by Perez-Benito method. Kinetics of L-methionine oxidation by colloidal MnO2 in perchloric acid (0.93x10(-4) to 3.72x10(-4) mol dm(-3)) has been studied spectrophotometrically. The reaction follows first-order kinetics with respect to [H+]. The first-order kinetics with respect to L-methionine at low concentration shifts to zero order at higher concentration. The effects of [Mn(II)] and [F-] on the reaction rate were also determined. Manganese (II) has sigmoidal effect on the rate reaction and act as auto catalyst. The exact dependence on [Mn(II)] cannot be explained due to its oxidation by colloidal MnO2. Methionine sulfoxide was formed as the oxidation product of L-methionine. Ammonia and carbon dioxide have not been identified as the reaction products. The mechanism with the observed kinetics has been proposed and discussed.