Mechanistic Study of Reaction between 5-Sulfosalicylic Acid and Colloidal MnO2

Abstract

The reaction between 5-sulfosalicylic acid (5-SSA) and colloidal MnO2 has been studied kinetically in acidic medium. During the reaction the concentration of 5-SSA was kept highly excess than the concentration of colloidal MnO2 to maintain the pseudo-first-order condition. The reaction was studied by following decrease in absorbance of colloidal MnO2 at 390 nm and the first order rate constants were determined from linear log (Abs.) against time plots. The linearity of the first-order plots did not involve any autocatalytic part. The oxidation of 5-sulfosalicylic acid (5-SSA) by colloidal MnO2 involves intervention of free radicals and Mn(III). The product of reaction in colloidal MnO2 was p-hydroxy benzene sulfonate ion as confirmed by LCMS-MS analysis. The oxidation by colloidal MnO2 consists of acid dependent and independent mechanisms. The results of added Mn(II), Na4P2O7 and acrylonitrile indicate involvement of Mn(III) and free radical during oxidation by colloidal MnO2. The probable mechanisms for acid dependent and independent paths were predicted and the rate expressions were also obtained. The activation parameters also support the proposed mechanisms.