Unusual stabilization of water-soluble colloidal MnO2 during the oxidation of paracetamol by MnO4-

The kinetics of the formation and decomposition of water-soluble colloidal MnO2 in the paracetamol-MnO4- redox system have been investigated spectrophotometrically in aqueous-neutral media at 30 degrees C. Upon mixing aqueous solutions of permanganate and paracetamol, a readily distinguishable brown color appears and then disappears slowly. Experiments have been done to confirm the nature of intermediate (Mn(IV)) formed during the reduction of permanganate by paracetamol. The stoichiometry was found to be 1:1. Formation and decomposition of water-soluble colloidal MnO2 depend upon the experimental conditions, i.e., [paracetamol] and [H+]. The effect of total [MnO4-], [paracetamol], and [H+] on the rate of the reaction was determined. On the basis of various observations, two mechanisms are proposed: one for MnO2 formation and the other for decomposition.