Unusual stabilization of water-soluble colloidal MnO₂ during the oxidation of paracetamol by \({\mathop {MnO_{4} }\nolimits^ - }\)

The kinetics of the formation and decomposition of water-soluble colloidal MnO₂ in the paracetamol–\({\mathop {MnO_{4} }\nolimits^ - }\) redox system have been investigated spectrophotometrically in aqueous-neutral media at 30 °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 \({\left[ {{\mathop {MnO_{4} }\nolimits^ - }} \right]},\) [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.