Uncatalyzed and ruthenium(III)‐catalyzed reaction of acidic chlorite with methylene violet

Abstract

AbstractThe kinetics and mechanism of the uncatalyzed and Ru(III)‐catalyzed oxidation of methylene violet (3‐amino‐7‐diethylamino‐5‐phenyl phenazinium chloride) (MV+) by acidic chlorite is reported. With excess concentrations of other reactants, both uncatalyzed and catalyzed reactions had pseudo‐first‐order kinetics with respect to MV+. The uncatalyzed reaction had first‐order dependence on chlorite and H+ concentrations, but the catalyzed reaction had first‐order dependence on both chlorite and catalyst, and a fractional order with respect to [H+]. The rate coefficient of the uncatalyzed reaction is (5.72 ± 0.19) M−2 s−1, while the catalytic constant for the catalyzed reaction is (22.4 ± 0.3) × 103 M−1 s−1. The basic stoichiometric equation is as follows: 2MV+ + 7ClO2− + 2H+ = 2P + CH3COOH + 4ClO2 + 3Cl−, where P+ = 3‐amino‐7‐ethylamino‐5‐phenyl phenazinium‐10‐N‐oxide. Stoichiometry is dependent on the initial concentration of chlorite present. Consistent with the experimental results, pertinent mechanisms are proposed. The proposed 15‐step mechanism is simulated using literature; experimental and estimated rate coefficients and the simulated plots agreed well with the experimental curves. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 294–303, 2003