Kinetics and Mechanism of the Reaction of Malachite Green and Dithionite Ion

The kinetics of the oxidation of malachite green, MG+, by dithionite ions, S2O42- have been studied spectrophotometrically in an aqueous acid free medium. The investigation was carried out under pseudo- first order conditions of an excess of dithionite concentration. Reaction conditions were ionic strength of reaction medium, µ = 0.1 mol dm–3, λmax = 620nm and T = 25.5±0.5°C. The stoichiometry of the reaction, determined by spectrophotometric titration, was 1:1. Reaction rates increased with increase in µ and dielectric constant (D) of reaction medium. Added ions catalysis of the reaction and the result of the Michaelis - Menten analysis suggest that the reaction proceeded through the outersphere pathway. A plausible mechanism is proposed.