Abstract

The redox kinetic and mechanistic studies of the reactions of malachite green (MG+) and MnO4– were carried out in aqueous acidic medium, at a temperature of 32.5 ± 0.5°C; ionic strength, m = 0.50 mol dm–3 (Na2SO4), [H+] = 5.00 x 10–3 mol dm–3 (H2SO4). In the stoichiometry, one mole of malachite green was consumed by one mole of MnO4–. The reaction is first order in both [MG+] and the [MnO4–]. The rates of redox reaction showed dependence on acid concentrations (in the acid range used). Rate equation for the reaction has been proposed as: –d[MG+]/ dt = (a + b[H+])[MG+][MnO4–]. At [H+] = 5.00 x 10–3 mol dm–3, the second order rate constant for the malachite green – MnO4– reaction was found to be (11.96 ± 0.13) x 10–3 dm3 mol–1 s–1. The rates of reaction displayed negative salt effect. Log k1 versus 1/D gave positive slope for the reaction. Added anions and cationscatalyzed the malachite green – MnO4– reaction. Results of the Michaelis- Menten analysis gave no evidence of intermediate complex formation. Based on the results obtained experimentally, the outer sphere mechanism is proposed for the malachite green – MnO4– reaction. Key words: Kinetics, mechanism, catalysis, salt effect.

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