Kinetic approach to the mechanism of the redox reaction of malachite green and permanganate ion in aqueous acidic medium

摘要

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 10–3mol dm–3(H2SO4). In thestoichiometry, 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 equationfor the reaction has been proposed as: –d[MG+]/ dt = (a + b[H+])[MG+][MnO4–]. At [H+] = 5.00 x 10–3mol dm–3,the second order rate constant for the malachite green – MnO4–reaction was found to be (11.96 ± 0.13) x 10–3dm3mol–1s–1. Therates of reactiondisplayed negative salt effect. Log k1versus 1/D gave positive slope for the reaction. Addedanions and cationscatalyzed the malachite green – MnO4– reaction. Results of theMichaelis- Mentenanalysis 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.