Kinetics and Mechanism of the Periodate Oxidation of Malachite Green in Acidic Medium

The kinetics of the periodate (IO4–) oxidation of malachite green (MG+) have been studied in aqueous acidic medium. The observed results at [H+] = 1 x 10–4 mol dm–3 (HCl), ionic strength of reaction medium, I = 0.5 mol dm–3 and T = 25.5±0.3°C are consistent with the rate law:

−d[MG+]/dt = k2[MG+][IO4-]

where k2 = (k7 + k6K5[H+])

The reaction was catalysed by increase in [H+] and added anions but displayed a negative BrØnsted–Debye salt effect. Spectrophotometric test showed the absence of intermediate complex formation. Based on these findings, a plausible mechanism is proposed.