Mechanism of Iodate Oxidation by Methylthioninum Chloride in Acidic Medium

The mechanism of iodate oxidation by methylthioninum chloride in acidic medium was investigated at 29±1ºC. The oxidation reaction is first order in both oxidant and reductant. The rate of reaction was unaffected by increase in ionic strength, dielectric constant, added cations and anion. The reaction rate showed positive acid dependence and obeys the rate law of

-d[MB] = a + b[H+][MB]

dt

where a = 1.19 dm3 mol-1 s-1, b = 0.628 dm3 mol-1 s-1 at 29±1°C, [H+] = 0.10 mol dm-3, 1.0 mol dm-3 (NaClO4) ionic strength and λmax = 663 nm. Investigation of spectroscopic test did not indicate the formation of intermediate complex during the course of the reaction. In line with the data obtained, plausible mechanism in favour of outer-sphere mechanism has been proposed.