Kinetic analysis of the oxidation of 1-methyl-2-thiourea by methylene blue in acid medium

The kinetics of the oxidation of 1-methyl-2-thiourea (MTU) by methylene blue (MB+) in acid medium has been investigated. The oxidation is first order in both oxidant and reductant and the reaction rate showed dependence on acid concentration. The reaction obeys the rate law: -d[MB+]/dt = (a + b [H+]0.5)[MB+][MTU] where a = 4.19 x 10-2 mol dm-3 s-1, b = 4.52 x 10-1 dm6 mol-2 s-1 at 29.0 ± 0.5oC, [H+] = 0.20 mol dm-3, 0.5 mol dm- 3(NaCl) ionic strength and λmax = 660 nm. The rate of reaction increased with increase in ionic strength and decreased as the dielectric constant of the medium increased. Added cations catalyzed the reaction. The result of spectroscopic and kinetic investigation did not indicate intermediate complex formation in the course of the reaction. Plausible mechanism for the reaction has been proposed in line with the outer-sphere reaction pathway.

Author(s): Osunlaja, Aliu Adekunle, Idris, Sulaiman Ola and Iyun, Johnson Femi

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