Kinetic Approach to the Mechanism of the Reduction of Permanganate Ion by Thioglycolic Acid in Aqueous Hydrochloric Acid Medium
DOI:
https://doi.org/10.33003/fjs-2026-1014-5748Keywords:
Kinetics, Mechanism, Electron Transfer, Pseudo-First-Order, ThiolAbstract
The kinetics and mechanism of the electron transfer reaction between permanganate ion (hereafter MnO4-) and thioglycolic acid (hereafter TSH) was studied spectrophotometrically under pseudo-first-order conditions of [TSH] >> [MnO4-] at T = 25 ± 0.1 °C, [H+] = 0.15 mol dm-3, I = 0.75 mol dm-3 (NaCl) and λmax = 530 nm. Spectrophotometric titration using the mole ratio method revealed that one mole of the permanganate ion reacted with five moles of the thioglycolic acid. The reaction followed first order kinetics with respect to the concentration of each reactant, giving an overall order of two. Reaction rates increased with increasing hydrogen ion concentration, ionic strength, dielectric constant and added ions. The Michaelis-Menten plot of 1/kobs versus 1/[TSH] was linear with a small positive intercept (5.46 s) relative to the range of 1/kobs values. Although a positive free radical test indicated the formation of transient radical intermediates, the combined kinetic evidence was consistent with a predominantly outer-sphere electron transfer mechanism. The reaction obeys the following rate law:
= (a + b[H+]) [TSH][MnO4-]
The findings contribute to the mechanistic understanding of TSH oxidation in aqueous media and provide a basis for future studies of related sulphur-containing redox systems.
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![Plot of 1/kobs versus 1/[TSH] for the reduction of MnO4- by TSH in aqueous hydrochloric acid medium at [MnO4-] = 1.0 × 10-3 mol dm-3, [H+] = 0.15 mol dm-3, I = 0.75 mol dm-3 (NaCl), λmax = 530 nm and T = 25 ± 0.1 ºC](https://fjs.fudutsinma.edu.ng/public/journals/1/submission_5748_5908_coverImage_en.png)
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Copyright (c) 2026 Peter Andrew Lungaka, Yilkur Nandul Lohdip, Japhet Joel Gongden
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