Kinetics and Mechanism of Oxidation of Methimazole by Chlorite in Slightly Acidic Media
This work was supported by Research Grant Number CHE 1056366 from the National Science Foundation and a Research Professor vote from the University of KwaZulu-Natal.
The Journal of Physical Chemistry A
The kinetics and mechanism of the oxidation of methimazole (1-methyl-3H-imidazole), MMI, by chlorite in mildly acidic environments were studied. It is a complex reaction that gives oligo-oscillations in chlorine dioxide concentrations in excess chlorite conditions. The stoichiometry is strictly 2:1, with the sulfur center being oxidized to sulfate and the organic moiety being hydrolyzed to several indeterminate species. In excess MMI conditions over chlorite, the sulfinic acid and sulfonic acid were observed as major intermediates. The sulfenic acid, which was observed in the electrochemical oxidation of MMI, was not observed with chlorite oxidations. Initial reduction of chlorite produced HOCl, an autocatalytic species in chlorite oxidations. HOCl rapidly reacts with chlorite to produce chlorine dioxide, which, in turn, reacts rapidly with MMI to produce more chlorite. The reaction of chlorine dioxide with MMI is competitive, in rate, with the chlorite–MMI and HOCl–ClO2– reactions. This explains the oligo-oscillations in ClO2concentrations.
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Chipiso, K., & Simoyi, R. H. (2016). Kinetics and Mechanism of Oxidation of Methimazole by Chlorite in Slightly Acidic Media. The Journal of Physical Chemistry. A, 120(21), 3767-3779.