| Abstract
| - The kinetics and mechanism of oxidation of an important xenobiotic, thionicotinamide (TNA), using peraceticacid in slightly acidic media were studied by spectrophotometric techniques. The reaction is characterized bya very rapid initial oxidation of the sulfur atom of the thioamide group to the S-oxide, followed by a muchslower decomposition of the S-oxide to form additional oxidation products, mainly the thionicotinamide sulfinicacid. In excess thionicotinamide, the stoichiometry of the reaction was determined to be CH3CO3H + (C5H5N)C(S)NH2 → (C5H5N)C(NH)SOH + CH3COOH, whereas in excess peracetic acid the stoichiometry was2:1, 2CH3CO3H + (C5H5N)C(S)NH2 + H2O → (C5H5N)C(NH)SO2H + 2CH3COOH + 2H+. The sulfoxideis quite stable, but there was no experimental evidence for the existence of any stable sulfone−sulfonic acidintermediates. Results show that the sulfur atom in thionicotinamide is the reactive center, undergoing astepwise addition of oxygen to form successively the sulfenic acid and the sulfinic acid. There appeared tobe no further oxidation past the sulfinic acid and no formation of sulfate was observed. A bimolecular rateconstant of (1.1 ± 0.3) × 103 M-1 s-1 was evaluated for initial rapid formation of the S-oxide, and an upperlimit rate constant of 0.10 ± 0.02 M-1 s-1 was evaluated for the slower decomposition of the S-oxide.
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