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Kinetics and mechanism of oxidation of dimethyl sulfoxide by chloramine‐T in aqueous solution

1979; Wiley; Volume: 11; Issue: 3 Linguagem: Inglês

10.1002/kin.550110304

1097-4601

D. S. Mahadevappa, M. B. Jadhav, H. M. K. Naidu,

Electrochemical Analysis and Applications

Abstract The kinetics of oxidation of dimethyl sulfoxide (DMSO) by chloramine‐T (CAT) is studied in HClO 4 and NaOH media with OsO 4 as a catalyst in the latter medium. In acid medium, the rate law is ‐ d [CAT]/ dt = k [CAT][DMSO][H + ]. Alkali retards the reaction and the rate law takes the form ‐ d [CAT]/ dt = k [CAT][DMSO][OsO 4 ]/[NaOH], but is reduced to ‐ d [CAT]/ dt = k [CAT][DMSO] at higher alkali concentrations. The reaction is subjected to changes in (a) ionic strength, (b) concentrations of added neutral salts, (c) concentrations of added reaction product, (d) dielectric constant, and (e) solvent isotope effect, and the subsequent effects on the reaction rate are studied. The reaction mechanism in acid medium assumes an electrophilic attack by the free acid RNHCl (CAT′) at the sulfur site in DMSO, forming a reaction intermediate which subsequently decomposes to dimethyl sulfone on hydrolysis. Formation of a cyclic complex between RNHCl and OsO 4 which interacts with the substrate in a slow step explains the observed results in alkaline medium. The simplification of the rate equation at higher alkali concentrations is attributed to a direct reaction between chloramine‐T and the substrate.