Proton chemical polarisation, autocatalysis and frontal kinetics of the oxidation of dialkylsulphides with nitric acid

Abstract

Abstract-The oxidation of dimethyl sulphide to dimethylsulphoxide with nitric acid displays CIDNP effects of protons and the phenomenon of frontal kinetics. The process is autocatalytic, with N,O, as the catalyst and the primary oxidant of sulphide. In the presence of the inhibitor (methylmercaptan) the frontal reaction takes place: in purified samples-the usual volume reaction. The interaction of ethyl, n-propyl and n-butyl sulphides with NOZ is accompanied by integral polarisation of the a-CH,-protons. In all the cases sulphide is negatively polarised and sulphoxide positively polarised. The reaction mechanism proposed includes the formation of a radical pair during the interaction of sulphide with N,O,. Disproportionation of the radical pair leads to the formation of polarised sulphoxide and the decay results in regeneration of sulphide. The rate of oxidation of sulphide during the volume reaction is proportional to the product polarisation.

Heterogeneous reaction of nitric acid with methyl sulfide

“…Unfortunately, there are no sufficient experimental data to allow formulation of a more detailed mechanism. In a recent study (2), the direct reaction in solution of HN03 with methyl sulfide was considered to be slow, with nitrous acid and dimethyl sulfoxide proposed as the products, and N2O4 the major oxidizing species. As mentioned above, there was no reaction between methyl sulfide and NO2 at the concentrations encountered in the present work.…”

“…Recent studies have examined the chemically-induced dynamic nuclear polarization of the protons (2) and the catalysis of the reaction by Au3+ (3). Thiols and disulfides are also known to undergo oxidation by HN03 in solution (4).…”