Studies of Some Sulphur Radicals by Electron Spin Resonance Spectroscopy

Abstract

The formation of organo-sulphur free radicals by the action of ultraviolet radiation on thiols and disulphides of the C1 to C4, alkanes, and certain other sulphur compounds is reported. Diethyl disulphide and di-isopropyl disulphide were found to form secondary radicals by reaction of the initially formed RS• species by hydrogen abstraction with disulphide molecules. Hyperfine splitting was observed in almost all cases. The formation of stable aliphatic organo-sulphur free radicals in solution is reported. These species were formed by dissolving aliphatic thiols, monosulphides and disulphides, and N-N'-dithiobisamines in concentrated sulphuric acid. Hyperfine splitting was observed in the esr spectra of these solutions. A structure is suggested for the radicals which is based on a sulphur-containing three membered ring. A mechanism is proposed for the formation of this species. Sulphur itself was found to react in sulphuric acid to form a free radical with hyperfine interaction. The esr spectra of the sulphuric acid solutions of a range of substituted thiophenols are presented. These solutions were found to contain two radical species, as observed by other workers for thiophenol and 4-methylthiophenol. The signal at lower g value is due to a radical formed from thianthrene, an oxidation product of thiophenol. The signal at higher g value has previously been attributed to a radical of the type(C6H5S.)H+. Although the spectra from some of the compounds examined are consistent with this, others do not appear so. Other alternative structures are tentatively proposed.