YO1 5DDEvidence has been adduced by e.s.r. spectroscopy for the formation of the sulphite radical anion, SO,-* [by the oxidation of sulphite ion with the hydroxyl or amino-radical. the sulphate radical anion, or ceriurn(1V) ion], of the thiosulphate radical anion, SaO3-* (from thiosulphate ion and the hydroxyl radical), and of the sulphide radical ion, S-• (pH 9) or the mercapto radical, *SH (pH 2) (from sulphide ion and the hydroxyl or amino-radical). The radical anions are efficiently captured by nitroalkane aci-anions. The sulphite radical anion shows marked selectivity in its reactions with olefinic carbon. The splitting constants of the radicals formed by addition of the species Sand *SH to two olefinic compounds suggest that there is an interaction between the sulphur substituent and t h t tervalent carbon atom. E.s.R. spectroscopy, together with flow-system techniques, has previously been used to study the reactions of organic compounds, in aqueous solution, with a number of reactive radicals and radical ions, such as -OH, -NH,, and SO,-*.2 We now report the results of a brief survey, carried out in a similar manner, of the generation and reactions of three sulphur-containing radical anions, namely, SO,-', S203-', and S-*, and the mercapto-radical, *SH.Oxidation of Sulphur-contairting Anions.-( a) Sulphite ion. When solutions of titanium(II1) ion and ethylenediaminetetra-acetic acid (EDTA) , hydrogen peroxide, and sodium sulphite were mixed immediately before passage of the resulting solution through the cavity of the e.s.r. spectrometer, the pH after mixing being 9, a spectrum consisting of a singlet, g 24030, was recorded. When the hydrogen peroxide was omitted, there was no e.s.r. absorption, but when it was replaced by either hydroxylamine or potassium persulphate, the same spectrum was observed, although its intensity in the latter case was very weak. The g-factor is identical with g, , for the sulphite radical anion, SO,-', generated by the irradiation of potassium sulphate single crystals? and we assign our spectrum to the same species.When titanium(rI1) ion was omitted, no e.s.r. absorption was detected with either the hydrogen peroxide or the potassium persulphate system, in accord with the results of a study of the persulphate-sulphite emulsion polymerisation of vinyl chloride which showed that radicals are generated only in the presence of metal ions.* We infer that the sulphite radical anion is formed in the presence of titanium(II1) ion by oneelectron oxidation of sulphite ion by the hydroxyl radical, amino-radical, or sulphate radical anion [which are known to be generated from titanium(rI1) ion with hydrogen peroxide, hydroxylamine, or persulphate ion, respectively2].