Free Radicals and Free‐Radical Reactions of Monovalent and Divalent Sulfur

Abstract

Abstract Organic free radicals of monovalent sulfur have not been hitherto observed in solution or in melts. Steric hindrance and resonance stabilization, which are responsible for the stability of the triarylmethyl, diphenylnitrogen, and phenoxyl radicals, are apparently insufficient to stabilize the organic free radicals of monovalent sulfur in such concentrations that they can be detected by current physical methods. – It was only in 1963 that aminopolysulfur radicals (R 2 NSnS·) were detected in solution, and arylsulfur radicals (Ar–S·) and phenylselenium radicals were isolated at ca. −180°C. – Organically bound sulfur can be stabilized in the free‐radical state if association of the radicals is prevented by fixing in a crystal lattice (“cystine radical”), by repulsion between radical ions (sulfinium salts), or by freezing‐in (arylsulfur radicals).