Electron spin resonance studies of the photolysis and radiolysis of O,O′-dialkyl hydrogen phosphorodithioates [(RO)2P(S)SH], their salts, corresponding disulphides, and related compounds: formation of thio and dithio radicals, radical ions, and phosphorus-centred radicals

Abstract

Isotropic and anisotropic e.s.r. parameters are reported for some dialkoxy(thiophosphoryl)thio radicals [(RO)₂P(S)S˙] generated by photolysis of some O,O′-dialkyl hydrogen phosphorodithioates, their salts, and corresponding disulphides [in some cases in the presence of (Bu^tO)₂]. The unpaired electron in these radicals is evidently shared equally between the two sulphur atoms in an in-plane orbital; the variation of the linewidth with viscosity and temperature is interpreted in terms of spin-rotation interaction. The radicals are very short-lived (with 2k_tca. 10⁹ dm³ mol^–1 s^–1); though they are apparently unreactive towards either aliphatic alkenes or oxygen, they react rapidly to give peroxyl radicals in the presence of both.

The analogous oxygen-substituted radicals (RO)₂P(O)S˙ possess the unpaired electron localized on sulphur : though they prove undetectable in fluid solution (presumably on account of marked line-broadening) their rapid reaction with the corresponding anion to give the σ*-species [(RO)₂P(O)S]₂^–˙ could be monitored. Solid-state spectra from photochemically generated dithio radicals (RO)₂P(X)S₂·(X = O or S) are also reported.

Finally, radiolysis of solid samples of these compounds leads to the characterization of anisotropic spectra from the appropriate thio and dithio radicals as well as those from electron-loss species (RSSR⁺˙) and electron-gain radicals [both of σ*-type (RSSR)^–˙ and phosphoranyl-type structure ^–˙P(OR)₂(X)SSP(X)(OR)₂]; structural aspects, matrix effects, and further reactions [e.g. to give phosphoryl radicals ˙PL₃ and alkyl radicals] are discussed.