UNUSUAL REACTIVITY OF THE RADICAL CATIONS OF SOME SIMPLE TRIVALENT ORGANOPHOSPHORUS COMPOUNDS TOWARD DIMETHYL DISULFIDE AND DIMETHYL DISELENIDE

Dimethyl disulfide and dimethyl diselenide are known to readily underg o charge exchange with gaseous conventional radical cations containing oxygen, nitrogen, and sulfur functionalities. In sharp contrast, the radical cations of trimethylphosphine and trimethyl phosphite rapidly abstract CH3S. and CH3Se. groups from dimethyl disulfide and dimethyl diselenide, respectively, in a dual-cell Fourier-transform ion cyclotr on resonance mass spectrometer, These sorts of abstraction reactions h ave been reported earlier only for distonic radical cations (ions with spatially separated charge and radical sites). Isomerization of the o rganophosphorus radical cations to their distonic forms prior to or du ring the reaction was ruled out by demonstrating that the connectivity in (CH3)(3)P-.+ does not change during the reaction: the CH3S. abstra ction product has the structure (CH3P+-SCH3. Instead, the abstraction reactions are likely initiated by thermoneutral charge exchange. The n eutral phosphorus compound then replaces a CH3S. or CH3Se. group in io nized dimethyl disulfide and ionized dimethyl diselenide, respectively , In support of this mechanism, three different neutral phosphorus com pounds were shown to replace CH3S. in the radical cation of dimethyl d isulfide. Phosphorus radical cations with high recombination energies were found to react with dimethyl disulfide by exclusive charge exchan ge, Hence, the abstraction reactions require a radical cation with a r ecombination energy close to the ionization energy of dimethyl disulfi de (8.1 eV) and dimethyl diselenide (7.9 eV). Further, the reactions s eem to be limited to phosphorus-containing ions since radical cations with nitrogen and sulfur functionalities do not undergo these reaction s even when their recombination energies are close to 8.1 eV.