Thiosulfoxides (X2S=S) and disulfanes (XSSX): first observation of organicthiosulfoxides

Using a combination of tandem mass spectrometry methodologies, collisional activation of fast (8 keV) or slow (20-30 eV) ion beams, neutralization-rei onization and ion-molecule reactions, it is shown that thiosulfoxides X2S=S (X = H, CH3, C2H5) are stable in the gas phase as radical cations as well as neutral molecules, The absence of isomerization into the more convention al disulfane structure, XSSX, is firmly demonstrated by ion-molecule reacti ons of the isomeric ions with methyl isocyanide and by collisional activati on of "survivor" ions generated in neutralization-reionization experiments. All the mass spectral data have been recorded with a single hybrid mass sp ectrometer of sectors-quadrupole-sectors configuration. Molecular orbital c alculations demonstrate that ionized thiosulfoxides and disulfanes are loca l minima on the MP2/6-31G* potential energy surface. The disulfane structur es are found to be the most stable species by 91, 65 and 59 kJ/mol for X = H, CH3 and C2H5, respectively. Heat of formation values of 1000, 810 and 76 0 kJ/mol are estimated for X2SS.+ ions (X = H, CH3 and C2H5, respectively). (C) 2000 Elsevier Science B.V.