Ion-molecule reaction of pyridine with CS3 radical cations: experimental evidence for the production of pyridineN-thioxide distonic ions

Abstract

Chemical ionization of pyridine using carbon disulphide as the reagent gas leads to the formation of new distonic ions, pyridine N-thioxide radical cations, 2+•. The origin of these ions is unambiguously attributed to the reaction of CS3+• ions with neutral pyridine owing to the use of a new hybrid mass spectrometer combining sectors and an r.f.-only quadrupole collision cell floated at a voltage similar to the accelerating voltage of the ions. Collisional activation (CA) of appropriate reference ions (the molecular ions of isomeric mercaptopyridines, 4–6+•) demonstrates the actual structure of the ions, while neutralization–reionization experiments indicate the stability of the corresponding neutral dipole in the gas phase. Several reactions were performed in the quadrupole collision cell with molecules recognized as excellent trapping reagents of distonic ions: dimethyl disulphide, dimethyl diselenide and nitric oxide. The 2+• ions react with nitric oxide generating NOS+ ions; this reaction is not observed for the reference 4–6+• ions. Although the transfer of thiomethyl radicals or selenomethyl radicals is observed for all the radical cations, the resulting [2(4–6)+S(Se)]+ cations are clearly differentiated by CA. It is also shown that the transfer of S+• to perdeuterated pyridine is a specific reaction of the distonic 2+• ions. © 1997 John Wiley & Sons, Ltd.