Soft-ionization mass spectrometric observation of isomeric effects occurring in the synthesis of bis-sulfonium salts from thiacyclanes/xylylene dibromides and collision induced dissociation of bis-sulfonium cations

Abstract

Micro-synthesis of bis-sulfonium salts from ortho-, meta- and para-xylylene dibromides and mono- and bicyclic sulfides was performed for their further investigation by tandem electrospray/ionization mass spectrometry (ESI-MS) with the use of collision-induced dissociation (CID). Reaction products were detected by ESI-MS (without chromatographic separation), combined high-performance liquid chromatography/ESI-MS and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). It was shown that only the reaction of ortho- and para-xylylene dibromides with cyclic sulfides gave rise to corresponding bis-sulfonium salts yielding products of elimination of protonated sulfide from doubly charged ions during ESI and MALDI ionization. Fragmentation pathways of bis-sulfonium even-electron dications generated in ESI conditions were examined for the first time. The mass spectra revealed peaks for only single charged fragments included thiacyclane hydrocarbon residues, benzene- and sulfur-containing ions. Drastic quantitative and qualitative differences between ortho- and meta(para)-isomers allowing their easy differentiation were observed and explained. They were manifested in the character of eliminated thiacyclane residue and in the peak intensity ratios of m/z 104 and 91 benzene-containing ions. Isomeric di-cations with regio-isomeric structures of monocyclic sulfides demonstrated strong differences in CID spectra.