Bond formation in mass spectrometry electron impact induced migration of arylthio groups and clustering reactions in chemical ionisation reagent gases

Abstract

Electron impact induced rearrangements have been observed in compounds containing either two arylthio groups or an arylthio group and an arylsulphonyl group. In addition to the loss of sulphur dioxide from the molecular ion and a sulphone-sulphinate rearrangement, 3-arylsulphonyl-2-arylthiopropenes exhibited the rearrangement a bisarylsulphide ion (analogous to that reported for the isomeric l-arylsulphonyl-2-arylthiopropenes). A series of l-arylsulphonyl-4-arylthio-2-butynes also underwent sulphone-sulphinate rearrangement and rearranged to the bisarylsulphide ions, in the absence of sulphur dioxide or sulphur extrusion. The formation of the bisarylsulphide ion from the molecular ion of these compounds is postulated to occur after an initial {1,3} arylthio shift giving an ion analogous to the molecular ion of 3-arylsulphonyl-2-arylthiopropene.A skeletal rearrangement of N-(4'-arylsulphonyl -2 '-butynyl)-N-(4"-arylthio-2"-butynyl)anilines1 2resulted in the elimination of Ar SC

SAr from the molecular ion, but notions arising from a sulphone-sulphinate rearrangement or extrusion of sulphur or sulphur dioxide.The rearrangement of N,N- bis(4'-arylthio-2'-butynyl)anilines via consecutive {1,3} arylthio shifts,followed by elimination of a bisaryldisulphide moiety, was supported by the behaviour of N-(4'-arylthio-2'-butynyl)-N-(2"-arylthio-2"-propenyl)-p-toluidines and N,N-bis(2'arylthio-2'-propenyl)-p-toluidines. Theirmolecular ions are analogous to the rearranged molecular ions of the N,N-bis(4'-arylthio-2'-butynyl)anilines after one or two arylthio shifts, respectively. No extrusion of sulphur is observed, but rather the elimination of a bisaryldisulphide moiety occurs.A series of 1,8-bis(arylthiomethyl)naph-thalenes and 1,2-bis(arylthio)acenaphthenes were1 2synthesised. Electron impact showed no loss of Ar SSAr from the naphthalene derivatives, owing to the predominance of C-S bond cleavage. However, the acenaph-thene derivatives readily eliminated a bisaryldi-sulphide moiety and a qualitative substituent effect was1 2 +observed for the formation of Ar SSAr ˙ ions. In a separate investigation, the kinetics of ion-molecule clustering reactions in a number of chemical ionisation reagent gases were studied. Rate coefficients were obtained at various ion-source field strengths for the formation of proton or deuteron bound dimers at pressures of ca.0.01-0.4 Torr (450°K).Changes from overall third to second order kinetics were observed with increasing pressure, in accord with an energy transfer mechanism. Using the higher values of pressure, rate coefficients were obtained and corresponded to the formation of the excited collision complexes. Rate coefficients for the association reaction of the MH (or MD ) ions in methylamine, dimethylamine, trimethyl-Simple kinetic methods for estimating the ion-source pressures of these gases are described. The disappearance rate coefficients for the major primary ions of the above gases were also determined.