Gas-phase ion–molecule reactions of thioic and dithioic acid derivatives. Condensation reactions with alkenes and alkynes

A Fourier transform–ion cyclotron resonance study of thioacyl compounds as binary mixtures with unsaturated hydrocarbons has revealed that thioacetylium ions CH₃CS⁺ generated by electron fragmentation fail to thioacyl-ate even the most reactive aromatic hydrocarbons. Among the hydrocarbons studied, only 3-hexyne and 2,4-dimethyl-2,5-hexadiene were observed to react with CH₃CS⁺. Apart from proton-transfer reactions, the major ionic reaction of thioesters with arenes, alkynes and alkenes is condensation of the molecular ion of one component, usually the ester, with a neutral molecule of the other, resulting in the cleavage of the S? C_alkyl bond of the thioester. The nature of this reaction is discussed and a possible mechanism is suggested.