Intermolecular alkyl transfer reactions in the fast atom bombardment mass spectrometry of esters

Fast atom bombardment mass spectrometry (FABMS) of five neat phthalates (dimethyl, diethyl, diallyl, dibutyl and dinonyl) were investigated and intermolecular alkyl transfer reactions were observed in the mass spectra. FABMS of some related compounds was also studied and the results indicate that intermolecular alkyl transfers can occur in the FABMS of esters, the transferred alkyl group being associated with the carboxylate group in the adduct ion [M +R]+. A possible mechanismis proposed which suggests that the transalkylationreactions in these non-ionic compounds arise from two routes: (i) nucleophilic attack by the electron-rich moiety of one energized desorbed molecule on to the electron-poor moiety of another and (ii) dissociation of the internally excited desorbed molecules. The study also demonstrated that the transalkylation reaction could be effectively controlled by addition of a suitable matrix, such as 3-nitrobenzyl alcohol.