Mechanism study of SO2 elimination from sulfonamides by negative electrospray ionization mass spectrometry.

The elimination of SO2 from deprotonated sulfonamides in the negative ion mode was confirmed by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) experiments. For a set of N-arylbenzenesulfonamides substituted at the para position of the arylamine, the ln([M-H-SO2](-)/[M-H]-) values were correlated with the sigmap(-) substituent constants but, instead of a linear relationship, a bent line was obtained. Analyses of the complex curve led to the identification of two competing routes, which were further investigated by Hartree-Fock theoretical calculations. Furthermore, collision-induced dissociation (CID) of deprotonated N-alkylbenzenesulfonamides containing the -CHCHNHSO2- structure yielded a [M-H-66](-) product ion This characteristic ion could help to distinguish the side-chain isomers.