Gas-Phase Fragmentation of Protonated N,2-Diphenyl-N'-(p-Toluenesulfonyl)Ethanimidamides: Tosyl Cation Transfer Versus Proton Transfer.

The gas-phase dissociation chemistry of protonated N,2-diphenyl-N'-(p-toluenesulfonyl) ethanimidamides was investigated by electrospray ionization mass spectrometry in combination with density functional theory calculation. The protonated molecules underwent fragmentation via two main competing channels: (1) migration of the tosyl cation to the anilinic N atom and the subsequent loss of 2-phenylacetonitrile to afford protonated N-phenyl p-toluenesulfonamide (m/z 248); and (2) transfer of the ionizing proton to the anilinic N atom to give an ion/neutral complex of [tosyl cation / 2-phenylacetonitrile] (m/z 272) and the subsequent decomposition to yield tosyl cation (m/z 155). To the best of our knowledge, the gas-phase tosyl cation transfer has not been reported previously. For the para-substituted sulfonamides, the presence of electron-donating groups on the anilinic ring inhibits the reaction channel of the tosyl cation migration, whereas the presence of electron-withdrawing groups favors this pathway.