Ft-icr Studies of Gas-phase Ionic Nitration of Benzene - the Role of Electron-transfer and Proton-transfer Processes

The detailed modes of reaction of (RONO2)H+ (R = H, CH3 or C2H5) with benzene(C6X6, X = H, D) were determined by Fourier transform ion cyclotron resonance mass spectrometry. Irrespective of the structure and energy of the potentially nitrating (RONO2)H+ reactants, benzene nitration and oxidation are found to proceed by two-step mechanisms, involving a fast, preliminary electron and proton transfer between (RONO2)H+ and C6X6, followed by the rate-determining attack of the C6X6+ and C6X6H+ daughters on the nucleophilic centres of RONO2. These reaction pathways, predominant under isolated-pair conditions, are discussed and compared with classical acid-induced aromatic nitration patterns both in the gas phase at atmospheric pressure and in solution.