Energetics and reaction mechanisms for the competitive Losses of H_2, CH_4 and C_2H_4 from protonated methylbenzenes-implications to the methanol-to-hydrocarbons (MTH) process

摘要

We report the unimolecular decomposition following collisional activation of protonated mono-, di- and trimethylbenzenes as a function of collision energy. The resulting energy-resolved mass spectra are then used for the quality control of high-level quantum chemical models of the respective potential energy surfaces. Distinction is made between direct dissociation products (CH_4 or H_2) and indirect products (alkenes), since formation of the latter requires extensive rearrangement of the molecular skeleton. Very good consistency was found between model and experiment. The models thereby provide a solid foundation for discussing the reaction mechanisms of the industrial methanol-to-hydrocarbon process. The losses of CH_4, C_2H_4 and C_3H_6 from mesitylenium ions have been studied by ~(13)C and ~2H labelling and the alkene losses were found to occur via irreversible isomerisation pathways.