Competing Reaction Pathways in Gas-Phase Oxidation of C6H6 by Protonated H2O2.

Reactions between protonated hydrogen peroxide and benzene (and benzene-d6) have been studied in the gas phase using an FT-ICR mass spectrometer. Four competing paths for the bimolecular system were identified, namely, proton transfer, hydride abstraction, dissociative single-electron transfer, and an electrophilic addition of HO+ to give the Wheland intermediate [C6H6, OH]+ followed by a subsequent elimination of water. The three latter pathways correspond to three different ways to oxidize benzene. All reaction mechanisms have been modeled using quantum chemical methods, and the calculations are in agreement with the experimental observations. The total reaction rate proceeds at collision rate (slightly higher than the calculated Langevin capture rate), which exemplifies the high reactivity of H3O2+ toward arenes. These observations demonstrate a much richer chemical landscape than previously inferred from the corresponding condensed phase reaction, where only electrophilic substitution by solvated HO+ was described.