Theoretical study of perbenzoate anion decomposition pathways in the gas phase

Perbenzoic acid (a weak organic acid) and its conjugate base (perbenzoate anion, C6H5C(O)O2−) are important organic reagents used extensively in synthetic chemistry. A few studies are available in the literature on the structure and reactivity of the perbenzoate anion. Gas phase dissociation of the perbenzoate anion and its substituted analogues by collision induced dissociation mass spectrometry experiments revealed carbon dioxide (CO2) loss as the major dissociation pathway. CO2 loss was proposed to occur via intramolecular nucleophilic attack by the negatively charged oxygen atom at the ipso or ortho position of the benzene ring. In the present work, we investigated decomposition pathways of perbenzoate anion in the gas phase via classical direct chemical dynamics simulations to establish the atomic level reaction mechanisms. Classical trajectories were integrated on-the-fly using the density functional B3LYP/6-31+G* level of electronic structure theory. Removal of CO3, CO2 from the perbenzoate anion and isomerization to an oxydioxirane intermediate were the primary reaction pathways observed in the simulations. In a major fraction of the trajectories, elimination of CO2 happened via initial CO3 loss from the perbenzoate anion followed by removal of O atom from the unstable neutral CO3 molecule.