Exploring the pyrolysis chemistry of prototype aromatic ester phenyl formate: Reaction pathways, thermodynamics and kinetics

We performed systematic ab initio calculations for the pyrolysis of phenyl formate (PF), the simplest aromatic ester, to establish the potential energy surfaces (PESs), thermodynamics and reaction kinetics. Reaction pathways considered in this work include direct bond fission and intramolecular H-shift, as well as subsequent radical decomposition and ipso-addition by H, O and OH radicals. The energies of reactants, transition states and products were determined at the ROCBS-QB3//M062X/cc-pVTZ level of theory. The standard enthalpy of formation of each species was determined using the atomization method, showing a good agreement with the literature results. For the PF unimolecular decomposition, the intramolecular H-shift reactions to produce phenol + CO and 2,4-cyclohexadienone + CO are the dominant decomposition pathways. Among the decomposition reactions of PF radicals, the isomerization and β-scission channels to form phenoxy + CO and C6H4OH + CO are the dominant pathways. Additionally, for the ipso-addition reactions, PF + H/O → HCOO + C6H6/C6H5O and PF + OH → HCOOH + C6H5O are the major pathways. Multi-well and multi-channel phenomenological rate constants were determined using the Rice–Ramsperger–Kassel–Marcus/master equation (RRKM/ME) method at 500−2000 K and the pressure range of 0.01 atm to the high-pressure limit. It is of interest to observe that the corresponding intermediates for PF radical decompositions with lower energy barriers are merged at higher temperatures and lower pressures. The rate constants of ipso-addition reactions are almost pressure-independence especially at higher temperatures (> 1000 K).