Quantum chemical and kinetic study of formation of 2-chlorophenoxy radical from 2-chlorophenol: Unimolecular decomposition and bimolecular reactions with H, OH, Cl, and O₂

This study investigates the kinetic parameters of the formation of me chlorophenoxy radical from the 2-chlorophenol molecule, a key precursor to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCCD/ F), in unimolecular and bimolecular reactions in the gas phase. The study develops the reaction potential energy surface for the unimolecular decomposition of 2-chlorophenol. The migration of the phenolic hydrogen to the ortho-C bearing the hydrogen atom produces 2-chlorocyclohexa-2,4-dienone through an activation barrier of 73.6 kcal/mol (0 K). This route holds more importance than the direct fission of Cl or the phenolic H. Reaction rate constants for the bimolecular reactions, 2-chlorophenol ← X-* X-H + 2-chlorophenoxy (X = H, OH, Cl, O ₂) are calculated and compared with the available experimental kinetics for the analogous reactions of X with phenol. OH reaction with 2-chlorophenol produces 2-chlorophenoxy by direct abstraction rather than through addition and subsequent water elimination. The results of the present study will find applications in the construction of detailed kinetic models describing the formation of PCDD/F in die gas phase.