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

Abstract

This study investigates the kinetic parameters of the formation of the 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, O2) 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 the gas phase.

Mechanism of Thermal Decomposition of Tetrabromobisphenol A (TBBA)

“…Our finding here differs somewhat from the behaviour of the self-decomposition of 2-chlorophenol system, 28 in which the transfer of phenolic H holds more importance than all other available channels.…”

Mechanisms for formation, chlorination, dechlorination and destruction of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs)

“…A rate constant of k (phenol) ¼ 2.67 Â 10 16 exp (À44 700 K/T) s À1 between 1070 and 1150 K for the unimolecular decomposition of the H-O bond in phenol was derived [31] by kinetic modelling of a complex mechanism for pyrolysis of phenol. A lower rate constant by one order of magnitude was calculated by Altarawneh et al [32]. Direct expulsion of a Cl atom from chlorobenzene was found to occur with a rate constant of k (chlorobenzene) ¼ 3.0 Â 10 15 exp (À48 100 K/ T) s À1 between 1070 and 1280 K [33].…”

Phenol dissociation on pristine and defective graphene

“…We have applied this theoretical approach in our recent studies on elemental adsorption on graphene [10].…”

“…However, O/H radical pool could readily abstracts the hydroxyl' H atom affording a phenoxy radical [10]. On the other hand, the saturated bonds in pristine graphene renders it relatively inert.…”