title: Theoretical study on the OH-initiated oxidation mechanism of polyfluorinated dibenzo-p-dioxins under the atmospheric conditions.
abstract: Density functional theory (DFT) calculations at the B3LYP/6-311++G(2df,p) level of theory have been carried out to investigate the atmospheric oxidation mechanisms of some polyfluorinated dibenzo-p-dioxins (PFDDs), initiated by OH radical. The computed results show that all OH addition reactions of PFDDs are thermodynamically spontaneous processes and the branch ratio of the PFDD-OH adducts is determined by the magnitude of the Gibbs free energies of activation (Δ(r)G(≠)) and hence rate constants (k) for addition reactions. The OH reactions with all studied PFDDs are dominated by Cγ-addition and the total rate constants for OH addition decrease with increasing the number of fluorine atom substituting at α positions. Under the atmospheric conditions, the subsequent O2 addition reactions of PFDD-OH adducts occur hardly thermodynamically and are slow kinetically. For PFDD-α(β)-OH adducts without F atom at same positions the main reaction pathway is H abstraction by O2, while PFDD-γ-OH adducts will undergo fused-ring C-O bond cleavage, affording the substituted phenoxy radicals.
authors.affiliation: State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China; College of Chemistry and Chemical Engineering, Xinyang Normal University, Henan, Xinyang 464000, China.
authors.forename: Xiaolan
authors.initials: X
authors.lastname: Zeng
authors.affiliation: State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
authors.forename: Xiaoling
authors.initials: X
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China. Electronic address: wangzy@nju.edu.cn.
authors.forename: Zunyao
authors.initials: Z
authors.lastname: Wang
mesh_terms: D001272:Atmosphere; D004147:Dioxins / Q000737:chemistry*; D005465:Fluorocarbon Polymers / Q000737:chemistry*; D006878:Hydroxides / Q000737:chemistry*; D007700:Kinetics; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D004147:Dioxins; D005465:Fluorocarbon Polymers; D006878:Hydroxides; D010636:Phenols; C042329:phenoxy radical; C031356:hydroxide ion
keywords: Atmospheric oxidation mechanism; DFT calculation; OH radical; PFDD-OH adducts; Polyfluorinated dibenzo-p-dioxins (PFDDs)