title: The oxidation mechanism of polychlorinated dibenzo-p-dioxins under the atmospheric conditions - a theoretical study.
abstract: The atmospheric polychlorinated dibenzo-p-dioxins (PCDDs) partition appreciably in the gas phase, where they undergo rapid oxidation. The atmospheric oxidation mechanisms of a few PCDDs, initiated by OH radical, are studied using density functional theory calculations. The oxidations start with OH-addition to the aromatic rings, dominantly at γ-sites, followed by the non-chlorinated β-sites; while additions to the α-sites or chlorinated sites are negligible. For PCDDs with all β-sites being chlorinated, formation of PCDD-γ-OH adducts become virtually the only reaction path. Under the atmospheric conditions, the PCDD-β/γ-OH adducts combine with O(2) slowly at rates <1s(-1). Instead, the PCDD-β-OH adducts will react with O(2) through hydrogen abstraction at rates <50s(-1), forming PCDD-β-ol, and the PCDD-γ-OH adducts will decompose to the substituted phenoxy radicals by fused-ring C-O bond cleavage at rates of 10(3) ~10(5) s(-1). The reaction mechanisms of PCDDs are drastically different from the peroxy mechanism for the atmospheric oxidations of benzene and dibenzofuran.
authors: School of Chemistry & Chemical Engineering, South China University of Technology, Guangzhou 510640, China. wanglm@scut.edu.cn
authors: Liming
authors: L
authors: Wang
authors: Aili
authors: A
authors: Tang
mesh_terms: D017665:Hydroxyl Radical / Q000737:chemistry; D008962:Models, Theoretical; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D010636:Phenols; D000072317:Polychlorinated Dibenzodioxins; C042329:phenoxy radical; D017665:Hydroxyl Radical