title: New understanding of the formation of PCDD/Fs from chlorophenol precursors: a mechanistic and kinetic study.
abstract: Although chlorophenols (CPs) are considered to be the most important and direct precursors of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), our understanding of the formation mechanism of PCDD/Fs is exclusively limited to an invariable idea that chlorophenoxy radicals (CPRs) are only necessary intermediates. The present work presents a systematic theoretical study that aims at providing new insight into the homogeneous formation of PCDD/Fs from CPs. Two different types of radicals from CPRs, i.e., substituted phenyl radicals and phenoxyl diradicals, are proposed to serve as potential sources contributing to the formation of PCDD/Fs. The thermodynamic and kinetic properties of reactions of 2-chlorophenol (2-CP), as a representative of CP congeners, with atomic H to produce various potential radicals forming PCDD/Fs are studied by performing density functional theory calculations and direct kinetics studies. The newly proposed radicals, especially substituted phenoxyl diradicals (the most direct intermediates of PCDD/Fs), can be formed via reactions of 2-CP with atomic H with small barriers and large reaction energies. They should be expected to be responsible for the homogeneous formation of PCDD/Fs under high temperature. Several typical PCDD/F products are predicated through direct self- and cross-couplings of the newly proposed radicals. The radical coupling patterns proposed in the present work expand our understanding of the formation mechanism of PCDD/Fs from CP precursors.
authors.affiliation: Institute of Theoretical Chemistry, Shandong University , Jinan 250100, P. R. China.
authors.forename: Yanfang
authors.initials: Y
authors.lastname: Zhang
authors.forename: Dongju
authors.initials: D
authors.lastname: Zhang
authors.forename: Jun
authors.initials: J
authors.lastname: Gao
authors.forename: Jinhua
authors.initials: J
authors.lastname: Zhan
authors.forename: Chengbu
authors.initials: C
authors.lastname: Liu
mesh_terms: D001572:Benzofurans / Q000737:chemistry*; D002733:Chlorophenols / Q000737:chemistry*; D007700:Kinetics; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D001572:Benzofurans; D002733:Chlorophenols; D000072317:Polychlorinated Dibenzodioxins; C023614:dibenzofuran