title: Molecular Mechanism of Dioxin Formation from Chlorophenol based on Electron Paramagnetic Resonance Spectroscopy.
abstract: Few studies have investigated the free radical intermediates involved in the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from chlorophenol. This study clarified the reaction pathways during thermochemical formation of PCDDs from 2,3,6-trichlorophenol (TCP) over a Cu(II)O/silica matrix, which was used to simulate fly ash, at 298-523 K. The reaction was studied using electron paramagnetic resonance (EPR) spectroscopy and theoretical calculations. In situ EPR indicated the TCP radical (TCPR) formed by hydrogen abstraction of TCP. Five elementary processes including dimerization of TCPR, ortho-chloride abstraction, Smiles rearrangement, ring closure, and intra-annular elimination of Cl were proposed to occur during formation of PCDDs. The proposed mechanism was further confirmed by the detection of PCDD products from thermochemical experiments in a tube furnace. Several dominant congeners, including 1,2,6,9-tetrachlorodibenzo-p-dioxin (TeCDD), 1,2,6,7-TeCDD, 1,2,8,9-TeCDD, and 1,4,6,9-TeCDD were detected by gas chromatography/quadrupole time-of-flight mass spectrometry, and further confirmed by gas chromatography/high resolution mass spectrometry. The detected PCDD products agree with the proposed PCDD formation mechanism. Relatively high temperatures were found to lead to dechlorination of TCPR to form phenoxy radicals in addition to PCDD/Fs. These radicals will be attached to particles, which will increase their lifetimes. These reactions were further verified by molecular orbital theory calculations. The discovery of persistent phenoxy radicals is of environmental significance because of their potential toxicity. The details of this mechanism could be used for controlling PCDD/F formation during industrial thermal processes.
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , P.O. Box 2871, Beijing 100085, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
authors.forename: Lili
authors.initials: L
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , P.O. Box 2871, Beijing 100085, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
authors.forename: Guorui
authors.initials: G
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , P.O. Box 2871, Beijing 100085, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
authors.forename: Minghui
authors.identifier: http://orcid.org/0000-0002-8462-6734
authors.initials: M
authors.lastname: Zheng
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , P.O. Box 2871, Beijing 100085, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
authors.forename: Yuyang
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , P.O. Box 2871, Beijing 100085, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
authors.forename: Rong
authors.identifier: http://orcid.org/0000-0001-9677-6177
authors.initials: R
authors.lastname: Jin
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , P.O. Box 2871, Beijing 100085, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , P.O. Box 2871, Beijing 100085, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Xu
mesh_terms: D001572:Benzofurans / Q000737:chemistry; D002733:Chlorophenols / Q000737:chemistry; D004147:Dioxins / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D000072317:Polychlorinated Dibenzodioxins
chemical_list: D001572:Benzofurans; D002733:Chlorophenols; D004147:Dioxins; D000072317:Polychlorinated Dibenzodioxins