【标题】Rulesof thumb for assessing reductive dechlorination pathways of PCDDs inspecific systems

【期刊】Journalof Hazardous Materials

【第一作者】卢桂宁

【摘要】Thispaper reports a theoretical validation and proposition of thereductive dechlorination pathways for polychlorinateddibenzo-p-dioxin (PCDD) congeners. Density functional theory (DFT)calculations were carried out at the B3LYP/6-31G(d) level for allPCDDs and Mulliken atomic charges on chlorine atoms were adopted asthe probe of the dechlorination reaction activity. The experimentallysubstantiated dechlorination pathways of1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) and its daughterproducts in the presence of zero-valent zinc were validated and thecomplete pathway of dechlorination of octachlorodibenzo-p-dioxin(OCDD) was proposed. The proposed pathways were found to beconsistent with anaerobic biotransformation of several PCDDcongeners. Four rules of thumb arrived from this study include (1)the chlorine atoms in the longitudinal (1,4,6,9) positions areremoved in preference to the chlorine atoms on lateral (2,3,7,8)positions; (2) the chlorine atom that has more neighboring chlorineatoms at ortho-, meta- and para-positions is to be eliminated; (3)reductive dechlorination prefers to take place on the benzene ringhaving more chlorine substitutions; and (4) a chlorine atom on theside of the longitudinal symmetry axis containing more chlorine atomsis preferentially eliminated. These rules of thumb can beconveniently used for rapidly predicting the major dechlorinationpathway for a given PCDD in specific systems.

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