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Quantum chemical investigation of formation of polychlorodibenzo-p-dioxins and dibenzofurans from oxidation and pyrolysis of 2-chlorophenol.
MedLine Citation:
PMID:  17388333     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Abstract/OtherAbstract:
Density functional theory (DFT) calculations have been used to obtain thermochemical parameters for formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) from the oxidation of 2-chlorophenol. Formation mechanisms of PCDD through radical-radical coupling have been investigated in detail. The sequence of 2-chlorophenoxy radical coupling has been studied. The formation of chlorinated bis keto dimers which results from cross coupling of 2-chlorophenoxy at the ortho carbon bearing hydrogen (a known direct route for PCDF formation) passes through a tight transition structure whose barrier is 9.4 kcal/mol (0 K). Three routes for the formation of the most abundant PCDD/PCDF species (viz., 4,6-dichlorodibenzofuran, 4,6-DCDF, and 1-monochlorodibenzo-p-dioxin, 1-MCDD) in oxidation and pyrolysis of 2-chlorophenol are discussed. In the case of 4,6-DCDF, formation through H or HO + keto-keto <==> H2 or H2O + keto-keto* <==> H2 or H2O + enol-keto* <==> H2 or H2O + 4,6-DCDF + HO is shown to be the preferred route. The other two routes proceed via closed shell processes (keto-keto <==> enol-keto <==> enol-enol <==> H2O + 4,6-DCDF) and (keto-keto <==> enol-keto <==> (H-,OH-) 4,6-DCDF <==> H2O + 4,6-DCDF). Results indicate that 1-MCDD should be the favored product in 2-chlorophenol pyrolysis in agreement with experimental findings. According to our results, tautomerization (inter-ring hydrogen transfer) and intra-annular displacement of HCl would not be competitive with paths deriving from H abstraction from the phenolic oxygen and the benzene ring followed by displacement of Cl in the formation of dibenzo-p-dioxin (DD) and 1-MCDD. The results presented here will assist in construction of detailed kinetic models to account for the formation of PCDD/PCDF from chlorophenols.
Authors:
Mohammednoor Altarawneh; Bogdan Z Dlugogorski; Eric M Kennedy; John C Mackie
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Publication Detail:
Type:  Journal Article     Date:  2007-03-09
Journal Detail:
Title:  The journal of physical chemistry. A     Volume:  111     ISSN:  1089-5639     ISO Abbreviation:  J Phys Chem A     Publication Date:  2007 Apr 
Date Detail:
Created Date:  2007-03-29     Completed Date:  2007-06-21     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9890903     Medline TA:  J Phys Chem A     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2563-73     Citation Subset:  -    
Affiliation:
Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, New South Wales 2308, Australia.
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