Theoretical study of reaction pathways of dibenzofuran and dibenzo-p-dioxin under reducing conditions.
A density functional theory (DFT) study was carried out to investigate possible reactions of dibenzofuran (DF) and dibenzo-p-dioxin (DD) in a reducing environment. Reaction energies, barrier heights, and molecular parameters for reactants, intermediates, products, and transition states have been generated for a wide range of possible reactions. It was found that C-O beta-scission in DF incurs a very large energy barrier (107 kcal/mol at 0 K), which is just 3 kcal/mol less than the direct H fission from C-H in DF to form dibenzofuranyl radicals. It was found that DF allows direct H addition to C1-C4 and C6-C9 as well as addition of two H atoms from a hydrogen molecule at sites 1 and 9 of DF. A bimolecular reaction of DF with H or H2 is found to have a significantly lower barrier than unimolecular decomposition through C-O beta-scission. An explanation for the predominance of polychlorinated dibenzofurans (PCDF) over polychlorinated dibenzo-p-dioxins (PCDD) in municipal waste pyrolysis is presented in the view of the facile conversion of DD into DF through ipso-addition at the four C sites of the two C-O-C central bonds in DD.
Altarawneh
Mohammednoor
M
Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia.
Dlugogorski
Bogdan Z
BZ
Kennedy
Eric M
EM
Mackie
John C
JC
D000393:Air Pollutants / Q000737:chemistry*; D000465:Algorithms; D001572:Benzofurans / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D002947:Cities; D004147:Dioxins / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D017745:Incineration; D008962:Models, Theoretical; D015394:Molecular Structure; D012037:Refuse Disposal; D013816:Thermodynamics
D000393:Air Pollutants; D001572:Benzofurans; D004147:Dioxins; D005609:Free Radicals; D002244:Carbon; D006859:Hydrogen; C023614:dibenzofuran; C020887:dibenzo(1,4)dioxin