Computational Study of the Oxidation and Decomposition of Dibenzofuran under Atmospheric Conditions

Abstract

The atmospheric degradation of dibenzofuran (DF) initiated by OH addition has been studied by using density functional theory (B3LYP method). Site C1 in DF is predicted to be the favored site for OH addition, with a branching ratio of 0.61 to produce a DF-OH(1) adduct. The calculated reaction rate constant for OH addition to DF has been used to predict the atmospheric lifetime of DF to be 0.45 day. Three different modes of attack of O2 ((3)Sigma(g)) on DF-OH(1) have been examined. Abstraction of hydrogen gem to OH in DF-OH(1) by O2 ((3)Sigma(g)) (producing 1-dibenzofuranol I) and dioxygen addition in the three radical sites in cis and trans orientation (relative to the ispo-added OH) of the pi-delocalized electron system of DF-OH(1) are feasible under atmospheric conditions. The free energy of activation (at 298.15 K) for the formation of 1-dibenzofuranol is 15.1 kcal/mol with a free energy change of -36.3 kcal/mol, while the formation of DF-OH(1)-O2 adducts are endergonic by 9.2-21.8 kcal/mol with a 16.3-23.6 kcal/mol free energy of activation. On the basis of the calculated reaction rate constants, the formation of 1-dibenzofuranol is more important than the formation of DF-OH-O2 adducts. The results presented here are a first attempt to gain a better understanding of the atmospheric oxidation of dioxin-like compounds on a precise molecular basis.

Conversion of polycyclic aromatic hydrocarbons, methyl naphthalenes and dibenzofuran by two fungal peroxygenases

“…A high hydroxylation activity was observed for Dbf, probably because of the presence of heterocyclic oxygen in the molecule, which may provide more reactivity to the aromatic rings and facilitate oxygenation (Altarawneh et al 2008). Several mono-and di-hydroxylated metabolites were detected after treatment of Dbf with monoxygenases of the ascomycetous mold Paecilomyces lilacinus (Gesell et al 2004) or with whole-cells of the zygomycete Cunninghamella elegans (Cerniglia et al 1979).…”

Homogeneous gas-phase formation of polychlorinated naphthalene from dimerization of 4-chlorophenoxy radicals and cross-condensation of phenoxy radical with 4-chlorophenoxy radical: Mechanism and kinetics study

“…CPs and phenol are the most important precursors in the gas-phase PCN formation [6][7][8][9][18][19][20]51]. In combustion and thermal processes, the phenolic-hydrogen of CPs and phenol can be abstracted by the active radicals H, OH, O( 3 P), and Cl to produce CPRs and PhR [51].…”

“…In combustion and thermal processes, the phenolic-hydrogen of CPs and phenol can be abstracted by the active radicals H, OH, O( 3 P), and Cl to produce CPRs and PhR [51]. Dimerization of CPRs or cross-condensation of PhR with CPRs to form chloro-DOHB intermediate are the initial and important step of PCN formation.…”

Partial physicochemical properties and relative stability of polyhydroxylated dibenzofurans: Theoretical and experimental study

“…The corresponding value for the control experiment is −4.40 • C. Thus, the t is respectively 0.52 • C and 1.20 • C. Thus the H o and H p are −11.216 kJ mol −1 and −25.883 kJ mol −1 respectively according to Eq. (8). The H ion calculated is −1.240 kJ mol −1 with MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) method [34], which is more accurate than the B3LYP/6-311G**.…”

“…But the reaction rates of PCDFs with NO 3 • and O 3 are so slow that the reaction with OH • is the primary pathway. So in the environment, polyhydroxylated dibenzofuran (PHODF) is an important degradation product of PCDF [8]. Manuela Gesell [9] found that in the soil, the biotransformation of the filamentous fungus Paecilomyces lilacinus can make the dibenzofuran (DF) hydroxylated.…”