Dibenzo l,4 dioxin

For polychlorinated biphenyls (PCBs), rate constants were highly dependent on the number of chlorine atoms, and calculated atmospheric lifetimes varied from 2 d for 3-chlorobiphenyl to 34 d for 236-25 pentachlorobiphenyl (Anderson and Hites 1996). It was estimated that loss by hydroxy-lation in the atmosphere was a primary process for the removal of PCBs from the environment. It was later shown that the products were chlorinated benzoic acids produced by initial reaction with a hydroxyl radical at the 1-position followed by transannular dioxygenation at the 2- and 5-positions followed by ring fission (Brubaker and Hites 1998). Reactions of hydroxyl radicals with polychlorinated dibenzo[l,4]dioxins and dibenzofurans also play an important role for their removal from the atmosphere (Brubaker and Hites 1997). The gas phase and the particulate phase are in equilibrium, and the results show that gas-phase reactions with hydroxyl radicals are important for the... 

Concern has been expressed over the formation of chlorinated dibenzo[l,4]dioxins and dibenzofurans during the thermal transformation of organic material in the presence of chloride or organochlorine compounds. 

The genus Staphylococcus is traditionally associated with disease in humans. The demonstration (Monna et al. 1993) that a strain of Staphylococcus auriculans—isolated by enrichment with dibenzofuran and with no obvions clinical association—could degrade this substrate and carry out limited biotransformation of hnorene and dibenzo[l,4]dioxin serves to illustrate the unsuspected metabolic potential of facultatively anaerobic Gram-positive organisms. 

Anaerobic dehalogenation has also been observed in aromatic ethers including polychlorinated dibenzo[l,4]dioxins (Fennell et al. 2004 Yoshida et al. 2005). The anaerobic debromination of decabromodiphenyl ether is considered here since it is analogous to the dehalogenation of polyhalogenated biphenyls. 

Whereas the degradation of the carboxylates of the monocyclic furan, thiophene, and pyrrole is initiated by hydroxylation, degradation of their benzo analogs is generally carried out by dioxygenation. The degradation of the analogs dibenzofuran and dibenzo-[l,4]-dioxin is discussed in Part 2 of this chapter. 

FIGURE 10.40 Degradation of dibenzo[l,4]dioxin. (From Neilson, A.H. and Allard, A.-S., The Handbook of Environmental Chemistry, Vol. 3J, pp. 1-80, Springer, Heidelberg, 1998. With permission.)... 

Partial anaerobic dechlorination of chlorinated dibenzo[l,4]dioxins has been observed in sediment slurries. The 1,2,3,4-tetrachloro compound produced predominantly l,3-dichlorodibenzo[l,4]-dioxin (Beurskens et al. 1995 Ballerstedt et al. 1997), and for substrates with five to seven chlorine substituents, chlorine was removed from both the peri and the lateral positions (Barkovskii and... 

A series of dibenzo[l,4]dioxins bearing nitro and trifluoromethyl substituents in one ring and chlorine in the other was synthesized for comparison with impurities in commercial samples of the lampricide 3-trifluoromethyl-4-nitrophenol, and to assess their ability to induce MFO activity (Hewitt et al. 1998). Although they appeared to be relatively weak inducers, there were other unidentified components that were highly active. 

Chemical/Physical. TCDD was dehalogenated by a solution of poly (ethylene glycol), potassium carbonate, and sodium peroxide. After 2 h at 85 °C, >99.9% of the applied TCDD decomposed. Chemical intermediates identified include tri-, di-, and chloro[Ae]dibenzo[l,4]dioxin, di-benzodioxin, hydrogen, carbon monoxide, methane, ethylene, and acetylene (Tundo et al., 1985). TCDD will not hydrolyze to any reasonable extent (Kollig, 1993). 

Chloro[6,e]dibenzo[l,4]dioxin, see TCDD Chlorodibenzofuran, see Dibenzofuran 2-Chlorodibenzo[6,e][l,4]dioxin, see TCDD Chlorodibromonaphthalene, see Naphthalene 2-Chloro-2, 6 -diethylacetanilide, see Alachlor... 

Radical 80 has been prepared as its perchlorate salt by anodic oxidation in ethyl acetate in the presence of hthium perchlorate. The reactivity toward nucleophiles of material so prepared was investigated nitrite and nitrate ions give 2-nitrodibenzo[l,4]dioxin although the mechanisms of the reactions are not clear. Pyridine gives 7V-(2-dibenzo[l,4]dioxinyl)pyridinium ion (84). Other nucleophiles acted as electron donors and largely reduced 80 back to the parent heterocycle they included amines, cyanide ion and water. In an earlier study, the reaction of 80 with water had been examined and the ultimate formation of catechol via dibenzo[l,4]dioxin-2,3-dione was inferred. The cation-radical (80) has been found to accelerate the anisylation of thianthrene cation-radical (Section lII,C,4,b) it has been found to participate in an electrochemiluminescence system with benzo-phenone involving phosphorescence of the latter in a fluid system, and it has been used in a study of relative diffusion coefficients of aromatic cations which shows that it is justified to equate voltammetric potentials for these species with formal thermodynamic redox potentials. The dibenzo[l,4]dioxin semiquinone 85 has been found to result from the alkaline autoxidation of catechol the same species may well be in-... 

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