Dioxin dechlorination

Yoshida N, N Takahashi, A Hiraishi (2005) Phylogenetic characterization of polychlorinated-dioxin-dechlorinating microbial community by use of microcosm studies. Appl Environ Microbiol 71 4325-4334. 

Barkovskii AI, P Adriaens (1996) Microbial dechlorination of historically present and freshly spiked chlorinated dioxins and diversity of dioxin-dechlorinating populations Appl Environ Microbiol 62 4556-4562. 

TCDD may be in a state of flux, resulting from dechlorination of octa-and hepta-CDD and being further dechlorinated to 2-mono-CDD [54]. Beside dechlorination reactions in sediments [4],dioxin dechlorination reactions have been demonstrated in the presence of microorganisms ([5, 12, 13, 431-433], dihydroxylated monoaromatic compounds [433], vitamin B12, and zero valent metals [3]. 

Observations of these reactions in the natural environment indicate that they take place on the order of years per chlorine removed for aryl halides in sediments (Brown et al., 1987 Adriaens et al., 1999 Fu et al., 2001 Gaus et al., 2002), and months to years for alkyl halides or pesticides in groundwater (Potter and Carpenter, 1995 Wiedemeier et al., 1999 Skubal et al., 2001). Accurate calculations account for the metabolic rates measured in sediments or soils (Henrichs and Reeburgh, 1987 Schlesinger, 1991 Murphy and Schramke, 1998). For example, Fu et al. (2001) estimated the rate of cometabolic dioxin dechlorination in estuarine Passaic River sediments at 3-8 pg of diCDD per gram sediment per year, based on sediment respiration rates, and the ratios of dioxin dechlorination as compared to methane production, which represented the dominant TEAP under which these reactions occurred. 

In an attempt to assess the quantitative contribution of reactive processes to the overall cycling of anthropogenic source contamination, two examples will be considered (i) vinyl chloride oxidation at groundwater-surface water interface (GSI) St. Joseph, Michigan (e.g., Lendvay et al., 1998a,b), and (ii) dioxin dechlorination in estuarine sediment cores collected from the Passaic River, New Jersey... 

Barabas N., Goovaerts P., and Adriaens P. (2003) Modified polytopic vector analysis to identify and quantify a dioxin dechlorination signature in sediments 2. Application to the Passaic River superfund site. Environ. Sci. Technol. 

Ifi-Ditritiodihenzo- -dioxin, prepared by reductive dechlorination of 1,6-dichlorodihenzo-p-dioxin with tritium gas, is chlorinated in chloroform solution, containing catalytic amounts of iodine and ferric chloride, to produce 1,6-ditritio-2,3,7,8-tefrachlorodibenzo-p-dioxin. 

Chlorinated dibenzo ip-dioxins are contaminants of phenol-based pesticides and may enter the environment where they are subject to the action of sunlight. Rate measurements showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is more rapidly photolyzed in methanol than octachlorodi-benzo-p-dioxin. Initially TCDD yields 2,3,7-trichlorodiben-zo-p-dioxin, and subsequent reductive dechlorination is accompanied by ring fission. Pure dibenzo-p-dioxin gave polymeric material and some 2,2 -dihydroxybiphenyl on irradiation. Riboflavin-sensitized photolysis of the potential precursors of dioxins, 2,4-dichlorophenol and 2,4,5-trichloro-phenol, in water gave no detectable dioxins. The products identified were chlorinated phenoxyphenols and dihydroxy-biphenyls. In contrast, aqueous alkaline solutions of purified pentachlorophenol gave traces of octachlorodibenzo-p-dioxin on irradiation. 

It seems that deep-seated cleavage of the dioxin nucleus must accompany dechlorination in methanol. When pure dibenzo-p-dioxin (II) was irradiated in cyclohexane solution in a quartz cuvette, it darkened in color, and a precipitate of intractable dark brown material was collected and was insoluble in the common solvents except for methanol. 

Other componnds have also been examined as primers for the dechlorination of hexachloro to nonachloro PCB congeners (DeWeerd and Bedard 1999) a nnmber of snbstituted brominated monocyclic aromatic componnds were examined, and 4-bromobenzoate was effective—though less so than 2,6-dibromobiphenyl. In contrast, the chlorobenzoates that are metabolites of aerobic degradation were ineffective. The positive effect of brominated biphenyls in priming the anaerobic dechlorination of CBs has also been encountered in the dechlorination of octachlorodibenzo[l,4] dioxin to the 2,3,7,8 congener indnced by 2-bromodibenzo[l,4]dioxin in the presence of (Albrecht... 

Albrecht ID, AL Barkovskii, P Adriaens (1999) Production and dechlorination of 2,3,7,8-tetrachlorodibenzo-/)-dioxin in historically-contaminated estuarine sediments. Environ Sci Technol 33 737-744. 

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... 

Ballerstedt H, A Kraus, U Lechner (1997) Reductive dechlorination of 1,2,3,4-tetrachlorodibenzo-p-dioxin and its products by anaerobic mixed cultures from Saale River sediment. Environ Sci Technol 31 1749-1753. 

The complete elimination of functional groups is often an undesirable side reaction in organic synthesis, but on the other hand it is a possibility for the recycling of environmentally harmful compounds, for example phenols and haloarenes such as polychlorinated dibenzodioxins (PCDDs or dioxins ). For example, aryl chlorides can be effectively dechlorinated with Pd(0) NPs in tetra-butylammonium salts with almost quantitative conversions also after 19 runs (entry H, Table 1.4) [96]. On the other hand, a C-0 bond cleavage reaction also seems suitable for the fragmentation of sugar-based biomass such as cellulose or cello-biose in that way, sugar monomers and bioalcohol can be derived from renewable resources (entry F, Table 1.4) [164]. 

Barkovskii, A.L. and P. Adriaens. 1998. Impact of humic constituents on microbial dechlorination of polychlorinated dioxins. Environ. Toxicol. Chem. 17 1013-1020. 

Despite the environmental stability of these compounds, a number of reports have indicated that under reducing conditions prevailing in sediments dioxins may undergo transformation reactions, including dechlorination. The potential importance of reductive dechlorination, and perhaps one of the reasons for the emphasis on this transformation process, is illustrated by recent evidence that... 

Hilarides and others (1994) investigated the destruction of TCDD on artificially contaminated soils using °Co y radiation. It appeared that TCDD underwent stepwise reduction dechlorination from tetra- to tri-, then di- to chlorodioxin, and then to presumably nonchlorinated dioxins and phenols. The investigators discovered that the greatest amount of TCDD destruction (92%) occurred when soils were amended with 25% water and 2% nonionic surfactant [alkoxylated fatty alcohol (Plurafac RA-40)]. Replicate experiments conducted without the surfactant lowered the rate of TCDD destruction. 

The APEG-PLUS process is a technology for the ex situ treatment of chlorinated contaminants in a number of media. It is a form of alkaline dechlorination that uses an alkaline metal hydroxide with polyethylene glycol (APEG) as a reagent. It has been used to treat dioxin-contaminated... 

The XeChlor process is a reductive dechlorination process for the treatment of a wide array of organic halides, including conversion of polychlorinated biphenyls (PCBs) into biphenyl or dioxins into simple dibenzofuran. The dechlorination catalyst is prepared in situ from titanocene dichloride sodium borohydride is the reducing agent. 

The addition of fluorine is successfully executed on various deactivated 7t-centers as well. Fluorine was used to prepare perfluorocyclopentadiene and its anion 6 for the first time by addition of fluorine to perchlorocyclopentadiene followed by total dechlorination.68 Fluorine undergoes addition to enones 7,65 including dioxine derivatives 9,69 chloroenone 1070 and even to the very deactivated double bond in maleic anhydride (11) forming difluorosuccinic acids.71... 

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