Octachlorodibenzo-p-dioxin

We report the crystal structures of four chlorinated dioxins—the 2,7-dichloro-, 2,8-dichloro-, 2,3,7,8-tetrachloro-, and octachlorodibenzo-p-dioxins. Thus, five crystal structures of chlorodioxins are now known. 

Figure 4. Bond distances and angles for octachlorodibenzo-p-dioxin. The molecule is located on an inversion center.

Figure 13. ESR spectrum of octachlorodibenzo-p-dioxin in TFMS acid...

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. 

The photolysis rate of several chlorinated dioxins was determined in methanol (20) (Figure 1). Solutions of 2,7-dichlorodibenzo-p-dioxin (5 mg/liter), TCDD (5 mg/liter), and octachlorodibenzo-p-dioxin (2.2 mg/ liter) were irradiated with light having an intensity of about 100 /mW/cm ... 

Figure 1. Photolysis rates of chlorinated dibenzo-p-dioxins in methanol under ultraviolet light 2J-dichlorodibenzo-p-dioxin (III) (5 mg/liter), 2,3,7,8-tetrachlorodiben-zo-p-dioxin (I) (5 mg/liter), 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin (IV) (2.2 mg/ liter) (20), 1971 by AAAS...

Octachlorodibenzo-p-dioxin was photolyzed much more slowly than TCDD (Figure 1). The rate of dioxin photolysis increased as the number of substituent chlorine atoms decreased. Octachlorodibenzo-p-dioxin gave what seemed to be a series of chlorinated dioxins of decreasing chlorine content (20). 

PCP presents a different picture from that of the lower chlorophenols and their derivatives. The corresponding dioxin shows much more stability to light than does TCDD, enough to permit its prolonged existence at low concentrations in a photoreactor. As a phenol it can directly yield dioxins, a process favored by its normal mode of application as the sodium salt. Although octachlorodibenzo-p-dioxin has much lower mammalian toxicity than TCDD (6), its formation, properties, and effects demand additional investigation. Technical preparations of PCP are frequently mixtures of tetra- and pentachlorophenols consequently, hepta-and possibly hexachlorodibenzo-p-dioxins might be expected as photolysis products in addition to the octachloro derivative. 

The toxicity of chlorodibenzodioxins other than those evaluated in this study has not been reported. Purified samples of trichloro-, penta-chloro-, and heptachlorodibenzo-p-dioxin which are free of tetrachloro-and hexachlorodibenzo-p-dioxin need to be synthesized for study. However, heptachlorodibenzo-p-dioxin cannot be highly toxic since studies on octachlorodibenzo-p-dioxin containing several percent of heptachloro-dibenzo-p-dioxin have tested the same as the pure product. 

Effects of Combustion and Heat. The results of combusting wood and paper treated with pentachlorophenol or sodium pentachlorophenate are shown in Table I. These results indicate that octachlorodibenzo-p-dioxin concentration did not increase as the result of combusting either wood or paper treated with pentachlorophenol. It seems that the concentration of octachlorodibenzo-p-dioxin concentration was actually decreased during combustion. However, paper treated with sodium pentachlorophenate did increase in octachlorodibenzo-p-dioxin concentration as the result of combustion. 

A small amount of octachlorodibenzo-p-dioxin, amounting to approximately 0.03%, was formed during the photolysis of sodium penta-chlorophenol buffered at pH 8 as shown by the data in Table IV. 

Very little change was observed in the octachlorodibenzo-p-dioxin on exposure to artificial sunlight. Over extended periods of time (18—24 hours) there was some evidence of decay. Approximately 20% photolysis was observed in isooctane at the end of 18 hours and about 6% photolysis of the octachlorodibenzo-p-dioxin after 20 hours exposure in 1-octanol. 

Combustion of wood or paper treated with pentachlorophenol resulted in no increase and more probably a decrease in octachlorodi-benzo-p-dioxin concentrations while octachlorodibenzo-p-dioxin increased slightly in paper treated with sodium pentachlorophenate. The pho-tolytic degradation of sodium pentachlorophenate at pH 8 is very rapid. Under these controlled conditions formation of no more than 0.03% octachlorodibenzo-p-dioxin was observed. The 2,3,7,8 isomer, one of the most active chloracnegens is seemingly stable towards air oxidation but... 

Chlorinated dibenzo-ip-dioxins were prepared on the gram scale for use as toxicological standards, 2,7-Dichlorodi-henzo-p-dioxin was prepared by catalytic condensation of potassium 2-bromo-4-chlorophenate in 70% yield. Thermal condensation of the potassium salt of 2,4,4 -trichloro-2 -hydroxy diphenyl ether gave a mixture of the 2,8- and 2,7-dichlorodibenzo-p-dioxins which were separated by fractional recrystallization. 2,3,7,8-T etrachlorodibenzo-p-dioxin of 99.9- -% purity was prepared by catalytic condensation of potassium 2,4,5-trichlorophenate. An isomeric mixture of hexachlorodibenzo-p-dioxins was prepared by pyrolytic condensation of sodium 2,3,4,6-tetrachlorophenate. Chlorination of pentachlorophenol (containing < 0.07% tetrachlorophenol) in trichlorobenzene gave octachlorodi-benzo-p-dioxin in 80% yield contaminated by 5-15% heptachlorodibenzo-p-dioxin. Oxidative methods were used to produce octachlorodibenzo-p-dioxin at 99.9% purity. 

The most convenient and successful synthetic preparation of octa-chlorodibenzo-p-dioxin has been described by Kulka (13). The procedure involves chlorination of pentachlorophenol in refluxing trichlorobenzene to give octachlorodibenzo-p-dioxin in 80% yield. Kulka has explained the reaction as coupling between two pentachlorophenoxy radicals. Large amounts (5—15%) of heptachlorodibenzo-p-dioxin were observed in the unpurified product. Since the pentachlorophenol used in this study contained 0.07% tetrachlorophenol, we feel that tetrachloro-phenol may be produced in situ (Reaction 4). Such a scheme would be analogous to the formation of 2,4-dichlorophenol and 3-chlorophenol produced from 2,4,4 -trichloro-2 -hydroxydiphenyl ether (Reaction 2). The solubility of octachlorodibenzo-p-dioxin was determined in various solvents data are presented in Table II. 

The general increase in concentration with increasing degree of chlorination can be observed, with OCDD (octachlorodibenzo-p-dioxin) as the predominant congener. This is consistent with previously reported data for sewage sludge in other countries. 

Korfmacher et al. [71] employed a short clean-up procedure followed by electron capture gas chromatography for the determination of octachlorodibenzo-p-dioxin in soils using a furzed silica capillary gas chromatographic column. The technique was suitable as a routine screening procedure for samples taken from contaminated sites. 

A number of toxicologically active 2,3,7,8-substituted PCDDs and PCDFs, planar PCBs and PCDD, PCDF, and PCDT homologs were measured in fish, SPMDs, and sediments. Only two target compounds exceeded the detection limits of 0.2-1 pg g in SPMD field blanks (see definition in Chapter 5). These exceptions were octachlorodibenzo-p-dioxin (OCDD) and octachlorodibenzofuran (OCDF) which were present in SPMDs at about 5 pg g However, negative... 

Note Technical grades typically contain many impurities, including but not limited to, hexachlorobenzene, PCBs, tetra- and trichlorophenols, hexa-, hepta-, and octachlorodibenzo-p dioxins. 

Octachlorodibenzo-p-dioxin S,F Biooxidation after reductive or oxidative biodechlorination... 

As discussed in the earlier survey (1), a biogenic source of polychlorinated dibenzo-p-dioxins and dibenzofurans is peroxidase-catalyzed transformation of chlorophenols as first reported by Oberg and Rappe (2041-2044). More recent studies confirm these observations (2045-2048). In addition to lactoperoxidase and horseradish peroxidase, human leukocyte myeloperoxidase catalyzes in vitro formation of dioxins and dibenzofurans from chlorophenols (2046, 2047). Formation rates are in the pmol/mol range (Scheme 3.6) demonstrating that a human biosynthesis of dioxins and furans is not only possible but also likely. These observations are reinforced by the reported in vivo (rats) conversion of the pre-dioxin nona-chloro-2-phenoxyphenol to octachlorodibenzo-p-dioxin (OCDD) (2049), and the production of hepta- and octachlorodibenzo-p-dioxin in the feces of cows fed pentachlorophenol-treated wood (Scheme 3.7) (2050, 2051). 

Huwe JK, Feil VJ, Zaylskie RG, Tieman TO (2000) An Investigation of the in Vivo Formation of Octachlorodibenzo-p-dioxin. Chemosphere 40 957... 

Opperhuizen et al. (1985) proposed that molecules with a minimal internal cross section exceeding 0.95 nm cannot cross biological membranes and thus are not bioavailable. This proposition was to account for the apparent lack of bioconcentration of some very hydro-phobic chemical substances such as hexabromobenzene, octachloronaphthalene, and octachlorodibenzo-p-dioxin. 

In follow-up experiments, Gobas et al. (1989) found that brominated biphenyls which have minimal internal cross sections somewhat greater than 0.95 nm were available for uptake in fish via the gills. In addition, Muir et al. (1986) and Muir and Yarechewski (1988) reported that octachlorodibenzo-p-dioxin, which has a minimal internal cross section greater than 0.95 nm, was present in internal tissues of trout exposed under field conditions. 

Muir, D.C.G., A.L. Yarechewski, A. Knoll, and G.R.B. Webster. 1986. Bioconcentration and disposition of 1,3,6,8-tetrachlorodibenzo-p-dioxin and octachlorodibenzo-p-dioxin by rainbow trout and fathead minnows. Environ. Toxicol. Chem. 5 261-272. 

Geyer, H.J., Schramm, K.-W., Feicht, E.A., Behechti, A., Steinberg, C., Bruggemann, R., Poiget, H., Henkelmann, B., Kettrup, A., 2002. Half-lives of tetra-, penta-, hexa-, hepta-, and octachlorodibenzo-p-dioxin in rats, monkeys, and humans-a critical review. Chemosphere 48, 631-644. 

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