Dioxins structures

Uniformly labeled 2,4-dichlorophenol- C (purchased from New England Nuclear Corp, Boston, Mass.) was used in the tracer preparation. This provided a label at all carbon positions in the dibenzo-dioxin structure. 2,7-Dichlorodibenzo-p-dioxin- C after initial cleanup by fractional sublimation, contained approximately 5% of an impurity, detected by thin layer chromatography (TLC) which gave mass peaks at 288, 290, 292, and 294 in the mass spectrometer, consistent with a trichloro-hydroxydiphenyl oxide. This is probably the initial condensation product of the Ullman reaction and is most likely 2-(2,4-dichlorophenoxy)-4-chlorophenol. It was removed easily by extractions with aqueous... 

This color transformation has been observed in dibenzo-p-dioxin (Structure I) and in its bromo, chloro, nitro, methyl, and ethyl derivatives in addition, the observed electron spin resonance (ESR) signals indicated the presence of paramagnetic species (2, 3). This phenomenon has been attributed to the formation of cation radicals in acid solution. 

Dioxins are not decomposed by heat or oxidation in a 700°C incinerator, but pure compounds are largely decomposed at 800°C. Chlorinated dioxins lose chlorine atoms on exposure to sunlight and to some types of gamma radiation, but the basic dioxin structure is largely unaffected. The biological degradation rate of chlorinated dioxins is slow, although measured rates differ widely. 

Mason G, Denomme MA, Safe L, et al. 1987. Polybrominated and chlorinated dibenzo-para-dioxins structure-activity relationships. Chemosphere 16 1729-1731. 

Structure related activity (SAR) is based on a chemical s structure as another potential source of supporting data. The chemical structure of a substance can, in some cases is used to predict its toxicity. An example of this is the family of dioxin compounds. Toxicity of tetra-substituted dioxins and furans are predicted based on what chemical groups are present at the active sites of the molecule. The tetra-substituted 2,3,7,8 TCDD is more toxic and persistent than an octa-substituted dioxins structure. Unfortunately, overall, this method has so far proved to be of little help in identifying and predicting carcinogenic potential of many chemicals. 

Strength as an oxidizing agent. There is, however, pressure to reduce the use of chlorine gas and organochlorine compounds, because they can lead to the environmental release of chlorinated hydrocarbons, which may cause cancer and other kinds of adverse health effects. The danger compounds include the notorious dioxin (Structure 6.2), which is a degradation product of organochlorine pesticides and other similar compounds. 

The biological properties of dioxin include an ability to bind to a protein known as the AH (aromatic hydrocarbon) receptor Dioxin IS not a hydrocarbon but it shares a certain structural property with aromatic hydrocarbons Try constructing molecular models of dioxin and anthracene to see these similarities... 

Structure— Function Relationships. Since PCBs and related HAHs are found in the environment as complex mixtures of isomers and congeners, any meaninghil risk and hazard assessment of these mixtures must consider the quaUtative and quantitative stmcture—function relationships. Several studies have investigated the stmcture—activity relationships for PCBs that exhibit 2,3,7,8-tetrachlorodibenzo-p-dioxin [1746-01-6] (1)... 

Chemical Acne Many chemical compounds induce skin lesions that are similar to acne. Oils, tar, creosote, and several cosmetic products induce chemical acne. These compounds induce keratinization of the sebaceous glands of the skin, obstruction of the glands, and formation of acne. Chloracne is a specific skin lesion that is induced by chemical compounds that are structurally similar to 2,5,7,8-tet-rachloro dibenzo-p-dioxin (TCDD). Chloracne is slow to heal and difficult to... 

Poiger, H. and Buser, H.R. (1983). Structure elucidation of mammalian TCDD metabolites In Tucker, R.E., Young, A.L., and Gray, A.P. (Eds.) Human and Environmental Risks of Chlorinated Dioxins and Related Compounds. New York Plenum Press, 483 92. 

The crystal structures of four chlorinated derivatives of di-benzo-p-dioxin have been determined by x-ray diffraction from diffractometer data (MoKa radiation). The compounds, their formulae, cell dimensions, space groups, the number of molecules per unit cell, the crystallographic B.-factors, and the number of observed reflections are given. The dioxin crystal structures were performed to provide absolute standards for assignment of isomeric structures and have been of considerable practical use in combination with x-ray powder diffraction analysis. 

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. 

This structure looks nothing like the structures of chlorine-containing compounds used in industrial processes. In fact, no dioxin is deliberately manufactured anywhere in the diverse chlorine industry. Nevertheless, dioxins are of concern for two reasons First, dioxins appear to be inevitable trace by-products of some reactions involving chlorine, particularly combustion and second, dioxins accumulate in the biosphere, where they have highly deleterious effects. 

C21-0098. Describe the ways in which the structures of DDT and dioxin (see Chemistry and the Environment Box) are similar. Describe the ways in which these structures differ. 

Naturally occurring oxaarenes based on polycyclic pyrans encompass a plethora of structures including the plant polyphenols such as anthocyanins and a-tocopherol (vitamin E). Halogenated dibenzo-p-dioxins and dibenzofurans are formed both as by-products during the manufacture of chlorophenols, and from the incineration of organic matter in the presence of inorganic halides. 

The oxidation behavior of 3-oxa-chromanols was mainly studied by means of the 2,4-dimethyl-substituted compound 2,4,5,7,8-pentamethylM /-benzo[ 1,3]dioxin-6-ol (59) applied as mixture of isomers 27a it showed an extreme dependence on the amount of coreacting water present. In aqueous media, 59 was oxidized by one oxidation equivalent to 2,5-dihydroxy-3,4,6-trimethyl-acetophenone (61) via 2-(l-hydroxyethyl)-3,5,6-trimethylbenzo-l,4-quinone (60) that could be isolated at low temperatures (Fig. 6.41). This detour explained why the seemingly quite inert benzyl ether position was oxidized while the labile hydroquinone structure remained intact. Two oxidation equivalents gave directly the corresponding para-quinone 62. Upon oxidation, C-2 of the 3-oxa-chroman system carrying the methyl substituent was always lost in the form of acetaldehyde. 

Certain structural features have been identified as being associated with high degrees of toxicity, AHH induction and receptor binding for the dibenzo-p-dioxins and related compounds (Poland and Knutson 1982). These are as follows ... 

Cheney, B. V. 1982. Structural Factors Affecting Aryl Hydrocarbon Hydroxylase Induction of Dibenzo-p-Dioxins and Dibenzofurans. Int. J. Quant. Chem. 21,445. 

Murray, J. S., P. Evans, and P. Politzer. 1990. A Comparative Analysis of the Electrostatic Potentials of Some Structural Analogues of 2,3,7,8-Tetrachlorodibenzo-p-dioxin and of Related Aromatic Systems. Int. J. Quant. Chem. 37, 271. 

Loonen, H., M. Tonkes, J.R. Parsons, and H.A.J. Govers. 1994b. Bioconcentration of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in guppies after aqueous exposure to a complex PCDD/PCDF mixture relationship with molecular structure. Aquai. Toxicol. 30 153-169. 

Fig. 7 Generic chemical structures of polyhalogenated compounds. X=C1, Br. (I) Polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs) (II) chlorophenols (CPs), bromophenols (BPs) (III) polychlorinated diphenyl ethers (PCDE), polybrominated diphenyl ethers (PBDE) (IV) polychlorinated dibenzo-p-dioxin (PCDD), polybrominated dibenzo-p-dioxin (PBDD) (V) polychlorinated dibenzofuran (PCDF), polybrominated dibenzofuran (PBDF) (VI) tetrabromobisphenol A (TBBPA)...

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