Dibenzo p dioxin

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... 

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in marine products and estimation of exposure through fishes and shellfishes 97YZ850. 

Owing to their extreme toxicity, polychlorinated dibenzo-p-dioxins are of particular interest [99CPL355, 99JA2561, 99JPC(A)7686]. Okamoto suggested a new... 

M. Freiberg, D.L. McAllister, C.J. Mazac, P. Ranken Analysis of Trace Levels of Polybrominated Dibenzo-p-dioxins and Dibenzofurans in Brominated Flame Retardants Presented on June 30, 1993 at Orgabrom 93 in Jerusalem. 

G.G. Choudhry, O. Hutzinger, Mechanistic Aspects of Thermal Formation of Halogenated Organic Compounds Including Polychlorinated Dibenzo-p-dioxins, Gordon Breach Publ. New York (1983). 

Fleischer 0, Wichmann H, Lorenz W. 1999. Release of polychlorinated dibenzo-p-dioxins and dibenzofurans by setting off fireworks. Chemosphere 39(6) 925-932. 

Ah-receptor-mediated toxicity is particularly associated with the highly toxic compound 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD), commonly referred to as dioxin. TCDD, and the concept of toxicity equivalency factors (TEFs) based on TCDDs, will be dealt with in Chapter 7. The main point to make at this juncture is that the toxicity of each individual coplanar congener in a mixture can be expressed in terms of a toxic equivalent calculated relative to the toxicity of dioxin. Summation of the toxic equivalents of the individual coplanar PCBs gives a measure of the toxicity of the whole mixture, as expressed through the Ah receptor mechanism. 

Dichlorodibenzo-p-dioxin was prepared from isotopic potassium 2,4-dichlorophenate uniformly labeled with Ullman conditions gave a 20.5% yield. Small amounts of dichlorophenoxy chlorophenol were removed from the product by extraction with sodium hydroxide before purification by fractional sublimation and recrystallization from anisole. Chlorination of 2,7-dichlorodibenzo-p-dioxin in chloroform solution containing trace amounts of FeCls and 12 yielded a mixture of tri-, tetra-, and pentachloro substitution products. Purification by digestion in boiling chloroform, fractional sublimation, and recrystallization from anisole was effective in refining this product to 92% 2,3,7,8-tetrachloro isomer, which also contained 7% of the tri- and 1% of the penta-substituted dibenzo-p-dioxin. Mass spectroscopy was used exclusively to monitor the quality of the products during the synthesis. 

Designation, Chromatographic Separation, and Analysis. The abbreviation DBpD is used for dibenzo-p-dioxin, and the positions of chlorine... 

Figure 5. Carbon-chlorine bond lengths (A) of chlorinated dibenzo-p-dioxins as a function of the number of chlorine substituents.

Compounds having the dibenzo-p-dioxin nucleus give a blue to blue- green color when dissolved in concentrated sulfuric acid with oxidizing agents, such as H .02 and KNO (I). 

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. 

Studies were made on a series of chlorinated dibenzo-p-dioxin cation radicals in trifluoromethanesulfonic acid (TFMS acid). TFMS acid was... 

The visible absorption maxima for a series of chlorinated dibenzo-p-dioxins in TFMS acid are tabulated in Table I. The visible absorption spectra of these compounds vary with the position and number of chlorine atoms. In general, a bathochromic shift was observed as more chlorine atoms were attached to the dibenzo-p-dioxin nucleus. 

Figure 1. ESR spectrum of dibenzo-p-dioxin in TFMS acid...

The 1-chloro- and 2-chlorodibenzo-p-dioxins, which readily dissolved in TFMS acid, formed cation radicals without UV irradiation or the addition of oxidizing agents. With the exception of broader resonance lines. Figure 3 shows that the five-line pattern observed with 1-chloro-dibenzo-p-dioxin is similar to that of the unsubstituted dibenzo-p-dioxin. Apparently, protons at the 2, 3, 7, and 8 positions became less equivalent... 

Helpful discussions with David N. Lincoln are acknowledged with pleasure. The 1,6-dibenzo-p-dioxin sample was kindly supplied by J. H. Vinopal and J. E. Casida, Division of Entomology, University of California, Berkeley, Calif. 

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. 

Variations in the manufacturing process of 2,4,5-trichloro- and pentachlorophenol (but not 2,4-dichlorophenol) have sometimes resulted in contamination of the product by small amounts of heterocyclic impurities (4,5). Of these, the chlorinated dibenzo-p-dioxins such as TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) have received much scientific and public attention because of their real or potential toxicity 6, 7), [Chick edema factor, a curious toxicological problem to poultry producers for several years, has been shown to be composed of chlorodibenzo-p-dioxins (8).]... 

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...

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. 

A more concentrated (1000 ppm) solution of dibenzo-p-dioxin in methanol was irradiated for 1.5 hours under a 450-watt lamp fitted with a borosilicate glass filter while nitrogen was bubbled continuously through, the solution. Unchanged starting material was recovered to the extent of 85%. The principal photolysis product again was a dark brown insoluble gum similar to that described above. Its mobility on thin layer chromatography (TLC) was very low in the benzene/ethyl acetate (4 1) solvent used to separate the other products. 

Acute Lethality. Samples of 2,7-dichlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin, hexachlorodibenzo-p-dioxin, and octachloro-dibenzo-p-dioxin were evaluated for acute oral lethality in the following animals. 

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. 

Studies on the chlorodibenzodioxins have led to the following conclusions (1) 2,7-dichlorodibenzo-p-dioxin and octachlorodibenzo-p-di-oxin have a low acute toxicity (2) 2,3,7,8-tetrachlorodibenzo-p-dioxin has an unusually high toxicity (3) hexachlorodibenzo-p-dioxin is highly toxic but less toxic than 2,3,7,8-tetrachlorodibenzo-p-dioxin (4) all chlorodibenzodioxins are not alike in their toxicological properties. Isomers of the same dibenzo-p-dioxin vary in toxicological properties, making it important to identify them specifically. 

Industrial workers involved in chlorinated aromatic production including chlorophenol suffered dioxin-induced chloracne 2,3). Chloracne and other serious health disturbances have been attributed to polychloro-dibenzo-p-dioxins in workers involved in manufacturing 2,4,5-T 4, 5). Dioxins are toxic to chick embryos, guinea pigs, rabbits, and monkeys 6, 7, 8, 9, 10). 

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