PolyChloro-DibenzoFurans,

Another development is due to the interest in polychlorodibenzofurans, spurred by their occurrence as environmental contaminants. Polychloro-phenols are manufactured in large amounts (150,000 tons per annum) and find a wide range of uses. The usual method of manufacture involves the hydrolysis of chlorobenzenes, and side reactions, favored by high temperature, can lead to the production of polychlorodibenzofurans and poly-chlorodibenzo-p-dioxins. The Seveso incident is well known." Polychloro-biphenyls are also widely used industrial chemicals, particularly in heat exchange systems, and their pyrolysis leads to the formation of polychloro-dibenzofurans. Polychlorodibenzofurans have also been detected in the fly ash and flue gases of incinerators and industrial heating plants. The most toxic of the polychlorodibenzofurans are 2,3,7,8-tetra-, 1,2,3,7,8-penta-, and 2,3,4,7,8-pentachlorodibenzofuran, and an extensive literature exists on the environmental pollution and the results of human exposure to these substances. A particularly tragic example of the latter occurred in 1968 in the Fukuoka prefecture of Japan after consumption of rice oil contaminated with a commercial polychlorobiphenyl. 

GC-MS, usually using the mass fragmentography technique (specific mass detection), is important in the analysis of mixtures containing polychloro-dibenzofurans, ... 

Lawn RE. 1988. Some aspects of the determination of polychlorodibenzo-p-dioxins and polychloro-dibenzofurans in environmental and biological samples. Anal Proc 25 49-50. 

Polychloro-dibenzodioxins and polychloro-dibenzofurans are basically contaminants which can be formed when chemicals containing the element chlorine are synthesized or subjected to heat. There are many of these substances (75 PCDDs and 135 PCDFs) which can have various numbers of chlorine atoms, when they are known as congeners. In some cases there can be compounds that have the same number of atoms but arranged differently, when they are called isomers. 

Pyrolysis of tri-, tetra-, and penta-chlorobenzenes affords mixtures of chlorinated dibenzofurans and dibenzo-p-dioxins, " and chlorinated diphenyl ethers cyclize in the presence of palladium acetate to polychloro-dibenzofurans/ The action of malononitrile on tetrahydroxy-p-benzoquinone leads to the benzo-difuran (79), contrary to a previous report/ The acid-catalysed condensation of quinones with phenols has been studied p-benzoquinone and resorcinol, for example, afford compound (80)/ Naphtho[2,3- >]furan-4,9-diones (81 R = Me or Ph R = Ac, Bz, C02Et, or CN) are obtained from 2,3-dichloronaphtho-1,4-quinone and compounds R COCHaR in DMF that contains potassium fluoride/ The action of mineral acids on p-benzoquinone produces a mixture of complex benzofurans, which includes (82) and (83)/ Bases convert the ben-zofuranone (84) into the tetrameric compound (85), contrary to an earlier... 

Toxic substances substances which generate very toxic or strongly malodorous fumes in fire water polluting substances highly malodorous subsbnces polychloro- dibenzofurans, dioxins, hydrochloric and sulfuric adds above 10% cone Separate fire compartments can be stored with low hazard substances up to total permissible level max. 250 tons per fire compartment block storage with and without pallets max. 2 rows or 8 ft deep, max. 4 layers or 16 ft high min. 4 ft between blocks... 

Polychlorodibenzo-p-dioxins, polychlorodi-benzofurans, poly-chlorobiphenyls Polychlorodibenzo-p-dioxins, polychloro-dibenzofurans... 

Dibenzofuran, 1,2,3,4,6,7,8,9-octahydro-synthesis, 4, 693 Dibenzofuran, polychloro-occurrence, 4, 709 Dibenzofuran, 2,4,6,8-tetra-t-butyl-synthesis, 4, 682... 

From limited data the generalization has been made that this method fails for the synthesis of 1-substituted dibenzofurans and for the synthesis of 4-substituted dibenzofurans unless the amino group and the potential 4-substituent are in the same ring. These generalizations are not substantiated in the synthesis of polychlorodibenzofurans. Polychloro-2-phenoxy-anilines are poorly soluble and nonbasic so that the usual method is precluded. In these cases aprotic diazotization with isopentyl nitrite in tetrachloroethylene at 80 C is the method of choice. Yields, as determined by GLC, are usually of the order of 40-50%. The yields of pure isolated... 

Schafer W, Ballschmiter K (1986), Chemosphere 15 755-763. Monobromo-polychloro-deri-vatives of benzene, biphenyl, dibenzofuran and dibenzodioxin formed in chemical-waste burning"... 

Luco, J.M., Galvez, J Garda-Domenech, R. and De Julian-Ortiz, V. (2004) Structural invariants for the prediction of relative toxidties of polychloro dibenzo-p-dioxins and dibenzofurans. Mol. Div., 8, 331-342. 

Kuehl, D.W., R.C. Dougherty, Y. Tondeur, D.L. Stalling and C. Rappe, Negative Chemical Ionization Studies of Polychloro-dibenzodioxins and Dibenzofurans in Environmental Samples, In Environmental Health Chemistry. The Chemistry of Environmental Agents As Potential Human Hazards, J.D. McKinney (ed.), Ann Arbor Science Publishing Co., Ann Arbor, Michigan, 1980, Chapter 12. 

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