Dioxins precursors

Many dioxins were, and still are, introduced into the environment together with phenoxyherbicides - derivatives of 2,4,5-T and 2,4-D. Therefore, the general toxic background created by these herbicides may be much higher than expected, since they can contain many other dioxins as additives along with 2,3,7,8-TCDD. Moreover, these compounds can evolve dioxins when transformed in natural conditions. Thus, the danger of all such pesticides must be measured in two ways by the content of highly toxic dioxins, and by the dioxin precursors [38]. 

High temperature of gasification processes effectively destroys any furan or dioxin precursors in the feed... 

The process has limited application for soils contaminated with polychlorinated biphenyls or any other dioxin precursor. Semivolatile compounds with boiling points greater than 800°F cannot be effectively removed from the soil in a one-pass treatment. The soil characteristic that most affects treatment is moisture content. All information in this summary is based on information provided by the vendor and has not been independently verified. 

Elementary reaction kinetic studies of CHCs and BHCs with specific emphasis on the reactions of chlorinated phenol and other dioxin precursors chemically activated displacement reactions Cl", Br H 0% and HO" reactions and ab initio molecular orbital calculations... 

Numerical and Experimental Investigation of Pyrolysis and Oxidation of Dioxin Precursors and other Toxic By Products ... 

Acute hazardous wastes" are those listed as such in 40 CFR 261.31 (the F020-27 series, the dioxin precursors) and 261.33 (e), the P list. 

Kinetic studies, carried out in parallel, showed that it was possible to achieve total conversion of PhCl2 at 300°C even without the addition of platinum for concentrations of about 10 ppm, which are much higher than those of dioxin precursors observed in industrial processes. 

Marie Rose, S., Belin, T., Mijoin, J., et al. (2009). Destruction of PAH and dioxin precursors using selective oxidation over zeolite catalysts. Influence of the presence of ammonia in the flue gas, Appl. Catal. B Environ., 93, pp. 106-111. 

Uses Defoamer, drainage aid for kraft pulp/paper applies, in brownstock washing, screen room, bleach plant, paper machine, and effluent Features Water-based does not contain EBS, min. oil, or dioxin precursors does not contribute to deposit formation suitable where batch or continuous pulp is employed... 

Soh, N., Tokuda, T., Watanabe, T., Mishima, K., Imato, T., Masadome, T., Asano, Y., Okutani, S., Niwa, O. and Brown, S. (2003) A surface plasmon resonance immunosensor for detecting a dioxin precursor using a gold binding polypeptide. Talanta, 60, 733-45. 

The proposed mechanism by which chlorinated dioxins and furans form has shifted from one of incomplete destmction of the waste to one of low temperature, downstream formation on fly ash particles (33). Two mechanisms are proposed, a de novo synthesis, in which PCDD and PCDF are formed from organic carbon sources and Cl in the presence of metal catalysts, and a more direct synthesis from chlorinated organic precursors, again involving heterogeneous catalysis. Bench-scale tests suggest that the optimum temperature for PCDD and PCDF formation in the presence of fly ash is roughly 300°C. 

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 synthetic preparation of 2,8-dichlorodibenzo-p-dioxin was facilitated in that the chemical precursor, 2,4,4 -trichloro-2 -hydroxydiphenyl ether, was available as a pure material. Condensation was induced by heating the potassium salt at 200 °C for 15 hours in bis (2-ethoxyethyl) ether. Product analysis by GLC and mass spectrometry revealed an unexpected dichlorophenol and a monochlorodibenzo-p-dioxin. Further, the product initially isolated by crystallization from the reaction mixture was 2,7-dichlorodibenzo-p-dioxin, rather than the expected 2,8-isomer. Cooling of the mother liquor yielded crystalline plates which were shown to be 2,8-dichlorodibenzo-p-dioxin by x-ray diffraction (Reaction 2). 

Miriyala and Williamson have described the synthesis of /i-kctocarboxam idcs from primary and secondary amines and 2,2-dimethyl-2H,4H-l,3-dioxin-4-ones as reactive a-oxoketene precursors (Scheme 6.158) [304], The experimental procedure involved heating a mixture of the dioxinone with 2-3 equivalents of the amine at ca. 180 °C for 1-3 min under solvent-free conditions in a sealed vessel by microwave irradiation. A small collection of 18 /3-ketocarboxamides was prepared in very high yields using this protocol. 

In Scheme 6.230, the multistep synthesis of 2,3-dihydro-4-pyridones is highlighted [411]. The pathway described by Panunzio and coworkers starts from a dioxin-4-one precursor, which is readed with 2 equivalents of benzyl alcohol under solvent-free microwave conditions to furnish the corresponding /1-diketo benzyl esters. Subsequent treatment with 1 equivalent of N,N-dimethylformamide dimethyl acetal (DMFDMA), again under solvent-free conditions, produces an enamine, which is then cyclized with an amine building block (1.1 equivalents) to produce the desired 4-pyridinone produds. All microwave protocols were conducted under open-vessel conditions using power control. 

Tetrachlorodibenzo-p-dioxin (TCDD) is believed to be a byproduct in chemical processing generated by a halophenol or chlorobenzene starting material. An intermediate reaction will occur at an elevated temperature (equal to or greater than 160°C), an alkaline condition, or in the presence of a free halogen. The end reaction results in either direct dioxin, intermediate dioxin, or predioxin formation that will ultimately form dibenzo-p-dioxins [10]. TCDD is suspected in wastewaters from pesticide manufacture that uses such raw materials as 2,4,5-trichlorophenol (2,4,5-T) and 1,2,4,5-tetra-chlorobenzene, which are characteristic of TCDD precursors. A TCDD level as high as 111 mg/L has been found in drums of waste from the production of the pesticide 2,4,5-T. 

A different reaction pathway and a remarkably stable ketene-containing l,3-dioxin-4-one has been prepared by cross dimerization of ketenes 213 and 214, generated in situ by FVP of appropriate precursors. The product, l,3-dioxin-4-one 215, was obtained in 40% yield after recrystallization from hexane <2002J(P1)599> (Equation 74). 

Some chemicals can affect other parts of the immune system. For example, polychlorinated hydrocarbons such as dioxins, dibenzofurans, and polychlorinated biphenyls (PCBs) damage the thymus, which is a lymphoid organ, producing mature T lymphocytes from the precursor cells, which are produced in the bone marrow. The result is depletion of the T cells in the thymus. 

A two-step synthesis of 1,4-dioxin from dioxane is via 2,3,5,6-tetrachloro-l,4-dioxane which is dechlorinated using magnesium and iodine (39JA3020). The route to 2,5-dimethyl-1,4-dioxin uses 2,5-diiodomethyl-l,4-dioxane (diepiiodohydrin) as precursor (Scheme 45) (57JA6219). 

Aromatic compounds are formed to some extent in most combustion processes in addition they are added in considerable quantities to unleaded gasolines in order to increase the octane number and prevent knock in engines. Aromatic species are of environmental concern, both because they are harmful to the environment and because they are important precursors to dioxins and soot. 

Dioxins and 1,4-dithiins have often been prepared by elimination reactions of appropriately substituted saturated analogues. However, in the more recent literature a number of examples of syntheses of 1,4-dithiins are described which utilize reactions involving unsaturated precursors. Examples of 1,4-oxathiins are relatively scarce and no general preparative routes have been developed. 

With one or two exceptions, dibenzo fused derivatives require quite different synthetic strategies to those above. Dibenzo[6,e][l,4]dioxin is nowadays frequently prepared in yields of 10-20% by heating a mixture of 2-chlorophenol, potassium carbonate and copper powder to 170-180 °C (57JA1439). 2-Bromophenol can also be used as the precursor but... 

The main idea of dioxin formation suppression is based on deactivating potential of its formation precursors, such as Cl2, 02, or catalysts. 

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