Polychlorinated hydrocarbons

Channels in crystals of thiourea [62-56-6] (87) are comparable but, as a consequence of the larger size of the sulfur atom, have larger cross-sectional areas (0.7 nm) and can trap branched-chain, aUcychc, and other molecules of similar dimensions including polychlorinated hydrocarbons. But they do not include the straight-chain hydrocarbons that work so well with urea. 

Dioxins are prominent members of the class of polychlorinated hydrocarbons that also includes diben-zofuran, biphenyls and others. Dioxins are highly toxic environmental contaminants. Like others small planar xenobiotics, some dioxins bind with high affinity to the arylhydrocarbon (Ah) receptor. Dioxins activate the receptor over a long time period, but are themselves poor substrates for the enzymes which are induced via the Ah-receptor. These properties of the dioxins and related xenobiotics may be important for the toxicity of these compounds. Dioxins like 2,3,7,8-tetrachloro-p-dibenzodioxin can cause persistent dermatosis, like chloracne and may have other neurotoxic, immunotoxic and carcinogenic effects. 

Goerlitz and Law [59] determined chlorinated insecticides in sediment and bottom material samples, which also contained polychlorobiphenyls by extracting the sample with acetone and hexane. The combined extracts were passed down an alumina column. The first fraction (containing most of the insecticides and some polychlorinated biphenyls and polychlorinated naphthalenes) was eluted with hexane and treated with mercury to precipitate sulphur. If the polychlorinated hydrocarbons interfered with the subsequent gas chromatographic analysis, further purification on a silica gel column was necessary. 

Rotenberg SA, Weinstein IB. 1991. Two polychlorinated hydrocarbons cause phospholipid-dependent protein kinase C activation in vitro in the absence of calcium. Molecular Carcinogenesis 4 477-481. 

Hendrickson CM, Bowden JA. 1976. In vitro inhibition of lactate dehydrogenase by insecticidal polychlorinated hydrocarbons I. Mechanism of inhibition Possible association of reduced nicotinamide adenine dinucleotide with mirex. J Agric Food Chem 24(2) 241-244. 

Although this chapter concentrates on environmental problems associated with metals, the discharge of organic compounds is also subjected to stringent limits. The compounds that cause most concern are pesticides, herbicides, phenols, biphenyls, polychlorinated hydrocarbons (PCBs), and polyaromatic hydrocarbons (PAHs). 

Polychlorinated hydrocarbons, such as polychlorinated dibenzodioxins, dibenzofurans, and biphenyls exist as a number of different congeners. Some of these are geometric isomers. Many cause a range of toxic effects that are believed to be mediated by interaction with the aryl hydrocarbon receptor (AhR) (they are known as pleiotropic effects). However, not all the isomers cause these effects because they do not all interact with the AhR receptor. To interact with this receptor, the molecule needs to be flat (planar). It can be seen in the diagram (Fig. 5.2)... 

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. 

Figure 2.14 Some examples of classical polychlorinated hydrocarbons that are globally distributed.

Fathepure, B. Z. Vogel, T. M. (1991)- Complete degradation of polychlorinated hydrocarbons by a two-stage biofilm reactor. Applied and Environmental Microbiology, 57, 3418-22. 

Ankley et al. (1993) studied the uptake of persistent polychlorinated hydrocarbons by four avian species at upper trophic levels of two aquatic food chains. Concentration of 2,3,7,8-TCDD toxic equivalents (TEQs) were evaluated in Forster s tem and common tem chicks and in tree-swallow and red-winged-blackbird nestlings from several areas in the watershed. Young birds accumulated small concentrations of 2,3,7,8-TCDD and several other 2,3,7,8-substituted CDDs and CDFs, including 1,2,3,6,7,8-HxCDD,... 

Chiu C, Thomas RS, Lockwood J, et al. 1983. Polychlorinated hydrocarbons from power plants, wood burning, and municipal incinerators. Chemosphere 12 607-616. 

S. Re and K. Morokuma, Own n-layered integrated molecular orbital and molecular mechanics study of the reaction of OH- with polychlorinated hydrocarbons CH Cl, (n = 2-4), Theor. Chem. Acc., 112 (2004) 59-67. 

The toxicity associated with polychlorinated hydrocarbons, including polychlorinated naphthalenes were recognized very early due to a variety of industrial accidents.75 However, the first evidences of bioaccumulation and toxicity on animals was noted in 1966 when emaciated seabird corpses with very high PCB body burdens washed up on beaches.74 Concern over the toxicity and persistence (chemical stability) of PCBs in the environment led the United States Congress to ban their domestic production in 1977, although some use continues in closed systems such as capacitors and transformers. PCBs are persistent organic pollutants and despite the production ban in the 1970s, they still persist in the environment and remain a focus of attention.76 Their use as fire retardants was discontinued when their toxicity was discovered. 

A wide variety of solvents has been used for epoxidations, but hydrocarbons are generally the solvent of choice 428 Recently, it has been shown434 that the highest rates and selectivities obtain in polar, noncoordinating solvents, such as polychlorinated hydrocarbons. Rates and selectivities were slightly lower in hydrocarbons and very poor in coordinating solvents, such as alcohols and ethers. The latter readily form complexes with the catalyst and hinder both the formation of the catalyst-hydroperoxide complex and its subsequent reaction with the olefin. 

Polychlorinated hydrocarbons Polychlorinated organic compounds Pesticides, polychlorinated biphenyls... 

Polychlorinated hydrocarbons from power plants, wood burning and municipal incinerators" Griffin RD (1986), Chemosphere 15 1987-1990. A new theory of dioxin formation in municipal waste incineration"... 

The column used was a SPB-608 fused silica capillary column, 30 m x 0.53 mm ID. with a 0.5 pm film of stationary phase. It was programmed from 50°C at l°/min to 150°C and then at 8°/min to 260°C. Helium was used as the carrier gas at a flow rate of 5 ml/min and the sample consisted of 0.6 pi of a solution of the pollutants in ndecane. The mass of each pollutant present was about 120 pg. The electron capture detector is also used extensively for monitoring the separation of polychlorinated hydrocarbons and in particular the herbicides. 

Polychlorinated hydrocarbons, besides being notoriously persistent pollutants, are exceedingly interesting compounds that frequently pose arduous mechanistic problems. The deep seated transformation of I into II proves to be no exception. This challenging mechanistic fortress will force us to appeal to almost every available reasoning weapon to attempt its assault. 

Jang, B. Conversion of Polychlorinated Hydrocarbons and Acetylene over a Nickel Modified Shape Selective Zeolite Catalyst, Ph.D. Thesis, University Of Texas, Arlington, 1992. 

Chars (coke) are also used at low temperatures (363-393 K). Kassebohm and Wolfering [141] developed a reactor system for the simultaneous removal of NO.v and SO2. It is a moving-bed reactor, the catalyst is char (Fig. 23) In the application of this reactor type for flue gas cleanup of a waste incinerator, the char removes both SO2 and HCl. Moreover, very low levels of mercury and polychlorinated hydrocarbons were found at the exit of the reactor. 

Letcher, R.J., R.J. Norstrom, and A. Bergman. 1995. An integrated analytical method for determination of polychlorinated aryl methyl sulfone metabolites and polychlorinated hydrocarbon contaminants in biological matrices. Anal. Chem. 67 4155-4163. 

The conventional route to phosphorothioite esters involves the conversion of elemental phosphorus to the trichloride, followed by reaction with a thiol in presence of base.1 This can be reduced to a one-stage process by treating white phosphorus with the thiol in the presence of an electrophile, in particular a polychlorinated hydrocarbon. 

Human cell response to environmental organic toxins. Holman et al. (2000) have investigated the changes in intracellular phosphate and lipid concentrations in human cells as a function of exposure to polychlorinated hydrocarbons and compared their findings to quantitative results from reverse transcription polymerase chain reaction (RT-PCR). The human cells were exposed to low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent and well-studied man-made toxin. TCDD causes harmful effects at exposure levels of hundreds to thousands of times lower doses than most chemicals of environmental concern. This polychlorinated hydrocarbon causes an increase in the production of the cytochrome P4501A1 (CYP1A1) gene, which can be monitored with RT-PCR. 

Other examples of nonbiodegradable organic pollutants are the chlorinated and polychlorinated hydrocarbons. Many of these compounds are used as insecticides (Section 19.5). The insect-kiUing ability of dichlorodi-phenyltrichloroethane (DDT) was first recognized in 1939. By the end of World War II, its insecticidal properties were legendary due to its ability to kill everything from malaria-causing mosquitoes to lice. This success prompted the introduction of numerous other chlorinated hydrocarbons as... 

Table 5,3 Examples of QSAR models for estimating toxicity to fish of non-polar non-specific toxicants (e.g. alkanes, alkenes, saturated and unsaturated halogenated aliphatic hydrocarbons, basic ethers, cyclic ethers, ketones, amides, secondary and tertiary aliphatic and aromatic amines, alkylbenzenes, halogenated benzenes, piperazines, pyrimidines, polychlorinated hydrocarbon pesticides) log LC50 correlations with various parameters. 

Air, copper, halogens (chlorine, bromine, iodine), alkali metals Acids, water, hydroxy compounds, polychlorinated hydrocarbons (for example, CCI, halogens, carbon dioxide, oxidants, terminal alkynes Halogens (bromine, chlorine. Iodine), hydrofluoric acid, liquid oxygen, calcium or sodium hypochlorite, heavy metals (silver, gold, mercury), nitric acid... 

Sheldon has considered the competing process of homolytic decomposition of hydroperoxides during the epoxidation of olefins with tert-h xty hydroperoxide in the presence of molybdenum complexes. It was found that homolytic decomposition of the hydroperoxide is initiated by electron transfer reactions of Mo(V) and Mo(VI) complexes with the hydroperoxide giving rise to free radical species. Reaction rates and products of hydroperoxide decomposition were dependent on the solvent and on the presence or absence of an olefin. The rates and selectivities of epoxidation were highest in polychlorinated hydrocarbons and very poor in coordinating solvents such as alcohols or ethers [387]. 

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