Chlorinated aromatic compounds production

The signiflcance of toxic metabolites is important in diverse metabolic situations (a) when a pathway results in the synthesis of a toxic or inhibitory metabolite, and (b) when pathways for the metabolism of two (or more) analogous substrates supplied simultaneously are incompatible due to the production of a toxic metabolite by one of the substrates. A number of examples are provided to illustrate these possibilities that have achieved considerable attention in the context of the biodegradation of chlorinated aromatic compounds (further discussion is given in Chapter 9, Part 1) ... 

Lauritsen FR, Lunding A (1998) A Study of the Bioconversion Potential of the Fungus Bjerkandera adusta with Respect to a Production of Chlorinated Aromatic Compounds. Enzyme Microbial Technol 22 459... 

Chlorinated aromatic compounds are commonly found as contaminants in environmental soil samples. For example, chlorobenzenes have been listed as priority pollutants and can be found in various matrixes such as water, soils, sediments and sewage sludges. Polychlorinated biphenyls are probable human carcinogens but have been applied in large doses in various industrial products. Analysis of these compounds in solid matrixes, such as soils and sediments, requires several steps. 

Despite their persistency, chlorinated aromatic compounds can be transformed by microflora and fauna as well as higher organisms. The products of these processes are different. Metabolism is an important process for vertebrates to regulate or detoxify their body burden of these compounds. Some products of the biotransformation process, however, may elicit toxic effects or accumulate themselves, thereby acting opposite to the goals of biotransformation. 

Py-MS (Py at 930 °C) shows that the major decomposition products of BPA and Chakon Il-polyacrylates are a series of phenols and some other flammable aromatic compounds (Figure 2.4). However, BPC Il-polyacrylate gives out less flammable compounds (such as phenols), but more CO2, CO and HCl and some chlorinated aromatic compounds which have relatively low fuel values and may also confer flame-retardant effects in the gas phase. Therefore, the reduced flammability of Chakon... 

It is beyond the scope of this paper to investigate all the health effects associated with PCBs but there is little doubt that PCBs are compounds of concern. The concentration at which this occurs is much higher than that of many other classes of chlorinated aromatic compounds. The risk associated with exposure to PCBs can be separated into a consideration of the biological activity of PCB isomers compounds contained in the PCBs as impurities and the biological activity and probability of formation of degradation products. 

PCBs and oxidation products were distributed throughout the 18-story structure via two ventilation shafts. Analysis of soot samples revealed high concentrations of PCBs, PCDFs, PCDDs and also other classes of toxic chlorinated aromatic compounds. 

Since 1979, many studies have identified other chlorinated aromatic compounds present in trace levels in the PCBs, or produced as incomplete oxidation products in PCB fires . These compounds include polychlorinated dibenzofurans (PCDFs), polychlorinated biphenylenes (PCBPs), polychlorinated pyrenes (PCPYs), and polychlorinated chrysenes (PCCYs), Polychlorinated dibenzodioxins (PCDDs) have also been detected from fires where trichlorobenzenes were present with PCBs as the dielectric fluid Animal tests and industrial incidents have shown some... 

It is worth noting that at 300°C benzofuran was completely converted on all the catalysts. The 1 %PtAl203 catalyst, which contains more platinum than the 0.6%PtH-FAU(5) catalyst, is, however, not the most active, and the 1.2%PtHFAU(5) catalyst, which has the same number of accessible platinum atoms, is twice as active and leads to a 1.6 times higher CO2 yield (Table 5.4). This clearly shows that the presence of acid sites has a strong influence on the oxidation process of the mixture PtHFAU(5) catalysts are then more adapted to the oxidation than polychlorinated aromatics and zeohte-based catalysts are suitable for the destruction of chlorinated aromatic compounds. In addition, the production of polychlorinated compounds (PhClx) is... 

Several imrelated groups of chlorinated aromatic compounds can be considered together based on their similar composition and toxicity polychlorinated biphenyl congeners (PCBs), dioxins and furans, chlor-onaphthalenes, and chlorodiphenyl ethers (see Figure 13.1). Most of these compoimds are included in the Stockholm Convention Agreements of 2001 and 2008, and their production is reduced or eliminated in most parts of the world. However, the compoimds are highly persistent in the environment and exhibit other properties associated with POPs. Because chlorinated aromatic compoimds are nonpolar and stable at elevated temperature, gas chromatography is the preferred approach for analysis. Numerous reviews have been published that detail GC methods of analysis for PCBs, dioxins, and other chlorinated aromatic compounds in environmental samples [6,9,54]. 

Apart from pesticides, chlorinated aromatic compounds have attracted, and continue to attract, more attention from scientists, legislative bodies, and pressure groups than any other class of compound. Polychlorinated biphenyls (PCB) are by far the best known members of the class, but many other chlorinated products, and some brominated materials, have considerable commercial significance. Fluorine and iodine derivates are of little importance, and will not be considered. 

Table 2. Production and uses of chlorinated aromatic compound (Benzene derivatives) [105]...

It is a typically aromatic compound and gives addition and substitution reactions more readily than benzene. Can be reduced to a series of compounds containing 2-10 additional hydrogen atoms (e.g. tetralin, decalin), which are liquids of value as solvents. Exhaustive chlorination gives rise to wax-like compounds. It gives rise to two series of monosubstitution products depending upon... 

The reductive dechlorination of chlorinated aromatics is more compHcated in that the initial dechlorination of more highly chlorinated compounds may be either chemical or enzymatic, eg, PGP, whereas the dechlorination of less chlorinated compounds or dechlorinated products is typically enzymatic. For example, the first dechlorination of 2,4-dichlorophenol (ortho position) can occur either chemically or enzymatically the second dechlorination (para position) is enzymatic (eq. 10). 

A chlorohydrin has been defined (1) as a compound containing both chloio and hydroxyl radicals, and chlorohydrins have been described as compounds having the chloro and the hydroxyl groups on adjacent carbon atoms (2). Common usage of the term appHes to aUphatic compounds and does not include aromatic compounds. Chlorohydrins are most easily prepared by the reaction of an alkene with chlorine and water, though other methods of preparation ate possible. The principal use of chlorohydrins has been as intermediates in the production of various oxitane compounds through dehydrochlorination. 

Oxidation of phenols with chlorine dioxide or chlorine produces chlorinated aromatic intermediates before ring rupture. Oxidation of phenols with either chlorine dioxide or ozone produces oxidized aromatic compounds as intermediates which undergo ring rupture upon treatment with more oxidant and/or longer reaction times. In many cases, the same nonchlorinated, ringruptured aliphatic products are produced using ozone or chlorine dioxide. 

The reactivity of Ce, C7, Cg aromatics is mainly associated with the benzene ring. Aromatic compounds in general are liable for electrophilic substitution. Most of the chemicals produced directly from benzene are obtained from its reactions with electrophilic reagents. Benzene could be alkylated, nitrated, or chlorinated to important chemicals that are precursors for many commercial products. 

The chlorine content of the fly ash is 4.9 %, the bromine content 0.065 %. A series of brominated aromatic compounds has been adsorbed on this fly ash and treated for 1 h. with air at 300°C. The extraction and analysis yield mixed brominated/chlorinated as well as completely chlorinated products. This is shown for 5 aromatic bromine compounds in Table 2. 

In the case of alkylation using allylsilancs in the presence of aluminum chloride as a catalyst, allylsilanes containing one or more chlorine substituents on the silicon react with aromatic compounds at room temperature or below 0 C to give alkylated products. 2-aryl-1 -silylpropanes.- while allyltrimethylsilane did not give the alkylated product but instead dimerized to give the allylsilylation product.. S-itrimethylsilyli-d-itrimethylsilylrnethyl)- 1-pentene (Eq. (1 )). In the alkylation reaction, the reactivity of allylsilanes increased as the number of chlorine... 

Chlorination of aromatic compounds under irradiation has been studied extensively (Wagner, 1969). With benzene, the product is a mixture of stereoisomeric hexachlorocyclohexanes with yields 104pmol.J 1. This certainly points to chain reaction with the initiation either from a dissociation, Cl2 2C1, or from the participation of the first excited singlet state of benzene 0B2u) giving... 

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