Chlorinated biphenyls, properties

PCBs were manufactured and sold under many names, even if the most common are the Aroclor series. Aroclor refers to a mixture of individual chlorinated biphenyl compounds with different degrees of chlorination. A PCB mixture with an Aroclor name usually includes a numerical identifier, which provides additional information on the properties of the mixture. The most common mixtures in the Aroclor series are Aroclor 1016, Aroclor 1242, Aroclor 1248, Aroclor 1254 and Aroclor 1260. 

Analytical Properties Separation of chlorinated biphenyls Reference 4... 

The physical properties determined using the ECD are important to different areas of chemistry. Analytical chemistry deals with how much and what are involved in a chemical reaction. Expressed differently, it establishes what we refer to as the QQQ quantitation, qualitative identification, and the quality of the results. The determination of the electron affinities of the chlorinated biphenyls, dioxins, and phenols and the prediction of the response of the ECD and NIMS are important to qualitative and quantitative analyses of environmental pollutants [21]. Polarographic reduction in solutions likewise gives accurate and precise qualitative and quantitative results. The quality of the analyses is expressed by the random and systematic uncertainties in the reported values. These are obtained from the same principle of weighted least squares used to obtain information from ECD data. Wentworth has described the application of the general least-squares procedure to chemical problems [22, 23]. 

Reports that reductive dechlorination of polychlorinated biphenyls (PCBs) may occur naturally in lake and river sediments has spurred efforts to develop remediation techniques for contaminated sediments. Widespread contamination of sediments has occurred because of the intensive uses of these chemicals as heat transfer fluids, hydraulic fluids, and flame retardants due to their excellent stability properties (Hutzinger et al., 1974). PCBs are a complex mixture of chlorinated biphenyls. Theoretically, there are 209 possible PCB congeners because of steric hindrance. 

Aroclors possess properties different from their individual chlorobiphenyl compounds. For example, the individual compounds are solids at room temperature, whereas the Aroclors are either mobile oils (Aroclor 1221, 1232, 1242, and 1248), viscous liquids (Aroclor 1254), or sticky resins (Aroclor 1260 and 1262). PCBs are sparingly soluble in water, and the solubility decreases with increasing chlorine content (Table 9.5). Consequently, the aqueous solubilities of some Aroclors are also variable as follows 1242, 200 fig L 1248, 100 fig L 1254, 40 fig L and 1260, 25 figVK Bias in these results owing to selective solubilization of lower chlorinated biphenyls (LCBPs) should be taken into account in considering the environmental behavior of specific PCBs and their toxicity to organisms. The relative pattern of partitioning into tissues often reflects the differential water solubilities of the compounds rather than preferential uptake. 

Chlorinated Biphenyls 80 5 Limited resistance noticible change in properties a prolonged time of exposure might cause irreversible damage (polymer degradation) II... 

Table 5. Chlorinated biphenyls - composition and properties of isomer groups [65, 95]...

In earlier editions of the Eniyclopedia there have been articles covering the properties, manufacture, capacities, etc, of polychlorinated biphenyls (PCBs), chlorinated naphthalenes, benzene hexachloride, and chlorinated derivatives of cyclopentadiene. These materials are no longer in commercial use because of their toxicity. However, they stiU impact on the chemical industry because of residual environmental problems. Their toxicity and environmental impact are discussed (see Cm.OROCARBONSANDCm.OROHYDROCARBONS, TOXIC aromatics). 

Special additives are often included in a carrier formulation to provide specific properties such as foam control, stabiUty, and fiber lubrication during dyeing. Most important are the solvents used to solubilize the soHd carrier-active chemicals. These often contribute to the general carrier activity of the finished product. For example, chlorinated benzenes and aromatic esters are good solvents for biphenyls and phenylphenols. Flammable compounds (flash point below 60°C) should be avoided. 

Table II gives estimated properties of a series of chloro-biphenyls and are average values for each chlorine number group of...

The second structural property described by the 4ypc index is the substitution pattern on the benzene ring. The value of the 4ypc index increases sharply with the degree of substitution, while in the isomeric classes of substituted benzenes it increases with the proximity of substituents. Thus, this structural parameter has also been found to be very useful in describing activities and properties of polysubstituted benzenes [103], chlorinated benzenes [279], and polychlorinated biphenyls [286]. 

PCBs are attractive for industrial applications because of their stability and dielectric properties [351-354]. Figure 1 shows the structure of the biphenyl molecule along with examples of chlorination that can occur at any of the positions on the rings. The physical and chemical properties of both isomers and mixtures used in industrial applications depend upon the degree and position of the chlorine atoms [355 -358]. There are 209 possible chlorobiphenyl isomers and Table 4 lists the number of isomers for various degrees of substitution. However, many of these isomers do not occur in significant amounts in commercial products, and isomers with four or five chlorine atoms on one ring but none on the other are not detectable in PCB mixtures [359-362]. 

The base biphenyl has 10 hydrogen atoms four of them (2, 6, 2, 6 ) are near the bridge and are named the a positions, four of them (3, 5, 3, 5 ) are away from the bridge and are named the p positions, and two of them (4, 4 ) are opposite the bridge and are named the y positions. There are three forms for mono-chloro biphenyl, depending on the position of the chlorine atom, and they each have different properties. The PCBs are a set of 210 compounds with 0 to 10 chlorine atoms in a molecule. Monsanto made them under the trade name Aroclor, and they came in a number of mixtures the light Araclor 1221 is basically mono- and di-chloro, the medium Aroclor 1248 is principally tri-, tetra- and penta-chloro, and the heavy Aroclor 1260 is principally hexa- and hepta-chloro. We are concerned with the transportation and concentration of these chemicals, particularly in fish and humans, which are controlled by the three parameters of vapor pressure (breathe in air), solubility in water (drink water), and octanol-water partitions (accumulation in fat). 

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