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Polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are a class of organic compounds with 1 to 10 chlorine atoms attached to biphenyl and a general chemicalformula of C12H10XClX. The 209 possible compounds are called congeners, from three monochlorinated isomers to the fully chlorinated decachlorobiphenyl isomer.
PCBs are mixtures of chlorinated hydrocarbons that have been used extensively since 1930 in a variety of industrial uses, including asdielectrics in transformers and large capacitors, as heat exchange fluids, as paint additives, in carbonless copy paper and in plastics, ascaulking materials, elastic sealants and heat insulation. The value of PCBs for industrial applications is related to their chemical inertness,resistance to heat, nonflammability, low vapour pressure and high dielectric constant. PCBs are generally inert, they are resistant toalkalies, acids and they have high thermal stability.
PCBs are produced by the chlorination of biphenyl by anhydrous chloride, under heated reaction conditions and in the presence of suitablecatalysts. The degree of chlorination varies depending on the reaction conditions. The result is a mixture of different congeners, and containsmany impurities. Commercial PCB mixtures were sold based on the percentage of chlorine by weight, with each manufacturer utilizing their ownsystem for identifying their products.

 


Structure formula of 2,2',3,4,5,6'-Hexachlorobiphenyl


3D structure of 2,2',3,4,5,6'-Hexachlorobiphenyl