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Concept
Reductive dechlorination
Résumé
In organochlorine chemistry, reductive dechlorination describes any chemical reaction which cleaves the covalent bond between carbon and chlorine via reductants, to release chloride ions. Many modalities have been implemented, depending on the application. Reductive dechlorination is often applied to remediation of chlorinated pesticides or dry cleaning solvents. It is also used occasionally in the synthesis of organic compounds, e.g. as pharmaceuticals.
Dechlorination is a well-researched reaction in organic synthesis, although it is not often used. Usually stoichiometric amounts of dechlorinating agent are required. In one classic application, the Ullmann reaction, chloroarenes are coupled to biphenyl]]s. For example, the activated substrate 2-chloronitrobenzene is converted into 2,2'-dinitrobiphenyl with a copper - bronze alloy.
Zerovalent iron effects similar reactions. Organophosphorus(III) compounds effect gentle dechlorinations. The products are alkenes and phosphorus(V).
Alkaline earth metals and zinc are used for more difficult dechlorinations. The side product is zinc chloride.
Vicinal reduction involves the removal of two halogen atoms that are adjacent on the same alkane or alkene, leading to the formation of an additional carbon-carbon bond.
Biological reductive dechlorination is often effected by certain species of bacteria. Sometimes the bacterial species are highly specialized for organochlorine respiration and even a particular electron donor, as in the case of Dehalococcoides and Dehalobacter. In other examples, such as Anaeromyxobacter, bacteria have been isolated that are capable of using a variety of electron donors and acceptors, with a subset of possible electron acceptors being organochlorines. These reactions depend on a molecule which tends to be very aggressively sought after by some microbes, vitamin B12.
Reductive dechlorination of chlorinated organic molecules is relevant to bioremediation of polluted groundwater.
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