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A chemical reaction in which a halogen atom is introduced into a compound. Halogenations are described as chlorination, fluorination, bromination, etc., according to the halogen involved. Halogenation reactions may take place by direct reaction with the halogen. This occurs with alkanes, where the reaction involves free radicals and requires high temperature, ultraviolet radiation, or a chemical initiator; e.g.C2H6+Br2 → C2H5Br+HBr The halogenation of aromatic compounds can be effected by electrophilic substitution using an aluminium chloride catalyst:C6H6+Cl2 → C6H5Cl+HCl Halogenation can also be carried out using compounds, such as phosphorus halides (e.g. PCl3) or sulphur dihalide oxides (e.g. SOCl2), which react with –OH groups. Such compounds are called halogenating agents. Addition reactions are also referred to as halogenations; e.g.C2H4+Br2 → CH2BrCH2Br

C2H6+Br2 → C2H5Br+HBr

C6H6+Cl2 → C6H5Cl+HCl

C2H4+Br2 → CH2BrCH2Br

Subjects: Chemistry.

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