Halogenate

Halogenate is a chemical term describing the introduction or substitution of one or more halogen atoms (fluorine, chlorine, bromine, or iodine) into a substrate. In practice, halogenation can involve replacing a hydrogen atom with a halogen (halogenation of hydrocarbons) or adding halogens across double or triple bonds (electrophilic or radical halogenation).

Common methods include electrophilic halogenation, using diatomic halogens or reagents that generate halogen cations, to convert alkenes into vicinal dihalides or to halogenate aromatic rings. Radical halogenation uses light or radical initiators to abstract a C–H bond and install halogens, often giving regioselective alkyl halides (Cl or Br). Nucleophilic halogenation employs halide nucleophiles in substitution reactions, including SN2 processes that form alkyl or aryl halides. Fluorination typically requires specialized reagents (e.g., Selectfluor, DAST) due to the reactivity of fluorine. Enzymatic halogenation occurs in nature via halogenases that insert chlorine or bromine into organic substrates during biosynthesis.

Applications span the synthesis of organohalogen compounds used as intermediates in pharmaceuticals, agrochemicals, and polymers. Halogenated motifs can alter reactivity, volatility, and metabolic stability, and are common in medicinal chemistry. Some organisms also perform halogenation enzymatically as part of natural product biosynthesis.

Safety and environmental considerations are important because many organohalogens are toxic or persistent. Reactions involving halogens can be exothermic and generate corrosive byproducts. The term halogenate derives from Latin halogenum (salt-producing) and Greek halos (salt) with gennaein (to produce). See also halogenation; halide; fluorination; chlorination; bromination; iodination.