Halohydrin

Halohydrin
General structure of a halohydrin, where X = I, Br, F, or Cl
Structure of the halohydrin 2-chloroethanol

A halohydrin or a haloalcohol is a type of organic compound or functional group in which one carbon atom has a halogen substituent, and an adjacent carbon atom has a hydroxyl substituent. They are derived from alcohols are therefore characterized by the presence of both the hydroxyl functional group (-OH) and a halogen functional group. Haloalcohols, especially chloroalcohols and bromoalcohols (in which the halogen atom is chlorine or bromine, respectively) are typically synthesized by halogenation of alkenes in the presence of water or an alcohol. As intramolecular ring closure between the carbons bearing the two functional groups can be induced readily by reaction with a base to give an epoxide, haloalcohols are useful as intermediates in chemical synthesis.

Halohydrin are formed from an alkene in a halohydrin formation reaction or from an epoxide by a hydrohalic acid. In presence of a base, such as potassium hydroxide, a halohydrin may undergo internal SN2 reaction to form an epoxide. This is the reverse of the formation reaction from an epoxide. Epoxidation in biological systems can be catalyzed by halohydrin dehalogenase.

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