halohydrin

A halohydrin, also called a haloalcohol, is an organic compound that bears both a halogen atom and a hydroxyl group on adjacent carbon atoms. The halogen is typically attached to one carbon and the hydroxyl group to the neighboring carbon, with common examples being chlorohydrins and bromohydrins. In general terms, the structure can be described as R-CH(OH)-CH2-X or X-CH(OH)-R, where X is a halogen.

Halohydrins are commonly prepared by the halogenation of alkenes in water, a reaction known as halohydration. When a diatomic halogen (Cl2, Br2, or I2) is added to an alkene in aqueous medium, a halonium ion forms, and water attacks the more substituted carbon. Deprotonation then yields the halohydrin with the hydroxyl group on the more substituted carbon and the halogen on the other carbon. The formation proceeds with anti stereochemistry for the added groups.

Many halohydrins are versatile intermediates in organic synthesis. Treatment with base promotes intramolecular nucleophilic displacement to give epoxides (three-membered cyclic ethers) via cyclization and loss of the halide. Halohydrins can also undergo further transformations, such as substitution at the halogen or oxidation at the alcohol, enabling access to a variety of products. They serve as useful building blocks in the preparation of polymers, pharmaceuticals, and agrochemicals.

Safety and properties vary with the specific halogen and substituents; halohydrins are typically polar compounds that can be reactive and corrosive.