Halohydrins

Halohydrins are organic compounds that contain both a halogen and a hydroxyl group on adjacent carbon atoms, also described as vicinal halohydrins. Depending on the halogen, they are commonly called chlorohydrins or bromohydrins. A typical structural motif is R-CH(OH)-CH2-X, where X is a halogen such as chlorine or bromine, though variations exist with the OH and X on either of the two adjacent carbons.

They are most often prepared by the halogenation of alkenes in water. In this halohydration reaction, a halogen adds to the double bond to form a halonium ion, which is opened by water to give the halohydrin with the hydroxyl group on the more substituted carbon and the halogen on the less substituted carbon. Halohydrins can also be formed by opening epoxides with hydrogen halides or by other routes that introduce a halogen and a hydroxyl group on neighboring carbons.

A key transformation of halohydrins is base-promoted dehydrohalogenation, which converts them into epoxides (oxiranes). This intramolecular cyclization occurs when a base abstracts the proton adjacent to the hydroxyl-bearing carbon, displacing the halide and forming the three-membered ring.

Halohydrins serve as useful intermediates in organic synthesis. They are precursors to epoxides, glycols, and other building blocks used in pharmaceuticals, fragrances, and polymer-related chemistry. Safety considerations include their potential toxicity and irritant properties; many halohydrins and their reagents require careful handling and appropriate protective equipment.