Chlorohydrination

Chlorohydrination is a chemical reaction in which a chlorine atom and a hydroxyl group are added to a carbon-carbon double bond or triple bond. This process typically involves the reaction of an alkene or alkyne with a source of hypochlorous acid (HOCl), which can be generated in situ from chlorine gas and water.

The reaction proceeds via an electrophilic addition mechanism. The pi electrons of the alkene or alkyne attack the electrophilic chlorine atom of hypochlorous acid, forming a cyclic chloronium ion intermediate. This intermediate is then attacked by the nucleophilic hydroxyl group, leading to the opening of the ring and the formation of a chlorohydrin. The regioselectivity of the addition, meaning which carbon atom receives the chlorine and which receives the hydroxyl group, is often governed by Markovnikov's rule, where the hydroxyl group adds to the more substituted carbon.

Chlorohydrins are versatile intermediates in organic synthesis. They can be further reacted to form epoxides, which are important building blocks for polymers and pharmaceuticals. They can also be oxidized to alpha-hydroxy ketones or alpha-diketones, or reduced to form vicinal diols. The synthesis of chlorohydrins is a fundamental reaction in organic chemistry, with applications in the production of various industrial chemicals.