Hell‐Volhard‐Zelinsky Reaction

AbstractThe synthesis of α‐bromocarboxylic acid by treatment of aliphatic acid containing α‐hydrogen with bromine in the presence of a catalytic amount of phosphorus or phosphorus tribromide is generally known as the Hell–Volhard–Zelinsky reaction or Zelinsky reaction. The appreciable amounts of carboxylic acids with chlorine atom at various positions rather than the α‐position are produced by the chlorination reaction. The bromination mechanism includes the formation of an enol instead of a ketene intermediate, which is analogous to the acid‐catalyzed halogenation of ketones. This reaction has been used to prepare α‐halo aliphatic acids.