Acylhalide

An acyl halide is a derivative of a carboxylic acid in which the hydroxyl group is replaced by a halogen atom. The general formula for an acyl halide is RCOX, where R is an alkyl or aryl group, and X is a halogen, typically chlorine. The most common acyl halides are acyl chlorides, where X = Cl.

Acyl halides are highly reactive compounds due to the electronegativity of the halogen atom, which makes the carbonyl carbon electron-deficient and susceptible to nucleophilic attack. This reactivity makes them valuable intermediates in organic synthesis, particularly for forming esters, amides, and other carboxylic acid derivatives. They are typically prepared by reacting carboxylic acids with halogenating agents such as thionyl chloride (SOCl2), phosphorus trichloride (PCl3), or phosphorus pentachloride (PCl5).

The reactions of acyl halides are characterized by the displacement of the halide ion by a nucleophile. For example, reaction with an alcohol in the presence of a base yields an ester, while reaction with an amine yields an amide. Acyl halides can also undergo Friedel-Crafts acylation reactions with aromatic compounds to form aryl ketones. Due to their reactivity and corrosive nature, acyl halides are often prepared and used in situ or handled with care in laboratories. Their pungent odor and tendency to hydrolyze in the presence of moisture necessitate specific handling precautions.