karbonyylihalides

Karbonyylihalides, also known as acyl halides, are a class of organic compounds with the general formula RCOX, where R is an alkyl or aryl group, and X is a halogen atom (typically chlorine or bromine). The carbon atom of the carbonyl group is bonded to both the oxygen atom and the halogen atom. This structure makes the carbonyl carbon highly electrophilic, due to the electronegativity of both oxygen and the halogen. This electrophilicity is a key factor in their reactivity.

Karbonyylihalides are typically prepared by reacting carboxylic acids with halogenating agents such as thionyl chloride (SOCl2), phosphorus pentachloride (PCl5), or phosphorus tribromide (PBr3). The reaction with thionyl chloride is particularly common as the byproducts, sulfur dioxide (SO2) and hydrogen chloride (HCl), are gases and easily removed, driving the reaction to completion.

Due to the highly electrophilic nature of the carbonyl carbon, karbonyylihalides are very reactive and readily undergo nucleophilic acyl substitution reactions. They react vigorously with water to form the corresponding carboxylic acids and hydrogen halides. They also react with alcohols to form esters, with amines to form amides, and with carboxylic acids to form anhydrides. These reactions are often exothermic and can be quite vigorous. Because of their high reactivity and the corrosive nature of the hydrogen halide byproducts, karbonyylihalides are usually handled with care and often synthesized and used in situ for subsequent reactions.