Acyl halide

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An acyl halide or less common acid halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group. If the acid is a carboxylic acid, the compound contains a R–C(=O)X functional group, which consists of a carbonyl group singly bonded to a halogen atom.


Acyl halides are liquids which react with water and have a pungent odor.


  • Acyl fluorides: Less encountered, they're more expensive and corrosive.
  • Acyl chlorides: The most common type of acyl halide. Examples include acetyl chloride.
  • Acyl bromides: Not as often as acyl chlorides, but still used for certain reactions.
  • Acyl iodide: Not as common as acyl chlorides, but more often used than acyl bromides and acyl fluorides.


Acyl halides can be prepared by reacting carboxylic acids with halogenating reagents such as cyanuric fluoride for acyl fluorides, phosphorus trichloride, phosphorus pentachloride or thionyl chloride for acyl chlorides, phosphorus tribromide for acyl bromides and phosphorus triiodide for acyl iodides.

Safety and handling

Acyl halides react with water and are corrosive. Wear gloves, mask and goggles when handling them.


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