An acyl halide also known as an acid halide is an organic compound derived from carboxylic acids by replacing a hydroxyl group with a halide group. An acyl halide is colorless fuming liquid which reacts with water to produce a hydrogen halide and an acid.
An acyl halide reacts with ammonia, water and alcohols to produce carboxylic acids, amides and esters respectively. Acyl halides are extremely reactive substances used in organic syntheses to produce the acyl group.
The most common halides of inorganic acids include chlorosulfuric acid and sulfuryl chloride resulting to the replacement of hydroxyl groups of sulfuric acid: thionyl chloride, phosphorus trichloride and phosphorus oxychloride.