, CH₃COCl, also known as ethanoyl chloride or acyl chloride, is an acid chloride derived from acetic acid. It belongs to the class of organic compounds called acyl halides. It is a colorless liquid. Acetyl chloride does not exist in nature, because contact with water would hydrolyze it into acetic acid and hydrogen chloride. Acetyl chloride is a kind of bulk pharmaceutical chemical. There are some basic informations about this crude drug: (1)IUPAC name: Acetyl chloride; (2)Other names: Ethanoyl chloride; (3)CAS number: ; (4)ChemSpider: 6127; (5)UNII: QD15RNO45K; (6)RTECS number: AO6390000; (7)Molecular formula: CH₃COCl ; (8)Molar mass: 78.49 g/mol; (9)Appearance: colorless liquid; (10)Solubility: in water Reacts.

It is a reagent for acetylation in the synthesis or derivatization of organic compounds. Examples of acetylation reactions include acylation processes such as esterification (see below) and the Friedel-Crafts reaction.

CH₃COCl + HO-CH₂-CH₃ → CH₃-COO-CH₂-CH₃ + H-Cl

Frequently such acylations are carried out in the presence of a base such as pyridine, triethylamine, or P, which as catalysts help to promote the reaction and as bases neutralize the resulting HCl. Such reactions will often proceed via ketene.