Acyl chloride preparation

The reaction of phosphorus(V) chloride with a carboxylic acid is exactly the same as that with an alcohol - the OH group is replaced by a chlorine atom:

CH₃COOH + PCl₅ ⇒ CH₃COCl + POCl₃ + HCl

The product in this case, CH₃OCl, is an acyl chloride (sometimes called acid chloride), It is an acid derivative (something made from a carboxylic acid) and is a very useful, reactive organic molecule. We shall meet the acyl chlorides and their reactions in the next practical.