Acyl Chlorides are formed when a chlorine atom replaces the –OH bond in a COOH carboxyl functional group in a carboxylic acid.
* swapping the -OH group in the -COOH group of a carboxylic acid for a chlorine atom to make acyl chlorides (acid chlorides)
Example: http://www.chemguide.co.uk/organicprops/acylchlorides/preparation.html#top
Using PCl5
* Phosphorus(V) chloride is a solid which reacts with carboxylic acids in the cold to give steamy acidic fumes of hydrogen chloride. It leaves a liquid mixture of the acyl chloride and a phosphorus compound, phosphorus trichloride oxide (phosphorus oxychloride) - POCl3.
The acyl chloride can be separated by fractional distillation.
Example:
