Can you explain acylation?

Acylation is a broad term for any reaction where an acyl group is added to a compound.

An acyl group is comprised of a ketone group (C=O) with an alkyl group attached to the carbon. RCO(-) is the general notation for an acylium ion.

The most common acylation reactions will use a compound known as acyl chloride to supply the acyl group. Acyl chloride is composed of an acyl group bound to a chloride ion (ROCl). Acyl chlorides are especially useful as chloride is an excellent leaving group. This means it can be easily removed by an appropriate reagent, such as aluminium trichloride, leaving an acylium ion. [Removal of chloride from acyl chloride to generate an acylium ion: RCOCl + AlCl3 --> RCO(+) + AlCl4(-)]

This acylium ion is positively charged, an electrophile, and is an attractive target for an electrophilic centre of the compound. Electrons are donated from the compound to the acylium ion to form a covalent bond, attaching the acyl group to the compound.