Acetylation

Salicylic acid is acetylated with acetic anhydride to form aspirin and acetic acid as a byproduct

In chemistry, acetylation is an organic esterification reaction with acetic acid. It introduces an acetyl group into a chemical compound. Such compounds are termed acetate esters or simply acetates. Deacetylation is the opposite reaction, the removal of an acetyl group from a chemical compound.