Acetylation is the process of introducing an acetyl group into a molecule.

With aliphatic amines: Primary and secondary amines( but not tertiary amines because they do not contain an H-atom on the N-atom) undergo nucleophilic substitution reaction when treated with acid chlorides to form N- substituted amides.

This reaction involves the replacement of Hydrogen atom of NH₂ or NH group of acetyl group which in turn leads to the production of amides.

With aromatic amine: Acylation of aromatic amines is usually carried out in the presence of a catalyst. For example, acetylation with acetyl chloride is carried out in the presence of a base stronger than the amide, like pyridine, which removes HCl formed during the reaction and shifts the equilibrium in the forward direction.

Note: Pyridine is a basic heterocyclic organic compound with the chemical formula C₅H₅N.