Acylation of amines

Both aliphatic and aromatic PRIMARY and SECONDARY amines undergo acylation reactions, because both classes retain at least one 'replaceable', positively-polarised hydrogen atom directly bonded to nitrogen (a tertiary amine, having no N-H hydrogen at all, cannot undergo this reaction). In acylation, one of these N-H hydrogens is replaced by an ACYL group -- such as the acetyl group -- through reaction of the amine with either acetyl chloride or acetic anhydride; the resulting product, an acetyl derivative of the original amine, is more generally called an AMIDE. It is worth noting explicitly that the amide product formed this way is LESS basic than the amine it came from (since the nitrogen lone pair in an amide is significantly delocalised into the adjacent carbonyl group, making it much less available to accept a proton than a simple amine's lone pair was). Mechanistically, acylation is classed as a nucleophilic substitution reaction (the amine's nitrogen lone pair attacks the acyl chloride's electrophilic carbonyl carbon, displacing chloride). The reaction is deliberately carried out in the presence of the strong base pyridine, whose role is to neutralise the HCl (or acetic acid) produced as a byproduct during the reaction, driving it to completion. Worked with two specific examples: (i) ethanamine (a primary amine) reacts with ethanoyl (acetyl) chloride, pyridine present, to give N-ethylethanamide plus HCl. (ii) N-methylaniline (a secondary amine) reacts likewise with …