Aliphatic and aromatic primary and secondary amines undergo acylation reaction as these amines contain replaceable hydrogen atoms (positively polarised H ) on the nitrogen atom. Triethylamine, i.e., $\left(\mathrm{CH}_3 \mathrm{CH}_2\right)_3 \mathrm{~N}$ is a tertiary amine, without any replaceable H -atom. Thus, it will not react with acetyl chloride.