Question

Why are amides the least reactive carboxylic acid derivative?

Answer 1

Amides:

Amides are functional groups in which a carbonyl carbon atom is linked to a nitrogen atom, as well as a hydrogen or carbon atom, by a single bond.

Amides are the least reactive among all carboxylic acid derivatives.

It is because the electrophilicity of the $\mathrm{C}=\mathrm{O}$ group is heavily reduced by the electron-donor nitrogen.