Why does the reactivity of NH2 get reduced in acetanilide?

Dear Student,

Acetanilide is prepared by acylation of amino group of aniline in presence of acetic anhydride.

Aniline  Acetanilide

In aniline NH₂ is strong activating group due to presence of lone pair of electrons on it. Lone pair of electrons present on amino group are in conjugation with benzene ring in aniline.

But due to presence of acyl group in conjugation with amino group in acetanilide, lone pair of electrons on NH₂ are no longer in resonance with benzene ring.

This is the reason, activity of NH₂ is reduced in acetanilide.