Substitution tends to occur at ortho- and para-positions If we
have to prepare monosubstituted  aniline derivative, how can
the activating effect of –NH2 group be controlled This can be
done by protecting the -NH2 group by acetylation with acetic
anhydride, then carrying out the desired substitution followed
by hydrolysis of the substituted amide to the substituted amine The lone pair of electrons on nitrogen of acetanilide  interacts
with oxygen atom due to resonance as shown below:
Rationalised 2023-24
273
Amines
Hence, the lone pair of electrons on nitrogen is less available for
donation to benzene ring by  resonance