Aromatic amines, like aniline, exhibit very high reactivity in electrophilic substitution, favoring ortho- and para-positions. To control the activating effect of the -NH₂ group for monosubstitution, acetylation with acetic anhydride can be performed, followed by desired substitution and hydrolysis of the substituted amide.
Describe the challenge encountered in electrophilic substitution reactions of aromatic amines, specifically with aniline, and propose a method to control the activating effect of the -NH₂ group for monosubstitution.
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The challenge in electrophilic substitution reactions of aromatic amines, like aniline, lies in the potential for poly-substitution due to the activating nature of the amino group. To control mono-substitution, N-acylation is often employed. By acylating the amino group with an acylating agent like acetic anhydride, the activating effect of -NH₂ is reduced. The acylated aniline is less reactive towards electrophiles, limiting the substitution to only one position. After mono-substitution, the acyl group can be removed to regenerate the amino group. This strategy allows for the controlled introduction of substituents in the presence of the amino group.