Electrophilic substitution of aromatic amines

Halogenation of Aromatic Arenes

 

This reaction is used as a test for aniline.

However, if monosubstituted derivative is desired, aniline is first acetylated with acetic anhydride and then halogenation is carried out. After halogenation, the acetyl group is removed by hydrolysis and only monosubstituted halogen derivative is obtained.

It may be noted that – NH₂ group directs the attacking group at o- and p-positions and therefore, both o- and p-derivatives are obtained.

Acetylation deactivates the ring and controls the reaction to monosubstitution stage only because acetyl group is electron withdrawing group and therefore, the electron pair of N-atom is withdrawn towards the carbonyl group.