A Friedel-Crafts reaction is carried out in the presence of AlCl3. But AlCl3 is acidic in
nature, while aniline is a strong base. Thus, aniline reacts with AlCl3 to form a salt as
shown in the following equation:
Due to the positive charge on the N-atom, electrophilic substitution in the benzene ring
is deactivated. Hence, aniline does not undergo the Friedel-Crafts reaction.