Aniline is acetylated before nitration reaction.

Direct nitration of aniline is not possible on account of oxidation of –NH 2 group. However, nitration can be carried after protecting the –NH 2group by acetylation to give acetanilide which is then nitrated and finally hydrolysed to give o- and p-nitroanilines. The acetyl group being electron-withdrawing attracts the lone pair of electrons of the N-atom towards carbonyl group. As a result, the activating effect –NH 2 group is reduced i.e., the lone pair of electrons on nitrogen is less available for donation to benzene ring by resonance. Therefore, activating effect of –NHCOCH 3 group is less than that of the –NH 2group.

To obtain p-Nitroaniline as the major product. Direct nitration of Aniline yields tarry oxidation products and nitro derivatives compounds. In acidic medium, aniline is protonated, results in the formation of anilinium ion which is meta-directing. Thus, ortho-, para- and meta-Nitroaniline compounds are formed. 51% of the total products is p-Nitroaniline, 47% m-Nitroaniline and 2% o-Nitroaniline. To control the nitration reaction and tarry oxidation products and nitro derivatives products formation, the NH 2 group of aniline is acetylated before carrying out nitration. Here, the major product is p-Nitroaniline. The amine group is protected by acetylation reaction with acetic anhydride.