CBSE · Class 12 · Chemistry · AminesExplain why aniline does not undergo Friedel-Crafts reaction.

Aniline, being an aromatic primary amine, acts as a Lewis base due to the presence of a lone pair of electrons on the nitrogen atom. In Friedel-Crafts alkylation or acylation reactions, anhydrous aluminium chloride ($AlCl_3$), which is a strong Lewis acid, is used as a catalyst. \nWhen aniline is treated with $AlCl_3$, the lone pair of electrons on the nitrogen atom of aniline coordinates with the Lewis acid $AlCl_3$ to form a stable salt-like coordination complex: $C_6H_5NH_2 + AlCl_3 \rightarrow C_6H_5NH_2^+ - AlCl_3^-$ \nDue to this coordination, a positive charge appears on the nitrogen atom of the complex. This positively charged nitrogen atom exerts a strong electron-withdrawing inductive effect (-I effect). Consequently, the benzene ring gets strongly deactivated, which completely stops further electrophilic substitution reactions like Friedel-Crafts alkylation and acylation. Furthermore, the catalyst gets permanently tied up, rendering it unavailable for generating the electrophile.