Account for the following:
Aniline does not undergo Friedel-Crafts reaction.
Friedel- Crafts reaction: When any benzene or its derivative is treated with alkyl halide (R-X, X=Cl) or acetyl chloride (CH3-COCl) in the presence of annhydrous aluminium chloride (AlCl3) to form alkyl or acetyl substituted benzene or its derivative, this reaction is called Friedel-Crafts reaction.
⇒ Friedel-Crafts alkylation: When any benzene or its derivative is treated with alkyl halides (R-X, X=Cl,Br) in the presence of annhydrous aluminium chloride (AlCl3) to form alkyl substituted benzene or its derivatives, this reaction is called Friedel-Crafts alkylation. For example:
⇒ Friedel-Crafts acylation: When any benzene or its derivative is treated with acetyl chloride (R-COCl) in the presence of annhydrous aluminium chloride (AlCl3) to form acetyl substituted benzene or its derivatives, this reaction is called Friedel-Crafts acylation. For example:
Aniline does not undergo Friedel-Crafts reaction.
Explanation: Aniline is a Lewis base (electron-pair acceptor) while AlCl3 is Lewis acid (electron-pair donor). They combine with each to form a salt.
Due to presence of positive charge on nitrogen (N) atom in the salt, the group N+H2AlCl3- acts as a strong electron withdrawing group (strong deactivating group). As a result, it reduces the electron density in the benzene ring and hence aniline does not undergo Friedel-Crafts (alkylation or acetylation) reaction