Question

Why doesnt aniline undergo friedel crafts reaction?

Answer 1

Despite the activation of the NH2NHX2group, Friedel-Crafts alkylations and acylations fail because the NH2NHX2group acts as Lewis base and interacts with the Lewis acid catalyst. ... A way to overcome this problem is to convert the NH2NHX2 group into an amido group prior to Friedel-Crafts reaction. ...The amide group can be hydrolysed back to aniline group after alkylation.

Answer 2

the friedel-crafts reaction is carried out in the presence of lewis acid such as agcl3. aniline being basic  in nature react with agcl3 and form salt . due to the positive charge on nitrogen electrophillic subsitution reaction on benzene ring deactivated. hence aniline does not under go friedel craft reaction.