Question

Explain the disadvantage of Friedal Craft alkylation over acylation

Answer 1

The disadvantage of the Friedal Craft alkylation is over alkylation because the incorporation of one alkyl group to the benzene ring increase the reactivity of the ring towards aromatic electrophilic substitution reaction like Friedal Craft alkylation. So if we desire to get mono alkylated product in Friedal Craft alkylation reaction it is almost impossible and instead of that we will get di and tri substituted product.

But in case of Friedal Craft acylation reaction, the over acylation does not take place since acyl group has an electron withdrawing effect which inhibit the further acylation. Now of reduce the mono acylated product by using Zn/conc. HCl we will get our desired mono alkylated product.