Question

friedel crafts acylation is more favourable than alkylation

Answer 1

During Friedel Crafts Alkylation, an alkyl group is substituted on the Benzene which activates the benzene due to its +I Effect. Due to this activation of Benzene, it is prone to more attacks and hence you get a polysubstituted Benzene and not the Alkyl Benzene which we wanted.

Friedel Crafts Acylation on the other hand substitutes an acyl(-R-C=O) group on the benzene which deactivates Benzene due to electron withdrawing effect of the Carbon double bond Oxygen substituent. Hence the benzene ring is just substituted once and isn’t prone to polysubstitution.

A better method for preparation of Alkyl Benzene would be Friedel Crafts Acylation followed by Reduction of the Carbonyl group by Zn-Hg/HCl (CLEMMENSON’S REDUCTION)

Answer 2

During Friedel Crafts Alkylation, an alkyl group is substituted on the Benzene which activates the benzene due to its +I Effect. Due to this activation of Benzene, it is prone to more attacks and hence you get a polysubstituted Benzene and not the Alkyl Benzene which we wanted.

Friedel Crafts Acylation on the other hand substitutes an acyl(-R-C=O) group on the benzene which deactivates Benzene due to electron withdrawing effect of the Carbon double bond Oxygen substituent. Hence the benzene ring is just substituted once and isn’t prone to polysubstitution. A better method for preparation of Alkyl Benzene would be Friedel Crafts Acylation followed by Reduction of the Carbonyl group by Zn-Hg/HCl