Question

Why is friedel crafts acylation better than alkylation?

Answer 1

Alkylation reactions are prone to carbocation rearrangements.

Deactivated benzenes are not reactive to Friedel-Crafts conditions, the benzene needs to be as or more reactive than a mono-halobenzene.

Over alkylation can be a problem since the product is more reactive than the starting material. This can usually be controlled with an excess of the benzene.The Lewis acid catalyst Aluminum Chloride often complexes to aryl amines making them very unreactive.

Whereas in Friedel Crafts acylation the acyl substituent is a deactivating group therefore this reaction does not have polyacylation occurring and there is no possibility of rearrangements making Friedel-Crafts acylation a more preferred choice over alkylation!