As noted in Assignment 1.4.1., alkylation of benzene with 1-chlorobutane in the presence of AlCl3 gives both butylbenzene and (1-methylpropyl) benzene as products. Propose a route to butylbenzene from benzene that does not also give the (1-methylpropyl) benzene side-product.

Use the Bromotriflouride catalyst, BF₃

Explanation:

The BF₃ is most likely to yield less desired side products. The effect lies in the reaction mechanism.

BF₃ is a Lewis acid. Its role is to promote the ionization of the HF. This is achieved through the electrophilic mechanism. The reaction mechanism is as follows:

2 - methylpropene + H-F-BF₃ → H-F + H₃C + benzene

butylbenzene + F-BF₃ → tert-butylbenzene + H-F + BF₃ (regenerated catalyst)