Question

Friedel–Crafts alkylations can be carried out with carbocations formed from reactions other than the reaction of an alkyl halide with AlCl₃. Propose amechanism for the following reaction:

Short answer

The mechanism is as follows:

Step-by-step solution

Electrophile generation

When but-2-ene is reacted with hydrogen fluoride, it forms into positive and negative ions wherein the positive charged one is the electrophile. This electrophile is further used in the reaction with benzene.

Generation of electrophile

Reaction of electrophile with benzene

When benzene reacts with the electrophile formed in the above step, electron delocalization occurs and the electrophile gets added to the benzene. Thus it forms the final product. The mechanism is shown below:

Reaction of electrophile with benzene