Question

How do you alkylate benzene?

Answer 1

You can do it via a Friedel-Crafts Alkylation, where you have an alkyl halide and a strong Lewis acid catalyst. Commonly we use `"FeX"_3` where `"X"` is often `"Cl"` or `"Br"`.

The mechanism is as follows, and is very similar to Friedel-Crafts Acylation (and even draws parallels with the benzene halogenation reaction where you have `"X"_2` in `"FeX"_3`...):

It is worth noting though that by adding an alkyl group onto benzene, you've added an activating group; that is, the alkyl group donates electrons to the ring, making it more nucleophilic, and thus more prone to reacting in this Friedel-Crafts Alkylation.

As a result, you have a pretty good chance for overalkylation if you don't add a controlled amount of catalyst and reactant.