How do you alkylate benzene?

1 Answer
Dec 1, 2015

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.