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What Friedel and Crafts discovered in 1877 was that halogenoalkanes can react with benzene in the presence of AlCl3 to give alkylbenzenes. Alcohols and alkenes can also be used.

Perhaps the single most important Friedel Crafts reaction is the production of ethylbenzene from benzene, the first stage in the manufacture of poly(phenylethene) or poly(styrene).Over
8 million tonnes is manufactured annually.

Benzene vapour and ethene pass over heated aluminium chloride.

There is a serious problem, common to Friedel-Crafts alkylations. Ethylbenzene is more reactive than benzene. So it is difficult to stop more ethyl groups attaching to the ring leading to a complicated mixture of substances.

The mixture of products which can result from Friedel Crafts alkylation

On a very different scale another useful product of Friedel -Crafts alkylation is

used as the coating on fax-paper