Friedel-Crafts Acylation and Alkylation

In 1877, C.Friedel and J.M. Crafts reacted amyl chloride with aluminum pieces in benzene, forming amyl benzene. The reaction of alkyl halides with benzene was found to be general, and aluminum chloride (AlCl₃) was identified as the catalyst. Since this discovery, the substitution of both aromatic and aliphatic compounds with a variety of alkylating agents in the presence of a Lewis acid is known as Friedel-Crafts alkylation.

Before the 1940s, the alkylation of aromatic compounds was the foremost application, but later the alkylation of aliphatic systems also gained in importance. In addition to aluminum chloride, other Lewis acids can also be used: BeCl₂, CdCl₂, BF₃, BBr₃, GaCl₃, AlBr₃, FeCl₃, TiCl₄, SnCl₄, SbCl₅, lanthanide trihalides, and alkyl aluminum halides.

Closely related to the Friedel-Crafts alkylation is the introduction of a keto group into an aromatic or aliphatic compound using an acyl halide or anhydride in the presence of a Lewis acid catalyst, known as the Friedel-Crafts acylation. Compounds that undergo the Friedel-Crafts alkylation are, in most cases, also easily acylated. One drawback of the Friedel-Crafts acylation reaction is that the Lewis acid catalyst often cannot be recovered once the reaction is complete. However, heterogeneous catalysts such as zeolites make this reaction more feasible on an industrial scale.