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The Friedel–Crafts reactions are a set of reactions that attach substituents to an aromatic ring via electrophilic aromatic substitution. There are two main types of reaction: alkylation and acylation.
Friedel–Crafts alkylation involves the alkylation of an aromatic ring with an alkyl halide using a strong Lewis acid, such as aluminium chloride, iron(III) chloride, or other MXn reagent, as catalyst. Anhydrous conditions are required, as the reaction is water-sensitive. This reaction suffers from the disadvantage that the product is more nucleophilic than the reactant because alkyl groups are activators for the Friedel–Crafts reaction. Consequently, overalkylation can occur
Friedel–Crafts acylation involves the acylation of aromatic rings. Typical acylating agents are acyl chlorides. Typical Lewis acid catalysts are acids and aluminium trichloride. However, because the product ketone forms a rather stable complex with Lewis acids such as AlCl3, a stoichiometric amount or more of the "catalyst" must generally be employed, unlike the case of the Friedel–Crafts alkylation, in which the catalyst is constantly regenerated. Friedel–Crafts acylation is also possible with acid anhydrides.