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The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. [1] Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reactions. Both proceed by electrophilic aromatic substitution. [2] [3] [4] [5]
The reaction is a type of Friedel-Crafts acylation with hydrogen chloride and a Lewis acid catalyst. The synthesis of 2,4,6-Trihydroxyacetophenone (THAP) from phloroglucinol is representative: [1] If two-equivalents are added, 2,4-Diacetylphloroglucinol is the product. Hoesch reaction example, 1-(2,4,6-trihydroxyphenyl)ethanone from phloroglucinol
Clemmensen reduction conditions are particularly effective at reducing aryl [4]-alkyl ketones, [5] [6] such as those formed in a Friedel-Crafts acylation. The two-step sequence of Friedel-Crafts acylation followed by Clemmensen reduction constitutes a classical strategy for the primary alkylation of arenes.
In chemistry, acylation is a broad class of chemical reactions in which an acyl group (R−C=O) is added to a substrate. The compound providing the acyl group is called the acylating agent. The substrate to be acylated and the product include the following: alcohols, esters; amines, amides; arenes or alkenes, [1] ketones
This reaction is typically catalyzed by the corresponding iron or aluminum trihalide. The Friedel–Crafts reaction can be performed either as an acylation or as an alkylation. Often, aluminium trichloride is used, but almost any strong Lewis acid can be applied. For the acylation reaction a stoichiometric amount of aluminum trichloride is ...
While nucleophilic acyl substitution reactions can be base-catalyzed, the reaction will not occur if the leaving group is a stronger base than the nucleophile (i.e. the leaving group must have a higher pK a than the nucleophile). Unlike acid-catalyzed processes, both the nucleophile and the leaving group exist as anions under basic conditions.
Important variants of the Friedel–Crafts reaction include chloromethylation (with formaldehyde and HCl), formylation (with HCl and CO or CN −), and acylation with a nitrile as the acyl source. The nitrile-based acylation is particularly useful because it allows direct ortho-acylation of aniline without protecting the amine group. [39]
Acylium ions are intermediates in several reactions, such as the Friedel-Crafts acylation of arenes by acetyl chloride in the presence of aluminium trichloride: C 6 H 5 R + CH 3 CO + + AlCl − 4 → CH 3 COC 6 H 4 R + HCl + AlCl 3. Such depictions may be simplistic because of ion-pairing between the acetyl cation (an acylium cation) and the ...