The Friedel-Crafts acylation is an example of an electrophilic aromatic substitution reaction. The overall transformation involves the displacement of an aryl hydrogen atom with an acyl moiety derived from the corresponding acyl chloride. The product of the reaction is an alkyl aryl ketone.

The acyl chloride is first converted to the acylium ion intermediate by reacting it with a Lewis acid catalyst such as aluminum trichloride. The Lewis acid coordinates to the chloride and the activated chloride ion is then eliminated to produce the acylium ion. The acylium ion is now sufficiently electrophilic to undergo nucleophilic attack by the π-system of the aromatic ring. Deprotonation at the aryl carbon that now bears the acyl group restores aromaticity and a neutral charge to the aromatic ring.

The acyl aromatic compound produced by the Friedel-Crafts acylation can undergo a number of different transformations and functional group manipulations. The carbonyl moiety can be reduced to a methylene by means of either the Clemmensen Reduction or the Wolff-Kishner Reduction. This sequence of reactions is formally equivalent to the Friedel-Crafts alkylation but does not suffer from the same problems such as carbocation rearrangements and polyalkylation.

The Friedel-Crafts alkylation reaction is related to the acylation in that both reactions are electrophilic aromatic substitution reactions and both employ aluminum trichloride to activate an organohalide. The starting material for the alkylation is an alkylhalide and the reaction introduces an alkyl group to the aromatic ring. See the synthesis of 1,1-diphenylacetone for an example of the laboratory procedure for this reaction.

Tags: acylation, chemistry, ketone, name reaction, Name Reactions, organic chemistry, synthesis

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