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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]
Friedel-Crafts acylation of benzene by ethanoyl chloride. This reaction is an example of electrophilic aromatic substitution. Acyl halides and acid anhydrides of carboxylic acids are also common acylating agents. In some cases, active esters exhibit comparable reactivity.
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.
Oxalyl chloride reacts with aromatic compounds in the presence of aluminium chloride to give the corresponding acyl chloride in a process known as a Friedel-Crafts acylation. [15] [16] The resulting acyl chloride can be hydrolysed to form the corresponding carboxylic acid.
water, to form a carboxylic acid. This hydrolysis is the most heavily exploited reaction for acyl halides as it occurs in the industrial synthesis of acetic acid. an alcohol to form an ester; an amine to form an amide; an aromatic compound, using a Lewis acid catalyst such as AlCl 3, to form an aromatic ketone. [7] See Friedel-Crafts acylation.
Freund reaction; Friedel–Crafts acylation; Friedel–Crafts alkylation; Friedländer synthesis; Fries rearrangement; Fritsch–Buttenberg–Wiechell rearrangement; Fujimoto–Belleau reaction; Fujiwara–Moritani reaction; Fukuyama coupling; Fukuyama indole synthesis; Fukuyama reduction
It can be used to promote reactions of carboxylic acids, including Friedel-Crafts acylation and acylation of other unsaturated compounds. Other electrophilic aromatic substitution reactions can also be promoted with trifluoroacetic anhydride, including nitration, sulfonation and nitrosylation. [2]
Acetylferrocene is prepared by Friedel-Crafts acylation of ferrocene, usually with acetic anhydride (Ac 2 O): . Fe(C 5 H 5) 2 + Ac 2 O → (C 5 H 5)Fe(C 5 H 4 Ac) + HOAc. The experiment is often conducted in the instructional laboratory to illustrate acylation as well as chromatographic separations.