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In certain cases, generally when the benzene ring is activated, Friedel–Crafts acylation can also be carried out with catalytic amounts of a milder Lewis acid (e.g. Zn(II) salts) or a Brønsted acid catalyst using the anhydride or even the carboxylic acid itself as the acylation agent.
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.
Similarly, in Friedel-Crafts acylation, a Lewis acid assists in the generation of an acylium ion from an acid chloride (or occasionally acid anhydride). Although the acylium ion is often assumed to be the active intermediate, [ 37 ] there is evidence that the protonated acylium dication is the active electrophile that undergoes subsequent ...
For example, Friedel–Crafts acylation uses acetyl chloride (CH 3 COCl) as the agent and aluminum chloride (AlCl 3) as a catalyst to add an acetyl group to benzene: [2] Friedel-Crafts acylation of benzene by ethanoyl chloride. This reaction is an example of electrophilic aromatic substitution.
Similarly, in Friedel-Crafts acylation of arenes (ArH): RC(O)OC(O)R + ArH → RC(O)Ar + RCO 2 H. As with acid halides, anhydrides can also react with carbon nucleophiles to furnish ketones and/or tertiary alcohols, and can participate in both the Friedel–Crafts acylation and the Weinreb ketone synthesis.
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]
Acylium ions are common reactive intermediates, for example in the Friedel–Crafts acylation and many other organic reactions such as the Hayashi rearrangement. Salts containing acylium ions can be generated by removal of the halide from acyl halides: RC(O)Cl + SbCl 5 → [RCO] + [SbCl 6] −
Friedel–Crafts acylation; Friedel–Crafts alkylation; Friedländer synthesis; Fries rearrangement; ... Gibbs phthalic anhydride process; Gilman reagent; Glaser ...