Organic reaction

Friedel-Crafts Acylation

Friedel-Crafts acylation installs an acyl group onto an aromatic ring through electrophilic aromatic substitution, commonly using an acyl chloride and Lewis acid.

Friedel–Crafts acylation scheme: benzene with acetyl chloride and AlCl3 gives acetophenone, with the new ring–carbonyl C–C bond highlighted
Friedel–Crafts acylation: benzene and acetyl chloride give acetophenone; the new C–C bond is highlighted.

Reaction Scheme

arene + acyl chloride -> aryl ketoneAlCl3 or another Lewis acid generates the acylium electrophile.

Primary reaction SMILES: c1ccccc1.CC(=O)Cl>>CC(=O)c1ccccc1

Two Common Examples

Benzene + acetyl chloride

Forms acetophenone under AlCl3 conditions.

Anisole acylation

Electron-rich anisole gives mostly para-acylated product.

MolDraw Use

Draw substituent effects, acyl chloride partners, and product regiochemistry in MolDraw.

How It Works

Friedel–Crafts acylation is an electrophilic aromatic substitution. A Lewis acid, typically AlCl3, coordinates to an acyl chloride (or anhydride) and generates a resonance-stabilised acylium ion, R–C≡O+. The aromatic ring attacks the acylium ion to form a σ-complex (arenium ion), and loss of a proton restores aromaticity, giving an aryl ketone.

Conditions and Scope

  • More than one equivalent of AlCl3 is usually needed, because the ketone product complexes the Lewis acid; aqueous workup releases it.
  • The acyl group deactivates the ring, so the product does not acylate again, unlike Friedel–Crafts alkylation, which tends to over-alkylate.
  • The acylium ion does not rearrange, another advantage over alkylation.
  • Strongly deactivated rings such as nitrobenzene do not react well.

FAQ

How do I get a straight-chain alkylbenzene? Acylate first, then reduce the ketone (for example by Clemmensen or Wolff–Kishner reduction), avoiding the carbocation rearrangements of direct alkylation. Where does the new group go? Existing substituents direct it: activating groups such as OMe direct ortho/para, with para usually favoured for steric reasons.

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