Friedel–Crafts Acylation

Reaction

The Friedel–Crafts acylation is the reaction of an arene with acyl chlorides or anhydrides using a strong Lewis acid catalyst. This reaction proceeds via electrophilic aromatic substitution to form monoacylated products.^1,2

Figure 1. Friedel–Crafts acylation reaction shown as molecular structures

Friedel–Crafts Acylation Mechanism

The Friedel–Crafts Acylation reaction involves formation of a complex between the Lewis acid and the chlorine atom of the acid chloride. An acylium ion is formed by the cleavage of C-Cl bond of the complex. The acylium ion has a positive charge on the carbon and is resonance stabilized. This acylium ion acts as an electrophile and reacts with the arene to yield the monoacylated product (aryl ketone).¹

Figure 2. Friedel-Crafts acylation mechanism with an AlCl₃ catalyst shown as molecular structures

The Friedel–Crafts acylation reaction is named after Charles Friedel and James Mason Crafts who developed the reaction in 1877 to attach substituents to an aromatic ring.³

Precautions

Please consult the Safety Data Sheet for information regarding hazards and safe handling practices.

Applications

The Friedel–Crafts acylation reaction is useful for the synthesis of:

• Diarylacetic acid derivatives⁴
• Poly(oxy-1,3-phenylenecarbonyl-1,4-phenylene) or mPEK⁵
• 1,5-Bis(4-fluorobenzoyl)-2,6-dimethylnaphthalene⁶
• Aromatic ketones⁷
• Dissymmetric aromatic amines⁸
• Cyclic ketones such as 1-indanone and 1-tetralone⁹
• 2-Acetyl-6-methoxynaphthalene, an intermediate for the synthesis of naproxen¹⁰

Research and Trends

• Poly(4-vinylpyridine) supported trifluoromethanesulfonic acid has been employed as efficient and an easy-to-handle, solid, superacid catalyst system in Friedel–Crafts reactions. One pot solvent-free synthesis of various diarylacetic acid derivatives was achieved by Friedel–Crafts hydroxyalkylation reaction of glyoxylic acid with arenes under mild conditions.⁴
  
  Scheme of the above synthesis:

Figure 3. One pot solvent-free synthesis of diarylacetic acid derivatives by Friedel–Crafts hydroxyalkylation reaction of glyoxylic acid

• An imidazolium-based ionic liquid catalyzed the Friedel–Crafts acylation of aromatic compounds with acetyl chloride.¹¹
• Erbium trifluoromethanesulfonate is reported to be a good catalyst for the microwave-assisted Friedel–Crafts acylation of arenes containing electron-donating substituents.¹²
• The intramolecular Friedel–Crafts acylation is used in the direct and short construction of the ACDE ring system of daphenylline, a novel daphniphyllum alkaloid.¹³
• The acid-promoted domino Friedel–Crafts acylation reaction has been developed for building the core 6,5,6-ABC tricyclic skeleton of taiwaniaquinoids. It is also used in the syntheses of diterpenoids (±)-taiwaniaquinol B and (±)-dichroanone.¹⁴
• Novel poly(aryl ether ketone)s and poly(aryl ether ketone sulfone)s containing 1,4-naphthylene units have been synthesized by electrophilic Friedel–Crafts acylation polycondensation reactions.¹⁵
• The Friedel–Crafts acylation of toluene with acetic anhydride over triphenyltin grafted on SBA-15 mesoporous silica has been reported.¹⁶
• Indium triflate in the ionic liquid, 1-isobutyl-3-methylimidazolium dihydrogen phosphate ([i-BMIM]H₂PO₄), forms an efficient green catalyst system for the Friedel–Crafts acylation of aromatic compounds with acid anhydrides.¹⁷
• Friedel–Crafts acylation of 25,27-dialkoxycalix[4]arenes using acyl chlorides and AlCl₃ in 1,2-dichloroethane have been reported.¹⁸

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3. Sartori G, Maggi R. Advances in Friedel-Crafts Acylation Reactions. https://doi.org/10.1201/9781420067934

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7. de Noronha RG, Fernandes AC, Romão CC. 2009. MoO2Cl2 as a novel catalyst for Friedel?Crafts acylation and sulfonylation. Tetrahedron Letters. 50(13):1407-1410. https://doi.org/10.1016/j.tetlet.2009.01.039

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9. Tran PH, Huynh VH, Hansen PE, Chau DN, Le TN. 2015. An Efficient and Green Synthesis of 1-Indanone and 1-Tetralone via Intramolecular Friedel-Crafts Acylation Reaction. Asian Journal of Organic Chemistry. 4(5):482-486. https://doi.org/10.1002/ajoc.201402274

10. Kobayashi S, Komoto I. 2000. Remarkable Effect of Lithium Salts in Friedel?Crafts Acylation of 2-Methoxynaphthalene Catalyzed by Metal Triflates. Tetrahedron. 56(35):6463-6465. https://doi.org/10.1016/s0040-4020(00)00610-4

11. Cai M, Wang X. 2014. Activity of Imidazolium-Based Ionic Liquids as Catalysts for Friedel-Crafts Acylation of Aromatic Compounds. Asian J. Chem.. 26(18):5981-5984. https://doi.org/10.14233/ajchem.2014.16354

12. Tran PH, Hansen PE, Nguyen HT, Le TN. 2015. Erbium trifluoromethanesulfonate catalyzed Friedel?Crafts acylation using aromatic carboxylic acids as acylating agents under monomode-microwave irradiation. Tetrahedron Letters. 56(4):612-618. https://doi.org/10.1016/j.tetlet.2014.12.038

13. Wang W, Li G, Wang S, Shi Z, Cao X. 2015. Direct and Short Construction of the ACDE Ring System of Daphenylline. Chem. Asian J.. 10(2):377-382. https://doi.org/10.1002/asia.201403152

14. Tang S, Xu Y, He J, He Y, Zheng J, Pan X, She X. 2008. Application of a Domino Friedel?Crafts Acylation/Alkylation Reaction to the Formal Syntheses of (±)-Taiwaniaquinol B and (±)-Dichroanone. Org. Lett.. 10(9):1855-1858. https://doi.org/10.1021/ol800513v

15. Wen H, Wang P, Cheng S, Yan T, Cai M. 2015. Synthesis and characterization of novel organosoluble poly(aryl ether ketone)s and poly(aryl ether ketone sulfone)s containing 1,4-naphthylene units. High Performance Polymers. 27(6):705-713. https://doi.org/10.1177/0954008314557707

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17. Tran PH, Hansen PE, Hoang HM, Chau DN, Le TN. 2015. Indium triflate in 1-isobutyl-3-methylimidazolium dihydrogen phosphate: an efficient and green catalytic system for Friedel?Crafts acylation. Tetrahedron Letters. 56(17):2187-2192. https://doi.org/10.1016/j.tetlet.2015.03.051

18. Skácel J, Budka J, Eigner V, Lhoták P. 2015. Regioselective Friedel?Crafts acylation of calix[4]arenes. Tetrahedron. 71(13):1959-1965. https://doi.org/10.1016/j.tet.2015.02.021