Acetyl Fluoride

(MeCOF)

[557-99-3]  · C2H3FO  · Acetyl Fluoride  · (MW 62.04) (EtCOF)

[430-71-7]  · C3H5FO  · Propionyl Fluoride  · (MW 76.07) (PhCOF)

[455-32-3]  · C7H5FO  · Benzoyl Fluoride  · (MW 124.11)

(precursors to acylium salts; acylating agents)

Physical Data: MeCOF: bp 20-21 °C; d 1.0024 g cm-3; EtCOF: bp 42-44 °C; d 0.972 g cm-3; PhCOF: bp 159-161 °C; d 1.140 g cm-3.

Preparative Methods: acetyl fluoride (but not other acyl fluorides) is most conveniently prepared by addition of Acetyl Chloride to a solution of Potassium Fluoride in AcOH; reaction is immediate. Warming the solution and condensing the gas gives nearly quantitiative yields.1 Procedures applicable to the preparation of a variety of acyl fluorides include reaction of the acid chloride or anhydride with nucleophilic fluorides2 and fluorination of the carboxylic acid.3

Handling, Storage, and Precautions: samples of acetyl fluoride sealed in glass ampoules slowly form a pyrylium salt.4 Acetyl fluoride is a corrosive lachrymator. Use in a fume hood.

Preparation of Acylium Salts.

Addition of Lewis acidic metal fluorides to a variety of acyl fluorides produces acylium salts (1), isolable as stable white solids (eq 1).5 Reaction of acyl fluorides with SO3 produces acyl fluorosulfates (2) (eq 2).6 Both (1) and (2) are powerful acylating agents.5,6

Acylation at Carbon.

Acyl fluorides usually have no advantages over acid chlorides for Friedel-Crafts reactions;7 however, with some poylcyclic aromatic substrates the acyl fluoride-BF3 system exhibits exceptional regioselectivity (eq 3).8 Silyl enol ethers are C-acetylated by reaction with acetyl fluoride and BF3 (eq 4).9 Lower yields are obtained with preformed acetyl tetrafluoroborate. Reaction of TlI enolates of b-dicarbonyl compounds with acetyl fluoride in ether gives C-acylated products in high yield.10

Acylation at Oxygen.

Esters of a variety of perfluoro alcohols are obtained by acylation of the metal alkoxides with acyl fluorides.11 Acetyl fluoride, in the presence of acid catalysts, cleaves certain methyl ethers via an acyl oxonium ion intermediate (eq 5).12

Related Reagents.

Acetyl Bromide; Acetyl Chloride; Acetyl Methanesulfonate; Chloroacetyl Fluoride.


1. Clark, J. H.; Emsley, J. JCS(D) 1975, 2129.
2. (a) Liu, H.; Wang, P.; Sun, P. JFC 1989, 43, 429. (b) Olah, G. A.; Welch, J. T.; Vankar, Y. D.; Nojima, M.; Kerekes, I.; Olah, J. A. JOC 1979, 44, 3872.
3. (a) Dmowski, W.; Kaminski, M. JFC 1983, 23, 219. (b) Olah, G. A.; Nojima, M.; Kerekes, I. S 1973, 487.
4. Eliassaf, J. JHC 1970, 7, 681.
5. (a) Olah, G. A.; Kuhn, S. J.; Tolgyesi, W. S.; Baker, E. B. JACS 1962, 84, 2733. (b) Seel, F. Z. Anorg. Allg. Chem. 1943, 250, 331.
6. (a) Effenberger, F.; Sohn, E.; Epple, G. CB 1983, 116, 1195. (b) Krespan, C. G.; England, D. C. JOC 1975, 40, 2937. (c) Gavrishova, T. N.; Shastin, A. V.; Balenkova, E. S. ZOR 1991, 27, 673.
7. Hilgetag, G.; Martini, A. Preparative Organic Chemistry, 4th ed.; Wiley: New York, 1972; p 242.
8. Hyatt, J. A.; Raynolds, P. W. JOC 1984, 49, 384.
9. Kopka, I.; Rathke, M. W. JOC 1981, 46, 3771.
10. Taylor, E. C.; Hawks, III, G. H.; McKillop, A. JACS 1968, 90, 2421.
11. (a) De Marco, R. A.; Couch, D. A.; Shreeve, J. M. JOC 1972, 37, 3332. (b) Walker, N. S.; Desmarteau, D. D. JFC 1975, 5, 135. (c) Falardeau, E. R.; Desmarteau, D. D. JFC 1976, 7, 409.
12. Suzuki, Z.; Morita, K. BCJ 1968, 41, 1724.

Michael Rathke & Robert Elghanian

Michigan State University, East Lansing, MI, USA



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