Formyl Fluoride1

[1493-02-3]  · CHFO  · Formyl Fluoride  · (MW 48.02)

(formylating agent for organic compounds1)

Physical Data: bp -29 °C; mp -142 °C.

Preparative Methods: HCOF, one of the stable halides of formic acid, is generally prepared by combining Formic Acid with a fluorinating agent.1 A variety of reagents such as Benzoyl Chloride/Potassium Fluoride,2 benzoyl fluoride,3 benzoyl chloride/KHF2,4 cyanuric fluoride,5 and tetramethyl-a-fluoroenamine6 has been employed for this purpose. HCOF was also successfully prepared by reaction of Acetic Formic Anhydride with Hydrogen Fluoride at atmospheric pressure with continuous removal of formyl fluoride.7 Combining benzoyl fluoride with sodium formate is another worthy procedure for its preparation.5 Ozonolysis of 1,2-difluoroethylene and vinyl fluoride offers a potential new route to HCOF.8 The best result among all the methods was achieved by fluorinating formic acid with tetramethyl-a-fluoroenamine.6 A 100% yield was reported.

Handling, Storage, and Precautions: decomposes rapidly at room temperature into CO and HF.1b The reaction is autocatalytic since the HF formed initially catalyzes the decarbonylation. Therefore, acid-free HCOF should be stored at low temperature (of the order of -70 °C) under pressure over anhydrous sodium fluoride, which is able to absorb the hydrogen fluoride formed in decomposition. Use in a fume hood.

Formylation.

Formyl fluoride is used for Friedel-Crafts type formylation of arenes (eq 1). The best catalyst found for the reaction is Boron Trifluoride.3

Formyl fluoride and BF3 form a complex at low temperature, which has been isolated and characterized.1b Boron Trichloride and Boron Tribromide are also effective for the reaction; however, Aluminum Chloride and Aluminum Bromide were found to catalyze the decomposition of HCOF, giving lower yields of formylation products. If the aromatic substances are reactive and have a low freezing point, the reaction can be carried out by dissolving the HCOF neat in an excess of the cold arenes followed by saturation of the mixture with BF3. When aromatic substrates are not sufficiently active to be formylated at low temperatures or have high freezing points, a solvent should be used. Solvents such as carbon disulfide or nitroalkanes are preferable for the reaction. The best results for such cases were obtained by passing HCOF and BF3 gases simultaneously into the arenes at room temperature or higher. It is necessary to mention that HF and BF3 should be removed from the reaction mixture as soon as the reaction is complete, since undesirable condensation reaction can occur with the aldehyde formed, which would decrease the yields.

Alkenes react in the presence of BF3 with HCOF to give a b-fluoroaldehyde (eq 2).1b However, further reaction of the secondary C-F bond with BF3 makes the isolation of pure products difficult.

Formyl fluoride is also found to react with alcohols and phenols in the presence of a base (such as Triethylamine) to form the corresponding formates (eq 3).4 Primary and secondary aliphatic alcohols are formylated in 73-92% yield, while benzyl alcohols and phenol give 69% and 75% yields, respectively. Formyl fluoride reacts with carboxylic acid salts to yield the corresponding mixed carboxylic formic anhydrides (eq 4). Even the elusive formic anhydride can be prepared by the reaction at -78 °C. Oximes have also been formylated by HCOF.9 This reaction has been employed to prepare 3-phenylethynyl-1,2,4-oxadiazole (eq 5).

Reaction between HCOF and thiols yields thioformates in good yields (eq 6).4

Formylation of amines can also be achieved.1a A large variety of primary and secondary amines react with HCOF to give N-alkylformamides in good to excellent yields (eq 7). However, reaction between tertiary amines and HCOF leads to elimination of carbon monoxide and formation of the amine hydrofluorides.

Related Reagents.

Acetic Formic Anhydride; Methyl Formate.


1. (a) Olah, G. A.; Ohannesian, L.; Arvanaghi, M. CRV 1987, 87, 671. (b) Olah, G. A.; Kuhn, S. J. In Friedel-Crafts and Related Reactions; Olah, G. A., Ed.; Wiley: New York, 1964; Vol. III, Part II, pp 1179-1187.
2. Nesmejanov, A. N.; Kahn, E. J. CB 1934, 67, 370.
3. Mashentsev, A. I. JGU 1946, 16, 203.
4. (a) Olah, G. A.; Kuhn, S. J. JACS 1960, 82, 2380. (b) Olah, G. A.; Kuhn, S. J.; Beke, S. CB 1956, 89, 862. (c) Olah, G. A.; Kuhn, S. J. CB 1956, 89, 866.
5. Olah, G. A.; Nojima, M.; Kerekes, I. S 1973, 487.
6. Devos, A.; Remion, J.; Frisque-Hesbain, A-M.; Colens, A.; Ghosez, L. CC 1979, 1180.
7. Olah, G. A.; Kuhn, S. J. JOC 1961, 26, 237.
8. Mazur, U.; Lattimer, R. P.; Lopata, A.; Kuczkowski, R. L. JOC 1979, 44, 3181.
9. Claisse, J. A.; Foxton, M. W.; Gregory, G. I.; Sheppard, A. H.; Tiley, E. P.; Warburton, W. K.; Wilson, M. J. JCS(P1) 1973, 2241.

George A. Olah, G. K. Surya Prakash, Qi Wang & Xing-ya Li

University of Southern California, Los Angeles, CA, USA



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