Cobalt(III) Fluoride1

CoF3

[10026-18-3]  · CoF3  · Cobalt(III) Fluoride  · (MW 115.94)

(powerful Lewis acid, used almost exclusively for fluorination of organic compounds in a solid-vapour phase reaction)

Physical Data: mp unknown; d 3.88 g cm-3.

Solubility: reacts violently with water and hydroxylic solvents; insol almost all solvents at room temperature.

Form Supplied in: buff/brown powder when freshly prepared; rapidly darkens in moist air. Not commercially available.

Preparative Methods: cobalt(III) fluoride is normally prepared by reaction of cobalt(II) fluoride with elemental Fluorine at 200-300 °C in a stirred reactor usually constructed of copper or nickel and is then reacted with organic substrates at 100-500 °C.1

Handling, Storage, and Precautions: normally prepared and used in situ immediately after preparation. Can be stored in sealed vessels under dry nitrogen. Must be handled with caution since it readily releases hydrogen fluoride in contact with air. This reagent should be handled in a fume hood.

General Considerations.

The use of cobalt(III) fluoride as a fluorinating agent was suggested in 1929 by Ruff,2 but it was not until the work on the so-called Manhattan project concerned with the development of atomic weapons in the 1940s by Fowler3 that it came to prominence as a powerful reagent for the preparation of highly fluorinated compounds.

Much of the further development of this reagent was carried out at the University of Birmingham by Tatlow and his group over the period between 1950 and 1980 and subsequently on an industrial scale by the RTZ group at Avonmouth, Bristol.

The degree of fluorination obtained with this reagent depends very largely on the reaction temperature and to a lesser extent on the substrate structure. Thus at temperatures in excess of 400 °C, most of the hydrogen is replaced by fluorine, all double bonds including aromatic unsaturation are saturated, and functional groups are destroyed. At lower temperatures, hydrogen atoms are retained and some functional groups remain in the molecules. These general principles are exemplified in the specific reactions discussed below.

Fluorination of Hydrocarbons.

Synthesis of Perfluorocarbons.

Much of the earlier work, particularly that associated with the atomic energy project, was concerned with the preparation of perfluorocarbons used as oils and greases in the diffusion process for the separation of uranium isotopes. A wide range of open chain aliphatic compounds ranging from butane to dodecane have thus been perfluorinated.4,5 Much of this work was carried out before the advent of modern analytical techniques and it was assumed that there was no isomerization of the hydrocarbon chain. Recent results6 indicate that this is not so and the degree of isomerization increases with increasing chain length. After a period of inactivity, there was a resurgence of interest in this area with the identification of perfluoro compounds as blood substitutes, evaporative coolants, and as potential chlorofluorocarbon replacements. This work was largely pioneered by the RTZ (now Rhône-Poulenc) group. Two kinds of reactors have been used: for small scale work, horizontal stirred reactors of the type described by Tatlow7 are employed, but the industrial scale reactors are largely of a fluidized-bed type. By this kind of fluorination a large number of alicyclic perfluorocarbons have been produced and have been marketed for the range of uses indicated above. The types of material produced are exemplified in Scheme 1.

Synthesis of Fluorohydrocarbons.

An important aspect of cobalt trifluoride chemistry has been the partial fluorination of a considerable number of substrates of varying structure, ranging from hydrocarbons through to heterocycles and ethers. In all of these fluorinations, mixtures of different levels of complexity, depending on the substrate, are obtained. As well as regioisomers, the products may also be stereoisomers. This pattern is exemplified in Scheme 2 for the fluorination of benzene at temperatures between 150 and 200 °C, much lower than those used for complete fluorination.

This kind of pattern is repeated for other cyclic systems including cyclopentane,8 cycloheptane,9 norbornane,10 and decalin11. Attempts at fluorination of cyclooctane and higher homologs result in very complex mixtures, including rearrangement products containing bicyclic systems.12 The fluorination of bicyclo[2.2.2]octane or adamantane13 result, somewhat surprisingly, in largely rearranged products. These rearrangements can readily be diminished or even prevented by the fluorination of analogs containing relatively small amounts of fluorine.12

Fluorination of Heterocycles.

A large range of heterocycles have been fluorinated including tetrahydrofuran and its alkyl and fluoroalkyl derivatives,14 thiophene,15 pyrrole and N-methylpyrrole,16 and a number of quinoline and isoquinoline derivatives.17 Attempts to fluorinate pyridine (unless there is already fluorine present) result in substantial degradation of the molecule.18 These reactions lead to products which may be further elaborated to the corresponding aromatic compounds in some cases. The kinds of products which may be obtained are shown in Scheme 3.

Fluorination of Ethers.

The fluorination of ethers has been of considerable interest in the anesthetic field and a number of ethers have been fluorinated to obtain products which have shown interesting activity as well as some interesting chemistry.19 More recently, fluorination of partly fluorinated ethers has been studied as a potential route to CFC alternatives (Scheme 4).20

Mechanistic Features.

An unusual feature of cobalt trifluoride fluorinations which produce partially fluorinated materials is that the fluorinations are not random and for any given substrate there is a distinct pattern as to the position of the residual hydrogen atoms; this can be seen from the benzene fluorination products and also from the ether fluorinations. These results have been elegantly explained by Burdon and Parsons in terms of oxidative processes20 and so far their postulates have stood the test of time.

Conclusions.

It must be concluded that cobalt trifluoride, although being a very useful reagent for producing highly fluorinated substances, is rather specialized and needs nonstandard equipment for its use. In particular it needs a source of elemental fluorine and to work efficiently needs to be run on a moderately large scale (5-25 kg of fluorinating agent).


1. Stacey, M.; Tatlow, J. C. Adv. Fluorine Chem. 1960, 1, 166.
2. Ruff, O.; Ascher, E. Z. Anorg. Allg. Chem. 1929, 183, 193.
3. Fowler, R. D.; Burford, W. B., III; Hamilton, J. M., Jr.; Sweet, R. G.; Weber, C. E.; Kasper, J. S.; Litant, I. Ind. Eng. Chem. 1947, 39, 292.
4. Burdon, J.; Ezmirly, S. T.; Huckerby, T. N. JFC 1988, 40, 83.
5. Haszeldine, R. N.; Smith, F. JCS 1950, 3617.
6. Burdon, J.; Creasey, J. C.; Proctor, L. D.; Plevey, R. G.; Yeoman, J. R. N. JCS(P2) 1991, 445.
7. Barbour, A. K.; Barlow, G. B.; Tatlow, J. C. J. Appl. Chem. 1952, 2, 127.
8. Bergomi, A.; Burdon, J.; Hodgins, T. M.; Stephens, R.; Tatlow, J. C. T 1966, 22, 43.
9. Oliver, J. A.; Stephens, R.; Tatlow, J. C. JFC 1983, 22, 21.
10. Campbell, S. F.; Stephens, R.; Tatlow, J. C. T 1965, 21, 2997.
11. Coe, P. L.; Mott, A. W.; Tatlow, J. C. JFC 1982, 20, 243.
12. Oliver, J. A.; Stephens, R.; Tatlow, J. C. JFC 1975, 6, 19.
13. Battersby, J.; Stephens, R.; Tatlow, J. C. TL 1970, 5041.
14. Burdon, J.; Chivers, G. E.; Mooney, E. F.; Tatlow, J. C. JCS(C) 1969, 1739.
15. Burdon, J.; Parsons, I. W.; Tatlow, J. C. JCS(C) 1971, 346.
16. Coe, P. L.; Smith, P.; Tatlow, J. C.; Wyatt, M. JCS(P1) 1975, 781.
17. Plevey, R. G.; Rendell, R. W.; Tatlow, J. C. JFC 1982, 21, 413.
18. Coe, P. L.; Tatlow, J. C.; Wyatt, M. JCS(P1) 1974, 1732.
19. Brandwood, M.; Coe, P. L.; Ely, C. S.; Tatlow, J. C. JFC 1975, 5, 521.
20. Burdon, J.; Parsons, I. W.; Tatlow, J. C. T 1972, 28, 43.

Paul L. Coe

University of Birmingham, UK



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