Cobalt trifluoride

Cobalt difluoride, used primarily for the manufacture of cobalt trifluoride, CoF, is available from Advance Research Chemicals, Inc., Aldrich Chemicals, and PCR in the United States, Fluorochem in the UK, and Schuhardt in Germany. The 1993 price varied from 60 to 200/kg depending on the quantity and the price of cobalt metal. C0F2 is shipped as a corrosive and toxic material in DOT-approved containers. 

Cobalt trifluoride is readily prepared by reaction of fluorine (qv) and C0CI2 at 250°C or C0F2 at 150—180°C. Direct fluorination of C0F2 leads to quantitative yields of 99.9% pure CoF (4). 

Many perfluoroaUphatic ethers and tertiary amines have been prepared by electrochemical fluorination (1 6), direct fluorination using elemental fluorine (7—9), or, in a few cases, by fluorination using cobalt trifluoride (10). Examples of lower molecular weight materials are shown in Table 1. In addition to these, there are three commercial classes of perfluoropolyethers prepared by anionic polymerization of hexafluoropropene oxide [428-59-1] (11,12), photooxidation of hexafluoropropene [116-15-4] or tetrafluoroethene [116-14-3] (13,14), or by anionic ring-opening polymeriza tion of tetrafluorooxetane [765-63-9] followed by direct fluorination (15). 

Tetrafluorobenzene. This compouad has beea prepared by fluoriaatioa of hen2ene with cobalt trifluoride and subsequent combination of the dehydrofluoriaation and defluoriaation steps. Its ioni2ation potential is 9.01 V. Nitration gives 2,3,4,5-tetrafluoronitroben2ene [5580-79-0] ia 75% yield, an iatermediate to fluoroquinolone antibacterials (218). 

Pentafluorobenzene. Pentafluoroben2ene has been prepared by several routes multistage saturation—rearomati2ation process based on fluorination of ben2ene with cobalt trifluoride reductive dechlorination of chloropentafluoroben2ene with 10% pabadium-on-carbon in 82% yield (226,227) and oxidation of penta uorophenylbydra2ine in aqueous copper sulfate at 80°C in 77% yield (228). Its ioni2ation potential is 9.37 V. One measure of toxicity is LD q = 710 mg/kg (oral, mouse) (127). 

Some derivatives of benzene can be fluorinated over cobalt trifluoride at lower temperatures. At 125 °C, 2H-tetrafluoronitrobenzene gives irans-2H,] -ni-trodecafluorocyclohexane, ci5-2ff, 1-nitrodecafluorocyclohexane, trans-5H,4-ni-... 

Fluorination of naphthalene in a stream of dilute fluorine over cobalt trifluoride yields a mixture of perfluorodecalins and partially fluorinated naphthalene derivatives that are fully fluorinated to perfluorodecalins by a subsequent treatment with dilute fluorine [23] Perfluorodecalins are also final products ot fluorination of tetralin over cobalt trifluoride at 250 °C. A more thorough investigation of this reacPon revealed seven additional compounds as products and intermediates [//] (equation 6). 

Fluorination of N-methylpyrrole over cobalt trifluoride gives six polyfluo-rinated Af-methylpyrrolidines The same compounds and two others and perfluoro-1-methylpyrrolidme are obtained by fluorination of N-methylpyrrolidine. The yields of the individual products are low [75] (equation 8)... 

Fluorination of aliphatic hydrocarbons with cobalt trifluoride gives complex mixtures Isobutane (2-methylpropane) fluorinated at 140-200 °C affords a mixture of 30 products of different degrees of fluorination and of isobutane as well as butane skeletons. The tertiary hydrogen is replaced preferentially Products containing 5-10 atoms of fluorine including a small amount of perfluoroisobutane were isolated [10]. 

Of alicyclic compounds, fluorination of cyclopentane and cyclohexane has been sufficiently investigated in the past. Cycloheptane on fluorination with cobalt trifluoride gives a mixture of highly fluorinated and perfluorinated cycloheptanes and methylcyclohexanes [/2] (equation 12). 

Fluorination of cis,rran.t,trani-l,5,9-cyclododecatriene with cobalt trifluoride gives a 50% yield of perfluoroperhydroacenaphthene [2[Pg.128]

Perfluorodimethyladamantane is prepared from adamantane dicarboxylic acid by treatment with sulfur tetrafluoride followed by energetic fluorination with cobalt trifluoride over two temperature ranges [S] (equation 15)... 

Fluorination of aliphatic ethers at gentle conditions with cobalt trifluoride or potassium tetrafluorocobaltate do not give perfluorinated products and cause only negligible cleavage of the ether bond. Complex mixtures are formed from ethyl methyl ether and from diethyl ether [9] (equations 16 and 17)... 

Cyclic ethers having perfluorinated side chains or perfluorinated rings attached in the a-position with respect to oxygen are remarkably stable toward cobalt trifluoride and can be successfully fluormated to perfluoro ethers at 440 °C without being cleaved to a considerable extent at the oxygen [16, 17], Selected examples are shown in Table 4. 

Fluorination of trimethylamine over cobalt trifluoride gives six fluorinated products [20] (equation 18). 

Methylmorpholine on treatment with cobalt trifluoride at 100 °C for 3 h yields 10 fluorinated morpholines and a small amount of bis(trifluoromethyl)-fluoromethylamine [/9] (equation 19)... 

Table 4. Selected Examples of Preparation of Perfluoro Ethers [16, 17] by Heating with Cobalt Trifluoride and Calcium Fluoride at 440 "C...

Cobalt trifluoride fluorination corresponds to the electron-transfer mechanism via a radical cation. RF groups attached to the ring enhance the stability of intermediate dienes and monoenes. Perfluoroalkyl pyridines, pyrazines, and pyrimidines were successfully fluorinated but pyridazines eliminated nitrogen. The lack of certain dienes was attributed to the difference in stability of FC=C and RFC=C and steric effects [81JCS(P1)2059]. 

The Vapour Phase Fluorination of Trichloroethylene with Cobalt Trifluoride and with Manganese Trifluoride, G. Fuller, M. Stacey, J. C. Tatlow, and C. R. Thomas, Tetrahedron, 18 (1962) 123-133. 

GL 12] [R 5] [P 9] [P 10] [P 11] Significantly lower temperature can be used to achieve a yield of the perfluorinated product as high as when employing the conventionally used cobalt trifluoride process with traditional reactors [15]. 

Chlorine Non-metals Cobalt trifluoride Silicon Fluorine Non-metals Iodine pentafluoride Metals, etc. 

Perfluorinated alkanes and cycloalkanes are prepared from the corresponding hydrocarbons, either by electrochemical fluorination or by cobalt trifluoride fluo-rination [3], Many perfluorinated solvents are available commercially covering a wide selection of boiling points and densities. Some examples of perfluorinated solvents are listed in Table 3.1 together with their key physical properties. 

Chromyl chloride, 4054 Cobalt(II) bromide, 0263 Cobalt(II) chloride, 4048 Cobalt(III) chloride, 4122 Cobalt trifluoride, 4200 Copper(I) bromide, 0265 Copper(I) chloride, 4056... 

Schultz, J., and M. Hauptschein The Fluorination of Thiophene with Cobalt Trifluoride. J. Amer. chem. Soc. 74, 848 (1952). 

Pyridine is converted into perfluoropiperidine (82) in low yield by reaction with fluorine in the presence of cobalt trifluoride (50JCS1966) quinoline affords (83) under similar conditions (56JCS783). Perfluoropiperidine can be obtained electrochemically. This is useful, as it may be readily aromatized to perfluoropyridine by passing it over iron or nickel at ca. 600 °C (74HC(14-S2)407). Recently, pyridine has been treated with xenon difluoride to yield 2-fluoropyridine (35%), 3-fluoropyridine (20%) and 2,6-difluoropyridine (11%), but it is not likely that this is simply an electrophilic substitution reaction (76MI20500). 

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