Process for preparing perfluoroethers by fluorination with elemental fluorine

Abstract: A process for fluorinating hydrogenated ether compounds by direct reaction with elemental F₂ diluted with an inert gas, wherein the starting compound is in the liquid phase, said fluorination being carried out in the presence of a perfluoro­ polyether compound and of an alkali metal fluoride.

Description: The present invention relates to the preparation of perfluoroethers starting from the corresponding hydrogenated compounds by fluorination with elemental fluorine conducted in the presence of a perfluoropolyether and of a fluoride of an alkali metal. Processes for fluorinating hydrogenated compounds with elemental fluorine are well-known in the art. For example,J.L.Adcock and H.L.Cherry describe in J.Fluorine Inor.,1985, 30 (3) 343 the preparation of perfluoroglymes such as perfluorotetramethyleneglycol dimethylether by direct fluorination using the aerosol-technique. Only 15 to 36 % of the desired product is obtained owing to fragmentation or incomplete reaction. R.D. Chambers and B. Grierson describe in J. Fluorine Chem., 1985, 29 , 323, the fluorination of ethers by means of CoF₃ at 400°C with yields up to 70 %. Such synthesis requires the use of particularly sophisticated apparatus capable of resisting both to the fluorine utilized for preparing CoF₃, which is reduced during the synthesis, and to the high temperatures which are usually necessary to the fluorination process. Furthermore, as the reaction proceeds, there is a tendency to loose the halogen different from fluorine. J.L. Margrave and R.J. Lagow describe in Prog. Inorg. Chem., 1979, 26 , 161 the fluorination of ethers through the La Mar process, whereby perfluoroethers are obtained with yields up to 60 %. Such direct fluorination process is carried out at very low temperatures, at least in the first reaction steps. In order to have a complete fluorination it is then necessary to operate at higher temperature, what requires the use of a plurality of reactors operating at different temperatures. W.H. Lin, W.I. Bailey, Sr. and M.S. Lagow describe in Chem. Soc. Chem. Commun. 1985, 1350, the fluorination through the La Mar process, of crown ethers by using NaF as a HF scavenger. However, the yields obtainable by this process are very low, about 30 % of the product to be obtained. C. Bliefert et al describe in Kunststoffe 75 (1986) pages 235 to 240 a surface treatment of polymer (polyethylene, PP) articles, powders or foils with elemental fluorine dissolved in either perfluoropolyether compounds or halogenated hydrocarbons. Owing to this treatment, a partially fluorinated surface containing also free radicals is obtained. EP-A-77114 discloses that perfluorinated ethers can be prepared by reacting the corresponding partially fluorinated compounds with pure molecular fluorine in an inert solvent (which preferably is a perfluorochemical and may be the reaction product itself) at a temperature of -75°C to 100°C, preferably under UV-irradiation. It has unexpectedly been found that according to the process of the invention, the fluorination occurs directly, in a single step, without using CoF₃, with high yields of thoroughyl fluorinated compounds, free from by-products due to the absence of scission reactions and furthermore, starting from hydrogenated chlorine-containing products it is possible to have a selective fluorination avoiding the substitution of the chlorine atoms. Such process, moreover, is easily utilizable on an industrial scale, other than the La Mar process with metal fluorides. The invention relates to the preparation of compounds having the general formula: wherein: R₁ = perfluoroalkyl containing from 1 to 10 carbon atoms or perfluoroalkylether containing from 2 to 10 carbon atoms; R₂, R₃ = equal to or different from each other, may be fluorine or perfluoroalkyl containing from 1 to 10 carbon atoms or perfluoroalkylether containing from 2 to 10 carbon atoms; R₄ = fluorine or fluoroalkyl containing from 2 to 10 carbon atoms, optionally containing halogen atoms other than F, in particular chlorine; R₁ and R₂ can also form together a divalent perfluoroalkyl radical containing from 2 to 10 carbon atoms, optionally comprising 1 to 2 oxygen atoms in the chain. Said perfluoroethers are obtainable through the process of the present invention by fluorination of hydrogenated compounds such as for example: a) Z = -CHCl-CH₂Cl, -CH₂-CH₂-CH₃, -CFCl-CHFCl, -CH₂-CH₂-OR, where R is alkyl with 1 to 3 carbon atoms b) where Z is the same as defined above c) R-O-CHXCH₂-O-(CH₂CHX-O) n -R′ where R and R′ are alkyl with 1 to 3 carbon atoms, X is H or CH₃ and n is an integer from 1 to 3. The process of the present invention comprises feeding gaseous F₂ diluted with an inert gas in a liquid phase consisting of a perfluoropolyether containing the starting product and an alkali flouride. F₂ is generally present in an amount of 20 to 30 % with respect to the inert gas, which preferably is N₂ or argon. The alkali flouride, preferably KF, is present in a dispersed form in an amount from 1 to 10 moles (preferably from 2 to 5 moles) for each hydrogen atom of the starting product which is to be substituted by fluorine. The process for preparing the perfluorinated ethers of the above mentioned classes can be carried out also starting from compounds containing chlorine, which is not substituted by fluorine in the reaction. The perfluoropolyethers utilizable as a solvent for the process according to the invention must have a boiling point which is higher than the reaction temperature and they can be selected from those composed of sequences of one or more oxyperfluoroalkylene units selected from: -CF₂-O-; -CF₂-CF₂-O-; -CF₂-CF₂-CF₂-O-; and having perfluoroalkyl groups as end groups. Suitable commercial products are those designated by trademarks Fomblin®, Galden®, Krytox®, Demnum®, produced by Daikin. The process temperature ranges from 20°C to 150°C, preferably from 40°C to 110°C. The products obtainable through the fluorination process according to the invention are free from incompletely fluorinated compounds and, as is known for the perfluorinated compounds, said products are endowed with an exceptional combination of excellent properties, which make them suitable for a broad range of uses in many industry sectors. The main characteristics are chemical inertia, thermal stability, non-inflammability, high electrical resistivity, low surface tension, low water-solubility, compatibility with many materials such as elastomers and plastomers. Furthermore, the process of the present inveniton does not give rise to scission reactions with consequent secondary reactions, wherefore the individual compounds are obtained in a pure state, with well defined boiling points and other physical properties. In view of the above cited characteristics, the perfluoroethers obtainable by the process according to the invention are particularly suitable for the tests in the field of electronics, such as the thermal shock test, or in operations such as vapor phase soldering or vapor phase curing. The following examples are given for merely illustrative purposes and are not to be construed as being limitative of the possible embodiments of the present invention. EXAMPLE 1 Into a glass reactor equipped with a stirrer there were charged 412 g of Fomblin® YO4 and 100 g of finely powdered KF. The solution was heated to 100°C whereafter, by means of a dipped pipe, a mixture of 3 Nl/h of F₂ and of 3 Nl/h of N₂ was sent into the reactor. The solution was allowed to saturate and then was fed at a rate of 1 ml/h for 9 hours. The gases leaving the reactor were collected in a trap cooled down to -78°C. At the end of the reaction, 10.3 g (yield = 52 %) of perfluorinated product characterized by a boiling point of 108°C were obtained. The ¹⁴F-NMR spectrum was in accordance with the compound of formula: In fact, the chemical shifts referred to CFCl₃ were as follows: A) -CF₂-Cl from -60 to -64 ppm B) -CF₂O from -80 to -85 ppm C) -CF₂, CF, CFCl many signals from -112 to -138 ppm. The corresponding intensities were in the following ratio: A:B:C = 2:2:6. Comparative Example 1 It was operated as is described in example 1, but without using KF. Only 0.5 g of product were obtained. A formation of gaseous products deriving from a fragmentation of the molecule and having boiling points <180°C was observed, and dark tar-like products had formed. Comparative Example 2 It was operated as is described in example 1, but using 1,1,2-trichlorotrifluoroethane instead of Fomblin® YO4. A yield of 10 % and a product having a boiling point equal to 108°C were obtained. EXAMPLE 2 The reactor of example 1 was charged with 400 g of Fomblin® Y04 and 100 g of finely powdered KF. The solution was heated to 100°C whereafter by means of a dipped pipe a mixture of 3 Nl/h of fluorine and N₂ was sent into the reactor. The solution was allowed to saturate and diglyme was introduced at a rate of 0.38 ml/h for 6 hours. Then in the cooled trap of example 1, 4.6 g of reaction products were collected. Said reaction products from GLC analysis contained 76 % of a compound which according to ¹⁹F-NMR had the following formula: The yield of this product was of 56 %. The perfluorinated diglyme has the following boiling point: 66°C. EXAMPLE 3 The reactor of example 1 was charged with 400 g of Fomblin® Y04 and 100 g of KF. Then the temperature was raised to 120°C and by means of a dipped pipe a mixture of 3 Nl/h of fluorine and N₂ was introduced into the reactor the solution was allowed to saturate and tetraglyme was introduced into the reactor at a rate of 0.38 ml/h for 6 hours. Then 3.7 g of reaction products were collected into the cooled trap of example 1. These products contained 75 % of a compound which according to ¹⁹F-NMR spectroscopy, was in accordance with the following formula; The yield of this product was 44 % and its boiling point 138°C. EXAMPLE 4 The reactor of example 1 was charged with 400 g of Fomblin® Y04 and 100 g of KF, then the temperature was raised to 100°C and a mixture of 3 Nl/h of N₂ and F₂ was sent into the reactor. The solution was allowed to saturate. Then was introduced at a rate of 0.95 ml/h. After 6.5 hours 13.4 g of reaction product were collected in the cooled trap of example 1 containing 80 % of a compound having a boiling point of 125°C and according to ¹⁹F-NMR having the following formula: The yield of this product was 74 %.

Claims: A process for preparing compounds having the general formula: wherein: R₁ is perfluoroalkyl containing 1 to 10 carbon atoms or perfluoroalkylether containing 2 to 10 carbon atoms; R₂ and R₃, either equal to or different from each other, can be fluorine or perfluoroalkyl containing 1 to 10 carbon atoms or perfluoroalkylether containing 2 to 10 carbon atoms; R₄ is fluorine or fluoroalkyl containing 2 to 10 carbon atoms, optionally containing halogen atoms other than fluorine; R₁ and R₂ together may form a divalent perfluoroalkyl radical containing 2 to 10 carbon atoms, optionally containing 1 to 2 oxygen atoms in the chain; which comprises reacting elemental fluorine with an at least partially hydrogenated ether compound, in the presence of a reaction solvent consisting of a perfluoropolyether, and of an alkali metal fluoride in an amount of from 1 to 10 moles per hydrogen atom of the starting product, at a temperature of from 20 to 150°C. The process according to claim 1, wherein the starting hydrogenated ether product contains also chlorine atoms. The process according to claim 1 or 2, wherein elemental fluorine is diluted with an inert gas. The process according to any one of claims 1 to 3, wherein the alkali metal fluoride is KF or NaF. The process according to any one of claims 1 to 4, wherein the perfluoroether solvent has a boiling point higher than the reaction temperature and comprises one or more oxyperfluoroalkylene units selected from: -CF₂-O; -CF₂-CF₂-O-; -CF₂-CF₂-CF₂-O-; and having perfluoroalkyl groups as end groups. The process according to any one of claims 1 to 5, wherein the temperature ranges from 40 to 110°C. The process according to any one of claims 1 to 6, wherein the starting hydrogenated compound is selected from the following compounds: a) wherein Z = -CHCl-CH₂Cl, -CH₂CH₂CH₃, -CFCl-CHFCl, -CH₂-CH₂-OR, where R is an alkyl with 1 to 3 carbon atoms; b) where Z is the same as defined above; c) R-O -CHXCH₂-O-(CH₂CHX-O) n -R', where R and R' are alkyl with 1 to 3 carbon atoms, X is H or CH₃ and n is an integer from 1 to 3.

Inventors: CALINI PIERANGELO, MODENA SILVANA DR, CALINI, PIERANGELO, MODENA, SILVANA, DR.
Applicants: AUSIMONT SPA, AUSIMONT S.P.A.
Application year: 1987
Main classification: C07D307
IPC codes: B23K35, C07D307, C07B61, C07C43, C07D319, B01J27, C07C67, C07C41