PROCESS FOR THE PURIFICATION OF FLUORINATED HYDROXYL COMPOUNDS

Abstract: The present invention has an object to provide a method for purifying a fluorinated hydroxyl compound of the formula 1 safely in a high yield under industrially practical conditions. Namely, a mixture containing a fluorinated hydroxyl compound of R f -CR 1 R 2 -OH (Formula 1, wherein R f is a C 1-20 polyfluoroalkyl group, and each of R 1 and R 2 is a hydrogen atom or a C 1-3 alkyl group) such as 2,2,3,3-tetrafluoropropanol, and a compound having an unshared electron pair, is distilled by heating in the presence of a solid acid catalyst such as a cation exchange resin catalyst, or by adding a proton source such as water.

Description: The present invention relates to a method for purifying a fluorinated hydroxyl compound according to claim 1. BACKGROUND ART A fluorinated hydroxyl compound is useful as a water and oil repellent, a surfactant or an intermediate for a color developing material for photograph (JP-A-54-154707). Further, a fluorinated hydroxyl compound does not dissolve a plastic substrate and thus is useful as a solvent for e.g. a dye for an optical recording material (JP-A-4-8585, JP-A-5-258346). Heretofore, purification of a fluorinated hydroxyl compound has been carried out by distillation. However, when a compound having an unshared electron pair (hereinafter referred to also as an unshared electron pair compound) is included in the process for producing a fluorinated hydroxyl compound, such an unshared electron pair compound interacts with the fluorinated hydroxyl compound, whereby there has been a problem that it can not be separated by usual distillation separation. For example, when the unshared electron pair compound is an aliphatic alcohol such as t-butanol, there has been a problem that it can not be separated by usual distillation, even if there is a difference in boiling point between the fluorinated hydroxyl compound and the aliphatic alcohol. US4219680 discloses a process for the purification of perfluoroalkyl alcohols by distillation in the presence of water, an alcohol and either an acid or a cation exchange resin catalyst. Further, a method has been proposed wherein methanol is reacted with tetrafluoroethylene or hexafluoropropylene in the presence of a polymerization initiator to obtain a reaction product containing a fluorinated alcohol, which is then heated to decompose an unreacted polymerization initiator, followed by distillation (EP968989A). However, this method requires heating of the reaction product, and there has been a problem such that the unreacted polymerization initiator can not be recovered. Further, a purification method is also proposed wherein a fluorinated alcohol containing water in an amount of not more than 2000 ppm, is distilled to remove water azeotropically or pseudoazeotropically to obtain a fluorinated alcohol as the residue (EP992476A). However, the fluorinated alcohol in such a method contains no unshared electron pair compound, and in such a method, the fluorinated alcohol is obtained as a residue, whereby there has been a problem that impurities which are likely to remain as evaporation residues, will remain in the fluorinated alcohol. DISCLOSURE OF THE INVENTION The present invention has been made to solve the above problems and is the following invention which provides a method for purifying a fluorinated hydroxyl compound, which is industrially practical and can be carried out by a simple operation in good yield. Namely, the present invention provides a method for purifying a fluorinated hydroxyl compound, which comprises distilling a mixture by heating in the presence of a solid acid catalyst wherein the mixture is a reaction crude product containing an alcohol compound (3) and a fluorinated hydroxyl compound (1a) formed by heating a perfluoroolefin (2) and an alcohol compound (3) in the presence of a radical initiator. R f1 CF = CF 2 CHR 1 R 2 OH R f1 CHFCF 2 CR 1 R 2 OH provided that the symbols in the formulae have the following meanings: R f1 : a C 1-18 polyfluoroalkyl group or a fluorine atom R 1 and R 2 : each independently, a hydrogen atom or a C 1-3 alkyl group. wherein said mixture further contains unreacted radical initiatior and decompositon product thereof. BEST MODE FOR CARRYING OUT THE INVENTION Here, the compound (Formula 1a) is preferably at least one member selected from the 2,2,3,3-tetrafluoropropanol, 2,2,3,3-tetrafluoro-1-methylpropanol, 2,2,3,3-tetrafluoro-1,1-dimethylpropanol, 2,2,3,4,4,4-hexafluorobutanol, 2,2,3,4,4,4-hexafluoro-1-methylbutanol and 2,2,3,4,4,4-hexafluoro-1,1-dimethylbutanol. The radical initiator may, for example, be an azo compound or a peroxyether compound. From the viewpoint of the half-value period and the reaction temperature, a peroxyether compound is preferred, and a commonly employed dialkyl peroxyether compound is particularly preferred. The reaction crude product is meant for a reaction product not subjected to e.g. chromatography or distillation. In a case where a solid content is included in the reaction crude product, the solid content may be removed by an operation such as filtration. The purification method of the present invention is an excellent method whereby the reaction crude product is not required to be heated prior to the distillation and may be distilled substantially as it is (namely, as it contains an unreacted radical initiator) whereby a fluorinated hydroxyl compound having a high purity can be obtained. In the present invention, purification is carried out by distilling the mixture by heating it in the presence of a solid acid catalyst. The solid acid catalyst may, for example, be SiO 2 ·Al 2 O 3 , SiO 2 ·MgO 2 , SiO 2 ·ZrO 2 , Al 2 O 3 ·B 2 O 3 , Al 2 O 3 , zeolite, heteropoly acid, a metal phosphate, a metal sulfate, a solid phosphoric acid catalyst (H 3 PO 4 /diatomaceous earth), a cation exchange resin catalyst, SbF 5 supported on an oxide, a sulfate supported on zirconium or a layered silicate. Zeolite is preferably of a proton type. Specifically, A-type zeolite, ZSM-5 type zeolite, mordenite, X-type zeolite or Y-type zeolite may, for example, be mentioned. Specific examples of the heteropoly acid include H 3 PW 12 O 40 , H 3 PMo 12 O 40 and CS 2.5 H 0.5 PW 12 O 40 . The metal phosphate may, for example, be BPO 4 , Ca 3 (PO 4 ) 2 , Zr(HPO 4 ) 2 , AlPO 4 , Cd 3 (PO 4 ) 2 , CePO 4 , Zn 3 (PO 4 ) 2 or Ca 10 (PO 4 ) 6 (OH) 2 . Further, the metal phosphate may be supported on e.g. SiO 2 . The metal sulfate may, for example, be MgSO 4 , CaSO 4 , ZnSO 4 , Al 2 (SO 4 ) 3 , CuSO 4 or FeSO 4 . Further, such a metal sulfate may be supported on e.g. SiO 2 or ZrO 2 . From the viewpoint of the reactivity, the cation exchange resin catalyst is preferably a cation exchange resin catalyst having super strong acid points, such as a fluorine resin catalyst having sulfonic groups or a fluorine resin catalyst having carboxyl groups. The cation exchange resin catalyst is commercially available, and for example, Nafion (tradename, manufactured by E.I. DuPont), SAC-13 (tradename, manufactured by E.I. DuPont) or NR-40 (tradename, manufactured by E.I. DuPont) may, for example, be mentioned. The layer silicate may, for example, be bentonite, montmorillonite, andalusite or kaolin. The shape of such a solid acid catalyst is preferably powdery, particulate or honeycomb, particularly preferably particulate from the viewpoint of efficiency in separation. Further, as the solid acid catalyst, a cation exchange resin catalyst or zeolite is preferred, which has high activity and can easily be regenerated. Zeolite is particularly preferred. The mixture is heated in the presence of the solid acid catalyst. The solid acid catalyst is capable of chemically changing the aliphatic alcohol compound (3), it may be decomposed and changed into an olefin, or it undergoes dehydration condensation with the fluorinated hydroxyl compound (Formula 1a) to form an ether compound. An olefin or an ether compound is usually a compound which can readily be separated by distillation from the fluorinated hydroxyl compound (Formula 1a). The solid acid catalyst is added to the mixture preferably all at once or successively, and from the viewpoint of the operation, it is added more preferably all at once. Further, the distillation may be carried out after the addition of the solid acid catalyst, or the distillation may be carried out while adding the solid acid catalyst. The amount of the solid acid catalyst is preferably from 0.5 to 100 wt% (mass%), particularly preferably from 1.0 to 50 wt% (mass%), based on the fluorinated hydroxyl compound (Formula 1a). Further, the heating temperature is preferably from 60 to 150°C, and the heating time is preferably from 0.5 to 10 hours. The pressure during the heating is preferably from 0.01 to 0.5 MPa. As the distillation conditions, conditions for usual distillation for purification of such a fluorinated hydroxyl compound may be employed. Usually, the tower top temperature is preferably from 40 to 200°C, and the pressure is preferably from 0.01 to 0.5 MPa (gauge pressure). A solvent may or may not be introduced to the reaction system, but it is preferred that the solvent is not introduced, from the viewpoint of the efficiency for separation and the volume efficiency. According to the purification method of the present invention, it is possible to readily separate, the alcohol (3) which used to be hardly separated. The fluorinated hydroxyl compound (Formula 1a) obtained after the distillation is, in a usual case, a fluorinated hydroxyl compound (Formula 1a), of high purity wherein the amount of alcohol (3) is at most 0.01 wt% (mass%), and such a compound can be used for various purposes without any problem. EXAMPLES Now, the present invention will be described in detail with reference Examples, but the present invention is by no means restricted by such Examples. REFERENCE EXAMPLE 1 Into a 1 ℓ hastelloy C autoclave, 408 g of methanol was charged, and tetrafluoroethylene was charged to the gas phase portion, whereupon the internal temperature was adjusted to 125°C. By a metering pump, a solution having 8.2 g of di-tert-butyl peroxide dissolved in 72 g of methanol, was supplied over a period of 16 hours. By an automatic valve, the pressure was set to be constant at the total pressure of 0.8 MPa (gauge pressure, the same applies hereinafter), and tetrafluoroethylene was continuously supplied to supplement the amount reduced by the reaction. The total amount of tetrafluoroethylene supplied, was 230 g. After cooling to 40°C, the reaction solution was analyzed by gas chromatography (GC), whereby a mixture comprising 2,2,3,3-tetrafluoropropanol and tert-butanol (weight ratio 98.5:1.5) was found to be formed. REFERENCE EXAMPLE 2 The reaction was carried out in the same manner as in Reference Example 1 except that the amounts of methanol, tetrafluoroethylene and di-tert-butyl peroxide were changed, to obtain a mixture comprising 616.4 g of methanol, 233.4 g of 2,2,3,3-tetrafluoropropanol, 8.5 g of tert-butanol and 5.3 g of di-tert-butyl peroxide. EXAMPLE 1: Example for purification by means of a solid acid catalyst A mixture comprising 5.0 g of tert-butanol and 45.0 g of 2,2,3,3-tetrafluoropropanol, was added to 131 g of Nafion SAC, whereby refluxing under heating was carried out at 120°C under atmospheric pressure. Upon expiration of 3 hours, distillation was carried out at 0.026 MPa and in a reflux ratio of 1/1 to obtain 42 g of a main fraction of 2,2,3,3-tetrafluoropropanol, at a tower top temperature of 70°C. The main fraction 2,2,3,3-tetrafluoropropanol was analyzed by GC, whereby the purity was found to be 99.7% (area % of the chromatogram, the same applies hereinafter). EXAMPLE 2: Example for purification by an addition of a proton source (Technical information) To a mixture comprising 12.6 kg of tert-butanol and 828 kg of 2,2,3,3-tetrafluoropropanol, 4.3 wt% (mass%) of water was added, followed by distillation at 0.10 MPa and in a reflux ratio of 10/1 to distill 21.1 kg of an azeotropic distillate of water and tert-butanol at a still pot temperature of from 70 to 90°C at a tower top temperature of from 65 to 82°C. Thereafter, as a acid removing agent, 5.6 wt% (mass%) of a 28% sodium methylate/methanol solution was added to obtain a fore-running fraction containing water, and then 612 kg of a main fraction of 2,2,3,3-tetrafluoropropanol was obtained at 0.026 MPa in a reflux ratio of 1/1 at a tower top temperature of 70°C. The 2,2,3,3-tetrafluoropropanol of the main fraction was analyzed by GC, whereby the purity was at least 99%, and tert-butanol was less than the detection limit. EXAMPLE 3: Example for purification by a solid acid catalyst The mixture obtained in Reference Example 2 comprising 616.4 g of methanol, 233.4 kg of 2,2,3,3-tetrafluoropropanol, 8.5 g of tert-butanol and 5.3 g of di-tert-butyl peroxide, was added by itself to 60 g of Nafion SAC, followed by distillation. As a low boiling point initial fraction 1 up to the distillate temperature of 64°C under room temperature in a reflux/distillate ratio of 3/1, a mixture comprising 220.1 g of methanol and 4.2 g of di-tert-butyl peroxide, was obtained. As a low boiling initial fraction 2 up to the distillate temperature of 100°C under the same conditions, a mixture comprising 250.1 g of methanol and 2.5 g of tert-butanol, was obtained. Thereafter, distillation was carried out under reduced pressure at 0.026 MPa in a reflux/distillate ratio of 20/1, to obtain 198.5 g of a main fraction of 2,2,3,3-tetrafluoropropanol at a tower top temperature of 70°C. The 2,2,3,3-tetrafluoropropanol of the main fraction, was analyzed by GC, whereby the purity was 99.9%. COMPARATIVE EXAMPLE 1 After obtaining the fore-running fraction from a mixture comprising 18 g of tert-butanol and 1182 g of 2,2,3,3-tetrafluoropropanol, 865 g of a main fraction of 2,2,3,3-tetrafluoropropanol was obtained at 200 torr in a reflux ratio of 1/1 at a tower top temperature of 70°C. The 2,2,3,3-tetrafluoropropanol of the main fraction was analyzed by GC, whereby the purity was 97%, and tert-butanol was 1.3%. INDUSTRIAL APPLICABILITY According to the method of the present invention, purification of a fluorinated hydroxyl compound (Formula 1a) can be carried out in good yield by a simple operation under industrially practical conditions, whereby a fluorinated hydroxyl compound (Formula 1a) of high purity containing no alcohol (3) compound, which used to be difficult to separate, can be obtained.

Claims: A method for purifying a fluorinated hydroxyl compound, which comprises distilling a mixture by heating in the presence of a solid acid catalyst, wherein the mixture is a reaction crude product containing an alcohol compound of the following formula 3 and a fluorinated hydroxyl compound of the following formula 1a formed by heating a perfluoroolefin of the following formula 2 and an alcohol compound of the formula 3 in the presence of a radical initiator: R f1 CF=CF 2 CHR 1 R 2 OH R f1 CHFCF 2 CR 1 R 2 OH provided that the symbols in the formulae have the following meanings: R f1 :a fluorine atom or a C 1-18 polyfluoroalkyl group; and R 1 and R 2 : each independently, a hydrogen atom or a C 1-3 alkyl group; wherein said mixture further contains unreacted radical initiator and decomposition product thereof. The purification method according to Claim 1, wherein the fluorinated hydroxyl compound is at least one member selected from 2,2,3,3-tetrafluoropropanol, 2,2,3,3-tetrafluoro-1-methylpropanol, 2,2,3,3-tetrafluoro-1,1-dimethylpropanol, 2,2,3,4,4,4-hexafluorobutanol, 2,2,3,4,4,4-hexafluoro-1-methylbutanol and 2,2,3,4,4,4-hexafluoro-1,1-dimethylbutanol. The purification method according to Claim 1 or 2, wherein the radical initiator is a peroxyether compound and the decomposition product thereof is an aliphatic alcohol compound. The purification method according to Claim 3, wherein the aliphatic alcohol compound is an aliphatic tertiary alcohol. The purification method according to any one of Claims 1 to 4, wherein the solid acid catalyst is a cation exchange resin catalyst. The purification method according to any one of Claims 1 to 4, wherein the solid acid catalyst is zeolite. The purification method according to any one of Claims 1 to 6, wherein the fluorinated hydroxyl compound is obtained as a distillate component by the distillation.

Inventors: OKAMOTO HIDEKAZU, TOMA TOSHIHIKO, WADA AKIHIRO, YAMAGISHI NOBUYUKI, OKAMOTO, HIDEKAZU, TOMA, TOSHIHIKO, WADA, AKIHIRO, YAMAGISHI, NOBUYUKI, Okamoto, Hidekazu, Asahi Glass Company, Limited, TOMA, Toshihiko, Asahi Glass Company, Limited, WADA, Akihiro, Asahi Glass Company, Limited, YAMAGISHI, Nobuyuki, Asahi Glass Company, Limited
Applicants: ASAHI GLASS CO LTD, ASAHI GLASS COMPANY LTD.
Application year: 2000
Main classification: C07C29
IPC codes: C07C29