Method for producing fluorine-containing carboxylic acid

Abstract

To provide a method for producing a fluorine-containing carboxylic acid which uses a raw material having excellent safety with no corrosiveness and achieves cost reduction.SOLUTION: There is produced a fluorine-containing carboxylic acid represented by the general formula (2) by hydrolyzing a fluorine-containing compound represented by the general formula (1) in the presence of an inorganic metal salt. CaR2a+1-O-(CbR2b-O)k-CcR2c-COF (1), CaR2a+1-O-(CbR2b-O)k-CcR2c-COOH (2). (In the general formulae (1) and (2), a, b, and c are each independently an integer of 1 or more; k is an integer of 0 or more; R is each independently a hydrogen atom or a fluorine atom; provided that at least one R is a fluorine atom).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a process for producing a fluorine-containing carboxylic acid. [Background technology]

[0002] Fluorine-containing carboxylic acids (fluorocarboxylic acids; carboxylic acid fluorides) are used in various industrial fields as surfactants, emulsifiers, polymerization aids, etc. For this reason, methods for producing fluorine-containing carboxylic acids have been studied.

[0003] For example, a fluorine-containing carboxylic acid can be produced by the reaction step shown in the following formula (A). [ka]

[0004] In the reaction step represented by the above formula (A), the fluorine-containing compound represented by (a) is reacted with methanol to methyl esterify and purify the compound (a) to obtain the methyl ester of the fluorine-containing compound represented by (b). Next, the compound (b) is reacted in the presence of KOH / methanol to obtain the potassium salt of the fluorine-containing compound represented by (c). After this, the compound (c) is reacted in the presence of concentrated sulfuric acid to obtain the fluorine-containing carboxylic acid represented by (d). After this, the fluorine-containing carboxylic acid is purified by distillation. In this reaction step, the fluorine-containing carboxylic acid is produced through a plurality of steps.

[0005] In Patent Document 1 (JP-A 2006-500423), a fluorocarboxylic acid is obtained by hydrolyzing a fluorocarboxylic acid fluoride with an aqueous sulfuric acid solution, and further washing the resulting reaction product containing a fluorocarboxylic acid and hydrogen fluoride with an aqueous sulfuric acid solution. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2006-500423 Summary of the Invention [Problem to be solved by the invention]

[0007] There has been a demand for a process for producing a fluorinated carboxylic acid which uses non-corrosive and highly safe materials and which is cost-effective. The present invention has been made in view of the above circumstances, and provides a method for producing a fluorinated carboxylic acid, which uses non-corrosive and excellently safe materials and at reduced costs. [Means for solving the problem]

[0008] The gist and configuration of the present invention are as follows. [1] A method for producing a fluorine-containing carboxylic acid, comprising hydrolyzing a fluorine-containing compound represented by the following general formula (1) in the presence of an inorganic metal salt to produce a fluorine-containing carboxylic acid represented by the following general formula (2): C a R 2a+1 -O-(C b R 2b -O) k -C c R 2c -COF (1) C a R 2a+1 -O-(C b R 2b -O) k -C c R 2c -COOH (2) (In the above general formulas (1) and (2), a, b, and c are each independently an integer of 1 or more, k is an integer of 0 or more, and R is each independently a hydrogen atom or a fluorine atom, with at least one R being a fluorine atom.) [2] A method for producing a fluorine-containing carboxylic acid, comprising hydrolyzing a fluorine-containing compound represented by the following general formula (3) in the presence of an inorganic metal salt to produce a fluorine-containing carboxylic acid represented by the following general formula (4): FOC-C d R 2d-(OC e R 2e ) l -OC f R 2f O-(C g R 2g O) m -C h R 2h -COF (3) HOOC-C d R 2d -(OC e R 2e ) l -OC f R 2f O-(C g R 2g O) m -C h R 2h -COOH (4) (In the above general formulas (3) and (4), d, e, f, g and h are each independently an integer of 1 or more, l and m are each independently an integer of 0 or more, and R is each independently a hydrogen atom or a fluorine atom, provided that at least one of R is a fluorine atom.) [3] A method for producing a fluorine-containing carboxylic acid, comprising hydrolyzing a fluorine-containing compound represented by the following general formula (5) in the presence of an inorganic metal salt to produce a fluorine-containing carboxylic acid represented by the following general formula (6): FOC-(CR2) n -COF (5) HOOC-(CR2) n -COOH (6) (In the above general formulas (5) and (6), n is an integer of 1 or more, and R is each independently a hydrogen atom or a fluorine atom, provided that at least one of R is a fluorine atom.) [4] The method for producing a fluorine-containing carboxylic acid according to any one of the above [1] to [3], wherein all of the R's are fluorine atoms. [5] The method for producing a fluorinated carboxylic acid according to any one of the above [1] to [4], wherein the inorganic metal salt is a salt of at least one metal selected from the group consisting of Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Ga. [6] The method for producing a fluorinated carboxylic acid according to any one of the above [1] to [5], wherein the inorganic metal salt is at least one inorganic metal salt selected from the group consisting of Al2(SO4)3, NaCl, KCl, CaCl2, Na2SO4, MgSO4, K2SO4, and K3PO4. Effect of the Invention

[0009] It is possible to provide a method for producing a fluorinated carboxylic acid at reduced cost, using raw materials which are non-corrosive and have excellent safety. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In one embodiment of the method for producing a fluorinated carboxylic acid, a fluorinated compound represented by the following general formula (1) is hydrolyzed in the presence of an inorganic metal salt to produce a fluorinated carboxylic acid represented by the following general formula (2). C a R 2a+1 -O-(C b R 2b -O) k -C c R 2c -COF (1) C a R 2a+1 -O-(C b R 2b -O) k -C c R 2c -COOH (2) (In the above general formulas (1) and (2), a, b, and c are each independently an integer of 1 or more, k is an integer of 0 or more, and R is each independently a hydrogen atom or a fluorine atom, with at least one R being a fluorine atom.)

[0011] In another embodiment of the method for producing a fluorinated carboxylic acid, a fluorinated compound represented by the following general formula (3) is hydrolyzed in the presence of an inorganic metal salt to produce a fluorinated carboxylic acid represented by the following general formula (4). FOC-C d R 2d -(OCe R 2e ) l -OC f R 2f O-(C g R 2g O) m -C h R 2h -COF (3) HOOC-C d R 2d -(OC e R 2e ) l -OC f R 2f O-(C g R 2g O) m -C h R 2h -COOH (4) (In the above general formulas (3) and (4), d, e, f, g and h are each independently an integer of 1 or more, l and m are each independently an integer of 0 or more, and R is each independently a hydrogen atom or a fluorine atom, provided that at least one of R is a fluorine atom.)

[0012] In another embodiment of the method for producing a fluorinated carboxylic acid, a fluorinated compound represented by the following general formula (5) is hydrolyzed in the presence of an inorganic metal salt to produce a fluorinated carboxylic acid represented by the following general formula (6). FOC-(CR2) n -COF (5) HOOC-(CR2) n -COOH (6) (In the above general formulas (5) and (6), n is an integer of 1 or more, and R is each independently a hydrogen atom or a fluorine atom, provided that at least one of R is a fluorine atom.)

[0013] The inorganic metal salt used in the method for producing fluorine-containing carboxylic acid in each of the above embodiments is a material that is not corrosive and has high safety. In addition, after the production of fluorine-containing carboxylic acid, it can be separated into an organic phase containing fluorine-containing carboxylic acid and an aqueous phase containing a hydride (typically hydrogen fluoride) which is a reaction by-product. At this time, it is considered that the hydride forms a complex with the inorganic metal salt in the aqueous phase. As a result, the purity of fluorine-containing carboxylic acid can be efficiently improved. In addition, since the hydride can be efficiently removed by taking it into the aqueous phase, unlike the case where a strong acid such as sulfuric acid is used, corrosion of the production equipment for fluorine-containing carboxylic acid, such as a reactor or piping, due to the hydride can be effectively prevented. In general, inorganic metal salts are less likely to have adverse effects on the human body, and therefore are easy to handle.

[0014] In the method for producing a fluorinated carboxylic acid in each embodiment, a fluorinated carboxylic acid can be produced in one step, so that the number of steps can be significantly reduced and a fluorinated carboxylic acid can be produced in a simple process. No corrosive material that may affect the human body, such as sulfuric acid, is used, and the cost of wastewater treatment of the solution after the reaction is cheaper than when sulfuric acid is used. As a result, costs can be reduced. In addition, since there is no step using methanol, the obtained fluorinated carboxylic acid does not turn into a methyl ester by a reverse reaction, and a fluorinated carboxylic acid can be obtained with high purity and high yield.

[0015] The inorganic metal salt is not particularly limited, but is preferably at least one metal salt selected from the group consisting of Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ga. Examples of the inorganic metal salt include salts derived from acids such as chloride salts, sulfate salts, and phosphate salts. Since it is an inexpensive and safe material, it is more preferable that the inorganic metal salt is at least one inorganic metal salt selected from the group consisting of aluminum sulfate Al2(SO4)3, NaCl, KCl, CaCl2, Na2SO4, MgSO4, K2SO4, and K3PO4.

[0016] More specifically, in one embodiment, the reaction of hydrolyzing a fluorine-containing compound represented by general formula (1) in the presence of aluminum sulfate Al2(SO4)3, which is an inorganic metal salt, to obtain a fluorine-containing carboxylic acid represented by general formula (2) is represented by the following formula (B). [ka] (In the above formula (B), a, b, and c are each independently an integer of 1 or greater, k is an integer of 0 or greater, and R are each independently a hydrogen atom or a fluorine atom, provided that at least one of R is a fluorine atom.) Note that, although the above formula (B) shows an example in which aluminum sulfate is used as the inorganic metal salt, a reaction similar to that of the above formula (B) occurs when an inorganic metal salt other than aluminum sulfate is used.

[0017] In another embodiment, the reaction of hydrolyzing a fluorine-containing compound represented by general formula (3) in the presence of aluminum sulfate Al2(SO4)3, which is an inorganic metal salt, to obtain a fluorine-containing carboxylic acid represented by general formula (4) is represented by the following formula (C). Note that, although the following formula (C) shows an example in which aluminum sulfate is used as the inorganic metal salt, a reaction similar to the following formula (C) also occurs when an inorganic metal salt other than aluminum sulfate is used. [ka] (In the above formula (C), d, e, f, g and h are each independently an integer of 1 or more, l and m are each independently an integer of 0 or more, and R is each independently a hydrogen atom or a fluorine atom, provided that at least one of R is a fluorine atom.)

[0018] In another embodiment, the reaction of hydrolyzing a fluorine-containing compound represented by general formula (5) in the presence of aluminum sulfate Al2(SO4)3, which is an inorganic metal salt, to obtain a fluorine-containing carboxylic acid represented by general formula (6) is represented by the following formula (D). Note that, although the following formula (D) shows an example in which aluminum sulfate is used as the inorganic metal salt, a reaction similar to the following formula (D) also occurs when an inorganic metal salt other than aluminum sulfate is used. [ka] (In the above formula (D), n is an integer of 1 or more, and each R is independently a hydrogen atom or a fluorine atom, provided that at least one of R is a fluorine atom.)

[0019] The reactions represented by the above formulae (B) to (D) are considered to occur as follows. The fluorine-containing compounds of the general formulae (1), (3) and (5) are electron-withdrawing because at least one R is a fluorine atom (F) having high electronegativity, and the carbonyl carbon constituting the carbonyl group (C=O) is in a state in which it is easy to become electron-deficient. When an inorganic metal salt (e.g., aluminum sulfate Al2(SO4)3) acts on this carbonyl carbon, polarization of electrons occurs, and the electron-deficient state of the carbonyl carbon is further promoted. Next, a hydrolysis reaction occurs on the carbonyl carbon, and the group R bonded to the carbonyl carbon is eliminated, and instead, an OH group is bonded to the carbonyl carbon. Therefore, the reactions represented by the above formulae (B) to (D) are considered to be a type of nucleophilic acyl substitution reaction catalyzed by an inorganic metal salt.

[0020] Inorganic metal salts (e.g., aluminum sulfate Al2(SO4)3) are usually solid in the temperature range where the reactions represented by the above formulas (B) to (D) occur, and are therefore dissolved in water used for hydrolysis to form an aqueous solution of inorganic metal salts. In this case, the reactions represented by the above formulas (B) to (D) occur in the aqueous solution of inorganic metal salts. After the reactions represented by the above formulas (B) to (D), the solution can be separated into an organic phase containing fluorinated carboxylic acid and an aqueous phase containing a hydride (typically, hydrogen fluoride) which is a reaction by-product. In this case, it is considered that the hydride forms a complex with the inorganic metal salt (e.g., aluminum sulfate Al2(SO4)3) in the aqueous phase. As a result, the purity of the fluorinated carboxylic acid can be efficiently improved. Since the hydride (typically, hydrogen fluoride) can be efficiently removed by incorporating it into the aqueous phase, corrosion of the production equipment for fluorinated carboxylic acid, such as a reactor or piping, due to the hydride can be effectively prevented. In addition, since inorganic metal salts (e.g., aluminum sulfate Al2(SO4)3) are very inexpensive, the production cost of fluorinated carboxylic acid can be efficiently reduced. The organic phase containing the fluorine-containing carboxylic acid obtained as described above is dehydrated by using concentrated sulfuric acid or by concentrating with an evaporator or the like. The organic phase after dehydration is then purified by simple distillation to obtain the desired fluorine-containing carboxylic acid. As described above, in each embodiment, there is no step of using methanol when obtaining the fluorine-containing carboxylic acid, so that the fluorine-containing carboxylic acid does not turn into a methyl ester by a reverse reaction, and the fluorine-containing carboxylic acid can be obtained with high purity and high yield.

[0021] The number and position of fluorine atoms in the fluorine-containing compounds of general formulae (1), (3) and (5) are not particularly limited, but in the fluorine-containing compounds of general formulae (1), (3) and (5), it is preferable that R bonded to the carbonyl carbon is a fluorine atom, and more preferably, all R are fluorine atoms (F). When R bonded to the carbonyl carbon in the compounds of general formulae (1), (3) and (5) is a fluorine atom, the carbonyl carbon is more likely to be in an electron-deficient state. In addition, when all R in the compounds of general formulae (1), (3) and (5) are fluorine atoms (F), the carbonyl carbon is more likely to be in an electron-deficient state. As a result, the hydrolysis reaction occurs more easily, and the reactions represented by the above formulae (B) to (D) are promoted. Therefore, a fluorine-containing carboxylic acid can be obtained in a high yield. When all R in the fluorine-containing compounds of the general formulae (1), (3) and (5) are fluorine atoms (F), all R in the corresponding fluorine-containing carboxylic acids of the general formulae (2), (4) and (6) are also fluorine atoms.

[0022] In the compounds of general formulae (1) and (2), a is preferably 1 to 12, more preferably 1 to 3, and even more preferably 3. b is preferably 1 to 12, more preferably 1 to 3, and even more preferably 3. c is preferably 1 to 12, more preferably 1 to 3, and even more preferably 2. k is preferably 0 to 100, more preferably 0 to 50, and even more preferably 0 to 20. When a, b, c, and k are within the above ranges, the hydrolysis reaction can proceed in any of them. C constituting the compounds of general formulae (1) and (2) a R 2a+1 , C b R 2b -O, C c R 2cThe portion may be linear or branched. The temperature at which the hydrolysis reaction of the above formula (B) is carried out is preferably 10 to 100°C, more preferably 10 to 60°C, and even more preferably 20 to 40°C. By carrying out the hydrolysis reaction at a temperature within the above range, it is possible to prevent the deposition of the inorganic metal salt and the volatilization of the compound of general formula (1). The time for carrying out the hydrolysis reaction of the above formula (B) is preferably 60 minutes or more, and a longer reaction time is more preferable. By carrying out the hydrolysis reaction for the above time, it is possible to enhance the effect of removing the hydride (hydrogen fluoride) from the target product. In addition, an organic solvent such as acetone or methyl ethyl ketone, or a fluorine-based solvent such as CELEFIN (registered trademark) 1233Z, Asahiklin AE-3000, or Vertrel (registered trademark) XF may be added to the aqueous solution of the inorganic metal salt used in the hydrolysis reaction of the above formula (B).

[0023] The fluorine-containing compound represented by general formula (1) is preferably a fluorine-containing compound represented by the following general formula (1a): The fluorine-containing carboxylic acid represented by general formula (2) is preferably a fluorine-containing carboxylic acid represented by general formula (2a): [ka] (In the above general formulas (1a) and (2a), o is 0 to 100.) The compound represented by the above general formula (1a) has a suitable chain length and branched side chain, so that the carbonyl carbon can be made more effectively electron-deficient, and as a result, the fluorine-containing carboxylic acid represented by the general formula (2a) can be efficiently produced in a higher yield.

[0024] In the compounds of the general formulae (3) and (4), d is preferably 1 to 12, more preferably 1 to 3, and even more preferably 2. e is preferably 1 to 12, more preferably 1 to 3, and even more preferably 3. f is preferably 1 to 12, more preferably 1 to 3, and even more preferably 2. g is preferably 1 to 12, more preferably 1 to 3, and even more preferably 3. h is preferably 1 to 12, more preferably 1 to 3, and even more preferably 2. l is preferably 1 to 50, more preferably 1 to 30, and even more preferably 1 to 20. m is preferably 1 to 50, more preferably 1 to 30, and even more preferably 1 to 20. When d, e, f, g, h, l, and m are within the above ranges, the reactivity of the hydrolysis reaction of the fluorine-containing compound of the general formula (3) can be increased. C constituting the compounds of the general formulae (3) and (4) d R 2d , O.C. e R 2e , O.C. f R 2f O, C g R 2g O, C h R 2h The portion may be linear or branched. The temperature at which the hydrolysis reaction of the above formula (C) is carried out is preferably 10 to 100°C, more preferably 10 to 60°C, and even more preferably 20 to 40°C. By carrying out the hydrolysis reaction at a temperature within the above range, it is possible to prevent the precipitation of the inorganic metal salt and the volatilization of the compound of general formula (3). The time for carrying out the hydrolysis reaction of the above formula (C) is preferably 60 minutes or more, and a longer reaction time is even more preferable. By carrying out the hydrolysis reaction for the above time, it is possible to enhance the effect of removing the hydride (hydrogen fluoride) from the target product. In addition, an organic solvent such as acetone or methyl ethyl ketone, or a fluorine-based solvent such as CELEFIN (registered trademark) 1233Z, Asahiklin AE-3000, or Vertrel (registered trademark) XF may be added to the aqueous solution of the inorganic metal salt used in the hydrolysis reaction of the above formula (C).

[0025] The fluorine-containing compound represented by general formula (3) is preferably a fluorine-containing compound represented by the following general formula (3a1): The fluorine-containing carboxylic acid represented by general formula (4) is preferably a fluorine-containing carboxylic acid represented by general formula (4a1): FOC-C2R4-OC2R4-OC3R6O-C2R4-COF (3a1) HOOC-C2R4-OC2R4-OC3R6O-C2R4-COOH (4a1) The fluorine-containing compound represented by general formula (3) is preferably a fluorine-containing compound represented by the following general formula (3a2): The fluorine-containing carboxylic acid represented by general formula (4) is preferably a fluorine-containing carboxylic acid represented by general formula (4a2): [ka] (p=8-9, q=36-40) In the compounds represented by the above general formulae (3a1) and (3a2), the carbonyl carbon can be made more effectively electron-deficient, and as a result, the fluorine-containing carboxylic acids represented by the general formulae (4a1) and (4a2) can be efficiently produced in higher yields.

[0026] In the compounds of the general formulae (5) and (6), n is preferably 1 to 50, more preferably 1 to 30, and even more preferably 1 to 20. By setting n within the above range, the reactivity of the hydrolysis reaction of the fluorine-containing compound of the general formula (5) can be increased. The CR2 moiety constituting the compounds of the general formulae (5) and (6) may be linear or branched. The temperature at which the hydrolysis reaction of the above formula (D) is carried out is preferably 10 to 100°C, more preferably 10 to 60°C, and even more preferably 20 to 40°C. By setting the temperature at which the hydrolysis reaction is carried out within the above range, it is possible to prevent the precipitation of inorganic metal salts and the volatilization of the compound of the general formula (5). The time for carrying out the hydrolysis reaction of the above formula (D) is preferably 60 minutes or more, and a longer reaction time is even more preferable. By setting the time for carrying out the hydrolysis reaction within the above range, it is possible to enhance the effect of removing hydrides (hydrogen fluoride) from the target product. In addition, an organic solvent such as acetone or methyl ethyl ketone, or a fluorine-based solvent such as CELEFIN (registered trademark) 1233Z, Asahiklin AE-3000, or Vertrel (registered trademark) XF may be added to the aqueous solution of the inorganic metal salt used in the hydrolysis reaction of the above formula (D).

[0027] The fluorine-containing carboxylic acid (fluorocarboxylic acid; carboxylic acid fluoride) produced by the production method of the present invention is useful in various industrial fields, and its application is not particularly limited. For example, the fluorine-containing carboxylic acid can be used as a surfactant, an emulsifier, a polymerization auxiliary, etc.

[0028] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and includes all aspects encompassed by the concept of the present invention and the scope of the claims, and can be modified in various ways within the scope of the present invention. EXAMPLES

[0029] Next, in order to further clarify the effects of the present invention, examples will be described, but the present invention is not limited to these examples.

[0030] Example 1 649g (0.512mol) of 27% by mass aluminum sulfate aqueous solution was added to a 1000ml reactor. While stirring the aluminum sulfate aqueous solution under water cooling, 340g (1.02mol) of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoyl fluoride was added dropwise to carry out a hydrolysis reaction. The resulting solution was stirred at room temperature for 1 hour, and then phase-separated to separate the lower phase (organic phase). 260g (0.205mol) of 27% by mass aluminum sulfate aqueous solution was added again to the separated lower phase (organic phase) to remove fluorine ions, and then the mixture was stirred and washed to separate the phases. After this, 374g of the lower organic phase (fluorine ion concentration 20ppm) was separated. Next, 98% by mass concentrated sulfuric acid was added to the separated organic phase under ice cooling to dehydrate it. The organic phase after the dropwise addition of concentrated sulfuric acid was returned to room temperature and stirred for 1 hour, and then phase-separated to obtain 318 g of an upper organic phase. This organic phase was subjected to simple distillation at a reduced pressure of 0.2 kPa and an internal temperature of 60 to 70°C, and 307 g of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoic acid (purity 99.1% by mass, yield 90.4%) represented by the following formula (E) was obtained as a fraction. The analysis results of the final product obtained are shown below. 19 F-NMR (300MHz, C6F6): ppm -78.50, -78.96(c), -80.42(e), -81.44(a), -84.91, -85.45(c), -128.74(b), -130.40(d) 1 H-NMR (300MHz, acetone-d6): ppm 12.98(f) [ka]

[0031] Example 2 A 2000 ml reactor was charged with 864 g (0.682 mol) of 27% by mass aluminum sulfate aqueous solution. While stirring the aluminum sulfate aqueous solution under water cooling, 500 g of 2-{1,1,2,2,3,3,3-heptafluoropropoxypoly[1-oxy(trifluoro-2-trifluoromethyl-1,2-ethanediyl)]}tetrafluoropropanoyl fluoride (n=4-12) was added dropwise to carry out a hydrolysis reaction. The resulting solution was stirred at room temperature for 1 hour, and then phase-separated, and 494 g of the lower phase (organic phase) was separated. This organic phase was concentrated by an evaporator under conditions of a reduced pressure of 0.2 kPa and a hot water bath of 60°C for 3 hours. After this, if a precipitate was present in the obtained concentrate, pressure filtration was performed to obtain 487 g of concentrate. The resulting concentrate was then subjected to thin-film distillation at a reduced pressure of 1 Pa and an internal temperature of 110 to 130° C. to obtain 400 g of 2-{1,1,2,2,3,3,3-heptafluoropropoxypoly[1-oxy(trifluoro-2-trifluoromethyl-1,2-ethanediyl)]}tetrafluoropropanoic acid represented by the following formula (F) as a fraction. The analytical results of the final product obtained are shown below. 19 F-NMR (300MHz, C6F6): ppm -77.24~-83.55(a, c, e, f, h), -128.54(b), -130.18(g), -143.25(d) 1 H-NMR (300MHz, TMS):ppm 11.91(i) [ka]

[0032] Example 3 A 20L reactor was charged with 14176g (11.2mol) of 27% by mass aluminum sulfate aqueous solution. While stirring the aluminum sulfate aqueous solution under water cooling, 7000g (13.6mol) of 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(heptafluoropropoxy)propoxy]propanoyl fluoride was added dropwise to carry out a hydrolysis reaction. The resulting solution was stirred at room temperature for 1 hour, and then phase-separated for 30 minutes, and 7320g of the lower phase (organic phase) was separated. Next, 6600g of the separated organic phase was subjected to precision distillation with 10 theoretical plates at a reduced pressure of 1.0kPa and 100-120℃ to obtain 5355g of 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(heptafluoropropoxy)propoxy]propionic acid represented by the following formula (G) as the main fraction (purity 99GC% or more, yield 87.5%). The analysis results of the final product obtained are shown below. 19 F-NMR (300MHz, C6F6): ppm -77.60~-84.19(a,c,e,f,h), -128.54(b), -130.33(g), -144.24(d) 1 H-NMR (300MHz, TMS): ppm 13.10~11.50(i) [ka]

[0033] Example 4 19.3 g (0.030 mol) of 27% by mass aluminum sulfate aqueous solution was added to a 50 mL glass reactor. While stirring the aluminum sulfate aqueous solution, 9.0 g (0.015 mol) of 2-[2-[1-[difluoro[1,2,2,2-tetrafluoro-1-(fluorocarboxy)ethoxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2-tetrafluoroethoxy]-2,3,3,3-tetrafluoropropanoyl fluoride was added dropwise to carry out a hydrolysis reaction. The resulting solution was stirred at room temperature for 2 hours, then phase-separated for 30 minutes, and the lower phase (organic phase) was separated to obtain 9.6 g of 2-[2-[2-(carboxydifluoromethoxy)-1,1,2,3,3,3-hexafluoropropoxy]-1,1,2,3,3,3-hexafluoropropoxy]-2,3,3,3-tetrafluoropropionic acid represented by the following formula (H). The analytical results of the final product obtained are shown below. 19 F-NMR(400Hz,C6F6):ppm -76.26~-89.64(a,c,c',e,f) -129.60(b) -143.92(d) [ka]

[0034] (Reference example 1) Several 500 ml beakers containing 200 g of city water were prepared, and NaCl, KCl, CaCl2, Na2SO4, MgSO4, Al2(SO4)3, K2SO4, and K3PO4 were dissolved in the city water of each beaker until it reached saturation. Next, 200 g of methyl 3,3,3-trifluoropyruvate (hydrogen fluoride concentration 86005 ppm) was dropped into the city water of each beaker, stirred, and then allowed to stand. Only the city water in the beaker to which Al2(SO4)3 had been added was phase-separated. The lower phase (organic phase) was separated, and the hydrogen fluoride concentration in the organic layer was measured, which showed a decrease to 695 ppm.

[0035] Example 5 8.0 g of 27% by mass aluminum sulfate was added to a 30 ml glass reactor, and 4.5 g of α,ω-difluoroethanoyl fluoride poly(difluorooxymethylene-co-tetrafluorooxyethylene) was added dropwise while stirring the aluminum sulfate aqueous solution to carry out a hydrolysis reaction. The resulting solution was stirred for 1 hour, then phase-separated for 30 minutes, and the lower phase (organic phase) was separated to obtain 4.8 g of α,ω-difluoroethanoic acid poly(difluorooxymethylene-co-tetrafluorooxyethylene) represented by the following formula (I). The analytical results of the final product obtained are shown below. 19 F-NMR(400Hz,C6F6):ppm -52.63~-57.18(b,b') -79.44~-81.22(a,a') -87.92~-91.97(c) [ka] (p=8-9, q=36-40)

[0036] Comparative Example 1 6.58 kg of methanol was added to a 20L reactor, and 12.39 kg of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoyl fluoride was added dropwise to the methanol while stirring in an ice bath to carry out a reaction. The resulting solution was then washed with water until the pH was 6 or higher, and pressure filtered after dehydration with Mg2SO4 to obtain 11.86 kg of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propionic acid methyl ester (yield 92.4%). After this, 600.40 g of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propionic acid methyl ester was added to a 1000 ml reactor, and 351.91 g of a methanol solution containing 27% by mass of potassium hydroxide was further added dropwise while stirring. Next, the solution was concentrated by an evaporator until the methanol content in the solution was 1% by mass or less, and 642.45 g of potassium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propionate was obtained (crude yield 100%). After this, 719.53 g of water and 915.75 g of potassium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propionate were added to a 1000 ml reactor, and 394.9 g of sulfuric acid was further added dropwise under stirring. Next, the obtained solution was allowed to stand, and the lower phase was recovered. Next, precision distillation of the lower phase was performed with a theoretical plate number of 3, and 544 g of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propionic acid was obtained as the main fraction (yield 66.2%). The yield of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propionic acid (purity: more than 99 mass %) through all steps was 61.2%.

[0037] Comparative Example 2 133.1 kg of methanol was added to the reactor, and while stirring under cooling, 605.1 kg of 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro 2-(heptafluoropropoxy)propoxy]propanoyl fluoride was added in portions to the methanol to perform hydrolysis. After the addition in portions, the mixture was aged for 2 hours or more, left to stand for 1 hour, and the lower phase was collected. Next, the obtained lower phase was neutralized with 157.0 kg of 5% by mass sodium bicarbonate water, and when the pH reached 6, the organic phase was collected. Furthermore, 400 kg of city water was added to the organic phase, stirred for 30 minutes or more, and left to stand for 1 hour or more, and 598.9 kg of 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro 2-(heptafluoropropoxy)propoxy]propionic acid methyl ester was obtained. After this, 150.5 kg of 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3,-hexafluoro-2-(heptafluoropropoxy)propoxy]propionic acid methyl ester was added to the reactor, and 61.5 kg of a methanol solution containing 30% by mass of potassium hydroxide was further added dropwise under stirring. Next, methanol was removed by reducing pressure and heating, and the solution was concentrated until it solidified. After this, 83 kg of water was added to the solid, and 43.6 kg of concentrated sulfuric acid was further added in portions under stirring, and the mixture was heated to 50°C, aged for 1 hour or more, and left to stand for 30 minutes or more, and the lower phase was recovered. The recovered lower phase was charged into a reactor, 8.0 kg of concentrated sulfuric acid was added, and the mixture was stirred for 15 minutes and allowed to stand for 30 minutes. The lower phase was recovered to obtain 150.5 kg of crude 3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(heptafluoropropoxy)propoxy]propionic acid. Next, a total of 300.3 kg was charged into a distillation column together with crude 3,3,3-tetrafluoro-2-[1,1,2,3,3,3,-hexafluoro-2-(heptafluoropropoxy)propoxy]propionic acid obtained in a separate batch, and low boiling point components were distilled off by reducing pressure and raising the temperature. The main fraction was then recovered at a reduced pressure of 0.4 kPa and 66 to 72°C, yielding 193.6 kg of 3,3,3-tetrafluoro-2-[1,1,2,3,3,3,-hexafluoro-2-(heptafluoropropoxy)propoxy]propionic acid (purity 98 GC% or more).

Claims

1. A method for producing a fluorine-containing carboxylic acid, which comprises hydrolyzing a fluorine-containing compound represented by the following general formula (1) in the presence of at least one inorganic metal salt selected from the group consisting of chloride salts, sulfate salts, and phosphate salts, to produce a fluorine-containing carboxylic acid represented by the following general formula (2): C ａ R ２ａ＋１ -O-(C ｂ R ２ｂ -O) ｋ -C ｃ R ２ｃ -COF (1) C ａ R ２ａ＋１ -O-(C ｂ R ２ｂ -O) ｋ -C ｃ R ２ｃ -COOH (2) (In the above general formulas (1) and (2), a, b, and c each independently represent an integer of 1 or greater, k represents an integer of 0 or greater, and R each independently represents a hydrogen atom or a fluorine atom, provided that at least one of R is a fluorine atom.)

2. The method for producing a fluorine-containing carboxylic acid described in claim 1, wherein the inorganic metal salt is a salt of at least one metal selected from the group consisting of Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ga.

3. A method for producing a fluorine-containing carboxylic acid according to claim 1 or 2, wherein the inorganic metal salt is at least one inorganic metal salt selected from the group consisting of Al2(SO4)3, NaCl, KCl, CaCl2, Na2SO4, MgSO4, K2SO4, and K3PO4.