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

[0005] In Patent Document 1 (JP-A No. 2006-500423), a fluorocarboxylic acid is obtained by hydrolyzing a fluorocarboxylic acid fluoride with an aqueous sulfuric acid solution, and then washing the resulting reaction product containing the 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 method for producing a fluorine-containing carboxylic acid which uses non-corrosive and highly safe materials and which can be produced at reduced cost. 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 highly safe materials and can be carried out 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 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] A method for producing a fluorine-containing carboxylic acid, which comprises 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 each independently represent an integer of 1 or greater, l and m each independently represent an integer of 0 or greater, and R each independently represent 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, which comprises 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 each R is independently a hydrogen atom or a fluorine atom, provided that at least one of the Rs 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 fluorine-containing 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 fluorine-containing 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. [Effects of the Invention]

[0009] It is possible to provide a method for producing a fluorine-containing carboxylic acid at reduced cost, using non-corrosive and highly safe raw materials. DETAILED DESCRIPTION OF THE INVENTION

[0010] In one embodiment of the method for producing a fluorine-containing carboxylic acid, a fluorine-containing compound represented by the following general formula (1) is hydrolyzed 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 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.)

[0011] In another embodiment of the method for producing a fluorine-containing carboxylic acid, a fluorine-containing compound represented by the following general formula (3) is hydrolyzed 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 -(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 each independently represent an integer of 1 or greater, l and m each independently represent an integer of 0 or greater, and R each independently represent 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 fluorine-containing carboxylic acid, a fluorine-containing compound represented by the following general formula (5) is hydrolyzed 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 each R is independently a hydrogen atom or a fluorine atom, provided that at least one of the Rs is a fluorine atom.)

[0013] The inorganic metal salt used in the method for producing a fluorinated carboxylic acid in each of the above embodiments is a non-corrosive and highly safe material. Furthermore, after the production of a fluorinated carboxylic acid, it can be separated into an organic phase containing the fluorinated carboxylic acid and an aqueous phase containing a hydride (typically, hydrogen fluoride) that is a reaction by-product. At this time, it is believed that the hydride forms a complex with the inorganic metal salt in the aqueous phase. As a result, the purity of the fluorinated carboxylic acid can be efficiently improved. Furthermore, since the hydride can be incorporated into the aqueous phase and efficiently removed, corrosion of the reactor, piping, and other production equipment for the fluorinated carboxylic acid by the hydride can be effectively prevented, unlike when a strong acid such as sulfuric acid is used. Inorganic metal salts generally have little adverse effect on the human body and are therefore easy to handle.

[0014] In the method for producing a fluorinated carboxylic acid according to each embodiment, a fluorinated carboxylic acid can be produced in one step, thereby significantly reducing the number of steps and producing a fluorinated carboxylic acid in a simple process. No corrosive material that may be harmful to the human body, such as sulfuric acid, is used, and the cost of wastewater treatment of the solution after the reaction is lower than when sulfuric acid is used. As a result, costs can be reduced. Furthermore, since there is no step using methanol, the obtained fluorinated carboxylic acid does not undergo a reverse reaction to become a methyl ester, 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 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. Examples of the inorganic metal salt include acid-derived salts such as chloride salts, sulfate salts, and phosphate salts. Because it is an inexpensive and highly safe material, the inorganic metal salt is more preferably 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 Al(SO) as 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): 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 each independently represent an integer of 1 or greater, l and m each independently represent an integer of 0 or greater, and R each independently represent 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): 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 the Rs is a fluorine atom.)

[0019] The reactions represented by the above formulas (B) to (D) are thought to occur as follows. The fluorine-containing compounds of general formulas (1), (3), and (5) are electron-withdrawing because at least one R is a highly electronegative fluorine atom (F), and the carbonyl carbon constituting the carbonyl group (C=O) is prone to electron deficiency. When an inorganic metal salt (e.g., aluminum sulfate Al2(SO4)3) acts on this carbonyl carbon, electron polarization occurs, further promoting the electron deficiency state of the carbonyl carbon. Next, a hydrolysis reaction occurs on the carbonyl carbon, resulting in the elimination of the group R bonded to the carbonyl carbon, and an OH group bonds to the carbonyl carbon instead. Therefore, the reactions represented by the above formulas (B) to (D) are thought 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. Therefore, they are dissolved in water to be used for hydrolysis to form an aqueous solution of the inorganic metal salt. In this case, the reactions represented by the above formulas (B) to (D) occur in the aqueous solution of the inorganic metal salt. After the reactions represented by the above formulas (B) to (D), the solution can be separated into an organic phase containing the fluorinated carboxylic acid and an aqueous phase containing a hydride (typically, hydrogen fluoride) that is a reaction by-product. In this case, it is believed 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 reactor, piping, and other production equipment for the fluorinated carboxylic acid due to the hydride can be effectively prevented. Furthermore, since inorganic metal salts (e.g., aluminum sulfate Al2(SO4)3) are very inexpensive, the production cost of the fluorinated carboxylic acid can be efficiently reduced. The organic phase containing the fluorine-containing carboxylic acid obtained as described above is dehydrated 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 is not converted 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 formulas (1), (3), and (5) are not particularly limited. However, in the fluorine-containing compounds of general formulas (1), (3), and (5), it is preferable that R bonded to the carbonyl carbon is a fluorine atom, and it is more preferable that all R are fluorine atoms (F). When R bonded to the carbonyl carbon in the compounds of general formulas (1), (3), and (5) is a fluorine atom, the carbonyl carbon is more likely to be in an electron-deficient state. Furthermore, when all R in the compounds of general formulas (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, accelerating the reactions represented by the above formulas (B) to (D). Therefore, a fluorine-containing carboxylic acid can be obtained in high yield. When all R in the fluorine-containing compounds of general formulas (1), (3) and (5) are fluorine atoms (F), all R in the corresponding fluorine-containing carboxylic acids of general formulas (2), (4) and (6) will also be fluorine atoms.

[0022] In the compounds of general formulas (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. C constituting the compounds of general formulas (1) and (2) a R 2a+1 , C b R 2b -O, C c R 2cThe moiety 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, precipitation of the inorganic metal salt and volatilization of the compound of general formula (1) can be prevented. 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, the effect of removing the hydride (hydrogen fluoride) from the target product can be enhanced. 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): Furthermore, 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 general formula (1a) has a suitable chain length and branched side chain, and therefore the carbonyl carbon can be made electron-deficient more effectively, and as a result, the fluorine-containing carboxylic acid represented by the general formula (2a) can be produced efficiently in a higher yield.

[0024] In the compounds of general formulas (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 general formula (3) can be increased. C constituting the compounds of general formulas (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 moiety 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, precipitation of the inorganic metal salt and volatilization of the compound of general formula (3) can be prevented. 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 more preferable. By carrying out the hydrolysis reaction for the above time, the effect of removing the hydride (hydrogen fluoride) from the target product can be enhanced. 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): Furthermore, 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): Furthermore, 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 produced efficiently in higher yields.

[0026] In the compounds of general formulas (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 general formula (5) can be increased. The CR2 moiety constituting the compounds of general formulas (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, precipitation of inorganic metal salts and volatilization of the compound of general formula (5) can be prevented. The time for which the hydrolysis reaction of the above formula (D) is carried out 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, the effect of removing the hydride (hydrogen fluoride) from the target product can be enhanced. Furthermore, an organic solvent such as acetone or methyl ethyl ketone, or a fluorine-containing 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 applications are not particularly limited. For example, the fluorine-containing carboxylic acid can be used as a surfactant, an emulsifier, a polymerization aid, etc.

[0028] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, but 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. [Example]

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

[0030] Example 1 A 1000 ml reactor was charged with 649 g (0.512 mol) of a 27% by mass aqueous aluminum sulfate solution. While stirring the aluminum sulfate solution under water cooling, 340 g (1.02 mol) 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, then phase-separated, and the lower phase (organic phase) was separated. To the separated lower phase (organic phase), 260 g (0.205 mol) of a 27% by mass aqueous aluminum sulfate solution was added again to remove fluoride ions, followed by stirring and washing to separate the phases. After this, 374 g of the lower organic phase (fluoride ion concentration 20 ppm) was separated. Next, 98% by mass concentrated sulfuric acid was added to the separated organic phase under ice cooling to dehydrate it. After the dropwise addition of concentrated sulfuric acid, the organic phase was returned to room temperature and stirred for 1 hour, after which the phases were 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 to obtain 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) as a fraction. The analytical 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 (300 MHz, acetone-d6): ppm 12.98 (f) [ka]

[0031] Example 2 A 2000 ml reactor was charged with 864 g (0.682 mol) of a 27% by weight aqueous aluminum sulfate solution. While stirring the aluminum sulfate 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, then phase-separated, and 494 g of the lower phase (organic phase) was collected. This organic phase was concentrated using an evaporator under reduced pressure of 0.2 kPa and a 60°C hot water bath for 3 hours. If precipitates were present in the resulting concentrate, it was then subjected to pressure filtration, yielding 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, yielding 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 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 14,176 g (11.2 mol) of a 27% by mass aqueous aluminum sulfate solution. While stirring the aqueous aluminum sulfate solution under water cooling, 7,000 g (13.6 mol) 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, then phase-separated for 30 minutes, and 7,320 g of the lower phase (organic phase) was collected. Next, 6600 g of the separated organic phase was subjected to precision distillation with 10 theoretical plates at a reduced pressure of 1.0 kPa and 100-120 ° C. to obtain 5355 g 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 99 GC% or more, yield 87.5%). The analytical results of the finally obtained product 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 A 50 mL glass reactor was charged with 19.3 g (0.030 mol) of a 27 mass % aqueous aluminum sulfate solution. While stirring the aqueous aluminum sulfate 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 the phases were separated for 30 minutes, and the lower (organic) phase was collected 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 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. Inorganic metal salts, NaCl, KCl, CaCl2, Na2SO4, MgSO4, Al2(SO4)3, K2SO4, and K3PO4, were dissolved in each beaker until saturated. Next, 200 g of methyl 3,3,3-trifluoropyruvate (hydrogen fluoride concentration: 86005 ppm) was added dropwise to each beaker, stirred, and then allowed to stand. Only the city water in the beaker containing added Al2(SO4)3 was subjected to phase separation. The lower (organic) phase was removed, and the hydrogen fluoride concentration in the organic layer was measured, showing 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 allowed to separate 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 20 L reactor, and while stirring in an ice bath, 12.39 kg of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoyl fluoride was added dropwise to the methanol to allow the reaction to proceed. The resulting solution was then washed with water until the pH reached 6 or higher, dehydrated with MgSO 4 , and then pressure filtered 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 then 351.91 g of a methanol solution containing 27% by mass of potassium hydroxide was added dropwise with stirring. The solution was then concentrated using an evaporator until the methanol content in the solution was 1% by mass or less, yielding 642.45 g of potassium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propionate (crude yield 100%). Then, 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 added dropwise with stirring. The resulting solution was then allowed to stand, and the lower phase was recovered. Next, the lower phase was subjected to precision distillation using three theoretical plates, yielding 544 g of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propionic acid as the main fraction (yield 66.2%). The yield of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propionic acid (purity of more than 99% by mass) throughout 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 carry out hydrolysis. After the portionwise addition, the mixture was aged for at least 2 hours and allowed to stand for 1 hour, and the lower phase was recovered. The resulting lower phase was then neutralized with 157.0 kg of 5% by mass sodium bicarbonate water, and when the pH reached 6, the organic phase was recovered. 400 kg of tap water was then added to the organic phase, and the mixture was stirred for at least 30 minutes and allowed to stand for at least 1 hour, yielding 598.9 kg of 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(heptafluoropropoxy)propoxy]propionic acid methyl ester. 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 added dropwise with stirring. Next, the methanol was removed by reducing the pressure and heating, and the solution was concentrated until solidified. After this, 83 kg of water was added to the solid, and 43.6 kg of concentrated sulfuric acid was added in portions with stirring. The mixture was heated to 50 ° C, aged for 1 hour or more, and allowed to stand for 30 minutes or more, and the lower phase was recovered. The recovered lower phase was placed in a reactor, and 8.0 kg of concentrated sulfuric acid was added. The mixture was stirred for 15 minutes and allowed to stand for 30 minutes, and the lower phase was recovered to give 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,-hexafluoro2-(heptafluoropropoxy)propoxy]propionic acid obtained in a separate batch, and low boiling point components were distilled off by reducing the pressure and increasing the temperature. The main fraction was then recovered at a reduced pressure of 0.4 kPa and 66 to 72 ° C. to obtain 193.6 kg of 3,3,3-tetrafluoro-2-[1,1,2,3,3,3,-hexafluoro2-(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.

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