Process 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 is reduced in cost.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. There is produced a fluorine-containing carboxylic acid represented by the general formula (4) by hydrolyzing a fluorine-containing compound represented by the general formula (3) in the presence of an inorganic metal salt. There is produced a fluorine-containing carboxylic acid represented by the general formula (6) by hydrolyzing a fluorine-containing compound represented by the general formula (5) in the presence of an inorganic metal salt.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a fluorinated carboxylic acid.

Background Art

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

[0003] For example, a fluorinated carboxylic acid can be produced by a reaction step represented by the following formula (A).

Chemical Formula

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

[0005] Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-500423) hydrolyzes a carboxylic acid fluoride with an aqueous sulfuric acid solution, and further washes the obtained reaction product containing a fluorinated carboxylic acid and hydrogen fluoride with an aqueous sulfuric acid solution to obtain a fluorinated carboxylic acid.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] Conventionally, there has been a demand for a method for producing a fluorine-containing carboxylic acid that uses a material having no corrosiveness and excellent safety and reduces costs. The present invention has been made in view of the above circumstances, and provides a method for producing a fluorine-containing carboxylic acid that uses a material having no corrosiveness and excellent safety and reduces costs.

MEANS FOR SOLVING THE PROBLEMS

[0008] The gist of the present invention is 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, but at least one of R is 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 each R is independently a hydrogen atom or a fluorine atom, provided that at least one of the Rs 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 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 [1] to [3] above, wherein all of the Rs are fluorine atoms. [5] The method for producing a fluorine-containing carboxylic acid according to any one of [1] to [4] above, 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 [1] to [5] above, 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.

Advantages of the Invention

[0009] It is possible to provide a method for producing a fluorine-containing carboxylic acid that uses a raw material having no corrosiveness and excellent safety and has a reduced cost.

Embodiments for Carrying Out the Invention

[0010] In a method for producing a fluorine-containing carboxylic acid according to one embodiment, in the presence of an inorganic metal salt, a fluorine-containing compound represented by the following general formula (1) is hydrolyzed 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 each R is independently a hydrogen atom or a fluorine atom, but at least one of the Rs is a fluorine atom.)

[0011] In a method for producing a fluorine-containing carboxylic acid according to another embodiment, in the presence of an inorganic metal salt, a fluorine-containing compound represented by the following general formula (3) is hydrolyzed 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 are each independently an integer of 1 or more, l and m are each independently an integer of 0 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.)

[0012] In the method for producing a fluorine-containing carboxylic acid according to another embodiment, in the presence of an inorganic metal salt, a fluorine-containing compound represented by the following general formula (5) is hydrolyzed 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 salts used in the method for producing the fluorine-containing carboxylic acid of each of the above embodiments are materials that are not corrosive and have high safety. Further, after producing the fluorine-containing carboxylic acid, it is possible to separate the organic phase containing the fluorine-containing carboxylic acid and the aqueous phase containing a hydride (typically hydrogen fluoride) that 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 the fluorine-containing carboxylic acid can be efficiently improved. Further, since the hydride can be efficiently removed by being incorporated into the aqueous phase, unlike the case where a strong acid such as sulfuric acid is used, corrosion of the production equipment for the fluorine-containing carboxylic acid such as the reactor and piping due to the hydride can be effectively prevented. Generally, inorganic metal salts are less likely to have an adverse effect on the human body, so they are also excellent in handleability.

[0014] In the method for producing the fluorine-containing carboxylic acid of each embodiment, since the fluorine-containing carboxylic acid can be produced in one step, the number of steps can be significantly reduced and the fluorine-containing carboxylic acid can be produced in a simple process. Without using corrosive materials that can affect the human body such as sulfuric acid, the wastewater treatment cost of the solution after the reaction is lower than when sulfuric acid is used. As a result, the cost can be reduced. Further, since there is no step of using methanol, the obtained fluorine-containing carboxylic acid does not become a methyl ester due to a reverse reaction, and the fluorine-containing 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 form 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 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 the 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 the general formula (2) is represented by the following formula (B).

Chemical formula

[0017] In another embodiment, the reaction of hydrolyzing a fluorine-containing compound represented by the 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 the general formula (4) is represented by the following formula (C). In addition, although the example using aluminum sulfate as the inorganic metal salt is shown in the following formula (C), the same reaction as the following formula (C) occurs even when an inorganic metal salt other than aluminum sulfate is used.

Chemical formula

[0018] In another embodiment, the reaction of hydrolyzing a fluorine-containing compound represented by the 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 the general formula (6) is represented by the following formula (D). In addition, although the example using aluminum sulfate as the inorganic metal salt is shown in the following formula (D), the same reaction as the following formula (D) occurs even when an inorganic metal salt other than aluminum sulfate is used. [Chemical formula] (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, and at least one of R is a fluorine atom.)

[0019] The reactions represented by the above formulas (B) to (D) are considered to occur as follows. Since at least one R in the fluorine-containing compounds of the general formulas (1), (3) and (5) is a fluorine atom (F) having a high electronegativity, they are electron-withdrawing, and the carbonyl carbon constituting the carbonyl group (C=O) is in a state where electrons are easily lacking. When an inorganic metal salt (for example, aluminum sulfate Al2(SO4)3) acts on this carbonyl carbon, electron polarization occurs, and the electron-deficient state of the carbonyl carbon is further promoted. Next, a hydrolysis reaction occurs on the carbonyl carbon, whereby 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 formulas (B) to (D) are considered to be a kind of nucleophilic acyl substitution reaction using an inorganic metal salt as a catalyst.

[0020] Inorganic metal salts (e.g., aluminum sulfate Al2(SO4)3) are usually solid within the temperature range where the reactions represented by the above formulas (B) to (D) occur. Therefore, they are dissolved in the water used for hydrolysis and used as an aqueous solution of the inorganic metal salt. In this case, the reactions of the above formulas (B) to (D) occur in the aqueous solution of the inorganic metal salt. Further, after the reactions of the above formulas (B) to (D), it is possible to separate into an organic phase containing a fluorine-containing carboxylic acid and an aqueous phase containing a hydride (typically hydrogen fluoride) which is a reaction by-product. At this time, in the aqueous phase, it is considered that the hydride forms a complex with the inorganic metal salt (e.g., aluminum sulfate Al2(SO4)3). As a result, the purity of the fluorine-containing carboxylic acid can be efficiently improved. Since the hydride (typically hydrogen fluoride) can be efficiently removed by being incorporated into the aqueous phase, corrosion of the manufacturing equipment of the fluorine-containing carboxylic acid such as reactors and pipes due to the hydride can be effectively prevented. Further, since the inorganic metal salt (e.g., aluminum sulfate Al2(SO4)3) is very inexpensive, the manufacturing cost of the fluorine-containing 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. Next, the dehydrated organic phase is purified by simple distillation to obtain the desired fluorine-containing carboxylic acid. Thus, in each embodiment, since there is no step of using methanol when obtaining the fluorine-containing carboxylic acid, the fluorine-containing carboxylic acid does not become a methyl ester due to 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 tends to be in an electron-deficient state. Also, when all R in the compounds of general formulas (1), (3), and (5) are fluorine atoms (F), the carbonyl carbon tends to be in an even more electron-deficient state. As a result, the hydrolysis reaction is more likely to occur and the reactions represented by the above formulas (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 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) also become fluorine atoms.

[0022] In the compounds of general formulas (1) and (2), it is preferable that a = 1 to 12, more preferably 1 to 3, and even more preferably 3. It is preferable that b = 1 to 12, more preferably 1 to 3, and even more preferably 3. It is preferable that c = 1 to 12, more preferably 1 to 3, and even more preferably 2. It is preferable that k = 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 all cases. The C that constitutes the compounds of general formulas (1) and (2) a R 2a+1 、C b R 2b -O、C c R 2cThe portion may be linear or branched. The temperature for carrying out the hydrolysis reaction of the above formula (B) is preferably 10 to 100 °C, more preferably 10 to 60 °C, and even more preferably 20 to 40 °C. By the temperature for carrying out the hydrolysis reaction being within the above range, precipitation of the inorganic metal salt and volatilization of the compound of the 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 even more preferable. By the time for carrying out the hydrolysis reaction being as above, the effect of removing hydride (hydrogen fluoride) from the target product can be enhanced. Further, organic solvents such as acetone and methyl ethyl ketone, fluorine-based solvents such as CELEFIN (registered trademark) 1233Z, Asahiklin AE-3000, and Vertrel (registered trademark) XF, etc. may be added to the aqueous solution of the inorganic metal salt used for the hydrolysis reaction of the above formula (B).

[0023] The fluorine-containing compound represented by the general formula (1) is preferably a fluorine-containing compound represented by the following general formula (1a). Further, the fluorine-containing carboxylic acid represented by the general formula (2) is preferably a fluorine-containing carboxylic acid represented by the general formula (2a). [Chemical formula] (In the above general formulas (1a) and (2a), o = 0 to 100.) Since the compound represented by the above general formula (1a) has a suitable chain length and side chain branching property, the carbonyl carbon can be made into a more effectively electron-deficient state. 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 general formulas (3) and (4), d is preferably from 1 to 12, more preferably from 1 to 3, and even more preferably 2. e is preferably from 1 to 12, more preferably from 1 to 3, and even more preferably 3. f is preferably from 1 to 12, more preferably from 1 to 3, and even more preferably 2. g is preferably from 1 to 12, more preferably from 1 to 3, and even more preferably 3. h is preferably from 1 to 12, more preferably from 1 to 3, and even more preferably 2. l is preferably from 1 to 50, more preferably from 1 to 30, and even more preferably from 1 to 20. m is preferably from 1 to 50, more preferably from 1 to 30, and even more preferably from 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 enhanced. The C d R 2d , OC e R 2e , OC f R 2f O, C g R 2g O, C h R 2h moieties may be linear or branched. The temperature for carrying out the hydrolysis reaction of the above formula (C) is preferably from 10 to 100 °C, more preferably from 10 to 60 °C, and even more preferably from 20 to 40 °C. When the temperature for carrying out the hydrolysis reaction is 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 even more preferred. When the time for carrying out the hydrolysis reaction is as above, the effect of removing hydride (hydrogen fluoride) from the target product can be enhanced. Further, organic solvents such as acetone and methyl ethyl ketone, and fluorine-based solvents such as CELEFIN (registered trademark) 1233Z, Asahiklin AE-3000, and 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 the general formula (3) is preferably a fluorine-containing compound represented by the following general formula (3a1). Further, the fluorine-containing carboxylic acid represented by the general formula (4) is preferably a fluorine-containing carboxylic acid represented by the general formula (4a1). FOC-C2R4-OC2R4-OC3R6O-C2R4-COF (3a1) HOOC-C2R4-OC2R4-OC3R6O-C2R4-COOH (4a1) Also, the fluorine-containing compound represented by the general formula (3) is preferably a fluorine-containing compound represented by the following general formula (3a2). Furthermore, the fluorine-containing carboxylic acid represented by the general formula (4) is preferably a fluorine-containing carboxylic acid represented by the general formula (4a2). [Chemical formula] (p = 8 to 9, q = 36 to 40) In the compounds represented by the above general formulas (3a1) and (3a2), the carbonyl carbon can be made to be in a more effectively electron-deficient state. As a result, the fluorine-containing carboxylic acids represented by the general formulas (4a1) and (4a2) can be efficiently produced in a higher yield.

[0026] In the compounds of general formulas (5) and (6), n is preferably from 1 to 50, more preferably from 1 to 30, and even more preferably from 1 to 20. When n is within the above range, the reactivity of the hydrolysis reaction of the fluorine-containing compound of general formula (5) can be enhanced. The CR2 moiety constituting the compounds of general formulas (5) and (6) may be linear or branched. The temperature for carrying out the hydrolysis reaction of the above formula (D) is preferably from 10 to 100 °C, more preferably from 10 to 60 °C, and even more preferably from 20 to 40 °C. When the temperature for carrying out the hydrolysis reaction is within the above range, precipitation of the inorganic metal salt and volatilization of the compound of general formula (5) can be prevented. 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 preferred. When the time for carrying out the hydrolysis reaction is as above, the effect of removing hydride (hydrogen fluoride) from the target product can be enhanced. Further, organic solvents such as acetone and methyl ethyl ketone, fluorine-based solvents such as CELEFIN (registered trademark) 1233Z, Asahiklin AE-3000, and Vertrel (registered trademark) XF, etc. 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 use is not particularly limited. For example, the fluorine-containing carboxylic acid can be used as a surfactant, an emulsifier, a polymerization aid, etc.

[0028] As described above, the embodiments of the present invention have been described, but the present invention is not limited to the above embodiments, and includes all aspects included in the concept and claims of the present invention, and can be variously modified 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) 649 g (0.512 mol) of an aqueous aluminum sulfate solution with a concentration of 27% by mass was added to a 1000 ml reactor. While stirring the aqueous 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 cause a hydrolysis reaction. The resulting solution was stirred at room temperature for 1 hour and then phase - separated, and the lower phase (organic phase) was separated. To the separated lower phase (organic phase), 260 g (0.205 mol) of an aqueous aluminum sulfate solution with a concentration of 27% by mass was added again for fluoride ion removal, followed by stirring, washing, and phase - separation. Thereafter, 374 g of the lower - phase 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 for dehydration. After the organic phase after the dropwise addition of concentrated sulfuric acid was returned to room temperature and stirred for 1 hour, it was phase - separated to obtain 318 g of the upper - phase organic phase. This organic phase was subjected to simple distillation at a reduced pressure of 0.2 kPa and an internal temperature of 60 - 70 °C, and 307 g of 2,3,3,3 - tetrafluoro - 2 - (heptafluoropropoxy) propanoic acid represented by the following formula (E) (purity 99.1% by mass, yield 90.4%) was obtained as a fraction. The analysis results of the finally obtained product are shown below. 19 F - NMR (300 MHz, 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) [Chemical formula]

[0031] (Example 2) 864 g (0.682 mol) of an aqueous aluminum sulfate solution containing 27% by mass of aluminum sulfate was added to a 2000 ml reactor. While stirring the aqueous 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 to 12) was added dropwise to cause 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 the conditions of a reduced pressure of 0.2 kPa and a warm water bath at 60 °C for 3 hours. Thereafter, if a precipitate was present in the resulting concentrate, pressure filtration was performed to obtain 487 g of the concentrate. Next, the resulting concentrate was 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 analysis results of the finally obtained product are shown below. 19 F-NMR (300 MHz, C6F6): ppm -77.24 to -83.55 (a, c, e, f, h), -128.54 (b), -130.18 (g), -143.25 (d) 1 H-NMR (300 MHz, TMS): ppm 11.91 (i)

Chemical formula

[0032] (Example 3) 14,176 g (11.2 mol) of an aqueous aluminum sulfate solution containing 27% by mass of aluminum sulfate was added to a 20 L reactor. 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 cause a hydrolysis reaction. After the resulting solution was stirred at room temperature for 1 hour, it was phase-separated for 30 minutes, and 7,320 g of the lower phase (organic phase) was separated. Next, 6,600 g of the separated organic phase was subjected to precision distillation with 10 theoretical plates at a reduced pressure of 1.0 kPa and a temperature of 100 to 120 °C to obtain 5,355 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 analysis results of the finally obtained product are shown below. 19 F-NMR (300 MHz, C6F6): ppm -77.60~-84.19 (a, c, e, f, h), -128.54 (b), -130.33 (g), -144.24 (d) 1 H-NMR (300 MHz, TMS): ppm 13.10~11.50 (i)

Chemical formula

[0033] (Example 4) To a 50 mL glass reactor, 19.3 g (0.030 mol) of an aqueous aluminum sulfate solution containing 27% by mass of aluminum sulfate was added. 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 and then phase-separated for 30 minutes. The lower phase (organic phase) was separated and 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) was obtained. The analysis results of the finally obtained product are shown below. 19 F-NMR (400 Hz, C6F6): ppm -76.26~-89.64 (a, c, c’, e, f) -129.60 (b) -143.92 (d)

Chemical formula

[0034] (Reference Example 1) A plurality of 500 ml beakers containing 200 g of tap water were prepared, and NaCl, KCl, CaCl2, Na2SO4, MgSO4, Al2(SO4)3, K2SO4, and K3PO4 were dissolved in the tap water in each beaker until saturated as inorganic metal salts. Next, 200 g of methyl 3,3,3-trifluoropyruvate (hydrogen fluoride concentration: 86005 ppm) was added dropwise to the tap water in each beaker, and after stirring, the mixture was allowed to stand. Only the tap water in the beaker to which Al2(SO4)3 was added was phase-separated. The lower phase (organic phase) was separated and the hydrogen fluoride concentration in the organic layer was measured, and it was found to have decreased 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. After stirring the obtained solution for 1 hour, it was 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 analysis results of the finally obtained product are shown below. 19 F-NMR (400 Hz, C6F6): ppm -52.63~-57.18 (b, b’) -79.44~-81.22 (a, a’) -87.92~-91.97 (c) [Chemical formula] (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 under an ice bath, 12.39 kg of 2,3,3,3 - tetrafluoro - 2 - (heptafluoropropoxy) propanoyl fluoride was added dropwise to the methanol to cause a reaction. Subsequently, the resulting solution was washed with water until the pH reached 6 or higher, dehydrated with Mg2SO4, and then pressure - filtered to obtain 11.86 kg of methyl 2,3,3,3 - tetrafluoro - 2 - (heptafluoropropoxy) propionate (yield 92.4%). Thereafter, 600.40 g of methyl 2,3,3,3 - tetrafluoro - 2 - (heptafluoropropoxy) propionate 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. Subsequently, the solution was concentrated by an evaporator until the methanol content in the solution became 1% by mass or less to obtain 642.45 g of potassium 2,3,3,3 - tetrafluoro - 2 - (heptafluoropropoxy) propionate (crude yield 100%). Thereafter, 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. Subsequently, the resulting solution was allowed to stand, and the lower phase was recovered. Next, the lower phase was precisely distilled in 3 theoretical plates to obtain 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 over 99% by mass) through the whole process 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 portionwise to the methanol to cause hydrolysis. After completion of the portionwise addition, aging was carried out for 2 hours or more, and then left standing for 1 hour, and the lower phase was recovered. Next, the obtained lower phase was neutralized with 157.0 kg of 5 mass% aqueous sodium bicarbonate solution, and when the pH reached 6, the organic phase was recovered. Further, 400 kg of city water was added to the organic phase, stirred for 30 minutes or more, left standing for 1 hour or more, and 598.9 kg of methyl 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(heptafluoropropoxy)propoxy]propionate was obtained. Thereafter, 150.5 kg of methyl 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(heptafluoropropoxy)propoxy]propionate was added to the reactor, and then 61.5 kg of a methanol solution containing 30 mass% potassium hydroxide was added dropwise with stirring. Next, methanol was removed by reduced pressure and heating, and the solution was concentrated until it solidified. Thereafter, 83 kg of water was added to the solid, 43.6 kg of concentrated sulfuric acid was added portionwise with stirring, heated to 50 °C, aged for 1 hour or more, left standing for 30 minutes or more, and the lower phase was recovered. The recovered lower phase was charged into the reactor, 8.0 kg of concentrated sulfuric acid was added, stirred for 15 minutes, left standing for 30 minutes, and 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 of the crude 3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(heptafluoropropoxy)propoxy]propionic acid obtained in a separate batch was charged into a distillation column, and after distilling off the low-boiling components by reduced pressure and temperature increase, the main distillate was recovered at a reduced pressure of 0.4 kPa and 66 - 72 °C to obtain 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, comprising hydrolyzing a fluorine-containing compound represented by the following general formula (3) in the presence of an inorganic metal salt (excluding sodium fluoride) 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 ) 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 ) 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, but at least one of R is a fluorine atom.)

2. The method for producing a fluorine-containing carboxylic acid according to claim 1, wherein e is 3.

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-(CR ２ ) ｎ -COF (5) HOOC-(CR ２ ) 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, and 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 claims 1 to 3, wherein all of the Rs are fluorine atoms.

5. The method for producing a fluorine-containing carboxylic acid according to any one of claims 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 inorganic metal salt is Al ２ (SO ４ ) ３ , NaCl, KCl, CaCl ２ , Na ２ SO ４ , MgSO ４ , K ２ SO ４ , and K ３ PO ４ The method for producing a fluorine-containing carboxylic acid according to any one of claims 1 to 5, which is at least one inorganic metal salt selected from the group consisting of.

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