JPH0564940B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing 2,3,4,5-tetrafluorobenzoic acid. Specifically, 3,4,5,6-tetrafluorophthalic acid was decarboxylated in an aqueous medium to obtain 2,3,
This invention relates to a new method for producing 4,5-tetrafluorobenzoic acid. [Prior Art] 2,3,4,5-tetrafluorobenzoic acid is a compound useful as an intermediate for pharmaceuticals, agricultural chemicals, and the like.
Conventionally, many techniques for decarboxylating phthalic acid derivatives in an aqueous medium have been provided [for example, Chemical Abstracts Vol.
41, 2083d (1947), U.S. Patent No. 1939212, etc.].
However, these are all methods for obtaining unsubstituted benzoic acid, and as in the present invention, 3,4,5, phthalic acid substituted with a fluorine atom,
It is difficult to efficiently decarboxylate 6-tetrafluorophthalic acid. According to the findings of the present inventors, even if the above-mentioned method is directly applied in the present invention, there are many by-products, and 2,3,4,
It turned out that it was not possible to obtain 5-tetrafluorobenzoic acid. Generally, a method for obtaining halogenated benzoic acid by decarboxylating phthalic acid substituted with halogen is not well known. Indeed, U.S. patent no.
No. 2439237 discloses that 3,4,5,6-tetrachlorophthalic anhydride is treated in an alkaline aqueous solution under pressure at
There are reports of obtaining 2,3,4,5-tetrachlorobenzoic acid by heating in a temperature range of 280°C. However, there is no description regarding fluorides. Whether the method of the above US Pat. No. 2,439,237 is applicable to 3,4,5,6-tetrafluorophthalic acid, which is the starting material in the present invention;
The present inventors conducted a study. As shown in the comparative example according to the above method, decarboxylation reaction was attempted by simply heating 3,4,5,6-tetrafluorophthalic acid in an alkaline aqueous solution. However, trifluorophenol in which a fluorine atom was substituted with a hydroxyl group was mainly produced, and 2,3,4,5-tetrafluorobenzoic acid could not be selectively obtained. That is, −
It can be said that the fluorine atom at the para position of the benzene nucleus, which has an electron-withdrawing group such as the COOH group, is more susceptible to nucleophilic substitution reactions than the chlorine atom at the same position. It is thought that alkaline substances replace fluorine atoms to produce phenols. That is, the method uses 3,4,5, which are the starting materials in the present invention.
It can be said that 6-tetrafluorophthalic acid cannot be used because side reactions tend to occur. Also, 3,
A method for decarboxylating 4,5,6-tetrafluorophthalic acid is described by GG Jacobson et al. in the Journal of General Chemistry.
General Chemistry, Volume 36, Issue 1, 144
(1966) and British Patent No. 2122190. In the former method, the reaction is carried out in a dimethylformamide solvent at a temperature of 145°C, but 2,3,
The yield of 4,5-tetrafluorobenzoic acid is as low as 44.0 mol%, which is unsatisfactory as an industrial production method. In addition, the latter method is also a reaction in an organic solvent, and although it is true that the reaction is carried out at a temperature of 200°C, 2,3,4,5-tetrafluorobenzoic acid is not obtained; Only 0.5% yield of 1,2,3,4-tetrafluorobenzene was obtained. [Objectives] Therefore, the objects of the present invention are 2, 3, 4, 5.
- To provide a new method for producing tetrafluorobenzoic acid. Another object of the invention is to provide 3,4,
The object of the present invention is to provide a new method for producing 2,3,4,5-tetrafluorobenzoic acid in good yield by decarboxylating 5,6-tetrafluorophthalic acid. [Means] In order to solve the above object, the present inventors
As a result of intensive research, the following “2, 3,
They found a method for producing 4,5-tetrafluorobenzoic acid and completed the present invention. (1) In an aqueous medium adjusted to a pH range of 0.7 to 2.2, 3,4,5,6-tetrafluorophthalic acid is mixed with ammonia, an alkali metal or alkaline earth metal hydroxide, carbonate, At least one compound selected from the group consisting of bicarbonates, sulfates, organic acid salts, and fluorides; alkaline earth metal oxides; organic bases and their sulfates is used as a catalyst, and the temperature is 100 to 220°C. 2, 3, characterized in that the decarboxylation reaction is carried out at a temperature in the range of
This is a method for producing 4,5-tetrafluorobenzoic acid. (2) The decarboxylation reaction reduces the pressure of the reaction from 0 to 15 kg/
This is the method described in (1) above, in which carbon dioxide gas generated is extracted from the system while maintaining the temperature at cm ² G. (3) 3,4,5,6-tetrafluorophthalonitrile using an aqueous sulfuric acid solution with a concentration of 30 to 90% by weight.
An aqueous medium containing 3,4,5,6-tetrafluorophthalic acid obtained by hydrolysis in the range of 100 to 180°C is adjusted to a pH range of 0.07 to 2.2, and then an aqueous medium containing sulfate ions is added. 3, 4,
5,6-tetrafluorophthalic acid, ammonia, alkali metal or alkaline earth metal hydroxides, carbonates, bicarbonates, sulfates, organic acid salts and fluorides; alkaline earth metal oxides;
2,3,4,5- characterized in that the decarboxylation reaction is carried out at a temperature in the range of 100 to 220°C using at least one compound selected from the group consisting of organic bases and sulfates thereof as a catalyst. This is a method for producing tetrafluorobenzoic acid. (4) The decarboxylation reaction reduces the pressure of the reaction from 0 to 15 kg/
This is the method described in (3) above, in which carbon dioxide gas generated is extracted from the system while maintaining the temperature at cm ² G. The present invention will be specifically explained below. According to the invention, PH0.7-2.2, preferably
100 to 100 in aqueous medium adjusted to the region of 1.2 to 2.0
3, at a temperature range of 220°C, preferably 120-195°C.
It is preferable to subject 4,5,6-tetrafluorophthalic acid to a decarboxylation reaction. If the PH is outside this range, the selectivity of the target substance 2,3,4,5-tetrafluorobenzoic acid will decrease, and if the PH is outside this range and the reaction temperature is high outside this range, it will be even more significant. This is not preferred because selectivity decreases. PH is
It is influenced by the concentration of 3,4,5,6-tetrafluorophthalic acid as a starting material, the amount of catalyst used, and the concentration of residual sulfate ions. Therefore, in the present invention,
It is required to control the above factors. 3,4,5,6-tetrafluorophthalic acid is preferably added in an amount of 10 to 200 parts by weight, preferably 20 to 120 parts by weight, per 100 parts by weight of the aqueous medium. In the method of the present invention, a catalyst is used to carry out the decarboxylation reaction, but the advantage of using a catalyst is that the reaction can be carried out at a lower temperature than usual, which lowers the spontaneous pressure, and therefore Since an autoclave with low pressure resistance can be used without providing a carbon dioxide removal device, the equipment cost for the autoclave can be reduced. Furthermore, since the reaction can be carried out at a low reaction temperature, corrosion due to generated hydrogen fluoride and the like can be prevented. In the present invention, ammonia, alkaline earth metals and alkali metal hydroxides, carbonates, bicarbonates, sulfates, organic acid salts and fluorides; alkaline earth metal oxides; organic bases and their At least one selected from the group consisting of sulfates
Preferably, a catalytic amount of the seed compound is used.
Since these catalysts affect pH, it is desirable to change the usage ratio depending on the compound. That is, 3, 4, 5, 6 in the aqueous medium described above.
- at the concentration of tetrafluorophthalic acid, 3,
The amount of ammonia, alkaline earth metal and alkali gold sulfates and fluorides, and organic base sulfates is 0.01 to 3.0 mol, preferably 0.05 to 1.0 mol, per 1 mol of 4,5,6-tetrafluorophthalic acid.
molar range, hydroxides, carbonates and organic acid salts of ammonia and oxides, hydroxides, carbonates and organic acid salts of alkaline earth metals from 0.01 to 0.4 mol;
Preferably in the range of 0.05 to 0.25 mol, for alkali metal hydroxides, carbonates and organic acid salts 0.002 to 0.1
mol, preferably in the range of 0.005 to 0.05 mol, and organic base in the range of 0.01 to 1.2 mol, preferably 0.1 to 0.9 mol. When these catalysts are used in combination, the amount of ammonia, alkali metal, alkaline earth metal, and organic base sulfate is 0.01 to 1 mole of 3,4,5,6-tetrafluorophthalic acid.
1.5 mol, preferably in the range of 0.05 to 0.5 mol,
The total amount of other catalysts is preferably in the range of 0.001 to 0.4 mol, preferably 0.005 to 0.25 mol.
Among other catalysts, alkaline earth metal hydroxides, carbonates and organic acid salts are particularly preferred, in which case 3,4,5,6-tetrafluorophthalic acid 1
0.02 to 0.4 mole to mole, preferably 0.05 to
Preferably it is 0.25 mol. By maintaining these ratios, it becomes easy to maintain the pH within the range of the present invention, and moreover, the effect as a catalyst can be obtained. Specific examples of sulfates of ammonia, alkali metals, alkaline earth metals, or organic bases include ammonium sulfate, sodium sulfate, potassium sulfate, rubidium sulfate, cesium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, and pyridine. Examples include sulfates, quinoline sulfates, and sulfates of organic amines. Specific examples of ammonia hydroxides, carbonates, organic acid salts and fluorides include aqueous ammonia, ammonium carbonate, ammonium 3,4,5,6-tetrafluorophthalate, 2,3,4,5
-Ammonium tetrafluorobenzoate, ammonium fluoride, and the like. Among these, aqueous ammonia or ammonium carbonate is usually 3,4,5,6-tetrafluorophthalic acid or its product 2,
It exists as a salt of 3,4,5-tetrafluorobenzoic acid. Specifically, alkaline earth metal oxides, hydroxides, carbonates, organic acid salts, and fluorides:
For example, magnesium oxide, magnesium hydroxide,
Magnesium carbonate, magnesium fluoride, calcium oxide, calcium hydroxide, calcium carbonate,
Calcium fluoride, strontium oxide, strontium hydroxide, strontium carbonate, strontium fluoride, barium oxide, barium hydroxide,
Barium carbonate, barium fluoride, 3, 4, 5, 6
-magnesium tetrafluorophthalate, 3,
Calcium 4,5,6-tetrafluorophthalate, Strontium 3,4,5,6-tetrafluorophthalate, Barium 3,4,5,6-tetrafluorophthalate, 2,3,4,5-tetrafluoro Magnesium benzoate, 2,3,4,5-calcium tetrafluorobenzoate, 2,3,4,
Strontium 5-tetrafluorobenzoate,
Examples include barium 2,3,4,5-tetrafluorobenzoate. During the reaction, these mutually change into salts of 3,4,5,6-tetrafluorophthalic acid or its product 2,3,4,5-tetrafluorobenzoic acid, and the reaction proceeds. As carbon dioxide gas is generated over time, it may exist as a carbonate. Specific examples of alkali metal hydroxides, carbonates, organic acid salts and fluorides include sodium hydroxide, sodium carbonate, sodium fluoride,
Potassium hydroxide, potassium carbonate, potassium fluoride, sodium 3,4,5,6-tetrafluorophthalate, potassium 3,4,5,6-tetrafluorophthalate, 2,3,4,5-tetrafluorobenzoin Examples include sodium acid, potassium 2,3,4,5-tetrafluorobenzoate, and the like. During the reaction, the alkali metal hydroxide is usually 3,4,5,6-tetrafluorophthalic acid,
It exists as a salt or carbonate of 2,3,4,5-tetrafluorobenzoic acid. Specific examples of the organic base include organic amines such as quinoline, isoquinoline, pyridine, triethylamine, trimethylamine, diisopropylamine, piperazine, hexamethylenediamine, and ethylenediamine. The tetrafluorophthalic acid used in the present invention is
For example, tetrachlorophthalonitrile is synthesized by supplying phthalonitrile together with chlorine onto activated carbon at a temperature range of 270 to 350°C, and the obtained tetrachlorophthalonitrile is synthesized by the method described in Japanese Patent Application No. 58-202590. Example 2) can be used to synthesize tetrafluorophthalonitrile by fluorination, and the obtained tetrafluorophthalonitrile can be synthesized by a method of carrying out a hydrolysis reaction. In the present invention, as a hydrolysis method, it is preferable to heat tetrafluorophthalonitrile in a 30 to 90% by weight aqueous sulfuric acid solution at a temperature in the range of 100 to 180°C to obtain tetrafluorophthalic acid. After hydrolysis with an aqueous sulfuric acid solution, the precipitated 3,4,5,6-tetrafluorophthalic acid is usually separated from the aqueous medium by filtration. 3,4,5,6-tetrafluorophthalic acid dissolves at a ratio of 85 parts by weight per 100 parts by weight of water at 25°C.On the other hand, its solubility decreases rapidly in acidic aqueous solutions, so it is simply washed with water. When purification is attempted, a large amount of 3,4,5,6-tetrafluorophthalic acid is dissolved in water, and 3,4,5,6-tetrafluorophthalic acid is dissolved in water.
-It is not preferred because the yield of tetrafluorophthalic acid decreases. The present invention does not require such purification. That is, 3,4,5,6-tetrafluorophthalic acid still containing sulfate ions can be effectively decarboxylated. More specifically, sulfate ions can be present in the hydrolysis reaction solution as sulfuric acid, ammonium hydrogen sulfate, or ammonium sulfate. That is, since ammonium sulfate, which is one of the catalysts for the decarboxylation reaction of the present invention, is present, the decarboxylation reaction can be carried out in the temperature range of 100 to 220°C. More preferably, the sulfuric acid ions and ammonium hydrogen sulfate mixed in the hydrolysis reaction product are ammonia water, an alkali metal hydroxide, an alkaline earth metal oxide or hydroxide, or an organic base. neutralized by etc.,
It is preferable to present them as their respective sulfates and use them as catalysts. In this way, when sulfate ions are changed to sulfate, which is effective as a catalyst, 3, 4, 5, 6
- Subjecting tetrafluorophthalic acid to a decarboxylation reaction can always be very advantageous from an industrial point of view. Therefore, in the present invention, it is particularly preferable to use these sulfates as catalysts. Furthermore, in the present invention, at least one of the above sulfates is used as a catalyst during the decarboxylation reaction, and furthermore, alkali metal and alkaline earth metal hydroxides, carbonates, or organic It is particularly preferable to use at least one of an acid salt, an oxide of an alkaline earth metal, or an organic base together. Among these, it is particularly preferable to coexist an alkaline earth metal oxide, hydroxide, carbonate, or organic acid salt as a cocatalyst. A synergistic effect as a catalyst is achieved by coexisting the above sulfate with at least one of an alkaline earth metal or an alkali metal hydroxide, an organic acid salt or carbonate, an alkaline earth metal oxide, or an organic base. bring about. That is, the reaction rate of 3,4,5,6-tetrafluorophthalic acid can be increased, and 2,3,4,5-tetrafluorobenzoic acid can be obtained in high yield. In addition, alkaline earth metals, alkali metal hydroxides, organic acid salts or carbonates, alkaline earth metal oxides, or organic bases may produce corrosive hydrogen fluoride, which may be produced in small amounts depending on the reaction conditions. It can be a trapping agent. When these are allowed to coexist, the ratio of ammonia, alkali metal, and alkaline earth metal sulfates is 0.01 to 1 mole of 3,4,5,6-tetrafluorophthalic acid.
1.5 mol, preferably in the range 0.05-1.0 mol, alkaline earth metal oxides, hydroxides, carbonates and organic acid salts 0.02-0.4 mol, preferably 0.05-0.25
The molar range of alkali metal hydroxides, carbonates and organic acid salts is from 0 to 0.1 mole, preferably from 0.005 to
in the range of 0.05 mol, and the organic base is 0 to 1.2 mol,
It is preferable to use each in a range of 0.1 to 0.9 mol. For example, in the case of calcium sulfate, 3, 4,
per mole of 5,6-tetrafluorophthalic acid
Preferably, it is present in a range of 0.01 to 1.5 mol,
In particular, good results are obtained when it is present in a range of 0.05 to 1.0 mol. These sulfates are further added with, for example, calcium hydroxide (which exists as calcium hydroxide during preparation, but during reaction, calcium 3,4,5,6-tetrafluorophthalate, 2,3,4,5 -calcium tetrafluorobenzoate or calcium carbonate) is preferably present in an amount of 0.02 to 0.4 mol, particularly 0.05 mol, per mol of 3,4,5,6-tetrafluorophthalic acid. Even better results are obtained when present in the range of ~0.25 mol. In this case, if the amount of co-catalyst is large, trifluorophenol tends to be generated, which is not preferable. If sulfate ions brought in from the hydrolysis reaction are present, part of the co-catalyst will change to sulfate, so these must also be taken into consideration when adding the necessary amount. For example, in the case of calcium hydroxide, a portion is converted to calcium sulfate. Therefore, the remaining calcium content converted to calcium sulfate is the cocatalyst amount. Of course, in the present invention, purified 3,4,5,6-tetrafluorophthalic acid that does not contain sulfate ions can also be used as a raw material for the decarboxylation reaction. In that case, in the present invention, 3,4,5,6-tetrafluorophthalic acid is added in an aqueous medium in the presence of at least one compound selected from ammonia, an alkali metal, an alkaline earth metal, and a sulfate of an organic base as a catalyst. Then, if necessary, a cocatalyst is added to carry out the decarboxylation reaction. In addition, copper, zinc, cadmium,
At least one compound selected from metals such as iron, cobalt, and nickel, oxides, hydroxides, and carbonates, particularly copper powder, cupric oxide, and zinc oxide may be added and used. . Furthermore, any cocatalyst that is commonly used as a catalyst for decarboxylation reactions can be used. In the present invention, 3,4,5,6-tetrafluorophthalic acid is dissolved or partially dispersed in water, and the reaction temperature when performing the decarboxylation reaction in the presence of a catalyst is as follows:
A range of 100 to 220°C is preferred. A temperature range of 130 to 180°C is particularly preferred. When the reaction temperature is high, further decarboxylated 1,
2,3,4-tetrafluorobenzene becomes more likely to be produced, and the yield of 2,3,4,5-tetrafluorobenzoic acid decreases. Also, if the reaction temperature is low,
This is not preferable because the rate of decarboxylation reaction decreases and productivity decreases. The reaction time for the decarboxylation reaction is not particularly limited, but it is desirable to carry out the reaction within a range of 2 to 40 hours, preferably 5 to 30 hours. The generated carbon dioxide gas may be reacted while being successively removed from the system using, for example, a back pressure valve or the like, or the reaction may be performed while the carbon dioxide gas is sealed inside the system. In the former case, the naturally occurring pressure based on carbon dioxide gas can be reduced, and the reaction can be performed under the naturally occurring pressure mainly based on an aqueous medium. For this reason,
Since the reaction can be carried out at low pressure, the pressure resistance of the autoclave can be lowered, thereby further reducing the equipment cost of the autoclave. Thus, when the reaction temperature is in the range of 100-200℃, the naturally occurring pressure can be reduced to 0.
It is preferable to carry out the reaction while removing carbon dioxide gas so as to maintain the temperature at ~15 Kg/cm ² ·G, particularly 1 to 10 Kg/cm ² ·G. In the latter case, in order to confine carbon dioxide gas within the system, the pressure increases as carbon dioxide gas is generated. The final pressure varies depending on the space ratio of the reaction vessel, the amount charged, and the concentration of raw materials charged. However, the influence of pressure is not recognized in the present invention. Water is preferred as the reaction medium, but in some cases, other organic solvents (e.g. alcohols such as methanol, ethanol, isopropanol, butanols, glycols such as ethylene glycol, propylene glycol, dimethylformamide, etc.) may be added to the aqueous medium. etc.) may be added and reacted. After the reaction is completed, for example, when an alkaline earth metal compound is used as a catalyst, it is neutralized with an aqueous sulfuric acid solution to convert all the alkaline earth metal compounds into sulfates, and then 2,3,4,5-tetrafluorobenzoic acid is added. 2, by removing the sulfate by hot filtration at a temperature above the precipitation temperature, and then cooling to room temperature.
A precipitate of 3,4,5-tetrafluorobenzoic acid is obtained, which can be removed from the aqueous medium by means such as eg filtration, which is a common method. 2, 3, obtained in this way
The crystals of 4,5-tetrafluorobenzoic acid contain water, and therefore a small amount of aqueous inorganic compounds such as ammonium sulfate remain. As a method for purifying and removing these substances, simply washing with water may be used. Furthermore, another method is to extract 2,3,4,5-tetrafluorobenzoic acid from an aqueous medium using a solvent such as ethers or ketones. After extraction, the solvent was removed by evaporation to dryness and 2,3,
4,5-tetrafluorobenzoic acid can be extracted. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. Example 1 3,4,5,6-tetrafluorophthalic acid containing no sulfate ions in the autoclave of 1
150 g (0.63 mol), 8.6 g (0.088 mol) sulfuric acid, 14.0 g (0.189 mol) calcium hydroxide, and 500 g water
[Calcium sulfate reacts after preparation]
It can be said that it has changed to 0.088 mol, and 0.101 mol equivalent to organic acid calcium, calcium carbonate, or calcium hydroxide. ] [PH at the time of preparation is 1.65 (70℃)],
Thereafter, the mixture was heated and stirred at 160°C for 16 hours to cause a reaction.
The final pressure was 35.5Kg/cm ² ·G. After the reaction
The mixture was cooled to 70°C and neutralized by adding 39.2 g of 30% sulfuric acid, and then filtered while hot while being kept at 70°C to remove solids such as calcium sulfate. The precipitate was then cooled to room temperature, filtered, washed with water and dried to give white 2,3,4,5-tetrafluorobenzoic acid.
110.2 g [yield 90.2 mol% of 3,4,5,6-tetrafluorophthalic acid] was obtained. mp 86-87℃ Elemental analysis value C (%) H (%) F (%) Logical value 43.30 1.03 39.18 Analysis value 43.4 1.2 39.2 In addition, the filtration was extracted with ether and 2, 3, 4,
An additional 7.1 g of 5-tetrafluorobenzoic acid was recovered. Calculated from both the filtered and extracted products, 2,3,4,5-
It can be said that 96.0 mol% of tetrafluorobenzoic acid was produced. Example 2 3,4,5,6-tetrafluorophthalic acid 150
The reaction was carried out in the same manner as in Example 1, except that 500 g of water and 54.2 g (0.315 mol) of calcium sulfate dihydrate as a catalyst were charged, and the mixture was heated and stirred at 170°C for 14 hours [PH at the time of charging was 1.37 ( 70℃].
The product after the reaction was separated in the same manner as in Example 1, and calculated in the same manner as 2,3,4,5-tetrafluorobenzoic acid.
86.4 mol% was obtained. Example 3 3,4,5,6-tetrafluorophthalic acid containing no sulfate ions in the autoclave of 1
150g (0.630mol), ammonium sulfate 29.1g
(0.220 mol) and 500 g of water were heated and stirred at 160°C for 21 hours to react [PH at the time of preparation was 1.74].
(30℃)]. After the reaction is completed, the suspension is cooled to room temperature,
After that, it is filtered, washed with water, and then dried.2, 3, 4, 5
- Tetrafluorobenzoic acid was obtained. 2,3,4,5- calculated from both the filtered product and the extracted product in the same manner as in Example 1.
85.8 mol% of tetrafluorobenzoic acid was obtained. Example 4 200 g (1.0 mol) of 3,4,5,6-tetrafluorophthalonitrile and 450 g of sulfuric acid were placed in flask 1.
and 391 g of water were added and heated and stirred under reflux for 17 hours. After the reaction was completed, the obtained 3, 4, 5,
The precipitate of 6-tetrafluorophthalic acid was filtered. Analysis of the cake revealed that in addition to 3,4,5,6-tetrafluorophthalic acid, 5.0% by weight of sulfuric acid,
It contained 2.0% by weight of ammonium sulfate and 7.2% by weight of water.
Of the 263 g of cake, 175 g (150 g as tetrafluorophthalic acid) was taken and charged into autoclave 1. Additionally, 14.0g of calcium hydroxide
(0.189 mol) and 500 g of water were heated and stirred at 160°C for 18 hours to perform a decarboxylation reaction [at the time of preparation].
PH is 1.90 (70℃)]. Thereafter, the same procedure as in Example 1 was carried out to obtain white 2,3,4,5-tetrafluorobenzoic acid. Calculated in the same manner as in Example 1, 2,3,4,5-tetrafluorobenzoic acid to 3,4,5,6-tetrafluorophthalic acid
Example 5 with a concentration of 96.4 mol% Same as in Example 1 except that the reaction was carried out at a constant pressure of 6 kg/cm ² G while extracting the generated carbon dioxide using an autoclave equipped with a pressure-resistant condenser and a back pressure valve. and reacted. After the reaction was completed, the product was separated in the same manner as in Example 1 and calculated in the same manner to obtain 96.3 mol% of 2,3,4,5-tetrafluorobenzoic acid. Example 6 3,4,5,6-tetrafluorophthalic acid 238
Thereafter, the same procedure as in Example 1 was carried out, except that 13.8 g (0.140 mol) of sulfuric acid, 5.5 g (0.042 mol) of ammonium sulfate, 22.2 g (0.30 mol) of calcium hydroxide, and 480 g of water were charged. 2,
3,4,5-tetrafluorobenzoic acid 95.4 mol%
[PH at the time of preparation was 1.89 (70℃)]. Example 7 3,4,5,6-tetrafluorophthalic acid 238
Thereafter, the same procedure as in Example 1 was carried out to obtain 86.5 mol% of 2,3,4,5-tetrafluorobenzoic acid, except that 11.1 g (0.15 mol) of calcium hydroxide and 480 g of water were charged. The pH at the time is 1.52 (30
℃)]. Example 8 3,4,5,6-tetrafluorophthalic acid 238
The reaction product was separated in the same manner as in Example 1, except that 480 g of water and 480 g of water were charged and the reaction was carried out at 190°C for 8 hours to obtain 87.5 mol% of 2,3,4,5-tetrafluorobenzoic acid. [PH at the time of preparation was 1.33 (30℃)]. Examples 9 to 15 Examples 9, 10 and 14 were reacted and operated in the same manner as in Example 1, except that the catalyst, reaction temperature and reaction time were as shown in Table 1, and the results shown in Table 1 were obtained. The reaction and operation were carried out in the same manner as in Example 1, and the results shown in Table 1 were obtained. In Examples 11 and 12, the catalyst, reaction temperature, and reaction time were as shown in Table 1.
After the reaction was completed, neutralization was carried out in the same manner as in Example 1, and other operations were carried out in the same manner as in Example 3.
I got the result. Examples 13 and 15 were reacted and operated in the same manner as in Example 3, except that the catalyst, reaction temperature and reaction time were as shown in Table 1, and the results shown in Table 1 were obtained.

[Table] Comparative Example 1 3.0 g (0.0126 mol) of 3,4,5,6-tetrafluorophthalic acid, which does not contain sulfate ions, and 0.5 g of sodium hydroxide in a 100 cc autoclave.
(0.0125 mol) and 50 g of water and heated to 200℃ for 25 minutes.
I let it react over time. After the reaction was completed, it was cooled to room temperature, extracted with 150 ml of diisopropyl ether, and analyzed using a gas chromatograph using a column packing material of SE52.2m and a column bath temperature of 50°C.
For 4,5,6-tetrafluorophthalic acid,
2.9 mol% of 1,2,3,4-tetrafluorobenzene and 89.1 mol% of trifluorophenol were obtained, and almost no 2,3,4,5-tetrafluorobenzoic acid was obtained [PH 2.75 at the time of preparation. (twenty five
℃)]. Comparative Example 2 1. 29.1 mol% of 2,3,4-tetrafluorobenzene and 60.3 mol% of trifluorophenol were obtained [PH2.55 at the time of preparation (70
℃)]. Comparative Example 3 Calcium sulfate was not present as a catalyst during the reaction, and only 23.4 g (0.316 mol) of calcium hydroxide was used as a catalyst.
The procedure was repeated in the same manner as in Example 1, except that the mixture was charged and reacted at 160°C for 18 hours. As a result, 24.7 mol% of unreacted 3,4,5,6-tetrafluorophthalic acid, 2,3,4,5-tetrafluorobenzoic acid
60.6 mol%, trifluorophenol 9.1 mol%
[PH2.30 (70℃) at the time of preparation]

Claims (1)

[Scope of Claims] 1. 3,4,5,6-tetrafluorophthalic acid is mixed with ammonia, alkali metal or alkaline earth metal hydroxide in an aqueous medium adjusted to a pH of 0.7 to 2.2. , carbonates, bicarbonates, sulfates,
Decarboxylation at a temperature in the range of 100 to 220°C using at least one compound selected from the group consisting of organic acid salts and fluorides; oxides of alkaline earth metals; organic bases and their sulfates as a catalyst. A method for producing 2,3,4,5-tetrafluorobenzoic acid, which comprises reacting it. 2 The decarboxylation reaction reduces the pressure of the reaction from 0 to 15 kg/
The method according to claim 1, wherein the carbon dioxide gas generated is extracted from the system while maintaining the temperature at cm ² G. 3 3,4,5,6-tetrafluorophthalonitrile using a sulfuric acid aqueous solution with a concentration of 30 to 90% by weight
An aqueous medium containing 3,4,5,6-tetrafluorophthalic acid obtained by hydrolysis in the range of 100 to 180°C is adjusted to a pH range of 0.7 to 2.2, and then the aqueous medium containing sulfate ions is 3,4,5,6-Tetrafluorophthalic acid can be added to ammonia, alkali metal or alkaline earth metal hydroxides, carbonates, bicarbonates, sulfates, organic acid salts and fluorides; Oxide; at least one selected from the group consisting of organic bases and sulfates thereof
1. A method for producing 2,3,4,5-tetrafluorobenzoic acid, characterized in that the decarboxylation reaction is carried out at a temperature in the range of 100 to 220°C using a seed compound as a catalyst. 4 The decarboxylation reaction reduces the pressure of the reaction from 0 to 15 kg/
The method according to claim 3, wherein the carbon dioxide gas generated is extracted from the system while maintaining the temperature at cm ² G.