JP2590206B2 - Method for producing 8-hydroxyquinoline-7-carboxylic acid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing 8-hydroxyquinoline-7-carboxylic acid.

2. Description of the Related Art 8-Hydroxyquinoline-7-carboxylic acid is a compound that has recently attracted attention as a chelating agent for separating rare metals [Int. J. Nucl. Med. Biol., 9 (1), 1-11]. (198
2)].

Conventionally, the following method has been reported as a method for producing 8-hydroxyquinoline-7-carboxylic acid.

(1) 8-hydroxyquinoline, sodium salt of carbon dioxide under pressure, 140 to 150 ° C., a method of heating 7-8 hours [Bar. 20
217 (1887)].

(2) A method of heating 8-hydroxyquinoline potassium salt in a dimethylformamide solvent at 160 ° C. under a normal pressure of carbon dioxide gas [J. Chem. Eng. Data., 14 (3), 388 (196)
9)].

(3) 8-hydroxyquinoline potassium salt is added to carbon dioxide gas 20
kg / cm ² · G under pressure, in dimethylformamide solvent, 160
Heating at ° C [Synthetic Organic Chemistry, 26 (5), 439 (196
8)].

(4) A method of mixing 8-hydroxyquinoline and potassium carbonate at least three times the molar amount of 8-hydroxyquinoline and heating at 200 to 140 kg / cm ² · G at 200 ° C. under carbon dioxide pressure [J. Org. Chem. 19 , 510 (1954)].

However, in the above method (1), the generated 8-
The structure of the hydroxyquinoline carboxylic acid is not specified, and the reaction pressure for selectively and economically providing the target product is not specified. Further, the reaction time is as long as 7 to 8 hours, which is not economical.

For example, according to the study by the present inventors, under the reaction conditions disclosed in the above-mentioned literature, a pressure exceeding 40 kg / cm ² · G is required to obtain the desired product, and the yield is 20 to 30%. It was low.

Furthermore, when 8-hydroxyquinoline sodium salt was used as a raw material, 8-hydroxyquinoline was released when the reaction temperature exceeded 180 ° C., and the desired product could not be obtained in high yield.

In the methods (2) and (3), since an aprotic polar solvent such as dimethylformamide is used as a solvent, the raw material and the potassium salt of the product are dissolved in dimethylformamide, and the reaction is performed in a homogeneous system. After the reaction, when isolating 8-hydroxyquinoline-7-carboxylic acid as the target substance from the reaction mixture, dimethylformamide dissolves the target substance unless the target substance is diluted with a large amount of water and precipitated by acid precipitation. The yield of the target decreases. Further, since dimethylformamide is well mixed with water, a large amount of water must be removed by distillation or the like in order to recover dimethylformamide from the filtrate and reuse it.

According to the description of the literature describing the above methods (2) and (3), the yields of the desired product are 57% and 7%, respectively, which are still insufficient. Further, according to the present inventors, when the reaction temperature was increased to 170 ° C. or higher in order to increase the yield, decomposition of dimethylformamide occurred, and unfavorable results were obtained.

In the method (4), in order to obtain 8-hydroxyquinoline-7-carboxylic acid with good yield, it is necessary to use potassium carbonate in excess, and a high pressure is required.

As a method for separating the target substance from the reaction mixture, a method in which an aqueous solution of the reaction mixture is adjusted to pH 4.7 and the resulting precipitate is purified by recrystallization [J. Chem. Eng. Data, 14 (3), 388 (196)
9)], a method in which the pH of the aqueous solution of the reaction mixture is adjusted to pH 1 or lower with hydrochloric acid, and the formed precipitate is filtered off [Synthetic Organic Chemistry, 26 (5), 439].
(1968)].

According to the present inventor, at pH 4.7, unreacted 8-hydroxyquinoline remains in the precipitated crystals, and the purity is low and a purification operation such as recrystallization is required. It was found that -7-carboxylic acid was redissolved as quinolinium ion and the yield was reduced.

DISCLOSURE OF THE INVENTION The present invention provides an improved method for producing 8-hydroxyquinoline-7-carboxylic acid in high yield by reacting 8-hydroxyquinoline potassium salt with carbon dioxide gas. Is what you do.

Means for Solving the Problems The present invention relates to a reaction temperature of 170 to 250 ° C. and a carbon dioxide gas pressure of 1 in the absence of an aprotic polar solvent when heating and reacting 8-hydroxyquinoline potassium salt under carbon dioxide gas pressure. 8 characterized by performing in the range of ~ 40kg / cm ² · G
-Hydroxyquinoline-7-carboxylic acid.

The second invention in the present application is a method for producing a polymer in the presence of a hydrophobic solvent.
8-hydroxyquinoline potassium salt was added under carbon dioxide gas pressure.
A method for producing 8-hydroxyquinoline-7-carboxylic acid, wherein the reaction is carried out by heating under the above conditions.

 Hereinafter, the present invention will be described in detail.

8-Hydroxyquinoline potassium salt as a starting material for the reaction of the present invention can be prepared by the following method.
8-Hydroxyquinoline and potassium hydroxide are reacted with water or a lower alcohol such as methanol or ethanol as a solvent, and then the solvent and the generated water are distilled off by heating to obtain 8-hydroxyquinoline potassium salt. .

In the step of producing the potassium salt of 8-hydroxyquinoline, when a hydrophobic solvent is used in the subsequent reaction step with carbon dioxide, the same hydrophobic solvent as the hydrophobic solvent to be used is used as the reaction solvent. Can also be used.
Thereby, the dispersion and contact of the reaction raw materials can be sufficiently performed by stirring, and the crystals can be prevented from becoming too large or solidified, and the reaction proceeds favorably. .

Since the neutralization reaction between 8-hydroxyquinoline and potassium hydroxide proceeds in the azeotropic dehydration step, even if the neutralization reaction is still incomplete, the process proceeds to the next azeotropic dehydration step. No problem.

As a method for removing by-produced water or water or a lower alcohol used as a solvent for potassium hydroxide from a reaction product obtained by reacting 8-hydroxyquinoline and potassium hydroxide, the reaction mixture is subjected to reduced pressure. Alternatively, there is a method in which water is distilled off by heating under normal pressure. At this time, if an azeotropic solvent is used, dehydration can be performed more quickly and completely. Examples of the azeotropic solvent used for this purpose include various solvents such as benzene, toluene, methanol, and ethanol.

When an azeotropic solvent is not used, the solution is concentrated and finally dried in vacuum at 100 to 150 ° C. to obtain a yellow solid of 8-hydroxyquinoline potassium salt. Next, the yellow solid of 8-hydroxyquinoline potassium salt is pulverized to not more than 20 mesh, preferably not more than 100 mesh by a ball mill or the like, and is subjected to a reaction with carbon dioxide.

The reaction with carbon dioxide largely depends on the reaction temperature and the pressure of carbon dioxide. The reaction temperature is 170-250 ° C, preferably 180
~ 230 ° C. Reaction pressure is 1kg / cm ²・ G ~ 40kg / cm ²・
G, preferably 3 to 30 kg / cm ² · G. Within this range, the yield of the target product can be 68% or more.

Reaction temperature is less than 170 ° C or carbon dioxide pressure is 1kg / cm ²
-If it is less than G, the conversion rate of the reaction is low, and it becomes necessary to recover a large amount of raw material 8-hydroxyquinoline, which is not economical. On the other hand, if the reaction temperature exceeds 250 ° C., the yield of the target product is reduced, and 8-hydroxyquinoline is liberated, the product is colored, and carbides are formed, which is not preferable.

Even if the pressure of the carbon dioxide gas during the reaction exceeds 40 kg / cm ² · G, the yield of the desired product hardly changes and there is no substantial economic advantage. If the reaction temperature and pressure are within the range of the present invention described above,
The reaction proceeds promptly in 1 to 5 hours.

Addition of a hydrophobic solvent that does not participate in the reaction during the reaction improves the reproducibility of the reaction by promoting heat transfer and mass transfer during the reaction, and facilitates handling of the reaction mixture. Bring.

That is, the second invention in the present application, in the presence of a hydrophobic solvent, 8-hydroxyquinoline potassium salt at a reaction temperature of 170 to 250 ° C, preferably 180 to 230 ° C under carbon dioxide gas pressure,
Reaction pressure ^{1~40kg / cm 2 · G, 2} · preferably 3 to 30 kg / cm
A method for producing 8-hydroxyquinoline-7-carboxylic acid, which comprises reacting with G.

Examples of such a hydrophobic solvent include benzene, toluene, xylene, naphthalene, biphenyl, methylnaphthalene, ethylnaphthalene, isopropylnaphthalene, ethylbiphenyl, diethylbiphenyl, and quinoline.
Aromatic hydrocarbons and heteroaromatic compounds which become liquids below 170 ° C, aliphatic and alicyclic hydrocarbons such as hexane, heptane, ligroin and cyclohexane, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and ethers such as diphenyl ether And the like.

These hydrophobic solvents are 8-hydroxyquinoline potassium salt and the product, 8-hydroxyquinoline-7-
It hardly dissolves the potassium carboxylate and therefore takes the form of a slurry. Therefore, after the reaction, since the solvent and the crude product can be easily separated by a filtration operation, it is easy to recover the solvent. Even if the crude product is charged into water together with the solvent, the non-aqueous solvent can be easily separated because it is insoluble in water.

On the other hand, alcohols as solvents to be added during the reaction with carbon dioxide gas inhibit the reaction, and aprotic polar solvents such as dimethylformamide dissolve the potassium salt and are easily soluble in water. Recovery and separation from the product are difficult and unsuitable.

These hydrophobic solvents can be used alone or as a mixture. The amount of the solvent used for this purpose is 8
1 to 1 part by weight of hydroxyquinoline potassium salt
~ 20 parts by weight is sufficient.

When a hydrophobic solvent is used after the completion of the reaction, the solvent is removed by filtration, solvent washing, or the like, and the separated reaction mixture powder is dissolved in water to obtain an aqueous solution. Subsequently, a mineral acid such as hydrochloric acid or sulfuric acid is added for acid precipitation. At this time, 8-hydroxyquinoline and 8-hydroxyquinoline-7-
Utilizing the fact that carboxylic acid is an amphoteric electrolyte, the desired 8-hydroxyquinoline-7-
A carboxylic acid can be obtained.

That is, in the purification method of the obtained product, the reaction product is dissolved in water to form an aqueous solution, and first, unreacted 8-hydroxyquinoline is released at pH 6.5 to 10.0, preferably pH 7 to 9, and filtered. 8-Hydroxyquinoline released by solvent extraction or the like is removed. Subsequently, pH 2 to 6, preferably pH 2 to
By setting it to 4, 8-hydroxyquinoline-7-carboxylic acid is precipitated and separated.

The amount of water added to the mixture is 3 to
The weight is 50 times, preferably 5 to 20 times the weight. When dissolving the reaction mixture in water, the reaction mixture is heated to room temperature or heated to 50 to 60 ° C. Even if some insolubles remain, the present invention can be achieved by heating and stirring at the time of acid precipitation.

As the acid that can be used when the pH is adjusted to 6.5 to 10.0, any water-soluble Brenstead acid can be used. For example, inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid and carbonic acid, organic acids such as acetic acid and propionic acid and the like can be exemplified. Further, carbon dioxide gas may be blown into the aqueous solution of the reaction mixture.

When adding the acid, it can be performed at room temperature or by heating. The pH of the aqueous solution of the reaction mixture is over 10. First, the pH is adjusted to 6.5 to 10.0, preferably pH 7 to 9, with the above-mentioned mineral acid, and unreacted 8-hydroxyquinoline is precipitated. If the pH at this time exceeds 10, precipitation of 8-hydroxyquinoline is not sufficient, and the purity of the subsequent 8-hydroxyquinoline-7-carboxylic acid decreases. When the pH falls below 6.5, precipitation of 8-hydroxyquinoline-7-carboxylic acid starts,
Later, the recovery rate of the target product decreases.

To remove the precipitated 8-hydroxyquinoline, a usual filtration operation or solvent extraction can be performed.
As an extraction solvent to be used, benzene, toluene, xylene, aromatic hydrocarbons such as methylnaphthalene, hexane,
Cyclohexane, aliphatic or alicyclic hydrocarbons such as ligroin, dichloromethane, aliphatic halides such as chloroform, diethyl ether, ethers such as diphenyl ether, ketones such as methyl ethyl ketone,
Esters such as ethyl acetate and butyl acetate and the like can be exemplified.

When a hydrophobic solvent is used in the reaction with carbon dioxide, it can be used as it is as an extraction solvent. That is, the reaction mixture dispersed in the hydrophobic solvent is poured into water without separating the solvent, and the aqueous layer is adjusted to pH 6.5 to 10 with a mineral acid or the like at room temperature or with heating, and the released 8-hydroxyquinoline is released. Is a method of separating

A mineral acid such as sulfuric acid is again added to the aqueous solution after removing 8-hydroxyquinoline to adjust the pH to 2 to 6, preferably 2 to 4, to precipitate 8-hydroxyquinoline-7-carboxylic acid. If the pH is higher than 6, the precipitation of the target product is insufficient, and the recovery rate decreases. On the other hand, when the pH is lower than 2, an acid more than necessary for neutralization is used, which is not economical. Further, since the target substance is an amphoteric electrolyte, it is dissolved again and the recovery rate is reduced.

When a small amount of unseparated 8-hydroxyquinoline is contained in this aqueous solution, it is effective to adjust the pH to 2 to 4 to separate 8-hydroxyquinoline-7-carboxylic acid.

This is because the remaining 8-hydroxyquinoline, which is an amphoteric electrolyte, is completely ionized at pH 4 or less and dissolved in water, so that the purity of precipitated 8-hydroxyquinoline-7-carboxylic acid is improved.

Once the aqueous solution of the reaction mixture obtained by the reaction with carbon dioxide is
It is also possible to collect 8-hydroxyquinoline-7-carboxylic acid, which is the target substance, at once at a pH of 2 to 4 without performing the operation of removing the 8-hydroxyquinoline by limiting the pH to 6.5 to 10. That is, this purification method is a method in which an acid is added to an aqueous solution of a reaction mixture to adjust the pH to 2 to 4, thereby precipitating and separating 8-hydroxyquinoline-7-carboxylic acid.

Unreacted 8-hydroxyquinoline is dissolved as quinolium ions at a pH of 4 or less, so that only 8-hydroxyquinoline-7-carboxylic acid, which is the target substance, can be precipitated. If the pH is lower than 2, the target substance dissolves and the recovery rate decreases. If the pH exceeds 4, crystals of 8-hydroxyquinoline remain, and the purity of the target product decreases. The separation method of the present invention is more advantageous as the content of the target substance in the reaction mixture is higher.

Separation of the precipitated 8-hydroxyquinoline-7-carboxylic acid is carried out by a conventional filtration operation, and if necessary, washing with the same acid-dilute solution used for acid precipitation at pH 2 to 4, followed by washing with water To isolate the desired 8-hydroxyquinoline-7-carboxylic acid.

Examples Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 Potassium hydroxide (15.2 g, purity 85%) was dissolved in water (350 ml), and raw material 8-hydroxyquinoline (33.5 g) was added. The mixture was heated to 40 to 50 ° C. and stirred at the same temperature until a homogeneous solution was obtained. . This solution was concentrated under reduced pressure, and further dried under vacuum at 150 ° C. and 5 mmHg for 2 hours to obtain 42 g of 8-hydroxyquinoline potassium salt.
I got

The obtained 8-hydroxyquinoline potassium salt was pulverized with a ball mill to 100 mesh or less, and 1.0 g thereof was charged into a 10 cc autoclave containing a glass inner tube. After replacing the inside of the autoclave several times with carbon dioxide, carbon dioxide is 7 kg / cm ²
-Heated to 230 ° C under G pressure and kept at the same temperature for 2 hours.

As the reaction progresses, carbon dioxide is consumed and the pressure drops, so supplement the carbon dioxide from outside and always keep 10 kg / cm ²
The G pressure was maintained. After the temperature and pressure were reduced, the reaction mixture was dissolved in 20 ml of warm water, and 8-hydroxyquinoline-7-carboxylic acid and 8-hydroxyquinoline were quantified by an internal standard method using high performance liquid chromatography. As a result, it was found that 8-hydroxyquinoline-7-carboxylic acid, which was the target substance, was produced at a yield of 87.2%, and 8-hydroxyquinoline was recovered at 7.0 mol%.

Examples 2 to 6 In the same manner as in Example 1, 8-hydroxyquinoline potassium salt was prepared, pulverized, charged into an autoclave, and reacted under the conditions shown in Table 1 under carbon dioxide gas pressure. After the reaction, the same post-treatment and analysis of the product as in Example 1 were performed. Table 1 shows the reaction conditions and results.

Comparative Examples 1 and 2 8-Hydroxyquinoline potassium salt was prepared in the same manner as in Example 1, and after pulverization, charged in an autoclave and reacted under the conditions shown in Table 1 under carbon dioxide gas pressure. After the reaction, the same post-treatment and analysis of the product as in Example 1 were performed. Table 1 shows the reaction conditions and results.

Comparative Examples 3, 48 5.12 g of 8-quinolinol were dispersed in 50 cc of water,
9.22ml of 4N NaOH (f = 1.004) aqueous solution while heating and stirring
And further stirred at the same temperature until a homogeneous solution was obtained.
The pH at this time was 11.3.

This solution was concentrated under reduced pressure and dried under vacuum at 150 ° C. and 5 mmHg for 2 hours to obtain 5.2 g of 8-hydroxyquinoline sodium salt.

The obtained 8-hydroxyquinoline sodium salt was pulverized with a ball mill, and reacted in the same manner as in Example 1 under carbon dioxide gas pressure under the conditions shown in Table 1. The obtained reaction mixture was dissolved in 50 cc of a 1N aqueous solution of NaOH, and the product was analyzed in the same manner as in Example 1. Table 1 shows the results.

Comparative Examples 5 and 6 15 g of 8-hydroxyquinoline and 3 times the molar amount of potassium carbonate of 8-hydroxyquinoline were placed in a dry nitrogen atmosphere.
The mixture was pulverized and mixed with milk stick, and about 20 g thereof was charged into an autoclave having an internal volume of 200 cc. After replacing the inside of the autoclave several times with carbon dioxide gas, the reaction was carried out under carbon dioxide gas pressure under the conditions shown in Table 1. The reaction mixture was poured into 200 cc of water, the remaining potassium carbonate was neutralized to pH 6 using 2N sulfuric acid, and a 1N aqueous KOH solution was added to make a homogeneous solution. The product in this solution was analyzed in the same manner as in Example 1.

Example 7 10 g of 8-hydroxyquinoline potassium salt and 30 g of kerosene prepared in the same manner as in Example 1 were charged into an autoclave having an internal volume of 200 cc. After replacing the inside of the autoclave several times with carbon dioxide, carbon dioxide was charged to 10 kg / cm ² · G, and the mixture was stirred until the pressure became constant. Continue heating to 200 ° C, supplementing the carbon dioxide consumed in the reaction.
The mixture was stirred at 10 ° C. and 10 kg / cm ² · G for 2 hours. After the temperature and pressure were lowered, the reaction mixture was added to 200 cc of water, and heated and stirred at 50 to 60 ° C. After separating the organic layer, the obtained aqueous solution was washed twice with 100 ml of toluene. The analysis of the product in the aqueous solution was carried out in the same manner as in Example 1. Table 2 shows the reaction conditions and the results.

Examples 8 and 9 A mixed solvent of diphenyl ether and biphenyl and a mixture of ethyl biphenyl were used as solvents.
The reaction was carried out in the same manner as in Example 7, except that the temperature was changed to 0 ° C. Table 2 shows the reaction conditions and the results.

Example 10 7.2 g of potassium hydroxide was dissolved in 50 ml of methanol, followed by 7.9 g of 8-hydroxyquinoline and 10 ml of ethyl biphenyl.
The suspension was subjected to dehydration distillation while raising the temperature to 80 to 150 ° C. in a nitrogen atmosphere to distill off methanol and by-product water. After cooling, about 42 g of the suspension was charged into an autoclave having an internal volume of 200 ml, except for a part of the above-mentioned ethyl biphenyl. Subsequently, stirring was carried out in the same manner as in Example 7 at 230 ° C. and 10 kg / cm ² · G for 2 hours. Post-treatment and analysis of the reaction product were performed in the same manner as in Example 7. Table 2 shows the reaction conditions and the results.

Comparative Example 7 A suspension of 8-hydroxyquinoline potassium salt and ethyl biphenyl was prepared in the same manner as in Example 10, and after dehydration, stirred at 200 ° C. for 3 hours while circulating carbon dioxide gas from a gas holder under normal pressure. Was performed.

Post-treatment and analysis of the reaction product were carried out as in Example 7. Table 2 shows the reaction conditions and results.

A method for separating and purifying the target product 8-hydroxyquinoline-7-carboxylic acid from the reaction products obtained in Examples 1 to 10 will be described with reference to the following Reference Examples.

Reference Example 1 A content of 15.9 g of 8-hydroxyquinoline potassium salt was 200
The same operation as in Example 1 was carried out except that the autoclave of cc was charged. 280 ml of a brown homogeneous aqueous solution was obtained (pH 10.5). To this was added 10.34 ml of 0.5N HCl aqueous solution (f = 1.065), and the pH was adjusted to 8.
05.

The aqueous solution was washed twice with 70 ml of ethyl acetate,
157.6 ml of 0.5N HCl was added to adjust the pH to 2.2. The crystals produced by the acid precipitation were collected by filtration, washed with 200 ml of a pH 2.1 aqueous HCl solution, and further washed with 100 cc of pure water.

The resulting yellow cake was vacuum dried at 60 ° C. to give 15.3 g of a yellow solid. The elemental analysis value of the yellow solid was Found: C 58.23; H 4.20; N 6.93 Calcd for C ₁₀ H ₇ NO ₃ .H ₂ O: C 57.99; H 4.35; N 6.76.

Further, when the amount of water vaporized at 150 ° C. in a dry nitrogen stream was determined by the Karl Fischer method, the water content was found to be 8.7.
%Met. Therefore, the obtained yellow solid was 8-hydroxyquinoline-7-carboxylic acid monohydrate.

The yellow solid was further vacuum-dried at 150 ° C. to obtain 13.9 g of a white solid (yield based on charged 8-hydroxyquinoline potassium salt: 84.9%, purity: 99.6%).

Elemental analysis Found: C 63.55; H 3.53; N 7.69: Calcd for C 10 H 7 NO 3: C 63.51; H 3.73; N 7.40; mp ^{254~256 ℃ 1 H NMR (DMSO-} d 6, 90MHz) 7.32 ( 1H, d = 9Hz), 7.80 (1H, dd = 4Hz, 4Hz), 7.92 (1H,
d, J = 9Hz), 8.61 (1H, dd, J = 9Hz, 2Hz), 8.92 (1H, dd, J
= 5Hz, 2Hz). Reference Example 2 Using the reaction mixture aqueous solution obtained in Example 5, 8-hydroxyquinoline-7-carboxylic acid was isolated. To 40 cc of the above aqueous solution, 0.17 ml of a 2N H ₂ SO ₄ (f = 1.007) aqueous solution was added to adjust the pH to 7.70, and the mixture was washed twice with 20 ml of ethyl acetate.
To the resulting aqueous solution was further added 3.01 ml of a 2N H ₂ SO ₄ aqueous solution.
The pH was adjusted to 2.38.

After filtering off the crystals, the crystals were washed with 30 ml of dilute aqueous sulfuric acid solution at pH 2,
Further, it was washed with 10 ml of pure water. 150 yellow cake obtained
Vacuum drying was performed at 2 ° C. for 2 hours to obtain 0.846 g of a white solid (yield: 77.7%, purity: 99.6%).

Reference Example 3 Water (300 ml) was added to the suspension of the reaction mixture obtained in Example 9 to dissolve the suspension solid in water. 2N H ₂ SO ₄ (f =
1.007) to adjust the pH to 7.72. 100 more, excluding oil layer
After washing twice with ml ethyl acetate, the resulting aqueous solution was adjusted to pH 2.40 by adding 26.8 ml of a 2N H ₂ SO ₄ aqueous solution.

The generated crystals are filtered off, and a sulfuric acid dilute aqueous solution of pH 2.6 100c
c. Further, the solid was washed with 100 cc of pure water to obtain a yellow solid. The yellow solid was dried under vacuum at 120 ° C. for 2 hours to obtain 8.33 g of a white solid (yield based on charged 8-hydroxyquinoline potassium salt: 77.5%, purity: 99.7%).

Reference Example 4 2N H ₂ SO 4 was added to 50 ml of the reaction mixture aqueous solution obtained in Example 3.
₄ (f = 1.007) 3.22 ml of an aqueous solution was added to adjust the pH to 2.32. The generated crystals were collected by filtration, washed with 40 ml of a dilute aqueous sulfuric acid solution of pH 2, and further washed with 30 cc of pure water. The obtained yellow cake was vacuum-dried at 150 ° C. to obtain 0.990 g of a white solid (yield 84%, purity 98.8%).

Comparative Example of Reference Example 2.40 ml of a 2N H ₂ SO ₄ aqueous solution (f = 1.007) was added to 40 ml of an aqueous solution of a reaction mixture obtained by performing a reaction in the same manner as in Example 5 to adjust the pH to 4.81. The obtained crystals were separated by filtration and washed with 50 ml of a dilute aqueous solution of sulfuric acid at pH 4.9 and further with 30 ml of pure water.

Dissolve the obtained yellow cake in 100 ml of N / 2KOH aqueous solution,
The contents were quantified by an internal standard method using high performance liquid chromatography. As a result, the yield of 8-hydroxyquinoline-7-carboxylic acid was 75 mol%, and the purity was 89.0%.
Met.

On the other hand, when a 12N HCl aqueous solution was added to 40 ml of an aqueous solution of the reaction mixture obtained by carrying out the reaction in the same manner as in Example 5 to adjust the pH to 1 or less, all the crystals precipitated once were dissolved to form a uniform brown solution.

Effect of the Invention According to the present invention, 8-hydroxyquinoline-7-carboxylic acid, which is expected to be used as a chelating agent for separating rare metals, can be produced at low cost.

Claims (2)

(57) [Claims] 1. A potassium salt of 8-hydroxyquinoline is prepared under a carbon dioxide gas pressure in the absence of an aprotic polar solvent at a reaction temperature of 170 to 250 ° C. and a carbon dioxide gas pressure of 1 to 40 kg / cm ² · G. A method for producing 8-hydroxyquinoline-7-carboxylic acid, which comprises reacting. 2. The 8-hydroxyquinoline-7- according to claim 1, wherein the reaction is carried out in the presence of a hydrophobic solvent.
A method for producing a carboxylic acid.