JPH11209341A - Production of mercaptocarboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce mercaptocarboxylic acids in high yield while suppressing the generation of by-product, thiodicarboxylic acids by reacting under a specific condition. SOLUTION: The objective mercaptocarboxylic acid of formula II is produced by reacting an unsaturated nitrile of formula I (R1 and R2 are each H, a 1-3C alkyl or phenyl; (n) is 0-3) with an alkali metal hydrosulfide, mixing the reaction liquid with an inorganic base, heating the mixture to remove the generated ammonia from the system, neutralizing the obtained reaction liquid with an acid, separating the product into liquid layers, separating the oil layer composed of mercaptopropionic acid, extracting mercaptocarboxylic acid dissolved in the water layer with an organic solvent and recovering the mercaptocarboxylic acid from the organic solvent layer and/or the oil layer or extracting the neutralized liquid with an organic solvent, separating into layers, separating the mercaptocarboxylic acid from the organic solvent layer and getting a high-purity aqueous solution of inorganic salt from the water layer after extraction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing mercaptocarboxylic acids with high yield and recovering by-products with high purity and high yield. Mercaptocarboxylic acids are rich in reactivity due to the mercapto group and carboxyl group present in the molecule, have the characteristic of being well soluble in organic solvents and water, and are used as a raw material for organic synthetic products such as agricultural chemicals and pharmaceuticals. Further, it is a compound useful as a raw material such as a stabilizer for vinyl chloride, a crosslinking agent for an epoxy resin or an acrylate polymer, and a plastic lens monomer.

[0002]

2. Description of the Related Art As a method for producing mercaptocarboxylic acids, it is generally known to obtain mercaptonitrile from unsaturated nitriles and then hydrolyze the mercaptonitrile.

For example, in Japanese Patent Application Laid-Open No. 58-198460, acrylonitrile is added to an aqueous solution of sodium bisulfide under predetermined conditions, and the resulting sodium salt of β-mercaptopropionitrile is neutralized and hydrolyzed with hydrochloric acid. A method for obtaining β-mercaptopropionic acid has been proposed. Here, it is stated that β-mercaptopropionic acid can be obtained with high yield while suppressing the production of thiodipropionic acid as a by-product. But with this method,
Since a mixed solution of salt and ammonium chloride is formed by the neutralization hydrolysis, the aqueous solution cannot be used effectively, and wastewater treatment is difficult.

According to Japanese Patent Application Laid-Open No. 4-305563, there is proposed a method for obtaining β-mercaptopropionic acid by adding an alkali salt of β-mercaptonitrile to an aqueous alkali hydroxide solution and hydrolyzing it. . Here, it is said that β-mercaptopropionic acid can be obtained in an extremely high yield by suppressing the generation of thiodipropionic acid as a by-product.However, the dropping method, temperature, time, and the like during the hydrolysis reaction are described as follows. It is severely restricted, and has a problem that the reaction requires a long time and is not suitable for actual industrialization.

Further, according to JP-A-63-6545, acrylonitrile is dropped and reacted with sodium sulfide and free sodium hydroxide with stirring, and the reaction solution is further heated by heating in a relatively short time. It is said that ammonia gas generated during the decomposition is absorbed by water and collected, and after neutralization with sulfuric acid, almost pure sodium sulfate can be obtained as a by-product.However, in this method, under severe conditions, Since the reaction is performed, many impurities are generated, and the yield of the target β-mercaptopropionic acid is insufficient. In addition, although the amount of ammonium sulfate in sodium sulfate is strictly regulated due to the environmental effects of nitrogen compounds, the removal of ammonia out of the system is incomplete with this method, and the resulting sodium sulfate contains considerable ammonium sulfate. And higher purification is desired.

[0006]

The present inventors have studied the reaction of unsaturated nitrile with alkali hydrosulfide and the production of mercaptocarboxylic acids by hydrolysis of the reaction solution. By improving the conditions of each step such as separation and purification, and the method, it is possible to solve the problems of the conventionally known methods, obtain the target product in high yield, and recover by-products as high-purity products. Was.

In the conventionally known hydrolysis with an aqueous solution of a mineral acid such as hydrochloric acid or sulfuric acid, a relatively high temperature is required, for example, the reaction conditions are heating and refluxing conditions, and the yield of the desired mercaptocarboxylic acid is remarkably reduced. In addition, many undesired by-products are produced.

In the conventional method, the hydrolysis reaction with an inorganic base is carried out at a high temperature of 100 ° C. or more, and the presence of α-active hydrogen of mercaptonitrile releases hydrogen sulfide to form unsaturated nitrile. The unsaturated nitriles formed have a drawback that they are liable to react with mercaptonitrile, resulting in thiodicarboxylic acids and other side reactions.

Therefore, in order to obtain mercaptocarboxylic acids in high yield from unsaturated nitriles and alkali hydrosulfides, it is a major problem to suppress the formation of by-products such as thiodicarboxylic acids.

[0010]

In order to obtain only a high yield of mercaptocarboxylic acids during the hydrolysis reaction, the present inventors have conducted a reaction between unsaturated nitrile and alkali hydrosulfide, and
As a result of intensive studies on the basic hydrolysis reaction of the reaction solution, it was found that by reacting under specific conditions, by-products of thiodicarboxylic acids were suppressed and mercaptocarboxylic acids could be obtained in high yield.

Rather than reacting by adding unsaturated nitrile to a solution in which alkali hydrosulfide and an inorganic base are mixed at once, first, alkali hydrosulfide and unsaturated nitrile are reacted and then hydrolyzed by an inorganic base. By doing so, it has been found that mercaptocarboxylic acids can be stably obtained in high yield.

Further, by reducing the pressure of the reaction system and removing the ammonia produced by the reaction outside the reaction system, absorbing the ammonia into water and recovering it, high-purity ammonia water can be obtained. After the alkali salt is neutralized with an acid and separated to separate an oil layer and an aqueous layer, the mercaptocarboxylic acids dissolved in the aqueous layer are extracted with an organic solvent to obtain mercaptocarboxylic acids. It was found that a high-purity aqueous solution of an inorganic salt containing almost no organic compound and no nitrogen compound can be obtained from the aqueous layer, and completed the present invention.

The unsaturated nitrile represented by the general formula (1) used in the present invention includes acrylonitrile, 2-phenylpropenenitrile, 3-butenenitrile, 5-pentenenitrile, 3-phenylpropenenitrile,
Examples thereof include methyl-3-phenylpropenenitrile, 3-phenyl-3-butenenitrile, 2-ethyl-5-hexenenitrile, 2-methyl-4-pentenenitrile, and 2-methyl-3-butenenitrile.

Hereinafter, the present invention will be described in detail.
For the sake of simplicity, a case where β-mercaptopropionic acid is produced using acrylonitrile as an unsaturated nitrile will be described as a typical example.

The alkali hydrosulfide used in the present invention includes, for example, sodium hydrosulfide, potassium hydrosulfide, calcium hydrosulfide and the like. In addition, sulfur and alkali polysulfide, for example, sodium polysulfide, potassium polysulfide, calcium polysulfide and the like can be mentioned.

The amount of alkali hydrogen sulfide or alkali polysulfide used is preferably 1.0 to 2.0 times mol of the unsaturated nitrile. If the molar ratio is less than 1.0, the amount of thiodinitrile is by-produced in a large amount. If the molar ratio exceeds 2.0, the amount of acid required for neutralization after the reaction is increased, which is uneconomical.

The inorganic base used in the present invention generally means an alkali metal hydroxide / carbonate / bicarbonate, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, carbonate Sodium hydrogen, potassium hydrogen carbonate and the like are used. Compounds capable of forming an inorganic base in the system are also included in the category of the inorganic base of the present invention. For example, an alkali sulfide or a mixture of an alkali sulfide and sulfur is included in the scope of the present invention because it can react with water in the system to generate an alkali metal hydroxide. Of these, alkali metal hydroxides are preferably used from the viewpoint of reaction kinetics, and the amount of the alkali metal hydroxide is preferably 1.0 to 2.0 moles per mole of the unsaturated nitrile. 1.0
At less than twice the mole, unreacted mercaptonitrile remains,
Use of more than 2.0 moles increases the amount of acid used for neutralization after the reaction, which is uneconomical.

In the hydrolysis, the reaction solution obtained by the reaction of the unsaturated nitrile with the alkali hydrosulfide and the aqueous solution of the inorganic base may be mixed at once, or the aqueous solution of the inorganic base may be added dropwise to the reaction solution. The reaction solution may be added dropwise to the aqueous inorganic base solution,
From the viewpoint of productivity and operability, it is preferable that the reaction solution and the aqueous inorganic base solution are mixed at once or the aqueous inorganic base solution is dropped into the reaction solution.

The hydrolysis is carried out at a temperature of 100 ° C. or lower, preferably 45 ° C. to 80 ° C., more preferably 60 ° C. to 80 ° C. At a temperature lower than 45 ° C., the reaction does not proceed sufficiently, and unreacted mercaptonitrile remains. At a temperature higher than 80 ° C., thiodicarboxylic acids and the like are produced as by-products simultaneously with hydrolysis, which is not preferable. The hydrolysis time is preferably 1 hour to 6 hours, more preferably 2 hours to 4 hours. If the time is less than 1 hour, the desired mercaptocarboxylic acid may not be stably obtained in a high yield, and even if the reaction is carried out for 6 hours or more, no particular effect is observed, which is not preferable in terms of productivity.

After the hydrolysis reaction, ammonia produced by the hydrolysis is dissolved in the reaction solution. The presence of ammonia causes ammonium salts to be by-produced during neutralization,
Not only does the commercial value of inorganic bases such as high-purity sodium sulfate are significantly reduced, but the inclusion of ammonium salts makes pollution treatment complicated and extremely uneconomical.

Therefore, after the hydrolysis reaction, it is necessary to remove and recover ammonia generated from the reaction system outside the reaction system. For removing ammonia, it is preferable to bubbling the inert gas into the reaction solution or to reduce the pressure of the system, and the dissolved concentration in the reaction solution is 1000 ppm or less, preferably 10 ppm or less.
Ammonia is removed until it becomes 0 ppm or less. By removing the removed ammonia with water, high-purity, high-concentration ammonia water can be easily obtained.

After recovering the ammonia, the mercaptocarboxylic acids are present as alkali metal salts in the reaction solution. Accordingly, mercaptocarboxylic acids can be isolated by a general method of first adding an acid, neutralizing and separating, and distilling an oil layer. As mineral acids used for neutralization, hydrochloric acid, sulfuric acid, phosphoric acid and the like are used.

Since the mercaptocarboxylic acid is dissolved in the aqueous layer obtained after the neutralization, the mercaptocarboxylic acid is extracted from the aqueous layer with an organic solvent. Can be obtained. Alternatively, the reaction solution after the neutralization may be collectively extracted with an organic solvent to obtain a mercaptocarboxylic acid from the organic solvent.
As the organic solvent used here, ethyl acetate, butyl acetate, chloroform, dichloromethane, diethyl ether, isopropyl ether, methyl ethyl ketone, isobutyl ketone and the like are used, and ethyl acetate and butyl acetate are preferably used.

The solution obtained after the extraction is a high-concentration sodium sulfate or an aqueous solution of an inorganic salt such as salt, and can be used, for example, as a high-purity sodium sulfate aqueous solution. If crystals are precipitated from a high-concentration sodium sulfate solution, the precipitated crystals can be used as very high-purity sodium sulfate. Furthermore, since the waste liquid contains almost no organic substances or nitrogen compounds, the pollution treatment is very simple and economical without affecting the environment.

[0025]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 Acrylonitrile (33.2 g) was kept at 45 ° C.
The resulting mixture was added dropwise to a 7% aqueous sodium hydrosulfide solution (130 g) at 45 ° C. for 2 hours with stirring, and then stirred at the same temperature for 1 hour. After 1 hour, a 48% aqueous sodium hydroxide solution (70%
g) was added dropwise over 30 minutes while stirring at 45 ° C to 50 ° C. After completion of the dropwise addition, the temperature was raised to 80 ° C., and the mixture was stirred at the same temperature for 2 hours. Further, the pressure of the reaction system was reduced, and deammonification was performed at the same temperature for 3 hours. Here, at a recovery rate of 99.9%, 5
2.6 g of aqueous ammonia was obtained. After cooling the reaction solution to room temperature, it was neutralized with 62.5% sulfuric acid (150 g) and extracted twice with 200 mL of ethyl acetate. The extracts were combined and the solvent was removed under reduced pressure. As a result of analysis by high performance liquid chromatography, the yield of β-mercaptopropionic acid was 85%,
Thiodipropionic acid was formed at 12%.

Comparative Example 1 Acrylonitrile (33.2 g) was maintained at 45 ° C.
The resulting mixture was added dropwise to a 7% aqueous sodium hydrosulfide solution (130 g) at 45 ° C. for 2 hours with stirring, and then stirred at the same temperature for 1 hour. One hour later, a 48% aqueous sodium hydroxide solution (7
1.5 g) was added dropwise over 30 minutes while stirring at 45-50 ° C. After completion of the dropwise addition, the mixture was stirred at the same temperature for 2 hours. After cooling the reaction solution to room temperature, it was neutralized with 62.5% sulfuric acid (150 g) and extracted twice with 200 mL of ethyl acetate. The extracts were combined and the solvent was removed under reduced pressure. As a result of analysis by high performance liquid chromatography, the yield of β-mercaptopropionic acid was remarkably low at 56%, and the yield of thiodipropionic acid was 8%.

Comparative Example 3 Acrylonitrile (33.2 g) was maintained at 45 ° C.
The resulting mixture was added dropwise to a 7% aqueous sodium hydrosulfide solution (130 g) at 45 ° C. for 2 hours with stirring, and then stirred at the same temperature for 1 hour. One hour later, a 48% aqueous sodium hydroxide solution (7
1.5 g) was added dropwise over 30 minutes while stirring at 45-50 ° C. After completion of the dropwise addition, the temperature was raised to 80 ° C., and the mixture was stirred at the same temperature for 2 hours. Thereafter, the temperature was further raised to 120 ° C., and the mixture was stirred at the same temperature for 2 hours. After cooling the reaction solution to room temperature, 6
Neutralized with 2.5% sulfuric acid (150 g),
Extracted twice with mL. The extracts were combined and the solvent was removed under reduced pressure. As a result of analysis by high performance liquid chromatography, β-mercaptopropionic acid was obtained in a yield of 73%, and thiodipropionic acid was in a yield of 19%.

Comparative Example 4 A 37% aqueous sodium hydrosulfide solution (130 g) and a 48% aqueous sodium hydroxide solution (71.5 g) were mixed at once, and acrylonitrile was stirred at 40 to 45 ° C. for 2 hours.
After dropwise addition over time, the mixture was stirred at the same temperature for 4 hours. afterwards,
The temperature was raised to 120 ° C. over 3 hours, and the mixture was stirred at the same temperature for 30 minutes. Here, 47.2 g of aqueous ammonia was obtained at a recovery rate of 50.0%. After cooling the reaction solution to room temperature, 62.5%
Neutralize with sulfuric acid (150 g) and add 200 mL of ethyl acetate.
Extracted times. The extracts were combined and the solvent was removed under reduced pressure.
As a result of analysis by high performance liquid chromatography, β-mercaptopropionic acid was obtained in a yield of 69%, and thiodipropionic acid was by-produced in a large amount of 24%.

[0030]

As described above, according to the present invention, a stable reaction is obtained by reacting an aqueous solution of an alkali hydrosulfide with an unsaturated nitrile, and then adding an inorganic base to carry out a hydrolysis reaction at 45 ° C to 80 ° C. Thus, mercaptocarboxylic acids can be obtained in high yield. After the hydrolysis reaction, remove the ammonia generated from the reaction system to the outside of the reaction system until the dissolved concentration in the reaction solution becomes 1000 ppm or less,
High-purity, high-concentration aqueous ammonia can be easily obtained by absorbing and removing the removed ammonia in water. Further, after recovering the ammonia, an acid is added for neutralization and separation, and then the oil layer is concentrated and distilled to obtain mercaptocarboxylic acids. The aqueous layer obtained at the time of neutralization and liquid separation is an aqueous solution of an inorganic base such as a high-concentration sodium sulfate solution.For example, if crystals are precipitated from this high-concentration sodium sulfate solution, the precipitated crystals are used as high-purity sodium sulfate. it can. Furthermore, since the waste liquid contains almost no organic matter, the pollution treatment is very simple and economical without affecting the environment.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hironao Taketsuna 5-1-1 Ebisshima-cho, Sakai-shi, Osaka Sakai Chemical Industry Co., Ltd.

Claims (9)

[Claims] 1. A method according to claim 1, General formula (1) [R ₁ and R ₂ represent a hydrogen atom, a C ₁ -C ₃ lower alkyl group or a phenyl group, and n represents an integer of 0-3. A) reacting an unsaturated nitrile represented by the formula (1) with an alkali hydrosulfide; The reaction solution and an inorganic base are mixed and heated to remove generated ammonia out of the reaction system; c. Next, after neutralizing the obtained reaction solution with an acid, liquid separation was performed to separate an oil layer composed of mercaptopropionic acids, and further, mercaptocarboxylic acids dissolved in the aqueous layer were extracted with an organic solvent. Separate the organic solvent layer containing mercaptocarboxylic acids, recover the mercaptocarboxylic acid from the organic solvent layer, and / or the oil layer, or extract the neutralized solution with an organic solvent to form an organic solvent layer containing mercaptocarboxylic acid. Separating and obtaining the mercaptocarboxylic acid from the organic solvent calendar; d. General formula (2) wherein an aqueous solution of a high-purity inorganic salt is obtained from the aqueous layer after the extraction. [R ₁ and R ₂ represent a hydrogen atom, a C ₁ -C ₃ lower alkyl group or a phenyl group, and n represents an integer of 0-3. ] A method for producing a mercaptocarboxylic acid represented by the formula: 2. a. Reacting an unsaturated nitrile represented by the general formula (1) with an alkali hydrosulfide; b. Mixing the reaction solution with an inorganic base and heating to remove the generated ammonia out of the reaction system, and recover the ammonia in high yield; c. Next, after neutralizing the obtained reaction solution with an acid, liquid separation was performed to separate an oil layer composed of mercaptopropionic acids, and further, mercaptocarboxylic acids dissolved in the aqueous layer were extracted with an organic solvent. Separate the organic solvent layer containing mercaptocarboxylic acids and recover the organic solvent calendar, and / or the mercaptocarboxylic acid from the oil layer, or extract the neutralized solution with an organic solvent to form an organic solvent layer containing mercaptocarboxylic acid. A method for producing mercaptocarboxylic acids represented by the general formula (2) and ammonia, comprising separating and obtaining a mercaptocarboxylic acid from an organic solvent layer. 3. A method according to claim 1, Reacting an unsaturated nitrile represented by the general formula (1) with an alkali hydrosulfide; b. Mixing the reaction solution with an inorganic base and heating to remove the generated ammonia out of the reaction system, and recover the ammonia in high yield; c. Then, after neutralizing the obtained reaction solution with an acid, liquid separation was performed to separate an oil layer composed of mercaptopropionic acids, and further, mercaptocarboxylic acids dissolved in the lunar calendar were extracted with an organic solvent. Separate the organic solvent layer containing mercaptocarboxylic acids, recover the mercaptocarboxylic acid from the organic solvent layer, and / or the oil layer, or extract the neutralized solution with an organic solvent to form an organic solvent layer containing mercaptocarboxylic acid. Separating to obtain a mercaptocarboxylic acid from the organic solvent layer, d. A method for producing a mercaptocarboxylic acid represented by the general formula (2), wherein an aqueous solution of a high-purity inorganic salt is obtained from the aqueous layer after the extraction. 4. An inorganic base is added to a reaction solution obtained by reacting an alkali hydrogen sulfide with an unsaturated nitrile.
The heating and stirring are performed at a temperature of not more than ℃.
Method 3. 5. A reaction solution obtained by reacting an alkali hydrosulfide with an unsaturated nitrile and an inorganic base at 45 ° C. to 80 ° C.
5. The method according to claim 1, wherein heating and stirring are performed for 1 hour to 6 hours. 6. The method according to claim 1, wherein ammonia produced from the reaction system is removed from the reaction system until the dissolved concentration in the reaction solution becomes 1000 ppm or less, and the ammonia is recovered. 7. A reaction solution obtained by reacting an alkali hydrogen sulfide with an unsaturated nitrile and an inorganic base are heated and stirred at 100 ° C. or less, and the concentration of the produced ammonia in the reaction solution becomes 1000 ppm or less. Removed outside the reaction system, absorbed in water and collected to obtain high-purity ammonia water, then, the reaction solution was neutralized with an acid, separated to separate an oil layer and an aqueous layer, Extract the mercaptocarboxylic acids dissolved in the water calendar with an organic solvent to separate the organic solvent layer containing the mercaptocarboxylic acids, and recover the mercaptocarboxylic acid from the organic solvent layer, and or the oil layer, or Extracting the neutralized solution with an organic solvent, separating an organic solvent layer containing mercaptocarboxylic acid, and obtaining mercaptocarboxylic acid from the organic solvent layer.
Method 6. 8. The method according to claim 1, wherein the aqueous layer after the extraction is treated to obtain a high-purity aqueous solution of an inorganic salt. 9. The method according to claim 1, wherein the acid used for neutralization is sulfuric acid.