JP4250780B2 - Method for producing mercaptocarboxylic acids - Google Patents

Description

[0001]
[Industrial application fields]
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 highly reactive due to the mercapto group and carboxyl group present in the molecule, and are well soluble in organic solvents and water. As raw materials for organic synthetic products such as agricultural chemicals and pharmaceuticals, Further, it is a compound useful as a raw material for a stabilizer of vinyl chloride, a crosslinking agent for an epoxy resin or an acrylic ester polymer, a plastic lens monomer, and the like.
[0002]
[Prior art]
As a method for producing mercaptocarboxylic acid, a method is generally known in which mercaptonitriles are obtained from unsaturated nitriles, and then mercaptonitriles are hydrolyzed.
[0003]
For example, in JP-A-58-198460, acrylonitrile is added to an aqueous sodium hydrosulfide solution under predetermined conditions, and the obtained sodium salt of β-mercaptopropionitrile is neutralized with hydrochloric acid and hydrolyzed to produce β- A method for obtaining mercaptopropionic acid has been proposed. Here, it is said that β-mercaptopropionic acid can be obtained with good yield by suppressing the production of thiodipropionic acid as a by-product. However, in this method, since a mixed solution of sodium chloride and ammonium chloride is formed by neutralization hydrolysis, the aqueous solution cannot be used effectively, and wastewater treatment is difficult.
[0004]
Japanese Patent Laid-Open No. 4-305563 proposes a method of 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 extremely high yield by suppressing the production of thiodipropionic acid as a by-product, but the dropping method, temperature, time, etc. during the hydrolysis reaction are There are problems such as being severely restricted, taking a long time for the reaction, and being inappropriate for actual industrialization.
[0005]
Furthermore, according to JP-A-63-6545, acrylonitrile is reacted dropwise with sodium sulfide and free sodium hydroxide with stirring, and the reaction solution is heated and hydrolyzed in a relatively short time. It is said that ammonia gas generated during this time is absorbed in water and recovered, and after neutralization with sulfuric acid, almost pure mirabilite can be obtained as a by-product. However, in this method, the reaction is performed under severe conditions. Therefore, many impurities are produced and the yield of the intended β-mercaptopropionic acid is insufficient. In addition, the amount of ammonium sulfate in mirabilite is severely regulated due to the environmental effects of nitrogen compounds, but this method is incomplete removal of ammonia out of the system, and the resulting mirabilite contains considerable ammonium sulfate. Therefore, higher purity is desired.
[0006]
[Problems to be solved by the invention]
As a result of examining the reaction of unsaturated nitrile with alkali hydrosulfide and the production method of mercaptocarboxylic acids by hydrolysis of the reaction solution, the present inventors have determined the conditions of each step such as reaction, hydrolysis, by-product separation, and purification. It has been found that, by improving the method, the problems of the conventionally known methods can be solved, the target product can be obtained in a high yield, and the by-product can be recovered as a high-purity product.
[0007]
In the conventional hydrolysis with a mineral acid aqueous solution such as hydrochloric acid and sulfuric acid, the reaction conditions are heating and reflux conditions, and a relatively high temperature is required. Therefore, the yield of the target mercaptocarboxylic acids is significantly reduced. Many by-products are generated.
[0008]
In addition, the hydrolysis reaction with an inorganic base is also performed at a high temperature of 100 ° C. or more in the conventional method, and hydrogen sulfide is eliminated due to the presence of α-active hydrogen of mercaptonitriles to produce unsaturated nitriles, The unsaturated nitriles react with the mercaptonitriles to result in side reactions such as thiodicarboxylic acids.
[0009]
Therefore, in order to obtain mercaptocarboxylic acids in high yields using unsaturated nitriles and alkali hydrosulfides as raw materials, it is a major issue to suppress the generation of side reaction products such as thiodicarboxylic acids.
[0010]
[Means for Solving the Problems]
As a result of earnestly examining the reaction of unsaturated nitrile with alkali hydrosulfide and the basic hydrolysis reaction of the reaction solution in order to obtain only the mercaptocarboxylic acids at a high yield during the hydrolysis reaction, It has been found that by reacting under specific conditions, by-products of thiodicarboxylic acids can be suppressed, and mercaptocarboxylic acids can be obtained in high yield.
[0011]
Rather than reacting by adding unsaturated nitrile to a solution in which alkali hydrosulfide and inorganic base are mixed together, first, alkali hydrosulfide and unsaturated nitrile are reacted and then hydrolyzed with inorganic base. It has been found that mercaptocarboxylic acids can be obtained stably at a high yield.
[0012]
Furthermore, by reducing the reaction system to a reduced pressure and removing the ammonia generated by the reaction from the reaction system and absorbing it into water to recover it, high-purity ammonia water can be obtained, and alkali salts of mercaptocarboxylic acids can be obtained. After separating the oil layer and aqueous layer by acid neutralization and separation, the mercaptocarboxylic acids dissolved in the aqueous layer are extracted with an organic solvent to obtain mercaptocarboxylic acids, so that the aqueous layer after extraction From this, it was found that a high-purity inorganic salt aqueous solution almost free of organic compounds and nitrogen compounds could be obtained, and the present invention was completed.
[0013]
Examples of the unsaturated nitrile represented by the general formula (1) used in the present invention include acrylonitrile, 2-phenylpropenenitrile, 3-butenenitrile, 5-pentenenitrile, 3-phenylpropenenitrile, and 2-methyl-3. -Phenylpropenenitrile, 3-phenyl-3-butenenitrile, 2-ethyl-5-hexenenitrile, 2-methyl-4-pentenenitrile, 2-methyl-3-butenenitrile and the like.
[0014]
Hereinafter, the present invention will be described in detail. In order to simplify the description, a case where β-mercaptopropionic acid is produced using acrylonitrile as an unsaturated nitrile will be described as a representative example.
[0015]
Examples of the alkali hydrosulfide used in the present invention include sodium hydrosulfide, potassium hydrosulfide, calcium hydrosulfide and the like. Moreover, sulfur and alkali polysulfide, for example, sodium polysulfide, potassium polysulfide, calcium polysulfide, etc. are mentioned.
[0016]
The amount of alkali hydrosulfide or alkali polysulfide used is preferably 1.0 to 2.0 times the mol of the unsaturated nitrile. If the amount is less than 1.0 times mol, a large amount of thiodinitriles are by-produced, and if the amount is more than 2.0 times mol, the amount of acid used for neutralization after the reaction increases, which is uneconomical.
[0017]
The inorganic base used in the present invention generally means an alkali metal hydroxide / carbonate / bicarbonate, such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, Potassium bicarbonate or the like is used. A compound capable of generating an inorganic base in the system is also included in the category of the inorganic base of the present invention. For example, alkali sulfide or a mixture of alkali sulfide and sulfur can be reacted with water in the system to produce an alkali metal hydroxide, and thus is included in the scope of the present invention. Of these, alkali metal hydroxides are preferably used from the viewpoint of reaction kinetics, and the amount used is preferably 1.0 to 2.0 times the mol of the unsaturated nitrile. If it is less than 1.0-fold mol, unreacted mercaptonitrile remains, and if it is more than 2.0-fold mol, the amount of acid used for neutralization after the reaction also increases, which is uneconomical.
[0018]
During the hydrolysis, the reaction solution obtained by the reaction of the unsaturated nitrile and the alkali hydrosulfide and the inorganic base aqueous solution can be mixed together, or the inorganic base aqueous solution can be added dropwise to the reaction solution. However, from the viewpoint of productivity and operability, the reaction solution and the inorganic base aqueous solution are preferably mixed at once or the inorganic base aqueous solution is preferably added dropwise to the reaction solution.
[0019]
The hydrolysis reaction is performed at 100 ° C. or lower, preferably 45 ° C. to 80 ° C., more preferably 60 ° C. to 80 ° C. Below 45 ° C, the reaction does not proceed sufficiently and unreacted mercaptonitriles remain, and at temperatures higher than 80 ° C, thiodicarboxylic acids and the like are by-produced simultaneously with hydrolysis, which is not preferable. The hydrolysis time is preferably 1 hour to 6 hours, and more preferably 2 hours to 4 hours. If it is less than 1 hour, the desired mercaptocarboxylic acid cannot be obtained stably in a high yield, and even if it reacts for more than 6 hours, no particular effect is seen, which is not preferable from the viewpoint of productivity.
[0020]
After the hydrolysis reaction, ammonia generated by the hydrolysis is dissolved in the reaction solution. The presence of ammonia causes by-production of ammonium salts during neutralization, not only significantly reduces the commercial value of inorganic bases such as high purity mirabilite, but also makes pollution treatment complicated by containing ammonium salts, It is extremely uneconomical.
[0021]
Therefore, after the hydrolysis reaction, it is necessary to remove and recover ammonia generated from the reaction system outside the reaction system. In order to remove ammonia, it is preferable that bubbling of inert gas into the reaction solution and the system be reduced in pressure, and ammonia is removed until the dissolved concentration in the reaction solution is 1000 ppm or less, preferably 100 ppm or less. By removing the ammonia to be removed by water, high purity and high concentration ammonia water can be easily obtained.
[0022]
After recovering ammonia, mercaptocarboxylic acids are present as alkali metal salts in the reaction solution. Accordingly, the mercaptocarboxylic acids can be isolated by a general method of adding an acid to neutralize and separate the solution and distilling the oil layer. As the mineral acid used for neutralization, hydrochloric acid, sulfuric acid, phosphoric acid and the like are used.
[0023]
Since the mercaptocarboxylic acids are dissolved in the aqueous layer obtained after neutralization, extraction from the aqueous layer with an organic solvent is performed, and the organic layer is distilled, for example, by distillation under reduced pressure to obtain the desired mercaptocarboxylic acids. Can do. Moreover, the reaction liquid after neutralization can be extracted together with an organic solvent, and mercaptocarboxylic acids can be obtained 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, butyl acetate and the like are preferably used.
[0024]
Moreover, the solution obtained after extraction is high concentration mirabilite or an aqueous inorganic salt solution such as salt, and can be used as, for example, a high purity mirabilite aqueous solution. Further, if crystals are precipitated from a high concentration of mirabilite solution, the deposited crystals can be used as very high purity mirabilite. In addition, since the waste liquid contains almost no organic matter or nitrogen compound, pollution treatment is very simple and economical without affecting the environment.
[0025]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, this invention is not limited only to these Examples.
[0026]
Example 1
Acrylonitrile (33.2 g) was added dropwise to a 37% aqueous sodium hydrosulfide solution (130 g) kept at 45 ° C. with stirring at 45 ° C. over 2 hours, 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 with stirring at 45 ° C to 50 ° C. After completion of the dropwise addition, the temperature was raised to 80 ° C. and stirred at the same temperature for 2 hours. Further, the reaction system was depressurized, and deammonia was performed at the same temperature for 3 hours. Here, 52.6 g of aqueous ammonia was obtained at a recovery rate of 99.9%. The reaction solution was cooled to room temperature, 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, β-mercaptopropionic acid was produced at a yield of 85% and thiodipropionic acid at 12%.
[0027]
Comparative Example 1
Acrylonitrile (33.2 g) was added dropwise to a 37% aqueous sodium hydrosulfide solution (130 g) kept at 45 ° C. with stirring at 45 ° C. over 2 hours, and then stirred at the same temperature for 1 hour. After 1 hour, a 48% aqueous sodium hydroxide solution (71.5 g) was added dropwise over 30 minutes with stirring at 45-50 ° C. After completion of dropping, the mixture was stirred at the same temperature for 2 hours. The reaction solution was cooled to room temperature, 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, β-mercaptopropionic acid was remarkably low in yield of 56%, and thiodipropionic acid was in yield of 8%, and a large amount of unknown compounds were by-produced.
[0028]
Comparative Example 3
Acrylonitrile (33.2 g) was added dropwise to a 37% aqueous sodium hydrosulfide solution (130 g) kept at 45 ° C. with stirring at 45 ° C. over 2 hours, and then stirred at the same temperature for 1 hour. After 1 hour, a 48% aqueous sodium hydroxide solution (71.5 g) was added dropwise over 30 minutes with stirring at 45 ° C to 50 ° C. After completion of the dropwise addition, the temperature was raised to 80 ° C. and 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. The reaction solution was cooled to room temperature, 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, β-mercaptopropionic acid was obtained in a yield of 73%, and at the same time, thiodipropionic acid was produced in a yield of 19% and a large amount of unknown compounds were by-produced.
[0029]
Comparative Example 4
A 37% aqueous solution of sodium hydrosulfide (130 g) and a 48% aqueous solution of sodium hydroxide (71.5 g) were mixed together, and acrylonitrile was added dropwise thereto at 40 to 45 ° C. with stirring for 2 hours, and then at the same temperature for 4 hours. Stir. Then, it heated up over 120 hours to 120 degreeC, and stirred for 30 minutes at the same temperature. Here, 47.2 g of ammonia water was obtained at a recovery rate of 50.0%. The reaction solution was cooled to room temperature, 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, β-mercaptopropionic acid was obtained in a yield of 69%, and at the same time, thiodipropionic acid was by-produced in a large amount of 24%.
[0030]
【The invention's effect】
As described above, according to the present invention, an alkali hydrosulfide aqueous solution and an unsaturated nitrile are reacted, and then an inorganic base is added and a hydrolysis reaction is performed at 45 ° C. to 80 ° C., thereby stably achieving a high yield. Thus, mercaptocarboxylic acids can be obtained. After the hydrolysis reaction, the ammonia generated from the reaction system is removed from the reaction system until the dissolved concentration in the reaction solution is 1000 ppm or less, and the removed ammonia is absorbed into water and recovered, thereby obtaining high purity. High-concentration aqueous ammonia can be easily obtained. Furthermore, after recovering ammonia, the acid can be added for neutralization and liquid separation, and the oil layer can be concentrated and distilled to obtain mercaptocarboxylic acids. The aqueous layer obtained at the time of neutralization / separation is an aqueous solution of an inorganic base such as high-concentration mirabilite solution. it can. Furthermore, since the waste liquid contains almost no organic matter, pollution treatment is very simple and economical without affecting the environment.

Claims (8)

a. General formula (1)

[R ₁ and R ₂ represent a hydrogen atom, a C _{1 to} C ₃ lower alkyl group or a phenyl group, and n represents an integer of 0 to 3. And an unsaturated nitrile represented by an alkali hydrosulfide;
b. Mixing and heating the reaction solution and an inorganic base , removing ammonia generated from the reaction system under reduced pressure until the dissolved concentration in the reaction solution is 1000 ppm or less, and recovering ammonia ;
c. Next, the resulting reaction solution is neutralized with an acid, and then separated to separate an oil layer composed of mercaptopropionic acids. Further, mercaptocarboxylic acids dissolved in the aqueous layer are extracted with an organic solvent. Separate the organic solvent layer containing mercaptocarboxylic acids and recover the mercaptocarboxylic acid from the organic solvent layer and / or the oil layer, or extract the neutralized solution with an organic solvent to remove the organic solvent layer containing the mercaptocarboxylic acid. Separating and obtaining mercaptocarboxylic acid from the organic solvent layer ;
d. A high-purity inorganic salt aqueous solution is obtained from the aqueous layer after extraction.

[R ₁ and R ₂ represent a hydrogen atom, a C _{1 to} C ₃ lower alkyl group or a phenyl group, and n represents an integer of 0 to 3. ] The manufacturing method of mercaptocarboxylic acid shown by z7. a. Reacting an unsaturated nitrile represented by the general formula (1) with an alkali hydrosulfide;
b. Mixing and heating the reaction solution and an inorganic base , removing ammonia generated from the reaction system under reduced pressure until the dissolved concentration in the reaction solution is 1000 ppm or less, and recovering ammonia ;
c. Next, the resulting reaction solution is neutralized with an acid, and then separated to separate an oil layer composed of mercaptopropionic acids. Further, mercaptocarboxylic acids dissolved in the aqueous layer are extracted with an organic solvent. Separate the organic solvent layer containing mercaptocarboxylic acids and recover the mercaptocarboxylic acid from the organic solvent layer and / or the oil layer, or extract the neutralized solution with an organic solvent to remove the organic solvent layer containing the mercaptocarboxylic acid. A method for producing ammonia and a mercaptocarboxylic acid represented by the general formula (2), wherein the mercaptocarboxylic acid is obtained by separating and obtaining a mercaptocarboxylic acid from the organic solvent layer. a. Reacting an unsaturated nitrile represented by the general formula (1) with an alkali hydrosulfide;
b. Mixing and heating the reaction solution and an inorganic base , removing ammonia generated from the reaction system under reduced pressure until the dissolved concentration in the reaction solution is 1000 ppm or less, and recovering ammonia ;
c. Next, the resulting reaction solution is neutralized with an acid, and then separated to separate an oil layer composed of mercaptopropionic acids. Further, mercaptocarboxylic acids dissolved in the aqueous layer are extracted with an organic solvent. Separate the organic solvent layer containing mercaptocarboxylic acids and recover the mercaptocarboxylic acid from the organic solvent layer and / or the oil layer, or extract the neutralized solution with an organic solvent to remove the organic solvent layer containing the mercaptocarboxylic acid. Separating to obtain mercaptocarboxylic acid from the organic solvent layer; d. A method for producing a mercaptocarboxylic acid represented by the general formula (2), wherein a highly pure inorganic salt aqueous solution is obtained from an aqueous layer after extraction. The method according to claim 1, wherein an inorganic base is added to a reaction solution obtained by reacting an alkali hydrosulfide and an unsaturated nitrile, and then heating and stirring are performed at 100 ° C. or lower. The method according to claim 1, wherein the reaction solution obtained by reacting the alkali hydrosulfide with the unsaturated nitrile and the inorganic base are heated and stirred at 45 ° C. to 80 ° C. for 1 to 6 hours. The reaction solution obtained by reacting the alkali hydrosulfide and the unsaturated nitrile and the inorganic base are heated and stirred at 100 ° C. or less, and the produced ammonia is removed from the reaction system until the dissolved concentration in the reaction solution becomes 1000 ppm or less. Removal, absorption in water and recovery to obtain high-purity ammonia water, followed by neutralization and separation of the reaction solution with an acid to separate an oil layer and an aqueous layer, and further into the aqueous layer The dissolved mercaptocarboxylic acids are extracted with an organic solvent, the organic solvent layer containing the mercaptocarboxylic acids is separated, and the mercaptocarboxylic acid is recovered from the organic solvent layer and / or the oil layer, or the neutralizing solution is used. 6. The method according to any one of claims 1 to 5 , wherein an organic solvent layer containing mercaptocarboxylic acid is separated by extraction with an organic solvent, and mercaptocarboxylic acid is obtained from the organic solvent layer. The method according to any one of claims 1 to 6 , wherein the aqueous layer after extraction is treated to obtain a high-purity inorganic salt aqueous solution. The method of claim 1-7 in which the acid used for neutralization is characterized in that it is a sulfate.