A preparation method of mercaptosuccinic acid

Abstract

The present application provides a preparation method of mercaptosuccinic acid, belonging to the technical field of fine chemical industry. The preparation method of mercaptosuccinic acid comprises the following steps: dissolving maleic anhydride and a combined catalyst in water and mixing them, then adding thioacetic acid to the mixed aqueous solution to obtain a precursor solution, wherein the combined catalyst comprises acidic pyridine and basic amine; performing a first heating treatment on the precursor solution to enable the addition reaction of maleic anhydride and thioacetic acid to obtain an intermediate reaction solution, and performing a second heating treatment on the intermediate reaction solution to enable the hydrolysis reaction of the intermediate in the intermediate reaction solution, and then performing a first cooling crystallization on the system after the hydrolysis of the intermediate reaction solution to enable the crystallization and precipitation of mercaptosuccinic acid. This preparation method can improve the problem of low purity of the prepared mercaptosuccinic acid. At the same time, it can also reduce the preparation cost of mercaptosuccinic acid and take into account the solution to the problem of environmental pollution.

Description

Technical Field

[0001] This application relates to the field of fine chemical technology. Specifically, it relates to a method for preparing mercaptosuccinic acid. Background Art

[0002] In the prior art, the preparation method of mercaptosuccinic acid usually involves hydrolysis under alkaline conditions. This hydrolysis method will result in a relatively low purity of the finally prepared mercaptosuccinic acid. At the same time, the existing preparation methods usually use organic solvents as solvents, which will lead to problems such as high cost and environmental pollution in the preparation of mercaptosuccinic acid. Summary of the Invention

[0003] The purpose of this application is to provide a method for preparing mercaptosuccinic acid, which can improve the problem of relatively low purity of the prepared mercaptosuccinic acid. At the same time, it can also reduce the preparation cost of mercaptosuccinic acid and take into account the solution of environmental pollution problems.

[0004] The embodiments of this application are implemented as follows:

[0005] The embodiments of this application provide a method for preparing mercaptosuccinic acid, including the following steps:

[0006] Dissolve maleic anhydride and a combined catalyst in water and mix them. Then, add thioacetic acid to the mixed aqueous solution to obtain a precursor solution. The combined catalyst includes acidic pyridine and basic amine; perform a first heat treatment on the precursor solution to enable the addition reaction of maleic anhydride and thioacetic acid to obtain an intermediate reaction solution, and perform a second heat treatment on the intermediate reaction solution. The lower limit of the temperature of the second heat treatment is not lower than the upper limit of the temperature of the first heat treatment to enable the hydrolysis reaction of the intermediate in the intermediate reaction solution. Then, perform a first cooling crystallization on the system after the hydrolysis of the intermediate reaction solution to enable the crystallization and precipitation of mercaptosuccinic acid.

[0007] In the above technical solution, when preparing mercaptosuccinic acid according to the preparation method provided by the embodiments of this application, on the one hand, it is not necessary to create an alkaline condition during the hydrolysis process, that is, it is not necessary to add alkaline substances, so no inorganic salts will be generated during the hydrolysis process. Compared with the existing preparation process, no inorganic salts will be generated to reduce the purity of mercaptosuccinic acid. Correspondingly, it is not necessary to use toxic acetone for the purification of mercaptosuccinic acid, so the purity of the prepared mercaptosuccinic acid can be improved. At the same time, it also has the advantage of better safety; on the other hand, directly using water as a solvent can effectively reduce the preparation cost of mercaptosuccinic acid and take into account the solution of environmental pollution problems compared with the existing preparation process.

[0008] In some alternative embodiments, after the first cooling crystallization, it further includes concentrating the mother liquor obtained after the first cooling crystallization and then performing a second cooling crystallization, so that mercaptosuccinic acid in the mother liquor crystallizes out.

[0009] In the above technical solution, performing a second cooling crystallization on the mother liquor after the first cooling crystallization can effectively collect the remaining mercaptosuccinic acid in the mother liquor. Correspondingly, the yield of mercaptosuccinic acid is equal to the sum of the yields obtained after the two cooling crystallizations, thereby effectively increasing the yield of mercaptosuccinic acid. Among them, concentrating the mother liquor before the second crystallization can increase the concentration of mercaptosuccinic acid in the mother liquor, thereby improving the efficiency of the second cooling crystallization.

[0010] In some alternative embodiments, the acidic pyridine includes at least one of pyridine-2-carboxylic acid, pyridine-3-carboxylic acid, and pyridine-4-carboxylic acid; and / or, the basic amine includes at least one of pyridine, piperidine, piperazine, 2-methylpyridine, 1-methylpiperidine, and N-methylpiperazine.

[0011] In the above technical solution, the types of acidic pyridine and basic amine applicable to the technical solution provided in this application are relatively rich, which can provide more alternative implementation solutions, thereby facilitating the popularization and application of the technical solution of this application.

[0012] In some alternative embodiments, the mass ratio of the acidic pyridine to the basic amine is 1:(0.8 - 1.2).

[0013] In the above technical solution, limiting the mass ratio of the acidic pyridine to the basic amine within a specific range can enable the combined catalyst to have good catalytic performance, so that the addition reaction of maleic anhydride and thioacetic acid has a high reaction efficiency.

[0014] In some alternative embodiments, at least one of the following conditions A - C is satisfied:

[0015] A The mass ratio of maleic anhydride to water is 1:(1 - 3).

[0016] B The mass ratio of maleic anhydride to the combined catalyst is 1:(0.01 - 0.04).

[0017] C The mass ratio of maleic anhydride to thioacetic acid is 1:(1 - 2).

[0018] In the above technical solution, limiting the mass ratios of maleic anhydride to water, maleic anhydride to the combined catalyst, and maleic anhydride to thioacetic acid within specific ranges can enable the concentrations of the reaction raw materials in the reaction system and the mass ratio of the combined catalyst to be within a better range, thereby making the reaction more complete.

[0019] In some alternative embodiments, during the first heat treatment, the treatment temperature is 40 to 80 °C.

[0020] In the above technical solution, the addition reaction in the first stage is an exothermic reaction. Controlling the treatment temperature during the first heat treatment within a specific range, on the one hand, setting the upper temperature limit can effectively avoid the reaction from being too violent, thereby effectively reducing the risk of generating by-products and further helping to improve the purity and yield of mercaptosuccinic acid; on the other hand, setting the lower temperature limit is to provide more suitable reaction conditions so that the reaction raw materials can react fully.

[0021] In some alternative embodiments, during the second heat treatment, the treatment temperature is 80 to 100 °C.

[0022] In the above technical solution, the second stage is a hydrolysis reaction. Limiting the treatment temperature during the hydrolysis process within a specific range can enable the reaction intermediate to be fully converted into mercaptosuccinic acid.

[0023] In some alternative embodiments, the step of adding thioacetic acid to the mixed aqueous solution includes: dropping thioacetic acid into the mixed aqueous solution within 5 to 8 hours.

[0024] In the above technical solution, controlling the dropping time of thioacetic acid under suitable conditions can make the mass ratio of thioacetic acid in the reaction system at a relatively low level, so that maleic anhydride and thioacetic acid can react fully under relatively mild conditions.

[0025] In some alternative embodiments, during the first cooling crystallization, the treatment temperature is 5 to 30 °C.

[0026] In the above technical solution, limiting the treatment temperature during the first cooling crystallization within a specific range can make the crystallization of mercaptosuccinic acid in the solution more complete.

[0027] In some alternative embodiments, the step of dissolving maleic anhydride and the combined catalyst in water and mixing them includes: dissolving maleic anhydride and the combined catalyst in water and mixing them under heating conditions, and the upper limit of the treatment temperature is not higher than the lower limit of the temperature of the first heat treatment.

[0028] Optionally, the treatment temperature is 25 to 35 °C.

[0029] In the above technical solution, heating during the process of dissolving maleic anhydride in water can improve the dissolution efficiency of maleic anhydride.

[0030] Furthermore, limiting the temperature of the heat treatment within a specific range can better improve the dissolution efficiency of maleic anhydride. Description of the Drawings

[0031] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following accompanying drawings only show some embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related accompanying drawings can also be obtained based on these drawings.

[0032] Figure 1 Process flow chart of a preparation method of mercaptosuccinic acid provided by an embodiment of the present application;

[0033] Figure 2 1H NMR spectrum of mercaptosuccinic acid provided by Embodiment 1 of the present application;

[0034] Figure 3 13C NMR spectrum of mercaptosuccinic acid provided by Embodiment 1 of the present application;

[0035] Figure 4 Infrared test result diagram of mercaptosuccinic acid provided by Embodiment 1 of the present application. Detailed implementation manners

[0036] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. For those conditions not specified in the embodiments, they shall be carried out according to conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0037] It should be noted that the "and / or" in the present application, such as "Feature 1 and / or Feature 2", all refer to the three cases of being "Feature 1" alone, being "Feature 2" alone, and "Feature 1" plus "Feature 2".

[0038] In addition, in the description of the present application, unless otherwise specified, the "multiple" in "one or more" means two or more; the range of "numerical value a to numerical value b" includes the two end values "a" and "b", and the "measurement unit" in "numerical value a to numerical value b + measurement unit" represents the "measurement unit" of both "numerical value a" and "numerical value b".

[0039] In the prior art, most of the current preparation processes of mercaptosuccinic acid use organic solvents as solvents in the initial stage of the reaction, and the subsequent hydrolysis process is usually carried out under alkaline conditions. This traditional preparation process has two major problems: on the one hand, hydrolysis under alkaline conditions usually produces a large amount of inorganic salts. The presence of inorganic salts will affect the purity of mercaptosuccinic acid. Moreover, in order to remove the inorganic salts, usually toxic acetone is used for purification. Since acetone is toxic and the management cost and raw material cost are relatively high, there are also problems in the preparation of mercaptosuccinic acid such as difficult safety guarantee and high cost; on the other hand, using organic solvents as solvents will result in relatively high raw material costs, and since the production waste liquid contains a large amount of organic solvents, it is also easy to cause environmental pollution.

[0040] Based on this, through creative research, the inventor provides a new preparation process of mercaptosuccinic acid, which can directly use water as a solvent, and the subsequent hydrolysis does not need to be carried out under alkaline conditions, so as to improve the problem of relatively low purity of the prepared mercaptosuccinic acid. At the same time, it can also reduce the preparation cost of mercaptosuccinic acid and take into account the problem of environmental pollution.

[0041] The following specifically describes a preparation method of mercaptosuccinic acid according to an embodiment of the present application.

[0042] The embodiment of the present application provides a preparation method of mercaptosuccinic acid, including the following steps:

[0043] Dissolve maleic anhydride and a combined catalyst in water and mix them, and then add thioacetic acid to the mixed aqueous solution to obtain a precursor solution. The combined catalyst includes acidic pyridine and basic amine; perform a first heating treatment on the precursor solution to enable the addition reaction of maleic anhydride and thioacetic acid to obtain an intermediate reaction solution, and perform a second heating treatment on the intermediate reaction solution. The lower limit of the temperature of the second heating treatment is not lower than the upper limit of the temperature of the first heating treatment to enable the hydrolysis reaction of the intermediate in the intermediate reaction solution, and then perform a first cooling crystallization on the system after the hydrolysis of the intermediate reaction solution to enable the crystallization and precipitation of mercaptosuccinic acid.

[0044] In the present application, when preparing mercaptosuccinic acid according to the preparation method provided by the embodiment of the present application, on the one hand, it is not necessary to create an alkaline condition during the hydrolysis process, that is, it is not necessary to add alkaline substances, so inorganic salts will not be generated during the hydrolysis process. Compared with the existing preparation process, inorganic salts will not be generated to reduce the purity of mercaptosuccinic acid. Correspondingly, it is not necessary to use toxic acetone for the purification of mercaptosuccinic acid, so the purity of the prepared mercaptosuccinic acid can be improved. At the same time, it also has the advantage of better safety; on the other hand, directly using water as a solvent can effectively reduce the preparation cost of mercaptosuccinic acid and take into account the problem of environmental pollution compared with the existing preparation process.

[0045] It is understandable that in order to better control the reaction process, it is necessary to monitor the content changes of reaction raw materials and reaction intermediates during the addition reaction and hydrolysis reaction respectively.

[0046] It should be noted that the monitoring method is not limited. For example, high performance liquid chromatography or gas-liquid chromatography can be used.

[0047] To better understand the technical solution, an auxiliary explanation is given here through reaction equations.

[0048] The reaction equation in the addition stage is as follows:

[0049]

[0050] The reaction equation in the hydrolysis stage is as follows:

[0051]

[0052] It is understandable that during the first cooling crystallization process, due to the large volume of the mixed system, it is difficult to crystallize out all the mercaptosuccinic acid. Therefore, considering the yield of mercaptosuccinic acid, secondary cooling crystallization can be carried out.

[0053] As an example, after the first cooling crystallization, it further includes concentrating and second cooling crystallizing the mother liquor obtained after the first cooling crystallization in sequence, so that the mercaptosuccinic acid in the mother liquor crystallizes out.

[0054] In this embodiment, carrying out the second cooling crystallization on the mother liquor after the first cooling crystallization can effectively collect the remaining mercaptosuccinic acid in the mother liquor. Correspondingly, the yield of mercaptosuccinic acid is equal to the sum of the yields obtained after the two cooling crystallizations, thereby effectively improving the yield of mercaptosuccinic acid; among them, concentrating the mother liquor before the second crystallization can increase the concentration of mercaptosuccinic acid in the mother liquor, thereby improving the efficiency of the second cooling crystallization.

[0055] It is understandable that the types of acidic pyridine and basic amine in the combined catalyst are not limited and can be set according to the conventional selection in the art.

[0056] As an example, the acidic pyridine includes at least one of pyridine-2-carboxylic acid, pyridine-3-carboxylic acid, and pyridine-4-carboxylic acid; and / or, the basic amine includes at least one of pyridine, piperidine, piperazine, 2-methylpyridine, 1-methylpiperidine, and N-methylpiperazine.

[0057] In this embodiment, the types of acidic pyridine and basic amine applicable to the technical solution provided by the embodiments of the present application are relatively rich, and many feasible implementation solutions can be provided, thereby facilitating the popularization and application of the technical solution of the present application.

[0058] It is understandable that, considering the catalytic performance of the combined catalyst, the mass ratio of the two monomer catalysts can be adjusted.

[0059] As an example, the mass ratio of acidic pyridine to basic amine is 1:(0.8 - 1.2), such as but not limited to any one of the point values of 1:0.8, 1:0.9, 1:1.0, 1:1.1, and 1:1.2 or the range values between any two of them.

[0060] In this embodiment, limiting the mass ratio of acidic pyridine to basic amine within a specific range can enable the combined catalyst to have good catalytic performance, so that the addition reaction of maleic anhydride and thioacetic acid has a high reaction efficiency.

[0061] It is understandable that under suitable reaction conditions (such as the concentration of reaction raw materials, the dosage of the combined catalyst, and the treatment temperature of the first heat treatment, etc.), both the efficiency of the addition reaction and the utilization rate of the reaction raw materials can be effectively improved.

[0062] As an example, at least one of the following conditions A - C is satisfied:

[0063] A The mass ratio of maleic anhydride to water is 1:(1 - 3), such as but not limited to any one of the point values of 1:1, 1:1.5, 1:2, 1:2.5, and 1:3 or the range values between any two of them.

[0064] B The mass ratio of maleic anhydride to the combined catalyst is 1:(0.01 - 0.04), such as but not limited to any one of the point values of 1:0.01, 1:0.02, 1:0.03, and 1:0.04 or the range values between any two of them.

[0065] C The mass ratio of maleic anhydride to thioacetic acid is 1:(1 - 2), such as but not limited to any one of the point values of 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, and 1:2.0 or the range values between any two of them.

[0066] In this embodiment, limiting the mass ratios of maleic anhydride to water, maleic anhydride to the combined catalyst, and maleic anhydride to thioacetic acid within specific ranges can enable the concentration of the reaction raw materials in the reaction system and the mass ratio of the combined catalyst to be within better ranges, thereby making the reaction more complete.

[0067] As an example, during the first heat treatment, the treatment temperature is 40 to 80 °C, such as but not limited to any one of the point values of 40 °C, 50 °C, 60 °C, 70 °C, and 80 °C or the range values between any two of them.

[0068] In this embodiment, the addition reaction in the first stage is an exothermic reaction. By controlling the treatment temperature during the first heat treatment within a specific range, on the one hand, setting the upper temperature limit can effectively avoid the reaction from being too violent, thereby effectively reducing the risk of generating by-products, and further contributing to improving the purity and yield of mercaptosuccinic acid; on the other hand, setting the lower temperature limit is to provide more suitable reaction conditions so that the reaction raw materials can fully react.

[0069] It can be understood that under suitable reaction conditions (such as the treatment temperature of the second heat treatment), in the hydrolysis reaction stage, the intermediate can be more completely converted into mercaptosuccinic acid.

[0070] As an example, during the second heat treatment, the treatment temperature is 80 to 100 °C, such as but not limited to any one of the point values of 80 °C, 85 °C, 90 °C, 95 °C, and 100 °C or the range values between any two of them.

[0071] In this embodiment, the second stage is a hydrolysis reaction. Limiting the treatment temperature during the hydrolysis process within a specific range can enable the reaction intermediate to be fully converted into mercaptosuccinic acid.

[0072] It should be noted that during the addition reaction, if the reaction is too violent, it will cause by-products to be generated after the raw materials react and the target product cannot be obtained. In order to create more mild reaction conditions, the dropping time of thioacetic acid can be adjusted.

[0073] As an example, the step of adding thioacetic acid to the mixed aqueous solution includes: dropping thioacetic acid into the mixed aqueous solution within 5 to 8 hours.

[0074] In this embodiment, controlling the dropping time of thioacetic acid under suitable conditions can enable the mass ratio of thioacetic acid in the reaction system to be at a relatively low level, so that maleic anhydride and thioacetic acid can react fully under more mild conditions.

[0075] It can be understood that the treatment temperature of cooling crystallization is related to the crystallization effect.

[0076] As an example, during the first cooling crystallization, the treatment temperature is 5 to 30 °C, such as but not limited to any one of the point values of 5 °C, 10 °C, 20 °C, and 30 °C or the range values between any two of them.

[0077] In this embodiment, the treatment temperature in the first cooling crystallization process is limited to a specific range, which can make the mercaptosuccinic acid in the solution crystallize more completely.

[0078] It should be noted that, due to the physical and chemical properties of the reaction raw materials themselves, maleic anhydride dissolves slowly in water. Considering the dissolution efficiency, the process of the dissolution stage can be adjusted.

[0079] As an example, the step of dissolving maleic anhydride and the combined catalyst in water and mixing includes: dissolving maleic anhydride and the combined catalyst in water and mixing under heating conditions, and the upper limit of the treatment temperature is not higher than the lower limit of the temperature of the first heating treatment.

[0080] In this embodiment, heating is performed during the process of dissolving maleic anhydride in water, which can improve the dissolution efficiency of maleic anhydride.

[0081] As an example, the processing temperature is 25-35° C., for example but not limited to, the processing temperature is any one of 25° C., 30° C., and 35° C., or a range between any two of them.

[0082] In this embodiment, the temperature of the heat treatment is limited to a specific range, which can better improve the dissolution efficiency of maleic anhydride.

[0083] It should be noted that any process or step not specifically described or limited in the method for preparing mercaptosuccinic acid may be arranged according to conventional selections in the art.

[0084] As an example, after cooling and crystallizing, filtering and drying are further performed in sequence.

[0085] As an example, the process flow chart of the preparation method of mercaptosuccinic acid is shown as follows: Figure 1 shown.

[0086] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0087] Example 1

[0088] The present invention provides a method for preparing mercaptosuccinic acid, comprising the following steps:

[0089] Dissolve maleic anhydride and the combined catalyst in water and stir and mix at 30°C to completely dissolve the maleic anhydride. Then, add thioacetic acid dropwise to the mixed aqueous solution to obtain a precursor solution; wherein the mass of maleic anhydride is 20 g (i.e., 1 equivalent), the mass of the combined catalyst is 0.02 equivalents (the mass ratio of 2-pyridinecarboxylate and pyridine is 1:1), the mass of thioacetic acid is 1.2 equivalents, and the addition time is 6 hours.

[0090] The precursor solution was heated to 60 °C and kept at this temperature for reaction. The remaining amount of maleic anhydride was tracked by HPLC until maleic anhydride was completely reacted, and an intermediate reaction solution was obtained.

[0091] The intermediate reaction solution was heated to 90 °C and kept at this temperature for reaction. The remaining amount of the intermediate was tracked by HPLC until the intermediate was completely reacted. Then, the temperature was lowered to 20 °C, followed by filtration and drying to obtain the first precipitate of mercaptosuccinic acid.

[0092] The mother liquor obtained after the first cooling crystallization was concentrated and then subjected to a second cooling crystallization in sequence to precipitate mercaptosuccinic acid in the mother liquor. Filtration and drying were carried out in sequence to obtain the second precipitate of mercaptosuccinic acid.

[0093] In the subsequent examples and comparative examples, unless otherwise specified, the process was carried out according to the process of Example 1.

[0094] To better understand the differences between each example and comparative example, a summary description is provided in the form of a table here.

[0095] Table 1 Process conditions of each example and comparative example

[0096]

[0097]

[0098] To better illustrate the differences between the technical solutions provided in the examples of the present application and the prior art, Comparative Example 4 is also provided in the present application.

[0099] Comparative Example 4

[0100] The comparative example of the present application provides a method for preparing mercaptosuccinic acid, and the difference from Example 1 is only that: sodium hydroxide was added to the intermediate reaction solution and heated to 90 °C for holding reaction. The remaining amount of the intermediate was tracked by HPLC until the intermediate was completely reacted. After the reaction ended, acid was added to adjust the pH of the mixed system to 2, and then the temperature was lowered to 20 °C, followed by filtration and drying to obtain the first precipitate of mercaptosuccinic acid.

[0101] The mother liquor obtained after the first cooling crystallization was concentrated and then subjected to a second cooling crystallization in sequence to precipitate mercaptosuccinic acid in the mother liquor. Filtration and drying were carried out in sequence to obtain the second precipitate of mercaptosuccinic acid.

[0102] Test Example 1

[0103] Purity test of mercaptosuccinic acid

[0104] Test method:

[0105] The preparation of mercaptosuccinic acid was carried out according to the preparation methods of Examples 1 to 17 and Comparative Examples 1 to 4 respectively. Then, the monohydrate of mercaptosuccinic acid in each example and comparative example was configured into a test sample for HPLC, and its product purity was tested by an HPLC device.

[0106] Table 2 Purity of the monohydrate of mercaptosuccinic acid in each example and comparative example

[0107] Number Purity (%) Number of impurities Largest single impurity (%) Sodium ion content Example 1 99.5 3 0.3 0.6 ppm Example 2 99.3 3 0.4 0.6 ppm Example 3 99.6 3 0.2 0.8 ppm Example 4 96.0 3 2.5 0.6 ppm Example 5 99.0 3 0.4 0.5 ppm Example 6 99.5 3 0.3 0.6 ppm Example 7 99.6 3 0.3 0.6 ppm Example 8 99.5 3 0.4 0.6 ppm Example 9 99.0 4 0.8 0.6 ppm Example 10 98.5 4 1.5 0.7 ppm Example 11 99.2 3 0.4 0.8 ppm Example 12 99.8 2 0.2 0.7 ppm Example 13 99.7 3 0.2 0.6 ppm Example 14 98.3 3 0.5 0.8 ppm Example 15 90.3 6 4.8 0.7 ppm Example 16 99.5 3 0.2 0.6 ppm Example 17 98.5 4 0.9 0.7 ppm Comparative Example 1 97.6 4 1.8 0.7 ppm Comparative Example 2 98.5 3 0.9 0.6 ppm Comparative Example 3 95.9 5 1.0 0.6 ppm Comparative Example 4 93.6 6 2.5 1.5％

[0108] Referring to Table 2, from the test results of Examples 1 to 3, Examples 5 to 8, Examples 11 to 14, and Examples 16 to 17 and Comparative Example 4, it can be seen that when prepared according to the preparation process provided in the examples of the present application, compared with hydrolysis under alkaline conditions, the mercaptosuccinic acid corresponding to the former has a higher purity.

[0109] From the test results of Example 4, Examples 9 to 10, and Example 15 and Example 1, it can be seen that according to the principle of single variable, when each corresponding parameter is controlled within the specific range provided in the examples of the present application, compared with not within the specific range, the mercaptosuccinic acid corresponding to the former has a higher purity.

[0110] From the test results of Comparative Examples 1 to 3 and Example 1, it can be seen that by using the combined catalyst provided in the examples of the present application, compared with using only one component as the catalyst and without setting a catalyst, the mercaptosuccinic acid corresponding to the former has a higher purity.

[0111] Test Example 2

[0112] Yield test of mercaptosuccinic acid

[0113] Test method:

[0114] The preparation of mercaptosuccinic acid was carried out according to the preparation methods of Examples 1 to 17 and Comparative Examples 1 to 4 respectively. Then, according to the theoretical yield (30.60 g) and the actual yield of the product, the yields of the monohydrate and dihydrate of mercaptosuccinic acid in each example and comparative example were calculated respectively.

[0115] Table 3 Yields of the monohydrate and dihydrate of mercaptosuccinic acid in each example and comparative example

[0116]

[0117]

[0118] Referring to Table 3, from the test results of Examples 1-3, Examples 5-8, Examples 11-14, and Examples 16-17 and Comparative Example 4, it can be seen that when prepared according to the preparation process provided in the embodiments of the present application, compared with hydrolysis under alkaline conditions, the mercaptosuccinic acid corresponding to the former has a higher total yield.

[0119] From the test results of Example 4, Examples 9-10, and Example 15 and Example 1, it can be seen that according to the principle of single variable, by controlling each corresponding parameter within the specific range provided in the embodiments of the present application, compared with not within the specific range, the mercaptosuccinic acid corresponding to the former has a higher total yield.

[0120] From the test results of Comparative Examples 1-3 and Example 1, it can be seen that by using the combined catalyst provided in the embodiments of the present application, compared with using only one component as the catalyst and without setting a catalyst, the mercaptosuccinic acid corresponding to the former has a higher total yield.

[0121] Test Example 3

[0122] Qualitative Characterization of Mercaptosuccinic Acid

[0123] Test Method:

[0124] Prepare mercaptosuccinic acid according to the preparation process of Example 1. Then, prepare samples of the mercaptosuccinic acid monohydrate during the preparation process according to the standards of nuclear magnetic resonance test requirements and infrared test requirements. Among them, the solvent in the nuclear magnetic resonance test sample is D2O, and the reference salt in the infrared test sample is potassium bromide.

[0125] Referring to Figure 2 It can be seen that the nuclear magnetic resonance hydrogen spectrum results show two groups of peaks, namely δ3.81-3.70 (m, 1H) and 3.04-2.80 (m, 2H). The signal attribution is shown in the following figure, and the integral ratio of the two groups of peaks is about 1:2 (corresponding to two kinds of hydrogen at different positions, and the number ratio is 1:2), which is consistent with the theoretical result, proving that the prepared product is mercaptosuccinic acid.

[0126]

[0127] Referring to Figure 3 It can be seen that the nuclear magnetic resonance carbon spectrum results show four groups of peaks, namely δ177.12, 175.27, 67.19, 39.93, and 36.42. The signal attribution is shown in the following figure, which is consistent with the theoretical result, proving that the prepared product is mercaptosuccinic acid.

[0128]

[0129] Referring to Figure 4 It can be seen that 3300-2405cm -1The region has an extremely wide band, which is the characteristic absorption peak of -COOH. The overlapping 2560 cm -1 absorption band is the characteristic absorption peak of -SH. 2962 cm -1 and 2910 cm -1 are the characteristic absorption peaks of saturated C-H. 1703 cm -1 is the characteristic absorption peak of the carbonyl group in -COOH, which is consistent with the theoretical results, proving that the prepared product is mercaptosuccinic acid.

[0130] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of this application claimed, but merely represents selected embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without making creative efforts fall within the scope of protection of this application.

Claims

1. A preparation method of mercaptosuccinic acid, characterized in that, Comprising the following steps; Dissolve maleic anhydride and a combined catalyst in water and mix them, then add thioacetic acid to the mixed aqueous solution to obtain a precursor solution, wherein the combined catalyst comprises acidic pyridine and basic amine; Conduct a first heating treatment on the precursor solution to enable an addition reaction between the maleic anhydride and the thioacetic acid to obtain an intermediate reaction solution; And Conduct a second heating treatment on the intermediate reaction solution, the lower limit of the temperature of the second heating treatment is not lower than the upper limit of the temperature of the first heating treatment, to enable hydrolysis reaction of the intermediate in the intermediate reaction solution, and then conduct a first cooling crystallization on the system after hydrolysis of the intermediate reaction solution to precipitate mercaptosuccinic acid crystals; The acidic pyridine includes at least one of pyridine-2-carboxylic acid, pyridine-3-carboxylic acid and pyridine-4-carboxylic acid; and / or, the basic amine includes at least one of pyridine, piperidine, piperazine, 2-methylpyridine, 1-methylpiperidine and N-methylpiperazine; The mass ratio of the acidic pyridine to the basic amine is 1:(0.8 - 1.2).

2. The preparation method of mercaptosuccinic acid according to claim 1, characterized in that, After the first cooling crystallization, it further includes successively concentrating and conducting a second cooling crystallization on the mother liquor obtained after the first cooling crystallization to precipitate mercaptosuccinic acid crystals in the mother liquor.

3. The preparation method of mercaptosuccinic acid according to claim 1 or 2, characterized in that, Meet at least one of the following conditions A - C: A The mass ratio of the maleic anhydride to the water is 1:(1 - 3); B The mass ratio of the maleic anhydride to the combined catalyst is 1:(0.01 - 0.04); C The mass ratio of the maleic anhydride to the thioacetic acid is 1:(1 - 2).

4. The preparation method of mercaptosuccinic acid according to claim 1 or 2, characterized in that, During the first heating treatment, the treatment temperature is 40 - 80°C.

5. The preparation method of mercaptosuccinic acid according to claim 1 or 2, characterized in that, During the second heating treatment, the treatment temperature is 80 - 100°C.

6. The preparation method of mercaptosuccinic acid according to claim 1 or 2, characterized in that, The step of adding thioacetic acid to the mixed aqueous solution includes: dropping thioacetic acid into the mixed aqueous solution within 5 - 8 h.

7. The preparation method of mercaptosuccinic acid according to claim 1 or 2, characterized in that, During the first cooling crystallization, the treatment temperature is 5 - 30°C.

8. The preparation method of mercaptosuccinic acid according to claim 1 or 2, characterized in that, The step of dissolving maleic anhydride and the combined catalyst in water and mixing them includes: dissolving maleic anhydride and the combined catalyst in water and mixing them under heating conditions, and the upper limit of the treatment temperature is not higher than the lower limit of the temperature of the first heating treatment.

9. The preparation method of mercaptosuccinic acid according to claim 8, characterized in that, The treatment temperature is 25 - 35°C.

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