High purity sodium 5-sulfoisophthalate and process for its preparation

Abstract

The application discloses high-purity sodium 5-sulfoisophthalate and a preparation method thereof, relates to the field of sodium 5-sulfoisophthalate, and provides the preparation method, which comprises the following steps: taking liquid SO2 as a solvent, compounding a cosolvent to form a reaction system, taking isophthalic acid as raw material, and taking SO3 as a sulfonating reagent; and then performing sulfonation, neutralization reaction and post-treatment to obtain high-purity sodium 5-sulfoisophthalate. In the application, liquid SO2 and the cosolvent are combined to form a highly-uniform reaction system, which provides a basis for subsequent high-selectivity sulfonation reaction, improves the selectivity of the sulfonation reaction and the raw material conversion rate, the liquid SO2 used in the application is cheap and easy to obtain, can be condensed and recycled, and is helpful to reduce three-waste emissions and production cost.

Description

Technical Field

[0001] This invention relates to the field of sodium isophthalic acid-5-sulfonate, and more specifically to a high-purity sodium isophthalic acid-5-sulfonate and its preparation method. Background Technology

[0002] Sodium isophthalate-5-sulfonate (also known as 5-(sodium sulfonyl)isophthalic acid, English code 5-SSIPA) is not only an important organic synthesis intermediate but also an excellent novel anionic surfactant, playing a crucial role in the dyeing modification of polyester. Compared to traditional polyester dyeing modifiers, sodium isophthalate-5-sulfonate, in the preparation of polyester fibers (such as CDP and ECDP), sodium isophthalate-5-sulfonate, as the third monomer in polymerization, can avoid the generation of flammable and explosive byproduct methanol during polymerization, thus improving the safety of the production process. Simultaneously, because polyester fibers contain sulfonic acid groups, sodium isophthalate-5-sulfonate has a good affinity for cationic dyes, enabling dyed fibers to have brighter colors, a complete color spectrum, and the ability to achieve deep dyeing, while also providing anti-pilling effects.

[0003] Sodium isophthalic acid-5-sulfonate is obtained by neutralization of isophthalic acid through a sulfonation reaction. Currently, the main methods for preparing sodium isophthalic acid-5-sulfonate include chlorosulfonic acid sulfonation, SO3 sulfonation, and fuming sulfuric acid sulfonation. While the fuming sulfuric acid sulfonation method has advantages such as simple operation and low raw material cost, it suffers from low product recovery rate, numerous byproducts, poor quality stability, high overall cost, and the generation of large amounts of strongly acidic waste. The investment in environmental protection equipment for treating this waste is several times that of the entire production equipment, thus limiting its practical application. SO3 is a strong electrophilic reagent and reacts more readily with isophthalic acid through a sulfonation reaction. From the perspective of the reaction mechanism, the SO3 sulfonation method is the most efficient method. However, in actual production, due to the high reactivity of SO3, the reaction conditions are not easy to control and side reactions are easily triggered. Moreover, affected by the freezing point of SO3, the viscosity of the isophthalic acid sulfonation system is relatively large, and the heat and mass transfer effects are poor. As the reaction proceeds and SO3 is continuously consumed, the viscosity of the system further increases. Industrial production places high demands on equipment.

[0004] Based on this, a new method for preparing sodium isophthalic acid-5-sulfonate using SO3 as a sulfonating agent was developed to solve the problems of high SO3 activity leading to difficulty in controlling reaction conditions and causing side reactions. This provides a new approach for the industrial production of sodium isophthalic acid-5-sulfonate and has good practical significance. Summary of the Invention

[0005] To address the technical problems mentioned in the background section, this invention provides a high-purity sodium isophthalate-5-sulfonate and its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions: A high-purity sodium isophthalic acid-5-sulfonate, the preparation method of which includes the following steps: Liquid SO2 was cooled and sealed, stirred, and a co-solvent was added. Stirring continued, followed by heating. Isophthalic acid was added and stirred, and SO3 was added dropwise. After the dropwise addition was completed, the temperature was raised and stirring continued. The pressure was then reduced to atmospheric pressure, and nitrogen gas was introduced to recover the SO2 gas. The reaction residue was rotary evaporated, and an alkaline solution was added to adjust the pH. The mixture was stirred, filtered, and the filter cake was washed with deionized water. Finally, it was dried under vacuum to obtain high-purity sodium isophthalic acid-5-sulfonate.

[0007] Furthermore, the preparation method of the high-purity sodium isophthalate-5-sulfonate includes the following specific steps: Liquid SO2 is cooled to -5°C to 0°C and sealed. Stirring is started for 10-12 minutes. A co-solvent is added, and the mixture is stirred at a constant temperature of -5°C to 0°C for 20-25 minutes. The temperature is then raised to 0-5°C, and isophthalic acid is added. The mixture is stirred for 50-60 minutes, and SO3 is added dropwise over 1-1.5 hours. After the addition is complete, the temperature is raised to room temperature, and stirring is continued for 3.5-4 hours. The pressure is then reduced to atmospheric pressure, and nitrogen gas is introduced for 2-3 hours. SO2 gas is recovered using a cold trap. The reaction residue is rotary evaporated, and an alkaline solution is added to adjust the pH to 5.5-6.5. The mixture is stirred for 1-1.2 hours, filtered, and the filter cake is washed with deionized water. Finally, the filter cake is vacuum dried at 60-70°C for 8-9 hours to obtain high-purity sodium isophthalate-5-sulfonate.

[0008] Furthermore, the mass ratio of liquid SO2, co-solvent, isophthalic acid, and SO3 is 30:(3.0-4.5):5.0:(2.5-3.5).

[0009] Furthermore, the cosolvent is obtained by mixing acetonitrile, trifluorotoluene, and carboxylated imidazole acetate in a mass ratio of (15-20):(10-15):(3-8).

[0010] Furthermore, the stirring speed was 300-400 rpm.

[0011] Furthermore, during the depressurization process, the depressurization rate is controlled at 4-5 kPa / min, and paused for 5-10 minutes every 50 kPa decrease; the nitrogen flow rate is 30-40 mL / min.

[0012] Furthermore, the alkaline solution is a sodium hydroxide solution with a mass fraction of 5-10%.

[0013] Furthermore, the cold trap is a dry ice-acetone cold trap.

[0014] Furthermore, the dry ice-acetone cold trap is prepared by adding acetone to a Dewar flask, adding solid carbon dioxide in batches while stirring, until there is an excess of solid carbon dioxide in the system and the temperature is stable at -78℃, thus obtaining the dry ice-acetone cold trap.

[0015] Furthermore, the preparation method of the carboxyl-containing imidazole acetate includes the following steps: Step (1): In a protective gas atmosphere, bromoacetic acid was added to toluene, and after stirring, 1,2-dimethylimidazole was added. The mixture was refluxed, heated and stirred, cooled, rotary evaporated, washed with ethyl acetate, and dried under vacuum to obtain carboxyl imidazole bromide. Step (2): Mix carboxyl imidazole bromide and anhydrous methanol, introduce a protective gas, stir, add anhydrous sodium acetate, heat and stir, filter, rotary evaporate the filtrate, and vacuum dry to obtain carboxyl imidazole acetate.

[0016] Furthermore, the preparation method of the carboxyl-containing imidazole acetate includes the following specific steps: Step (1): In a protective gas atmosphere, add bromoacetic acid to toluene, stir for 10-15 min, add 1,2-dimethylimidazole, turn on reflux, heat to 80-95℃, stir for 5-6 h, cool to room temperature, rotary evaporate, wash with ethyl acetate, and vacuum dry to obtain carboxyl imidazole bromide. Furthermore, the ratio of toluene, bromoacetic acid, and 1,2-dimethylimidazole is (30-35) g : (7.5-8) g : (5-5.5) g.

[0017] In step (1), bromoacetic acid reacts with 1,2-dimethylimidazole to obtain a carboxyl-containing imidazolium bromide.

[0018] Step (2): Mix carboxyl imidazole bromide and anhydrous methanol, introduce a protective gas, stir for 30-35 min, add anhydrous sodium acetate, heat to 35-40℃, stir for 8-9 h, filter, rotary evaporate the filtrate, and vacuum dry to obtain carboxyl imidazole acetate.

[0019] Furthermore, the ratio of carboxyl imidazole bromide, anhydrous methanol, and anhydrous sodium acetate is (13.5-14.5) g : (45-55) g : (5.5-6.5) g.

[0020] In step (2), the carboxyl imidazole bromide reacts with anhydrous sodium acetate to replace the bromide ions with acetate ions, thus obtaining the carboxyl imidazole acetate.

[0021] A high-purity sodium isophthalic acid-5-sulfonate is prepared by the above-described method for preparing a high-purity sodium isophthalic acid-5-sulfonate.

[0022] This invention discloses a high-purity sodium isophthalic acid-5-sulfonate and its preparation method. The preparation method uses liquid SO2 as a solvent and a compound co-solvent to form a reaction system. Isophthalic acid is used as a raw material and SO3 is used as a sulfonating agent. The target product is obtained through sulfonation, neutralization reaction and post-treatment steps.

[0023] It has the following beneficial effects: 1. By using liquid SO2 as the reaction solvent, its weak electron-donating ability can form a weak coordination complex with SO3 through the lone pair electrons of sulfur, thereby reducing the reactivity of SO3, alleviating its violent exothermic reaction and over-sulfonation problems, improving the selectivity of the sulfonation reaction and the raw material conversion rate, and effectively solving the problems of high SO3 reactivity, difficult reaction control, viscous reaction system, and difficult heat and mass transfer in the traditional SO3 sulfonation method. At the same time, the liquid SO2 used in this invention is inexpensive and readily available, and can be condensed, recovered and recycled, which helps to reduce the emission of waste gas, wastewater, and solid waste and production costs.

[0024] 2. In this invention, a co-solvent is added after liquid SO2 and before isophthalic acid. This co-solvent is obtained by mixing acetonitrile, trifluorotoluene, and carboxyl-containing imidazole acetate in a specific ratio. Acetonitrile has strong polarity and dielectric constant, which can improve the overall solvation ability of liquid SO2, stabilize the dispersion state of isophthalic acid, reduce agglomeration, and make the system more homogeneous. Trifluorotoluene has moderate hydrophobicity and an aromatic ring structure, which can form a weak π-interaction with the aromatic ring of isophthalic acid to improve dispersion, and can also... The system viscosity is adjusted to improve mass transfer and prevent excessively high local concentrations of raw materials from precipitation. Furthermore, the strong electron-withdrawing effect of trifluoromethyl groups makes them difficult to sulfonate, preventing ineffective consumption of SO3. The carboxyl and acetate groups in carboxyl-containing imidazole acetate can form intermolecular hydrogen bonds with the carboxyl groups of isophthalic acid, weakening the intermolecular hydrogen bonds and lattice stacking of isophthalic acid, thus improving its dispersibility and solvation in the system. Simultaneously, the imidazole cations and the aromatic rings of isophthalic acid generate π-π stacking interactions, further improving dispersion. Through the synergistic effect of liquid SO2 and the co-solvent, a highly homogeneous reaction system can be formed, providing a foundation for subsequent highly selective sulfonation reactions. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1 The preparation method of carboxyl imidazole acetate includes the following steps: Step (1): In a nitrogen atmosphere, bromoacetic acid was added to toluene and stirred at room temperature for 10 min. Then, 1,2-dimethylimidazole was added, reflux was started, and the mixture was heated to 80°C and stirred for 5 h. After cooling to room temperature, the mixture was rotary evaporated at 40°C, washed three times with ethyl acetate, and dried under vacuum at 40°C for 6 h to obtain carboxyl imidazole bromide. The ratio of toluene, bromoacetic acid, and 1,2-dimethylimidazole was 30 g: 7.5 g: 5 g.

[0027] Step (2): Mix carboxyl imidazole bromide and anhydrous methanol, purge with nitrogen, stir at room temperature for 30 min, add anhydrous sodium acetate, heat to 35℃, stir for 8 h, filter, rotary evaporate the filtrate at 40℃, and then vacuum dry at 60℃ for 12 h to obtain carboxyl imidazole acetate. The ratio of carboxyl imidazole bromide, anhydrous methanol, and anhydrous sodium acetate is 13.5 g: 45 g: 5.5 g.

[0028] Example 2 The preparation method of carboxyl imidazole acetate includes the following steps: Step (1): In a nitrogen atmosphere, bromoacetic acid was added to toluene and stirred at room temperature for 13 min. Then, 1,2-dimethylimidazole was added, reflux was started, and the mixture was heated to 88°C and stirred for 5.5 h. The mixture was then cooled to room temperature, rotary evaporated at 40°C, washed four times with ethyl acetate, and vacuum dried at 43°C for 6.5 h to obtain carboxyl imidazole bromide. The ratio of toluene, bromoacetic acid, and 1,2-dimethylimidazole was 33 g: 7.8 g: 5.3 g.

[0029] Step (2): Mix carboxyl imidazole bromide and anhydrous methanol, purge with nitrogen, stir at room temperature for 33 min, add anhydrous sodium acetate, heat to 38℃, stir for 8.5 h, filter, rotary evaporate the filtrate at 40℃, and then vacuum dry at 60℃ for 12 h to obtain carboxyl imidazole acetate. The ratio of carboxyl imidazole bromide, anhydrous methanol, and anhydrous sodium acetate is 14.0 g: 50 g: 6.0 g.

[0030] Example 3 The preparation method of carboxyl imidazole acetate includes the following steps: Step (1): In a nitrogen atmosphere, bromoacetic acid was added to toluene and stirred at room temperature for 15 min. Then, 1,2-dimethylimidazole was added, reflux was started, and the mixture was heated to 95°C and stirred for 6 h. The mixture was cooled to room temperature, rotary evaporated at 40°C, washed three to five times with ethyl acetate, and dried under vacuum at 45°C for 7 h to obtain carboxyl imidazole bromide. The ratio of toluene, bromoacetic acid, and 1,2-dimethylimidazole was 35 g: 8 g: 5.5 g.

[0031] Step (2): Mix carboxyl imidazole bromide and anhydrous methanol, purge with nitrogen, stir at room temperature for 35 min, add anhydrous sodium acetate, heat to 40℃, stir for 9 h, filter, rotary evaporate the filtrate at 40℃, and then vacuum dry at 60℃ for 12 h to obtain carboxyl imidazole acetate. The ratio of carboxyl imidazole bromide, anhydrous methanol, and anhydrous sodium acetate is 14.5 g: 55 g: 6.5 g.

[0032] Example 4 A high-purity sodium isophthalic acid-5-sulfonate, the preparation method of which includes the following steps: Liquid SO2 was cooled to -5°C and sealed. Stirring was started and continued for 10 minutes. A co-solvent was added, and the mixture was stirred at -5°C for another 20 minutes. The temperature was then raised to 0°C, and isophthalic acid was added. The mixture was stirred for 50 minutes, and then SO3 was added dropwise over 1 hour. After the addition was complete, the temperature was raised to room temperature, and stirring was continued for 3.5 hours. The pressure was then reduced to atmospheric pressure, and nitrogen gas was introduced for 2 hours. SO2 gas was recovered using a cold trap. The reaction residue was rotary evaporated at 55°C, cooled to room temperature, and the pH was adjusted to 5.5 with alkali solution. The mixture was stirred at room temperature for 1 hour, filtered, and the filter cake was washed three times with deionized water. Finally, the filter cake was vacuum dried at 60°C for 8 hours to obtain high-purity sodium isophthalate-5-sulfonate.

[0033] The mass ratio of liquid SO2, co-solvent, isophthalic acid, and SO3 was 30:3.0:5.0:2.5. The co-solvent was prepared by mixing acetonitrile, trifluorotoluene, and the carboxyl imidazole acetate obtained in Example 1 in a mass ratio of 15:10:3. The stirring speed was 300 rpm. During the depressurization process, the depressurization rate was controlled at 4 kPa / min, and the pressure was paused for 5 min after every 50 kPa reduction. The nitrogen flow rate was 30 mL / min. The alkaline solution was a 5% sodium hydroxide solution. The cold trap was a dry ice-acetone cold trap, which was prepared by adding 330 mL of acetone to a 500 mL Dewar flask and adding 330 g of solid carbon dioxide in three batches (110 g per batch) while stirring at 100 rpm. The temperature was stabilized at -78 °C to obtain the dry ice-acetone cold trap.

[0034] Example 5 A high-purity sodium isophthalic acid-5-sulfonate, the preparation method of which includes the following steps: Liquid SO2 was cooled to -3°C and sealed. Stirring was started and continued for 11 minutes. A co-solvent was added, and the mixture was stirred at -3°C for another 23 minutes. The temperature was then raised to 3°C, and isophthalic acid was added. The mixture was stirred for 55 minutes, and then SO3 was added dropwise over 1.3 hours. After the addition was complete, the temperature was raised to room temperature, and stirring was continued for 3.7 hours. The pressure was then reduced to atmospheric pressure, and nitrogen gas was introduced for 2.5 hours. SO2 gas was recovered using a cold trap. The reaction residue was rotary evaporated at 55°C, cooled to room temperature, and the pH was adjusted to 6.0 with alkali solution. The mixture was stirred at room temperature for 1.1 hours, filtered, and the filter cake was washed four times with deionized water. Finally, the filter cake was vacuum dried at 65°C for 8.5 hours to obtain high-purity sodium isophthalate-5-sulfonate.

[0035] The mass ratio of liquid SO2, co-solvent, isophthalic acid, and SO3 was 30:3.7:5.0:3.0; the co-solvent was obtained by mixing acetonitrile, trifluorotoluene, and the carboxyl imidazole acetate obtained in Example 2 in a mass ratio of 17:13:5.5; the stirring speed was 350 rpm; the pressure reduction rate was controlled at 4.5 kPa / min during the pressure reduction process, and the pressure was paused for 8 min after every 50 kPa reduction; the nitrogen flow rate was 35 mL / min; the alkaline solution was an 8% sodium hydroxide solution; the cold trap was a dry ice-acetone cold trap, which was prepared by adding 330 mL of acetone to a 500 mL Dewar flask, and then adding 330 g of solid carbon dioxide in three batches (110 g per batch) while stirring, and stabilizing the temperature at -78 °C to obtain the dry ice-acetone cold trap.

[0036] Example 6 A high-purity sodium isophthalic acid-5-sulfonate, the preparation method of which includes the following steps: Liquid SO2 was cooled to 0°C and sealed. Stirring was started and continued for 12 minutes. A co-solvent was added, and stirring was continued at 0°C for 25 minutes. The temperature was then raised to 5°C, and isophthalic acid was added. Stirring was continued for 60 minutes, and then SO3 was added dropwise over 1.5 hours. After the addition was completed, the temperature was raised to room temperature, and stirring was continued for 4 hours. The pressure was then reduced to atmospheric pressure, and nitrogen gas was introduced for 3 hours. SO2 gas was recovered using a cold trap. The reaction residue was rotary evaporated at 55°C, cooled to room temperature, and the pH was adjusted to 6.5 with alkali solution. The mixture was stirred at room temperature for 1.2 hours, filtered, and the filter cake was washed five times with deionized water. Finally, the filter cake was vacuum dried at 70°C for 9 hours to obtain high-purity sodium isophthalic acid-5-sulfonate.

[0037] The mass ratio of liquid SO2, co-solvent, isophthalic acid, and SO3 was 30:4.5:5.0:3.5; the co-solvent was obtained by mixing acetonitrile, trifluorotoluene, and the carboxyl imidazole acetate obtained in Example 3 in a mass ratio of 20:15:8; the stirring speed was 400 rpm; the pressure reduction rate was controlled at 5 kPa / min during the pressure reduction process, and the pressure was paused for 10 min after every 50 kPa reduction; the nitrogen flow rate was 40 mL / min; the alkaline solution was a 10% sodium hydroxide solution; the cold trap was a dry ice-acetone cold trap, which was prepared by adding 330 mL of acetone to a 500 mL Dewar flask, and then adding 330 g of solid carbon dioxide in three batches (110 g per batch) while stirring, and stabilizing the temperature at -78 °C to obtain the dry ice-acetone cold trap.

[0038] Comparative Example 1 Compared with Example 6, the 1,2-dimethylimidazole in the preparation process of carboxylated imidazole acetate was replaced with N,N-dimethylaniline, and the rest was exactly the same as in Example 6, to obtain high-purity sodium isophthalic acid-5-sulfonate.

[0039] Comparative Example 2 Compared with Example 6, bromoacetic acid in the preparation process of carboxylated imidazole acetate was replaced with ethyl 4-bromobutyrate, while the rest was exactly the same as in Example 6, to obtain high-purity sodium isophthalic acid-5-sulfonate.

[0040] Comparative Example 3 Compared with Example 6, the cosolvent was replaced with cosolvent-1, and everything else was exactly the same as in Example 6 to obtain high-purity sodium isophthalic acid-5-sulfonate; cosolvent-1 was obtained by mixing acetonitrile and trifluorotoluene in a mass ratio of 24:19.

[0041] Comparative Example 4 Compared with Example 6, the cosolvent was replaced with cosolvent-2, and everything else was exactly the same as in Example 6, to obtain high-purity sodium isophthalic acid-5-sulfonate; cosolvent-2 was obtained by mixing acetonitrile and carboxyl imidazole acetate in a mass ratio of 28:15.

[0042] Comparative Example 5 Compared with Example 6, the cosolvent was replaced with cosolvent-3, and everything else was exactly the same as in Example 6, to obtain high-purity sodium isophthalic acid-5-sulfonate; cosolvent-3 was obtained by mixing trifluorotoluene and carboxyl imidazole acetate in a mass ratio of 25:18.

[0043] Comparative Example 6 Compared with Example 6, liquid SO2 was replaced with dichloromethane, and everything else was exactly the same as in Example 6, to obtain high-purity sodium isophthalic acid-5-sulfonate.

[0044] The high-purity sodium isophthalate-5-sulfonate prepared in Examples 4-6 and Comparative Examples 1-6 of this invention were further tested below, and the test results are shown in the figure.

[0045] Yield: Yield = (actual mass of sodium isophthalic acid-5-sulfonate × purity of sodium isophthalic acid-5-sulfonate) / theoretical mass of sodium isophthalic acid-5-sulfonate × 100%.

[0046] Platinum-cobalt color (20% aqueous solution): Visually inspected under fluorescent light.

[0047] Sodium isophthalic acid-5-sulfonate purity (%): quantified using external standard method in liquid chromatography.

[0048] Acid value (mgKOH / g): The acid value was determined using acid-base titration.

[0049] Sulfate content (mg / kg): The sulfate content was determined by gravimetric method.

[0050] Iron content (mg / kg): Iron content was determined using ICP-MS.

[0051] Chloride content (mg / kg): Chloride content was determined by gravimetric method.

[0052] Moisture content (%): Moisture content was determined using a Karl Fischer moisture analyzer.

[0053] Absorbance: The obtained sodium isophthalic acid-5-sulfonate was prepared into a 5% aqueous solution. Using deionized water as a reference solution, the absorbance was measured at 450 nm using a UV-Vis spectrophotometer with a 1 cm cuvette.

[0054] The product is considered qualified if it simultaneously meets the following performance test results: Platinum-cobalt color (20% aqueous solution): ≤20; Sodium isophthalic acid-5-sulfonate purity (%): ≥99; Acid value (mgKOH / g): 415-421; Sulfate content (mg / kg): ≤200; Iron content (mg / kg): ≤5; Chloride content (mg / kg): ≤1; Moisture (%): ≤0.5%; Absorbance: ≤0.05.

[0055] The specific test results are shown in Table 1; Table 1: Performance Test Results According to the data in Table 1, the performance indicators of the high-purity sodium isophthalate-5-sulfonate prepared in Examples 4-6 of this invention all meet the performance indicator requirements of qualified products.

[0056] Comparing Example 6 with Comparative Example 1, it can be seen that replacing 1,2-dimethylimidazole in the preparation process of carboxylated imidazole acetate with N,N-dimethylaniline indicates that the sodium isophthalic acid-5-sulfonate prepared by using 1,2-dimethylimidazole in this invention has better performance test results.

[0057] A comparison of Example 6 and Comparative Example 2 shows that replacing bromoacetic acid in the preparation process of carboxylated imidazole acetate with ethyl 4-bromobutyrate indicates that the sodium isophthalic acid-5-sulfonate prepared by bromoacetic acid in this invention has better performance test results.

[0058] Comparing Example 6 with Comparative Examples 3, 4, and 5, it can be seen that replacing the cosolvent with cosolvent-1, cosolvent-2, and cosolvent-3 respectively demonstrates that the sodium isophthalic acid-5-sulfonate prepared by the present invention using a cosolvent obtained by mixing acetonitrile, trifluorotoluene, and carboxylated imidazole acetate in a specific ratio yields better performance test results.

[0059] A comparison of Example 6 and Comparative Example 6 shows that replacing liquid SO2 with dichloromethane indicates that the sodium isophthalic acid-5-sulfonate prepared by the present invention using liquid SO2 exhibits better performance results.

[0060] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing high-purity sodium isophthalic acid-5-sulfonate, characterized in that: Includes the following steps: Liquid SO2 was cooled and sealed, stirred, and a co-solvent was added. Stirring continued, followed by heating. Isophthalic acid was added and stirred, and SO3 was added dropwise. After the dropwise addition was completed, the temperature was raised and stirring continued. The pressure was then reduced to atmospheric pressure, and nitrogen gas was introduced to recover the SO2 gas. The reaction residue was rotary evaporated, and an alkaline solution was added to adjust the pH. The mixture was stirred, filtered, and the filter cake was washed with deionized water. Finally, it was dried under vacuum to obtain high-purity sodium isophthalic acid-5-sulfonate.

2. The method for preparing high-purity sodium isophthalic acid-5-sulfonate according to claim 1, characterized in that: The specific steps include the following: Liquid SO2 is cooled to -5°C to 0°C and sealed. Stirring is started for 10-12 minutes. A co-solvent is added, and the mixture is stirred at a constant temperature of -5°C to 0°C for 20-25 minutes. The temperature is then raised to 0-5°C, and isophthalic acid is added. The mixture is stirred for 50-60 minutes, and SO3 is added dropwise over 1-1.5 hours. After the addition is complete, the temperature is raised to room temperature, and stirring is continued for 3.5-4 hours. The pressure is then reduced to atmospheric pressure, and nitrogen gas is introduced for 2-3 hours. SO2 gas is recovered using a cold trap. The reaction residue is rotary evaporated, and an alkaline solution is added to adjust the pH to 5.5-6.

5. The mixture is stirred for 1-1.2 hours, filtered, and the filter cake is washed with deionized water. Finally, the filter cake is vacuum dried at 60-70°C for 8-9 hours to obtain high-purity sodium isophthalate-5-sulfonate.

3. The method for preparing high-purity sodium isophthalic acid-5-sulfonate according to claim 2, characterized in that: The mass ratio of liquid SO2, co-solvent, isophthalic acid, and SO3 is 30:(3.0-4.5):5.0:(2.5-3.5).

4. The method for preparing high-purity sodium isophthalic acid-5-sulfonate according to claim 2, characterized in that: The co-solvent is obtained by mixing acetonitrile, trifluorotoluene, and carboxylated imidazole acetate in a mass ratio of (15-20):(10-15):(3-8).

5. The method for preparing high-purity sodium isophthalic acid-5-sulfonate according to claim 2, characterized in that: During the depressurization process, the depressurization rate is controlled at 4-5 kPa / min, and paused for 5-10 minutes every 50 kPa decrease; the nitrogen flow rate is 30-40 mL / min.

6. The method for preparing high-purity sodium isophthalic acid-5-sulfonate according to claim 2, characterized in that: The cold trap is a dry ice-acetone cold trap.

7. The method for preparing high-purity sodium isophthalic acid-5-sulfonate according to claim 4, characterized in that: The preparation method of the carboxyl-containing imidazole acetate includes the following steps: Step (1): In a protective gas atmosphere, bromoacetic acid was added to toluene, and after stirring, 1,2-dimethylimidazole was added. The mixture was refluxed, heated and stirred, cooled, rotary evaporated, washed with ethyl acetate, and dried under vacuum to obtain carboxyl imidazole bromide. Step (2): Mix carboxyl imidazole bromide and anhydrous methanol, introduce a protective gas, stir, add anhydrous sodium acetate, heat and stir, filter, rotary evaporate the filtrate, and vacuum dry to obtain carboxyl imidazole acetate.

8. The method for preparing high-purity sodium isophthalic acid-5-sulfonate according to claim 7, characterized in that: In step (1), the ratio of the amount of toluene, bromoacetic acid, and 1,2-dimethylimidazole is (30-35) g: (7.5-8) g: (5-5.5) g.

9. The method for preparing high-purity sodium isophthalic acid-5-sulfonate according to claim 7, characterized in that: In step (2), the ratio of the amount of carboxyl imidazole bromide, anhydrous methanol, and anhydrous sodium acetate is (13.5-14.5) g: (45-55) g: (5.5-6.5) g.

10. A high-purity sodium isophthalic acid-5-sulfonate prepared by the method for preparing a high-purity sodium isophthalic acid-5-sulfonate according to any one of claims 1-9.

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