A method for refining 1,4-naphthalene dicarboxylic acid

Abstract

The present application relates to a kind of 1,4-naphthalene dicarboxylic acid refining method, belong to the technical field of pharmaceutical intermediates synthesis.In order to solve the problem of low yield and large solid waste, provide a kind of 1,4-naphthalene dicarboxylic acid refining method, its characterized in that, the method includes that 1,4-naphthalene dicarboxylic acid crude product is added to acetic acid solvent system, the residual amount of 4-methyl-1-naphthalene carboxylic acid in the 1,4-naphthalene dicarboxylic acid crude product is within 10%, the content of 1,4-naphthalene dicarboxylic acid is more than 90%, the temperature is controlled at 40 DEG C to reflux temperature under the condition of heat preservation, then recool to precipitate solid product, obtain the 1,4-naphthalene dicarboxylic acid after refining.The present application can improve the purity of 1,4-naphthalene dicarboxylic acid, purity reaches 99.5% or more, yield reaches 82% or more.

Description

Technical Field

[0001] This invention relates to a purification method for 1,4-naphthoic acid, belonging to the field of pharmaceutical intermediate synthesis technology. Background Technology

[0002] 1,4-Naphthalenedicarboxylic acid is used in the manufacture of high-performance polyester fibers and insulating materials, and is an important monomer for polyethylene naphthalate (PEN), liquid crystal polymers, and polyurethane resins. The main synthetic methods for this intermediate include oxidation of 1-methyl-4-acetylnaphthalene with potassium dichromate at 200-300°C and under pressure of approximately 4 MPa for at least 18 hours. Alternatively, it can be obtained by liquid-phase oxidation of 1,4-dimethylnaphthalene using cobalt-manganese-bromine as a catalyst at approximately 120°C and under pressure of approximately 3 kPa. Both of these synthetic routes involve high temperature, high pressure, and high catalyst concentrations, which presents operational challenges. Furthermore, high temperatures can easily introduce impurities into the product, affecting its purity, quality, and yield.

[0003] Another synthetic route uses potassium permanganate as an oxidant and water as a solvent to synthesize 1,4-naphthalenedicarboxylic acid at room temperature. Potassium permanganate is added in batches during the oxidation reaction. The synthetic route is as follows:

[0004]

[0005] The process conditions are mild, but the main problem with this synthetic route is the strong oxidizing power of potassium permanganate and the large amount used. During oxidation, this leads to ring-opening of the naphthalene ring. The reason for this ring-opening is that, during the oxidation reaction, as the amount of potassium permanganate added increases, the amount of 4-methyl-1-naphthylcarboxylic acid starting material gradually decreases, while the amount of 1,4-naphthalenedicarboxylic acid gradually increases, showing a slow upward trend. Initially, when potassium permanganate is added, the oxidation mainly occurs at the -1 methyl group of 4-methyl-1-naphthylcarboxylic acid. As the oxidation reaction proceeds, the amount of the reactant 4-methyl-1-naphthylcarboxylic acid gradually decreases in the reaction system. In existing synthetic reactions, the conversion of the substrate 4-methyl-1-naphthylcarboxylic acid is usually controlled, and the reaction is terminated when the content of 4-methyl-1-naphthylcarboxylic acid is below 0.5%. During the reaction, as the content of 4-methyl-1-naphthylcarboxylic acid decreases, the probability of contact with the added potassium permanganate becomes lower and lower, while the probability of contact between the product 1,4-naphthoic acid and potassium permanganate becomes higher and higher. This causes the main oxidation site of potassium permanganate to gradually transfer from the -1 site of 4-methyl-1-naphthylcarboxylic acid to the naphthalene ring of 1,4-naphthoic acid. As the reaction proceeds, the ring-opening probability of 1,4-naphthalenedicarboxylic acid increases. In actual research and development of synthetic routes, it was found that when the content of 1,4-naphthalenedicarboxylic acid in the reaction system reaches more than 90%, it becomes quite difficult to completely oxidize the remaining substrate when further oxidizing the substrate 4-methyl-1-naphthylcarboxylic acid to the product. A large amount of potassium permanganate is required for further oxidation, which in turn leads to the ring-opening of the naphthalene ring in the product and reduces the yield. The molar yield of the crude product is only about 50%, and the amount of oxidant such as potassium permanganate is greatly increased, which is about three times the amount of substrate. This not only wastes raw materials, but also generates a large amount of solid waste, which will cause environmental pollution problems. Summary of the Invention

[0006] To address the shortcomings of the existing technology, this invention provides a purification method for 1,4-naphthalenedicarboxylic acid, solving the problem of how to improve the yield and purity of the product.

[0007] The objective of this invention is achieved through the following technical solution: a method for purifying 1,4-naphthalenedicarboxylic acid, characterized in that the method includes adding crude 1,4-naphthalenedicarboxylic acid to an acetic acid solvent system, wherein the residual amount of 4-methyl-1-naphthylcarboxylic acid in the crude 1,4-naphthalenedicarboxylic acid is less than 10%, and the content of 1,4-naphthalenedicarboxylic acid is more than 90%, heating and maintaining the temperature at 40°C to reflux temperature, and then cooling down to precipitate a solid product to obtain purified 1,4-naphthalenedicarboxylic acid.

[0008] By using an acetic acid solvent system, it was found that 4-methyl-1-naphthylcarboxylic acid and 1,4-naphthylcarboxylic acid contained in crude 1,4-naphthylcarboxylic acid have different solubilities in the acetic acid solvent system. When there is a higher content of 4-methyl-1-naphthylcarboxylic acid, 4-methyl-1-naphthylcarboxylic acid can be dissolved well in the acetic acid solvent, while 1,4-naphthylcarboxylic acid has poor solubility, thereby improving the purity of 1,4-naphthylcarboxylic acid, which reaches a purity of over 99.5%. Therefore, by utilizing the purification method of the present invention, the problem of subsequent naphthalene ring opening during the synthesis of 1,4-naphthalenedicarboxylic acid from 4-methyl-1-naphthylcarboxylic acid as a substrate by oxidation with a strong oxidant can be effectively solved. This purification method eliminates the need for complete oxidation of the substrate 4-methyl-1-naphthylcarboxylic acid to 1,4-naphthalenedicarboxylic acid during the synthesis of crude 1,4-naphthalenedicarboxylic acid. It only requires ensuring that the residual amount of 4-methyl-1-naphthylcarboxylic acid in the crude 1,4-naphthalenedicarboxylic acid is less than 10%, and the content of 1,4-naphthalenedicarboxylic acid is above 90%, at which point the reaction can be directly terminated. Using the purification method of the present invention, the crude product only requires one purification treatment to effectively remove residual 4-methyl-1-naphthylcarboxylic acid and other impurities, yielding high-purity 1,4-naphthalenedicarboxylic acid with a purity of over 99.5% and a yield of over 82%.

[0009] Meanwhile, since the purification method of this invention can maintain the purity and quality of the purified product even when the residual amount of 4-methyl-1-naphthylcarboxylic acid is less than 10%, it eliminates the need to control the residual amount of the substrate 4-methyl-1-naphthylcarboxylic acid in the crude 1,4-naphthalenedicarboxylic acid to a low content (less than 0.5%). This effectively reduces and avoids the problem of ring-opening and yield reduction caused by strong oxidants acting on the naphthalene ring of 1,4-naphthalenedicarboxylic acid when the content of 1,4-naphthalenedicarboxylic acid reaches more than 90% in the subsequent crude product synthesis process. This results in an overall improved yield and lower impurity content in the crude product synthesis. Furthermore, the mother liquor after purification can be recycled, and the substrate 4-methyl-1-naphthylcarboxylic acid in the mother liquor can be recovered and reused as raw material, greatly improving the atom utilization rate of the raw material. Even if the substrate content is still high (less than 10%) in the crude product synthesis, there will be no waste.

[0010] In the above-described purification method for 1,4-naphthalenedicarboxylic acid, preferably, an alcohol solvent is also added to the acetic acid solvent system. By adding an alcohol solvent to the main solvent acetic acid system, the presence of a small amount of alcohol solvent can better promote the dissolution of the substrate 4-methyl-1-naphthylcarboxylic acid, which is then removed during the purification process. This better ensures the purity and quality of the product, achieving a purity of 99.8% or higher. The alcohol solvent can be a low-grade C1-C4 alcohol solvent. As a further preferred embodiment, the alcohol solvent is selected from one or more of methanol, ethanol, and propanol.

[0011] In the above-described purification method for 1,4-naphthalenedicarboxylic acid, the acetic acid solvent system can be configured to use acetic acid as the sole reaction solvent, or it can contain a mixture of acetic acid and an organic solvent (such as an alcohol solvent). Preferably, the acetic acid content in the acetic acid solvent system is above 90%. This effectively ensures the removal of residual raw materials during the purification process and also ensures the full extraction of 1,4-naphthalenedicarboxylic acid. Preferably, the mass ratio of acetic acid to alcohol solvent is 10:1.0 to 3.0.

[0012] In the above-described purification method for 1,4-naphthalenedicarboxylic acid, preferably, the mass ratio of crude 1,4-naphthalenedicarboxylic acid to acetic acid is 1:10-15. This allows for more effective dissolution of the substrate while leaving the product undissolved, thus better ensuring the purity and quality of the purified product.

[0013] In the above-described purification method for 1,4-naphthalenedicarboxylic acid, preferably, the holding temperature is controlled between 75°C and the reflux temperature. This allows for better dissolution of residual raw materials, facilitates better removal of residues during subsequent cooling and crystallization processes, and improves the purity and quality of the purified product.

[0014] In the above-described purification method for 1,4-naphthalenedicarboxylic acid, preferably, the cooling temperature is lowered to 15°C to 30°C. This allows for more effective precipitation of the 1,4-naphthalenedicarboxylic acid product and effectively removes residual raw materials and other impurities, resulting in a high product purity of 99.5% or higher.

[0015] In the above-mentioned purification method for 1,4-naphthalenedicarboxylic acid, preferably, the crude 1,4-naphthalenedicarboxylic acid is obtained by the following method:

[0016] Using potassium permanganate as an oxidant, the substrate 4-methyl-1-naphthylcarboxylic acid is oxidized under alkaline conditions in the presence of alkali metal hydroxides. The reaction is stopped when the content of the product 1,4-naphthyldicarboxylic acid reaches 90% or higher, yielding crude 1,4-naphthyldicarboxylic acid. Because this purification method effectively removes high levels of residual 4-methyl-1-naphthylcarboxylic acid from the crude 1,4-naphthyldicarboxylic acid, the strong oxidant method only requires ensuring the 1,4-naphthyldicarboxylic acid content reaches 90% (or higher) during the oxidation process to stop the reaction. This avoids the need for complete substrate reaction, effectively preventing the naphthalene ring-opening phenomenon caused by subsequent oxidation processes, and ensuring a product yield and purity of over 90% in the crude product synthesis. Ideally, during the synthesis process, when the content of 1,4-naphthoic acid in the reaction solution reaches 90% (or higher), the residual amount of 4-methyl-1-naphthoic acid should be less than 10%, and more preferably, the residual amount of 4-methyl-1-naphthoic acid should be between 9.0% and 10%. This can more effectively avoid the oxidative ring-opening of the naphthalene ring in the product during the oxidation process, which is beneficial to improving the product yield and purity. As a further preferred embodiment, the mass of potassium permanganate added is 1.5 to 2.0 times the mass of 4-methyl-1-naphthoic acid added, and the potassium permanganate is added in batches during the reaction process, with the mass of potassium permanganate added every 5 to 10 minutes being 0.5% to 1.5% of the mass of 4-methyl-1-naphthoic acid added. This method avoids the problem of excessive oxidizing power from a single addition of potassium permanganate oxidant. By adding it in batches every 5-10 minutes, with each addition controlled within the aforementioned small range, the effective reaction and product purity are better ensured. It also allows for better monitoring of the product content during the oxidation reaction, making the process more convenient. Since the reaction can be stopped when the product content reaches 90% or higher, the amount of potassium permanganate oxidant used is effectively reduced. The total amount of potassium permanganate used is only 1.5-2.0 times that of 4-methyl-1-naphthylcarboxylic acid, reducing solid waste and environmental pollution, which is beneficial for industrial production.

[0017] In summary, compared with the prior art, the present invention has the following advantages:

[0018] 1. The purification method of the present invention can effectively dissolve 4-methyl-1-naphthylcarboxylic acid in a solvent, while 1,4-naphthyldicarboxylic acid has good solubility, thereby improving the purity of 1,4-naphthyldicarboxylic acid to a purity of over 99.5% and a yield of over 82%.

[0019] 2. This invention eliminates the need to control the residual amount of the substrate 4-methyl-1-naphthylcarboxylic acid in the crude 1,4-naphthylcarboxylic acid to a low level. This effectively avoids the problem that when the content of 1,4-naphthylcarboxylic acid reaches more than 90% in the subsequent synthesis process, the strong oxidant potassium permanganate is more likely to act on the naphthalene ring of 1,4-naphthylcarboxylic acid, leading to ring opening and a decrease in yield. Overall, this invention also improves the yield of crude product synthesis and has the advantage of low impurity content. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below through specific embodiments, but the present invention is not limited to these embodiments.

[0021] Example 1

[0022] Add 218g of water and 17.5g of caustic soda flakes to a three-necked flask and stir until dissolved. Add 30g of dried 4-methyl-1-naphthylcarboxylic acid raw material at once and stir until dissolved. Then heat the system to 35℃ and start adding potassium permanganate as an oxidant to initiate the reaction. During the reaction, add 0.2g of potassium permanganate every 5 minutes while stirring. When the 1,4-naphthylcarboxylic acid content reaches ≥90% (monitor the reaction progress via HPLC; when the 1,4-naphthylcarboxylic acid content is ≥90%), stop the reaction, filter, and rinse the filter cake with an appropriate amount of water. Slowly adjust the pH of the system with 30% hydrochloric acid until a large amount of solid precipitates. Filter to obtain crude 1,4-naphthylcarboxylic acid, which is 28.1g dry. The residual amount of 4-methyl-1-naphthylcarboxylic acid in the crude 1,4-naphthylcarboxylic acid is less than 10%, and the 1,4-naphthylcarboxylic acid content is 91.2%.

[0023] Example 2

[0024] 25g of crude 1,4-naphthalenedicarboxylic acid obtained by the method in Example 1 was added to a single-necked flask and magnetically stirred. 250g of acetic acid was added, and the mixture was kept at a temperature under micro-reflux for 1 hour. The temperature was then slowly lowered to room temperature for crystallization. The mixture was then filtered. The filter cake was washed with an appropriate amount of water and dried to obtain 21.3g of the purified product, 1,4-naphthalenedicarboxylic acid, with a yield of 85.2% and a purity of 99.6%.

[0025] The collected filtrate can be further recycled. Specifically, the filtrate is concentrated to dryness, an appropriate amount of water is added to the residue to precipitate a solid, which is then filtered and collected. The solid is then used as a raw material for 4-methyl-1-naphthylcarboxylic acid and added to the reaction system for the next batch of reaction to continue oxidation.

[0026] Example 3

[0027] Add 218g of water and 20g of caustic soda flakes to a three-necked flask and stir until dissolved. Add 30g of 4-methyl-1-naphthylcarboxylic acid raw material (dry weight) all at once and stir until dissolved. Heat the system to 40℃ and begin adding potassium permanganate as an oxidant to initiate the reaction. Add 0.18g of potassium permanganate every 5 minutes while stirring. When the 1,4-naphthylcarboxylic acid content reaches ≥90% (monitor the reaction progress via HPLC; stop the reaction when the 1,4-naphthylcarboxylic acid content ≥90%), stop the reaction. After the reaction is complete, filter and rinse the filter cake with an appropriate amount of water. Slowly adjust the pH of the filtrate with 30% hydrochloric acid until a large amount of solid precipitates. Filter to obtain wet product: crude 1,4-naphthylcarboxylic acid; 28.6g dry weight. The residual amount of 4-methyl-1-naphthylcarboxylic acid in the crude 1,4-naphthylcarboxylic acid is less than 10%, and the 1,4-naphthylcarboxylic acid content is 91.3%.

[0028] Example 4

[0029] 25g of crude 1,4-naphthalenedicarboxylic acid obtained by the method in Example 3 was added to a single-necked flask and magnetically stirred. 230g of acetic acid solvent was added, and the mixture was kept at a temperature under micro-reflux for 1.5h. After stirring, the temperature was slowly lowered to room temperature for crystallization. The mixture was then filtered, the filter cake was washed with an appropriate amount of water, and the filter cake was dried to obtain 21.5g of purified 1,4-naphthalenedicarboxylic acid, with a yield of 86% and a purity of 99.7%.

[0030] The collected filtrate can be further recycled. Specifically, the filtrate is concentrated to dryness, an appropriate amount of water is added to the residue to precipitate a solid, which is then filtered and collected. The solid is then used as a raw material for 4-methyl-1-naphthylcarboxylic acid and added to the reaction system for the next batch of reaction to continue oxidation.

[0031] Example 5

[0032] Add 230g of water and 18.5g of caustic soda flakes to a three-necked flask and stir until dissolved. Add 30g of dried 4-methyl-1-naphthylcarboxylic acid raw material at once and stir until dissolved. Then heat the system to 40℃ and start adding potassium permanganate as an oxidant to initiate the reaction. During the reaction, add 0.2g of potassium permanganate every 5 minutes while stirring. When the 1,4-naphthylcarboxylic acid content reaches ≥90% (monitor the reaction progress via HPLC; when the 1,4-naphthylcarboxylic acid content is ≥90%), stop the reaction. After the reaction is complete, filter and rinse the filter cake with an appropriate amount of water. Slowly adjust the pH of the system with 30% hydrochloric acid until a large amount of solid precipitates. Filter to obtain crude 1,4-naphthylcarboxylic acid, which is 28.4g dry. The residual amount of 4-methyl-1-naphthylcarboxylic acid in the crude 1,4-naphthylcarboxylic acid is less than 10%, and the 1,4-naphthylcarboxylic acid content is 90.8%.

[0033] Example 6

[0034] 25g of crude 1,4-naphthalenedicarboxylic acid obtained by the method in Example 5 was added to a single-necked flask and magnetically stirred. An acetic acid-ethanol system (250g acetic acid, 25g ethanol) was added, and the mixture was kept at around 80°C and stirred for 1 hour. The mixture was then slowly cooled to room temperature for crystallization and filtered. The filter cake was washed with an appropriate amount of water and dried to obtain 21.4g of purified 1,4-naphthalenedicarboxylic acid, with a yield of 85.6% and a purity of 99.7%.

[0035] The collected filtrate can be further recycled. Specifically, the filtrate is concentrated to dryness, an appropriate amount of water is added to the residue to precipitate a solid, which is then filtered and collected. The solid is then used as a raw material for 4-methyl-1-naphthylcarboxylic acid and added to the reaction system for the next batch of reaction to continue oxidation.

[0036] Example 7

[0037] Add 230g of water and 18.5g of caustic soda flakes to a three-necked flask and stir until dissolved. Add 30g of dried 4-methyl-1-naphthylcarboxylic acid raw material at once and stir until dissolved. Then heat the system to 40℃ and start adding potassium permanganate as an oxidant to initiate the reaction. During the reaction, add 0.2g of potassium permanganate every 5 minutes while stirring. When the 1,4-naphthylcarboxylic acid content reaches ≥90% (monitor the reaction progress via HPLC; when the 1,4-naphthylcarboxylic acid content is ≥90%), stop the reaction. After the reaction is complete, filter and rinse the filter cake with an appropriate amount of water. Slowly adjust the pH of the system with 30% hydrochloric acid until a large amount of solid precipitates. Filter to obtain crude 1,4-naphthylcarboxylic acid, which is wet solid and weighs 28.7g when dried. The residual amount of 4-methyl-1-naphthylcarboxylic acid in the crude 1,4-naphthylcarboxylic acid is less than 10%, and the 1,4-naphthylcarboxylic acid content is 91.5%.

[0038] Example 8

[0039] 25g of crude 1,4-naphthalenedicarboxylic acid obtained by the method in Example 7 was added to a single-necked flask and magnetically stirred. An acetic acid-ethanol system (250g acetic acid, 40g ethanol) was added, and the mixture was kept at 78℃-80℃ and stirred for 1 hour. The mixture was then slowly cooled to room temperature for crystallization and filtered. The filter cake was washed with an appropriate amount of water and dried to obtain 21.3g of purified 1,4-naphthalenedicarboxylic acid, with a yield of 85.2% and a purity of 99.5%.

[0040] The collected filtrate can be further recycled. Specifically, the filtrate is concentrated to dryness, an appropriate amount of water is added to the residue to precipitate a solid, which is then filtered and collected. The solid is then used as a raw material for 4-methyl-1-naphthylcarboxylic acid and added to the reaction system for the next batch of reaction to continue oxidation.

[0041] The specific embodiments described in this invention are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

[0042] Although the present invention has been described in detail and specific embodiments have been cited, it will be apparent to those skilled in the art that various changes or modifications can be made without departing from the spirit and scope of the invention.

Claims

1. A method for purifying 1,4-naphthalenedicarboxylic acid, characterized in that, The method involves adding crude 1,4-naphthalenedicarboxylic acid to an acetic acid solvent system, wherein the residual amount of 4-methyl-1-naphthylcarboxylic acid in the crude 1,4-naphthalenedicarboxylic acid is less than 10%, and the content of 1,4-naphthalenedicarboxylic acid is more than 90%. The mixture is heated and kept at a temperature controlled at 40°C to reflux temperature, and then cooled to precipitate a solid product to obtain purified 1,4-naphthalenedicarboxylic acid.

2. The purification method for 1,4-naphthalenedicarboxylic acid according to claim 1, characterized in that, An alcohol solvent is also added to the acetic acid solvent system.

3. The purification method for 1,4-naphthalenedicarboxylic acid according to claim 2, characterized in that, The alcohol solvent is selected from one or more of methanol, ethanol and propanol.

4. The method for purifying 1,4-naphthalenedicarboxylic acid according to claim 2 or 3, characterized in that, The mass ratio of acetic acid to alcohol solvent in the acetic acid solvent system is 10:1.0 to 3.

0.

5. The method for purifying 1,4-naphthalenedicarboxylic acid according to claim 1, 2, or 3, characterized in that, The mass ratio of crude 1,4-naphthalenedicarboxylic acid to acetic acid is 1:10-15.

6. The method for purifying 1,4-naphthalenedicarboxylic acid according to claim 1, 2, or 3, characterized in that, The insulation temperature is controlled between 75°C and the reflux temperature.

7. The method for purifying 1,4-naphthalenedicarboxylic acid according to claim 1, 2, or 3, characterized in that, The temperature is reduced to 20℃~30℃.

8. The method for purifying 1,4-naphthalenedicarboxylic acid according to claim 1, 2, or 3, characterized in that, The crude 1,4-naphthoic acid was obtained by the following method: Using potassium permanganate as an oxidant, the substrate 4-methyl-1-naphthic acid was oxidized under alkaline conditions in the presence of alkali metal hydroxides. The reaction was stopped when the content of the product 1,4-naphthic acid reached more than 90% during the oxidation process, and crude 1,4-naphthic acid was obtained.

9. The method for purifying 1,4-naphthalenedicarboxylic acid according to claim 8, characterized in that, The mass of potassium permanganate added is 1.5 to 2.0 times the mass of 4-methyl-1-naphthylcarboxylic acid added, and the potassium permanganate is added in batches during the reaction process, with the mass of potassium permanganate added every 5 to 10 minutes being 0.5% to 1.5% of the mass of 4-methyl-1-naphthylcarboxylic acid added.

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