Refining method of 2-hydroxy-6-naphthoic acid

Abstract

The invention relates to the technical field of preparation of 2-hydroxy-6-naphthoic acid, and discloses a refining method of 2-hydroxy-6-naphthoic acid, which comprises the following steps: step 1, dissolving crude 2-hydroxy-6-naphthoic acid in an organic solvent, and heating until the crude 2-hydroxy-6-naphthoic acid is completely dissolved to obtain a 2-hydroxy-6-naphthoic acid solution; step 2, adding activated carbon into the 2-hydroxy-6-naphthoic acid solution, stirring and decoloring, and filtering to remove the activated carbon to obtain a decolored solution; and step 3, recrystallizing through a step-by-step cooling method, separating crystals, and drying to obtain 2-hydroxy-6-naphthoic acid coarse crystals. Compared with the prior art, the method has the advantages of simplicity in operation, mild conditions and easiness in realization of industrial production. According to the method disclosed by the invention, a method of combining activated carbon decoloration, a step-by-step cooling method and an ultrasonic dispersion and centrifugal separation combined process is adopted, so that impurities in the 2-hydroxy-6-naphthoic acid can be effectively removed, and the purity and the yield of the product are improved. The organic solvent used in the method can be recycled, so that the environmental pollution is reduced, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of 2-hydroxy-6-naphthoic acid, and specifically refers to a refining method of 2-hydroxy-6-naphthoic acid. Background Art

[0002] 2-Hydroxy-6-naphthoic acid, also known as 2,6-acid, English name: 2-Hydroxy-6-naphthoic acid. It can be used as an important organic intermediate for engineering plastics, organic pigments, liquid crystal materials, and pharmaceuticals. Especially as a monomer for heat-resistant synthetic materials, it is a off-white powder crystal, with a melting point of 243-246°C, showing weak acidity, soluble in alkali, basically insoluble in water, and easily soluble in organic solvents such as alcohols, ethers, and benzene. Industrially produced 2-hydroxy-6-naphthoic acid usually contains various impurities, such as unreacted raw materials, by-products, isomers, etc. The presence of these impurities will affect the purity and performance of 2-hydroxy-6-naphthoic acid, and thus affect its application effect.

[0003] Currently, the existing refining methods of 2-hydroxy-6-naphthoic acid mainly include recrystallization method, solvent extraction method, and column chromatography method. However, these methods have certain deficiencies. For example:

[0004] Recrystallization method: The operation is cumbersome, the yield is low, and it is difficult to effectively remove certain impurities.

[0005] Solvent extraction method: The solvent consumption is large, and the environmental pollution is serious.

[0006] Column chromatography method: The operation is complex, the cost is high, and it is difficult to realize industrial production. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the above technical difficulties and provide a refining method of 2-hydroxy-6-naphthoic acid, which can overcome the deficiencies of the existing "recrystallization method, solvent extraction method, and column chromatography method".

[0008] To solve the above technical problem, the technical solution provided by the present invention is:

[0009] A refining method of 2-hydroxy-6-naphthoic acid, comprising the following steps:

[0010] Step 1: Dissolve the crude 2-hydroxy-6-naphthoic acid in an organic solvent and heat it until completely dissolved to obtain a 2-hydroxy-6-naphthoic acid solution;

[0011] Step 2: Add activated carbon to the 2-hydroxy-6-naphthoic acid solution, stir for decolorization, and filter to remove the activated carbon to obtain a decolorized solution;

[0012] Step 3: Perform recrystallization by the stepwise cooling method, separate the crystals and dry them to obtain the crude crystals of 2-hydroxy-6-naphthoic acid;

[0013] Step 4: After further purification by ultrasonic dispersion combined with centrifugal separation process, a high-purity 2-hydroxy-6-naphthoic acid product is obtained.

[0014] Preferably, the organic solvent in the step 1 is one or a mixture of more than one of DMF, petroleum ether or n-tetradecane. And the mass-volume ratio of the crude 2-hydroxy-6-naphthoic acid to the organic solvent is 5:1 to 9:1.

[0015] Preferably, in the step 2, the addition amount of activated carbon is 2% to 10% of the mass of the crude 2-hydroxy-6-naphthoic acid. And in the step 2, the decolorization temperature is 60 to 90 °C, and the time is 1 to 2.5 hours.

[0016] Preferably, in the step 3, the recrystallization process includes: 1. Heating the filtrate to 80 to 100 °C to completely dissolve; 2. Cooling at a rate of 2 to 5 °C / min to 40 to 60 °C to precipitate crystals; 3. Cooling again at a rate of 1 to 2 °C / min to 10 to 25 °C to complete crystallization.

[0017] Preferably, in the step 3, drying is carried out by vacuum drying, the temperature is 50 to 80 °C, the vacuum degree ≤ -0.08 MPa, and the drying time is 5 to 12 hours.

[0018] The advantages of the present invention compared with the prior art are as follows:

[0019] 1. The operation of the present invention is simple, the conditions are mild, and it is easy to realize industrial production.

[0020] 2. The present invention combines the methods of decolorization with activated carbon, stepwise cooling method and ultrasonic dispersion combined with centrifugal separation process, which can effectively remove impurities in 2-hydroxy-6-naphthoic acid and improve the product purity and yield.

[0021] 3. The organic solvent used in the present invention can be recycled, reducing environmental pollution and production costs. Specific embodiments

[0022] In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more. In addition, the term "comprising" and any variation thereof are intended to cover non-exclusive inclusion.

[0023] The following further elaborates on the present invention in combination with the embodiments.

[0024] When the embodiment of the present invention is specifically implemented:

[0025] Embodiment 1

[0026] A refining method of 2-hydroxy-6-naphthoic acid, comprising the following steps:

[0027] Step 1: Dissolve the crude 2-hydroxy-6-naphthoic acid in DMF and heat it until completely dissolved. The mass-volume ratio of the crude 2-hydroxy-6-naphthoic acid to the organic solvent is 5:1 to obtain a 2-hydroxy-6-naphthoic acid solution.

[0028] Step 2: Add activated carbon to the 2-hydroxy-6-naphthoic acid solution, stir for decolorization. The addition amount of the activated carbon is 2% of the mass of the crude 2-hydroxy-6-naphthoic acid. The decolorization temperature is 60 °C and the time is 1 hour. Filter to remove the activated carbon to obtain a decolorized solution.

[0029] Step 3: Perform recrystallization by the stepwise cooling method. After separating the crystals and drying, obtain the crude crystals of 2-hydroxy-6-naphthoic acid. The recrystallization process includes: 1. Heat the filtrate to 80 °C until completely dissolved; 2. Cool it at a rate of 2 °C / min to 40 °C to precipitate crystals; 3. Then cool it again at a rate of 1 °C / min to 10 °C to complete crystallization. The drying is carried out by vacuum drying at a temperature of 50 °C, a vacuum degree of ≤ -0.08 MPa, and a drying time of 5 hours.

[0030] Step 4: Further purify it by using an ultrasonic dispersion combined with a centrifugal separation process to obtain a high-purity 2-hydroxy-6-naphthoic acid product.

[0031] Example 2

[0032] A refining method of 2-hydroxy-6-naphthoic acid, comprising the following steps:

[0033] Step 1: Dissolve the crude 2-hydroxy-6-naphthoic acid in petroleum ether and heat it until completely dissolved to obtain a 2-hydroxy-6-naphthoic acid solution. The mass-volume ratio of the crude 2-hydroxy-6-naphthoic acid to the organic solvent is 7:1.

[0034] Step 2: Add activated carbon to the 2-hydroxy-6-naphthoic acid solution, stir for decolorization. The addition amount of the activated carbon is 6% of the mass of the crude 2-hydroxy-6-naphthoic acid. The decolorization temperature is 70 °C and the time is 2 hours. Filter to remove the activated carbon to obtain a decolorized solution.

[0035] Step 3: Perform recrystallization by the stepwise cooling method. After separating the crystals and drying, obtain the crude crystals of 2-hydroxy-6-naphthoic acid. The recrystallization process includes: 1. Heat the filtrate to 90 °C until completely dissolved; 2. Cool it at a rate of 3 °C / min to 50 °C to precipitate crystals; 3. Then cool it again at a rate of 1.5 °C / min to 20 °C to complete crystallization. The drying is carried out by vacuum drying at a temperature of 70 °C, a vacuum degree of ≤ -0.08 MPa, and a drying time of 8 hours.

[0036] Step 4: After further purification by ultrasonic dispersion combined with centrifugal separation process, a high-purity 2-hydroxy-6-naphthoic acid product is obtained.

[0037] Example 3

[0038] A refining method of 2-hydroxy-6-naphthoic acid, comprising the following steps:

[0039] Step 1: Dissolve the crude 2-hydroxy-6-naphthoic acid in n-tetradecane and heat it until completely dissolved to obtain a 2-hydroxy-6-naphthoic acid solution. The mass-volume ratio of the crude 2-hydroxy-6-naphthoic acid to the organic solvent is 9:1.

[0040] Step 2: Add activated carbon to the 2-hydroxy-6-naphthoic acid solution, stir for decolorization. The addition amount of activated carbon is 10% of the mass of the crude 2-hydroxy-6-naphthoic acid. The decolorization temperature is 90 °C and the time is 2.5 hours. Filter to remove the activated carbon to obtain a decolorized solution.

[0041] Step 3: Perform recrystallization by stepwise cooling method. After separating the crystals and drying, a crude crystal of 2-hydroxy-6-naphthoic acid is obtained. The recrystallization process includes: 1. Heat the filtrate to 100 °C until completely dissolved; 2. Cool it at a rate of 5 °C / min to 60 °C to precipitate crystals; 3. Then cool it again at a rate of 2 °C / min to 25 °C to complete crystallization. The drying is carried out by vacuum drying, the temperature is 80 °C, the vacuum degree ≤ -0.08 MPa, and the drying time is 12 hours.

[0042] Step 4: After further purification by ultrasonic dispersion combined with centrifugal separation process, a high-purity 2-hydroxy-6-naphthoic acid product is obtained.

[0043] The above describes the present invention and its implementation manners, and such description is not restrictive. If those of ordinary skill in the art are inspired by it and design similar embodiments to this technical solution without creative efforts without departing from the purpose of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A refining method of 2-hydroxy-6-naphthoic acid, characterized in that, It includes the following steps: Step 1: Dissolve the crude 2-hydroxy-6-naphthoic acid in an organic solvent and heat it until completely dissolved to obtain a 2-hydroxy-6-naphthoic acid solution; Step 2: Add activated carbon to the 2-hydroxy-6-naphthoic acid solution, stir for decolorization, and filter to remove the activated carbon to obtain a decolorized solution; Step 3: Perform recrystallization by the stepwise cooling method. After separating the crystals and drying, obtain the crude crystals of 2-hydroxy-6-naphthoic acid; Step 4: Further purify by using the ultrasonic dispersion combined with centrifugal separation process to obtain a high-purity 2-hydroxy-6-naphthoic acid product.

2. The refining method of 2-hydroxy-6-naphthoic acid according to claim 1, characterized in that: The organic solvent in Step 1 is one or a mixture of DMF, petroleum ether, or n-tetradecane.

3. The refining method of 2-hydroxy-6-naphthoic acid according to claim 2, characterized in that: The mass-volume ratio of the crude 2-hydroxy-6-naphthoic acid to the organic solvent is 5:1 to 9:

1.

4. A refining method of 2-hydroxy-6-naphthoic acid according to claim 1, characterized in that: In Step 2, the addition amount of activated carbon is 2% to 10% of the mass of the crude 2-hydroxy-6-naphthoic acid.

5. The refining method of 2-hydroxy-6-naphthoic acid according to claim 4, characterized in that: In Step 2, the decolorization temperature is 60 to 90 °C and the time is 1 to 2.5 hours.

6. The refining method of 2-hydroxy-6-naphthoic acid according to claim 1, wherein: In Step 3, the recrystallization process includes:

1. Heat the filtrate to 80 to 100 °C until completely dissolved; 2. Cool it at a rate of 2 to 5 °C / min to 40 to 60 °C to precipitate crystals; 3. Cool it again at a rate of 1 to 2 °C / min to 10 to 25 °C to complete crystallization.

7. A refining method of 2-hydroxy-6-naphthoic acid according to claim 1, characterized in that: In Step 3, vacuum drying is used, the temperature is 50 to 80 °C, the vacuum degree ≤ -0.08 MPa, and the drying time is 5 to 12 hours.