A method for purifying 2,3,4,4'-tetrahydroxybenzophenone

Abstract

This application provides a method for purifying 2,3,4,4'-tetrahydroxybenzophenone (4HBP), comprising: S1) adding crude 4HBP to a good solvent for 4HBP, stirring and heating to dissolve, then adding a second solvent (a good solvent for impurities generated during the synthesis of 4HBP) and activated carbon, heating and stirring, and filtering out the activated carbon to obtain a filtrate; S2) adding a first batch of pure water to the filtrate and maintaining the temperature at 70-75°C, adding alkali to adjust the pH, stirring, adding a second batch of pure water to reduce the solubility of 4HBP in the solvent, stirring, cooling to precipitate crystals, and filtering to obtain a wet crude product; S3) adding pure water or a mixture of pure water and alcohol to the wet crude product, heating to dissolve, adding resin, maintaining the temperature and stirring, filtering, cooling the filtrate to precipitate crystals, rinsing with low-temperature pure water, and drying to obtain purified 4HBP. The purification method of this application has good purification effect, simple process, low cost using a single resin, and less pollution, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This application relates to the field of synthetic technology of 2,3,4,4'-tetrahydroxybenzophenone, and specifically to a purification method for 2,3,4,4'-tetrahydroxybenzophenone. Background Technology

[0002] 2,3,4,4'-Tetrahydroxybenzophenone (4HBP) is an important chemical intermediate widely used in pharmaceutical intermediates, ultraviolet absorbers, and electronic chemicals. With the rapid development of electronic chemicals, the demand for high-purity 2,3,4,4'-tetrahydroxybenzophenone and other polyhydroxybenzophenone products has increased dramatically, while more stringent requirements have been placed on product quality, especially purity and metal ion content.

[0003] The purification method proposed in patent CN102304034A uses three types of resins for adsorption and impurity removal. However, in industrial production, resin regeneration is time-consuming, and it is difficult to recycle and reuse the two types of resins after mixing. The process is complex and the resin cost is high, making it unsuitable for large-scale production. The reported product purity is 99.5%, and the content of major metal ions is less than 100 ppb.

[0004] However, the purity requirement for electronic-grade 2,3,4,4'-tetrahydroxybenzophenone is greater than 99.9% and the metal ion content is less than 10 ppb. Existing technologies cannot meet this requirement, so there is an urgent need for a better method for purifying 2,3,4,4'-tetrahydroxybenzophenone. Summary of the Invention

[0005] In view of the above-mentioned problems in the prior art, the embodiments of this application propose a purification method for 2,3,4,4'-tetrahydroxybenzophenone. This purification method has good purification effect, simple process, low cost of using a single resin, and less pollution, and is suitable for large-scale industrial production.

[0006] According to one aspect of this application, a method for purifying 2,3,4,4'-tetrahydroxybenzophenone is provided, the purification method comprising the following steps: S1) adding crude 2,3,4,4'-tetrahydroxybenzophenone into a first solvent, stirring and heating to dissolve, then adding a second solvent and activated carbon, heating to 60-80℃, stirring, and filtering out the activated carbon to obtain a filtrate; S2) adding a first batch of pure water to the filtrate from step S1 and maintaining the temperature at 70-75℃, where 2,3,4,4'-tetrahydroxybenzophenone will not precipitate, then adding an alkali to promote the hydrolysis of impurities and dissolve them in water, stirring, and then adding a second batch of pure water. To reduce the solubility of 2,3,4,4'-tetrahydroxybenzophenone in a solvent, the mixture is stirred, cooled to crystallize, and filtered to obtain a wet crude product; S3) A third solvent is added to the wet crude product from step S2, the temperature is raised to dissolve, resin is added, the mixture is kept warm and stirred, filtered, the filtrate is cooled to crystallize, washed with low-temperature pure water, and dried to obtain refined 2,3,4,4'-tetrahydroxybenzophenone; wherein, the first solvent is a good solvent for 2,3,4,4'-tetrahydroxybenzophenone, the second solvent is a good solvent for impurities generated during the synthesis of 2,3,4,4'-tetrahydroxybenzophenone, and the third solvent is pure water or a mixed solution of pure water and alcohol.

[0007] In some embodiments, the first solvent is an alcohol solvent or an ester solvent, and the second solvent is a benzene derivative; preferably, the first solvent is one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, and ethyl acetate, and the second solvent is one or more of benzene, toluene, and xylene.

[0008] In some embodiments, step S1 includes one or more of the following features: 1) the weight ratio of the first solvent to crude 2,3,4,4'-tetrahydroxybenzophenone is 3-5:1; 2) the weight ratio of the second solvent to crude 2,3,4,4'-tetrahydroxybenzophenone is 3-15:1; 3) the weight ratio of activated carbon to crude 2,3,4,4'-tetrahydroxybenzophenone is 0.01-0.05:1.

[0009] In some embodiments, the weight ratio of the first pure water to the crude 2,3,4,4'-tetrahydroxybenzophenone is 7-9:1; the weight ratio of the second pure water to the crude 2,3,4,4'-tetrahydroxybenzophenone is 4-6:1.

[0010] In some embodiments, step S2 includes one or more of the following features: 1) the alkali is one or more of NaOH, KOH, Na2CO3, NaHCO3, K2CO3, and NaHCO3; 2) alkali is added to adjust the pH to 6.0-6.8; 3) the temperature is lowered to 5-10°C to crystallize.

[0011] In some embodiments, the third solvent is a mixed solution of pure water and alcohol, with a volume ratio of pure water to alcohol of 4-80:1; preferably, the volume ratio of pure water to alcohol is 4:1.

[0012] In some embodiments, a third solvent is added and the temperature is raised to 60-80°C to dissolve.

[0013] In some embodiments, the resin is a strongly acidic cation exchange resin.

[0014] In some embodiments, the strongly acidic cation exchange resin is porous or gel-type, and the strongly acidic group is a sulfonic acid group.

[0015] In some embodiments, step S3 includes one or more of the following features: 1) the third solvent is a mixed solution of pure water and alcohol, the volume ratio of pure water to alcohol is 4:1, and the weight ratio of the third solvent to crude 2,3,4,4'-tetrahydroxybenzophenone is 4-8:1; 2) the weight ratio of resin to crude 2,3,4,4'-tetrahydroxybenzophenone is 0.1-0.5:1; 3) the low-temperature pure water is pure water at 0-10℃.

[0016] Compared with the prior art, the above-described technical solution conceived in this application has the following advantages and effects: the purification method provided in this application has good purification effect; the process is simple; a single resin can be used, resulting in low cost and less pollution; and it is suitable for large-scale industrial production. The purification method of this application can purify the final product to a purity greater than 99.9% and a metal ion content less than 10 ppb. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer and to fully convey the scope of this application to those skilled in the art, exemplary embodiments are described in detail below. However, these exemplary embodiments can be implemented in different ways and should not be construed as being limited to the embodiments described in this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this application are within the scope of protection of this application. It should be understood that the technical features involved in the various embodiments of this application described below can be combined with each other as long as they do not conflict with each other. Specific experimental or operating conditions not specified in the embodiments can be prepared under conventional conditions or according to the conditions recommended by the material supplier. Unless otherwise specified, the reagents, materials, or instruments used in the following embodiments are commercially available.

[0018] During the synthesis of 2,3,4,4'-tetrahydroxybenzophenone, raw materials, catalysts, and byproducts are mixed in the product, which also contains metal ions. This application provides a purification method for 2,3,4,4'-tetrahydroxybenzophenone, comprising the following steps: S1) Crude 2,3,4,4'-tetrahydroxybenzophenone is added to a first solvent, which is a good solvent for 2,3,4,4'-tetrahydroxybenzophenone. The mixture is stirred and heated to dissolve the crude 2,3,4,4'-tetrahydroxybenzophenone. Then, a second solvent and activated carbon are added. The second solvent is a good solvent for impurities generated during the synthesis of 2,3,4,4'-tetrahydroxybenzophenone. The mixture is heated to 60-80°C, stirred, and then the activated carbon is filtered out to obtain a filtrate; S2) [The process continues with steps S1...] Add pure water to the filtrate and keep it at 70-75℃. 2,3,4,4'-Tetrahydroxybenzophenone will not precipitate. Then add alkali to promote the hydrolysis of impurities and dissolve them in water. After stirring, add pure water a second time to reduce the solubility of 2,3,4,4'-Tetrahydroxybenzophenone in the solvent. After stirring, cool down to allow crystallization, and filter to obtain a wet crude product. S3) Add a third solvent, which is pure water or a mixture of pure water and alcohol, to the wet crude product from step S2. Heat until dissolved, add resin, keep warm and stir, filter, cool the filtrate to allow crystallization, rinse with low-temperature pure water, and dry to obtain a refined 2,3,4,4'-Tetrahydroxybenzophenone. In step S1, the purpose of adding activated carbon is decolorization, used to adsorb colored substances, such as colored impurities formed by the oxidation of pyrogallol, a raw material used in the synthesis of 2,3,4,4'-tetrahydroxybenzophenone, and byproducts generated during the synthesis of 2,3,4,4'-tetrahydroxybenzophenone. In addition, the first solvent in step S1 is a good solvent for 2,3,4,4'-tetrahydroxybenzophenone, ensuring complete dissolution of the material. The second solvent has a high solubility for impurities, allowing the activated carbon to fully adsorb the impurities. Combined with the addition of pure water in step S2 in two stages, after the first addition of pure water, alkali is added to promote the hydrolysis and dissolution of ester impurities in water to remove the impurities. Then, pure water is added a second time to reduce the solubility of the product, allowing for cooling and crystallization to obtain a relatively pure 2,3,4,4'-tetrahydroxybenzophenone. In other words, this application first removes impurities such as raw materials and byproducts through steps S1 and S2, and also removes some metal ions. Then, in step S3, a single resin is used to further reduce the content of metal ions. The purification method described in this application has good purification effect; the process is simple; it can use a single resin, resulting in low cost and low pollution; and it is suitable for large-scale industrial production. The refined 2,3,4,4'-tetrahydroxybenzophenone obtained in this application can be high-purity electronic-grade 2,3,4,4'-tetrahydroxybenzophenone, suitable for electronic chemicals.

[0019] In step S1, the temperature of stirring and heating after adding the first solvent can be 30-40℃. It should be understood that in step S2, the first and second pure water are both pure water, and the naming is only to distinguish the pure water added at different times; the drying in step S3 can be vacuum drying.

[0020] In step S1, the reason for heating to 60-80℃ and then filtering out activated carbon after stirring is that this temperature can fully dissolve 2,3,4,4'-tetrahydroxybenzophenone and impurities; if the temperature is below 60℃, the crude 2,3,4,4'-tetrahydroxybenzophenone will not dissolve completely; if the temperature is above 80℃, the solvent will evaporate severely, resulting in waste.

[0021] In step S2, the reason for adding pure water to the filtrate from step S1 and maintaining the temperature at 70-75℃ is that 2,3,4,4'-tetrahydroxybenzophenone will not precipitate at this temperature range; if the temperature is below 70℃, 2,3,4,4'-tetrahydroxybenzophenone will partially precipitate; if the temperature is above 75℃, the solvent will evaporate severely, resulting in waste.

[0022] In some embodiments, the first solvent is an alcohol solvent or an ester solvent, preferably, specifically one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, and ethyl acetate; the second solvent is a benzene derivative, preferably, specifically one or more of benzene, toluene, and xylene.

[0023] In some embodiments, the weight ratio of the first solvent to crude 2,3,4,4'-tetrahydroxybenzophenone is 3-5:1. When the weight ratio is less than 3, 2,3,4,4'-tetrahydroxybenzophenone is not completely dissolved, affecting the subsequent purification effect; when the weight ratio is greater than 5, the subsequent crystallization time increases, and the yield decreases. In some preferred embodiments, isopropanol is selected as the first solvent, and the weight ratio of isopropanol to crude 2,3,4,4'-tetrahydroxybenzophenone is 3:1.

[0024] In some embodiments, the weight ratio of the second solvent to crude 2,3,4,4'-tetrahydroxybenzophenone is 3-15:1. When the weight ratio is less than 3, the second solvent is insufficient to dissolve impurities, leading to a decrease in product purity; when the weight ratio is greater than 15, the product purity is not significantly improved, but rather the yield decreases. In some preferred embodiments, toluene is selected as the second solvent, and the weight ratio of toluene to crude 2,3,4,4'-tetrahydroxybenzophenone is 8:1.

[0025] In some embodiments, the weight ratio of activated carbon to crude 2,3,4,4'-tetrahydroxybenzophenone is 0.01-0.05:1. In some preferred embodiments, the weight ratio of activated carbon to crude 2,3,4,4'-tetrahydroxybenzophenone is 0.03.

[0026] In some embodiments, the weight ratio of the first purified water to the crude 2,3,4,4'-tetrahydroxybenzophenone is 7-9:1. When the weight ratio is less than 7, less of the impurities remaining in the product are exposed and free in the water, resulting in a reduced impurity removal effect. When the weight ratio is greater than 9, excessive water causes a large amount of 2,3,4,4'-tetrahydroxybenzophenone to crystallize and become encapsulated. Impurities are still present, and the impurity removal effect is still reduced. The weight ratio of the second batch of pure water to crude 2,3,4,4'-tetrahydroxybenzophenone is 4-6:1. When the weight ratio of the second batch of pure water to crude 2,3,4,4'-tetrahydroxybenzophenone is less than 4, less 2,3,4,4'-tetrahydroxybenzophenone crystals are formed, resulting in a decrease in yield. When the weight ratio of the second batch of pure water to crude 2,3,4,4'-tetrahydroxybenzophenone is greater than 6, the product purity does not change significantly, but the crystallization time increases, resulting in resource waste. In some preferred embodiments, the weight ratio of the first batch of pure water to crude 2,3,4,4'-tetrahydroxybenzophenone is 8:1; and the weight ratio of the second batch of pure water to crude 2,3,4,4'-tetrahydroxybenzophenone is 5:1.

[0027] In some embodiments, the alkali added in step S2 is one or more of NaOH, KOH, Na2CO3, NaHCO3, K2CO3, and NaHCO3.

[0028] In some embodiments, an alkali is added in step S2 to adjust the pH to 6.0-6.8. When the pH is less than 6.0, it indicates the presence of unreacted acidic impurities in the system; when the pH is greater than 6.8, the alkali is excessive, resulting in an overly high pH that affects the subsequent use of acidic resin to adsorb metal ion impurities in step S3, making it difficult to remove the metal ion impurities. In some preferred embodiments, NaOH is selected as the alkali to adjust the pH to 6.4.

[0029] In some embodiments, in step S2, the temperature is lowered to 5-10°C to induce crystallization.

[0030] In some embodiments, the third solvent is a mixed solution of pure water and alcohol. The alcohol can be one or more of methanol, ethanol, ethylene glycol, propanol, and isopropanol, and the volume ratio of pure water to alcohol is 4-80:1. In some preferred embodiments, the volume ratio of pure water to alcohol is 4:1. Since alcohol is a good solvent for 2,3,4,4'-tetrahydroxybenzophenone, increasing the amount of alcohol can increase solubility, reduce the amount of pure water used, and avoid using a large amount of pure water, thus achieving complete dissolution of the crude product. However, excessive water usage is detrimental to subsequent cooling and crystallization.

[0031] In some embodiments, the third solvent is a mixed solution of pure water and alcohol, with a volume ratio of pure water to alcohol of 4:1. The weight ratio of the third solvent to the crude 2,3,4,4'-tetrahydroxybenzophenone is 4-8:1. When the weight ratio of the third solvent to the crude 2,3,4,4'-tetrahydroxybenzophenone is less than 4, incomplete dissolution of the wet crude product leads to a reduced metal ion removal effect. When the weight ratio of the third solvent to the crude 2,3,4,4'-tetrahydroxybenzophenone is greater than 8, incomplete crystallization of 2,3,4,4'-tetrahydroxybenzophenone results in a decreased yield. In a preferred embodiment, the weight ratio of the third solvent to the crude 2,3,4,4'-tetrahydroxybenzophenone is 6:1.

[0032] In some embodiments, in step S3, after adding the third solvent, the temperature is raised to 60-80°C to dissolve the 2,3,4,4'-tetrahydroxybenzophenone dissolves completely within this temperature range, and this temperature range is the optimal temperature range for the resin to adsorb metal ions.

[0033] In some embodiments, the resin is a strongly acidic cation exchange resin, more specifically, the strongly acidic cation exchange resin is porous or gel-type, and the strongly acidic group is a sulfonic acid group. Examples of strongly acidic cation exchange resins include, for example, Amberlite (1006FH, IRP-69, IR-118, IRC-76, IR120BHAG, etc.) and Amberlyst (15H, 15DRY, 15JWET, 16WET, 31WET, 35WET, XN1010, etc.) manufactured by Rohm and Haas; Diaion (SK1B, SK104, SK110, SK112, SK116, PK208, PK212, PK216, PK220, PK22, UBK550, PK208, PK208, UBK530, etc.) manufactured by Mitsubishi Chemical Co., Ltd.; and Dowex manufactured by Dow Chemical Co., Ltd. Monosphere (650C, 650HXC, 650HXCNG, 575CNG, 650CUPW, 650CNG, 575C, MP525C, 750C) and Dowex (HCR-NG, HCR-W2, HGRW2, MSC1C, 50, 88, 88MB, etc.); Bayer's MP-62, etc.

[0034] In some embodiments, the weight ratio of resin to crude 2,3,4,4'-tetrahydroxybenzophenone is 0.1-0.5:1. When the weight ratio is less than 0.1, the resin has insufficient adsorption sites for metal ions, leading to an increase in metal ion content. When the weight ratio is greater than 0.5, the metal ion content remains almost unchanged, but the increased adsorption by the resin results in a decreased yield. In some preferred embodiments, the weight ratio of resin to crude 2,3,4,4'-tetrahydroxybenzophenone is 0.2:1.

[0035] In some embodiments, the low-temperature pure water in step S3 is pure water at 0-10°C. Within this temperature range, the solubility of pure water for 2,3,4,4'-tetrahydroxybenzophenone is extremely low, allowing for the rinsing removal of residual metal ions on the surface of the material crystals without material loss. Pure water temperatures above 10°C will lead to a decrease in yield. In some preferred embodiments, the temperature of the low-temperature pure water in step S3 is selected as 0-5°C.

[0036] This application utilizes the difference in solubility between 2,3,4,4'-tetrahydroxybenzophenone and impurities, activated carbon adsorption, and resin adsorption methods to improve product purity to over 99.9% and the content of various metal ions to less than 10 ppb. Steps S1 and S2 mainly remove impurities such as raw materials and by-products, which can reduce the metal ion content to about 100 ppb. Step S3 further reduces the metal ion content to less than 10 ppb.

[0037] The present application will be described in more detail below through examples.

[0038] Example 1

[0039] In a clean apparatus, 1000g of crude 2,3,4,4'-tetrahydroxybenzophenone was added to 3000g of a first solvent (isopropanol), stirred, and heated to 40°C to dissolve. Then, 8000g of a second solvent (toluene) and 30g of activated carbon were added, and the mixture was heated to 75°C and stirred for 4 hours. The activated carbon was then filtered out, yielding a filtrate. 8000g of pure water (first pure water) was added to the filtrate, and the mixture was stirred at 75°C for 20 minutes. An appropriate amount of NaOH was added to adjust the pH to 6.4, and the mixture was stirred for 1 hour. Then, 5000g of pure water (second pure water) was added, stirred, and cooled to 5°C to allow crystallization. The resulting wet crude product was then filtered out. Add 4800g of pure water and 1200g of isopropanol (the third solvent) to the wet crude product, heat to 70℃, dissolve, then add 200g of porous strong acid cation exchange resin (HA-8G type resin produced by Xi'an Hairun New Materials Co., Ltd.), keep warm and stir for 6 hours, filter out the resin, cool the filtrate to 5℃ to precipitate crystals, filter under vacuum, wash with pure water at 5℃, and vacuum dry to obtain high-purity 2,3,4,4'-tetrahydroxybenzophenone, with a yield of 84.6%, a purity of 99.9%, and the content of various metal ions <10ppb.

[0040] Example 2

[0041] The only difference from Example 1 is that the first solvent is ethyl acetate.

[0042] Example 3

[0043] The only difference from Example 1 is that after adding the second solvent and activated carbon, the temperature is raised to 60°C, and then kept at that temperature and stirred for 4 hours before filtering out the activated carbon.

[0044] Example 4

[0045] The only difference from Example 1 is that after adding the second solvent and activated carbon, the temperature is raised to 80°C, and then kept warm and stirred for 4 hours before filtering out the activated carbon.

[0046] Example 5

[0047] The only difference from Example 1 is that the amount of pure water added initially is 7000g.

[0048] Example 6

[0049] The only difference from Example 1 is that the amount of pure water added initially is 9000g.

[0050] Example 7

[0051] The only difference from Example 1 is that after adding the first batch of pure water, the mixture is kept at 70°C and stirred for 20 minutes, and then an appropriate amount of NaOH is added.

[0052] Example 8

[0053] The only difference from Example 1 is the addition of an appropriate amount of NaOH to adjust the pH to 6.

[0054] Example 9

[0055] The only difference from Example 1 is the addition of an appropriate amount of NaOH to adjust the pH to 6.8.

[0056] Example 10

[0057] The only difference from Example 1 is that the third solvent is 6000g of pure water.

[0058] Example 11

[0059] The only difference from Example 1 is that the third solvent is a mixture of 5925g of pure water and 75g of isopropanol.

[0060] Example 12

[0061] The only difference from Example 1 is that the temperature was raised to 60°C after the addition of the third solvent to dissolve it.

[0062] Example 13

[0063] The only difference from Example 1 is that the temperature was raised to 80°C after the addition of the third solvent to dissolve it.

[0064] Example 14

[0065] The only difference from Example 1 is that the cation exchange resin is a gel-type strong acid cation exchange resin (650C type resin manufactured by Dow Chemical).

[0066] Comparative Example 1

[0067] The only difference from Example 1 is that no second solvent was added.

[0068] Comparative Example 2

[0069] The only difference from Example 1 is that after adding the second solvent and activated carbon, the temperature is raised to 50°C, and then kept warm and stirred for 4 hours before filtering out the activated carbon.

[0070] Comparative Example 3

[0071] The only difference from Example 1 is that the amount of pure water added initially is 6000g.

[0072] Comparative Example 4

[0073] The only difference from Example 1 is that the first addition of pure water is 10,000g.

[0074] Comparative Example 5

[0075] The only difference from Example 1 is that no second batch of pure water was added.

[0076] Comparative Example 6

[0077] The only difference from Example 1 is that 13,000g of pure water was added for the first time, and no pure water was added for the second time.

[0078] Comparative Example 7

[0079] The only difference from Example 1 is that after adding the first batch of pure water, the mixture is kept at 65°C and stirred for 20 minutes, and then an appropriate amount of NaOH is added.

[0080] Comparative Example 8

[0081] The only difference from Example 1 is that the pH was adjusted to 5.5.

[0082] Comparative Example 9

[0083] The only difference from Example 1 is that the pH was adjusted to 7.5.

[0084] Comparative Example 10

[0085] The only difference from Example 1 is that the third solvent is a mixture of 4500 pure water and 1500 isopropanol (water: alcohol = 3:1).

[0086] Comparative Example 11

[0087] The only difference from Example 1 is that the temperature was raised to 50°C after the addition of the third solvent to dissolve it.

[0088] Comparative Example 12

[0089] The only difference from Example 1 is that the temperature was raised to 90°C after the addition of the third solvent to dissolve it.

[0090] See Table 1 below for a summary of the results from the various embodiments and comparative examples.

[0091] serial number yield purity Metal ion content Example 1 84.6% 99.9% <10ppb Example 2 80.4% 99.6% <10ppb Example 3 83.1% 99.3% <10ppb Example 4 84.5% 99.9% <10ppb Example 5 84.1% 99.8% <10ppb Example 6 83.9% 99.9% <10ppb Example 7 83.8% 99.9% <10ppb Example 8 84.1% 99.6% <10ppb Example 9 84.2% 99.7% <10ppb Example 10 83.8% 99.7% <10ppb Example 11 84.1% 99.8% <10ppb Example 12 84.2% 99.8% <10ppb Example 13 84.1% 99.7% <10ppb Example 14 84.3% 99.8% 12ppb Comparative Example 1 72.0% 98.2% <10ppb Comparative Example 2 75.6% 98.1% <10ppb Comparative Example 3 80.6% 98.6% <10ppb Comparative Example 4 76.1% 98.9% <10ppb Comparative Example 5 74.9% 98.6% <10ppb Comparative Example 6 73.2% 98.8% <10ppb Comparative Example 7 83.6% 99.1% <10ppb Comparative Example 8 83.5% 98.5% <10ppb Comparative Example 9 84.1% 99.2% 20ppb Comparative Example 10 82.8% 99.6% 18ppb Comparative Example 11 81.2% 99.3% 26ppb Comparative Example 12 82.7% 99.6% 43ppb

[0092] Table 1

[0093] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for purifying 2,3,4,4'-tetrahydroxybenzophenone, characterized in that, Includes the following steps: S1) Add crude 2,3,4,4'-tetrahydroxybenzophenone to the first solvent, stir and heat to dissolve, then add the second solvent and activated carbon, heat to 60-80℃ and stir, then filter out the activated carbon to obtain the filtrate; S2) Add the first pure water to the filtrate from step S1 and keep it at 70-75℃. 2,3,4,4'-tetrahydroxybenzophenone will not precipitate. Then add alkali to promote the hydrolysis of impurities and dissolve them in water. After stirring, add the second pure water to reduce the solubility of 2,3,4,4'-tetrahydroxybenzophenone in the solvent. After stirring, cool down to allow crystals to precipitate. Filter to obtain the wet crude product. S3) Add a third solvent to the wet crude product from step S2, heat to dissolve, add resin, keep warm and stir, filter, cool the filtrate to precipitate crystals, rinse with low-temperature pure water, and dry to obtain 2,3,4,4'-tetrahydroxybenzophenone (PTA) product. Wherein, the first solvent is a good solvent for 2,3,4,4'-tetrahydroxybenzophenone, the second solvent is a good solvent for impurities generated during the synthesis of 2,3,4,4'-tetrahydroxybenzophenone, and the third solvent is pure water or a mixed solution of pure water and alcohol.

2. The purification method according to claim 1, characterized in that, The first solvent is an alcohol solvent or an ester solvent, and the second solvent is a benzene derivative; Preferably, the first solvent is one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, and ethyl acetate, and the second solvent is one or more of benzene, toluene, and xylene.

3. The purification method according to claim 1, characterized in that, Step S1 includes one or more of the following features: 1) The weight ratio of the first solvent to the crude 2,3,4,4'-tetrahydroxybenzophenone is 3-5:1; 2) The weight ratio of the second solvent to the crude 2,3,4,4'-tetrahydroxybenzophenone is 3-15:1; 3) The weight ratio of the activated carbon to the crude 2,3,4,4'-tetrahydroxybenzophenone is 0.01-0.05:

1.

4. The purification method according to claim 1, characterized in that, The weight ratio of the first batch of purified water to the crude 2,3,4,4'-tetrahydroxybenzophenone is 7-9:1; the weight ratio of the second batch of purified water to the crude 2,3,4,4'-tetrahydroxybenzophenone is 4-6:

1.

5. The purification method according to claim 1, characterized in that, Step S2 includes one or more of the following features: 1) The alkali is one or more of NaOH, KOH, Na2CO3, NaHCO3, K2CO3, and NaHCO3; 2) Add alkali to adjust the pH to 6.0-6.8; 3) Cool down to 5-10℃ to crystallize.

6. The purification method according to claim 1, characterized in that, The third solvent is a mixed solution of pure water and alcohol, with a volume ratio of pure water to alcohol of 4-80:

1. Preferably, the volume ratio of pure water to alcohol is 4:

1.

7. The purification method according to claim 1, characterized in that, Add the third solvent and heat to 60-80℃ to dissolve.

8. The purification method according to claim 1, characterized in that, The resin is a strongly acidic cation exchange resin.

9. The purification method according to claim 8, characterized in that, The strongly acidic cation exchange resin is porous or gel-type, and the strongly acidic group is a sulfonic acid group.

10. The purification method according to claim 1, characterized in that, Step S3 includes one or more of the following features: 1) The third solvent is a mixed solution of pure water and alcohol, with a volume ratio of pure water to alcohol of 4:1, and a weight ratio of the third solvent to the crude 2,3,4,4'-tetrahydroxybenzophenone of 4-8:

1. 2) The weight ratio of the resin to the crude 2,3,4,4'-tetrahydroxybenzophenone is 0.1-0.5:1; 3) The low-temperature pure water is pure water at 0-10℃.