Method for crystallizing and purifying 3, 3 '-diaminobenzidine

Abstract

The invention relates to the technical field of preparation of 3, 3 '-diaminobenzidine, and discloses a method for crystallizing and purifying 3, 3'-diaminobenzidine, which comprises the following steps: (1) dissolving a 3, 3 '-diaminobenzidine crude product in a good solvent; (2) contacting the dissolved 3, 3 '-diaminobenzidine crude product with activated carbon, and then carrying out solid-liquid separation to obtain a solution; (3) adding at least part of a solvating-out agent into the solution obtained in the step (2), and growing crystals; after crystal growing is finished, adding the residual solvating-out agent, and then carrying out first aging; (4) cooling a product obtained by the first aging, carrying out second aging at the temperature, carrying out solid-liquid separation, washing and drying; the cooling rate is 0.1 to 0.4 DEG C / min. According to the method disclosed by the invention, the 3, 3 '-diaminobenzidine product with high purity and high yield can be obtained.

Description

Technical Field

[0001] This invention relates to the field of 3,3′-diaminobenzidine preparation technology, and specifically to a method for crystallizing and purifying 3,3′-diaminobenzidine. Background Technology

[0002] 3,3′-Diaminobenzidine, as an important monomer for polymers, can be used to prepare high-performance polymer resins and fibers, such as polybenzimidazole and polyamides. Simultaneously, due to its mutagenic properties, 3,3′-diaminobenzidine can be used for chemical staining of nucleic acids and proteins. As an analytical reagent, it is commonly used for spectrophotometric determination of selenium content. The purity of 3,3′-diaminobenzidine directly affects the accuracy of analytical detection and the value and performance of subsequent synthesized products. Therefore, increasing the production scale of 3,3′-diaminobenzidine and achieving purification of 3,3′-diaminobenzidine through the development and optimization of crystallization processes have significant practical implications and broad development prospects. CN117756640A employs a two-step heating method to synthesize 3,3′-diaminobenzidine. During purification, it requires dissolving 3,3′-diaminobenzidine in water (40-50 times its mass of the crude product) at approximately 100°C. Simultaneously, activated carbon and ammonium sulfate hydrochloride (mass ratio 1:1) are added. Due to the high operating temperature, nitrogen protection is required throughout the process, and multiple purification steps are necessary to obtain high-purity 3,3′-diaminobenzidine, resulting in a low overall yield. EP0522577B1 also requires a large amount of water as a solvent and a dissolution temperature above 100°C during the purification of crude 3,3′-diaminobenzidine. US3943175 uses large amounts of acid and alkali through an acid-base reaction and dissolution in large quantities of boiling water, followed by cooling to obtain a solid product of 3,3′-diaminobenzidine. This method involves high operating temperatures and low product purity. US3481984 uses sodium chloride as a flocculant to remove insoluble colloidal impurities by passing an aqueous solution of 3,3′-diaminobenzidine through an activated carbon column at 120-125°C. This method is costly and inefficient.

[0003] In summary, water is often used as a solvent for the purification of 3,3′-diaminobenzidine. However, due to its low solubility in water, a large amount of water is required at a high temperature of around 100°C to dissolve it. Since 3,3′-diaminobenzidine is easily oxidized and deteriorates at high temperatures, nitrogen protection is required throughout the process. Multiple purifications are needed to obtain high-purity 3,3′-diaminobenzidine products. This process suffers from disadvantages such as low equipment utilization, high energy consumption, small batch throughput, and low yield. Summary of the Invention

[0004] The purpose of this invention is to overcome the aforementioned problems in the prior art and to provide a method for the crystallization and purification of 3,3′-diaminobenzidine.

[0005] To achieve the above objectives, the present invention provides a method for purifying 3,3′-diaminobenzidine by crystallization, the method comprising the following steps:

[0006] (1) Dissolve crude 3,3′-diaminobenzidine in a good solvent, wherein the good solvent includes at least one of nitrogen-containing organic compounds, sulfur-containing organic compounds and oxygen-containing organic compounds;

[0007] (2) The dissolved crude 3,3′-diaminobenzidine was contacted with activated carbon, and then a solution was obtained by solid-liquid separation;

[0008] (3) Add at least part of the precipitant to the solution obtained in step (2) and then perform crystal growth; after the crystal growth is completed, add the remaining precipitant and then perform the first aging; wherein the precipitant includes water and / or a monohydric alcohol;

[0009] (4) The product obtained from the first aging is cooled down, and a second aging, solid-liquid separation, washing and drying are carried out at the same temperature; the cooling rate is 0.1-0.4℃ / min.

[0010] Through the above technical solution, the present invention achieves the following beneficial effects:

[0011] (1) Crude 3,3′-diaminobenzidine contains numerous impurities (mainly soluble benzidine triamine or benzidine diamine and other benzidine compounds), which originate from upstream processes. This invention employs a specific good solvent and a specific precipitant for crystallization purification, adding the precipitant twice and aging it twice at different temperatures. This method yields high-purity, high-yield 3,3′-diaminobenzidine. Furthermore, this method offers advantages such as mild conditions, simple process, low energy consumption, no need for nitrogen protection, low solvent consumption, and large batch throughput. The method meets green environmental protection requirements and has high industrial application value.

[0012] (2) In a preferred embodiment, the method of the present invention can obtain crystals with uniform particle size and blocky morphology; the average particle size of the crystals is 75-90 μm. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the dissolution and crystallization of high-purity 3,3′-diaminobenzidine according to the present invention;

[0014] Figure 2 Microscopic photograph of the 3,3′-diaminobenzidine crystal product obtained in Example 1;

[0015] Figure 3 Microscopic photograph of the 3,3′-diaminobenzidine crystal product obtained in Example 2;

[0016] Figure 4 Microscopic photograph of the 3,3′-diaminobenzidine crystal product obtained in Example 8;

[0017] Figure 5 Microscopic photograph of the 3,3′-diaminobenzidine crystal product obtained in Comparative Example 1;

[0018] Figure 6 Microscopic photograph of the 3,3′-diaminobenzidine crystal product obtained in Comparative Example 2. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] This invention provides a method for purifying 3,3′-diaminobenzidine by crystallization, the method comprising the following steps:

[0021] (1) Dissolve crude 3,3′-diaminobenzidine in a good solvent, wherein the good solvent includes at least one of nitrogen-containing organic compounds, sulfur-containing organic compounds and oxygen-containing organic compounds;

[0022] (2) The dissolved crude 3,3′-diaminobenzidine was contacted with activated carbon, and then a solution was obtained by solid-liquid separation;

[0023] (3) Add at least part of the precipitant to the solution obtained in step (2) and then perform crystal growth; after the crystal growth is completed, add the remaining precipitant and then perform the first aging; wherein the precipitant includes water and / or a monohydric alcohol;

[0024] (4) The product obtained from the first aging is cooled down, and a second aging, solid-liquid separation, washing and drying are carried out at the same temperature; the cooling rate is 0.1-0.4℃ / min.

[0025] The inventors of this invention have discovered that when the specific good solvent and specific precipitant of this invention are used for crystallization and purification, and the precipitant is added twice and aged twice at different temperatures, a high-purity, high-yield 3,3′-diaminobenzidine product can be obtained.

[0026] In this invention, the purity of the crude 3,3′-diaminobenzidine is not particularly limited and can be selected within a wide range. Typically, the purity of the crude 3,3′-diaminobenzidine is 95-97%.

[0027] According to the present invention, preferably, in step (1), the dissolution temperature is 25-35°C.

[0028] According to the present invention, the good solvent can be an organic compound containing 2-10 carbon atoms, such as an organic compound containing methyl, an organic compound containing ethyl, an organic compound containing a nitrogen heterocycle, or an organic compound containing an oxygen heterocycle; in order to further improve the purity and yield of the 3,3′-diaminobenzidine product, preferably, the good solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran.

[0029] According to the present invention, taking into account the purity and yield of the 3,3′-diaminobenzidine product and reducing the amount of good solvent and precipitant, preferably, the amount of good solvent used is 10-35 mL (for example, it can be 10 mL, 15 mL, 20 mL, 21 mL, 22 mL, 23 mL, 24 mL, 25 mL, 26 mL, 27 mL, 28 mL, 30 mL, 35 mL, and any two of the above) relative to 12 g of crude 3,3′-diaminobenzidine.

[0030] According to the present invention, preferably, the amount of activated carbon used is 0.01-1g relative to 12g of crude 3,3′-diaminobenzidine (for example, it can be 0.01g, 0.05g, 0.1g, 0.2g, 0.3g, 0.35g, 0.4g, 0.5g, 0.6g, 0.8g, 0.10g, and any two of the above ranges).

[0031] According to the present invention, preferably, in step (2), the contact conditions include: a temperature of 5-35°C and a time of 0.5-1h.

[0032] According to the present invention, preferably, the solvent is a C1-C5 monohydric alcohol and / or water, and more preferably at least one of methanol, ethanol, water, isopropanol and n-propanol.

[0033] According to the present invention, preferably, in step (3), the volume ratio of the total amount of the solvent to the volume of the good solvent is 1-4:1 (for example, it can be 1:1, 2:1, 3:1, 4:1, or any two of the above). The total amount of the solvent includes the sum of at least a portion of the solvent and the remaining solvent.

[0034] According to the present invention, preferably, in step (3), the amount of at least a portion of the solvent is such that crystals begin to precipitate from the solution obtained in step (2).

[0035] According to the present invention, preferably, the temperature at which the solvent is added is 5-30°C.

[0036] According to the present invention, preferably, the solvent is added dropwise. More preferably, the dropping rate of the solvent is 100-300 μL / min relative to 12 g of crude 3,3′-diaminobenzidine. In the present invention, the dropping rate of at least a portion of the solvent may be the same as or different from that of the remaining solvent.

[0037] According to the present invention, in order to further improve product quality, preferably, the crystal growth conditions include: a temperature of 5-35°C and a time of 0.5-1.5h.

[0038] According to the present invention, in order to further improve product quality, preferably, the conditions for the first aging include: a temperature of 5-35°C and a time of 0.5h-2h.

[0039] According to the present invention, in order to further improve product quality, preferably, in step (4), the conditions for the second aging include: a temperature of 0-5°C and a time of 0.5-2h.

[0040] According to the present invention, preferably, the detergent used for washing is a C1-C5 monohydric alcohol and / or water, more preferably at least one selected from methanol, ethanol, water, isopropanol, and n-propanol. Typically, the detergent is the same type as the solvent used to avoid introducing more types of impurities.

[0041] In this invention, the drying conditions can be those commonly used in the art, as long as they allow the detergent to evaporate. For example, the drying conditions include: vacuum conditions, a temperature of 40-60°C, and a time of 3-8 hours.

[0042] According to a preferred embodiment of the present invention, the method employed is as follows: Figure 1 The process described above involves crystallizing and purifying crude 3,3′-diaminobenzidine. The crystallization and purification process includes: firstly, dissolving the crude 3,3′-diaminobenzidine in a good solvent, then adding activated carbon for adsorption, and then filtering the activated carbon to obtain a filtrate; adding a solvent to the filtrate for dissolution and crystallization to obtain a solid-liquid mixture I, wherein the solvent is added in two parts; then cooling and crystallizing the solid-liquid mixture I to obtain a solid-liquid mixture II; and then filtering, washing, and drying the solid-liquid mixture II to obtain the product.

[0043] According to a particularly preferred embodiment of the present invention, the method for purifying 3,3′-diaminobenzidine by crystallization includes the following steps:

[0044] Take crude 3,3′-diaminobenzidine raw material and pour it into a batch crystallizer containing N,N-dimethylacetamide (the amount of N,N-dimethylacetamide is 20-26 mL relative to 12 g of crude 3,3′-diaminobenzidine). Maintain the temperature in the crystallizer at 28-30℃ and stir constantly until the crude product is completely dissolved. Then add activated carbon to the batch crystallizer (the amount of activated carbon is 0.3-0.4 g relative to 12 g of crude 3,3′-diaminobenzidine). Continue stirring constantly for 35-40 minutes, then quickly vacuum filter. Pour the filtrate obtained from the vacuum filtration into the batch crystallizer. Measure the amount of water (the total amount of water is equal to the amount of N,N-dimethylacetamide). The volume ratio of methylacetamide used is 1.8-2.2:1. The crystallization temperature is set at 28-30℃, and the water dropping rate is 100-120μL / min. After crystals appear in the solution, the dropping is stopped. The mixture is stirred at a constant temperature for 1-1.2 hours to allow crystals to grow. Then, water is added dropwise to the reactor at 100-120μL / min. After the water is added, the mixture is stirred at a constant temperature for 1-1.2 hours to allow it to age. The solid-liquid mixture is cooled uniformly to 4-5℃ at a cooling rate of 0.1-0.15℃ / min and aged at this temperature for 1-1.2 hours. The slurry is then rapidly vacuum filtered, the solid product is washed multiple times with water, and then the solid product is vacuum dried.

[0045] The present invention will be described in detail below through embodiments. In the following embodiments,

[0046] Purity was tested using high performance liquid chromatography;

[0047] The formula for calculating product yield is: product weight ÷ weight of crude 3,3′-diaminobenzidine × 100%.

[0048] Example 1

[0049] Take 12.00 g of crude 3,3′-diaminobenzidine raw material with a purity of 95.00%, pour it into a batch crystallizer containing 25 mL of N,N-dimethylformamide, and maintain the temperature in the crystallizer at 35.0℃. Stir at this temperature until the crude product is completely dissolved. Then add 0.36 g of activated carbon to the batch crystallizer, continue stirring at 35.0℃ for 40 min, and then quickly vacuum filter. Pour the filtrate into the batch crystallizer, measure 100 mL of methanol, set the dissolution and crystallization temperature to 35.0℃, and the methanol dropping rate to 100 μL / min. Stop adding methanol after crystals appear in the solution. Continue stirring at this temperature for 1.0 h to allow crystals to grow. Methanol was added dropwise to the batch crystallizer at a rate of 100 μL / min. After the methanol addition was complete, the mixture was stirred at a constant temperature and aged for 1.0 h. The solid-liquid mixture was then cooled uniformly to 5.0 °C at a cooling rate of 0.4 °C / min and aged at this temperature for 1.0 h. The slurry was then rapidly vacuum filtered, and the solid was washed multiple times with methanol. The solid product was then vacuum dried at 45 °C for 3.0 h, finally yielding 8.40 g of 3,3′-diaminobenzidine product with a purity of 98.81%, a yield of 72.9%, and an impurity removal rate of 76.2%.

[0050] Electron micrographs of the 3,3′-diaminobenzidine product are shown below. Figure 2 As shown in the figure, the obtained 3,3′-diaminobenzidine products are all block crystals with uniform particle size distribution and no agglomeration.

[0051] Example 2

[0052] Take 12.00 g of crude 3,3′-diaminobenzidine raw material with a purity of 95.00%, pour it into a batch crystallizer containing 25 mL of N,N-dimethylacetamide, and maintain the temperature in the crystallizer at 30.0℃. Stir at this constant temperature until the crude product is completely dissolved. Then add 0.36 g of activated carbon to the batch crystallizer, continue stirring at 30.0℃ for 40 min, and then quickly vacuum filter. Pour the filtrate into the batch crystallizer, measure 62.5 mL of isopropanol, set the dissolution and crystallization temperature to 30.0℃, and the isopropanol dropping rate to 200 μL / min. After crystals appear in the solution... Stop the dropwise addition; continue constant temperature stirring and crystallize for 1.0 h; then continue to add isopropanol dropwise at a rate of 200 μL / min to the solid-liquid mixture in the batch crystallizer. After the isopropanol addition is complete, continue constant temperature stirring and age for 1.0 h; then cool uniformly to 2.5 °C at a cooling rate of 0.25 °C / min and age at this temperature for 1.0 h; quickly vacuum filter the slurry, wash the solid product multiple times with isopropanol, and then vacuum dry the solid product at 45 °C for 3.0 h, finally obtaining 9.49 g of 3,3′-diaminobenzidine product with a purity of 98.18%, a yield of 79.08%, and an impurity removal rate of 63.6%.

[0053] Electron micrographs of the 3,3′-diaminobenzidine product are shown below. Figure 3 As shown in the figure, the obtained 3,3′-diaminobenzidine products are all block crystals with uniform particle size distribution and no agglomeration.

[0054] Example 3

[0055] Take 12.00 g of crude 3,3′-diaminobenzidine raw material with a purity of 95.00%, pour it into a batch crystallizer containing 25 mL of dimethyl sulfoxide, and maintain the temperature in the crystallizer at 25.0℃. Stir at this constant temperature until the crude product is completely dissolved. Then add 0.36 g of activated carbon to the batch crystallizer and continue stirring at 25.0℃ for 40 min. Then quickly vacuum filter the mixture. Pour the filtrate obtained from the filtration into the batch crystallizer, measure 50 mL of water, and set the dissolution and crystallization temperature to 25℃. At 0℃, water was added at a rate of 150 μL / min. Once crystals appeared in the solution, the addition was stopped. The mixture was then stirred at a constant temperature for 1.0 h to allow crystals to grow. Water was then added dropwise at a rate of 150 μL / min to the reactor crystallizer. After the water addition was complete, the mixture was stirred at a constant temperature for 1.0 h to allow aging. The solid-liquid mixture was then cooled uniformly to 5.0℃ at a rate of 0.1℃ / min and aged at this temperature for 1.0 h. The slurry was then rapidly vacuum filtered, and the solid product was washed multiple times with water. The solid product was then vacuum dried at 45℃ for 3.0 h to obtain 9.84 g of 3,3′-diaminobenzidine product with a purity of 99.20%, a yield of 82.0%, and an impurity removal rate of 84%.

[0056] Electron micrographs of the 3,3′-diaminobenzidine product and Figure 1 Similarly, the products are all block crystals with uniform particle size distribution and no agglomeration.

[0057] Example 4

[0058] Take 12.00 g of crude 3,3′-diaminobenzidine raw material with a purity of 95.00%, pour it into a batch crystallizer containing 25 mL of N,N-dimethylformamide, and maintain the temperature in the crystallizer at 35.0℃. Stir at this constant temperature until the crude product is completely dissolved. Then add 0.36 g of activated carbon to the batch crystallizer, continue stirring at 35.0℃ for 40 min, and then quickly vacuum filter. Pour the filtrate into the batch crystallizer, measure 75.0 mL of n-propanol, set the dissolution and crystallization temperature to 35.0℃, and the dropping rate of n-propanol to 300 μL / min. After crystals appear in the solution... Stop adding the solution; continue stirring at a constant temperature for 1.0 h to allow crystals to grow. Then, continue adding n-propanol dropwise to the batch crystallizer at a rate of 300 μL / min. After the n-propanol addition is complete, continue stirring at a constant temperature for 1.0 h to allow aging. Then, cool the solid-liquid mixture uniformly to 5.0℃ at a cooling rate of 0.1℃ / min and age it at this temperature for 1.0 h. Quickly vacuum filter the slurry, wash the solid product multiple times with n-propanol, and then vacuum dry the solid product at 45℃ for 3.0 h to finally obtain 9.35 g of 3,3′-diaminobenzidine product with a purity of 99.10%, a yield of 77.9%, and an impurity removal rate of 82%.

[0059] Electron micrographs of the 3,3′-diaminobenzidine product and Figure 1 Similarly, the products are all block crystals with uniform particle size distribution and no agglomeration.

[0060] Example 5

[0061] Take 12.00 g of crude 3,3′-diaminobenzidine raw material with a purity of 95.00%, and pour it into a container containing 25 mL of... In a batch crystallizer of N,N-dimethylacetamide, the temperature was controlled at 30.0℃, and the mixture was stirred at a constant temperature until the crude product was completely dissolved. Then, 0.36g of activated carbon was added to the batch crystallizer, and the mixture was stirred at 30.0℃ for 40min, followed by rapid vacuum filtration. The filtrate was poured into the batch crystallizer, and 50mL of water was added. The crystallization temperature was set at 30.0℃, and the water dropping rate was 100μL / min. Once crystals appeared in the solution, the dropping was stopped. The mixture was stirred at a constant temperature for 1.0h to allow crystals to grow. Then, water was added to the batch crystallizer at a rate of 100μL / min. After the water was added, the mixture was stirred at a constant temperature for 1.0h to allow aging. The solid-liquid mixture was cooled uniformly to 5℃ at a cooling rate of 0.1℃ / min and aged at this temperature for 1.0h. The slurry was then rapidly vacuum filtered, and the solid product was washed several times with water. Finally, the solid product was vacuum dried at 45℃ for 3.0h to obtain 9.61g of the final product. The 3,3′-diaminobenzidine product has a purity of 99.59%, a yield of 80.1%, and an impurity removal rate of 91.8%.

[0062] Electron micrographs of the 3,3′-diaminobenzidine product and Figure 1 Similarly, the products are all block crystals with uniform particle size distribution and no agglomeration.

[0063] Example 6

[0064] Take 12.00 g of crude 3,3′-diaminobenzidine raw material with a purity of 95.00%, pour it into a batch crystallizer containing 25 mL of tetrahydrofuran, maintain the temperature in the crystallizer at 30.0℃, and stir at a constant temperature until the crude product is completely dissolved; then add 0.36 g of activated carbon to the batch crystallizer, continue stirring at 30.0℃ for 40 min, and then quickly vacuum filter; pour the filtrate obtained by vacuum filtration into the batch crystallizer, measure 100 mL of isopropanol, set the dissolution and crystallization temperature to 30.0℃, and the isopropanol dropping rate to 200 μL. The rate of addition was 1.5 h / min. Once crystals appeared in the solution, the addition was stopped. Stirring was continued at a constant temperature for 1.0 h. Then, isopropanol was added dropwise to the reactor at a rate of 200 μL / min. After the isopropanol addition was complete, stirring was continued at a constant temperature for 1.0 h. The solid-liquid mixture was then cooled uniformly to 2.5℃ at a cooling rate of 0.4℃ / min and aged at this temperature for 1.0 h. The slurry was rapidly vacuum filtered, and the solid product was washed multiple times with isopropanol. The solid product was then vacuum dried at 45℃ for 3.0 h, finally yielding 9.12 g of 3,3′-diaminobenzidine product with a purity of 98.76%, a yield of 76.0%, and an impurity removal rate of 75.2%.

[0065] Electron micrographs of the 3,3′-diaminobenzidine product and Figure 1 Similarly, the products are all block crystals with uniform particle size distribution and no agglomeration.

[0066] Example 7

[0067] Take 12.00 g of crude 3,3′-diaminobenzidine raw material with a purity of 95.00%, and pour it into a container containing 25 mL of... In a batch crystallizer of N,N-dimethylformamide, the temperature was controlled at 25.0℃, and the mixture was stirred at a constant temperature until the crude product was completely dissolved. Then, 0.36g of activated carbon was added to the batch crystallizer, and the mixture was stirred at 25.0℃ for 40min, followed by rapid vacuum filtration. The filtrate was poured into the batch crystallizer, and 75mL of ethanol was added. The crystallization temperature was set at 25.0℃, and the ethanol dropping rate was 150μL / min. Once crystals appeared in the solution, the dropping was stopped. The mixture was stirred at a constant temperature for 1.0h to allow crystals to grow. Then, ethanol was added dropwise to the batch crystallizer at a rate of 150μL / min. After the ethanol was added, the mixture was stirred at a constant temperature for 1.0h to allow aging. The solid-liquid mixture was cooled to 0℃ at a cooling rate of 0.25℃ / min and aged at this temperature for 1.0h. The slurry was then rapidly vacuum filtered, and the solid product was washed multiple times with ethanol. Finally, the solid product was vacuum dried at 45℃ for 3.0h to obtain 8.53g of the final product. The 3,3′-diaminobenzidine product had a purity of 98.92%, a product yield of 71.1%, and an impurity removal rate of 78.4%.

[0068] Electron micrographs of the 3,3′-diaminobenzidine product and Figure 1 Similarly, the products are all block crystals with uniform particle size distribution and no agglomeration.

[0069] Example 8

[0070] The procedure was carried out according to Example 1, except that methanol was replaced with n-butanol.

[0071] The final product had a purity of 98.19%, a yield of 74.1%, and an impurity removal rate of 63.8%.

[0072] Electron micrographs of the 3,3′-diaminobenzidine product are shown below. Figure 4 As shown in the figure, the obtained 3,3′-diaminobenzidine is in the form of long flakes with a dispersed particle size distribution and varying sizes.

[0073] Comparative Example 1

[0074] The method was carried out according to Example 1, except that the cooling rate was changed to 0.8℃ / min.

[0075] The final product had a purity of 96.63%, a yield of 71.8%, and an impurity removal rate of 32.6%.

[0076] Electron micrographs of the 3,3′-diaminobenzidine product are shown below. Figure 5As shown in the figure, the crystals are in the form of small, elongated plates and exhibit a certain degree of aggregation, which may lead to the inclusion of impurities and severely reduce the purity of the product.

[0077] Comparative Example 2

[0078] The procedure was carried out according to Example 1, except that methanol was replaced with an equal volume of diethyl ether.

[0079] The final product had a purity of 97.19%, a yield of 73.4%, and an impurity removal rate of 43.8%.

[0080] Electron micrographs of the 3,3′-diaminobenzidine product are shown below. Figure 6 As shown in the figure, the crystals are small, elongated plates with extremely uneven grain size distribution and a certain degree of agglomeration, which may lead to 1240399

[0081] I96197BHY

[0082] This leads to the inclusion of impurities, severely reducing product purity.

[0083] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for purifying 3,3′-diaminobenzidine by crystallization, characterized in that, The method includes the following steps: (1) Dissolve crude 3,3′-diaminobenzidine in a good solvent, wherein the good solvent includes at least one of nitrogen-containing organic compounds, sulfur-containing organic compounds and oxygen-containing organic compounds; (2) The dissolved crude 3,3′-diaminobenzidine was contacted with activated carbon, and then a solution was obtained by solid-liquid separation; (3) Add at least part of the precipitant to the solution obtained in step (2) and then perform crystal growth; after the crystal growth is completed, add the remaining precipitant and then perform the first aging; wherein the precipitant includes water and / or a monohydric alcohol; (4) The product obtained from the first aging is cooled down, and a second aging, solid-liquid separation, washing and drying are carried out at the same temperature; the cooling rate is 0.1-0.4℃ / min.

2. The method according to claim 1, wherein, In step (1), the dissolution temperature is 25-35℃.

3. The method according to claim 1, wherein, The good solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran; And / or, relative to 12 g of crude 3,3′-diaminobenzidine, the amount of the good solvent used is 10-35 mL.

4. The method according to claim 1, wherein, The amount of activated carbon used is 0.01-1g relative to 12g of crude 3,3′-diaminobenzidine; And / or, in step (2), the contact conditions include: a temperature of 5-35°C; The time is 0.5-1 hour.

5. The method according to claim 1, wherein, The solvent is a C1-C5 monohydric alcohol and / or water, preferably at least one of methanol, ethanol, water, isopropanol and n-propanol.

6. The method according to claim 1, wherein, In step (3), the total volume ratio of the solvent to the good solvent is 1-4:

1. And / or, in step (3), the amount of at least a portion of the solvent used is such that crystals begin to precipitate from the solution obtained in step (2); And / or, the temperature at which the solvent is added is 5-30°C; And / or, the solvent is added dropwise.

7. The method according to claim 1, wherein, The conditions for crystal growth include: a temperature of 5-35℃ and a time of 0.5-1.5h.

8. The method according to claim 1, wherein, The conditions for the first aging process include: a temperature of 5-35℃ and a time of 0.5-2 hours.

9. The method according to claim 1, wherein, In step (4), the conditions for the second aging include: a temperature of 0-5℃ and a time of 0.5-2h.

10. The method according to claim 1, wherein, The washing agent used is a C1-C5 monohydric alcohol and / or water, preferably at least one of methanol, ethanol, water, isopropanol and n-propanol; And / or, the drying conditions include: under vacuum conditions, at a temperature of 40-60°C, for a time of 3-8 hours.

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