Method for improving purity of thermosensitive dye ODB-2

Abstract

The invention belongs to the technical field of fine chemical engineering, and particularly relates to a method for improving the purity of thermosensitive dye ODB-2. According to the sectional type controlled nitrogen pressurization ODB-2 crystallization technology provided by the invention, efficient improvement of the purity of an ODB-2 product is realized through five-step operation of charging, heating, pressurization, crystal precipitation and crystal growth, and impurities generated by sulfonation, ring-opening reaction and the like in an ODB-2 crude product can be efficiently removed; the technical bottlenecks that complex impurities are difficult to separate, the purity is low, a large amount of organic solvent is used for stirring and washing or leaching and the like in the existing ODB-2 preparation process are overcome, and the purity of the obtained ODB-2 product reaches 99.8%. The method is simple and convenient to operate, the production cost is reduced, a new way is provided for industrial preparation of the high-purity thermosensitive dye ODB-2, and the economic benefit is remarkable.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical technology, specifically relating to a method for improving the purity of the thermosensitive dye ODB-2. Background Technology

[0002] 2-Phenylamino-3-methyl-6-dibutylaminofluorane (ODB-2) is an important thermosensitive dye widely used in the field of thermosensitive recording materials, especially in the production of thermal paper. It possesses advantages such as high sensitivity, good color development intensity, excellent thermal stability, strong light and heat resistance, high environmental friendliness and safety, good solubility, and processability. In terms of applications, the thermosensitive dye ODB-2 is mainly used in commercial invoice printing, electronic scale labels, vending machine receipts, and medical record paper.

[0003] Currently, the industrial synthesis method for ODB-2 dye involves a three-step reaction: concentrated sulfuric acid catalytic condensation, water washing and curing, and alkali-catalyzed ring closure. This synthesis process faces challenges such as numerous reaction sites and side reactions, often accompanied by sulfonation, ring opening, decomposition, and multi-site condensation, resulting in products with high impurities, low color grades, and poor thermal stability, leading to poor product quality. Therefore, improving the purity of the thermosensitive dye ODB-2 is extremely important.

[0004] .

[0005] Existing methods for purifying crude ODB-2 mainly involve large-volume organic solvent washing or rinsing (EP2289896, CN1854201A, CN101190920A, WO2000012513, CN108191883A, CN101323619 A, CN105838105A), resulting in high solvent consumption and low production efficiency. Furthermore, these methods are ineffective at purifying complex and difficult-to-treat impurities generated during ODB-2 synthesis, as well as compounds with properties (such as solubility) similar to the main product, making it difficult to obtain high-purity ODB-2 products and weakening the product's competitive advantage. Therefore, achieving efficient improvement in the purity of ODB-2 products is a current technical challenge in the synthesis of the thermosensitive dye ODB-2. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for improving the purity of the thermosensitive dye ODB-2.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for improving the purity of the thermosensitive dye ODB-2 includes the following steps: (1) Feeding: Add crude ODB-2 and solvent to the high-pressure reactor, evacuate and replace with nitrogen. The solvent is one of methanol, ethanol and isopropanol. (2) Heating: Turn on the stirring and raise the temperature of the system to 70-100°C; (3) Pressurization: Turn on the nitrogen pressurization pipeline to raise the pressure in the reactor to 0.8-10.2 MPa and stir for 1-2 hours; (4) Crystal precipitation: Control the cooling rate to 0.1°C / min-1°C / min, and after the system is cooled to 40-45 °C, release the pressure to atmospheric pressure and stir at a constant temperature for 2 hours; (5) Crystal growth: Reopen the nitrogen pressurization pipeline and raise the pressure in the reactor to 0.8-10.2 MPa. Under stirring, control the cooling rate to 0.1°C / min-0.5°C / min and lower the reactor temperature to 5-10°C. Stir at this final temperature for 1 hour and then release the reactor to atmospheric pressure. Filter and dry to obtain pure ODB-2.

[0008] Preferably, the mass of the solvent in step (1) is 1-2 times the mass of the crude ODB-2. In step (1), nitrogen is used for purging at least three times.

[0009] Preferably, the heating rate in step (2) is 1°C / min-5°C / min.

[0010] Preferably, the pressure in step (3) is 0.8-10.2 MPa; the stirring rate is 150-250 rpm.

[0011] Preferably, in step (4), the stirring rate is 60-120 rpm.

[0012] Preferably, in step (5), the stirring is continued during the cooling process, and the stirring rate is controlled at 100-150 rpm.

[0013] The beneficial effects of this invention are: The one or more technical solutions provided by this invention have the following advantages compared with the prior art: This invention develops a segmented controlled nitrogen-pressurized ODB-2 crystallization technology. Through five steps—feeding, heating, pressurization, crystal precipitation, and crystal growth—it achieves a high efficiency improvement in the purity of ODB-2 products. This technology effectively removes impurities from crude ODB-2 generated by sulfonation, ring-opening reactions, etc., overcoming the technical bottlenecks in existing ODB-2 preparation processes, such as the difficulty in separating complex impurities, low purity, and the need for extensive organic solvent washing or rinsing. The resulting ODB-2 product achieves a purity of 99.8%. This method is simple to operate, reduces production costs, and provides a new approach for the industrial preparation of high-purity thermosensitive dye ODB-2, resulting in significant economic benefits.

[0014] This invention provides a method suitable for purifying crude ODB-2 with a purity of 90% or higher, and can be used to process crude ODB-2 synthesized by various methods. When preparing the crude product, a lower-cost and easier-to-operate synthesis method can be chosen, and combined with the simple purification method of this invention, high-purity ODB-2 can be produced. Attached Figure Description

[0015] Figure 1 This is the HPLC chromatogram of the pure thermosensitive dye ODB-2 purified by the method of the present invention in Example 4. Detailed Implementation

[0016] The present invention provides the following specific embodiments to further describe the technical solution of the present invention, but the scope of protection of the present invention is not limited to these embodiments. All changes or equivalent substitutions that do not depart from the concept of the present invention are included within the scope of protection of the present invention.

[0017] The crude ODB-2 dye used in this method embodiment was prepared using a conventional method, as follows: 650 g of 100% concentrated sulfuric acid was cooled to 4°C, and 173.7 g of 4-dibutylketo acid was added in portions over 1 hour with stirring until fully dissolved. Then, 100 g of 2-methyl-4-methoxydiphenylamine was added in portions over 5 hours while maintaining the temperature at 4°C. After the addition was complete, the reaction mixture was allowed to react at room temperature for 11 hours. After the reaction was completed, the resulting reaction solution was added dropwise to 2800 mL of deionized water over 3 hours while maintaining the temperature at 15°C. After the addition was complete, the mixture was stirred for 0.5 hours, filtered, and the filter cake was washed twice with 100 g of deionized water (2 minutes each time). The resulting filter cake was then added to 1000 mL of toluene, stirred to disperse fully, and the pH of the system was adjusted to 8 with 5% sodium hydroxide solution. The system was then slowly heated to 90°C. After the system became clear, it was allowed to stand and separate into layers. 10% sodium hydroxide solution was added to the toluene phase at 90℃ to adjust the pH of the system to 13. The system was then gradually heated to reflux and reacted for 2 h. After standing and separating the layers, the toluene phase was washed with 250 mL of deionized water at 85℃. The lower aqueous phase was separated again, and the toluene was recovered by vacuum distillation. 200 mL of hot water was added, and the toluene was distilled off. The mixture was cooled to 25℃, filtered, and washed twice with 300 mL of water to obtain crude ODB-2 (purity 96%).

[0018] Example 1: A method for improving the purity of the thermosensitive dye ODB-2 includes the following steps: (a) Feeding: At room temperature, add crude ODB-2 (1000g) and ethanol (1000g) to the high-pressure reactor, evacuate and replace with nitrogen three times.

[0019] (b) Heating: Turn on the stirrer and control the heating rate to 5°C / min to raise the system to 100°C.

[0020] (c) Pressurization: Turn on the nitrogen pressurization pipeline to increase the pressure in the reactor to 7±0.2MPa and stir at 150 rpm for 1 hour.

[0021] (d) Crystal precipitation: After cooling the system to 40-45°C by controlling the cooling rate at 1°C / min, release the pressure to atmospheric pressure and stir at a constant temperature of 60 rpm for 2 hours.

[0022] (e) Crystal growth: Reopen the nitrogen pressurization line and slowly increase the pressure inside the reactor to 7±0.2 MPa. Control the stirring speed (100 rpm) and cooling rate (0.1°C / min) to slowly lower the reactor temperature to 5-10°C. After stirring at this final temperature for 1 hour, release the reactor to atmospheric pressure, filter, and dry to obtain the ODB-2 product (965 g of white solid, yield 96.5%, purity 99.811%).

[0023] Example 2: A method for improving the purity of the thermosensitive dye ODB-2 includes the following steps: (a) Feeding: At room temperature, add crude ODB-2 (1000g) and methanol (1000g) to the high-pressure reactor, evacuate the reactor and replace it with nitrogen three times.

[0024] (b) Heating: Turn on the stirrer and control the heating rate at 3.5°C / min to raise the system to 70°C.

[0025] (c) Pressurization: Turn on the nitrogen pressurization pipeline to increase the pressure in the reactor to 10±0.2MPa and stir at 250 rpm for 1.5h.

[0026] (d) Crystal precipitation: After cooling the system to 40-45°C by controlling the cooling rate at 1°C / min, release the pressure to atmospheric pressure and stir at a constant temperature of 120 rpm for 2 hours.

[0027] (e) Crystal growth: Reopen the nitrogen pressurization line and slowly increase the pressure inside the reactor to 10±0.2 MPa. Control the stirring speed (150 rpm) and cooling rate (0.5°C / min) to slowly lower the reactor temperature to 5-10°C. After stirring at this final temperature for 1 hour, release the reactor to atmospheric pressure, filter, and dry to obtain the ODB-2 product (965 g of white solid, yield 97%, purity 99.809%).

[0028] Example 3: A method for improving the purity of the thermosensitive dye ODB-2 includes the following steps: (a) Feeding: At room temperature, add crude ODB-2 (1000g) and isopropanol (1500g) to the high-pressure reactor, evacuate the reactor and replace it with nitrogen three times.

[0029] (b) Heating: Turn on the stirrer and control the heating rate to 2.2°C / min to raise the system to 90°C.

[0030] (c) Pressurization: Turn on the nitrogen pressurization pipeline to increase the pressure in the reactor to 1±0.2MPa and stir at 180 rpm for 2 hours.

[0031] (d) Crystal precipitation: After cooling the system to 40-45°C by controlling the cooling rate at 0.4°C / min, release the pressure to atmospheric pressure and stir at a constant temperature of 100 rpm for 2 h.

[0032] (e) Crystal growth: The nitrogen pressurization line was restarted, and the pressure inside the reactor was slowly increased to 1±0.2 MPa. The stirring speed (120 rpm) and cooling rate (0.25°C / min) were controlled to slowly lower the reactor temperature to 5-10°C. After stirring at this final temperature for 1 hour, the reactor was released to atmospheric pressure, filtered, and dried to obtain the ODB-2 product (968 g of white solid, yield 96.8%, purity 99.817%).

[0033] Example 4: A method for improving the purity of the thermosensitive dye ODB-2 includes the following steps: (a) Feeding: At room temperature, add crude ODB-2 (1000g) and ethanol (2000g) to the high-pressure reactor, evacuate and replace with nitrogen three times.

[0034] (b) Heating: Turn on the stirrer and control the heating rate to 1°C / min to raise the system to 85°C.

[0035] (c) Pressurization: Turn on the nitrogen pressurization pipeline to increase the pressure in the reactor to 4±0.2MPa and stir at 210 rpm for 2 hours.

[0036] (d) Crystal precipitation: After cooling the system to 40-45°C by controlling the cooling rate at 0.1°C / min, release the pressure to atmospheric pressure and stir at a constant temperature of 65 rpm for 2 hours.

[0037] (e) Crystal growth: The nitrogen pressurization line was restarted, and the pressure inside the reactor was slowly increased to 4±0.2 MPa. The stirring speed (50 rpm) and cooling rate (0.35°C / min) were controlled to slowly lower the reactor temperature to 5-10°C. After stirring at this final temperature for 1 h, the reactor was released to atmospheric pressure, filtered, and dried to obtain the ODB-2 product (968 g of white solid, yield 97.2%, purity 99.824%).

[0038] The HPLC chromatogram of the purified thermosensitive dye ODB-2 is shown below. Figure 1 As shown in the figure, the retention time of 7.451 min is for the thermosensitive dye ODB-2.

[0039] Comparative Example 1 A method for improving the purity of the thermosensitive dye ODB-2, compared with Example 4, involves step (3) without nitrogen gas, and after heating to 85°C, the pressure inside the reactor is 0.131 MPa. The yield of pure ODB-2 is 97.5%, and the purity is 96.81%.

[0040] Comparative Example 2 A method for improving the purity of the thermosensitive dye ODB-2, compared with Example 4, involves a pressure of 0.7 MPa in step (3). The yield of pure ODB-2 is 97.1%, and the purity is 97.46%.

Claims

1. A method for improving the purity of the thermosensitive dye ODB-2, characterized in that, Includes the following steps: (1) Feeding: Add crude ODB-2 and solvent to the high-pressure reactor, evacuate and replace with nitrogen. The solvent is one of methanol, ethanol and isopropanol. (2) Heating: Turn on the stirring and raise the temperature of the system to 70-100°C; (3) Pressurization: Turn on the nitrogen pressurization pipeline to raise the pressure in the reactor to 0.8-10.2 MPa and stir for 1-2 hours; (4) Crystal precipitation: Control the cooling rate to 0.1°C / min-1°C / min, and after the system is cooled to 40-45°C, release the pressure to atmospheric pressure and stir at a constant temperature for 2 hours; (5) Crystal growth: Reopen the nitrogen pressurization pipeline and raise the pressure in the reactor to 0.8-10.2 MPa. Under stirring, control the cooling rate to 0.1°C / min-0.5°C / min and lower the reactor temperature to 5-10°C. Stir at this final temperature for 1 hour and then release the reactor to atmospheric pressure. Filter and dry to obtain pure ODB-2.

2. The method for improving the purity of the thermosensitive dye ODB-2 according to claim 1, characterized in that, The mass of the solvent in step (1) is 1-2 times the mass of the crude ODB-2.

3. The method for improving the purity of the thermosensitive dye ODB-2 according to claim 1, characterized in that, In step (2), the heating rate is 1°C / min-5°C / min.

4. The method for improving the purity of the thermosensitive dye ODB-2 according to claim 1, characterized in that, The pressure in step (3) is 2.8-5.2 MPa; the stirring rate is 150-250 rpm.

5. The method for improving the purity of the thermosensitive dye ODB-2 according to claim 1, characterized in that, In step (4), the stirring rate is 60-120 rpm.

6. The method for improving the purity of the thermosensitive dye ODB-2 according to claim 1, characterized in that, In step (5), the stirring rate is 100-150 rpm.

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