Preparation device and method of m-nitrobenzonitrile

Abstract

The invention belongs to the technical field of organic synthesis, and particularly relates to a preparation device and method of m-nitrobenzonitrile. Comprising the following steps: step S10: acylating chlorination reaction: taking m-nitrobenzoic acid as a raw material, and reacting the m-nitrobenzoic acid with thionyl chloride in a preparation device of a constant temperature device under the catalysis of a nitrogen-containing organic matter to generate m-nitrobenzoyl chloride; step S20, amidation reaction: enabling the m-nitrobenzoyl chloride obtained in the step S10 to react with ammonia gas to generate m-nitrobenzamide; and step S30: dehydration reaction: dehydrating and filtering the m-nitrobenzamide obtained in the step S20 and thionyl chloride in a negative pressure filtering device in the presence of a nitrogen-containing organic matter to obtain the m-nitrobenzonitrile. According to the scheme, the problems of long preparation time and low yield of the m-nitrobenzonitrile are solved.

Description

An apparatus and method for preparing m-nitrobenzonitrile Technical Field

[0001] This invention belongs to the field of organic synthesis technology, and specifically relates to an apparatus and method for preparing m-nitrobenzonitrile. Background Technology

[0002] m-Nitrobenzonitrile, also known as 3-nitrobenzene, is an organic compound primarily used as a pharmaceutical and pesticide intermediate. It can also be used as an organic synthesis intermediate in the production of pharmaceutical chemicals such as imidazolidinyl hydrochloride and imidazolidinyl dipropionate. However, its high price limits its applications.

[0003] There are few reports on the preparation of m-nitrobenzene in the prior art. Patent application CN114456087A discloses a method for preparing m-nitrobenzene using a microchannel reactor, which includes passing benzonitrile and mixed acid separately into the microchannel reactor for nitration reaction. After the reaction, post-processing is performed to obtain m-nitrobenzene. However, the raw materials for this process are expensive, and the investment in the microchannel reactor equipment is substantial.

[0004] Patent application CN116283659A discloses a preparation method in a microchannel reactor, which uses m-nitrobenzoic acid as a raw material to undergo acylation, amidation, and dehydration reactions in a microchannel reactor to obtain m-nitrobenzonitrile. This method can shorten the reaction time and improve the safety and yield of the reactants; however, it requires significant equipment investment and is currently not suitable for large-scale production in general factories.

[0005] Therefore, there is a need to develop a method for preparing m-nitrobenzene that has a short preparation time, high yield, and low raw material price, making it economical and suitable for large-scale production in existing batch reactors in ordinary chemical plants. Summary of the Invention

[0006] This solution provides a method for preparing m-nitrobenzonitrile, which addresses the problems of long preparation time, low yield, and unsuitability for large-scale production in existing batch reactors in ordinary chemical plants.

[0007] This solution provides a method for preparing m-nitrobenzene, comprising the following steps: Step S10: Acyl chloride reaction: using m-nitrobenzeneic acid as raw material, reacting with thionyl chloride in a preparation device under the catalysis of nitrogen-containing organic matter in a constant temperature device to generate m-nitrobenzeneyl chloride; Step S20: Amide reaction: reacting the m-nitrobenzeneyl chloride obtained in step S10 with ammonia to generate m-nitrobenzeneamide; Step S30: Dehydration reaction: dehydrating and filtering the m-nitrobenzeneamide obtained in step S20 with thionyl chloride in the presence of nitrogen-containing organic matter in a negative pressure filtration device to obtain m-nitrobenzene.

[0008] The beneficial effect of this scheme is that when nitrogen-containing organic compounds are used for catalysis, the rate of thionyl chloride reaction to generate m-nitrobenzoyl chloride is accelerated, the reaction time is shortened, and thus the preparation time of nitrobenzene is reduced.

[0009] Meanwhile, since steps S10 and S20 of this scheme can be adapted to existing reactors, costs are saved.

[0010] Furthermore, the nitrogen-containing organic compound mentioned in step S10 is N,N-dimethylformamide, and its amount is 1-2% of m-nitrobenzoic acid. When the amount of nitrogen-containing organic compound is 1-2% of m-nitrobenzoic acid, the yield of m-nitrobenzoyl chloride can be guaranteed while shortening the reaction time.

[0011] Furthermore, in step S10, the reaction temperature is 80-85℃, and the reaction time is 6-24 hours. Appropriate heating can accelerate the collision frequency between molecules, thereby speeding up the reaction rate; while choosing the relatively mild temperature range of 80-85℃ is to avoid the formation of unnecessary byproducts due to excessively high temperatures. Within this temperature range, the reaction rate is moderate, ensuring the effective progress of the reaction without causing side reactions due to excessively high temperatures. Providing a longer reaction time (6-24 hours) ensures that as much of the raw material as possible is converted into the desired product, increasing the overall yield.

[0012] Furthermore, in step S20, the amount of ammonia introduced is such that the pH of the reaction system reaches 10, the reaction temperature is 30-60°C, and the reaction time is 2-4 hours. Appropriate alkaline conditions help suppress side reactions, such as preventing the hydrolysis of acyl chloride into acid or the formation of other unwanted byproducts. By adjusting the pH of the reaction system to 10 and conducting the reaction under mild conditions of 30-60°C for 2-4 hours, the amidation reaction between acyl chloride and ammonia can be effectively promoted, reducing the formation of byproducts and improving the yield and purity of the target product—m-nitrobenzamide.

[0013] Furthermore, in step S30, the solvent for the dehydration reaction is dichloromethane or isopropanol, the reaction temperature is 40-45℃, and the reaction time is 2-6 hours. By selecting a suitable solvent (dichloromethane or isopropanol) and carrying out the reaction under mild conditions of 40-45℃ for 2-6 hours, the conversion of m-nitrobenzoamide to m-nitrobenzonitrile can be effectively promoted, the formation of by-products can be reduced, and the yield and purity of the target product can be improved.

[0014] Furthermore, after the dehydration reaction in steps S20 and S30, the following post-processing steps, connected sequentially from left to right, are included: vacuum concentration, solvent crystallization, washing, and vacuum drying. Through this series of post-processing steps, the purity and yield of m-nitrobenzoamide and m-nitrobenzonitrile can be significantly improved. Each step is designed for a different purpose, from reducing solvent volume to refined crystallization, and finally to drying, all working together to ensure the high quality of the final product.

[0015] Furthermore, both the acyl chloride reaction and the dehydration reaction are carried out under nitrogen protection.

[0016] An apparatus for preparing m-nitrobenzonitrile includes: a preparation device for preparing a reaction solution; and a negative pressure filtration device for dehydrating m-nitrobenzoamide and m-nitrobenzonitrile. The negative pressure filtration device includes a cylinder, a conveyor belt, a motor, a collection box, and a vacuum pump. The cylinder is provided with a feed pipe and a vacuum pipe. The conveyor belt, motor, and collection box are disposed inside the cylinder. The conveyor belt is made of filter cloth. The vacuum pump is connected to the cylinder through a vacuum pipe. The shaft of the motor is fixedly connected to the rollers of the conveyor belt. The conveyor belt cooperates with the feed pipe and the collection box.

[0017] The preparation device is used to prepare reaction solutions, ensuring that raw materials (such as m-nitrobenzoic acid, thionyl chloride, ammonia, etc.) are mixed uniformly under appropriate conditions. By precisely controlling the temperature, stirring speed, and other process parameters, it ensures that the reactants are fully dissolved or dispersed, providing ideal starting conditions for subsequent reactions.

[0018] The negative pressure filtration device includes a cylinder, a motor, a collection box, and a vacuum pump. The cylinder, containing the feed pipe and vacuum pipe, serves as the outer shell of the entire system, providing a closed environment to maintain negative pressure. A motor-driven conveyor belt transports material from the feed inlet to the collection box. The motor provides power for the continuous operation of the conveyor belt, which uses filter cloth as its belt material. The collection box receives the processed solid product. The vacuum pump, connected to the cylinder via a vacuum pipe, removes gas from the system, creating a negative pressure environment to promote solvent evaporation and material drying.

[0019] The principle of this method is as follows: a slurry of m-nitrobenzoamide or m-nitrobenzonitrile enters the cylinder through the feed pipe by gravity. The material is placed on a conveyor belt and moves slowly under the drive of a motor. A vacuum pump is activated, drawing air out of the cylinder to create a low-pressure environment, which forces the solvent through the filter plate and is then removed by the vacuum pump, thus achieving preliminary drying of the material. After dehydration, the solid material moves to the end of the conveyor belt and falls into a collection box, completing the entire process.

[0020] The beneficial effects of this solution are as follows: 1. Improved production efficiency: The use of conveyor belts and automatic feeding systems enables continuous production, significantly increasing efficiency. 2. High degree of automation: Reduces the need for manual operation, lowering labor intensity and the possibility of human error. 3. Precise control of the dehydration process by adjusting parameters such as vacuum and temperature, ensuring high product purity and consistency. 4. Conducting the dehydration reaction under negative pressure helps suppress side reactions, further improving the quality of the target product.

[0021] Furthermore, it also includes an adjusting cylinder and a rotating plate. The conveyor belt and motor are rotatably connected to the cylinder body via the rotating plate. The adjusting cylinder is disposed inside the cylinder body and includes an adjusting cylinder body, an adjusting piston, and an adjusting rod. The adjusting cylinder is fixedly connected to the cylinder body, the adjusting piston is slidably sealed to the adjusting cylinder body, and one end of the adjusting rod is hinged to the adjusting piston, while the other end is hinged to the rotating plate. When vacuum filtration begins, the operator turns on the vacuum pump, creating a negative pressure inside the cylinder. This negative pressure causes the adjusting cylinder body to expand, causing the adjusting piston to move downwards. The downward movement of the adjusting piston drives the adjusting rod downwards, causing the rotating plate to rotate. The rotation of the rotating plate causes the entire conveyor belt to rotate, tilting the conveyor belt so that the conveyor belt at the collection box is at a higher position. Thus, when the conveyor belt starts and moves the material, the liquid will naturally fall off the conveyor belt under the influence of gravity, preventing the liquid from flowing into the collection box.

[0022] The filter cloth covering the conveyor belt effectively intercepts solid particles, while liquid solvents can freely pass through the pores. When the conveyor belt tilts, the liquid flows down the filter cloth surface and drips under gravity, while the solid particles remain attached to the conveyor belt surface due to the filter cloth's obstruction and inter-particle friction until they are peeled off by the scraper. The conveyor belt speed is controlled at 0.1-0.5 m / min to ensure that the liquid has sufficient time to detach from the solid layer.

[0023] After vacuum filtration is completed, the cylinder will return to normal pressure. At this time, the adjusting cylinder will cause the adjusting piston to move back, which in turn moves the adjusting rod back, so that the conveyor belt away from the collection box is in a high position. This allows the filter cake remaining on the conveyor belt to be sent into the collection box by gravity.

[0024] This device changes the angle of the conveyor belt by starting and stopping the vacuum pump, ensuring that liquid on the conveyor belt does not flow into the collection tank during vacuum filtration. When the work is complete, the filter cake remaining on the conveyor belt is sent into the collection tank.

[0025] Furthermore, it also includes a rinsing mechanism, which comprises a hydraulic cylinder, a rack, a half gear, a return spring, and a nozzle. The half gear is fixedly connected to the shaft of the motor, and the rack meshes with the half gear. The hydraulic cylinder includes a hydraulic cylinder body and a hydraulic piston. The hydraulic cylinder body is fixedly connected to the cylinder body, and the hydraulic piston is slidably sealed to the hydraulic cylinder body. The rack is fixedly connected to the hydraulic piston. One end of the return spring is fixedly connected to the piston, and the other end is fixedly connected to the hydraulic cylinder body. The hydraulic cylinder body is provided with an inlet pipe and an outlet pipe. The nozzle communicates with the outlet pipe and cooperates with the conveyor belt. The inlet pipe is used to deliver clean water into the hydraulic cylinder.

[0026] When the motor starts the conveyor belt, it also drives the half-gear to rotate. As the half-gear rotates, it meshes with the rack, causing the rack to rise. This rise in the rack drives the hydraulic piston upward, drawing clean water from the inlet pipe into the hydraulic cylinder. When the half-gear rotates to its toothless position, the rack disengages from the half-gear. At this point, the return spring moves the rack and hydraulic piston back down, squeezing the clean water out of the hydraulic cylinder. The water then flows from the outlet pipe to the nozzle, which is aimed at the filter cloth below the conveyor belt. This rinses the filter cloth with clean water, ensuring its permeability and preventing clogging, which would reduce the effectiveness of the negative pressure drying process.

[0027] Furthermore, it also includes a scraper, one end of which cooperates with the conveyor belt, and the other end is fixedly connected to the collection box. The scraper can remove the filter cake adhering to the filter cloth on the conveyor belt and make it fall into the collection box. Attached Figure Description

[0028] Figure 1 is a structural diagram of an apparatus for preparing m-nitrobenzonitrile, Figure 2 is a state diagram of the apparatus for preparing m-nitrobenzonitrile under negative pressure filtration, and Figure 3 is a state diagram of the apparatus for preparing m-nitrobenzonitrile at the end of the preparation process.

[0029] The reference numerals in the accompanying drawings include: 1. Temperature control device; 2. Preparation device; 3. Vacuum pump; 4. Negative pressure filtration device; 5. Feed pipe; 6. Liquid inlet pipe; 7. Vacuum pipe; 8. Adjusting piston; 9. Adjusting cylinder; 10. Adjusting rod; 11. Rotating plate; 12. Nozzle; 13. Liquid outlet pipe; 14. Hydraulic piston; 15. Return spring; 16. Hydraulic cylinder; 17. Rack; 18. Rotating shaft; 19. Half gear; 20. Cylinder; 21. Scraper; 22. Collection box. Detailed Implementation

[0030] Example 1, as shown in Figure 1, provides an apparatus for preparing m-nitrobenzonitrile, including a constant temperature device 1, a preparation device 2, a negative pressure filtration device 4, a filtrate recovery device, and a cleaning device. The constant temperature device 1 is used for temperature control of the acylation and amidation reactions, and has a built-in stirring system to ensure uniform mixing of the reactants.

[0031] The preparation device 2 and the constant temperature device 1 adopt an integrated constant temperature reaction design. The preparation device 2 consists of a double-layered glass reactor, and the constant temperature device 1 consists of an external circulating water bath system. The reactor is equipped with: a four-bladed folding impeller (speed adjustable from 50-300 rpm); a high-precision PT100 temperature sensor (±0.5℃ control accuracy); and a dropping device (500ml constant pressure dropping funnel).

[0032] The filtrate recovery device is used to recover the filtrate separated by the negative pressure filtration device 4, and the filtrate recovery device is connected to the bottom of the cylinder 20.

[0033] As shown in Figure 2, the negative pressure filtration device 4 includes a cylinder 20, a conveyor belt, a vacuum pump 3, an adjustment mechanism, and a rinsing mechanism. The cylinder 20 is equipped with a feed pipe 5, a vacuum pipe 7, and a collection box 22. The cylinder 20 is made of 304 stainless steel. The conveyor belt is made of polytetrafluoroethylene (PTFE) filter cloth, with a width of 400 mm and a pore size of 20 μm. It is driven by a motor, and both the conveyor belt and the motor are fixed on a rotating plate 11. The conveyor belt works in conjunction with the feed pipe 5 to transport materials. The vacuum pump 3 draws gas from inside the cylinder 20 through the vacuum pipe 7, creating a negative pressure environment to promote solvent evaporation. The vacuum pump 3 is an explosion-proof vacuum pump with a pumping speed of 30 m³ / h and an ultimate vacuum of 0.08 MPa.

[0034] The adjustment mechanism includes an adjustment cylinder and a rotating plate 11. The conveyor belt and motor are rotatably connected to the cylinder 20 via the rotating plate 11. The rotating plate 11 is equipped with a rotating shaft 18, and the rotation point is located at the left motor. This rotation prevents the half gear 19 from shifting, thus avoiding poor meshing. It also prevents the scraper 21 from becoming mismatched with the conveyor belt.

[0035] The regulating cylinder is installed inside the cylinder 20. The regulating cylinder includes a regulating cylinder body 9, a regulating piston 8 and a regulating rod 10. The regulating cylinder is fixedly connected to the cylinder 20. The regulating piston 8 is slidably and sealed to the regulating cylinder body 9. One end of the regulating rod 10 is hinged to the regulating piston 8 and the other end is hinged to the rotating plate 11.

[0036] During vacuum startup, the regulating cylinder drives the conveyor belt to tilt via the piston and regulating rod 10, causing the left side of the conveyor belt to be in a higher position and the right side to be lowered, preventing liquid from flowing into the collection box 22. At atmospheric pressure, it resets, causing the right side to tilt upwards and the left side to be in a lower position, allowing the filter cake to fall into the collection box 22.

[0037] The rinsing mechanism includes a hydraulic cylinder, a rack 17, a half gear 19, a return spring, and a nozzle 12. The half gear 19 is fixedly connected to the shaft of the motor, and the rack 17 meshes with the half gear 19. The hydraulic cylinder includes a hydraulic cylinder body 16 and a hydraulic piston 14. The hydraulic cylinder body 16 is fixedly connected to the cylinder 20, and the hydraulic piston 14 is slidably sealed to the hydraulic cylinder body 16. The rack 17 is fixedly connected to the hydraulic piston 14. One end of the return spring is fixedly connected to the piston, and the other end is fixedly connected to the hydraulic cylinder body 16. The hydraulic cylinder body 16 is provided with an inlet pipe 6 and an outlet pipe 13. The nozzle 12 is connected to the outlet pipe 13 and cooperates with the conveyor belt. The inlet pipe 6 is located in the lower half of the cylinder 20 and is used to send clean water into the hydraulic cylinder.

[0038] It also includes a scraper 21, one end of which is engaged with the conveyor belt, and the other end is fixedly connected to the collection box 22. The scraper 21 can remove the filter cake adhering to the filter cloth on the conveyor belt and make it fall into the collection box 22.

[0039] This method provides a procedure for preparing m-nitrobenzene. The preparation apparatus 2 is placed within a constant temperature apparatus 1. Under nitrogen protection, 150 g (0.90 mol) of m-nitrobenzeneic acid and 800 g of toluene are added to a 2000 ml three-necked flask (preparation apparatus 2). Stirring is initiated for 5-10 minutes until the system is completely dissolved. 1.2 g (0.008 w / w) of N,N-dimethylformamide (DMF) is added as a catalyst, and the temperature is raised to 80-85°C with thorough stirring. 120.0 g (1.01 mol) of thionyl chloride is added dropwise while maintaining the temperature at 80-85°C. The reaction is continued at 80-85°C for 17 hours. After sampling and confirming the reaction is satisfactory, the temperature is lowered to 20-30°C, and dried ammonia gas is introduced. The reaction is exothermic. When introducing ammonia gas, control the temperature and slowly raise it to 60℃. Continue introducing ammonia gas until the solution reaches an alkaline pH of 10. Maintain the temperature between 30 and 60℃ and stir the reaction for 2 hours. After the sample passes the control test, add 900g of purified water while maintaining the temperature at ≤15℃. Stir and quench for 1 hour, then cool to 0-5℃ and stir to induce crystallization for 2 hours.

[0040] As shown in Figures 2 and 3: Filtration and drying are carried out in the negative pressure filtration device 4. The material enters the cylinder 20 through the feed pipe 5 by gravity or a pump. The conveyor belt runs under negative pressure. The solvent is drawn away by the vacuum pump 3 through the filter cloth. Some liquid flows to the bottom of the cylinder 20 due to the inclination of the conveyor belt. The solid material is temporarily stored on the conveyor belt. As the conveyor belt moves, the filter cake will come to the scraper 21. The scraper 21 will scrape off the filter cake, and then the filter cake will fall into the collection box 22.

[0041] During conveyor belt transport, the motor drives the half gear 19 to rotate. When the half gear 19 rotates, it meshes with the rack 17, causing the rack 17 to rise. The rising rack 17 then drives the hydraulic piston 14 to rise, drawing clean water from the inlet pipe 6 into the hydraulic cylinder. When the half gear 19 rotates to the toothless section, the rack 17 disengages from the half gear 19. At this point, the return spring 15 drives the rack 17 and hydraulic piston 14 to return to their original positions and move downwards, squeezing the clean water out of the hydraulic cylinder 16. The water then flows from the outlet pipe 13 to the nozzle 12, which is positioned above the filter cloth below the conveyor belt, rinsing the filter cloth. After filtration, the cylinder 20 returns to normal pressure, and the adjusting cylinder resets, causing the right side of the conveyor belt to tilt upwards. The remaining filter cake on the conveyor belt slides down into the collection box 22 due to gravity.

[0042] After the filter cake is collected in the collection box, the negative pressure filtration device 4 is turned off. The filter cake is then removed from the collection box and washed with purified water from the washing device. The filter cake is collected and dried under reduced pressure for 16 hours at a controlled temperature of 45~55℃ and a pressure of -0.09~-0.095MPa. After the moisture content is found to be within acceptable limits, 138.5 g of yellow powder intermediate A, m-nitrobenzamide, is discharged, with a yield of 93% and a purity of 99%.

[0043] The reaction route for compound A, m-nitrobenzamide, is as follows:

[0044] Under nitrogen protection, 20.0 g (0.12 mol) of the intermediate m-nitrobenzamide and 200.0 g of dichloromethane were added to preparation apparatus 2 (250 ml three-necked reaction flask). Stirring was started for 5-10 minutes, resulting in a solid-liquid suspension. Then, 13.2 g of N,N-dimethylformamide was added. The temperature was raised to 40-45°C, and the mixture was stirred thoroughly. The dehydration reaction was carried out in a constant-temperature apparatus 1 equipped with a reflux condenser. Initially, N,N-dimethylformamide reacted with thionyl chloride, releasing a large amount of heat (exothermic effect), causing the system temperature to naturally rise to 40-45°C and maintain a self-reflux state. The volatilized dichloromethane vapor was liquefied by the condenser and returned to the reaction system, ensuring a stable total solvent volume.

[0045] Add 28.6.0 g (0.24 mol) of thionyl chloride dropwise at a controlled temperature of 40-45℃. React at 40-45℃ for 6 hours until dissolved. After passing HPLC control, cool to 35-45℃ and concentrate under reduced pressure (-0.09 to -0.095 MPa) until dry. Add 40.0 g of isopropanol, heat to 75-80℃, and stir until dissolved. Slowly cool to -10-0℃, stir to crystallize for 4 hours, filter using a negative pressure filter, and dry under vacuum. Wash the filter cake with isopropanol pre-frozen to 0℃ in a washing device. Collect the filter cake and dry under reduced pressure (-0.09 to -0.095 MPa) at a controlled temperature of 40-50℃ for 16 hours. After passing rapid drying test, discharge 11.5 g of yellow powder product, yield approximately 65%, purity 99.7%, and overall yield of 61% for both steps.

[0046] The reaction route for m-nitrobenzene is as follows:

[0047] The preparation of m-nitrobenzoyl chloride from m-nitrobenzoic acid and thionyl chloride typically requires a reaction time of around 24 hours. The applicant discovered that adding a certain amount of N,N-dimethylformamide as a nitrogen-containing organic compound during the reaction can promote the reaction and shorten the reaction time. This is mainly due to the nucleophilicity of the lone pair electrons on the oxygen atom of N,N-dimethylformamide and the electrophilicity of the carbonyl carbon of thionyl chloride as driving forces for a series of nucleophilic addition and leaving reactions.

[0048] Because N,N-dimethylformamide is a nitrogen-containing organic compound, the electron-induced activity of the nitrogen atom in N,N-dimethylformamide can not only activate the carboxyl group on m-nitrobenzoic acid, lowering the activation energy of the reaction, but also promote the chlorine atom on thionyl chloride to easily attack the hydroxyl group on m-nitrobenzoic acid, resulting in nucleophilic substitution, thereby accelerating the reaction and facilitating the formation of m-nitrobenzoyl chloride. However, its addition should not be excessive; too much will react with the starting material m-nitrobenzoic acid, affecting the yield of the intermediate nitrobenzoyl chloride. When the amount of nitrogen-containing organic compound is 1-2% of that of m-nitrobenzoic acid, the reaction time can be shortened while ensuring the yield of m-nitrobenzoyl chloride.

[0049] The beneficial effects of this scheme are as follows: 1. When the amount of nitrogen-containing organic matter is 1-2% of that of m-nitrobenzoic acid, the reaction time can be shortened while ensuring the yield of m-nitrobenzoyl chloride. 2. Improved production efficiency: The use of a conveyor belt and automatic feeding system enables continuous operation of the dehydration section, significantly improving production efficiency. 3. This mechanism changes the angle of the conveyor belt by starting and stopping the vacuum pump 3, ensuring that liquid on the conveyor belt does not flow into the collection box 22 during negative pressure filtration. Upon completion, the filter cake remaining on the conveyor belt is sent into the collection box 22. 4. The filter cloth is rinsed with cleaning water from the cleaning mechanism. This ensures the permeability of the filter cloth, prevents clogging, and avoids reducing the negative pressure drying effect.

[0050] In Example 2, under nitrogen protection, 600 g (3.59 mol) of m-nitrobenzoic acid and 6000.0 g of toluene were added to preparation apparatus 2 (10000 ml three-necked reaction flask). Stirring was started for 5-10 minutes until the system was completely dissolved. 4.8 g (0.008 w / w) of N,N-dimethylformamide was added, and the temperature was raised to 80-85°C with thorough stirring. 480.0 g (4.03 mol) of thionyl chloride was added dropwise while maintaining the temperature at 80-85°C. The reaction was maintained at 80-85°C for 6-24 hours. After sampling and confirming the reaction was satisfactory, the temperature was lowered to 20-30°C, and dried ammonia gas was introduced. The reaction was exothermic. While introducing ammonia gas, the temperature was controlled and slowly increased to 60°C. Ammonia gas was introduced until the solution reached an alkaline pH of 10. The reaction was then maintained at 30-60°C (45°C recommended) with stirring for 2-4 hours. After sampling and controlling the temperature to ≤15℃, add 3600g of purified water. Stir and quench for 1 hour, then cool to 0-5℃ and stir at 0-5℃ for 2-4 hours to induce crystallization. Filter, dry under vacuum, and wash the filter cake with purified water. Collect the filter cake and dry it under reduced pressure in a negative pressure filtration device 4 at 45~55℃ and -0.09~-0.095MPa for 16~24 hours. After sampling and testing for moisture content, discharge to obtain 511.0 g of yellow powder intermediate A, with a yield of 86% and a purity of 99%.

[0051] Under nitrogen protection, add 100.0 g (0.60 mol) of intermediate m-nitrobenzamide and 600.0 g of dichloromethane to preparation apparatus 2 (1000 ml three-necked reaction flask). Stir for 5-10 minutes until a solid-liquid suspension is formed. Add 44.0 g of N,N-dimethylformamide. Heat to 40-45℃ and stir thoroughly. Maintain the temperature at 40-45℃ and add 107.0 g (0.90 mol) of thionyl chloride dropwise. React at 40-45℃ for 2-6 hours until dissolved. After passing HPLC control, cool to 35-45℃ and concentrate under reduced pressure (-0.09 to -0.095 MPa) to dryness. Add 400.0 g of dichloromethane and stir until homogeneous. After one distillation, add 300.0 g of isopropanol and heat to 75-80℃, stirring until dissolved. Slowly cool to -10 to 0℃, stir and crystallize for 4-6 hours, then filter through a negative pressure filter device 4 and dry. The filter cake is washed with isopropanol pre-frozen to 0℃. Collect the filter cake, control the temperature at 40-50℃, and dry under reduced pressure (-0.09 to -0.095 MPa) for 16-24 hours. After sampling and testing for rapid drying, 73.2 g of a yellow powder product is obtained, with a yield of approximately 81% and a purity of 99.1%. The overall yield of the two steps is 70%.

[0052] The above are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing m-nitrobenzonitrile, characterized in that, Includes the following steps: Step S10: Acyl chloride reaction: Using m-nitrobenzoic acid as raw material, in the preparation device (2) of the constant temperature device (1), it reacts with thionyl chloride under the catalysis of nitrogen-containing organic matter to generate m-nitrobenzoyl chloride. The solvent of the acyl chloride reaction is toluene. Step S20: Amide reaction: The m-nitrobenzoyl chloride obtained in step S10 is reacted with ammonia to generate m-nitrobenzoamide. Step S30: Dehydration reaction: The m-nitrobenzoamide obtained in step S20 is dehydrated and filtered with thionyl chloride in the presence of nitrogen-containing organic matter in the negative pressure filtration device (4) to obtain m-nitrobenzonitrile.

2. The preparation method according to claim 1, characterized in that, The nitrogen-containing organic compound mentioned in step S10 is N,N-dimethylformamide, and its amount of substance is 1-2% of that of m-nitrobenzoic acid.

3. The preparation method according to claim 1, characterized in that, In step S10, the reaction temperature is 80-85℃ and the reaction time is 6-24 hours.

4. The preparation method according to claim 1, characterized in that, In step S20, the amount of ammonia introduced is such that the pH of the reaction system reaches 10, the reaction temperature is 30-60℃, and the reaction time is 2-4 hours.

5. The preparation method according to claim 1, characterized in that, The solvent for the dehydration reaction in step S30 is dichloromethane or isopropanol, the reaction temperature is 40-45℃, and the reaction time is 2-6 hours.

6. The preparation method according to claim 1, characterized in that, After the dehydration reaction in steps S20 and S30, the following post-processing steps are connected in sequence from left to right: vacuum concentration, dissolution and crystallization, washing and vacuum drying.

7. The preparation method according to claim 1, characterized in that, Both the acyl chloride reaction and the dehydration reaction were carried out under nitrogen protection.

8. An apparatus for preparing m-nitrobenzonitrile, using the method for preparing m-nitrobenzonitrile as described in claim 1, comprising: Preparation apparatus (2): used for preparing reaction solutions; Thermostat (1): used for temperature control of acyl chloride and amidation reactions; characterized in that it further includes: The negative pressure filtration device (4) is used for dehydration of m-nitrobenzoamide and m-nitrobenzonitrile. The negative pressure filtration device (4) includes a cylinder (20), a conveyor belt, a motor, a collection box (22) and a vacuum pump (3). The cylinder (20) is provided with a feed pipe (5) and a vacuum pipe (7). The conveyor belt, motor and collection box (22) are located inside the cylinder (20). The belt of the conveyor belt is made of filter cloth. The vacuum pump (3) is connected to the cylinder (20) through the vacuum pipe (7). The shaft of the motor is fixedly connected to the roller of the conveyor belt. The conveyor belt is matched with the feed pipe (5) and the conveyor belt is matched with the collection box (22).

9. The apparatus for preparing m-nitrobenzonitrile according to claim 8, applied to the method for preparing m-nitrobenzonitrile according to claim 1, characterized in that, It also includes an adjusting cylinder and a rotating plate (11). The conveyor belt and the motor are rotatably connected to the cylinder (20) through the rotating plate (11). The adjusting cylinder is set inside the cylinder (20). The adjusting cylinder includes an adjusting cylinder body (9), an adjusting piston (8), and an adjusting rod (10). The adjusting cylinder is fixedly connected to the cylinder (20). The adjusting piston (8) is slidably sealed to the adjusting cylinder body (9). One end of the adjusting rod (10) is hinged to the adjusting piston (8), and the other end is hinged to the rotating plate (11).

10. The apparatus for preparing m-nitrobenzonitrile according to claim 8, applied using the method for preparing m-nitrobenzonitrile according to claim 1, characterized in that, It also includes a rinsing mechanism, which includes a hydraulic cylinder, a rack (17), a half gear (19), a return spring (15), and a nozzle (12). The half gear (19) is fixedly connected to the shaft of the motor, and the rack (17) meshes with the half gear (19). The hydraulic cylinder includes a hydraulic cylinder body (16) and a hydraulic piston (14). The hydraulic cylinder body (16) is fixedly connected to the cylinder body (20), and the hydraulic piston (14) is slidably sealed to the hydraulic cylinder body (16). The rack (17) is fixedly connected to the hydraulic piston (14). One end of the return spring (15) is fixedly connected to the piston, and the other end is fixedly connected to the hydraulic cylinder body (16). The hydraulic cylinder body (16) is provided with an inlet pipe (6) and an outlet pipe (13). The nozzle (12) is connected to the outlet pipe (13). The nozzle (12) cooperates with the conveyor belt. The inlet pipe (6) is used to send clean water into the hydraulic cylinder.

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