A process for the synthesis of p-nitroaniline

Abstract

The application relates to the technical field of organic compound synthesis, and particularly discloses a synthesis process of p-nitroaniline. The synthesis process of p-nitroaniline comprises the following steps: (1) preparing concentrated ammonia water with a concentration of 38%-42% by using an ammonia water preparation unit; (2) adding p-nitrochlorobenzene, concentrated ammonia water and an additive into a reaction kettle, and then carrying out heat preservation reaction under the condition of 150-170 DEG C and 5.6-6.2 MPa for 14-16 h; the additive comprises modified cyclodextrin and trehalose; (3) after pressure relief, the materials in the reaction kettle are transferred into a water washing kettle to carry out water washing and stirring for 1-2 h, and the material liquid after water washing is subjected to centrifugal separation to obtain p-nitroaniline. According to the synthesis process, the modified cyclodextrin and the trehalose are compounded and synergized, the balance problem of the main reaction efficiency and the side reaction inhibition is solved from the reaction mechanism level, and finally the high yield and the high purity in the synthesis process of p-nitroaniline are simultaneously achieved.

Description

Technical Field

[0001] This application relates to the field of organic compound synthesis technology, and more specifically, to a process for synthesizing p-nitroaniline. Background Technology

[0002] p-Nitroaniline is an important organic fine chemical intermediate, chemically known as 4-nitroaniline (molecular formula C6H6N2O2). It appears as yellow needle-like crystals with a melting point of 148-149℃. It is slightly soluble in cold water, readily soluble in hot water and organic solvents such as ethanol and ether, and possesses stable chemical properties. As a key intermediate, it is used in dyes, pigments, pharmaceuticals, and pesticides. It can be used to synthesize various dye products, including direct dyes, acid dyes, and reactive dyes. It can also be used to prepare rubber antioxidants, explosive intermediates, and pharmaceutical raw materials, occupying an important position in the fine chemical industry with consistently stable market demand.

[0003] Currently, the mainstream industrial process for synthesizing p-nitroaniline is the amination reaction of p-nitrochlorobenzene with ammonia. The core reaction involves the substitution of the chlorine atom in p-nitrochlorobenzene with an amino group to generate the target product. Based on different reaction conditions, it is mainly divided into two categories: low-pressure and high-pressure methods. The low-pressure method typically controls the reaction pressure at 2-4 MPa and the temperature at 120-140℃, allowing for amination under mild conditions. The high-pressure method uses a reaction pressure of 5-7 MPa and a reaction temperature of 150-170℃ to enhance the reaction rate and raw material contact efficiency. Both methods require subsequent processes such as separation and purification to obtain the finished product. The amination reaction of p-nitrochlorobenzene with ammonia to synthesize p-nitroaniline has advantages such as readily available raw materials, a simple and clear reaction path, mature and reliable technology, strong equipment compatibility, relatively controllable production costs, and the absence of highly toxic reagents, making it more environmentally friendly than other processes such as nitration reduction. Therefore, it has become the mainstream choice in the industry.

[0004] However, existing synthesis processes still have some unavoidable technical defects in actual production. Specifically, although the low-pressure synthesis process can suppress side reactions such as hydrolysis and diamine formation of raw materials through low temperature and low pressure, the solubility of ammonia in water decreases significantly with decreasing pressure, resulting in insufficient free ammonia concentration in the reaction system, insufficient conversion of p-nitrochlorobenzene, and difficulty in completely separating a large amount of unreacted raw material residue, resulting in a product purity of only about 97%. The high-pressure method increases ammonia solubility by increasing pressure, significantly improving the raw material conversion rate and reducing raw material residue, thus improving product purity. However, high temperature and high pressure can exacerbate side reactions, with byproducts consuming 1.3%-2.5% of the raw materials, and the byproducts also carry away the target product, making it difficult to break through 96% yield. Ultimately, this creates a trade-off between "low purity of low-pressure method and low yield of high-pressure method." Therefore, the existing synthesis processes cannot simultaneously achieve high product purity and high yield. Summary of the Invention

[0005] In order to overcome the technical bottleneck of the difficulty in achieving both high purity and high yield in existing processes and to realize the efficient and high-quality synthesis of p-nitroaniline, this application provides a synthesis process for p-nitroaniline.

[0006] The synthesis process of p-nitroaniline provided in this application adopts the following technical solution:

[0007] A process for synthesizing p-nitroaniline includes the following steps:

[0008] (1) Prepare concentrated ammonia solution with a concentration of 38%-42% using the ammonia solution preparation unit;

[0009] (2) Add p-nitrochlorobenzene, concentrated ammonia and additives to the reaction vessel, and then keep it at 150-170℃ and 5.6-6.2MPa for 14-16h; the additives include modified cyclodextrin and trehalose, wherein the modified cyclodextrin is obtained by substituting β-cyclodextrin with 2-chloropropanol;

[0010] (3) The ammonia gas in the reactor is depressurized to the buffer tank at a rate of 0.06-0.10 MPa / min. When the pressure in the reactor drops to 0.2 MPa, the material in the reactor is transferred to the water washing tank for water washing and stirring for 1-2 hours. The water washing temperature is 35-45℃. The washed liquid is centrifuged to obtain p-nitroaniline.

[0011] The reason why the technical solution of this application can break through the dilemma of "low purity in low pressure method and low yield in high pressure method" in the existing process is that it is based on the structural advantages of β-cyclodextrin, and its performance is enhanced by modification and optimization. Then, it is combined with trehalose to form a synergistic effect. Combined with the optimization of high pressure system and separation process, side reactions are suppressed from the source, the efficiency of main reaction is guaranteed, and no product residue is guaranteed. Finally, high yield and high purity are achieved simultaneously.

[0012] β-Cyclodextrin, a typical representative of natural cyclodextrins, possesses its core advantage in its unique "externally hydrophilic, internally hydrophobic" cavity structure. The inner diameter of this cavity closely matches the molecular size of p-nitrochlorobenzene, granting it specific inclusion capabilities. In the synthesis of p-nitroaniline, the chlorine atom of p-nitrochlorobenzene initiates a hydrolysis side reaction (being destroyed by the OH groups in the system). － The key active sites of the attack) and diamine side reaction (attacked by excess NH3) are β-cyclodextrin, which can precisely encapsulate the chlorine atom of p-nitrochlorobenzene and adjacent active groups inside the cavity through intermolecular hydrophobic interactions and van der Waals forces, forming a stable inclusion complex.

[0013] This encapsulation is not indiscriminate but highly selective. It exposes only the target site (para-nitro group) in p-nitrochlorobenzene where amination with ammonia occurs, allowing ammonia molecules to preferentially bind to this site and complete the main reaction. Simultaneously, it effectively shields the chlorine atom, preventing it from being absorbed by the OH groups in the system. － Excessive NH3 attack reduces the formation of hydrolysis byproducts (p-nitrophenol) and diamineation byproducts (diaminonitrobenzene) at the source. Furthermore, β-cyclodextrin itself has good biocompatibility and low toxicity, and is readily soluble in water, providing a natural advantage for subsequent separation and removal, avoiding impurity residue problems caused by the introduction of additives, and laying the foundation for ensuring product purity.

[0014] While conventional β-cyclodextrin possesses basic inclusion capabilities, it still exhibits significant shortcomings under high-temperature and high-pressure reaction conditions: firstly, its limited water solubility easily leads to self-aggregation, affecting the uniformity of inclusion; secondly, its cavity structure lacks stability, potentially undergoing slight deformation at reaction temperatures of 150-170℃, reducing the inclusion strength at active sites. This application addresses these shortcomings by modifying β-cyclodextrin with 2-chloropropanol through hydroxypropyl substitution.

[0015] The modified hydroxypropyl-β-cyclodextrin (HP-β-CD) features two major performance upgrades: Firstly, the introduction of the hydroxypropyl side chain enhances the hydrophobic effect within the cavity and improves the overall structural stability of the molecule. This allows it to maintain its intact cavity structure even under high-pressure reaction conditions of 150-170℃ and 5.6-6.2MPa, continuously and stably encapsulating the active site of p-nitrochlorobenzene and preventing side reaction rebounds caused by auxiliary agent structural damage. Secondly, the hydrophilic nature of the hydroxypropyl group significantly improves the water solubility of the cyclodextrin, increasing the solubility to over 60g / 100mL after modification. This significantly reduces the risk of auxiliary agent residue during subsequent separation and avoids the problem of concentrated localized side reactions caused by auxiliary agent aggregation. Furthermore, the modification process, through precise control of reaction conditions and purification processes, ensures that the modified cyclodextrin has a purity ≥99.95%, with no additional impurities introduced, further guaranteeing product purity.

[0016] Although modified cyclodextrin alone can efficiently encapsulate active sites, the stability and selectivity of the reaction system still need to be further enhanced under high temperature and high pressure. Therefore, this application introduces trehalose as a synergist and combines it with modified cyclodextrin at a mass ratio of (3-5):1 to form a dual mechanism of action of "encapsulation inhibition + stabilization synergy".

[0017] Trehalose possesses unique "molecular chaperone" properties. Its molecular structure contains multiple hydroxyl groups that can form a stable hydrogen bond network with ammonia and water molecules in the reaction system, producing two key synergistic effects: First, it enhances reaction selectivity—the hydrogen bond network stabilizes the nucleophilic activity of ammonia molecules, guiding them to preferentially bind to the target sites exposed by the modified cyclodextrin inclusion complex, reducing the probability of ammonia molecules contacting chlorine atoms, and further inhibiting diamineization side reactions; simultaneously, this network can also inhibit OH groups in the system. - The modified cyclodextrin exhibits enhanced activity, reducing its attack on chlorine atoms and assisting in the inhibition of hydrolysis side reactions, resulting in a 10%-15% increase in the overall inhibition rate of both types of side reactions compared to modified cyclodextrin alone. Secondly, it protects the structure of the adjuvant—trehalose's hydrogen-bonded network can encapsulate the modified cyclodextrin molecule, preventing deformation of the cavity structure due to excessive molecular vibration under high temperature and pressure. This ensures the inclusion effect persists throughout the 14-16 hour incubation process, preventing the rebound of later side reactions. Furthermore, trehalose itself is a highly water-soluble, food-grade, high-purity raw material, non-toxic, free of volatile impurities, and biodegradable, complementing the water-soluble advantage of modified cyclodextrin and facilitating subsequent separation and removal.

[0018] In summary, this application solves the problem of balancing the efficiency of the main reaction and the inhibition of side reactions by combining modified cyclodextrin and trehalose in a synergistic manner from the reaction mechanism level. It retains the high conversion rate advantage of the high-pressure method, makes up for its shortcoming of aggravated side reactions, and solves the risk of residual additives. Finally, it achieves high yield and high purity in the synthesis process of p-nitroaniline.

[0019] Optionally, in step (1), when preparing concentrated ammonia using the ammonia preparation unit, the temperature is controlled at 40-45℃ and the pressure at 1.0-1.8MPa.

[0020] By adopting the above technical solution, the preparation temperature is controlled at 40-45℃ and the pressure at 1.0-1.8MPa. Under these conditions, the mixing of liquid ammonia and water is more uniform, and a stable concentration of 38%-42% concentrated ammonia water can be prepared. This avoids problems such as aggravated diamineation side reactions and insufficient raw material conversion caused by excessively high or low ammonia concentrations in certain areas. The stable concentrated ammonia water raw material and the synergistic effect of the composite additives ensure that the ammonia concentration in the reaction system is always within the optimal range. This not only ensures the efficient progress of the main reaction but also inhibits the occurrence of side reactions, laying a raw material foundation for the simultaneous improvement of product purity and yield.

[0021] Optionally, in step (3), the ammonia gas depressurized to the buffer tank is cooled and absorbed by a cooler to obtain ammonia water, which is then reused in step (1).

[0022] Optionally, in step (2), the mass ratio of p-nitrochlorobenzene to concentrated ammonia is 1:(0.76-0.80).

[0023] Optionally, in step (2), the amount of the additive added is 1.5%-2.5% of the mass of p-nitrochlorobenzene.

[0024] By adopting the above technical solution, the range of compound additive dosage is clearly defined, maximizing its side reaction inhibition effect while avoiding waste or insufficient effect. Existing processes lack targeted control over additive dosage; too little dosage results in limited side reaction inhibition, while too much may lead to additive residue or increased separation burden. This solution determines the additive dosage to be 1.5%-2.5% of the mass of p-nitrochlorobenzene. At this dosage, modified cyclodextrin can fully encapsulate the active sites of p-nitrochlorobenzene, and trehalose can effectively stabilize the reaction system. Together, they achieve highly efficient inhibition of hydrolysis and diamineization side reactions. Simultaneously, this dosage range is compatible with subsequent washing and centrifugation processes, ensuring the additive is completely dissolved in the aqueous phase and removed without residue in the solid phase product. This guarantees both side reaction inhibition and avoids the additive's impact on product purity, achieving the dual goals of suppressing side reactions and ensuring purity.

[0025] Optionally, in step (2), the adjuvant is a compound obtained by mixing modified cyclodextrin and trehalose in a mass ratio of (3-5):1.

[0026] By adopting the above technical solution and the specified ratio, the inclusion effect of modified cyclodextrin and the stabilizing effect of trehalose achieve optimal synergy: modified cyclodextrin precisely includes active sites, while trehalose enhances the stability of the inclusion complex through a hydrogen bond network and improves the reactivity selectivity of ammonia molecules. The synergistic effect significantly reduces the amount of byproducts generated. At this compound ratio, the composite additive can effectively suppress side reactions and adapt to high-temperature and high-pressure reaction conditions, avoiding its own structural decomposition and ensuring its full effectiveness throughout the process. This provides core technical support for the simultaneous improvement of product purity and yield.

[0027] Optionally, the modified cyclodextrin is prepared by the following method:

[0028] β-Cyclodextrin and 2-chloropropanol were mixed, and then sodium hydroxide solution was added. The mixture was reacted at 35-45℃ and a stirring rate of 60-80 r / min for 3-5 h. After the reaction was completed, the pH of the system was adjusted to 6.5-7.5 with hydrochloric acid, and the mixture was subjected to vacuum distillation at 0.08-0.09 MPa and 60-70℃ for 1-2 h. The remaining product was recrystallized twice with anhydrous ethanol, filtered, and then dried under vacuum at 50-60℃ for 4-6 h to obtain modified cyclodextrin.

[0029] The water solubility of ordinary β-cyclodextrin, as described above, needs improvement, making complete separation during the washing step difficult. Furthermore, its inclusion stability is insufficient, hindering its ability to withstand high-temperature and high-pressure reaction conditions. This proposed method introduces modified groups through etherification, followed by purification steps such as vacuum distillation, recrystallization, and vacuum drying to produce a structurally stable modified cyclodextrin with excellent water solubility. The cavity structure of this modified cyclodextrin precisely includes the active sites of p-nitrochlorobenzene, and its solubility is significantly enhanced at a washing temperature of 35-45℃. It can be completely removed by centrifugation, solving the problem of residual β-cyclodextrin affecting purity and enhancing the inhibition of side reactions. When combined with trehalose, it further consolidates the dual advantages of high purity and high yield.

[0030] Optionally, the mass ratio of β-cyclodextrin to 2-chloropropanol is 1:(4.2-4.8).

[0031] Optionally, the mass concentration of the sodium hydroxide solution is 28%-32%; the amount of sodium hydroxide solution added is 8%-12% of the mass of β-cyclodextrin.

[0032] By employing the above technical solution, the determined concentration of 28%-32% and addition amount of 8%-12% can precisely catalyze the etherification reaction of β-cyclodextrin and 2-chloropropanol, ensuring that the modified cyclodextrin achieves a suitable degree of substitution while avoiding structural damage caused by excessive reaction. The prepared modified cyclodextrin has a stable structure and excellent performance. When combined with trehalose, it can fully exert a synergistic effect, inhibiting side reactions and ensuring separation efficiency, thus helping to simultaneously improve product purity and yield.

[0033] Optionally, the β-cyclodextrin has a purity of ≥99.9% and a particle size of 10-20 μm.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. This application innovatively employs a compound additive system of modified cyclodextrin and trehalose, fundamentally solving the core challenge of achieving both high purity and high yield in existing processes. Leveraging the inherent cavity structure of β-cyclodextrin, its inclusion stability and water solubility are significantly improved after hydroxypropyl substitution modification, precisely shielding the side-reactive active sites of p-nitrochlorobenzene. Combined with trehalose, a synergistic effect is formed, enhancing the reactivity selectivity of ammonia molecules while protecting the additive structure from damage under high temperature and pressure, significantly suppressing hydrolysis and diamineization side reactions. This system, coupled with high-pressure reaction conditions, retains the high conversion rate advantage of the high-pressure method while avoiding the problems of byproduct consumption of raw materials and loss of target products, achieving efficient conversion of raw materials to target products. Simultaneously, it reduces the generation of difficult-to-separate impurities, providing core support for achieving both high purity and high yield simultaneously.

[0036] 2. This application constructs a stable and efficient reaction system by optimizing process parameters and material ratios, further consolidating the dual advantages of high purity and high yield. In the ammonia preparation stage, by precisely controlling temperature and pressure, a stable concentration of concentrated ammonia is prepared, avoiding the aggravation of side reactions or insufficient conversion caused by fluctuations in ammonia concentration. In the feeding stage, the optimal mass ratio of p-nitrochlorobenzene to concentrated ammonia, as well as the amount and proportion of compound additives, are clearly defined to ensure that the concentration of each component in the reaction system is within the optimal range. This ensures both the efficient progress of the main reaction and avoids performance shortcomings caused by excessive raw materials or insufficient additives. Simultaneously, the design for recovering and reusing ammonia after depressurization reduces raw material waste and further suppresses diamine side reactions by regulating the ammonia concentration in the reaction system through circulation, providing process assurance for product quality improvement.

[0037] 3. This application optimizes the separation process and selects appropriate additives to ensure the highest possible product purity while also considering the environmental friendliness and practicality of the process. The selected modified cyclodextrin and trehalose both possess excellent water solubility, completely dissolving in the aqueous phase during washing at a specific temperature. Centrifugation then thoroughly separates them from the solid product, preventing the introduction of new impurities due to additive residues. The modified cyclodextrin is prepared through multi-step purification to ensure high purity, with no additional impurities introduced into the reaction system. This highly efficient design for suppressing side reactions and achieving complete separation without residue effectively addresses the purity limitations of existing low-pressure methods, which suffer from raw material residues, and high-pressure methods, which involve byproduct entrainment. Attached Figure Description

[0038] Figure 1 This is a chromatogram of p-nitroaniline prepared in Example 1 of this application;

[0039] Figure 2 This is a chromatogram of p-nitroaniline prepared in Example 2 of this application;

[0040] Figure 3 This is a chromatogram of p-nitroaniline prepared in Example 3 of this application. Detailed Implementation

[0041] The present application will be further described in detail below with reference to the embodiments.

[0042] Preparation example of modified cyclodextrin

[0043] Preparation Example 1

[0044] Modified cyclodextrin was prepared using the following method:

[0045] 1 kg of β-cyclodextrin (particle size 10 μm) and 4.2 kg of 2-chloropropanol were mixed, and then 0.08 kg of 28% sodium hydroxide solution was added. The mixture was reacted at 35 °C and a stirring rate of 60 r / min for 3 h. After the reaction was completed, the pH of the system was adjusted to 6.5 with 10% hydrochloric acid. The mixture was then subjected to vacuum distillation at 0.08 MPa and 60 °C for 1 h. The remaining product was recrystallized twice with anhydrous ethanol, filtered, and then dried under vacuum at 50 °C for 4 h to obtain modified cyclodextrin.

[0046] Preparation Example 2

[0047] Modified cyclodextrin was prepared using the following method:

[0048] 1 kg of β-cyclodextrin (particle size 15 μm) and 4.5 kg of 2-chloropropanol were mixed, and then 0.1 kg of 30% sodium hydroxide solution was added. The mixture was reacted at 40 °C and a stirring rate of 70 r / min for 4 h. After the reaction was completed, the pH of the system was adjusted to 7.0 with 10% hydrochloric acid. The mixture was then subjected to vacuum distillation at 0.09 MPa and 65 °C for 1.5 h. The remaining product was recrystallized twice with anhydrous ethanol, filtered, and then dried under vacuum at 55 °C for 5 h to obtain modified cyclodextrin.

[0049] Preparation Example 3

[0050] Modified cyclodextrin was prepared using the following method:

[0051] 1 kg of β-cyclodextrin (particle size 20 μm) and 4.8 kg of 2-chloropropanol were mixed, and then 0.12 kg of 32% sodium hydroxide solution was added. The mixture was reacted at 45 °C and a stirring rate of 80 r / min for 5 h. After the reaction was completed, the pH of the system was adjusted to 7.5 with 10% hydrochloric acid. The mixture was then subjected to vacuum distillation at 0.09 MPa and 70 °C for 2 h. The remaining product was recrystallized twice with anhydrous ethanol, filtered, and then dried under vacuum at 60 °C for 6 h to obtain modified cyclodextrin.

[0052] Example

[0053] Example 1

[0054] A process for synthesizing p-nitroaniline includes the following steps:

[0055] (1) Start the ammonia water preparation unit, control the preparation temperature at 40℃ and the pressure at 1.0MPa, add primary water and liquid ammonia to the ammonia water metering tank to prepare concentrated ammonia water with a concentration of 38% for later use;

[0056] (2) Take the modified cyclodextrin and trehalose prepared in Preparation Example 1 and mix them in a mass ratio of 3:1. Stir evenly to prepare an auxiliary agent; add 100 kg of p-nitrochlorobenzene to the amination reactor R10201A, then add 76 kg of the concentrated ammonia water prepared above through the pipeline flow meter, and then add 1.5 kg of auxiliary agent; close the pipeline valve, start stirring at 70 r / min, turn on the jacket steam and inner coil steam, and keep the reaction at 150℃ and 5.6 MPa for 14 h.

[0057] (3) After the heat preservation is completed, the ammonia gas in the reactor is depressurized to the buffer tank V10401A at a rate of 0.06 MPa / min. The ammonia gas depressurized to the buffer tank V10401A is cooled and absorbed by the cooler to obtain ammonia water. The ammonia water is reused in step (1) to prepare concentrated ammonia water. When the pressure in the reactor drops to 0.2 MPa, the material in the reactor is transferred to the water washing tank R10301 for water washing and stirring for 1 hour. The water washing temperature is 35℃ and the stirring rate is 80 r / min. The water-washed liquid is transferred to a high-speed centrifuge for centrifugal separation to obtain p-nitroaniline.

[0058] Example 2

[0059] A process for synthesizing p-nitroaniline includes the following steps:

[0060] (1) Start the ammonia water preparation unit, control the preparation temperature at 42℃ and the pressure at 1.4MPa, add primary water and liquid ammonia to the ammonia water metering tank to prepare a 40% concentrated ammonia water for later use;

[0061] (2) Take the modified cyclodextrin and trehalose prepared in Preparation Example 1 and mix them in a mass ratio of 4:1. Stir evenly to make an auxiliary agent. Add 100 kg of p-nitrochlorobenzene to the amination reactor R10201A, then add 78 kg of the above-prepared concentrated ammonia water through the pipeline flow meter, and then add 2 kg of auxiliary agent. Close the pipeline valve, start stirring at 70 r / min, turn on the jacket steam and inner coil steam, and keep the reaction at 160℃ and 5.9 MPa for 15 h.

[0062] (3) After the heat preservation is completed, the ammonia gas in the reactor is depressurized to the buffer tank V10401A at a rate of 0.08 MPa / min. The ammonia gas depressurized to the buffer tank V10401A is cooled and absorbed by the cooler to obtain ammonia water. The ammonia water is reused in step (1) to prepare concentrated ammonia water. When the pressure in the reactor drops to 0.2 MPa, the material in the reactor is transferred to the water washing tank R10301 for water washing and stirring for 1.5 h. The water washing temperature is 40℃ and the stirring rate is 80 r / min. The water-washed liquid is transferred to a high-speed centrifuge for centrifugal separation to obtain p-nitroaniline.

[0063] Example 3

[0064] A process for synthesizing p-nitroaniline includes the following steps:

[0065] (1) Start the ammonia water preparation unit, control the preparation temperature at 45℃ and the pressure at 1.8MPa, add primary water and liquid ammonia to the ammonia water metering tank to prepare concentrated ammonia water with a concentration of 42% for later use;

[0066] (2) Take the modified cyclodextrin and trehalose prepared in Preparation Example 1 and mix them in a mass ratio of 5:1. Stir evenly to prepare an auxiliary agent. Add 100 kg of p-nitrochlorobenzene to the amination reactor R10201A, then add 80 kg of the above-prepared concentrated ammonia water through a pipeline flow meter, and then add 2.5 kg of auxiliary agent. Close the pipeline valve, start stirring at 70 r / min, turn on the jacket steam and inner coil steam, and keep the temperature at 170℃ and 6.2 MPa for 16 h.

[0067] (3) After the heat preservation is completed, the ammonia gas in the reactor is depressurized to the buffer tank V10401A at a rate of 0.10 MPa / min. The ammonia gas depressurized to the buffer tank V10401A is cooled and absorbed by the cooler to obtain ammonia water. The ammonia water is reused in step (1) to prepare concentrated ammonia water. When the pressure in the reactor drops to 0.2 MPa, the material in the reactor is transferred to the water washing tank R10301 for water washing and stirring for 2 hours. The water washing temperature is 45℃ and the stirring rate is 80 r / min. The water-washed liquid is transferred to a high-speed centrifuge for centrifugal separation to obtain p-nitroaniline.

[0068] Example 4

[0069] A process for synthesizing p-nitroaniline differs from Example 3 in that, in step (2) of this example, the modified cyclodextrin in the auxiliary agent is selected from the modified cyclodextrin prepared in Preparation Example 2.

[0070] Example 5

[0071] A process for synthesizing p-nitroaniline differs from that in Example 3 in that, in step (2) of this example, the modified cyclodextrin in the auxiliary agent is selected from the modified cyclodextrin prepared in Example 3.

[0072] Comparative Example

[0073] Comparative Example 1

[0074] A process for synthesizing p-nitroaniline differs from that in Example 3 in that no additives are added in step (2) of this comparative example.

[0075] Comparative Example 2

[0076] A process for synthesizing p-nitroaniline differs from that in Example 3 in that, in step (2) of this comparative example, an equal amount of unmodified β-cyclodextrin is used instead of modified cyclodextrin in the auxiliary agent.

[0077] Comparative Example 3

[0078] A process for synthesizing p-nitroaniline differs from that in Example 3 in that, in step (2) of this comparative example, trehalose was not added to the auxiliary agent, and only a single modified cyclodextrin was used.

[0079] Comparative Example 4

[0080] A process for synthesizing p-nitroaniline differs from that in Example 3 in that the concentration of concentrated ammonia in step (2) of this comparative example is 30%.

[0081] Performance testing

[0082] The purity and yield of p-nitroaniline prepared in Examples 1-5 and Comparative Examples 1-4 were tested, and the results are shown in Table 1. The chromatographic peaks of p-nitroaniline prepared in Examples 1-3 are shown in Tables 2-4.

[0083] Table 1 Test Results

[0084]

[0085] Table 2. Chromatographic peaks of p-nitroaniline prepared in Example 1

[0086]

[0087] Table 3. Chromatographic peaks of p-nitroaniline prepared in Example 2.

[0088]

[0089] Table 4. Chromatographic peaks of p-nitroaniline prepared in Example 3.

[0090]

[0091] refer to Figures 1-3 The chromatograms of p-nitroaniline and the detection results in Table 1 show that the p-nitroaniline prepared in Examples 1-5 exhibited good performance in terms of yield and purity, with yields exceeding 98.69% and purities above 99.871%. In contrast, the yields and purities of Comparative Examples 1-4 were significantly lower. This indicates that the synthetic process used in this application can effectively improve the synthesis effect of p-nitroaniline. Comparative Example 1, without the addition of auxiliaries, had a yield and purity of 95.38% and 97.365%, respectively, which were much lower than those of the examples. This demonstrates that the auxiliaries played a crucial role in the synthesis process.

[0092] Comparative Example 2 used unmodified β-cyclodextrin instead of modified cyclodextrin, resulting in improved yield and purity, but still not as good as the examples. This is because ordinary β-cyclodextrin has limited water solubility, is prone to aggregation, and has insufficient stability in its cavity structure. Under high temperature and high pressure reaction conditions, it is difficult to continuously and stably encapsulate the active sites of p-nitrochlorobenzene, leading to poor side reaction inhibition. In contrast, the modified hydroxypropyl-β-cyclodextrin enhances hydrophobic interaction and structural stability, improves water solubility, and can better exert its inclusion effect.

[0093] In Comparative Example 3, no trehalose was added; only modified cyclodextrin was used, resulting in a decrease in yield and purity compared to the previous example. This demonstrates the synergistic effect of the combination of trehalose and modified cyclodextrin. Trehalose possesses unique "molecular chaperone" properties; its hydrogen bond network can stabilize the nucleophilic activity of ammonia molecules, guiding them to preferentially bind to the target sites exposed by the modified cyclodextrin inclusion complex, while simultaneously inhibiting OH groups in the system. - It enhances the activity of the cyclodextrin, strengthens the reaction selectivity, and protects the modified cyclodextrin structure, preventing it from deforming under high temperature and pressure. This ensures that the inclusion effect continues throughout the reaction process, thereby effectively suppressing side reactions and improving product yield and purity.

[0094] In Comparative Example 4, the concentration of concentrated ammonia was 30%, with a yield and purity of 95.49% and 97.936%, respectively, lower than those in the example. This application controls the concentration of concentrated ammonia at 38%-42%, and maintains a temperature of 40-45°C and a pressure of 1.0-1.8 MPa during preparation. This ensures more uniform mixing of liquid ammonia and water, resulting in a stable concentration of concentrated ammonia. The stable concentrated ammonia raw material, combined with the composite additives, ensures that the ammonia concentration in the reaction system remains within the optimal range. This guarantees efficient main reaction while suppressing side reactions. If the ammonia concentration is too low, insufficient raw material conversion will occur, affecting product purity and yield.

[0095] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A process for synthesizing p-nitroaniline, characterized in that, Includes the following steps: (1) Prepare concentrated ammonia solution with a concentration of 38%-42% using the ammonia solution preparation unit; (2) Add p-nitrochlorobenzene, concentrated ammonia and additives to the reaction vessel, and then keep it at 150-170℃ and 5.6-6.2MPa for 14-16h; the additives include modified cyclodextrin and trehalose, wherein the modified cyclodextrin is obtained by substituting β-cyclodextrin with 2-chloropropanol; (3) The ammonia gas in the reactor is depressurized to the buffer tank at a rate of 0.06-0.10 MPa / min. When the pressure in the reactor drops to 0.2 MPa, the material in the reactor is transferred to the water washing tank for water washing and stirring for 1-2 hours. The water washing temperature is 35-45℃. The washed liquid is centrifuged to obtain p-nitroaniline.

2. The synthesis process of p-nitroaniline according to claim 1, characterized in that: In step (1), when preparing concentrated ammonia using the ammonia preparation unit, the temperature is controlled at 40-45℃ and the pressure at 1.0-1.8MPa.

3. The synthesis process of p-nitroaniline according to claim 1, characterized in that: In step (3), the ammonia gas depressurized into the buffer tank is cooled and absorbed by the cooler to obtain ammonia water, which is then reused in step (1).

4. The synthesis process of p-nitroaniline according to claim 1, characterized in that: In step (2), the mass ratio of p-nitrochlorobenzene to concentrated ammonia is 1:(0.76-0.80).

5. The synthesis process of p-nitroaniline according to claim 4, characterized in that: In step (2), the amount of the additive added is 1.5%-2.5% of the mass of p-nitrochlorobenzene.

6. The synthesis process of p-nitroaniline according to claim 5, characterized in that: In step (2), the adjuvant is a compound obtained by mixing modified cyclodextrin and trehalose in a mass ratio of (3-5):

1.

7. The synthesis process of p-nitroaniline according to claim 6, characterized in that, The modified cyclodextrin was prepared using the following method: β-Cyclodextrin and 2-chloropropanol were mixed, and then sodium hydroxide solution was added. The mixture was reacted at 35-45℃ and a stirring rate of 60-80 r / min for 3-5 h. After the reaction was completed, the pH of the system was adjusted to 6.5-7.5 with hydrochloric acid, and the mixture was subjected to vacuum distillation at 0.08-0.09 MPa and 60-70℃ for 1-2 h. The remaining product was recrystallized twice with anhydrous ethanol, filtered, and then dried under vacuum at 50-60℃ for 4-6 h to obtain modified cyclodextrin.

8. The synthesis process of p-nitroaniline according to claim 7, characterized in that, The mass ratio of β-cyclodextrin to 2-chloropropanol is 1:(4.2-4.8).

9. The synthesis process of p-nitroaniline according to claim 7, characterized in that, The sodium hydroxide solution has a mass concentration of 28%-32%; the amount of sodium hydroxide solution added is 8%-12% of the mass of β-cyclodextrin.

10. The synthesis process of p-nitroaniline according to claim 7, characterized in that, The β-cyclodextrin has a purity of ≥99.9% and a particle size of 10-20 μm.

Images