A method for preparing 2,4-dinitroaniline

Abstract

This invention relates to the field of organic chemical synthesis technology, specifically to a method for preparing 2,4-dinitroaniline. The method comprises: S1, nitrification of benzene in a concentrated sulfuric acid system to obtain a system containing nitrobenzene; S2, dilution of the nitrobenzene-containing system with water, followed by catalytic hydrogenation to convert the nitrobenzene to aniline; after the reaction, the catalyst is filtered off to obtain a system containing aniline; S3, para-nitration of the aniline-containing system with concentrated nitric acid; after the reaction, dehydration of the system, followed by ortho-nitration of the system with concentrated nitric acid; and post-treatment to obtain 2,4-dinitroaniline. This preparation method is green, safe, efficient, simple to operate, low in cost, uses inexpensive raw materials, and yields high purity of the target product, making it more suitable for industrial applications.

Description

Technical Field

[0001] This invention relates to a method for preparing 2,4-dinitroaniline, belonging to the field of organic chemical synthesis technology. Background Technology

[0002] 2,4-Dinitroaniline is an important fine chemical intermediate widely used in the production of disperse dyes, neutral dyes, sulfur dyes, and organic pigments, such as sulfur deep blue 3R, disperse red B, and disperse violet 2R. It is also used in the synthesis of the pesticide dinitrophenyl ether and as a raw material for colorants and preservatives in printing inks. Its molecular formula is C6H5N3O4, and its molecular weight is 183.12. It typically appears as yellow to brownish-yellow lumps and is flammable.

[0003] Currently, all reported industrial synthesis methods for 2,4-dinitroaniline use 2,4-dinitrochlorobenzene as the starting material, obtaining the target product through ammonolysis. For example, patent application CN104130138A discloses a continuous ammoniation process for 2,4-dinitroaniline, using 2,4-dinitrochlorobenzene and ammonia as raw materials, reacting continuously at a temperature of 160-170℃ and a pressure of 0.5-1.0 MPa; patent application CN85104924A discloses a method for preparing 2,4-dinitroaniline under normal pressure, using 2,4-dinitrochlorobenzene as the raw material, reacting it with ammonia in an amide solvent; and patent application CN113214088A discloses a method using a microreactor, conducting an ammonolysis reaction using 2,4-dinitrochlorobenzene and ammonia as raw materials.

[0004] Although the ammonolysis process using 2,4-dinitrochlorobenzene as a raw material can yield 2,4-dinitroaniline, it suffers from the following common problems: High raw material costs: 2,4-dinitrochlorobenzene itself needs to be produced from chlorobenzene through multiple nitration steps, and its price is much higher than that of basic chemical raw materials such as benzene, resulting in high production costs for the target product.

[0005] The reaction conditions are harsh: ammonolysis usually requires high temperature (above 160℃) and high pressure (0.5~1.0MPa) conditions, which places high demands on the pressure resistance and corrosion resistance of the equipment, and there are safety risks in high-pressure ammonia operation.

[0006] Severe equipment corrosion: The hydrogen chloride released during ammonolysis is highly corrosive to metal materials such as reactors and pipelines under high temperature and pressure, significantly shortening equipment life and increasing maintenance costs.

[0007] The pressure of treating waste is high: Although some processes can recover ammonium chloride as a byproduct, a certain amount of high-salt organic wastewater will still be generated, resulting in high environmental treatment costs.

[0008] Therefore, developing a new route for the synthesis of 2,4-dinitroaniline that uses inexpensive and readily available raw materials, has mild reaction conditions, is environmentally friendly, and suitable for industrialization has significant practical implications and market value. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method for preparing 2,4-dinitroaniline. This method is green, safe, efficient, simple to operate, low in cost, uses inexpensive raw materials, and yields high purity of the target product.

[0010] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a method for preparing 2,4-dinitroaniline, wherein the preparation method is as follows: S1. In a concentrated sulfuric acid system, benzene undergoes a nitration reaction to obtain a system containing nitrobenzene; S2. After diluting the nitrobenzene-containing system with water, a catalytic hydrogenation reaction is carried out to react the nitrobenzene into aniline. After the reaction is completed, the catalyst is filtered off to obtain the aniline-containing system. S3. Add concentrated nitric acid to the aniline-containing system to carry out para-nitration reaction. After the reaction is completed, the system is dehydrated and concentrated nitric acid is added again to carry out ortho-nitration reaction. After the reaction is completed, 2,4-dinitroaniline is obtained by post-treatment.

[0011] Further, in step S1, nitric acid is added to carry out a nitration reaction, and the molar ratio of benzene to nitric acid is 1:(1-1.2).

[0012] Furthermore, in step S1, the reaction temperature of the system is controlled at 0-10℃ and the reaction time is 0.5-1.0h.

[0013] Further, in step S1, the mass ratio of benzene to concentrated sulfuric acid is 1:(5.0-5.5). In step S2, the amount of water added is 10%-20% of the total mass of the nitrobenzene-containing system.

[0014] Further, in step S2, the catalyst is selected from at least one of Pd / C and Raney nickel; The molar ratio of benzene in step S1 to catalyst in step S2 is 1:(0.03-0.08).

[0015] Furthermore, in step S2, hydrogen gas is introduced to carry out a catalytic hydrogenation reaction at a pressure of 2-3 MPa and a temperature of 50-80℃.

[0016] Furthermore, in step S3, the reaction temperature for the para-nitration reaction is 0-5℃ and the reaction time is 0.5-1.0h.

[0017] Furthermore, in step S3, the molar ratio of nitric acid added during the para-nitration reaction to benzene in step S1 is (0.9-1.1):1.

[0018] Furthermore, in step S3, the ortho-nitration reaction is carried out at a temperature of 5-10°C and a reaction time of 0.5-1.0 h.

[0019] Furthermore, in step S3, the molar ratio of nitric acid added during the ortho-nitration reaction to benzene in step S1 is (1.0-1.2):1.

[0020] The beneficial effects of this invention are: This invention uses benzene as a starting material, avoiding the high-cost route of existing technologies that use 2,4-dinitrochlorobenzene as a raw material. Benzene is a basic chemical raw material that is widely available and inexpensive. Furthermore, the concentrated sulfuric acid, concentrated nitric acid, and catalyst used in each step of this invention can all be recycled and reused, resulting in high atom economy and a significantly lower overall production cost compared to existing ammonolysis processes.

[0021] This invention designs step S1 (nitration of benzene to nitrobenzene) and step S2 (catalytic hydrogenation of nitrobenzene to aniline) as a one-pot series operation: after the S1 reaction is completed, water is directly added to the system for dilution, and the catalytic hydrogenation reaction can proceed without separating nitrobenzene. This design eliminates intermediate operations such as separation, washing, and drying of nitrobenzene, reduces solvent consumption and operational losses, lowers equipment investment and labor intensity, and improves the overall economic efficiency and operability of the process.

[0022] In step S3 of this invention, a stepwise nitration strategy of "para-nitration followed by dehydration and then ortho-nitration" is employed, which is more conducive to obtaining the target product with high yield and high purity. The principle is as follows: In the para-nitration stage, water dilution exists in the system, the acid concentration is low, and aniline mainly exists in the free state. The strong ortho-para-positional directing effect of -NH2 allows the first nitro group to be selectively introduced into the para position, effectively avoiding the formation of meta-byproducts. In the ortho-nitration stage after dehydration, the dehydration treatment increases the acid concentration of the system. After the p-nitroaniline is protonated, the second nitro group is selectively introduced into the ortho position (2-position) of the amino group under high acid conditions, while avoiding excessive nitration to generate byproducts such as 2,4,6-trinitroaniline. The crude 2,4-dinitroaniline obtained by this method can achieve an HPLC purity of over 99%, which can meet the requirements for industrial use without complex purification, and the product yield is high.

[0023] Compared with existing ammonolysis processes (160-170℃, 0.5-1.0MPa), the main reaction conditions of this invention are milder. The nitration reactions in steps S1 and S3 are both performed at atmospheric pressure, with the reaction temperature controlled within the range of 0-10℃, effectively suppressing the exothermic risk of the nitration reaction and avoiding the safety hazards caused by high-temperature nitration. The catalytic hydrogenation reaction in step S2 is carried out at a pressure of 2-3MPa and a temperature of 50-80℃, which are conventional hydrogenation conditions, facilitating industrial-scale safety control. No highly corrosive substances such as hydrogen chloride are generated throughout the process, resulting in minimal corrosion to reaction equipment, extending equipment lifespan, and reducing maintenance costs.

[0024] Furthermore, the process of this invention enables the recycling and reuse of various materials: concentrated sulfuric acid in the nitration reaction can be recovered and reused after concentration and dehydration; the catalyst in the catalytic hydrogenation reaction can also be recovered and recycled; the overall process generates little wastewater and there is no discharge of high-salt organic wastewater; the reaction system is entirely aqueous, requiring no organic solvents, thus meeting the requirements of green chemistry and clean production. Each step uses conventional reaction equipment, eliminating the need for unconventional equipment such as microreactors or special corrosion-resistant alloys; the wide operating parameter window facilitates technology transfer and large-scale production from the laboratory to industrial applications. Attached Figure Description

[0025] Figure 1 The synthetic route for 2,4-dinitroaniline; Figure 2 The diagram shows the synthesis process of 2,4-dinitroaniline. Figure 3 The HPLC spectrum of 2,4-dinitroaniline obtained in Example 1; Figure 4 The HPLC spectrum of 2,4-dinitroaniline obtained in Example 2; Figure 5 The image shows the 1H NMR spectrum of 2,4-dinitroaniline. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0028] A method for preparing 2,4-dinitroaniline, wherein the preparation method comprises: S1. In a concentrated sulfuric acid system, benzene undergoes a nitration reaction to obtain a system containing nitrobenzene; S2. After diluting the nitrobenzene-containing system with water, a catalytic hydrogenation reaction is carried out to react the nitrobenzene into aniline. After the reaction is completed, the catalyst is filtered off to obtain the aniline-containing system. S3. Concentrated nitric acid is added to the aniline-containing system to carry out the para-nitration reaction. After the reaction, the system is dehydrated, and concentrated nitric acid is added again to carry out the ortho-nitration reaction. After the reaction, post-treatment yields 2,4-dinitroaniline. The specific synthetic route and process are as follows: Figure 1 and Figure 2 As shown.

[0029] Specifically, in step S1, nitric acid is added to carry out a nitration reaction, and the molar ratio of benzene to nitric acid is 1:(1-1.2).

[0030] Specifically, in step S1, the reaction temperature of the system is controlled at 0-10℃ and the reaction time is 0.5-1.0h.

[0031] More specifically, in step S1, when the nitration reaction is carried out, benzene is first added to the concentrated sulfuric acid system, and then concentrated nitric acid is slowly added to carry out the nitration reaction. By slowly adding concentrated nitric acid, the temperature in the system is controlled to not exceed 10°C.

[0032] Specifically, in step S1, the mass ratio of benzene to concentrated sulfuric acid is 1:(5.0-5.5). In step S2, the amount of water added is 10%-20% of the total mass of the nitrobenzene-containing system.

[0033] Specifically, in step S2, the catalyst is selected from at least one of Pd / C and Raney nickel; The molar ratio of benzene in step S1 to catalyst in step S2 is 1:(0.03-0.08).

[0034] Specifically, in step S2, hydrogen gas is introduced to carry out a catalytic hydrogenation reaction at a pressure of 2-3 MPa and a temperature of 50-80°C.

[0035] More specifically, the catalytic hydrogenation reaction in step S2 ends when the pressure no longer decreases, and the reaction time is 2-6 hours.

[0036] Specifically, in step S3, controlling the reaction temperature at 0-5℃ allows for better control of the reaction process and avoids the generation of excessive byproducts. Furthermore, operating at 0-5℃ allows for the removal of reaction heat at low temperatures, preventing "runaway" phenomena caused by localized overheating and mitigating the risk of polynitration or explosion.

[0037] Specifically, in step S3, the molar ratio of nitric acid added during the para-nitration reaction to benzene in step S1 is (0.9-1.1):1. Since para-nitration is carried out under low acid concentration (containing water) conditions, there is a significant amount of water in the system, diluting the nitric acid, but it is still sufficient as a source of the electrophilic reagent NO⁺. Excessive nitric acid increases the risk of side reactions in the ortho-nitration stage (premature introduction of a second nitro group). Insufficient nitric acid results in incomplete para-nitration, leaving some aniline residue. In the ortho-nitration stage, para- and ortho-nitration competition will occur simultaneously, reducing regioselectivity.

[0038] More specifically, after the para-nitration reaction is completed, the system is dehydrated by distillation until the water content in the system is no more than 10 wt% (the water content in the system can be calculated theoretically before dehydration, and the water content in the system after dehydration can be judged based on the distillation water). Then, concentrated nitric acid is added to carry out the ortho-nitration reaction.

[0039] Specifically, in step S3, the ortho-nitration reaction is carried out at a temperature of 5-10℃ for a time of 0.5-1.0 h. After para-nitration, p-nitroaniline (p-NA) is generated in the system. Due to the strong electron-withdrawing effect of the nitro group, the electron cloud density on the benzene ring of p-nitroaniline is significantly reduced, and its further nitration reaction rate is slower than that of aniline. To maintain a reasonable reaction rate, the temperature needs to be appropriately increased to increase the molecular collision energy so that the reaction can be completed within an acceptable time. Although the temperature is slightly higher, it is still controlled at ≤10℃ because p-nitroaniline is easily further nitrated to 2,4,6-trinitroaniline or undergoes oxidative degradation at high temperatures. The 5-10℃ range provides a sufficiently fast but not excessive reaction window, which ensures the selectivity of ortho-nitration (the ortho position remains relatively activated after amino protonation) while suppressing the trinitration side reaction.

[0040] Specifically, in step S3, the molar ratio of nitric acid added during the ortho-nitration reaction to benzene in step S1 is (1.0-1.2):1.

[0041] In step S3 of this invention, a stepped temperature control mode is used, first performing para-nitration at low temperature (0-5℃), then ortho-nitration at medium-low temperature (5-10℃), and the acid concentration is adjusted in conjunction with the dehydration step, thus achieving precise control over the introduction positions of the two nitro groups. This ensures high purity (>97%) while avoiding the cumbersome group protection-nitration-hydrolysis route in traditional methods.

[0042] More specifically, after the reaction is complete, the reaction solution in the system is slowly poured into crushed ice (the mass of the crushed ice is 1-2 times the mass of the reaction solution), stirred for 20-40 minutes, filtered, and dried to obtain the target product 2,4-dinitroaniline. The filtered aqueous phase is concentrated and dehydrated, allowing for the recovery and reuse of sulfuric acid.

[0043] More specifically, in the preparation process of the 2,4-dinitroaniline, the sulfuric acid used is concentrated sulfuric acid or fuming sulfuric acid with a mass concentration of not less than 98%; and the nitric acid used is concentrated nitric acid with a mass concentration of 68%-98%.

[0044] Example 1: Preparation of 2,4-dinitroaniline.

[0045] The preparation method of 2,4-dinitroaniline is as follows: (1) Preparation of the nitrobenzene-containing system: 98% concentrated sulfuric acid was added to a stirred reactor, the stirring was turned on, and the temperature was lowered to 0-10℃ by circulating coolant. Benzene was added while stirring. After the system was mixed evenly, 98% concentrated nitric acid was slowly added. The temperature inside the reactor was controlled at 0-10℃ during the feeding process. After the addition was completed, the system was kept at 5℃ and stirred for 30 min to obtain the nitrobenzene-containing system. The molar ratio of benzene to nitric acid was 1:1, and the mass ratio of benzene to concentrated sulfuric acid was 1:5.2.

[0046] (2) Preparation of the aniline-containing system: After diluting the nitrobenzene-containing system with water, a Pd / C catalyst was added, hydrogen gas was introduced to purge and completely replace the air in the reactor, the pressure was controlled at 2-3 MPa, the reaction temperature was 60℃, and the reaction was stopped when the pressure no longer decreased. After the reaction, the catalyst was filtered off to obtain the aniline-containing system. The amount of water added was 15% of the total mass of the nitrobenzene-containing system, and the molar ratio of benzene to catalyst was 1:0.03.

[0047] (3) Preparation of 2,4-dinitroaniline: The temperature of the aniline-containing system is controlled at 0-5℃. 98% concentrated nitric acid is slowly added to the aniline-containing system (the molar ratio of the amount of nitric acid added to benzene in step (1) is 1:1). The para-nitration reaction is carried out at 3℃ for 0.5h.

[0048] The system was dehydrated by distillation (to the point that the water content in the system was ≤7.5wt%), and the temperature in the system was controlled at 5-10℃. Then, 98% concentrated nitric acid was slowly added again (the molar ratio of the amount of nitric acid added to benzene in step (1) was 1:1). The ortho-nitration reaction was carried out at 8℃ for 0.5h.

[0049] After the reaction was complete, the reaction solution was slowly poured into crushed ice (the mass of the crushed ice was equal to the mass of the reaction solution). After stirring for 30 minutes, the mixture was filtered and dried to obtain the target product, 2,4-dinitroaniline. The yield of 2,4-dinitroaniline was 94.3%, and the purity determined by HPLC was 99.64%. The HPLC chromatogram is shown below. Figure 3 As shown in Table 1 below, the specific data and the MRI results are as follows. Figure 5As shown, the NMR test conditions and data are as follows: 1 H NMR (DMSO- d 6 300MHz): δ=7.32(d, 1H), δ=7.42(s, 2H), δ=8.31(d, 1H), δ=8.43(s, 1H).

[0050] Table 1 HPLC data of Example 1

[0051] Example 2: Preparation of 2,4-dinitroaniline.

[0052] The preparation method of 2,4-dinitroaniline is as follows: (1) Preparation of the nitrobenzene-containing system: 98% concentrated sulfuric acid was added to a stirred reactor, the stirring was turned on, and the temperature was lowered to 0-10℃ by circulating coolant. Benzene was added while stirring. After the system was mixed evenly, 98% concentrated nitric acid was slowly added. The temperature inside the reactor was controlled at 0-10℃ during the feeding process. After the addition was completed, the system was kept at 0℃ and stirred for 30 min to obtain the nitrobenzene-containing system. The molar ratio of benzene to nitric acid was 1:1.2, and the mass ratio of benzene to concentrated sulfuric acid was 1:5.5.

[0053] (2) Preparation of the aniline-containing system: After diluting the nitrobenzene-containing system with water, Raney nickel catalyst was added, hydrogen gas was introduced to purge and completely replace the air in the reactor, the pressure was controlled at 2-3 MPa, the reaction temperature was 60℃, and the reaction was stopped when the pressure no longer decreased. After the reaction, the catalyst was filtered off to obtain the aniline-containing system. The amount of water added was 20% of the total mass of the nitrobenzene-containing system, and the molar ratio of benzene to catalyst was 1:0.08.

[0054] (3) Preparation of 2,4-dinitroaniline: The temperature of the aniline-containing system is controlled at 0-5℃. 98% concentrated nitric acid is slowly added to the aniline-containing system (the molar ratio of the amount of nitric acid added to benzene in step (1) is 1.1:1). The para-nitration reaction is carried out at 5℃ for 0.5h.

[0055] The system was dehydrated by distillation (the water content in the system was ≤9wt%), the temperature in the system was controlled at 5-10℃, and 98% concentrated nitric acid was slowly added again (the molar ratio of the amount of nitric acid added to benzene in step (1) was 1:1). The ortho-nitration reaction was carried out at 10℃ for 0.5h.

[0056] After the reaction was complete, the reaction solution was slowly poured into crushed ice (the mass of the crushed ice being equal to the mass of the reaction solution). After stirring for 30 minutes, the mixture was filtered and dried to obtain the target product, 2,4-dinitroaniline. The yield of 2,4-dinitroaniline was 93.2%, and the purity determined by HPLC was 99.97%. Figure 4 As shown in Table 2 below, the specific data is as follows.

[0057] Table 2 HPLC data of Example 2

[0058] Example 3: Preparation of 2,4-dinitroaniline.

[0059] The preparation method of 2,4-dinitroaniline is as follows: (1) Preparation of the nitrobenzene-containing system: 98% concentrated sulfuric acid was added to a stirred reactor, the stirring was turned on, and the temperature was lowered to 0-10℃ by circulating coolant. Benzene was added while stirring. After the system was mixed evenly, 98% concentrated nitric acid was slowly added. The temperature inside the reactor was controlled at 0-10℃ during the feeding process. After the addition was completed, the system was kept at 0℃ and stirred for 60 min to obtain the nitrobenzene-containing system. The molar ratio of benzene to nitric acid was 1:1, and the mass ratio of benzene to concentrated sulfuric acid was 1:5.0.

[0060] (2) Preparation of the aniline-containing system: After diluting the nitrobenzene-containing system with water, a Pd / C catalyst was added, hydrogen gas was introduced to purge and completely replace the air in the reactor, the pressure was controlled at 2-3 MPa, the reaction temperature was 60℃, and the reaction was stopped when the pressure no longer decreased. After the reaction, the catalyst was filtered off to obtain the aniline-containing system. The amount of water added was 10% of the total mass of the nitrobenzene-containing system, and the molar ratio of benzene to catalyst was 1:0.05.

[0061] (3) Preparation of 2,4-dinitroaniline: The temperature of the aniline-containing system is controlled at 0-5℃. 98% concentrated nitric acid is slowly added to the aniline-containing system (the molar ratio of the amount of nitric acid added to benzene in step (1) is 0.9:1). The para-nitration reaction is carried out at 0℃ for 1.0h.

[0062] The system was dehydrated by distillation (until the water content in the system was ≤5wt%), the temperature in the system was controlled at 5-10℃, and 98% concentrated nitric acid was slowly added again (the molar ratio of the amount of nitric acid added to benzene in step (1) was 1.2:1). The ortho-nitration reaction was carried out at 5℃ for 1.0h.

[0063] After the reaction was complete, the reaction solution was slowly poured into crushed ice (the mass of the crushed ice being equal to the mass of the reaction solution). After stirring for 30 minutes, the mixture was filtered and dried to obtain the target product, 2,4-dinitroaniline. The yield of 2,4-dinitroaniline was 93.1%, and the purity determined by HPLC was 99.45%. Preparation of Comparative Example 1: 2,4-Dinitroaniline.

[0064] 2,4-Dinitroaniline was prepared using the same method as in Example 1, except that in step (3) of Comparative Example 1, the para-nitration reaction and the ortho-nitration reaction were carried out simultaneously, and the specific conditions were as follows: (1) Preparation of nitrobenzene-containing system: Same as in Example 1.

[0065] (2) Preparation of aniline-containing system: Same as in Example 1.

[0066] (3) Preparation of 2,4-dinitroaniline: The system was dehydrated by distillation (the water content in the system was ≤7.5wt%), the temperature in the system was controlled at 0-10℃, and 98% concentrated nitric acid was slowly added (the molar ratio of the amount of nitric acid added to benzene in step (1) was 2:1). The reaction was carried out at 5℃ for 1.0h.

[0067] After the reaction was completed, the reaction solution in the system was slowly poured into crushed ice (the mass of the crushed ice was 1 times the mass of the reaction solution), stirred for 30 min, filtered and dried to obtain the target product 2,4-dinitroaniline. The yield of 2,4-dinitroaniline was 89%, and the purity determined by HPLC was 81.40%.

[0068] A comparison of the results from Comparative Example 1 and Example 1 shows that in the one-step nitration process, the high concentration of nitric acid and the exothermic reaction can lead to over-nitration and the formation of 2,4,6-trinitroaniline. Furthermore, the one-step method makes it difficult to precisely control the order of introduction of the two nitro groups. When the first nitro group is introduced, the orientation effect of the second nitro group changes, resulting in the simultaneous presence of multiple nitration intermediates in the system and cross-reactions leading to an increase in byproducts. In contrast, the stepwise nitration method of this invention first selectively generates p-nitroaniline with a near-theoretical amount of nitric acid in the para-nitration stage, followed by dehydration and then ortho-nitration, avoiding a chaotic reaction pathway and thus achieving higher yield and purity.

[0069] Comparative Example 2: Preparation of 2,4-dinitroaniline.

[0070] 2,4-Dinitroaniline was prepared using the same method as in Example 1, except that in step (3) of Comparative Example 2, the aniline-containing system was first dehydrated before undergoing the para-nitration reaction. The specific steps and conditions are as follows: (1) Preparation of nitrobenzene-containing system: Same as in Example 1.

[0071] (2) Preparation of aniline-containing system: Same as in Example 1.

[0072] (3) Preparation of 2,4-dinitroaniline: The system was dehydrated by distillation (the water content in the system was ≤7.5wt%), the temperature of the aniline-containing system was controlled at 0-5℃, and 98% concentrated nitric acid was slowly added to the aniline-containing system (the molar ratio of the amount of nitric acid added to benzene in step (1) was 1:1). The para-nitration reaction was carried out at 3℃ for 0.5h.

[0073] The temperature within the system was controlled at 5-10℃, and concentrated nitric acid (98% concentration) was slowly added again (the molar ratio of the added nitric acid to benzene in step (1) was 1:1). The ortho-nitration reaction was carried out at 8℃ for 0.5 h. After the reaction was completed, the reaction solution in the system was slowly poured into crushed ice (the mass of the crushed ice was 1 times the mass of the reaction solution), stirred for 30 min, filtered, and dried to obtain the target product 2,4-dinitroaniline. The yield of 2,4-dinitroaniline was 90%, and the purity determined by HPLC was 80.13%.

[0074] A comparison of the results from Comparative Example 2 and Example 1 shows that the para-nitration stage requires a low acid concentration environment to maintain aniline in a free state, thereby fully utilizing the strong ortho-para directing effect of -NH2. If dehydration is performed first, the water content in the system decreases, and the concentrations of sulfuric acid and nitric acid increase, making it easier for aniline to be protonated into aniline salt (Ph-NH3⁺). The -NH3⁺ of the aniline salt is a strong meta-directing group, and the nitration reaction will mainly occur at the meta position, generating a large amount of meta-nitroaniline byproducts. Therefore, para-nitration under conditions of no dehydration and low acid concentration is beneficial for improving para-selectivity and reducing meta-byproducts. Example 1 first completed highly selective para-nitration in a low-acid system without dehydration, and then performed ortho-nitration after dehydration, which is more conducive to the high purity and high yield of the final product.

[0075] Comparative Example 3: Preparation of 2,4-dinitroaniline.

[0076] 2,4-Dinitroaniline was prepared using the same method as in Example 1, except that in step (3) of Comparative Example 3, no dehydration treatment was performed. The specific conditions for the steps are as follows: (1) Preparation of nitrobenzene-containing system: Same as in Example 1.

[0077] (2) Preparation of aniline-containing system: Same as in Example 1.

[0078] (3) Preparation of 2,4-dinitroaniline: The temperature of the aniline-containing system is controlled at 0-5℃. 98% concentrated nitric acid is slowly added to the aniline-containing system (the molar ratio of the amount of nitric acid added to benzene in step (1) is 1:1). The para-nitration reaction is carried out at 3℃ for 0.5h.

[0079] The temperature in the system is controlled at 5-10℃. 98% concentrated nitric acid is added slowly again (the molar ratio of the amount of nitric acid added to benzene in step (1) is 1:1). The ortho-nitration reaction is carried out at 8℃ for 0.5h.

[0080] After the reaction was completed, the reaction solution in the system was slowly poured into crushed ice (the mass of the crushed ice was 1 times the mass of the reaction solution), stirred for 30 min, filtered and dried to obtain the target product 2,4-dinitroaniline. The yield of 2,4-dinitroaniline was 64%, and the purity determined by HPLC was 65.03%.

[0081] A comparison of the results from Comparative Example 3 and Example 1 shows that the ortho-nitration reaction requires a high acid concentration. When the system contains a large amount of water, the nitric acid is diluted, and the concentration of the electrophilic reagent NO2⁺ decreases significantly. Due to the strong electron-withdrawing effect of the nitro group, the electron cloud density of the benzene ring in p-nitroaniline is significantly reduced, and its further nitration reaction rate is inherently slower than that of aniline. If carried out under conditions containing a large amount of water, the reaction rate is extremely low, and even with extended reaction time, complete conversion is difficult, resulting in a large amount of p-nitroaniline residue, leading to a significant decrease in yield and purity. Example 1, by performing dehydration treatment between the two nitrations, controls the moisture content of the system to a low level, ensuring the high acid concentration and strong nitration capacity required for ortho-nitration, thereby achieving the efficient conversion of p-nitroaniline to 2,4-dinitroaniline.

[0082] Comparative Example 4: Preparation of 2,4-dinitroaniline.

[0083] 2,4-Dinitroaniline was prepared using the same method as in Example 1, except that in step (3) of Comparative Example 4, the temperature conditions for the para-nitration reaction were increased. The specific conditions are as follows: (1) Preparation of nitrobenzene-containing system: Same as in Example 1.

[0084] (2) Preparation of aniline-containing system: Same as in Example 1.

[0085] (3) Preparation of 2,4-dinitroaniline: The temperature of the aniline-containing system is controlled at 5-10℃. 98% concentrated nitric acid is slowly added to the aniline-containing system (the molar ratio of the amount of nitric acid added to benzene in step (1) is 1:1). The para-nitration reaction is carried out at 10℃ for 0.5h.

[0086] The system was dehydrated by distillation (to the point that the water content in the system was ≤7.5wt%), and the temperature in the system was controlled at 5-10℃. Then, 98% concentrated nitric acid was slowly added again (the molar ratio of the amount of nitric acid added to benzene in step (1) was 1:1). The ortho-nitration reaction was carried out at 8℃ for 0.5h.

[0087] After the reaction was completed, the reaction solution in the system was slowly poured into crushed ice (the mass of the crushed ice was 1 times the mass of the reaction solution), stirred for 30 min, filtered and dried to obtain the target product 2,4-dinitroaniline. The yield of 2,4-dinitroaniline was 90.22%, and the purity determined by HPLC was 81.02%.

[0088] The comparison between the results of Comparative Example 4 and Example 1 shows that controlling the ortho-nitration reaction temperature at 0-5℃ can better control the reaction process, avoid the generation of too many by-products, and improve the yield and purity of the product.

[0089] Comparative Example 5: Preparation of 2,4-dinitroaniline.

[0090] 2,4-Dinitroaniline was prepared using the same method as in Example 1, except that in step (3) of Comparative Example 5, the amount of nitric acid added was increased during the para-nitration reaction. The specific conditions are as follows: (1) Preparation of nitrobenzene-containing system: Same as in Example 1.

[0091] (2) Preparation of aniline-containing system: Same as in Example 1.

[0092] (3) Preparation of 2,4-dinitroaniline: The temperature of the aniline-containing system is controlled at 0-5℃. 98% concentrated nitric acid is slowly added to the aniline-containing system (the molar ratio of the amount of nitric acid added to benzene in step (1) is 1.5:1). The para-nitration reaction is carried out at 3℃ for 0.5h.

[0093] The system was dehydrated by distillation (to the point that the water content in the system was ≤7.5wt%), and the temperature in the system was controlled at 5-10℃. Then, 98% concentrated nitric acid was slowly added again (the molar ratio of the amount of nitric acid added to benzene in step (1) was 1:1). The ortho-nitration reaction was carried out at 8℃ for 0.5h.

[0094] After the reaction was completed, the reaction solution in the system was slowly poured into crushed ice (the mass of the crushed ice was 1 times the mass of the reaction solution), stirred for 30 min, filtered and dried to obtain the target product 2,4-dinitroaniline. The yield of 2,4-dinitroaniline was 85.33%, and the purity determined by HPLC was 81.03%.

[0095] A comparison of the results from Comparative Example 5 and Example 1 shows that excess nitric acid in the aqueous system increases the acid concentration, causing some aniline to protonate into aniline salts, reducing para-selectivity and increasing meta-byproducts. Secondly, the residual nitric acid is not removed in the subsequent dehydration step. When the system enters the ortho-nitration stage after dehydration, the total amount of nitric acid exceeds the design value, leading to over-nitration and the generation of byproducts such as 2,4,6-trinitroaniline. Controlling the amount of nitric acid used in para-nitration within a suitable range ensures complete conversion while avoiding the aforementioned problems, achieving high selectivity and high yield in para-nitration and providing a high-purity p-nitroaniline intermediate for subsequent ortho-nitration.

[0096] Comparative Example 6: Preparation of 2,4-dinitroaniline.

[0097] 2,4-Dinitroaniline was prepared using a conventional method (using 2,4-dinitrochlorobenzene as a raw material). The specific preparation method is as follows: 101g of 2,4-dinitrochlorobenzene, 45g of urea, and 150g of 50% ethanol aqueous solution were added to a reaction vessel. The reaction vessel was heated to 110°C, the pressure was controlled at 0.2MPa, and the reaction was maintained at this temperature for 3 hours. The reaction endpoint was detected by liquid chromatography. After the reaction was completed, the reaction product was centrifuged, filtered, and washed to obtain a yellow powdery 2,4-dinitroaniline product. The purity of the product prepared in this example was tested to be 90.03%, and the yield was 88.1%.

[0098] A comparison of the results from Comparative Example 6 and Example 1 reveals the following significant differences in the traditional process: high raw material costs (2,4-dinitrochlorobenzene is much more expensive than benzene), demanding reaction conditions requiring high pressure, severe equipment corrosion (HCl release during the reaction), and high waste treatment pressure (high-salt organic wastewater). In contrast, this application uses benzene as the starting material, employing a one-pot process involving hydrogenation and stepwise nitration, operating entirely at atmospheric or low-to-medium pressure, generating no highly corrosive substances, and allowing for the recycling of sulfuric acid and catalyst, resulting in minimal wastewater generation. It surpasses this invention in terms of safety, environmental friendliness, and economic efficiency. This invention provides a greener, safer, lower-cost, and easily industrialized new route.

[0099] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0100] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing 2,4-dinitroaniline, characterized in that, The preparation method is as follows: S1. In a concentrated sulfuric acid system, benzene undergoes a nitration reaction to obtain a system containing nitrobenzene; S2. After diluting the nitrobenzene-containing system with water, a catalytic hydrogenation reaction is carried out to react the nitrobenzene into aniline. After the reaction is completed, the catalyst is filtered off to obtain the aniline-containing system. S3. Add concentrated nitric acid to the aniline-containing system to carry out para-nitration reaction. After the reaction is completed, the system is dehydrated and concentrated nitric acid is added again to carry out ortho-nitration reaction. After the reaction is completed, 2,4-dinitroaniline is obtained by post-treatment.

2. The method for preparing 2,4-dinitroaniline according to claim 1, characterized in that, In step S1, nitric acid is added to carry out a nitration reaction, and the molar ratio of benzene to nitric acid is 1:(1-1.2).

3. The method for preparing 2,4-dinitroaniline according to claim 1, characterized in that, In step S1, the reaction temperature of the system is controlled at 0-10℃ and the reaction time is 0.5-1.0h.

4. The method for preparing 2,4-dinitroaniline according to claim 1, characterized in that, In step S1, the mass ratio of benzene to concentrated sulfuric acid is 1:(5.0-5.5). In step S2, the amount of water added is 10%-20% of the total mass of the nitrobenzene-containing system.

5. The method for preparing 2,4-dinitroaniline according to claim 1, characterized in that, In step S2, the catalyst is selected from at least one of Pd / C and Raney nickel; The molar ratio of benzene in step S1 to catalyst in step S2 is 1:(0.03-0.08).

6. The method for preparing 2,4-dinitroaniline according to claim 1, characterized in that, In step S2, hydrogen gas is introduced to carry out a catalytic hydrogenation reaction at a pressure of 2-3 MPa and a temperature of 50-80℃.

7. The method for preparing 2,4-dinitroaniline according to claim 1, characterized in that, In step S3, the reaction temperature is 0-5℃ and the reaction time is 0.5-1.0h during the para-nitration reaction.

8. The method for preparing 2,4-dinitroaniline according to claim 1, characterized in that, In step S3, the molar ratio of nitric acid added during the para-nitration reaction to benzene in step S1 is (0.9-1.1):

1.

9. The method for preparing 2,4-dinitroaniline according to claim 1, characterized in that, In step S3, the ortho-nitration reaction is carried out at a temperature of 5-10℃ and a reaction time of 0.5-1.0h.

10. The method for preparing 2,4-dinitroaniline according to claim 1, characterized in that, In step S3, the molar ratio of nitric acid added during the ortho-nitration reaction to benzene in step S1 is (1.0-1.2):1.

Images