A process for preparing p-phenylenediamine from nitrobenzene in one pot

Abstract

The present invention relates to the technical field of organic chemical synthesis, and in particular to a process for preparing p-phenylenediamine by a one-pot process from nitrobenzene, wherein the process is as follows: S1, aminating reaction: under an inert gas, in a solvent system, nitrobenzene and an amino salt are subjected to an aminating reaction under heating and pressurization conditions, and a reaction solution is obtained after the reaction is completed; S2, reduction reaction: a catalyst is added to the reaction solution, hydrogen is passed through for a hydrogenation reduction reaction, and p-phenylenediamine is obtained by hydrolysis and post-processing after the reaction is completed. The amino salt is at least one of sodium amide, lithium amide, and potassium amide. The aminating reaction temperature is 120-180°C, the aminating reaction pressure is 3-8Mpa, and the aminating reaction time is 6-10h. The process route is rationally designed, raw material cost is low and easily available, conversion rate is high, atom utilization rate is high, operation is simple, loss is reduced, and there is potential for industrial application.

Description

Technical Field

[0001] The invention relates to a process for preparing p-phenylenediamine by a one-pot process from nitrobenzene, belonging to the technical field of organic chemical synthesis. Background Art

[0002] Paraphenylenediamine, abbreviated as p-PAD, appears as white to pale purple flaky crystals at room temperature. It readily oxidizes to purple or dark brown crystals upon exposure to air. Paraphenylenediamine is an important chemical intermediate with a wide range of applications in dyes, rubber antioxidants, polymers, and other fields. Paraphenylenediamine is an intermediate in azo disperse dyes, direct dyes, acid dyes, sulfur dyes, and fur dyes, and is an active ingredient in hair dyes. It has a strong affinity for keratin in hair. Paraphenylenediamine (PPTA), derived from paraphenylenediamine, has a wide range of applications in aerospace, military, and other fields, such as bulletproof vests and tank armor, due to its low density, high strength, excellent toughness, high-temperature resistance, and ease of processing and molding. Paraphenylenediamine-based rubber antioxidants also play an important role among rubber antioxidants. Antioxidants prepared from p-phenylenediamine are highly effective anti-ozonants, excellent antioxidants, anti-flex cracking agents, chain breakage inhibitors, and metal chelating agents. p-phenylenediamine can be used as a curing agent for epoxy resins, significantly increasing the glass transition temperature of the cured product. This demonstrates that p-phenylenediamine is an important organic synthesis intermediate with a wide range of applications.

[0003] Currently, p-phenylenediamine is primarily produced industrially using chlorobenzene as a starting material through processes such as mixed acid nitration, liquid ammonia ammonolysis, and hydrogenation reduction. For example, patent application publication number CN117486729A discloses a method and apparatus for producing p-phenylenediamine, which comprises amination with liquid ammonia, filtration, melting, dehydration, rectification, crystallization, and secondary crystallization. Patent application publication number CN112209836A discloses a method for producing p-phenylenediamine, which comprises reacting p-dichlorobenzene with ammonia in the presence of a copper catalyst and a ligand to produce p-phenylenediamine. Patent application publication number CN109336769A discloses a method for producing p-phenylenediamine, which utilizes p-dichlorobenzene and ammonia as raw materials, a copper salt as a catalyst, and a Mannich base as a ligand in the reaction system to produce p-phenylenediamine.

[0004] However, existing preparation methods produce large amounts of acidic wastewater during the mixed acid nitration process, which causes severe pollution. Liquid ammonia ammonolysis is carried out in a high-temperature, high-pressure system, posing high safety risks. Furthermore, halide salts, as byproducts of ammonolysis, can cause severe environmental pollution. Therefore, developing a scientific, green, safe, and efficient synthesis method and route is of great significance and value for the industrial production of p-phenylenediamine. Summary of the Invention

[0005] The present invention addresses the deficiencies in the prior art and provides a process for preparing p-phenylenediamine from nitrobenzene in a one-pot process. The process has a reasonable route design, low raw material cost and easy availability, high conversion rate, high atom utilization rate, simple operation, reduced losses, and potential industrial application prospects.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: a process for preparing p-phenylenediamine from nitrobenzene in a one-pot process, wherein:

[0007] S1. Amination reaction:

[0008] Under inert gas, in a solvent system, nitrobenzene and amino salt undergo an amination reaction under heating and pressurizing conditions, and a reaction liquid is obtained after the reaction is completed;

[0009] S2, reduction reaction:

[0010] A catalyst is added to the reaction solution, and hydrogen is introduced to carry out a hydrogenation reduction reaction. After the reaction is completed, p-phenylenediamine is obtained through hydrolysis and post-treatment.

[0011] Furthermore, in step S1, the solvent is at least one of toluene, chloroform, dichloromethane, benzene, xylene, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0012] Furthermore, in step S1, the amino salt is at least one of sodium amide, lithium amide, and potassium amide.

[0013] Furthermore, in step S1, the molar ratio of nitrobenzene to amino salt is 1:(1.2-1.8).

[0014] Furthermore, in step S1, the amination reaction temperature is 120-180° C., the amination reaction pressure is 3-8 MPa, and the amination reaction time is 6-10 h.

[0015] Furthermore, in step S2, the catalyst is at least one of Raney Ni, Pd / C, and Zn.

[0016] Furthermore, in step S2, the hydrogen pressure in the hydrogenation reduction reaction system is 1-3 MPa.

[0017] Furthermore, in step S2, the hydrogenation reduction reaction temperature is 60-100° C., and the hydrogenation reduction reaction time is 2-5 h.

[0018] Furthermore, in step S2, the hydrolysis and post-treatment process is as follows: the reaction system cooled to room temperature is slowly added to cooling water for hydrolysis, the insoluble matter is filtered out and the pH is adjusted to acidic, the organic phase is allowed to stand for phase separation, the organic phase is extracted with acidic water, the aqueous phases are combined, and then the pH is adjusted to alkaline, and finally the p-phenylenediamine product is obtained by evaporation, crystallization, and distillation purification.

[0019] Furthermore, the pH is adjusted to an acidic pH range of less than 4, and the pH is adjusted to an alkaline pH range of more than 8.

[0020] The beneficial effects of the present invention are:

[0021] The process of the present invention synthesizes p-phenylenediamine through a one-pot process, eliminating the need for intermediate separation, resulting in simple operation, low three-waste emissions, reduced labor intensity during the production process, reduced process losses, and high material utilization. Under preferred conditions, a crude p-phenylenediamine product with a purity of over 97% and a yield of over 95% can be directly obtained without purification. After distillation and purification, a p-phenylenediamine product with a purity of over 99% and a total yield of over 90% can be obtained.

[0022] The raw materials used in the process of the present invention are cheap and easily available, and the entire process has the advantages of low cost and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the GC spectrum of the crude p-phenylenediamine obtained in Example 1;

[0024] Figure 2 The GC spectrum of the p-phenylenediamine product obtained in Example 1 is shown in FIG. DETAILED DESCRIPTION

[0025] The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0027] A process for preparing p-phenylenediamine from nitrobenzene in a one-pot process, the process comprising:

[0028] S1. Amination reaction:

[0029] Under inert gas, in a solvent system, nitrobenzene and amino salt undergo an amination reaction under heating and pressurizing conditions, and a reaction liquid is obtained after the reaction is completed;

[0030] S2, reduction reaction:

[0031] A catalyst is added to the reaction solution, and hydrogen is introduced to carry out a hydrogenation reduction reaction. After the reaction is completed, p-phenylenediamine is obtained through hydrolysis and post-treatment.

[0032] Specifically, in step S1, the solvent is at least one of toluene, chloroform, dichloromethane, benzene, xylene, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0033] The principle equation of the process for preparing p-phenylenediamine from nitrobenzene in one pot is as follows:

[0034] .

[0035] The reaction process is as follows:

[0036] .

[0037] Preferably, the solvent is toluene. When toluene is used as the solvent, it is more conducive to obtaining a high-purity crude p-phenylenediamine product in a one-step process.

[0038] More specifically, the amount of the solvent used is 3-8 times the mass of nitrobenzene.

[0039] Specifically, in step S1, the amino salt is at least one of sodium amide, lithium amide, and potassium amide.

[0040] Preferably, in step S1, the amino salt is sodium amide.

[0041] Specifically, in step S1, the molar ratio of nitrobenzene to amino salt is 1:(1.2-1.8).

[0042] Specifically, in step S1, the amination reaction temperature is 120-180° C., the amination reaction pressure is 3-8 MPa, and the amination reaction time is 6-10 h.

[0043] Specifically, in step S2, the catalyst is at least one of Raney Ni, Pd / C, and Zn.

[0044] Specifically, the amount of the catalyst used is 1%-10% of the mass of nitrobenzene.

[0045] Specifically, in step S2, the hydrogen pressure in the hydrogenation reduction reaction system is 1-3 MPa.

[0046] Specifically, in step S2, the hydrogenation reduction reaction temperature is 60-100° C., and the hydrogenation reduction reaction time is 2-5 h.

[0047] Specifically, in step S2, the hydrolysis and post-treatment process is as follows: the reaction system cooled to room temperature is slowly added to cooling water for hydrolysis, the insoluble matter is filtered out and the pH is adjusted to acidic, the organic phase is allowed to stand for phase separation, the organic phase is extracted with acidic water, the aqueous phases are combined, and then the pH is adjusted to alkaline, and finally the p-phenylenediamine product is obtained by evaporation, crystallization, and distillation.

[0048] Specifically, the pH is adjusted to an acidic pH range below 4, and the pH is adjusted to an alkaline pH range above 8.

[0049] More specifically, in the embodiments of the present invention, an inorganic acid such as hydrochloric acid or sulfuric acid is used to adjust the pH to acidic, and the acidic water used in the extraction is an aqueous solution of an inorganic acid such as hydrochloric acid or sulfuric acid, and the pH is lower than 4; an alkali such as sodium hydroxide, potassium hydroxide, or aqueous ammonia is used to adjust the pH to alkaline.

[0050] Example 1

[0051] Step 1: Add 300 mL of toluene, 0.5 mol of nitrobenzene, and 0.75 mol of sodium amide to the autoclave, tighten the autoclave lid, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the feed port of the autoclave lid, heat to 140°C, and keep the reaction temperature for 8 hours to ensure that the reaction system is in the best state for amination reaction.

[0052] Step 2: After the reactor is heated to 140°C, fill it with N2 to a pressure of 4 MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8 MPa, release the pressure to 4 MPa in time. Repeat this operation until the pressure in the reactor no longer increases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, and the N2 in the reactor is discharged.

[0053] Step 3: Add the Raney Ni catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 80°C, and keep the reaction at this temperature for 3 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0054] Step 4: After the reactor is heated to 80°C, H2 is added to the pressure of 2MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 2MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0055] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0056] Step 6: Adjust the pH of the filtrate from the previous step to 3.0, let it stand for phase separation, extract the organic phase with acidic water with pH < 4.0 three times, and combine the aqueous phases. Adjust the pH of the aqueous phase to 9.0 again, remove most of the water by vacuum rotary evaporation or cool it down, and the white solid product precipitated is the crude p-phenylenediamine. The purity of the GC test can reach 97.2%. The GC test spectrum is as follows: Figure 1 As shown, the yield is 97.8%; the GC chromatogram data of the crude p-phenylenediamine are shown in Table 1 below.

[0057] Table 1 GC chromatographic data of crude p-phenylenediamine

[0058]

[0059] The crude p-phenylenediamine was purified by distillation, and the purity of the product was up to 99.1% by GC detection. The GC detection spectrum was as follows: Figure 2 The GC chromatogram data of the purified p-phenylenediamine product are shown in Table 2 below.

[0060] Table 2 GC chromatographic data of p-phenylenediamine products

[0061]

[0062] Example 2

[0063] Step 1: Add 600 mL of toluene, 0.5 mol of nitrobenzene, and 0.6 mol of sodium amide to the autoclave, tighten the autoclave cover, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the autoclave cover, raise the temperature to 140°C, and keep the reaction temperature for 8 hours to ensure that the reaction system is in the best state for amination reaction.

[0064] Step 2: After the reactor is heated to 140°C, fill it with N2 to a pressure of 4 MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8 MPa, release the pressure to 4 MPa in time. Repeat this operation until the pressure in the reactor no longer increases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, and the N2 in the reactor is discharged.

[0065] Step 3: Add the Raney Ni catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 80°C, and keep the reaction at this temperature for 3 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0066] Step 4: After the reactor is heated to 80°C, H2 is added to the pressure of 2MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 2MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0067] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0068] Step 6: Adjust the pH of the filtrate from the previous step to 2. Allow the filtrate to stand and separate. Extract the organic phase three times with acidic water (pH < 4.0). Combine the aqueous phases. Adjust the pH of the aqueous phase to 10. Remove most of the water by vacuum rotary evaporation or cool the mixture to precipitate a white solid product, crude p-phenylenediamine. The purity as determined by GC is 97.3%, and the yield is 97.2%. Purify the crude p-phenylenediamine by distillation. The purity as determined by GC is 99.0%, and the yield is 92.0%.

[0069] Example 3

[0070] Step 1: Add 900 mL of toluene, 5.0 mol of nitrobenzene, and 6 mol of sodium amide to the autoclave, tighten the autoclave lid, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the autoclave lid charging port, raise the temperature to 140°C, and keep the reaction temperature for 8 hours to ensure that the reaction system is in the best state for amination reaction.

[0071] Step 2: After the reactor is heated to 140°C, fill it with N2 to a pressure of 4 MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8 MPa, release the pressure to 4 MPa in time. Repeat this operation until the pressure in the reactor no longer increases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, and the N2 in the reactor is discharged.

[0072] Step 3: Add the Raney Ni catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 80°C, and keep the reaction at this temperature for 3 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0073] Step 4: After the reactor is heated to 80°C, H2 is added to the pressure of 2MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 2MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0074] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0075] Step 6: Adjust the pH of the filtrate from the previous step to 1.0. Allow the filtrate to stand and separate. Extract the organic phase three times with acidic water (pH < 4.0). Combine the aqueous phases. Adjust the pH of the aqueous phase to 8.5. Remove most of the water by vacuum rotary evaporation or cool the mixture to precipitate a white solid product, crude p-phenylenediamine. The purity as determined by GC is 97.1%, and the yield is 97.0%. Purify the crude p-phenylenediamine by distillation. The purity as determined by GC is 99.1%, and the yield is 91.5%.

[0076] Example 4

[0077] Step 1: Add 600 mL of toluene, 0.5 mol of nitrobenzene, and 0.9 mol of potassium amide to the autoclave, tighten the autoclave cover, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the autoclave cover, raise the temperature to 180°C, and keep the reaction temperature for 6 hours to ensure that the reaction system is in the best state for amination reaction.

[0078] Step 2: After the reactor is heated to 180°C, fill it with N2 to a pressure of 3MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8MPa, release the pressure to 3MPa in time. Repeat this operation until the pressure in the reactor no longer increases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, and the N2 in the reactor is discharged.

[0079] Step 3: Add Pd / C catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 60°C, and keep the reaction warm for 5 hours to ensure that the reaction system is in the best state for reduction reaction.

[0080] Step 4: After the reactor is heated to 60°C, H2 is added to the pressure of 3MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 3MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0081] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0082] Step 6: The pH of the filtrate from the previous step was adjusted to 2. The filtrate was allowed to stand for phase separation. The organic phase was extracted three times with acidic water at pH < 4.0, and the aqueous phases were combined. The pH of the aqueous phase was further adjusted to 10. Most of the water was removed by vacuum rotary evaporation or cooling. A white solid product, crude p-phenylenediamine, precipitated. The purity determined by GC was 97.5%, and the yield was 97.0%. The crude p-phenylenediamine was purified by distillation, and the purity determined by GC was 99.1%, with a yield of 91.3%.

[0083] Example 5

[0084] Step 1: Add 600 mL of toluene, 0.5 mol of nitrobenzene, and 0.6 mol of lithium amide to the autoclave, tighten the autoclave cover, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the autoclave cover, raise the temperature to 120°C, and keep the reaction temperature for 10 hours to ensure that the reaction system is in the best state for amination reaction.

[0085] Step 2: After the reactor is heated to 120°C, fill it with N2 to a pressure of 8MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8MPa, release the pressure to 8MPa in time. Repeat this operation until the pressure in the reactor no longer increases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, and the N2 in the reactor is discharged.

[0086] Step 3: Add Zn catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 100°C, and keep the reaction at this temperature for 2 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0087] Step 4: After the reactor is heated to 100°C, H2 is added to the pressure of 1MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 1MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be completed, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0088] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0089] Step 6: The pH of the filtrate from the previous step was adjusted to 2. The filtrate was allowed to stand for phase separation. The organic phase was extracted three times with acidic water at pH < 4.0, and the aqueous phases were combined. The pH of the aqueous phase was further adjusted to 10. Most of the water was removed by vacuum rotary evaporation or cooling. A white solid product, crude p-phenylenediamine, precipitated. The purity of the product was 97.4% as determined by GC, and the yield was 96.9%. The crude p-phenylenediamine was purified by distillation, and the purity of the product was 99.0% as determined by GC, with a yield of 91.0%.

[0090] Example 6

[0091] Step 1: Add 300 mL of xylene, 0.5 mol of nitrobenzene, and 0.75 mol of sodium amide to the autoclave, tighten the autoclave cover, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the autoclave cover, raise the temperature to 140°C, and keep the reaction temperature for 8 hours to ensure that the reaction system is in the best state for amination reaction.

[0092] Step 2: After the reactor is heated to 140°C, fill it with N2 to a pressure of 4 MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8 MPa, release the pressure to 4 MPa in time. Repeat this operation until the pressure in the reactor no longer increases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, and the N2 in the reactor is discharged.

[0093] Step 3: Add the Raney Ni catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 80°C, and keep the reaction at this temperature for 3 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0094] Step 4: After the reactor is heated to 80°C, H2 is added to the pressure of 2MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 2MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0095] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0096] Step 6: Adjust the pH of the filtrate from the previous step to 3.0. Allow the filtrate to stand and separate. Extract the organic phase three times with acidic water (pH < 4.0). Combine the aqueous phases. Adjust the pH of the aqueous phase to 9.0. Remove most of the water by vacuum rotary evaporation or cool the mixture to precipitate a white solid product, crude p-phenylenediamine. The purity as determined by GC is 77.1%, and the yield is 97.8%. Purify the crude p-phenylenediamine by distillation. The purity as determined by GC is 99.1%, and the yield is 75%.

[0097] Example 7

[0098] Step 1: Add 300 mL of N,N-dimethylformamide, 0.5 mol of nitrobenzene, and 0.75 mol of sodium amide to the autoclave, tighten the autoclave cover, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the autoclave cover, raise the temperature to 140°C, and keep the reaction temperature for 8 hours to ensure that the reaction system is in the best state for amination reaction.

[0099] Step 2: After the reactor is heated to 140°C, fill it with N2 to a pressure of 4 MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8 MPa, release the pressure to 4 MPa in time. Repeat this operation until the pressure in the reactor no longer increases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, and the N2 in the reactor is discharged.

[0100] Step 3: Add the Raney Ni catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 80°C, and keep the reaction at this temperature for 3 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0101] Step 4: After the reactor is heated to 80°C, H2 is added to the pressure of 2MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 2MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0102] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0103] Step 6: The pH of the filtrate from the previous step was adjusted to 3.0. The filtrate was allowed to stand for phase separation. The organic phase was extracted three times with acidic water at pH < 4.0, and the aqueous phases were combined. The pH of the aqueous phase was further adjusted to 9.0. Most of the water was removed by vacuum rotary evaporation or cooling. A white solid product, crude p-phenylenediamine, precipitated. The purity determined by GC was 75.8%, and the yield was 97.9%. The crude p-phenylenediamine was purified by distillation, and the purity determined by GC was 99.0%, with a yield of 74.8%.

[0104] Example 8

[0105] Step 1: Add 300 mL of N,N-dimethylacetamide, 0.5 mol of nitrobenzene, and 0.75 mol of sodium amide to the autoclave, tighten the autoclave cover, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the autoclave cover, raise the temperature to 140°C, and keep the reaction temperature for 8 hours to ensure that the reaction system is in the best state for amination reaction.

[0106] Step 2: After the reactor is heated to 140°C, fill it with N2 to a pressure of 4 MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8 MPa, release the pressure to 4 MPa in time. Repeat this operation until the pressure in the reactor no longer increases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, and the N2 in the reactor is discharged.

[0107] Step 3: Add the Raney Ni catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 80°C, and keep the reaction at this temperature for 3 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0108] Step 4: After the reactor is heated to 80°C, H2 is added to the pressure of 2MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 2MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0109] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0110] Step 6: The pH of the filtrate from the previous step was adjusted to 3.0. The filtrate was allowed to stand for phase separation. The organic phase was extracted three times with acidic water at pH < 4.0, and the aqueous phases were combined. The pH of the aqueous phase was further adjusted to 9.0. Most of the water was removed by vacuum rotary evaporation or cooling. A white solid product, crude p-phenylenediamine, precipitated. The purity determined by GC was 76.3%, and the yield was 97.9%. The crude p-phenylenediamine was purified by distillation, and the purity determined by GC was 99.1%, with a yield of 75.2%.

[0111] The experimental results of Examples 1-8 above demonstrate that the process of the present invention can achieve a one-pot synthesis of p-phenylenediamine, which has significant advantages such as simple operation, low cost, and readily available and inexpensive raw materials. Furthermore, a comparison of the data from Examples 1, 6, 7, and 8 demonstrates that using toluene as the solvent is more conducive to obtaining a high yield and high purity p-phenylenediamine product.

[0112] Comparative Example 1

[0113] The same method as in Example 1 was used to prepare p-phenylenediamine, except that the amination reaction pressure was reduced. In this comparative example 1, the amination reaction pressure was 1 MPa. The specific process was as follows:

[0114] Step 1: Add 300 mL of toluene, 0.5 mol of nitrobenzene, and 0.75 mol of sodium amide to the autoclave, tighten the autoclave lid, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the feed port of the autoclave lid, heat to 140°C, and keep the reaction temperature for 8 hours to ensure that the reaction system is in the best state for amination reaction.

[0115] Step 2: After the reactor is heated to 140°C, fill it with N2 to a pressure of 1 MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 3 MPa, release the pressure to 1 MPa in time. After reacting for 8 hours, cool the reaction liquid to room temperature and discharge the N2 in the reactor.

[0116] Step 3: Add the Raney Ni catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 80°C, and keep the reaction at this temperature for 3 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0117] Step 4: After the reactor is heated to 80°C, H2 is added to the pressure of 2MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 2MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0118] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0119] Step 6: Adjust the pH of the filtrate from the previous step to 3.0. Allow the filtrate to stand and separate. Extract the organic phase three times with acidic water at pH < 4.0, and combine the aqueous phases. Adjust the pH of the aqueous phase to 9.0. Remove most of the water by vacuum rotary evaporation or cool the mixture to precipitate a white solid product, crude p-phenylenediamine, with a purity of 87% as determined by GC and a yield of 60.5%. Purify the crude p-phenylenediamine by distillation, achieving a purity of 99.0% as determined by GC and a yield of 42.5%.

[0120] From the comparison of the experimental results of Comparative Example 1 and Example 1, it can be seen that if the amination reaction pressure is reduced, the yield of the product decreases significantly. Therefore, the amination reaction pressure described in the present invention is more conducive to obtaining a high-yield, high-purity p-phenylenediamine product.

[0121] Comparative Example 2

[0122] The same method as in Example 1 was used to prepare p-phenylenediamine, except that the amount of sodium amide was increased. In this comparative example 2, the molar ratio of nitrobenzene to sodium amide was 1:3. The specific process was as follows:

[0123] Step 1: Add 300 mL of toluene, 0.5 mol of nitrobenzene, and 1.5 mol of sodium amide to the autoclave, tighten the lid, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the feed port of the autoclave, heat to 140°C, and keep the reaction temperature for 8 hours to ensure that the reaction system is in the best state for amination reaction.

[0124] Step 2: After the reactor is heated to 140°C, fill it with N2 to a pressure of 4 MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8 MPa, release the pressure to 4 MPa in time. Repeat this operation until the pressure in the reactor no longer increases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, and the N2 in the reactor is discharged.

[0125] Step 3: Add the Raney Ni catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 80°C, and keep the reaction at this temperature for 3 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0126] Step 4: After the reactor is heated to 80°C, H2 is added to the pressure of 2MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 2MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0127] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0128] Step 6: The pH of the filtrate from the previous step was adjusted to 3.0. The filtrate was allowed to stand for phase separation. The organic phase was extracted three times with acidic water at pH < 4.0, and the aqueous phases were combined. The pH of the aqueous phase was further adjusted to 9.0. Most of the water was removed by vacuum rotary evaporation or cooling. A white solid product, crude p-phenylenediamine, precipitated. The purity was 89.2% by GC, and the yield was 64.3%. The crude p-phenylenediamine was purified by distillation, and the purity reached 99.0% by GC, with a yield of 43.2%.

[0129] Comparison of the experimental results of Comparative Example 2 and Example 1 shows that increasing the dosage of the amino salt will lead to side reactions in the system (such as the attachment of amino groups at positions other than the para position on nitrobenzene), ultimately resulting in a decrease in the yield and purity of the product.

[0130] Comparative Example 3

[0131] The same method as in Example 1 was used to prepare p-phenylenediamine, except that the amination reaction temperature was lowered. In this comparative example 3, the amination reaction temperature was 100° C. The specific process was as follows:

[0132] Step 1: Add 300 mL of toluene, 0.5 mol of nitrobenzene, and 0.75 mol of sodium amide to the autoclave, tighten the autoclave lid, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the feed port of the autoclave lid, heat to 100°C, and keep the reaction temperature for 8 hours to ensure that the reaction system is in the best state for amination reaction.

[0133] Step 2: After the reactor is heated to 100°C, fill it with N2 to a pressure of 4MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8MPa, release the pressure to 4MPa in time. Repeat this operation. After 8 hours of reaction, the reaction liquid is cooled to room temperature and the N2 in the reactor is discharged.

[0134] Step 3: Add the Raney Ni catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 80°C, and keep the reaction at this temperature for 3 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0135] Step 4: After the reactor is heated to 80°C, H2 is added to the pressure of 2MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 2MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0136] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0137] Step 6: The pH of the filtrate from the previous step was adjusted to 3.0. The filtrate was allowed to stand for phase separation. The organic phase was extracted three times with acidic water at pH < 4.0, and the aqueous phases were combined. The pH of the aqueous phase was further adjusted to 9.0. Most of the water was removed by vacuum rotary evaporation or cooling. A white solid product, crude p-phenylenediamine, precipitated. The purity was 92.3% by GC, and the yield was 70.3%. The crude p-phenylenediamine was purified by distillation, and the purity reached 99.0% by GC, with a yield of 62.0%.

[0138] Comparative Example 4

[0139] The same method as in Example 1 was used to prepare p-phenylenediamine, except that the amination reaction temperature was increased. In this comparative example 4, the amination reaction temperature was 190° C. The specific process was as follows:

[0140] Step 1: Add 300 mL of toluene, 0.5 mol of nitrobenzene, and 0.75 mol of sodium amide to the autoclave, tighten the autoclave lid, and keep the reactor in a well-sealed state. Replace the air with N2 for more than 1 minute, close the feed port of the autoclave lid, heat to 190°C, and keep the reaction temperature for 8 hours to ensure that the reaction system is in the best state for amination reaction.

[0141] Step 2: After the reactor is heated to 190°C, fill it with N2 to a pressure of 4MPa to allow the raw materials to react fully. When the pressure in the reactor exceeds 8MPa, release the pressure to 4MPa in time. Repeat this operation. After 8 hours of reaction, the reaction liquid is cooled to room temperature and the N2 in the reactor is discharged.

[0142] Step 3: Add the Raney Ni catalyst directly to the reaction liquid obtained in the previous step without treatment, tighten the kettle cover, and keep the reactor in a well-sealed state. Replace the air with H2 for more than 3 minutes, close the kettle cover feeding port, raise the temperature to 80°C, and keep the reaction at this temperature for 3 hours to ensure that the reaction system is in the best state for the reduction reaction.

[0143] Step 4: After the reactor is heated to 80°C, H2 is added to the pressure of 2MPa to allow the raw materials to react fully. When the pressure in the reactor is lower than 0.5MPa, H2 is added to 2MPa in time. Repeat this operation until the pressure in the reactor no longer decreases. At this time, the reaction is considered to be complete, the reaction liquid is cooled to room temperature, the H2 in the reactor is discharged, and N2 replaces the residual gas in the reactor.

[0144] Step 5: The reaction solution from the previous step was slowly poured into cooling water (500 g), stirred thoroughly for hydrolysis, insoluble matter was filtered out, and the catalyst was recovered.

[0145] Step 6: The pH of the filtrate from the previous step was adjusted to 3.0. The filtrate was allowed to stand for phase separation. The organic phase was extracted three times with acidic water at pH < 4.0, and the aqueous phases were combined. The pH of the aqueous phase was further adjusted to 9.0. Most of the water was removed by vacuum rotary evaporation or cooling. A white solid product, crude p-phenylenediamine, precipitated. The purity was 91.4% by GC, and the yield was 72.0%. The crude p-phenylenediamine was purified by distillation, and the purity reached 99.0% by GC, with a yield of 64.1%.

[0146] Comparison of the experimental results in Comparative Examples 3 and 4 with Example 1 reveals that both decreasing and increasing the amination reaction temperature results in a decrease in the yield of the target product, p-phenylenediamine. Lowering the amination reaction temperature results in incomplete conversion, ultimately leading to a decrease in the yield of p-phenylenediamine. Higher amination reaction temperatures increase the likelihood of side reactions occurring within the amination reaction system, ultimately leading to a decrease in the yield of the target product, p-phenylenediamine. Therefore, employing the amination reaction temperature conditions described herein is more conducive to obtaining high-yield, high-purity p-phenylenediamine.

[0147] The technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0148] For those skilled in the art, several variations and improvements may be made without departing from the scope of the present invention, which all fall within the scope of protection of the present invention. The scope of protection of the present invention shall be based on the appended claims.

Claims

1. A process for preparing p-phenylenediamine from nitrobenzene in one pot, characterized in that: The process is as follows: S1. Amination reaction: Under inert gas, in a solvent system, nitrobenzene and amino salt undergo an amination reaction under heating and pressurizing conditions, and a reaction liquid is obtained after the reaction is completed; S2, reduction reaction: A catalyst is added to the reaction solution, hydrogen is introduced to carry out a hydrogenation reduction reaction, and after the reaction is completed, p-phenylenediamine is obtained through hydrolysis and post-treatment; In step S1, the amino salt is at least one of sodium amide, lithium amide, and potassium amide; The molar ratio of nitrobenzene to amino salt is 1:(1.2-1.8); The amination reaction temperature is 120-180°C, and the amination reaction pressure is 3-8 MPa.

2. The process for preparing p-phenylenediamine from nitrobenzene in one pot according to claim 1, characterized in that: In step S1, the solvent is at least one of toluene, chloroform, dichloromethane, benzene, xylene, N,N-dimethylformamide, and N,N-dimethylacetamide.

3. The process for preparing p-phenylenediamine from nitrobenzene in one pot according to claim 1, wherein: In step S1, the amination reaction time is 6-10 hours.

4. The process for preparing p-phenylenediamine from nitrobenzene in one pot according to claim 1, wherein: In step S2, the catalyst is at least one of Raney Ni, Pd / C, and Zn.

5. The process for preparing p-phenylenediamine from nitrobenzene in one pot according to claim 1, wherein: In step S2, the hydrogen pressure in the hydrogenation reduction reaction system is 1-3 MPa.

6. The process for preparing p-phenylenediamine from nitrobenzene in one pot according to claim 1, characterized in that: In step S2, the hydrogenation reduction reaction temperature is 60-100° C., and the hydrogenation reduction reaction time is 2-5 h.

7. The process for preparing p-phenylenediamine from nitrobenzene in one pot according to claim 1, characterized in that: In step S2, the hydrolysis and post-treatment process is as follows: the reaction system cooled to room temperature is slowly added to cooling water for hydrolysis, the insoluble matter is filtered out and the pH is adjusted to acidic, the organic phase is allowed to stand for phase separation, the organic phase is extracted with acidic water, the aqueous phases are combined, and then the pH is adjusted to alkaline, and finally the p-phenylenediamine product is obtained by evaporation, crystallization, and distillation.

8. The process for preparing p-phenylenediamine from nitrobenzene in one pot according to claim 7, characterized in that: Adjust the pH to the acidic pH range below 4 and the alkaline pH range above 8.

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