A method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants.

Abstract

This invention belongs to the field of fine chemical synthesis technology and relates to a method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants. Aniline and m-dinitrobenzene undergo a catalytic nucleophilic substitution reaction under negative pressure to obtain a reaction system with 2,4-dinitrodiphenylamine as the main product. The reaction system with 2,4-dinitrodiphenylamine as the main product is diluted with methanol and then subjected to catalytic hydrogenation. After the reaction, post-treatment yields 2,4-diaminodiphenylamine. This invention uses m-dinitrobenzene as the reactant, which is halogen-free and does not produce halogen-containing wastewater. It also has lower requirements for the corrosion resistance of production equipment, higher atom economy, and is more in line with the concept of green chemistry. The solvent and catalyst in this invention are recyclable, resulting in low cost.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical synthesis technology and relates to a method for preparing 2,4-diaminodiphenylamine, an intermediate of p-phenylenediamine antioxidants. Background Technology

[0002] p-Phenylenediamine antioxidants (PPDs) are currently the most widely used and best-performing class of antioxidants in the rubber industry, with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) long holding a dominant position. However, recent studies have shown that 6PPD and its oxidation product, 6PPD-quinone (6PPD-Q), are highly lethal to aquatic organisms such as salmon and pose potential risks to human health. With increasingly stringent global environmental regulations, tire manufacturers and antioxidant producers are urgently seeking green alternatives to 6PPD.

[0003] Existing technologies, such as CN119241371 B, propose a novel class of p-phenylenediamine antioxidants, which exhibit excellent anti-ozone and anti-fatigue properties and are environmentally friendly. The key intermediate in this class of antioxidants is 2,4-diaminodiphenylamine. Currently, the industrial preparation of 2,4-diaminodiphenylamine or its precursors mainly employs the halobenzene process, which involves the condensation of 2,4-dinitrochlorobenzene with aniline. This process route uses halogen atoms in the raw materials, and generates large amounts of saline wastewater, such as metal chloride wastewater, which is difficult and costly to treat. Furthermore, the intermediate product 2,4-dinitrodiphenylamine typically requires cumbersome washing, crystallization, and purification steps before proceeding to the next reaction step, resulting in a long process flow, significant yield loss, and high energy consumption, which is unfavorable for large-scale industrial production. Summary of the Invention

[0004] This invention addresses the problems of severe environmental pollution, poor atom economy, and complex processes in the traditional production of 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants, by proposing a method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants.

[0005] To achieve the above objectives, the present invention is implemented using the following technical solution: A method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants, comprises the following steps: (1) Aniline and m-dinitrobenzene were subjected to a catalytic nucleophilic substitution reaction under negative pressure to obtain a reaction system with 2,4-dinitrodiphenylamine as the main product. The reaction equation is as follows: .

[0006] (2) The reaction system with 2,4-dinitrodiphenylamine as the main product was diluted with methanol and then subjected to catalytic hydrogenation. After the reaction was completed, 2,4-diaminodiphenylamine was obtained through post-treatment. The reaction equation is as follows: .

[0007] Preferably, in step (1), the molar ratio of aniline to m-dinitrobenzene is (2-15):1, and the catalyst is a combination of quaternary ammonium base or alkali metal hydroxide and quaternary ammonium salt, with a molar ratio of catalyst to m-dinitrobenzene of (0.2-1.0):1.

[0008] Preferably, the reaction temperature in step (1) is 40-90℃ and the vacuum degree is -(0.08-0.1)MPa.

[0009] Preferably, the reaction temperature in step (1) is 60-70℃ and the vacuum degree is -(0.085-0.095)MPa.

[0010] Preferably, the hydrogenation catalyst in step (2) is a supported metal catalyst, and the metal is selected from any one of nickel, cobalt, copper, platinum and palladium. The mass ratio of the hydrogenation catalyst to the reaction system is (0.5-5):100.

[0011] Preferably, in step (2), the solvent is one or more of methanol, ethanol, isopropanol, tetrahydrofuran, dioxane, diethyl ether, toluene, and water; the volume ratio of the solvent to the reaction system is (10-50):100; the hydrogenation reaction pressure is 0.5-5 MPa, and the reaction temperature is 40-100℃.

[0012] Preferably, the post-processing method in step (2) is liquid separation and vacuum distillation.

[0013] In the first step of the process proposed in this invention, the m-dinitrobenzene molecule contains two strongly electron-withdrawing nitro groups located at the meta position. When aniline is activated by a basic catalyst such as a quaternary ammonium base, the amino nitrogen atom on the aniline exhibits strong nucleophilicity. Due to the strong electron-withdrawing inductive effect and conjugation effect of the nitro groups, the electron cloud density at the ortho and para positions of the nitro group on the benzene ring is significantly reduced, making it highly susceptible to attack by nucleophiles. Aniline attacks the carbon atom at a specific site on m-dinitrobenzene, forming a Meisenheimer complex intermediate, which then, under negative pressure, loses a hydrogen atom, selectively generating 2,4-dinitrodiphenylamine. In the second step, a solvent is added for dilution. This reduces the system viscosity, increases the solubility of hydrogen in the liquid phase, and enhances the gas-liquid-solid three-phase mass transfer. Furthermore, the solvation effect helps stabilize the intermediate state and prevents side reactions caused by localized overheating. The nitro groups are chemically adsorbed on the surface of the metal catalyst and reduced to amino groups by hydrogen, ultimately yielding the target product in high yield.

[0014] Compared with the prior art, the advantages and positive effects of the present invention are as follows: 1. This invention uses m-dinitrobenzene as the reaction raw material, which is halogen-free and does not produce halogen-containing waste brine. It has lower requirements for the corrosion resistance of production equipment, higher atom economy, and is more in line with the concept of green chemistry.

[0015] 2. The preferred nucleophilic substitution catalyst of this invention is a quaternary ammonium base that is an organic strong base, readily soluble in water, and can be extracted and separated using the water generated after the reaction for recycling.

[0016] 3. The hydrogenation of the intermediate product 2,4-dinitrodiphenylamine in this invention does not require separating 2,4-dinitrodiphenylamine from the reaction system in the previous step. It can be directly introduced into the hydrogenation reactor for catalytic hydrogenation under solvent dilution, which greatly reduces the post-processing cost.

[0017] 4. After the hydrogenation reaction is completed, the hydrogenation catalyst can be filtered and separated to achieve recycling.

[0018] 5. The solvent and catalyst in the system can be recovered and reused, and high-purity 2,4-diaminodiphenylamine can be obtained by distillation. Detailed Implementation

[0019] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0020] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein. Therefore, the invention is not limited to the specific embodiments disclosed in the following specification. Unless otherwise specified, the percentage content of substances in the following embodiments is a mass fraction. Example 1

[0021] 93.1 g of aniline was added to a 500 mL four-necked flask, followed by 41.6 g of a 25% tetramethylammonium hydroxide aqueous solution. The mixture was stirred at 200 rpm under reduced pressure and heated, maintaining a vacuum of -0.088 MPa. When the system reached 55 °C, a mixture of m-dinitrobenzene and aniline (containing 48.0 g of m-dinitrobenzene and 93.1 g of aniline) was added dropwise at a uniform rate over 1 hour. The reaction was then carried out at 55 °C and 200 rpm, with samples taken every 0.5 hours for liquid chromatography monitoring. The reaction was terminated when the m-dinitrobenzene content in the reaction system reached or fell below 1.0%, for a total of 5.5 hours (in this example, the m-dinitrobenzene content in the reaction system was 0.94% at this point). The above reaction system was diluted with 60 mL of methanol and transferred to a high-pressure reactor. 7.2 g of Raney nickel catalyst (Liaoning Zhongli Catalyst Technology Co., Ltd., ZL-N211 type) was weighed. The air in the reactor was replaced with nitrogen three times, followed by hydrogen replacement three times. After this, the system was heated to 73°C, and hydrogen was introduced until the pressure in the reactor reached 2.0 MPa. When the pressure in the reactor dropped to 1.0 MPa, hydrogen was added until it reached 2.0 MPa. The reaction was considered complete when the pressure in the reactor remained stable and no longer decreased. The total reaction time was 8 hours. After cooling to room temperature with cooling water, the pressure was released, and the catalyst in the reaction system was filtered out. Methanol was removed by vacuum distillation at -0.085 MPa and 70°C for 0.5 hours. The residue was then transferred to a 500 mL separatory funnel and allowed to stand for 20 minutes to separate the lower organic phase and the upper aqueous phase containing the catalyst. The product was subjected to vacuum distillation again at a vacuum of -0.097 MPa and a maximum temperature of 150 °C until no more fractions were distilled off (approximately 40 min) to obtain 2,4-diaminodiphenylamine. HPLC analysis showed a mass fraction of 98.2%, with an overall two-step yield of 92.0% based on m-dinitrobenzene. The product's 1H NMR (500 MHz, DMSO-d6) data were as follows: δ 7.25 (t, J=7.5 Hz, 2H), 6.73 (s, 1H), 6.61 (d, J=8.3 Hz, 1H), 6.49–6.55 (m, 3H), 5.99 (d, J=2.5 Hz, 1H), 5.83 (dd, J=8.2, 2.5 Hz, 1H), 4.66 (s, 2H), 4.44 (s, 2H). Example 2

[0022] Unless otherwise specified in this embodiment and the following embodiments, the provisions are the same as in Embodiment 1.

[0023] 95g of aniline was added to a 500mL four-necked flask, followed by 42g of a 25% tetramethylammonium hydroxide aqueous solution. The mixture was stirred at 200rpm and heated under reduced pressure to dehydrate the aniline. The vacuum was controlled at -0.095MPa. When the system reached 70℃, a mixture containing 48.0g of m-dinitrobenzene and 93.1g of aniline was added dropwise over 1 hour. The reaction was carried out at 70℃, and samples were taken every 0.5 hours for liquid chromatography monitoring. The reaction was stopped when the m-dinitrobenzene content in the reaction system was lower than 1.0%. The total reaction time was 4.5 hours. The above reaction system was diluted with 60 mL of methanol and transferred to a high-pressure reactor. 8.5 g of Raney nickel catalyst was weighed, and the system was purged three times consecutively with nitrogen and hydrogen, respectively. The system was then heated to 80 °C, and hydrogen was introduced until the pressure in the reactor reached 1.5 MPa. When the pressure in the reactor dropped to 1.0 MPa, hydrogen was added again until it reached 1.5 MPa. The reaction was considered complete when the pressure in the reactor remained stable and no longer decreased. The total reaction time was 9 h. After cooling to room temperature with cooling water, the pressure was released, and the catalyst in the reaction system was filtered out. The methanol was distilled off under reduced pressure, and the aqueous catalyst phase was allowed to stand for separation. The organic phase was then distilled again under reduced pressure to recover aniline, yielding 2,4-diaminodiphenylamine. HPLC analysis showed that its mass fraction was 98.3%, and the overall yield of the two steps (based on m-dinitrobenzene) was 92.8%. Example 3

[0024] 90g of aniline was added to a 500mL four-necked flask, followed by 40g of a 25% tetramethylammonium hydroxide aqueous solution. The mixture was stirred at 200rpm and heated under reduced pressure to dehydrate the aniline. The vacuum was controlled at -0.09MPa. When the system reached 60℃, a mixture containing 48.0g of m-dinitrobenzene and 93.1g of aniline was added dropwise over 1 hour. The reaction was carried out at 60℃, and samples were taken every 0.5 hours for liquid chromatography monitoring. The reaction was stopped when the m-dinitrobenzene content in the reaction system was lower than 1.0%. The total reaction time was 5 hours. The above reaction system was diluted with 60 mL of methanol and transferred to a high-pressure reactor. 10 g of Raney nickel catalyst was weighed, and the system was purged three times consecutively with nitrogen and hydrogen, respectively. The system was then heated to 60 °C, and hydrogen was introduced until the pressure in the reactor reached 2.0 MPa. When the pressure in the reactor dropped to 1.0 MPa, hydrogen was added again until it reached 2.0 MPa. The reaction was considered complete when the pressure in the reactor remained stable and no longer decreased. The total reaction time was 9.5 h. After cooling to room temperature with cooling water, the pressure was released, and the catalyst in the reaction system was filtered out. The methanol was distilled off under reduced pressure, and the aqueous catalyst was allowed to stand for separation. Aniline was recovered by distillation under reduced pressure again to obtain 2,4-diaminodiphenylamine. HPLC analysis showed that its mass fraction was 98.0%, and the overall yield of the two steps (based on m-dinitrobenzene) was 94.7%.

[0025] Comparative Example 1 The difference between this comparative example and Example 1 is that the amount of 25% tetramethylammonium hydroxide aqueous solution was adjusted to 166.4g, while the other conditions remained the same as in the example. After obtaining the product, the mass fraction of 2,4-diaminodiphenylamine was determined by HPLC to be 78.1%, and the total yield of the two steps based on m-dinitrobenzene was 78.4%. The remaining substances were mainly disubstituted products.

[0026] Comparative Example 2 The difference between this comparative example and Example 1 is that the reaction temperature in the first step was adjusted to 100°C. After 3 hours of reaction, the content of intermediate dinitrobenzene in the system was 8.3%, but the reaction basically stopped. The second step reaction was carried out directly. The other conditions were kept the same as in Example 1. After obtaining the product, the mass fraction of 2,4-diaminodiphenylamine was 82.3% as determined by HPLC. The total yield of the two steps based on m-dinitrobenzene was 82.0%. The remaining substances were mainly m-phenylenediamine and some disubstituted products. In the first step reaction, some catalyst decomposed, which prevented the reaction from continuing.

[0027] Comparative Example 3 The difference between this comparative example and Example 3 is that the hydrogen pressurization in the second step was adjusted to 0.3 MPa. When the pressure dropped to 0.15 MPa, hydrogen was added again to bring it back to 0.3 MPa. This process was repeated until the pressure in the reactor was maintained and no longer decreased. The other conditions remained the same as in Example 3. After obtaining the product, the mass fraction of 2,4-diaminodiphenylamine was determined by HPLC to be 79.4%, and the total yield of the two steps based on m-dinitrobenzene was 77.0%. The remaining substances were mainly intermediates from incomplete hydrogenation.

[0028] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants, characterized in that, The steps are as follows: (1) Aniline and m-dinitrobenzene were subjected to a catalytic nucleophilic substitution reaction under negative pressure to obtain a reaction system with 2,4-dinitrodiphenylamine as the main product; (2) The reaction system with 2,4-dinitrodiphenylamine as the main product was diluted with methanol and then subjected to catalytic hydrogenation. After the reaction was completed, 2,4-diaminodiphenylamine was obtained by post-treatment.

2. The method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants, according to claim 1, is characterized in that... In step (1), the molar ratio of aniline to m-dinitrobenzene is (2-15):1, and the catalyst is a combination of quaternary ammonium base or alkali metal hydroxide and quaternary ammonium salt, with a molar ratio of catalyst to m-dinitrobenzene of (0.2-1.0):

1.

3. The method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants according to claim 1, is characterized in that, The reaction temperature in step (1) is 40-90℃; the negative pressure vacuum degree is -(0.08-0.1)MPa.

4. The method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants according to claim 1, is characterized in that, The reaction temperature in step (1) is 60-70℃; the negative pressure vacuum degree is -(0.085-0.095)MPa.

5. The method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants according to claim 1, is characterized in that, In step (2), the hydrogenation catalyst is a supported metal catalyst, and the metal is selected from any one of nickel, cobalt, copper, platinum and palladium. The mass ratio of the hydrogenation catalyst to the reaction system is (0.5-5):

100.

6. The method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants according to claim 1, is characterized in that, In step (2), the solvent is one or more of methanol, ethanol, isopropanol, tetrahydrofuran, dioxane, diethyl ether, toluene, and water; the volume ratio of the solvent to the reaction system is (10-50):100; the hydrogenation reaction pressure is 0.5-5 MPa, and the reaction temperature is 40-100℃.

7. The method for preparing 2,4-diaminodiphenylamine, an intermediate in p-phenylenediamine antioxidants according to claim 1, is characterized in that, The post-processing method in step (2) is separation and vacuum distillation.