Preparation method of dialkyl p-phenylenediamine and anti-aging agent mixture

Abstract

The invention discloses a method for synthesizing N, N '-dialkyl p-phenylenediamine as shown in a formula (I) or a mixture thereof and an anti-aging agent mixture produced by adopting the method. Comprising the following steps: adding a raw material A selected from paranitroaniline and p-phenylenediamine, a raw material B selected from a compound as shown in a formula (II), a compound as shown in a formula (III) and cyclohexanone, and a catalyst into a reaction device, and carrying out hydrogenation reaction under a hydrogen condition to obtain N, N '-dialkyl p-phenylenediamine as shown in a formula (I) or a mixture thereof, wherein the raw material A and the raw material B are fed in a liquid form; in the formula (I), the formula (II) and the formula (III), R1, R2, R3 and R4 are respectively and independently H or C1-C6 alkyl, or-CHR1R2 and-CHR3R4 are independently cyclohexyl. According to the method disclosed by the invention, high-selectivity and low-cost production of the N, N '-dialkyl p-phenylenediamine can be realized, and the reaction conditions are milder and more controllable. (I) (II) (III)

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of compound synthesis, and particularly relates to a preparation method of dialkyl-p-phenylenediamine and an antioxidant mixture. BACKGROUND

[0002] Derivatives of p-phenylenediamine are commonly used as rubber antioxidants, and have good comprehensive protection effect, mainly preventing thermal oxidation, ozone and fatigue aging, including dialkyl-p-phenylenediamine, alkylaryl-p-phenylenediamine and diaryl-p-phenylenediamine. These p-phenylenediamine derivatives have different physical and chemical properties, so their antioxidant effects are different. Among the three derivatives, dialkyl-p-phenylenediamine has the best anti-aging speed and static ozone resistance function, and is suitable for rubber products such as wires, cables, hoses and tapes used outdoors, and can also be used for general industrial rubber products.

[0003] A representative product of dialkyl-p-phenylenediamine is N,N'-di(1,4-dimethylpentyl)-p-phenylenediamine, also known as antioxidant 77PD, which is a high-efficiency ozone-resistant protective agent for natural rubber and various synthetic rubbers, and has excellent static ozone aging resistance, which is significantly better than the main ozone-resistant aging alkylaryl-p-phenylenediamine antioxidants 4010NA and 4020 used at home and abroad.

[0004] At present, the N-alkylation reaction of aromatic amine mainly adopts substitution alkylation reaction and reduction alkylation reaction. The substitution alkylation reaction uses halogenated alkanes (iodoalkane, bromoalkane and chloroalkane), ester and alcohol as the alkylation reagent, and has mild reaction conditions and less pollution, but the alkylation of aromatic amine is a continuous reaction, and the aromatic amine first reacts with the alkylation reagent to generate a mono-substituted product, and then generates a dialkyl aromatic amine, so the alkylation product obtained by substitution alkylation reaction has low selectivity, and there are many double-substituted or multi-substituted products; the reduction alkylation reaction includes chemical reduction catalysis and catalytic hydrogenation reduction of borohydride and the like. The chemical reducing agent has strong reducing property, and can easily hydrogenate aldehyde and ketone to the corresponding alcohol byproduct. The catalytic hydrogenation reduction uses palladium, platinum, copper, nickel and molybdenum and the like transition metal hydrogenation catalyst, and can realize N-alkyl derivatization product of aromatic amine with high conversion rate, high yield and high purity, but the price is expensive, and the production cost is high.

[0005] Therefore, there is a need in the art for an economical and efficient method for preparing dialkyl-p-phenylenediamine antioxidant. SUMMARY

[0006] Therefore, in a first aspect, the present application provides a method for synthesizing N,N'-dialkyl-p-phenylenediamine or a mixture thereof represented by the following formula (I): The process involves adding raw material A, selected from p-nitroaniline and p-phenylenediamine, raw material B, selected from compounds of formula (II), compounds of formula (III), and cyclohexanone, and a catalyst to a reaction apparatus. Preferably, raw material B and the catalyst are added to the reaction apparatus first, followed by the addition of molten raw material A. A hydrogenation reaction is carried out under hydrogen conditions to prepare N,N′-dialkylp-phenylenediamine or a mixture thereof as shown in formula (I). (I) (II) (III) In this compound, R1, R2, R3 and R4 are each independently H or C1-C6 alkyl, or -CHR1R2 and -CHR3R4 are independently cyclohexyl, and the compound shown in formula (II) is the same as or different from the compound shown in formula (III). Raw materials A and B are fed in liquid form.

[0007] Furthermore, the hydrogenation reaction under hydrogen conditions includes charging the reaction apparatus with hydrogen to a predetermined pressure and controlling the temperature at a predetermined temperature to carry out the hydrogenation reaction; and replenishing the reaction apparatus with hydrogen to maintain the predetermined pressure, thereby obtaining a product mixture.

[0008] Preferably, the molar ratio of raw material A to raw material B is 1:(2.5~6).

[0009] Furthermore, the catalyst is selected from one or more noble metal catalysts selected from palladium catalysts and platinum catalysts, and the noble metal content in the noble metal catalyst is 1.5~3% based on the mass of the noble metal catalyst.

[0010] Preferably, the amount of the precious metal catalyst used is 0.5 to 5% of the mass of raw material A.

[0011] Furthermore, the hydrogenation reaction is carried out at a temperature of 50~150℃ and a pressure of 0.5~3 MPa.

[0012] Furthermore, raw material B is one or more of cyclohexanone, butanone, and methyl isopentyl ketone.

[0013] Furthermore, the N,N′-dialkyl-p-phenylenediamine represented by formula (I) is one or more of the following compounds: N,N'-Diisobutyl-p-phenylenediamine, N,N'-Bis(1,4-dimethylpentyl)p-phenylenediamine, N,N'-Dicyclohexyl-p-phenylenediamine, N-Isobutyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine, N-Cyclohexyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine and N-Isobutyl-N'-Cyclohexyl-p-phenylenediamine.

[0014] Further, after the reaction stops, the product mixture is filtered, and the filtrate is subjected to vacuum distillation to obtain N,N'-dialkyl-p-phenylenediamine or a mixture thereof.

[0015] Furthermore, the method further includes pre-melting the solid components of raw material A and raw material B into liquid state, and then conveying them to the reaction device through a heat preservation device.

[0016] On the other hand, the present invention also provides an antioxidant mixture comprising N,N′-dialkyl-p-phenylenediamine or a mixture thereof as shown in the above formula (I).

[0017] The method of the present invention includes taking a liquid raw material A selected from p-nitroaniline and p-phenylenediamine and a raw material B selected from compounds of formula (II), compounds of formula (III) and cyclohexanone, and synthesizing N,N′-dialkylp-phenylenediamine or mixtures thereof of formula (I) directly in a one-step process under the action of a catalyst in a low-temperature and low-pressure synthesis environment. By separating the products through filtration and recycling the catalyst, high conversion rate, high selectivity, high safety and low production cost can be achieved, so that the selectivity of N,N′-dialkylp-phenylenediamine products of formula (I) in the product reaches more than 98%. Attached Figure Description

[0018] Figure 1 The above is a gas chromatogram of the product mixture according to Example 1 of the present invention; Figure 2 The above is a gas chromatogram of the product mixture according to Example 2 of the present invention; Figure 3 The above is a gas chromatogram of the product mixture according to Example 3 of the present invention; Figure 4 The above is a gas chromatogram of the product mixture according to Example 4 of the present invention; Figure 5 The image shows the gas chromatogram of the product mixture from Comparative Example 1. Detailed Implementation

[0019] Existing synthetic processes for dialkyl-p-phenylenediamine compounds suffer from poor selectivity, numerous byproducts, and high production costs. To address this issue, the inventors provide a method for synthesizing N,N′-dialkyl-p-phenylenediamine or mixtures thereof, as shown in formula (I): (I) R1, R2, R3 and R4 are each independently H or C1-C6 alkyl, or -CHR1R2 and -CHR3R4 may be the same or different, and are independently cyclohexyl.

[0020] In the method of the present invention, a raw material A selected from p-nitroaniline and p-phenylenediamine, a raw material B selected from the compound shown in formula (II), the compound shown in formula (III), and cyclohexanone, and a catalyst are first added to the reaction apparatus, and a hydrogenation reaction is carried out under hydrogen conditions to prepare N,N′-dialkylp-phenylenediamine or a mixture thereof shown in formula (I): (II); (III) In this configuration, R1, R2, R3, and R4 are each independently H or C1-C6 alkyl groups, or -CHR1R2 and -CHR3R4 may be the same or different, and are independently cyclohexyl groups; and The compounds shown in formula (II) and the compounds shown in formula (III) may be the same or different.

[0021] In the method of this invention, raw material A can be selected from p-nitroaniline and p-phenylenediamine, preferably p-nitroaniline (melting point 148.5°C). In the above hydrogenation reaction, the main process is the reductive alkylation of aromatic amines. In industrial production, the aromatic amines produced by N-alkylation reactions using aromatic amines as initial raw materials mainly originate from the chemical reduction or catalytic hydrogenation of aromatic nitro compounds. Therefore, using p-nitroaniline or p-phenylenediamine as raw materials allows for the continuous generation and reductive alkylation of p-phenylenediamine within a single reaction apparatus, simplifying the production process, increasing production efficiency, lowering production costs, avoiding the separation of intermediate products, and overcoming the disadvantages of aromatic amines such as high toxicity, easy deterioration, and poor storage.

[0022] In the method of the present invention, raw material B can be selected from one or more of cyclohexanone, butanone, and methyl isopentyl ketone. The molar ratio of raw material A to raw material B in the above feeding step can be 1:(2.5~6), preferably 1:(3.5~5), for example 1:4.

[0023] The method of the present invention further includes pre-melting the solid components of raw material A into a liquid state and conveying it to the reaction apparatus through a heat preservation device. According to one embodiment, ketone raw material B (also used as a solvent) and a catalyst are first added to the reaction apparatus, the reaction apparatus is sealed, nitrogen is introduced for purging, and stirring is started; simultaneously, p-nitroaniline (or p-phenylenediamine) is preheated to a molten state (approximately 148°C), pumped into the reaction apparatus through a pipeline, and hydrogen is introduced to begin the reaction. This step changes the previous method of feeding solid powder, adopting a closed-loop liquid-phase feeding method, preventing chemical dust from scattering and avoiding the rapid oxidation, blackening, and penetration of p-phenylenediamine dust onto other surfaces. The entire operation is environmentally friendly and operator-friendly.

[0024] In the method of this invention, raw material A and raw material B are fed in liquid form, which eliminates the need for additional organic solvents. This facilitates uniform mixing and full contact of the raw materials in the reaction system, promotes uniform reaction, increases reaction rate, reduces side reactions, improves the conversion rate of raw materials and the yield of target products, reduces reaction time and energy consumption, and simplifies post-processing.

[0025] Raw material A is usually in solid form at room temperature. This invention obtains raw material A in liquid form by pre-melting or by customizing it in a heat-insulating device. Raw material B is usually in liquid form at room temperature and can be used directly.

[0026] Specifically, on the one hand, in the reaction apparatus, the pumped-in p-nitroaniline (or p-phenylenediamine) molten liquid (i.e., raw material A) will rapidly mix and disperse with the solvent system (i.e., raw material B) under stirring. Since the temperature of the molten liquid can be around 148°C, and raw material B, as the solvent, is a room-temperature system, the temperature of the entire material will rapidly transfer until equilibrium is reached after mixing. The molar ratio of raw material A to raw material B is 1:(2.5~6) (e.g., 1:4), and the temperature equilibrium of the entire material is around 80°C. Therefore, the reaction apparatus does not require heating; the reaction temperature can be reached by directly mixing the raw materials by adjusting the ratio. Furthermore, since the hydrogenation reaction is an exothermic reaction, subsequent reactions can proceed spontaneously. Therefore, the entire reaction process only requires temperature monitoring and does not require heating of the reaction apparatus, thus significantly reducing the overall energy consumption of the production process.

[0027] The insulation temperature of the insulation device is set 10-20°C above the melting point of raw material A to ensure its molten state and chemical stability. For example, when raw material A is p-nitroaniline, the insulation temperature can be set to 158-168°C. In actual production, a jacketed reactor can be used to uniformly heat the coenzyme material, and a temperature sensor can be used to detect and control the temperature, keeping the temperature fluctuation within ±2°C.

[0028] According to one specific embodiment, a solid raw material (e.g., p-nitroaniline) is placed in a container with a heating function, such as a jacketed melting vessel. A heat transfer medium, such as heat transfer oil or steam, can be introduced into the jacket to heat the raw material above its melting point through heat exchange, causing it to melt into a liquid state.

[0029] In addition, a conveying pipeline connects the insulation device and the reaction device, and a reaction pump is used to transport the material from the insulation device to the reaction device, ensuring the temperature of the liquid raw materials entering the reaction system and preventing the raw materials from cooling and solidifying during transportation. The material of the aforementioned conveying pipeline should be compatible with the raw materials and have a smooth inner wall to reduce material residue.

[0030] The aforementioned hydrogenation reaction under hydrogen conditions includes adding raw material B and catalyst to the reaction apparatus, sealing the apparatus after feeding, purging with nitrogen to maintain pressure, and then introducing hydrogen to maintain a predetermined pressure value, for example, 0.5~3 MPa, preferably 1~2.5 MPa, such as 2 MPa, and maintaining a predetermined temperature, for example, 50~150℃, preferably 70~130℃, such as 90℃ and 110℃. This temperature and pressure range is relatively low, the reaction is mild, the inherent safety of the reaction is high, the requirements for production equipment and processes are significantly reduced, and the operational safety is higher.

[0031] The above reaction steps may include a reaction step of hydrogenating the synthetic raw materials, and a separation step of separating the reaction products.

[0032] The catalyst of this invention can be one or more noble metal catalysts selected from palladium catalysts and platinum catalysts, preferably palladium-carbon catalysts or platinum-carbon catalysts. Further, the mass percentage content of the noble metal in the noble metal catalyst can be 1.5-3%, preferably 2-2.5%, for example, 2.8%. The amount of noble metal catalyst used is determined according to the mass of the synthesis raw material, for example, 0.5-5% of the mass of raw material A, preferably 1-4.5%, more preferably 1.5-4%, further preferably 2-3.5%, for example, 3%. The noble metal catalyst selected from palladium catalysts and platinum catalysts used in this invention is a composite catalyst containing a single noble metal component, which ensures good catalytic effect and has a low production cost due to the small amount of noble metal and its recyclability.

[0033] The mechanism of the method of the present invention may include the hydrogenation reaction mechanism of aromatic amines. Specifically, in the above hydrogenation step, the synthetic raw material A undergoes a reductive alkylation process under the action of a catalyst and under the temperature and pressure conditions described above to obtain N,N′-dialkyl-p-phenylenediamine as shown in formula (I).

[0034] According to one embodiment, the N,N′-dialkyl-p-phenylenediamine of formula (I) prepared by the above hydrogenation process can be one or more of N,N′-diisobutyl-p-phenylenediamine, N,N′-bis(1,4-dimethylpentyl)-p-phenylenediamine, N,N′-dicyclohexyl-p-phenylenediamine, N-isobutyl-N′-(1,4-dimethylpentyl)-p-phenylenediamine, N-cyclohexyl-N′-(1,4-dimethylpentyl)-p-phenylenediamine and N-isobutyl-N′-cyclohexyl-p-phenylenediamine. The selectivity of the N,N′-dialkyl-p-phenylenediamine product of formula (I) in the product of the above reaction steps can reach more than 98%.

[0035] According to the method of the present invention, an antioxidant mixture can be prepared, comprising N,N′-dialkyl-p-phenylenediamine or a mixture thereof as shown in formula (I) prepared according to the above method.

[0036] According to one embodiment, in the method of the present invention, the separation step of the product mixture may include filtering the product mixture to remove the catalyst, and subjecting the filtrate to vacuum distillation to obtain the N,N'-dialkyl-p-phenylenediamine or a mixture thereof. Vacuum distillation may be performed under a negative pressure of -0.1 MPa and a first-stage distillation temperature of 160°C to remove low-boiling-point materials and intermediates from the filtrate, yielding a high-purity product, N,N'-dialkyl-p-phenylenediamine. The final N,N'-dialkyl-p-phenylenediamine obtained has a purity of over 99%. The present invention uses liquid feedstock, does not add additional solvents, produces few byproducts, has a simple purification process for the product mixture, and yields high product purity.

[0037] According to one embodiment, the precious metal catalyst obtained by filtration is further recovered, processed, and reused. The raw materials of this invention are fed in liquid form without the addition of additional solvents, and the raw material conversion rate is high, the product selectivity is high, and the by-products are few. Therefore, the catalyst is not easily poisoned, the recovery rate is high, and this helps to reduce production costs.

[0038] Gas chromatography analysis method: Gas chromatograph: Agilent 7890B HP-5 capillary column: 30m × 0.320mm × 0.25μm (column length × column inner diameter × film thickness) Detector temperature: 300℃ Vaporization chamber temperature: 300℃ Carrier gas: High-purity nitrogen Carrier gas flow rate: 1.3 mL / min Flow split ratio: 80:1 Hydrogen: 30 mL / min Column temperature: Initial temperature 50℃, hold for 2 min, increase to 270℃ at a rate of 15℃ / min, then increase to 280℃ in 1 min and hold for 18 min. Injection volume: 1µL; The optimal analysis conditions can be selected depending on the instrument.

[0039] The method of the present invention has the following advantages: The reaction is conducted under mild temperature and pressure conditions, which improves the inherent safety of the reaction. One-step batch reactor reaction has a simple reaction process, low cost, and is easy to promote; The synthesis system uses molten liquid feed, has a simple composition, does not require additional solvents, and does not require heating. The mixing heat conduction speed is very fast, the liquid-liquid homogeneous mixing and dispersion are uniform, the initial reaction temperature is high, and the reaction rate is rapid. Therefore, compared with conventional operation, no preheating process is required, and the reaction speed is fast, saving reaction time. Conventional reaction batches take 3-4 hours, while this design only takes 1-2 hours, saving half of the reaction time. In liquid-phase reaction systems, the reaction rate is fast and the mixing state is good, resulting in short reaction time, high raw material conversion rate, high product selectivity, and few by-products. The catalyst can be reused, which improves production efficiency and economic benefits.

[0040] The present invention will be described in detail below with reference to specific implementation schemes and embodiments, thereby making the advantages and various effects of the present invention more clearly apparent. Those skilled in the art should understand that these specific implementation schemes and embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0041] In the following examples and comparative examples, the gas chromatography analysis conditions were as follows: Gas chromatograph: Agilent 7890B HP-5 capillary column: 30m × 0.320mm × 0.25μm (column length × column inner diameter × film thickness) Detector temperature: 300℃ Vaporization chamber temperature: 300℃ Carrier gas: High-purity nitrogen Carrier gas flow rate: 1.3 mL / min Split ratio: 80:1 Hydrogen: 30 mL / min Column temperature: Initial temperature 50℃, hold for 2 min, increase to 270℃ at a rate of 15℃ / min, then increase to 280℃ in 1 min and hold for 18 min. Injection volume: 1µL.

[0042] In the following examples and comparative examples, the vacuum distillation steps are as follows: The product mixture was filtered to remove the catalyst; under a negative pressure of -0.1 MPa, the first-stage distillation temperature was 160 °C to remove low-boiling-point materials and intermediates from the filtrate, and to distill off the high-purity product N,N′-dialkyl-p-phenylenediamine.

[0043] All percentages used in the following examples and comparative examples are mass percentages.

[0044] Example 1 (Butanone as raw material B) Using a 1L hydrogenation experimental vessel, first add 420g of butanone (raw material B, 5.83mol) as a solvent and 5g of palladium on carbon catalyst (2.5%). Seal the hydrogenation experimental vessel, purge with nitrogen to maintain pressure, open the molten liquid material delivery valve, start the pump, and add 200g of molten liquid p-nitroaniline (raw material A, 1.45mol) to make the molar ratio of raw material A to raw material B 1:4. The reaction process does not require heating. Control the molar ratio of raw materials to control the temperature at 85℃~100℃. Replace nitrogen with hydrogen, add pressure to 2 MPa, start stirring, and heat to 85°C to start the reaction. The reaction is exothermic, so keep the temperature below 100°C. During the reaction, the amount of hydrogen consumed is replenished, and no hydrogen is absorbed after about 1.5 hours of reaction. The pressure is maintained for 30 minutes.

[0045] The reaction mixture was subjected to gas chromatography, yielding 98.29% N,N'-diisobutyl-p-phenylenediamine (solvent-de-solvent peak), as shown below. Figure 1 As shown.

[0046] The reaction mixture was filtered and distilled under reduced pressure to give N,N'-diisobutyl-p-phenylenediamine product with 99.2% purity.

[0047] Example 2 (Methyl isopentyl ketone as raw material B) Using a 1L hydrogenation experimental vessel, first add 670g of methyl isopentyl ketone (raw material B, 5.23mol) as a solvent, add 5g of palladium on carbon catalyst (2.5%), seal the hydrogenation experimental vessel, purge with nitrogen to maintain pressure, open the molten liquid material delivery valve, start the pump, and add 200g of molten liquid p-nitroaniline (raw material A, 1.45mol) to make the molar ratio of raw material A to raw material B 1:3.6; Replace nitrogen with hydrogen, add pressure to 2 MPa, start stirring, and heat to 85°C to start the reaction. The reaction is exothermic, so keep the temperature below 100°C. During the reaction, the amount of hydrogen consumed is replenished, and no hydrogen is absorbed after about 1.5 hours of reaction. The pressure is maintained for 30 minutes.

[0048] The reaction mixture was subjected to gas chromatography, yielding 98.19% N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (solvent peak removed). Figure 2 As shown.

[0049] The reaction mixture was filtered and distilled under reduced pressure to give 99.3% N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine.

[0050] Example 3 (Two ketones in a 1:1.3 ratio as raw material B) Using a 1L hydrogenation experimental vessel, first add 210g of butanone (1.94mol) and 330g of methyl isopentyl ketone (2.57mol) (raw material B) as solvents, add 5g of palladium on carbon catalyst (2.5%), seal the hydrogenation experimental vessel, purge with nitrogen to maintain pressure, open the molten liquid material delivery valve, start the pump, and add 200g of molten liquid p-nitroaniline (raw material A, 1.45mol), so that the molar ratio of raw material A to raw material B is 1:3.1. The reaction process does not require heating, and the molar ratio of raw materials is controlled to control the temperature at 85℃~100℃. Replace nitrogen with hydrogen, add pressure to 2 MPa, start stirring, and heat to 85°C to start the reaction. The reaction is exothermic, so keep the temperature below 100°C. During the reaction, the amount of hydrogen consumed is replenished, and no hydrogen is absorbed after about 1.5 hours of reaction. The pressure is maintained for 30 minutes.

[0051] The reaction mixture was subjected to gas chromatography, yielding 49.45% N-isobutyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine, 22.43% N,N'-diisobutyl-p-phenylenediamine, and 26.22% N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine. Figure 3 As shown.

[0052] The reaction mixture was filtered and distilled under reduced pressure to obtain a 99.3% p-phenylenediamine antioxidant mixture.

[0053] Example 4 (using two ketones in a 2.3:1 ratio as raw materials) Using a 1L hydrogenation experimental vessel, first add 280g of butanone (3.9mol) and 220g of methyl isopentyl ketone (1.7mol) (molar ratio 2.3:1) (raw material B) as solvent, add 5g of palladium on carbon catalyst (2.5%), seal the hydrogenation experimental vessel, purge with nitrogen to maintain pressure, open the molten liquid material delivery valve, start the pump, and add 200g of molten liquid p-nitroaniline (raw material A, 1.45mol) to make the molar ratio of raw material A to raw material B 1:3.9; Replace nitrogen with hydrogen, add pressure to 2 MPa, start stirring, and heat to 85°C to start the reaction. The reaction is exothermic, so keep the temperature below 100°C. During the reaction, the amount of hydrogen consumed is replenished, and no hydrogen is absorbed after about 1.5 hours of reaction. The pressure is maintained for 30 minutes.

[0054] The reaction mixture was subjected to gas chromatography, yielding 45.77% N-isobutyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine, 44.52% N,N'-diisobutyl-p-phenylenediamine, and 7.99% N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine. Figure 4 As shown.

[0055] The reaction mixture was filtered and distilled under reduced pressure to obtain a 99.4% p-phenylenediamine antioxidant mixture.

[0056] Comparative Example 1 Using a 1L hydrogenation experimental vessel, add 200 g of solid p-nitroaniline, 420 g of butanone (molar ratio 1:4), 300 mL of dimethylformamide and 60 mL of benzene, and add 5 g of palladium on carbon catalyst (2.5%). Seal the reaction vessel and maintain pressure by purging with nitrogen. Replace nitrogen with hydrogen, add pressure to 2 MPa, start stirring, and heat to 110°C to start the reaction. The reaction is exothermic, so control the temperature below 125°C. During the reaction, the amount of hydrogen consumed is replenished, the reaction is kept at a constant temperature for about 20 hours without absorbing hydrogen, and the pressure is maintained for 30 minutes.

[0057] The reaction solution was filtered and distilled under reduced pressure to remove benzene, dimethylformamide, and a small excess of the raw material, yielding 54.2 g of residue. Gas chromatography analysis of the residue revealed N,N'-diisobutyl-p-phenylenediamine with a purity of 90.66%. Figure 5 As shown.

Claims

1. A method for synthesizing N,N′-dialkyl-p-phenylenediamine or mixtures thereof as shown in formula (I): Its features are, The method includes adding a raw material A selected from p-nitroaniline and p-phenylenediamine, a raw material B selected from the compound shown in formula (II), the compound shown in formula (III), and cyclohexanone, and a catalyst to a reaction apparatus, and carrying out a hydrogenation reaction under hydrogen conditions to prepare N,N′-dialkylp-phenylenediamine or a mixture thereof shown in formula (I): (I) (II) (III) In this compound, R1, R2, R3 and R4 are each independently H or C1-C6 alkyl, or -CHR1R2 and -CHR3R4 are independently cyclohexyl, and the compound shown in formula (II) is the same as or different from the compound shown in formula (III). In this process, raw material A and raw material B are fed in liquid form.

2. The method according to claim 1, wherein, The hydrogenation reaction under hydrogen conditions includes charging the reaction apparatus with hydrogen to a predetermined pressure and controlling the temperature at a predetermined temperature to carry out the hydrogenation reaction; and replenishing the reaction apparatus with hydrogen to maintain the predetermined pressure, thereby obtaining a product mixture.

3. The method according to claim 1, wherein, The molar ratio of raw material A to raw material B is 1:(2.5~6).

4. The method according to claim 1, wherein, The catalyst is selected from one or more noble metal catalysts selected from palladium catalysts and platinum catalysts, and the noble metal content in the noble metal catalyst is 1.5-3% based on the mass of the noble metal catalyst.

5. The method according to any one of claims 1 to 4, wherein, The amount of the precious metal catalyst used is 0.5 to 5% of the mass of the raw material A.

6. The method according to any one of claims 1 to 4, wherein, The hydrogenation reaction is carried out at a temperature of 50~150℃ and a pressure of 0.5~3 MPa.

7. The method according to claim 1, wherein, Raw material B is one or more of cyclohexanone, butanone, and methyl isopentyl ketone.

8. The method according to claim 1, wherein, The N,N′-dialkyl-p-phenylenediamine represented by formula (I) is one or more of the following compounds: N,N'-Diisobutyl-p-phenylenediamine, N,N'-Bis(1,4-dimethylpentyl)p-phenylenediamine, N,N'-Dicyclohexyl-p-phenylenediamine, N-Isobutyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine, N-Cyclohexyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine and N-Isobutyl-N'-Cyclohexyl-p-phenylenediamine.

9. The method according to any one of claims 1 to 4, further comprising pre-melting the solid components of raw material A and raw material B into liquid state, and conveying them to the reaction apparatus through a heat preservation device.

10. An antioxidant mixture, characterized in that, Includes N,N′-dialkyl-p-phenylenediamine or mixtures thereof of formula (I) prepared by the method according to any one of claims 1 to 9.

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