A process for the preparation of 1,2-propanediamine

Abstract

The application discloses a preparation method of 1,2-propylenediamine, which comprises the following steps: (1) 2-phenyl-5-methyl-2-oxazoline, ZIF-8 catalyst and liquid ammonia are added into a high-pressure reaction kettle, and after temperature rising, stirring and filtration, benzoyl 1,2-propylenediamine is obtained; (2) the benzoyl 1,2-propylenediamine obtained in the step (1), methanol and an alkali metal catalyst are added into an atmospheric pressure reaction kettle with a reflux device, after temperature rising and stirring, sulfuric acid is added to neutralize the alkali metal catalyst, after neutralization, the mixture is filtered, and the filtrate is subjected to distillation to obtain a mixture of methyl benzoate and 1,2-propylenediamine; (3) the mixture obtained in the step (2) is separated by rectification to obtain 1,2-propylenediamine products. The preparation method can reduce the production cost, the process condition is relatively mild, hydrogen is not needed to participate in the amination reaction, the process safety is higher, the raw material conversion rate is high, close to 100% conversion, the synthesis yield is higher than 90%, the preparation process is efficient and safe.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and specifically to a method for preparing 1,2-propanediamine. Background Technology

[0002] 1,2-Propanediamine is a widely used organic chemical intermediate and raw material, with important applications in pharmaceuticals, pesticides, organic synthesis, lubricating oil rust inhibitors, epoxy resin curing accelerators, spandex, modified shellac coatings, and other fields. Its derivatives can also be used as rubber, coatings, raw materials, chelating agents, mineral processing agents, etc.

[0003] Currently, the main preparation method for 1,2-propanediamine involves using 1,2-propanediol or monoisopropanolamine in the presence of a metal composite oxide via a hydroammoniation reaction. Related patent literature reports, such as patent CN112121812A, which uses a guanidine-modified γ-Al₂O₃ support, with NiO, CuO, WO₃, Sb₂O₃, and ThO₂ as the active components in a modified metal oxide composite catalyst. Propylene glycol is used as a raw material in the presence of hydrogen for ammoniaation, achieving a raw material conversion rate and synthesis selectivity of over 99%. However, this method requires high temperature and high pressure reaction conditions, and hydrogen is required for the reaction. The reaction conditions are harsh, and the process safety is relatively low due to the presence of hydrogen. Furthermore, the catalyst raw material cost is high, and the preparation process is complex. Patent CN101891628B discloses a 1 A method for preparing 1,2-propanediamine involves adding isopropanolamine, water, ammonia, hydrogen, and a catalyst to a high-pressure reactor, stirring at high speed, and carrying out a catalytic amination reaction at a temperature of 100–250℃ and a pressure of 5–15 MPa to obtain a mixture with 1,2-propanediamine as the main component, with a product selectivity greater than 80%. This method uses a batch reactor and requires the addition of water as a solvent, thus necessitating intermittent operation. Subsequent separation of the catalyst and product is complex, and the need to separate large amounts of water increases the complexity and cost of the operation. Patent CN113105337B uses a mixture of propylene oxide, hydrogen, and ammonia in a fixed-bed reactor under the action of Ni, Mo, and Pd catalysts supported on H-ZSM-5 to synthesize 1,2-propanediamine through a gas-solid phase reaction. Essentially, it still involves the reaction of propylene oxide with liquid ammonia to produce isopropanolamine, which is then aminated with liquid ammonia under the action of a catalyst to produce 1,2-propanediamine. This method still fails to overcome the defects of the method described in patent CN101891628B.

[0004] The above process schemes are the main methods for preparing 1,2-propanediamine. These technical schemes all require hydrogen to participate in the reaction to reduce the imine intermediate and finally obtain 1,2-propanediamine. Due to the wide explosion limit range of hydrogen and the risk of hydrogen embrittlement between hydrogen and the reactor metal material under high temperature and high pressure, the above process schemes have low safety and high investment costs for related safety facilities.

[0005] Patent CN102718661A discloses a method for the combined preparation of 1,2-propanediamine and dimethylpiperazine. Ammonia and isopropanolamine are mixed, preheated, and vaporized, then introduced into a fixed-bed reactor. Under conditions of condensation amination catalyst, pressure 1.0 MPa–4.0 MPa, and temperature 300°C–350°C, the product stream consists of 1,2-propanediamine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine, and unreacted ammonia and isopropanolamine. The product stream is then separated by distillation to obtain 1,2-propanediamine, 2,5-dimethylpiperazine, and 2,6-dimethylpiperazine. The weight ratio of ammonia to isopropanolamine is 10–16:1, and the weight percentage composition of the condensation amination catalyst is: HZSM-5 97–99%, phosphorus 1–3%. This method is mainly used for the preparation of 1,2-propanediamine and dimethylpiperazine. Although this method eliminates the need for hydrogen in the reaction, thus improving process safety, the catalyst used is a weakly acidic HZSM-5 molecular sieve containing phosphorus. Therefore, the stability of the catalyst needs to be further improved, and there is also the problem of phosphorus loss, which will cause some environmental pollution. Summary of the Invention

[0006] To address the issues of high cost, complex reaction, harsh reaction conditions, and low process safety in the preparation of 1,2-propanediamine, while ensuring a high yield of 1,2-propanediamine, this invention provides a method for preparing 1,2-propanediamine.

[0007] The technical solution adopted in this invention is: a method for preparing 1,2-propanediamine, the detailed steps of which are as follows: (1) 2-Phenyl-5-methyl-2-oxazoline, ZIF-8 catalyst and liquid ammonia were added to a high-pressure reactor, stirring was started, the temperature was raised to the reaction temperature, and the amination reaction was started. The reaction solution was filtered to obtain benzoyl-1,2-propanediamine. (2) Add the benzoyl 1,2-propanediamine, methanol and alkali metal catalyst obtained in step (1) to a reactor equipped with a reflux device, heat and stir, add sulfuric acid to neutralize the alkali metal catalyst, filter the mixture after neutralization, and distill the filtrate to obtain a mixture of methyl benzoate and 1,2-propanediamine. (3) The mixture obtained in step 2 is separated into high-purity 1,2-propanediamine product and methyl benzoate by-product by distillation. Methyl benzoate can be recycled as a raw material for the preparation of 2-phenyl-5-methyl-2-oxazoline.

[0008] The synthetic reaction process for preparing the 1,2-propanediamine is as follows:

[0009]

[0010] As shown in formulas (I) and (II), 2-phenyl-5-methyl-2-oxazoline first undergoes a ring-opening ammoniation reaction with liquid ammonia under the action of a catalyst to generate benzoyl-1,2-propanediamine. Benzoyl-1,2-propanediamine then undergoes an alcoholysis reaction with methanol under the action of an alkaline catalyst to produce methyl benzoate and 1,2-propanediamine. Methyl benzoate can be recycled as a raw material for the preparation of 2-phenyl-5-methyl-2-oxazoline.

[0011] This application uses ZIF-8 as the reaction catalyst. Compared with conventional Lewis acid catalysts, such as zinc acetate and zinc chloride, the zinc ions in the catalyst can form a complex with 2-phenyl-5-methyl-2-oxazoline, resulting in a homogeneous reaction, and the catalyst is difficult to separate from the reaction system; while the ZIF-8 catalyst is composed of zinc ions (Zn... 2+ The organic framework (MOF) material formed by the self-assembly of ZIF-8 and 2-methylimidazolium ligand possesses a three-dimensional porous network with a high specific surface area (up to 1000-2000 m² / g) and tunable pore size (approximately 3.4 Å). This structure endows ZIF-8 with excellent chemical stability (resistance to strong alkalis and high temperatures) and abundant Lewis acidic catalytic sites, which can effectively catalyze the ring-opening ammoniation reaction of 2-oxazoline described in this invention, and the catalyst can be recovered by filtration. The 2-phenyl-5-methyl-2-oxazoline raw material used is chemically active and readily reacts with ammonia or organic amines under certain conditions. The N-benzoyl-1,2-propanediamine generated by the reaction can be debenzoylated by alcoholysis to obtain the 1,2-propanediamine product. The process does not require the participation of hydrogen and has high process safety.

[0012] Preferably, the catalyst feed amount is 1.0%-10.0% of the mass of 2-phenyl-5-methyl-2-oxazoline.

[0013] Preferably, the molar ratio of 2-phenyl-5-methyl-2-oxazoline to liquid ammonia is 1.0:1.3-3.0; the reaction temperature is 100℃-140℃; and the reaction time is 2.0h-8.0h.

[0014] Limiting the amount of liquid ammonia to an excess of 2-phenyl-5-methyl-2-oxazoline is beneficial for the full conversion of 2-phenyl-5-methyl-2-oxazoline. If the amount of liquid ammonia fed is too high, it will cause more ammonolysis side reactions. The reaction temperature is 100℃-140℃. Within this temperature range, the reaction can be carried out smoothly while reducing ammonolysis side reactions.

[0015] Preferably, the alkali metal catalyst is sodium methoxide or potassium methoxide; the catalyst feed amount is 0.01%-0.1% of the total mass of benzoyl-1,2-propanediamine and methanol.

[0016] Preferably, the molar ratio of benzoyl 1,2-propanediamine to methanol is 1.0:6.0-18.0; the alcoholysis reaction temperature is 60℃-100℃; and the alcoholysis reaction time is 2.0h-6.0h.

[0017] Since the alcoholysis reaction is a reversible reaction, a higher methanol feed rate is beneficial for shifting the reaction equilibrium to the right, promoting the full conversion of benzoyl-1,2-propanediamine.

[0018] Preferably, the theoretical molar ratio of sulfuric acid to alkali metal catalyst is 0.5:1.0, and the neutralization reaction time is 0.5h-1.0h.

[0019] The purpose of neutralization is to quench the sodium methoxide catalyst in the alcoholysis reaction system, which is beneficial for the subsequent removal of methanol and avoids the reaction equilibrium shifting to the left as the amount of methanol in the system decreases under alkaline conditions. The neutralization reaction time is 0.5h-1.0h, within which the catalyst can be effectively quenched completely.

[0020] The beneficial effects of this invention are: Compared with the traditional hydroammoniation process, the 1,2-propanediamine preparation method adopted in this invention has the advantages of low catalyst cost, relatively mild process conditions, no need for hydrogen to participate in the ammoniation reaction, higher process safety, and the overall process yield can reach more than 90%, making the preparation process efficient and safe. Detailed Implementation

[0021] The technical solution of the present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the embodiments described. Example 1

[0022] 1. 161.21 g of 2-phenyl-5-methyl-2-oxazoline and 1.79 g of ZIF-8 catalyst (1.11% of the mass of 2-phenyl-5-methyl-2-oxazoline) were added to a 500 ml high-pressure reactor. The reactor lid was closed, and 20.45 g of liquid ammonia (the molar ratio of liquid ammonia to 2-phenyl-5-methyl-2-oxazoline was 1.3:1.0) was introduced. The mixture was stirred and heated to 100 °C for 8.0 hours. The resulting reaction solution was filtered, and excess liquid ammonia and the remaining 2-phenyl-5-methyl-2-oxazoline were removed by distillation to obtain 163.09 g of benzoyl-1,2-propanediamine, with a yield of 91.5% and a gas chromatography purity of 99.65%. 2. The obtained benzoyl 1,2-propanediamine was added to a 2L reactor equipped with a reflux device, along with 175.90g of anhydrous methanol (the molar ratio of methanol to benzoyl 1,2-propanediamine was 6.0:1.0) and 0.034g of sodium methoxide (0.01% of the total mass of benzoyl 1,2-propanediamine and methanol). The mixture was stirred and heated to 60℃. After reacting for 6.0 hours, 0.031g of 98% concentrated sulfuric acid was added, and the reaction was continued for another 0.5 hours. After the reaction was completed, the reaction solution was filtered, and excess methanol was removed by distillation to obtain a mixture of methyl benzoate and 1,2-propanediamine. 3. The mixture was separated by distillation, and the light phase obtained was 64.57 g of 1,2-propanediamine. The overall process yield was 87.1%, and the product purity was 99.5%. Example 2

[0023] 1. 161.21 g of 2-phenyl-5-methyl-2-oxazoline and 8.95 g of ZIF-8 catalyst (5.0% of the mass of 2-phenyl-5-methyl-2-oxazoline) were added to a 500 ml high-pressure reactor. The reactor lid was closed, and 30.67 g of liquid ammonia (the molar ratio of liquid ammonia to 2-phenyl-5-methyl-2-oxazoline was 1.8:1.0) was introduced. Stirring was started, and the temperature was raised to 120 °C. The reaction was carried out for 5.0 hours. The obtained reaction solution was filtered and the excess liquid ammonia and the remaining 2-phenyl-5-methyl-2-oxazoline were removed by distillation to obtain 169.51 g of benzoyl-1,2-propanediamine, with a yield of 95.1% and a gas chromatography purity of 99.1%. 2. The obtained benzoyl 1,2-propanediamine was added to a 2L reactor equipped with a reflux device, along with 365.65g of anhydrous methanol (molar ratio of methanol to benzoyl 1,2-propanediamine 12.0:1.0) and 0.27g of sodium methoxide (0.05% of the total mass of benzoyl 1,2-propanediamine and methanol). The mixture was stirred and heated to 80℃. After reacting for 4.0 hours, 0.25g of 98% concentrated sulfuric acid was added, and the reaction was continued for another 1.0 hour. After the reaction was completed, the reaction solution was filtered, and excess methanol was removed by distillation to obtain a mixture of methyl benzoate and 1,2-propanediamine. 3. The mixture was separated by distillation, and the light phase obtained was 68.11 g of 1,2-propanediamine. The overall process yield was 91.9%, and the product purity was 99.6%. Example 3

[0024] 1. 161.21 g of 2-phenyl-5-methyl-2-oxazoline and 17.9 g of ZIF-8 catalyst (10.0% of the mass of 2-phenyl-5-methyl-2-oxazoline) were added to a 500 ml high-pressure reactor. The reactor lid was closed, and 30.67 g of liquid ammonia (the molar ratio of liquid ammonia to 2-phenyl-5-methyl-2-oxazoline was 1.8:1.0) was introduced. The mixture was stirred and heated to 140 °C for 2.0 hours. The resulting reaction solution was filtered and the excess liquid ammonia and the remaining 2-phenyl-5-methyl-2-oxazoline were removed by distillation to obtain 166.48 g of benzoyl-1,2-propanediamine, with a yield of 93.4% and a gas chromatography purity of 99.4%. 2. The obtained benzoyl 1,2-propanediamine was added to a 2L glass reactor equipped with a reflux device, along with 538.67g of anhydrous methanol (molar ratio of methanol to benzoyl 1,2-propanediamine 18.0:1.0) and 0.71g of sodium methoxide (0.1% of the total mass of benzoyl 1,2-propanediamine and methanol). The mixture was stirred and heated to 70℃. After reacting for 4.0 hours, 0.66g of 98% concentrated sulfuric acid was added, and the reaction was continued for another 0.5 hours. After the reaction was completed, the reaction solution was filtered, and excess methanol was removed by distillation to obtain a mixture of methyl benzoate and 1,2-propanediamine. 3. The mixture was separated by distillation, and the light phase obtained was 68.20 g of 1,2-propanediamine. The overall process yield was 92.0%, and the product purity was 99.5%. Example 4

[0025] 1. 161.21 g of 2-phenyl-5-methyl-2-oxazoline and 8.95 g of ZIF-8 catalyst (5.0% of the mass of 2-phenyl-5-methyl-2-oxazoline) were added to a 500 ml high-pressure reactor. The reactor lid was closed, and 51.12 g of liquid ammonia (the molar ratio of liquid ammonia to 2-phenyl-5-methyl-2-oxazoline was 3.0:1.0) was introduced. The mixture was stirred and heated to 120 °C for 8.0 hours. The resulting reaction solution was filtered and the excess liquid ammonia and the remaining 2-phenyl-5-methyl-2-oxazoline were removed by distillation to obtain 159.35 g of benzoyl-1,2-propanediamine, with a yield of 89.4% and a gas chromatography purity of 99.4%. 2. The obtained benzoyl 1,2-propanediamine was added to a 2L glass reactor equipped with a reflux device, along with 515.60g of anhydrous methanol (molar ratio of methanol to benzoyl 1,2-propanediamine 18.0:1.0) and 0.34g of sodium methoxide (0.05% of the total mass of benzoyl 1,2-propanediamine and methanol). The mixture was stirred and heated to 80℃. After reacting for 2.0 hours, 0.31g of 98% concentrated sulfuric acid was added, and the reaction was continued for another 0.5 hours. After the reaction was completed, the reaction solution was filtered, and excess methanol was removed by distillation to obtain a mixture of methyl benzoate and 1,2-propanediamine. 3. The mixture was separated by distillation, and the light phase obtained was 65.22 g of 1,2-propanediamine. The overall process yield was 88.0%, and the product purity was 99.6%. Example 5

[0026] 1. 161.21 g of 2-phenyl-5-methyl-2-oxazoline and 17.9 g of ZIF-8 catalyst (10.0% of the mass of 2-phenyl-5-methyl-2-oxazoline) were added to a 500 ml high-pressure reactor. The reactor lid was closed, and 51.12 g of liquid ammonia (the molar ratio of liquid ammonia to 2-phenyl-5-methyl-2-oxazoline was 3.0:1.0) was introduced. The mixture was stirred and heated to 140 °C for 2.0 hours. The resulting reaction solution was filtered and the excess liquid ammonia and the remaining 2-phenyl-5-methyl-2-oxazoline were removed by distillation to obtain 152.57 g of benzoyl-1,2-propanediamine, with a yield of 85.6% and a gas chromatography purity of 99.3%. 2. The obtained benzoyl 1,2-propanediamine was added to a 2L glass reactor equipped with a reflux device, along with 493.66g of anhydrous methanol (molar ratio of methanol to benzoyl 1,2-propanediamine 18.0:1.0) and 0.32g of sodium methoxide (0.05% of the total mass of benzoyl 1,2-propanediamine and methanol). The mixture was stirred and heated to 60℃. After reacting for 4.0 hours, 0.30g of 98% concentrated sulfuric acid was added, and the reaction was continued for another 0.5 hours. After the reaction was completed, the reaction solution was filtered, and excess methanol was removed by distillation to obtain a mixture of methyl benzoate and 1,2-propanediamine. 3. The mixture was separated by distillation, and the light phase obtained was 62.38 g of 1,2-propanediamine. The overall process yield was 84.1%, and the product purity was 99.6%. Example 6

[0027] 1. 161.21 g of 2-phenyl-5-methyl-2-oxazoline and 17.9 g of ZIF-8 catalyst (10.0% of the mass of 2-phenyl-5-methyl-2-oxazoline) were added to a 500 ml high-pressure reactor. The reactor lid was closed, and 34.08 g of liquid ammonia (the molar ratio of liquid ammonia to 2-phenyl-5-methyl-2-oxazoline was 2.0:1.0) was introduced. Stirring was started, and the temperature was raised to 130 °C. The reaction was carried out for 4.0 hours. The obtained reaction solution was filtered and the excess liquid ammonia and the remaining 2-phenyl-5-methyl-2-oxazoline were removed by distillation to obtain 168.62 g of benzoyl-1,2-propanediamine, with a yield of 94.6% and a gas chromatography purity of 99.4%. 2. The obtained benzoyl 1,2-propanediamine was added to a 2L glass reactor equipped with a reflux device, along with 545.59g of anhydrous methanol (molar ratio of methanol to benzoyl 1,2-propanediamine 18.0:1.0) and 0.36g of sodium methoxide (0.05% of the total mass of benzoyl 1,2-propanediamine and methanol). The mixture was stirred and heated to 70℃. After reacting for 4.0 hours, 0.33g of 98% concentrated sulfuric acid was added, and the reaction was continued for another 0.5 hours. After the reaction was completed, the reaction solution was filtered, and excess methanol was removed by distillation to obtain a mixture of methyl benzoate and 1,2-propanediamine. 3. The mixture was separated by distillation, and the light phase obtained was 69.43 g of 1,2-propanediamine. The overall process yield was 93.7%, and the product purity was 99.5%. Example 7

[0028] 1. 161.21 g of 2-phenyl-5-methyl-2-oxazoline and 17.9 g of ZIF-8 catalyst (10.0% of the mass of 2-phenyl-5-methyl-2-oxazoline) were added to a 500 ml high-pressure reactor. The reactor lid was closed, and 34.08 g of liquid ammonia (the molar ratio of liquid ammonia to 2-phenyl-5-methyl-2-oxazoline was 2.0:1.0) was introduced. The mixture was stirred and heated to 140 °C for 4.0 hours. The resulting reaction solution was filtered and the excess liquid ammonia and the remaining 2-phenyl-5-methyl-2-oxazoline were removed by distillation to obtain 166.12 g of benzoyl-1,2-propanediamine, with a yield of 93.2% and a gas chromatography purity of 99.5%. 2. The obtained benzoyl 1,2-propanediamine was added to a 2L glass reactor equipped with a reflux device, along with 537.5g of anhydrous methanol (molar ratio of methanol to benzoyl 1,2-propanediamine 18.0:1.0) and 0.35g of sodium methoxide (0.05% of the total mass of benzoyl 1,2-propanediamine and methanol). The mixture was stirred and heated to 70℃. After reacting for 4.0 hours, 0.32g of 98% concentrated sulfuric acid was added, and the reaction was continued for another 0.5 hours. After the reaction was completed, the reaction solution was filtered, and excess methanol was removed by distillation to obtain a mixture of methyl benzoate and 1,2-propanediamine. 3. The mixture was separated by distillation, and the light phase obtained was 68.06 g of 1,2-propanediamine. The overall process yield was 91.8%, and the product purity was 99.5%. Example 8

[0029] 1. 161.21 g of 2-phenyl-5-methyl-2-oxazoline and 17.9 g of ZIF-8 catalyst (10.0% of the mass of 2-phenyl-5-methyl-2-oxazoline) were added to a 500 ml high-pressure reactor. The reactor lid was closed, and 34.08 g of liquid ammonia (the molar ratio of liquid ammonia to 2-phenyl-5-methyl-2-oxazoline was 2.0:1.0) was introduced. The mixture was stirred and heated to 130 °C for 4.0 hours. The resulting reaction solution was filtered and the excess liquid ammonia and the remaining 2-phenyl-5-methyl-2-oxazoline were removed by distillation to obtain 170.31 g of benzoyl-1,2-propanediamine, with a yield of 95.6% and a gas chromatography purity of 99.6%. 2. The obtained benzoyl 1,2-propanediamine was added to a 2L glass reactor equipped with a reflux device, along with 545.59g of anhydrous methanol (molar ratio of methanol to benzoyl 1,2-propanediamine 18.0:1.0) and 0.36g of potassium methoxide (0.05% of the total mass of benzoyl 1,2-propanediamine and methanol). The mixture was stirred and heated to 100℃. After reacting for 2.0 hours, 0.25g of 98% concentrated sulfuric acid was added, and the reaction was continued for another 0.75 hours. After the reaction was completed, the reaction solution was filtered, and excess methanol was removed by distillation to obtain a mixture of methyl benzoate and 1,2-propanediamine. 3. The mixture was separated by distillation, and the light phase obtained was 70.35 g of 1,2-propanediamine. The overall process yield was 94.9%, and the product purity was 99.6%.

[0030] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also within the protection scope of the present invention.

Claims

1. A method for preparing 1,2-propanediamine, characterized in that, Includes the following steps: (1) 2-Phenyl-5-methyl-2-oxazoline, ZIF-8 catalyst and liquid ammonia were added to a high-pressure reactor, stirring was started, the temperature was raised to the reaction temperature, and the amination reaction was started. After filtration, benzoyl-1,2-propanediamine was obtained. (2) Add the benzoyl 1,2-propanediamine, methanol and alkali metal catalyst obtained in step (1) to a reactor equipped with a reflux device, heat to the reaction temperature, stir the reaction, add sulfuric acid to neutralize the alkali metal catalyst, filter the mixture after neutralization, and distill the filtrate to obtain a mixture of methyl benzoate and 1,2-propanediamine. (3) The mixture obtained in step 2 is separated into 1,2-propanediamine product by distillation.

2. The preparation method according to claim 1, characterized in that, In step (1), the amount of catalyst fed is 1.0%-10.0% of the mass of 2-phenyl-5-methyl-2-oxazoline.

3. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of 2-phenyl-5-methyl-2-oxazoline to liquid ammonia is 1.0:1.3-3.0; the reaction temperature is 100℃-140℃; and the reaction time is 2.0h-8.0h.

4. The preparation method according to claim 1, characterized in that, In step (2), the alkali metal catalyst is sodium methoxide or potassium methoxide; the catalyst feed amount is 0.01%-0.1% of the total mass of benzoyl 1,2-propanediamine and methanol.

5. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of benzoyl 1,2-propanediamine to methanol is 1.0:6.0-18.0; the reaction temperature is 60℃-100℃; and the reaction time is 2.0h-6.0h.

6. The preparation method according to claim 1, characterized in that, In step (2), the theoretical molar ratio of sulfuric acid to alkali metal catalyst is 0.5:1.0, and the neutralization reaction time is 0.5h-1.0h.

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