Method for preparing aliphatic diamine from hypervalent iodine and binary amide eutectic system

Abstract

The invention discloses a synthesis method of aliphatic diamine, which comprises the following steps: mixing a hypervalent iodine reagent and aliphatic binary amide as raw materials to form a eutectic system, and then carrying out Hofmann rearrangement reaction to obtain an acetylated diamine intermediate product; wherein the structural formula of the aliphatic binary amide is shown in the specification; wherein n is 2 to 16; and hydrolyzing the obtained acetylated diamine intermediate product to obtain the aliphatic diamine. According to the invention, the hypervalent iodine compound and the binary amide mixture form a eutectic system and are subjected to a rearrangement reaction to obtain the diamine derivative, and the diamine derivative is applied to preparation of aliphatic diamine, so that the method has the characteristics of milder reaction conditions, high yield, simpler and more convenient post-treatment and the like; and a new way is provided for the synthetic reaction in which the eutectic system participates and the preparation of the high-molecular polyamide material monomer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical synthesis, and in particular to a method for preparing aliphatic diamine by using high-valence iodine and binary amide eutectic system. BACKGROUND

[0002] Aliphatic diamine has important applications in the fields of organic synthesis, surfactants and polymer materials. As one of the important polymerization monomers in the field of materials, aliphatic diamine is widely used in the synthesis of polyurethane and polyamide, and has a large demand. At present, the production of diamine mainly uses binary acid as raw material to react with ammonia to generate ammonium salt, and then undergoes high temperature and twice dehydration to obtain nitrile. The nitrile is catalytically hydrogenated under high temperature and high pressure to obtain diamine product. This traditional method requires high temperature and high pressure, noble metal catalyst and other conditions, has high cost and potential safety risk, and is mainly applied to the synthesis of hexamethylenediamine and decanediamine. The preparation of other long-chain (more than ten carbons) aliphatic diamine is rarely reported, and it is necessary to study a more mild and extensive diamine preparation technology.

[0003] The eutectic system refers to a physical mixture composed of two or more substances, which has a significantly reduced melting point due to the change of intermolecular forces and exhibits wetting or liquefaction phenomenon, and has a wide range of applications. In organic synthesis, it can be used as a solvent or catalyst with dual functions, which can significantly reduce the activation energy and temperature of the reaction, and improve the efficiency of the reaction. Generally, the eutectic system is formed by adding an additional solid hydrogen bond donor and acceptor in a specific ratio at a certain temperature to form a liquid state. However, there are few reports on designing reaction substrates as eutectic systems and subsequent reactions. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a simple, rapid and efficient method for preparing aliphatic diamine.

[0005] The present application solves the above technical problems by the following technical means: A method for synthesizing aliphatic diamine, comprising the following steps: First step: using high-valence iodine reagent and aliphatic binary amide as raw materials, mixing them to form a eutectic system, and then undergoing Hofmann rearrangement reaction to obtain acetylated diamine intermediate product, which is easily separated and purified by solvent precipitation method; The structure of the aliphatic binary amide is as follows: wherein n is 2-16; Second step: hydrolyzing the obtained acetylated diamine intermediate product to obtain the aliphatic diamine.

[0006] Preferably, the hypervalent iodine reagent is selected from a mixture of one or more of hydroxyl toluenesulfonyl iodobenzene, [bis(trifluoroacetoxy)iodo]benzene, iodoacetic acid benzene, iodosylbenzene, diaryliodonium salts, dichloroiodobenzene.

[0007] Preferably, the hypervalent iodine reagent is selected from a mixture of one or more of hydroxyl toluenesulfonyl iodobenzene, [bis(trifluoroacetoxy)iodo]benzene, iodoacetic acid benzene, iodosylbenzene, diaryliodonium salts, dichloroiodobenzene.

[0008] Preferably, the molar ratio of the aliphatic dibasic amide to the hypervalent iodine reagent is 1:2-3.5; preferably one of 1:2, 1:2.5, 1:3, 1:3.2, 1:3.5.

[0009] Preferably, the molar ratio of the aliphatic dibasic amide to the hypervalent iodine reagent is 1:2.

[0010] Preferably, n is 6-16; preferably n is 8-14; preferably one of 6, 8, 12, 14.

[0011] Preferably, in the first step reaction, the temperature for forming the eutectic system is room temperature to 100°C, and the time is 30 minutes to 24 hours; more preferably, the reaction temperature is 40°C to 100°C, and the reaction time is 1 hour to 10 hours.

[0012] Preferably, the eutectic system is formed at a temperature in the range of 60-80°C.

[0013] Preferably, in the second step reaction, the hydrolysis is carried out under acidic or basic conditions.

[0014] Preferably, the basic conditions are provided using a base; the base is selected from common inorganic bases or organic bases; the molar amount of the base used is 2.0-10.0 times the molar amount of the acetylated diamine intermediate product.

[0015] Preferably, the molar amount of the base used is 2.0-6.0 times the molar amount of the acetylated diamine intermediate product.

[0016] Preferably, the base is one or more of sodium hydroxide and potassium hydroxide.

[0017] Preferably, the acidic conditions are provided using an acid; the acid used is a common inorganic acid such as hydrochloric acid or an organic acid.

[0018] Preferably, the acid used is added in an amount of 2.0-6.0 times the molar amount of the acetylated diamine intermediate product.

[0019] Preferably, during the second step reaction, the temperature for the hydrolysis is 40°C to 100°C, and the time is 30 minutes to 24 hours.

[0020] Preferably, in the first step of the reaction, the eutectic system can be a mixture of aliphatic diamide and high-valent iodine reagent. It is also possible to add common solvents to form a three-component or multi-component mixture of eutectic systems.

[0021] Preferably, after forming a eutectic system in the first step of the reaction, an organic solvent is added to participate in the subsequent Hoffmann rearrangement reaction.

[0022] Preferably, the organic solvent is selected from one or more of petroleum ether, 1,2-dichloroethane, 1,4-dioxane, and ethyl acetate, or a mixture thereof.

[0023] Preferably, in the first step of the reaction, after the Hoffmann rearrangement reaction is completed, the mixture is cooled and then one or more of methyl tert-butyl ether, petroleum ether, and n-hexane are added. The liquid mixture forms a solid due to the decrease in solubility. After washing and drying the solid, the acetylated diamine intermediate is obtained.

[0024] Preferably, in the first step of the reaction, after the Hoffmann rearrangement reaction is completed, the mixture is cooled and then one or more of methyl tert-butyl ether, petroleum ether, and n-hexane are added. Due to the reduced solubility of the product in the eutectic, a solid precipitates. The solid is further washed with petroleum ether to remove impurities and dried to obtain the pure acetylated diamine intermediate. The post-processing operation is simple and the purification efficiency is high. However, it is not ruled out that other solvents may be used to reduce the product solubility and precipitate a solid.

[0025] Preferably, in the first step, the aliphatic diamide and the high-valent iodine reagent are mixed under solvent-free conditions to form a eutectic system.

[0026] Preferably, the reaction route of the synthesis method of the present invention is shown in the following reaction formula:

[0027] In step 1, the diamide and high-valent iodine (taking iodobenzene acetate as an example) form a eutectic system and prepare a carbon chain-shortened diamine acylated product, namely acetylated diamine intermediate, through an end-to-end rearrangement process. In step 2, the diamine acylation product is directly hydrolyzed to prepare an aliphatic diamine product.

[0028] Preferably, The aliphatic diamine shown is one of the diamines with a chain length of eight to eighteen carbons.

[0029] This invention provides a novel method for preparing a eutectic system of high-valent iodine and a diamide and its application in the synthesis of aliphatic diamines. The synthesis includes the following steps: 1) Under solvent-free conditions, an aliphatic diamide and a high-valent iodine oxide form a eutectic system and undergo a Hofmann rearrangement reaction (forming a eutectic mixture without adding solvent; the mixture is liquid and can replace the solvent, thus promoting the reaction). 2) After the reaction is complete, the molten mixture is directly added to a solvent such as methyl tert-butyl ether, resulting in the precipitation of a white solid. This solid is then filtered, washed, and dried to obtain... (n is 2-16) shows the diamine acylation products. 3) The diamine acylation products are directly hydrolyzed to obtain aliphatic diamine products.

[0030] This invention forms a eutectic system by mixing a high-valent iodine compound with a diamide and undergoes a rearrangement reaction to obtain a diamine derivative, which is then applied to the preparation of aliphatic diamines. This method features milder reaction conditions, higher yield, and simpler post-processing, providing a new approach for synthetic reactions involving eutectic systems and the preparation of monomers for polymeric polyamide materials. Attached Figure Description

[0031] Figure 1 The diagram shows the formation of a eutectic state by mixing sebacic acid diamide and iodobenzene acetate in solid form and stirring at 60°C for 1.5 hours. Figure 2 The 1H and 1C NMR spectra of the reaction products of sebacate diamide according to the method of the present invention are shown below. Figure 3 The 1H and 1C NMR spectra of the reaction products of dodecanodiamide according to the method of the present invention are shown below. Figure 4 The 1H NMR spectrum and 1C NMR spectrum of the hexadecanediamide reaction product obtained by the method of the present invention; Figure 5 The 1H NMR spectrum and 1C NMR spectrum of the octadecadiamide reaction product obtained by the method of the present invention; Figure 6 The 1H NMR spectrum of the decanediamine product produced by the method of this invention; Figure 7 This is a flowchart illustrating the post-reaction processing of the method of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0034] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0035] The preparation of sebacic acid diamide described below is based on the method described in the reference (Zhang Chunhua, Xie Congxia, Yu Shitao, et al. Synthesis of sebacic acid diamide. Journal of Qingdao University of Science and Technology: Natural Science Edition, 2004, 25(4): 300-303). Specifically, the following steps are included: sebacic acid is placed in a three-necked flask, heated to melt, and then heated to 160℃. Urea is added in two batches to obtain a mixture, with a half-hour interval between the two batches. The molar ratio of sebacic acid to urea is 1:2.2. The mixture is preheated to melt at 160℃, and then heated to 220℃ for 4 hours. After the reaction, the mixture is extracted with ethanol and recrystallized to obtain the sebacic acid diamide product.

[0036] The preparation of dodecanoic diamide, hexadecanoic diamide, and octadecanoic diamide is based on the preparation method of sebacic diamide, except that dodecanoic acid, hexadecanoic acid, and octadecanoic acid are used respectively to replace sebacic acid in the preparation of dodecanoic diamide, hexadecanoic acid, and octadecanoic acid.

[0037] Aromatic diamide terephthalic acid diamide can be purchased directly.

[0038] Example 1 Preparation of eutectic mixtures Taking sebacic acid diamide as an example, firstly, sebacic acid diamide 1a (5.0 mmol, 1.0 g) and iodobenzene acetate (10.0 mmol, 3.2 g) were weighed. After the two solids were thoroughly mixed, the experimental conditions for the formation of a eutectic mixture between the two solid raw materials were studied at different temperatures. The procedure is as follows:

[0039] Since the melting points of the two solids before mixing both exceed 100°C, the temperature at which the eutectic is formed should be lower than the melting point of either reactant. Table 1 shows the time required for sebacic acid diamide and iodobenzene acetate to form an eutectic at different temperatures.

[0040] Table 1

[0041] As shown in Table 1, below 100℃, both solids can form a eutectic state within a certain time. The higher the temperature, the shorter the time required to form the eutectic state, and the 60-80℃ range is the most suitable temperature range for eutectic formation. Further reactions will be carried out within this temperature range. Figure 1 Diagram showing the eutectic state formed by stirring sebacic acid diamide (1a) and iodobenzene acetate (2) at 60°C for 1.5 h.

[0042] Example 2 Sebacic acid diamide forms a eutectic mixture with iodobenzene acetate and further undergoes a Hoffmann rearrangement reaction.

[0043] Add sebacic acid diamide (5.0 mmol, 1.0 g) and iodobenzene acetate (10.0 mmol, 3.2 g) to a 50 mL single-necked reaction tube. After thoroughly mixing the two solid components, heat to 60 °C. After approximately 1.5 h, the solid completely forms a eutectic liquid. Continue stirring the mixture at 60 °C for 2.5 h until the total time reaches 4 h. After cooling the mixture, add 20 mL of methyl tert-butyl ether (MTBE). Solids immediately precipitate from the eutectic mixture. Filter (vacuum filtration), wash with petroleum ether, and dry to obtain 0.96 g of white solid (see procedure below). Figure 7 The structure of this compound was determined by nuclear magnetic resonance (NMR), and the NMR data are as follows: 1 H NMR (600MHz, CDCl3) delta 5.61 (br, 2H), 3.22 (q, J =6.6 Hz, 4H), 1.96 (s, 6H), 1.48-1.47(m, 4H), 1.30 (s, 8H); 13 C NMR (150 MHz, CDCl3) delta 170.3, 39.7, 29.6, 29.1, 26.8, 23.5; spectral values ​​as shown. Figure 2 As shown, the compound obtained by NMR analysis is the target compound 3a, with a yield of 84%.

[0044] Example 3 Comparison of eutectic Hoffmann rearrangement reactions with reactions involving traditional organic solvents The key feature of this invention is that iodobenzene acetate and a diamide form a eutectic mixture under solvent-free conditions and further undergo a Hoffmann reaction. The advantages are the absence of organic solvents, a milder reaction temperature, shorter reaction time, higher reaction efficiency, and simpler product purification. To contrast with existing eutectic system methods, we also attempted a conventional method involving iodobenzene acetate in a solvent for the Hoffmann rearrangement reaction. Referring to the optimized method in the literature (J. Org. Chem. 2021, 86, 2820-2826), we attempted a reaction in which sebacic acid diamide and iodobenzene acetate undergo a Hoffmann rearrangement in the organic solvent 1,2-dichloroethane (DCE) to obtain diacetyloctanediamine, as detailed below:

[0045] Sebacic acid diamide (5.0 mmol, 1.0 g) and iodobenzene acetate (10.0 mmol, 3.2 g) were added to a 250 mL flask. The solid mixture was dissolved in 50 mL of 1,2-dichloroethane. After being connected to a reflux apparatus, the mixture was reacted at 100 °C for 48 h. After the reaction was completed, the solvent was evaporated under vacuum, and 20 mL of methyl tert-butyl ether was added. The mixture was filtered, washed with petroleum ether, and dried to obtain 0.21 g of white solid, with a yield of 18%. Comparative experiments show that the reaction conditions under solvent-free eutectic system conditions are milder, safer, and more efficient, and have advantages over traditional preparation methods.

[0046] Example 4 Hoffmann rearrangement reaction involving the addition of organic solvents after the formation of the eutectic state. Further investigation was conducted on the reaction effect of first forming a eutectic state between iodobenzene acetate and a diamide, followed by the addition of a solvent. The details are as follows:

[0047] Sebacic acid diamide (5.0 mmol, 1.0 g) and iodobenzene acetate (10.0 mmol, 3.2 g) were added to a 50 mL single-necked reaction tube. After thorough mixing of the two solid components, the mixture was heated to 60 °C. After approximately 1.5 h, the solids completely formed a eutectic liquid. Subsequently, 1,4-dioxane (5 mL) was added to the eutectic state, and the mixture was stirred at 60 °C for another 2.5 h until the total time reached 4 h. The solvent 1,4-dioxane was removed by rotary evaporation, and 20 mL of methyl tert-butyl ether was added. A solid precipitated out, which was filtered, washed with petroleum ether, and dried to obtain 0.82 g of white solid, which was the target product 3a, with a yield of 72%. This indicates that the addition of solvent reduced the yield of the target product and complicated the post-processing.

[0048] Example 5 Dodecanoic acid diamide forms a eutectic mixture with iodobenzene acetate and further undergoes a Hoffmann rearrangement reaction.

[0049] Dodecanoic acid diamide (5.0 mmol, 1.1 g) and iodobenzene acetate (10.0 mmol, 3.2 g) were added to a 50 mL single-necked reaction tube. The two solid components were thoroughly mixed and heated to 60 °C. After approximately 1.5 h, the solids completely formed a eutectic liquid. The mixture was stirred at 60 °C for another 2.5 h until the total time reached 4 h. After cooling, 20 mL of methyl tert-butyl ether was added. A solid immediately precipitated from the eutectic mixture. After filtration, washing with petroleum ether, and drying, 1.09 g of white solid was obtained. The structure of this compound was determined by nuclear magnetic resonance (NMR), and the NMR data are as follows: 1 H NMR (400 MHz, CDCl3) delta 5.54 (br, 2H), 3.23 (q, J =6.8 Hz, 4H), 1.98 (s, 6H), 1.50-1.45 (m, 4H), 1.29-1.25 (m, 12H); 13 C NMR (150 MHz, CDCl3) delta 170.2, 39.8, 29.7, 29.4, 29.2, 26.9, 23.5; Spectrum as shown Figure 3 As shown, the compound obtained by NMR analysis is the target compound 3b, with a yield of 84%.

[0050] Example 6 Hexadecanoic acid diamide forms a eutectic mixture with iodobenzene acetate and further undergoes a Hoffmann rearrangement reaction.

[0051] Hexadecanoic acid diamide (5.0 mmol, 1.4 g) and iodobenzene acetate (10.0 mmol, 3.2 g) were added to a 50 mL single-necked reaction tube. After thorough mixing of the two solid components, the mixture was heated to 80 °C. After approximately 1.5 h, the solid completely formed a eutectic liquid. The mixture was stirred at 80 °C for another 4.5 h until the total stirring time reached 6 h. After cooling, 20 mL of methyl tert-butyl ether was added. A solid immediately precipitated from the eutectic liquid mixture. After filtration, washing with petroleum ether, and drying, 1.26 g of white solid was obtained. The structure of this compound was determined by nuclear magnetic resonance (NMR), and the NMR data are as follows: 1 H NMR (600 MHz, CDCl3) delta 5.47 (br, 2H), 3.23 (q, J=6.6 Hz, 4H), 1.97 (s, 6H), 1.48-1.47 (m, 4H), 1.29-1.25 (m, 20H); 13 C NMR (150 MHz, CDCl3) delta 170.3, 39.8, 29.7-29.6, 29.4, 27.0, 23.4; spectral values ​​as shown. Figure 4 As shown, the compound obtained by NMR analysis is the target compound 3c, with a yield of 81%.

[0052] Example 7 Octadecanamide forms a eutectic mixture with iodobenzene acetate and further undergoes a Hoffmann rearrangement reaction.

[0053] Octadecanediamide (5.0 mmol, 1.5 g) and iodobenzene acetate (10.0 mmol, 3.2 g) were added to a 50 mL single-necked reaction tube. The two solid components were thoroughly mixed and heated to 80 °C. After approximately 1.5 h, the solids completely formed a eutectic liquid. The mixture was stirred at 80 °C for another 4.5 h until the total stirring time reached 6 h. After cooling, 20 mL of methyl tert-butyl ether was added. A solid immediately precipitated from the eutectic mixture. After filtration, washing with petroleum ether, and drying, 1.33 g of white solid was obtained. The structure of this compound was determined by nuclear magnetic resonance (NMR), and the NMR data are as follows: 1 H NMR (400 MHz, CDCl3) delta 5.45 (br, 2H),3.25-3.20 (m, 4H), 1.97 (s, 6H), 1.49 (t, J =7.2 Hz,6H), 1.28-1.25 (m, 22H); 13 C NMR (150 MHz, CDCl3) delta 170.2, 39.9, 29.8-29.6, 29.4, 27.1, 23.5; Spectrum as shown Figure 5 As shown, the compound obtained by NMR analysis is the target compound 3d, with a yield of 78%.

[0054] Example 8 Preparation of decanediamine by hydrolysis of diacetyldecanediamine The above diacetyldiamine intermediates can be hydrolyzed to yield aliphatic diamine products. Taking the hydrolysis of diacetyldecyldiamine 3b under alkaline conditions as an example, the hydrolysis process is illustrated below:

[0055] Diacetyldecanediamine 3b (2.0 mmol, 0.5 g) and potassium hydroxide (10.0 mmol, 0.56 g) dissolved in a mixture of water and methanol (15 mL, v / v 1:2) were added to a 50 mL round-bottom flask. The mixture was refluxed at 100 °C for 24 h. The solvent was removed by rotary evaporation, and the target product was dissolved in an appropriate amount of methanol. The filtrate was collected and rotary evaporated to give 0.23 g of white solid (68% yield). 1 HNMR (400 MHz, CDCl3) delta 2.67 (t, J =6.8 Hz, 4H), 1.44–1.39 (m, 4H), 1.31–1.20 (m, 16H); spectrum as shown Figure 6 As shown, the compound obtained by NMR analysis is the target compound 4b. This compound is a common and known compound, and its NMR spectrum is consistent with the standard spectrum.

[0056] Example 9 Preparation of other aliphatic diamines Following the steps of Example 8, diacetyldecanediamine was replaced with equimolar amounts of diacetyloctanediamine 3a, diacetyltetradecanediamine 3c, and diacetylhexadecanediamine 3d, and hydrolyzed under the same conditions to obtain the corresponding aliphatic diamine products.

[0057] Example 10 Comparison of eutectic rearrangement reactions of aliphatic and aromatic diamides Examples 2 and 4-7 illustrate the formation of a eutectic system between aliphatic diamides and iodobenzene acetate, and further reaction. We also tried examples of aromatic diamides with iodobenzene acetate, and the results are as follows:

[0058] Terephthalic acid diamide (5.0 mmol, 0.82 g) and iodobenzene acetate (10.0 mmol, 3.2 g) were added to a 50 mL single-necked reaction tube. After thorough mixing of the two solid components, the mixture was heated to 60 °C. After approximately 1.5 h, the solids completely formed a eutectic liquid. Unlike the aliphatic diamide phenomenon described above, the eutectic liquid was black. The mixture was stirred at 60 °C for another 2.5 h until the total time reached 4 h, at which point the mixture became a black paste. After cooling, 20 mL of methyl tert-butyl ether was added, and no solid precipitated. Thin-layer chromatography and column chromatography analysis revealed no obvious target product.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for synthesizing an aliphatic diamine, characterized in that: Includes the following steps: Step 1: Using high-valent iodine reagent and aliphatic diamide as raw materials, the two are mixed to form a eutectic system, followed by a Hoffmann rearrangement reaction to obtain acetylated diamine intermediate; The structural formula of the aliphatic diamide is shown below: Where n is 2-16; Step 2: Hydrolyze the obtained acetylated diamine intermediate to obtain the aliphatic diamine.

2. The method for synthesizing aliphatic diamines according to claim 1, characterized in that: The high-valent iodine reagent is selected from one or more of the following: hydroxytoluenesulfonyl iodobenzene, [bis(trifluoroacetoxy)iodo]benzene, iodobenzene acetate, iodobenzene iodosulfonyl, diaryl iodide, and dichloroiodobenzene.

3. The method for synthesizing aliphatic diamines according to claim 1, characterized in that: The molar ratio of the aliphatic diamide to the high-valent iodine reagent is 1:2-3.

5.

4. The method for synthesizing aliphatic diamines according to claim 1, characterized in that: The value of n is 6-16.

5. The method for synthesizing aliphatic diamines according to claim 1, characterized in that: In the first step of the reaction, the temperature at which the eutectic system is formed is between room temperature and 100°C, and the time is between 30 minutes and 24 hours.

6. The method for synthesizing aliphatic diamines according to claim 1, characterized in that: It forms a eutectic system at temperatures in the range of 60-80℃.

7. The method for synthesizing aliphatic diamines according to claim 1, characterized in that: In the second step of the reaction, the hydrolysis temperature is between 40°C and 100°C, and the time is between 30 minutes and 24 hours.

8. The method for synthesizing aliphatic diamines according to claim 1, characterized in that: In the first step of the reaction, after the formation of the eutectic system, an organic solvent is added to participate in the subsequent Hoffmann rearrangement reaction.

9. The method for synthesizing aliphatic diamines according to claim 8, characterized in that: The organic solvent is selected from one or more of petroleum ether, 1,2-dichloroethane, 1,4-dioxane, and ethyl acetate, or a mixture thereof.

10. The method for synthesizing an aliphatic diamine according to any one of claims 1-9, characterized in that: In the first step of the reaction, after the Hoffmann rearrangement reaction is completed, the mixture is cooled and then one or more of methyl tert-butyl ether, petroleum ether, and n-hexane are added. The liquid mixture forms a solid due to the decrease in solubility. After washing and drying the solid, the acetylated diamine intermediate is obtained.

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