A polyurethane chain extender 2-(3,5-diamino-4-chlorophenyl) methyl acetate and its preparation method

Abstract

The present invention provides a polyurethane chain extender, methyl 2-(3,5-diamino-4-chlorophenyl)acetate, and a preparation method thereof. The preparation method comprises the following steps: After fully mixing 4-chlorophenylacetic acid with concentrated sulfuric acid or acetic anhydride, any one of concentrated nitric acid, sodium nitrate and sodium nitrite is added, the temperature is raised and then kept warm, and then the reaction solution is added to excessive water to precipitate a solid, which is obtained as product A after filtration and drying; Product A is added to methanol and concentrated sulfuric acid for reflux reaction, then methanol is removed by vacuum distillation, a solid is precipitated, and after filtration, washing and drying, product B is obtained; Product B is added to methanol and / or ethanol and a saturated ammonium chloride solution, then iron powder is added, after reflux reaction for a period of time, it is cooled to room temperature, filtered, and the liquid phase is subjected to vacuum distillation to obtain the final product. The prepared methyl 2-(3,5-diamino-4-chlorophenyl)acetate, as a substitute for MOCA chain extender, has no carcinogenic risk, and the preparation process is simple and easy to realize industrialization.

Description

Technical Field

[0001] The present invention relates to the technical field of chain extender preparation, and in particular to a polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate and a preparation method thereof. Background Art

[0002] Polyurethane elastomers are an important class of chemical materials, usually obtained by reacting isocyanates with polyether (ester) polyols to obtain prepolymers and then chain-extending. Among them, MOCA (3,3'-dichloro-4,4'-diaminodiphenylmethane) is the most widely used aromatic diamine chain extender at present, and is widely used in the automotive industry, electronic appliances, construction engineering, medical devices, sports facilities and other aspects.

[0003] Low molecular weight diamine compounds react very violently with diisocyanates, and gels are produced rapidly and are not easy to control. However, the reaction with isocyanates generates urea groups with high cohesive energy, which can endow polyurethane polymers with good physical and mechanical properties. To solve the disadvantages of too fast reaction rate and difficult control, hindered amine compounds are generally used. Considering the product cost, product color, reaction rate and safety performance comprehensively, 3,3'-dichloro-4,4'-diaminodiphenylmethane is widely used. It was first developed by an American company, and the trade name is Moca (MOCA), which is prepared by condensing o-chloroaniline and formaldehyde and undergoing steps such as neutralization, alcohol washing, and recrystallization.

[0004] The melting point of MOCA is above 100°C, and it is a needle-shaped crystal at room temperature. Therefore, when using MOCA as a chain extender to react with prepolymers, a high-temperature (>100°C) and long-term curing process is required. The processing operation is complex, the reaction is not easy to control and consumes energy, otherwise the system will not cure and the mechanical strength of the material will be seriously insufficient. When the mixture of MOCA and prepolymer is heated above 70°C, the -NCO group may further undergo side reactions with urethane bonds or urea bonds to generate urethane formate, biuret, etc., resulting in an increase in crosslinking degree, and thus a decrease in elasticity and service life. On the other hand, the raw material 2-chloroaniline for producing MOCA has a carcinogenic risk, which limits the application of polyurethane elastomer materials in some fields. Therefore, it is urgent to research and develop substitutes for MOCA chain extenders, which is also a research hotspot in polyurethane technology. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems in the related technologies to some extent. For this reason, an embodiment of the present invention provides a polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate and a preparation method thereof. The prepared methyl 2-(3,5-diamino-4-chlorophenyl)acetate is used as a substitute for the MOCA chain extender, has no carcinogenic risk, and the preparation process is simple and easy to realize industrialization.

[0006] In one embodiment of the present invention, a polyurethane chain extender, methyl 2-(3,5-diamino-4-chlorophenyl)acetate, is provided, and its molecular formula is:

[0007]

[0008] In another embodiment of the present invention, a method for preparing the above-mentioned polyurethane chain extender, methyl 2-(3,5-diamino-4-chlorophenyl)acetate, is provided, which includes the following steps:

[0009] S1. After fully mixing 4-chlorophenylacetic acid with concentrated sulfuric acid, any one of concentrated nitric acid, sodium nitrate, and sodium nitrite is added, and the temperature is raised to 30-70 °C and then kept warm to obtain a reaction solution. Then, the reaction solution is added to excessive water to precipitate a solid. After filtering and drying the obtained solid, product A is obtained, and the chemical formula of product A is:

[0010]

[0011] S2. The nitration product A is added to methanol and concentrated sulfuric acid for reflux reaction, and then methanol is removed by vacuum distillation, and a solid is precipitated. After filtering, washing, and drying, product B is obtained, and the chemical formula of product B is:

[0012]

[0013] S3. Product B is added to methanol and a saturated ammonium chloride solution, and then iron powder is added. After reflux reaction for a period of time, it is cooled to room temperature and filtered. After vacuum distillation of the liquid phase, methyl 2-(3,5-diamino-4-chlorophenyl)acetate is obtained.

[0014] In some embodiments, in step S1, concentrated sulfuric acid is replaced by acetic anhydride.

[0015] In some embodiments, in step S1, the heat preservation time is 1-4 h.

[0016] In some embodiments, in step S2, the solid-liquid ratio of 4-chlorophenylacetic acid to methanol and concentrated sulfuric acid is 30 g:50-420 ml:5-20 ml.

[0017] In some embodiments, in step S2, the reflux reaction time is 2-12 h.

[0018] In some embodiments, in step S3, methanol is replaced by ethanol or a mixture of methanol and ethanol.

[0019] In some embodiments, in step S3, the solid-liquid ratio of 4-chlorophenylacetic acid to methanol and a saturated ammonium chloride solution is 30 g:50-400 ml:50-500 ml.

[0020] In some embodiments, in the step S3, the mass ratio of 4-chlorophenylacetic acid to iron powder is 30:16 to 42.

[0021] In some embodiments, in the step S3, the reflux reaction time is 1 to 4 h. Description of the Drawings

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of the embodiments in conjunction with the drawings.

[0023] Wherein:

[0024] Figure 1 is the nuclear magnetic resonance hydrogen spectrum of methyl 2-(3,5-diamino-4-chlorophenyl)acetate prepared in the embodiment of the present invention; Detailed Description of the Embodiments

[0025] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0026] The polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate and its preparation method according to the embodiments of the present invention will be described below with reference to the drawings.

[0027] One embodiment of the present invention provides a polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate, and its molecular formula is:

[0028]

[0029] Its nuclear magnetic resonance hydrogen spectrum is as Figure 1 shown.

[0030] The methyl 2-(3,5-diamino-4-chlorophenyl)acetate prepared in the embodiment of the present invention has a molecular structure similar to that of MOCA. The electron-withdrawing effect and steric hindrance function of the chlorine atoms exist at the ortho positions of the two amino groups, so that the reaction activity of the amino groups is appropriately reduced, and it can well adapt to the polyurethane gel process; at the same time, an ester group carbon chain structure is introduced into the benzene ring structure, making the melting point of this chain extender significantly reduced and easy to process; its aromatic amine structure characteristics can endow the material with excellent physical and mechanical properties; the synthesis of this chain extender uses 4-chlorophenylacetic acid as a raw material. Compared with directly connecting a carbonyl group, the methylene structure connected to the benzene ring is easier to introduce an amino group, and at the same time, the potential carcinogenic risk of the raw material 2-chloroaniline required for producing MOCA is avoided, and the process is simple and easy to realize industrialization. Therefore, it has broad application prospects.

[0031] Another embodiment of the present invention provides a method for preparing the above-mentioned polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate, comprising the following steps:

[0032] S1. After fully mixing 4-chlorophenylacetic acid with concentrated sulfuric acid, add any one of concentrated nitric acid, sodium nitrate and sodium nitrite, heat up to 30-70 °C and keep warm to obtain a reaction solution. Then add the reaction solution to excess water to precipitate a solid. After filtering and drying the obtained solid, product A is obtained. The chemical formula of product A is:

[0033]

[0034] S2. Add product A to methanol and concentrated sulfuric acid for reflux reaction, then remove methanol by vacuum distillation, precipitate a solid, and after filtering, washing and drying, product B is obtained. The chemical formula of product B is:

[0035]

[0036] S3. Add product B to methanol and saturated ammonium chloride solution, then add iron powder, reflux for a period of time, cool to room temperature, filter, and after vacuum distilling the liquid phase, methyl 2-(3,5-diamino-4-chlorophenyl)acetate is obtained.

[0037] The methyl 2-(3,5-diamino-4-chlorophenyl)acetate prepared in the embodiments of the present invention as a substitute for MOCA chain extender has no carcinogenic risk, the preparation process is simple and easy to realize industrialization. Using the preparation method of the present invention, the yield of the final product is 86-93%.

[0038] It should be noted that in step S1, the reaction temperature is limited to 30-70 °C because too high or too low reaction temperature will affect the rate and selectivity of the nitration reaction. Generally speaking, the higher the reaction temperature, the faster the reaction rate; the lower the reaction temperature, the slower the reaction rate. However, if the reaction temperature is too high (greater than 70 °C), poly-nitro compounds and oxidation side reactions are likely to occur, reducing the purity and yield of the nitration product. When the reaction temperature is too low (less than 30 °C), the reaction rate will be very slow. Considering comprehensively, the reaction temperature is limited to 30-70 °C, which can not only ensure the reaction rate as much as possible, but also improve the purity and yield of the nitration product and reduce the occurrence of side reactions.

[0039] Furthermore, in step S1, the solid-liquid ratio of 4-chlorophenylacetic acid to concentrated nitric acid is 30 g: 25-70 ml. When concentrated nitric acid is replaced by sodium nitrate, the mass ratio of 4-chlorophenylacetic acid to sodium nitrate is 30: 30-92. When concentrated nitric acid is replaced by sodium nitrite, the mass ratio of 4-chlorophenylacetic acid to sodium nitrite is 30: 25-75.

[0040] In some embodiments, in step S1, concentrated sulfuric acid is replaced with acetic anhydride.

[0041] Furthermore, in step S1, the solid-liquid ratio of 4-chlorophenylacetic acid to concentrated sulfuric acid is 30 g: 20 - 170 ml. When concentrated sulfuric acid is replaced with acetic anhydride, the solid-liquid ratio of 4-chlorophenylacetic acid to acetic anhydride is 30 g: 35 - 290 ml.

[0042] In some embodiments, in step S1, the heat preservation time is 1 - 4 h.

[0043] It should be noted that the heat preservation time is the reaction time. Limiting the heat preservation time to 1 - 4 h in the embodiments of the present invention has the advantages of controlling the reaction process, optimizing the reaction efficiency, increasing the yield and purity of the target product, reducing the generation of by-products and waste, and saving energy. Too long or too short reaction time will affect the nitration reaction effect. Too long reaction time (greater than 4 h) may lead to excessive nitration reaction, resulting in unnecessary side reactions, generating polynitro compounds and oxidation by-products, reducing the yield and purity of the nitration product, increasing the difficulty of separation and purification, and at the same time increasing the corrosion and safety risks of the reactor. Too short reaction time (less than 1 h) may lead to incomplete nitration reaction, resulting in loss of reactants, generating unnitrated raw materials and mononitro compounds, reducing the yield and purity of the nitration product, increasing the workload of subsequent treatment, affecting the repeatability and reliability of the reaction, and at the same time causing waste of nitrating agent.

[0044] In some embodiments, in step S2, the solid-liquid ratio of 4-chlorophenylacetic acid to methanol and concentrated sulfuric acid is 30 g: 50 - 420 ml: 5 - 20 ml.

[0045] In some embodiments, in step S2, the reflux reaction time is 2 - 12 h.

[0046] It should be noted that too long or too short reaction time will affect the esterification reaction effect. If the reaction time is too long (greater than 12 h), it will lead to excessive reaction, increased by-products, reducing the purity and yield of the esterification product, and at the same time increasing the corrosion and safety risks of the reactor. If the reaction time is too short (less than 2 h), it will lead to incomplete esterification reaction, increased unesterified raw materials, reducing the yield and quality of the esterification product, causing waste of raw materials. Therefore, limiting the reflux reaction time to 2 - 12 h can not only ensure the purity and yield of the esterification product, but also ensure the complete progress of the esterification reaction without causing waste of raw materials.

[0047] In some embodiments, in step S3, methanol is replaced with ethanol or a mixture of methanol and ethanol.

[0048] In some embodiments, in step S3, the solid-liquid ratio of 4-chlorophenylacetic acid to methanol (or ethanol, or a mixture of methanol and ethanol) and saturated ammonium chloride solution is 30 g: 50 - 400 ml: 50 - 500 ml.

[0049] Furthermore, if in step S3, methanol is replaced by ethanol or a mixture of methanol and ethanol, then the solid-liquid ratio of 4-chlorophenylacetic acid to ethanol (or a mixture of methanol and ethanol) and saturated ammonium chloride solution is 30 g: 50 - 400 ml: 50 - 500 ml.

[0050] In some embodiments, in step S3, the mass ratio of 4-chlorophenylacetic acid to iron powder is 30: 16 - 42.

[0051] It should be noted that iron powder has a reducing effect. If too much is added, unnecessary side reactions will occur, reducing the yield and purity of the target product, increasing the difficulty of separation and purification, and increasing the workload of subsequent processing. If too little is added, the reaction may not proceed completely, reducing the yield and purity of the target product and affecting the repeatability and reliability of the reaction. Therefore, the mass ratio of 4-chlorophenylacetic acid to iron powder is limited to 30: 16 - 42, which not only improves the yield and purity of the target product but also enables the reaction to proceed completely.

[0052] In some embodiments, in step S3, the reflux reaction time is 1 - 4 h.

[0053] It should be noted that if the reflux reaction time is too short (less than 1 h), the reaction will not be sufficient and the experimental repeatability will be reduced. If the reflux reaction time is too long (more than 4 h), side reactions are likely to occur, resulting in a decrease in yield and purity. Therefore, the reflux reaction time is limited to 1 - 4 h, which not only ensures the sufficiency of the reaction but also ensures the yield and purity of the final product.

[0054] The following further elaborates on the present invention through specific examples.

[0055] Example 1

[0056] A preparation method of polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate, comprising the following steps:

[0057] (1) Weigh 30 g of 4-chlorophenylacetic acid and mix it thoroughly with 50 ml of concentrated sulfuric acid, then slowly add 25 ml of concentrated nitric acid, heat to 50 °C and keep warm for 4 h, then add the reaction solution to excessive water to precipitate a solid, and after filtering and drying the obtained solid, a beige solid, i.e., product A, is obtained.

[0058] (2) Add the above product A to 300 ml of methanol and 15 ml of concentrated sulfuric acid, reflux for 5 h, then distill off the solvent methanol under reduced pressure. A large amount of yellow solid precipitates from the reaction solution. After filtration, washing, and drying, a yellow solid is obtained, which is product B.

[0059] (3) Add the above product B to 150 ml of methanol and 150 ml of saturated ammonium chloride solution, then add 35 g of iron powder. After refluxing for 3 h, cool to room temperature, filter, and distill the liquid phase under reduced pressure to obtain the final product methyl 2-(3,5-diamino-4-chlorophenyl)acetate, with a yield of 93%. Its nuclear magnetic resonance hydrogen spectrum is as Figure 1 shown.

[0060] Example 2

[0061] A preparation method of polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate, comprising the following steps:

[0062] (1) Weigh 30 g of 4-chlorophenylacetic acid and mix it thoroughly with 270 ml of acetic anhydride, then slowly add 89 g of sodium nitrate. After heating to 60 °C and keeping warm for 3 h, add the reaction solution to excessive water to precipitate a solid. After filtering and drying the obtained solid, a beige solid is obtained, which is product A.

[0063] (2) Add the above product A to 380 ml of methanol and 10 ml of concentrated sulfuric acid, reflux for 10 h, then distill off the solvent methanol under reduced pressure. A large amount of yellow solid precipitates from the reaction solution. After filtration, washing, and drying, a yellow solid is obtained, which is product B.

[0064] (3) Add the above product B to 60 ml of ethanol and 70 ml of saturated ammonium chloride solution, then add 20 g of iron powder. After refluxing for 4 h, cool to room temperature, filter, and distill the liquid phase under reduced pressure to obtain the final product methyl 2-(3,5-diamino-4-chlorophenyl)acetate, with a yield of 90%.

[0065] Example 3

[0066] A preparation method of polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate, comprising the following steps:

[0067] (1) Weigh 30 g of 4-chlorophenylacetic acid and mix it thoroughly with 100 ml of concentrated sulfuric acid, then slowly add 40 g of sodium nitrite. After heating to 40 °C and keeping warm for 1 h, add the reaction solution to excessive water to precipitate a solid. After filtering and drying the obtained solid, a beige solid is obtained, which is product A.

[0068] (2) Add the above product A to 75 ml of methanol and 5 ml of concentrated sulfuric acid, reflux for 7 h, then distill off the solvent methanol under reduced pressure. A large amount of yellow solid precipitates from the reaction solution. Filter, wash, and dry to obtain a yellow solid, which is product B.

[0069] (3) Add the above product B to 200 ml of methanol, 150 ml of ethanol, and 420 ml of saturated ammonium chloride solution, then add 40 g of iron powder. After refluxing for 1 h, cool to room temperature, filter, and distill the liquid phase under reduced pressure to obtain the final product methyl 2-(3,5-diamino-4-chlorophenyl)acetate, with a yield of 87%.

[0070] Example 4

[0071] A preparation method of polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate, comprising the following steps:

[0072] (1) Weigh 30 g of 4-chlorophenylacetic acid and mix it thoroughly with 160 ml of concentrated sulfuric acid. Then slowly add 50 ml of concentrated nitric acid, heat to 65 °C and keep warm for 2 h. Then add the reaction solution to an excessive amount of water to precipitate a solid. After filtering and drying the obtained solid, a beige solid, which is product A, is obtained.

[0073] (2) Add the above product A to 200 ml of methanol and 20 ml of concentrated sulfuric acid, reflux for 11 h, then distill off the solvent methanol under reduced pressure. A large amount of yellow solid precipitates from the reaction solution. Filter, wash, and dry to obtain a yellow solid, which is product B.

[0074] (3) Add the above product B to 200 ml of methanol and 200 ml of saturated ammonium chloride solution, then add 25 g of iron powder. After refluxing for 2 h, cool to room temperature, filter, and distill the liquid phase under reduced pressure to obtain the final product methyl 2-(3,5-diamino-4-chlorophenyl)acetate, with a yield of 91%.

[0075] Example 5

[0076] A preparation method of polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate, comprising the following steps:

[0077] (1) Weigh 30 g of 4-chlorophenylacetic acid and mix it thoroughly with 50 ml of acetic anhydride. Then slowly add 65 ml of concentrated nitric acid, heat to 35 °C and keep warm for 2 h. Then add the reaction solution to an excessive amount of water to precipitate a solid. After filtering and drying the obtained solid, a beige solid, which is product A, is obtained.

[0078] (2) Add the above product A to 250 ml of methanol and 10 ml of concentrated sulfuric acid, reflux for 3 h, then distill off the solvent methanol under reduced pressure. A large amount of yellow solid precipitates from the reaction solution. Filter, wash, and dry to obtain a yellow solid, which is product B.

[0079] (3) Add the above product B to 50 ml of methanol, 200 ml of ethanol, and 250 ml of saturated ammonium chloride solution, then add 18 g of iron powder. After refluxing for 4 h, cool to room temperature, filter, and distill the liquid phase under reduced pressure to obtain the final product methyl 2-(3,5-diamino-4-chlorophenyl)acetate, with a yield of 86%.

[0080] The following further elaborates on the usage method of the polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate of the present invention through Example 6, and compares the mechanical properties of the chain-extended polyurethane samples between Example 6 and Comparative Example 1.

[0081] Example 6

[0082] Add polytetrahydrofuran diol (PTMEG, molecular weight 2000, 48 g, 24 mmol) to a reaction kettle equipped with a stirrer, a heating oil bath, a thermometer, and a nitrogen inlet and outlet. Add TDI (8.36 g, 48 mmol), raise the temperature to 80 °C, and react for 3 h to obtain a prepolymer; pour the prepolymer into a mixer and add the chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate (5.15 g, 24 mmol), stir for 30 s, quickly pour it into a dumbbell-shaped mold, and cure at 50 °C for 4 h to obtain a methyl 2-(3,5-diamino-4-chlorophenyl)acetate chain-extended polyurethane sample, and its mechanical properties are shown in Table 1.

[0083] Comparative Example 1

[0084] Add polytetrahydrofuran diol (PTMEG, molecular weight 2000, 48 g, 24 mmol) to a reaction kettle equipped with a stirrer, a heating oil bath, a thermometer, and a nitrogen inlet and outlet. Add TDI (8.36 g, 48 mmol), raise the temperature to 80 °C, and react for 3 h to obtain a prepolymer; pour the prepolymer into a mixer and add the chain extender MOCA (6.41 g, 24 mmol), stir for 30 s, quickly pour it into a dumbbell-shaped mold, and cure at 50 °C for 4 h to obtain a MOCA chain-extended polyurethane sample, and its mechanical properties are shown in Table 1.

[0085] Table 1

[0086]

[0087] It can be seen from the comparison of the mechanical properties of the chain-extended polyurethane samples between Example 6 and Comparative Example 1 that: the reaction temperature in Example 6 of the present invention is low, and there is no need for a high-temperature curing process at a temperature higher than 100°C for a long time. The tensile strength and elongation at break of the chain-extended polyurethane sample obtained by using the polyurethane chain extender methyl 2-(3,5-diamino-4-chlorophenyl)acetate in Example 6 of the present invention both meet the actual use requirements. Comparative Document 1 uses the same usage method as in Example 6, but since the reaction temperature does not reach above 100°C, the finally obtained chain-extended polyurethane sample cannot be formed.

[0088] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples.

[0089] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a polyurethane chain extender 2-(3,5-diamino-4-chlorophenyl)acetic acid methyl ester, characterized in that: The steps include: S1, after fully mixing 4-chlorophenylacetic acid and substance a, add substance b, heat to 30-70°C and keep warm to obtain a reaction solution, then add the reaction solution to excess water to precipitate a solid, filter and dry the obtained solid to obtain product A, the chemical formula of product A is: The substance a is concentrated sulfuric acid or acetic anhydride; When the substance a is concentrated sulfuric acid, the substance b is concentrated nitric acid or sodium nitrite; When the substance a is acetic anhydride, the substance b is concentrated nitric acid or sodium nitrate; S2, adding product A to methanol and concentrated sulfuric acid for reflux reaction, then removing methanol by reduced pressure distillation, precipitating solid, filtering, washing and drying to obtain product B, the chemical formula of product B is: the liquid-solid ratio of the amount of methanol and concentrated sulfuric acid used to the raw material 4-chlorophenylacetic acid is: 50-420ml: 5-20ml: 30g; S3, adding product B to methanol and saturated ammonium chloride solution, then adding iron powder, after reflux reaction for a period of time, cooling to room temperature, filtering, and distilling the liquid phase under reduced pressure to obtain methyl 2-(3,5-diamino-4-chlorophenyl)acetate.

2. The preparation method according to claim 1, characterized in that: In step S1, the insulation time is 1 to 4 hours.

3. The preparation method according to claim 1, characterized in that: In the step S2, the reflux reaction time is 2 to 12 hours.

4. The preparation method according to claim 1, characterized in that: In the step S3, the liquid-to-solid ratio of the methanol and saturated ammonium chloride solution to 4-chlorophenylacetic acid is: 50-400 ml: 50-500 ml: 30 g.

5. The preparation method according to claim 1, characterized in that: In the step S3, the mass ratio of the amount of iron powder to 4-chlorophenylacetic acid is 16-42:

30.

6. The preparation method according to claim 1, characterized in that: In the step S3, the reflux reaction time is 1 to 4 hours.

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