Synthesis method of 2-amino-4-nitrophenol

Abstract

The present application discloses a method for synthesizing 2-amino-4-nitrophenol, comprising the following steps: Step 1): 2,4-dinitrochlorobenzene and NaOH solution are hydrolyzed at 90-105°C to obtain a reaction solution containing 2,4-dinitrophenol sodium; Step 2): sublimed sulfur is added to the NaOH solution, and the reaction is stirred at 50-70°C for 1-3h to obtain a reaction solution containing sodium polysulfide; dichloromethane and vitamin C are added to the obtained reaction solution containing sodium polysulfide to obtain a reduced solution; Step 3): the reduced solution is dropped into the reaction solution containing 2,4-dinitrophenol sodium, after the dropwise addition, the reaction is reacted, the temperature is lowered, crystallization is performed, and filtration is performed to obtain 2-amino-4-nitrophenol sodium. The yield of 2-amino-4-nitrophenol of the present invention is as high as 90% or more, the purity is more than 99.5%, it is environmentally friendly, safe to use, and easy to industrialize.

Description

Technical Field

[0001] The present application relates to the technical field of organic chemistry, and in particular to a method for synthesizing 2-amino-4-nitrophenol. Background Art

[0002] 2-Amino-4-nitrophenol is an important organic chemical synthesis intermediate, widely used in the preparation of dyes and medicines. For example, the synthesis of reactive dye black series, antihypertensive drug acebutolol, 2-butyl-6-nitroindole, etc. all require 2-amino-4-nitrophenol as an intermediate.

[0003] In the prior art, the preparation method of 2-amino-4-nitrophenol mainly includes selective chemical reduction, selective electrochemical reduction and selective catalytic hydrogenation reduction. However, due to factors such as high production cost and lack of electrochemical facilities, the selective electrochemical reduction method is not yet at an industrial level. Using hydrazine hydrate as a reducing agent to selectively reduce 2,4-dinitrophenol to 2-amino-4-nitrophenol solves the technical problem of large pollution in traditional reduction processes to a certain extent, but hydrazine hydrate is a highly toxic compound, highly corrosive, and expensive, and is not suitable for large-scale production and use in the field of fine chemicals.

[0004] The prior art also discloses a method for synthesizing 2-amino-4-nitrophenol by using 5-nitro-2-methoxyaniline as a main raw material, 70-99% acetic acid as a solvent, reflux conditions, and 40% hydroiodic acid to catalyze the breaking of the carbon-oxygen bond of the methoxy group in the molecular structure of 5-nitro-2-methoxyaniline. However, after the reaction is completed, acetic acid needs to be recovered under high temperature and reduced pressure conditions. This method has high energy consumption, wastewater containing hydroiodic acid is difficult to treat, and the main raw material 5-nitro-2-methoxyaniline is not easy to obtain, so it is not suitable for industrialization.

[0005] Therefore, it is necessary to provide a method for preparing 2-amino-4-nitrophenol which is efficient and easy to industrialize. Summary of the invention

[0006] The present invention aims to solve at least one of the problems of the prior art. Thus, the present invention provides a method for synthesizing 2-amino-4-nitrophenol, comprising the following steps:

[0007] Step 1): Synthesis of sodium 2,4-dinitrophenolate: 2,4-dinitrochlorobenzene and NaOH solution undergo hydrolysis reaction at 90-105°C to obtain a reaction solution containing sodium 2,4-dinitrophenolate;

[0008] Step 2): Preparation of reducing solution: adding sublimed sulfur to NaOH solution, stirring and reacting at 50-70°C for 1-3h to obtain a reaction solution containing sodium polysulfide; adding dichloromethane and vitamin C to the obtained reaction solution containing sodium polysulfide to obtain a reducing solution;

[0009] Step 3): Add the reducing solution obtained in step 2) dropwise into the reaction solution containing sodium 2,4-dinitrophenolate obtained in step 1), react at 70-80° C. for 2-4 hours, cool, crystallize, and filter to obtain sodium 2-amino-4-nitrophenolate;

[0010] Step 4): Add the sodium 2-amino-4-nitrophenolate obtained in step 3) into water, heat it to 70-80°C, stir and dissolve it, add hydrochloric acid solution, adjust the pH to 4.5-4.8, cool it to 10-15°C, crystallize it, centrifuge it, and dry it to obtain 2-amino-4-nitrophenol.

[0011] Preferably, in step 1), the concentration of the NaOH solution is 25-35 wt%, and the molar ratio of 2,4-dinitrochlorobenzene to NaOH is 1:(2-3).

[0012] In a specific embodiment, the concentration of the NaOH solution may be 25-30 wt %, 30-35 wt %.

[0013] In a specific embodiment, the concentration of the NaOH solution may be 25 wt%, 30 wt%, or 35 wt%.

[0014] In a specific embodiment, the molar ratio of 2,4-dinitrochlorobenzene to NaOH can be 1:(2-2.5), 1:(2.5-3).

[0015] In a specific embodiment, the molar ratio of 2,4-dinitrochlorobenzene to NaOH can be 1:2, 1:2.5, or 1:3.

[0016] Preferably, in step 1), the reaction solution containing sodium 2,4-dinitrophenolate is concentrated so that the concentration of sodium 2,4-dinitrophenolate in the reaction solution containing sodium 2,4-dinitrophenolate is 2.4-2.9 g / mL.

[0017] The inventors have found that by controlling the concentration of sodium 2,4-dinitrophenolate in a reaction solution containing sodium 2,4-dinitrophenolate, the progress of sodium polysulfide reduction of sodium 2,4-dinitrophenolate can be controlled, thereby increasing the yield.

[0018] In a specific embodiment, the reaction solution containing sodium 2,4-dinitrophenolate is concentrated so that the concentration of sodium 2,4-dinitrophenolate in the reaction solution containing sodium 2,4-dinitrophenolate can be 2.4-2.7 g / mL or 2.7-2.9 g / mL.

[0019] In a specific embodiment, in the reaction solution containing sodium 2,4-dinitrophenolate, the concentration of sodium 2,4-dinitrophenolate may be 2.4 g / mL, 2.7 g / mL, or 2.9 g / mL.

[0020] Preferably, in step 2), the concentration of the NaOH solution is 25-35wt%, the molar ratio of sublimated sulfur to NaOH is 1:(1-1.4), and the molar ratio of sublimated sulfur to 2,4-dinitrochlorobenzene in step 1) is (3-3.2):1.

[0021] In a specific embodiment, in step 2), the concentration of the NaOH solution may be 25-30wt%, 30-35wt%.

[0022] In a specific embodiment, in step 2), the concentration of the NaOH solution can be 25wt%, 30wt%, or 35wt%.

[0023] In a specific embodiment, the molar ratio of sublimated sulfur to NaOH can be 1:(1-1.25), 1:(1.25-1.4).

[0024] In a specific embodiment, the molar ratio of sublimated sulfur to NaOH can be 1:1, 1:1.25, or 1:1.4.

[0025] In a specific embodiment, the molar ratio of sublimated sulfur to 2,4-dinitrochlorobenzene in step 1) is (3-3.1):1, (3.1-3.2):1.

[0026] In a specific embodiment, the molar ratio of sublimated sulfur to 2,4-dinitrochlorobenzene in step 1) is 3:1, 3.1:1, or 3.2:1.

[0027] Preferably, in step 2), the mass volume ratio of sublimated sulfur to dichloromethane is controlled to be 100 g: (300-450) mL.

[0028] Adding dichloromethane to the reducing solution can, on the one hand, increase the yield of the reduction reaction and improve the purity of the product; on the other hand, the solvent dichloromethane can be recycled and reused multiple times, reducing wastewater discharge and being environmentally friendly.

[0029] In a specific embodiment, in step 2), the mass volume ratio of sublimated sulfur to dichloromethane is controlled to be 96-102.4 g: 300-440 mL, 96-99.2 g: 300-440 mL, and 99.2-102.4 g: 300-440 mL.

[0030] In a specific embodiment, in step 2), the mass volume ratio of sublimed sulfur to dichloromethane is controlled to be 96 g:300 mL, 102.4 g:400 mL, and 99.2 g:440 mL.

[0031] Preferably, in step 2), the mass volume ratio of sublimated sulfur to vitamin C is controlled to be (96-103):(40-90).

[0032] The inventors have found that adding vitamin C to the reducing solution can effectively improve the reduction efficiency and increase the yield of the final product.

[0033] In a specific embodiment, in step 2), the mass ratio of sublimated sulfur to vitamin C is controlled to be 96:(30-40), (96-99.2):(40-90), (99.2-103):(40-90).

[0034] In a specific embodiment, in step 2), the mass ratio of sublimated sulfur to vitamin C is controlled to be 96:30, 96:40, 102.4:60, or 99.2:90.

[0035] Preferably, in step 3), the reducing solution obtained in step 2) is dripped into the reaction solution containing sodium 2,4-dinitrophenolate obtained in step 1) at a dripping speed of 5-25 mL / min.

[0036] In a specific embodiment, in step 3), the drop rate of the reducing solution obtained in step 2) into the reaction solution containing sodium 2,4-dinitrophenolate obtained in step 1) can be controlled to be 5-30 mL / min, preferably 5-25 mL / min.

[0037] In a specific embodiment, in step 3), the droplet speed of the reducing solution obtained in step 2) into the reaction solution containing sodium 2,4-dinitrophenolate obtained in step 1) can be controlled to be 5-8 mL / min, 8-10 mL / min, 10-18 mL / min, 18-20 mL / min, 20-25 mL / min, or 25-30 mL / min.

[0038] In a specific embodiment, in step 3), the droplet speed of the reducing solution obtained in step 2) into the reaction solution containing sodium 2,4-dinitrophenolate obtained in step 1) can be controlled to be 5 mL / min, 8 mL / min, 10 mL / min, 18 mL / min, 20 mL / min, 25 mL / min, or 30 mL / min.

[0039] Preferably, in step 3), the reducing solution obtained in step 2) is dripped into the reaction solution containing sodium 2,4-dinitrophenolate obtained in step 1) in two stages, wherein 1 / 3-1 / 2 of the volume of the reducing solution obtained in step 2) is dripped in the first stage, and the remaining part of the reducing solution obtained in step 2) is dripped in the second stage.

[0040] By controlling the dropping method and speed of the reducing solution, the progress of the reduction reaction can be effectively controlled, the generation of by-products can be reduced, and the yield of the final product can be increased.

[0041] In a specific embodiment, 1 / 3-2 / 5, 3 / 10-2 / 5, or 2 / 5-1 / 2 of the volume of the reducing solution obtained in step 2) can be dripped in the first stage, and the remaining portion of the reducing solution obtained in step 2) can be dripped in the second stage.

[0042] In a specific embodiment, 0.3, 0.4, or 0.5 of the volume of the reducing solution obtained in step 2) can be dripped in the first stage, and the remaining portion of the reducing solution obtained in step 2) can be dripped in the second stage.

[0043] Preferably, the dripping rate in the first stage is controlled to be 18-25 mL / min, and the dripping rate in the second stage is controlled to be 5-10 mL / min.

[0044] In a specific embodiment, the dripping speed in the first stage is controlled to be 18-20 mL / min, 20-25 mL / min, and the dripping speed in the second stage is controlled to be 5-8 mL / min, 5-10 mL / min.

[0045] Preferably, the time interval between the end of the first stage of dripping and the start of the second stage of dripping is controlled to be 20-40 minutes.

[0046] In a specific embodiment, the time interval between the end of the dripping in the first stage and the start of the dripping in the second stage can be controlled to be 20-30 minutes or 30-40 minutes.

[0047] In a specific embodiment, the time interval between the end of the dripping in the first stage and the start of the dripping in the second stage can be controlled to be 20 minutes, 30 minutes, or 40 minutes.

[0048] Preferably, in step 3), the temperature is lowered to 10-25°C, preferably 10-20°C.

[0049] In summary, the beneficial technical effects of this application are:

[0050] 1. The present invention reduces 2,4-dinitrophenol to 2-amino-4-nitrophenol by adding vitamin C to reduce sodium polysulfide, a reducing agent. The reduction efficiency is high, the environment is friendly, the use is safe, and the industrialization is easy.

[0051] 2. The present invention uses dichloromethane and water as reaction solvents for reducing 2,4-dinitrophenol to 2-amino-4-nitrophenol. The addition of dichloromethane can promote the reduction reaction. In addition, dichloromethane can be recycled, thereby reducing the amount of wastewater discharged.

[0052] 3. The present invention also improves the yield and purity of 2-amino-4-nitrophenol by controlling the concentration of sodium 2,4-dinitrophenol in the reaction solution containing sodium 2,4-dinitrophenol, the dropping method and concentration of the reducing solution, etc.

[0053] 4. The yield of 2-amino-4-nitrophenol of the present invention is as high as over 90%, even over 95%, over 98%, and the purity is over 99.5%. DETAILED DESCRIPTION

[0054] The present invention is further described below in conjunction with specific examples, but the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. In the following examples, if no specific conditions are specified, they are carried out according to conventional conditions or conditions recommended by the manufacturer. The methods used are conventional methods known in the art unless otherwise specified, and the consumables and reagents used are commercially available unless otherwise specified. Unless otherwise specified, the professional and scientific terms used in this article have the same meanings as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the recorded content can also be applied to the present invention. Vitamin C (CAS No.: 50-81-7) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0055] Example 1

[0056] Step 1): Synthesis of sodium 2,4-dinitrophenolate: Add 2,4-dinitrochlorobenzene (1 mol) to a hydrolysis kettle, add 200 mL of water, heat to 60°C, stir to dissolve, add 30 wt% NaOH solution (the molar amount of NaOH is 2.5 mol) from a metering tank, and hydrolyze at 100°C to obtain a reaction solution containing sodium 2,4-dinitrophenolate. The reaction solution containing sodium 2,4-dinitrophenolate is concentrated to a concentration of 2.7 g / mL in the reaction solution containing sodium 2,4-dinitrophenolate.

[0057] The reaction formula is as follows:

[0058]

[0059] Step 2): Preparation of reducing solution: Prepare 30wt% NaOH solution (the molar amount of NaOH is 3.75mol) in a beaker, add 3mol of sublimed sulfur while stirring at 60°C to obtain a reaction solution containing sodium polysulfide. The reaction formula is as follows:

[0060] 6S +6NaOH = 2Na2S2+ Na2S2O3+ 3H2O

[0061] 300 mL of dichloromethane and 60 g of vitamin C were added to the obtained reaction solution containing sodium polysulfide to obtain a reducing solution.

[0062] Step 3): The reaction solution containing sodium 2,4-dinitrophenolate obtained after the concentrated treatment in step 1) is sent to the reduction kettle, and 0.4 times the volume of the reduction solution obtained in step 2) is added dropwise to the reduction kettle, and the dropwise addition rate is controlled to be 20 mL / min. Stir the reaction while dropping, and after the dropwise addition is completed, pause for 30 minutes, and continue to dropwise add the remaining part of the reduction solution obtained in step 2), and control the dropwise addition rate to be 8 mL / min. After the dropwise addition is completed, react at 75°C for 2-4 hours, cool to 15°C, crystallize, and filter to obtain sodium 2-amino-4-nitrophenolate. The reaction formula for reducing sodium 2,4-dinitrophenolate with sodium polysulfide is as follows:

[0063]

[0064] Step 4): Add the sodium 2-amino-4-nitrophenolate obtained in step 3) to 1L of water, heat to 80°C and stir to dissolve, add 31wt% hydrochloric acid solution, adjust the pH to 4.5-4.8, and neutralize the sodium 2-amino-4-nitrophenolate with hydrochloric acid in the mixed solution, cool to 12°C, crystallize, and obtain 2-amino-4-nitrophenol. The reaction formula is as follows:

[0065]

[0066] The yield of 2-amino-4-nitrophenol was calculated based on the molar amount of the 2,4-dinitrochlorobenzene raw material in step 1), and the yield of 2-amino-4-nitrophenol was 99.3%. The HPLC purity was 99.7%, and no 2,4-diaminophenol was detected.

[0067] Example 2

[0068] Step 1): Synthesis of sodium 2,4-dinitrophenolate: Add 2,4-dinitrochlorobenzene (1 mol) to a hydrolysis kettle, add 200 mL of water, heat to 60°C, stir to dissolve, add 25 wt% NaOH solution (the molar amount of NaOH is 3 mol) from a metering tank, and hydrolyze at 95°C to obtain a reaction solution containing sodium 2,4-dinitrophenolate. The reaction solution containing sodium 2,4-dinitrophenolate is concentrated to a concentration of 2.4 g / mL in the reaction solution containing sodium 2,4-dinitrophenolate.

[0069] The reaction formula is as follows:

[0070]

[0071] Step 2): Preparation of reducing solution: Prepare 25wt% NaOH solution (NaOH molar amount is 4.5mol) in a beaker, add 3.2mol of sublimed sulfur while stirring at 50°C to obtain a reaction solution containing sodium polysulfide. The reaction formula is as follows:

[0072] 6S +6NaOH = 2Na2S2+ Na2S2O3+ 3H2O

[0073] 400 mL of dichloromethane and 40 g of vitamin C were added to the obtained reaction solution containing sodium polysulfide to obtain a reducing solution.

[0074] Step 3): The reaction solution containing sodium 2,4-dinitrophenolate obtained after the concentrated treatment in step 1) is sent to the reduction kettle, and 0.3 times the volume of the reduction solution obtained in step 2) is added dropwise to the reduction kettle, and the dropwise addition speed is controlled to be 18 mL / min. Stir the reaction while dropping, and after the dropwise addition is completed, pause for 20 minutes, and continue to dropwise add the remaining part of the reduction solution obtained in step 2), and control the dropwise addition speed to be 5 mL / min. After the dropwise addition is completed, react at 80°C for 2-4 hours, cool to 10°C, crystallize, and filter to obtain sodium 2-amino-4-nitrophenolate. The reaction formula for reducing sodium 2,4-dinitrophenolate with sodium polysulfide is as follows:

[0075]

[0076] Step 4): Add the sodium 2-amino-4-nitrophenolate obtained in step 3) to 1L of water, heat to 70°C and stir to dissolve, add 31wt% hydrochloric acid solution, adjust the pH to 4.5-4.8, and neutralize the sodium 2-amino-4-nitrophenolate with hydrochloric acid in the mixed solution, cool to 10°C, crystallize, and obtain 2-amino-4-nitrophenol. The reaction formula is as follows:

[0077]

[0078] The yield of 2-amino-4-nitrophenol was calculated based on the molar amount of the 2,4-dinitrochlorobenzene raw material in step 1), and the yield of 2-amino-4-nitrophenol was 98.1%. The HPLC purity was 99.5%, and no 2,4-diaminophenol was detected.

[0079] Example 3

[0080] Step 1): Synthesis of sodium 2,4-dinitrophenolate: Add 2,4-dinitrochlorobenzene (1 mol) to a hydrolysis kettle, add 200 mL of water, heat to 60°C, stir to dissolve, add 35 wt% NaOH solution (the molar amount of NaOH is 2.2 mol) from a metering tank, and hydrolyze at 90°C to obtain a reaction solution containing sodium 2,4-dinitrophenolate. The reaction solution containing sodium 2,4-dinitrophenolate is concentrated to a concentration of 2.9 g / mL in the reaction solution containing sodium 2,4-dinitrophenolate.

[0081] The reaction formula is as follows:

[0082]

[0083] Step 2): Preparation of reducing solution: Prepare 35wt% NaOH solution (the molar amount of NaOH is 3.25mol) in a beaker, add 3.1mol of sublimed sulfur while stirring at 70°C to obtain a reaction solution containing sodium polysulfide. The reaction formula is as follows:

[0084] 6S +6NaOH = 2Na2S2+ Na2S2O3+ 3H2O

[0085] 440 mL of dichloromethane and 90 g of vitamin C were added to the obtained reaction solution containing sodium polysulfide to obtain a reduced solution.

[0086] Step 3): The reaction solution containing sodium 2,4-dinitrophenolate obtained after the concentrated treatment in step 1) is sent to the reduction kettle, and 0.5 times the volume of the reduction solution obtained in step 2) is added dropwise to the reduction kettle, and the dropwise addition speed is controlled to be 25 mL / min. Stir the reaction while dropping, and after the dropwise addition is completed, pause for 40 minutes, and continue to dropwise add the remaining part of the reduction solution obtained in step 2), and control the dropwise addition speed to be 10 mL / min. After the dropwise addition is completed, react at 70°C for 2-4 hours, cool to 20°C, crystallize, and filter to obtain sodium 2-amino-4-nitrophenolate. The reaction formula for reducing sodium 2,4-dinitrophenolate with sodium polysulfide is as follows:

[0087]

[0088] Step 4): Add the sodium 2-amino-4-nitrophenolate obtained in step 3) to 1L of water, heat to 80°C and stir to dissolve, add 31wt% hydrochloric acid solution, adjust the pH to 4.5-4.8, and neutralize the sodium 2-amino-4-nitrophenolate with hydrochloric acid in the mixed solution, cool to 15°C, crystallize, and obtain 2-amino-4-nitrophenol. The reaction formula is as follows:

[0089]

[0090] The yield of 2-amino-4-nitrophenol was calculated based on the molar amount of the 2,4-dinitrochlorobenzene raw material in step 1), and the yield of 2-amino-4-nitrophenol was 98.3%. The HPLC purity was 99.6%, and no 2,4-diaminophenol was detected.

[0091] Example 4

[0092] The reaction conditions of Example 4 refer to those of Example 1. The only difference between Example 4 and Example 1 is that the amount of vitamin C added in step 2) of Example 4 is 30 g. The yield of 2-amino-4-nitrophenol obtained is 92.3%, the HPLC purity is 99.6%, and no 2,4-diaminophenol is detected.

[0093] Example 5

[0094] The reaction conditions of Example 5 refer to those of Example 1. The only difference between Example 5 and Example 1 is that in step 3), the reaction solution containing sodium 2,4-dinitrophenolate obtained after the concentration treatment in step 1) is sent to the reduction kettle, and the reduced solution obtained in step 2) is added dropwise to the reduction kettle, and the dropping speed is controlled to be 30 mL / min, and the dropping is not added in stages. As a result, the yield of 2-amino-4-nitrophenol obtained is 93.3%, the HPLC purity is 99.3%, and the content of 2,4-diaminophenol detected is 0.3%.

[0095] Example 6

[0096] The reaction conditions of Example 6 refer to those of Example 1. The only difference between Example 6 and Example 1 is that in step 1), the reaction solution containing sodium 2,4-dinitrophenolate is not concentrated. Finally, the yield of 2-amino-4-nitrophenol obtained is 90.1%, the HPLC purity is 99.6%, and no 2,4-diaminophenol is detected.

[0097] Example 7

[0098] The reaction conditions of Example 7 refer to those of Example 1. The only difference between Example 7 and Example 1 is that the amount of dichloromethane added in step 2) of Example 7 is 250 mL. The yield of 2-amino-4-nitrophenol obtained is 91.2%, the HPLC purity is 99.1%, and the detected 2,4-diaminophenol content is 0.5%.

[0099] Example 8

[0100] The reaction conditions of Example 8 refer to those of Example 1. The only difference between Example 8 and Example 1 is that, in step 3) of Example 8, the reaction mixture is cooled to 25° C., crystals are precipitated, and filtered to obtain sodium 2-amino-4-nitrophenol. The yield of 2-amino-4-nitrophenol obtained is 90.2%, the HPLC purity is 99.6%, and no 2,4-diaminophenol is detected.

[0101] Comparative Example 1

[0102] The reaction conditions of Comparative Example 1 refer to those of Example 1. The only difference between Comparative Example 1 and Example 1 is that vitamin C is not added in step 2) of Comparative Example 1. The yield of 2-amino-4-nitrophenol obtained is 82.3%, the HPLC purity is 98.1%, and the content of 2,4-diaminophenol detected is 0.8%.

[0103] Comparative Example 2

[0104] The reaction conditions of Comparative Example 2 refer to those of Example 1. The only difference between Comparative Example 2 and Example 1 is that no dichloromethane is added in step 2) of Comparative Example 1. The yield of 2-amino-4-nitrophenol obtained is 85.1%, the HPLC purity is 98.6%, and the content of 2,4-diaminophenol detected is 0.3%.

[0105] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for synthesizing 2-amino-4-nitrophenol, characterized in that: The steps include: Step 1): Synthesis of sodium 2,4-dinitrophenolate: 2,4-dinitrochlorobenzene and NaOH solution undergo hydrolysis reaction at 90-105°C to obtain a reaction solution containing sodium 2,4-dinitrophenolate; Step 2): Preparation of reducing solution: adding sublimed sulfur to NaOH solution, stirring and reacting at 50-70°C for 1-3h to obtain a reaction solution containing sodium polysulfide; adding dichloromethane and vitamin C to the obtained reaction solution containing sodium polysulfide to obtain a reducing solution; Step 3): Add the reducing solution obtained in step 2) dropwise into the reaction solution containing sodium 2,4-dinitrophenolate obtained in step 1), react at 70-80° C. for 2-4 hours, cool, crystallize, and filter to obtain sodium 2-amino-4-nitrophenolate; Step 4): Add the sodium 2-amino-4-nitrophenolate obtained in step 3) into water, heat it to 70-80°C, stir and dissolve it, add hydrochloric acid solution, adjust the pH to 4.5-4.8, cool it to 10-15°C, crystallize it, centrifuge it, and dry it to obtain 2-amino-4-nitrophenol.

2. The synthetic method of 2-amino-4-nitrophenol according to claim 1, characterized in that: In the step 1), the concentration of the NaOH solution is 25-35wt%, and the molar ratio of 2,4-dinitrochlorobenzene to NaOH is 1:(2-3).

3. The synthetic method of 2-amino-4-nitrophenol according to claim 1, characterized in that, In the step 1), the reaction solution containing sodium 2,4-dinitrophenolate is concentrated so that the concentration of sodium 2,4-dinitrophenolate in the reaction solution containing sodium 2,4-dinitrophenolate is 2.4-2.9 g / mL.

4. The method for synthesizing 2-amino-4-nitrophenol according to claim 1, wherein In the step 2), the concentration of the NaOH solution is 25-35wt%, the molar ratio of sublimated sulfur to NaOH is 1:(1-1.4), and the molar ratio of sublimated sulfur to 2,4-dinitrochlorobenzene in the step 1) is (3-3.2):

1.

5. The method for synthesizing 2-amino-4-nitrophenol according to claim 1, characterized in that: In the step 2), the mass volume ratio of sublimated sulfur to dichloromethane is controlled to be 100 g: (300-450) mL.

6. The method for synthesizing 2-amino-4-nitrophenol according to claim 1, characterized in that: In the step 2), the mass ratio of sublimated sulfur to vitamin C is controlled to be (96-103):(40-90).

7. The method for synthesizing 2-amino-4-nitrophenol according to claim 1, characterized in that: In the step 3), the reducing solution obtained in the step 2) is dripped into the reaction solution containing sodium 2,4-dinitrophenolate obtained in the step 1) at a dripping speed of 5-30 mL / min.

8. The method for synthesizing 2-amino-4-nitrophenol according to claim 1, characterized in that: In the step 3), the reducing solution obtained in step 2) is dripped into the reaction solution containing sodium 2,4-dinitrophenolate obtained in step 1) in two stages, 1 / 3-1 / 2 of the volume of the reducing solution obtained in step 2) is dripped in the first stage, and the remaining part of the reducing solution obtained in step 2) is dripped in the second stage.

9. The method for synthesizing 2-amino-4-nitrophenol according to claim 8, characterized in that: The dripping rate of the first stage is controlled to be 18-25 mL / min, the dripping rate of the second stage is controlled to be 5-10 mL / min, and the time interval between the end of the dripping of the first stage and the start of the dripping of the second stage is controlled to be 20-40 minutes.

10. The method for synthesizing 2-amino-4-nitrophenol according to claim 1, characterized in that: In the step 3), the temperature is lowered to 10-25°C.

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