Preparation of cu-sn alloy electrode and method for direct electro-synthesis of 3-amino phthalic acid based on the electrode

Abstract

The application discloses a preparation of a Cu-Sn alloy electrode and a method for directly electro-synthesizing 3-amino phthalic acid based on the electrode. The preparation method of the copper-tin alloy electrode provided by the application improves the specific surface area of the electrode and enhances the catalysis of copper-tin in the electrolytic reaction on the process of the electrolytic synthesis of 3-amino phthalic acid. Compared with the traditional process, the method for directly electro-synthesizing 3-amino phthalic acid based on the Cu-Sn alloy electrode has the advantages of lower cost, more controllable production, no by-product, less environmental pollution and the problem of decarboxylation caused by hydrogen substitution of carboxyl can be avoided.

Description

Technical Field

[0001] This invention relates to a method for preparing a Cu-Sn alloy electrode and a method for directly electrosynthesizing the chemical raw material 3-aminophthalic acid based on the electrode. Background Technology

[0002] 3-Aminophthalic acid (3-aminophthalic acid) is an important chemical intermediate with a wide range of applications. Its main uses include: synthesis of various dyes and pigments; synthesis of apremilast, a drug for active psoriatic arthritis; development of β-lactamase inhibitors; preparation of luminol-based luminescent materials; application in various chemiluminescent systems; preparation of organic ligands; and synthesis of various coordination polymers. Current methods for synthesizing 3-aminophthalic acid include chemical reduction, catalytic hydrogenation, and photocatalytic synthesis. Patent (CN106986783A) discloses a catalytic hydrogenation method for synthesizing 3-aminophthalic acid. This method utilizes a palladium-on-carbon catalyst under high temperature and pressure to hydrogenate 3-aminophthalic acid. However, this method suffers from drawbacks such as demanding reaction conditions (e.g., high temperature or high pressure and large excess reactants), the use of precious metal catalysts (e.g., Pt, Pd, etc.) and high-purity hydrogen, high equipment requirements, poor selectivity, high production costs, significant safety hazards, and large emissions of waste. Therefore, there is an urgent need to develop feasible and green methods to synthesize 3-aminophthalic acid.

[0003] Electrochemical synthesis is a method that uses "electrons" as a clean reducing agent to reduce aromatic nitro compounds on the electrode surface. It can significantly reduce pollution from waste gas, wastewater, and solid waste, and produce high-purity products. However, there are currently no reports on the preparation of 3-aminophthalic acid by electrochemical synthesis. Summary of the Invention

[0004] The first technical problem to be solved by the present invention is to provide a method for preparing a copper-tin alloy electrode for the direct electrosynthesis of 3-aminophthalic acid, so as to improve the specific surface area of ​​the electrode and enhance the catalytic effect of copper and tin on the electrolytic synthesis of 3-aminophthalic acid in the electrolytic reaction.

[0005] The second technical problem to be solved by the present invention is to provide a method for direct electrosynthesis of 3-aminophthalic acid based on Cu-Sn alloy electrode. Compared with the traditional process, the method of the present invention has lower cost, more controllable production, no by-products, less environmental pollution, and can avoid the problem of decarboxylation caused by the replacement of carboxyl groups with hydrogen.

[0006] The present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a Cu-Sn alloy electrode for the direct electrosynthesis of 3-aminophthalic acid, comprising the following steps:

[0008] (a) Cu-Sn alloy is prepared by electroplating, wherein the mass fraction of Sn is 3-13%;

[0009] (b) Immerse the Cu-Sn alloy obtained in step (a) in an HCl solution (preferably with a concentration of 0.5 to 1.2 mol / L), sonicate it (preferably for 13 to 17 min), and then take it out and wash it with deionized water. The purpose of this step is to remove the surface oxide layer.

[0010] (c) Use metallographic sandpaper of #1 to #7 to polish the surface of Cu-Sn alloy obtained in step (b). After completion, rinse the surface of Cu-Sn alloy with deionized water.

[0011] (d) Use Al2O3 powder to polish the surface of Cu-Sn alloy obtained in step (c) to a mirror finish. After completion, rinse the surface of Cu-Sn alloy with deionized water. The two-step polishing process removes some of the loose copper-tin alloy on the surface of the electroplated Cu-Sn alloy to avoid the problem of loose copper-tin alloy easily falling off during later use.

[0012] (e) Immerse the Cu-Sn alloy treated in step (d) in deionized water, sonicate it (preferably for 12 to 17 minutes), and then take it out and dry it.

[0013] (f) The Cu-Sn alloy treated in step (e) is placed in a 0.5-2 mol / L NaOH solution and kept in a vacuum oven at 60-80℃ for 1-5 hours. Then, the treated Cu-Sn alloy is thoroughly washed with anhydrous ethanol and deionized water, and dried to obtain a Cu-Sn alloy with a rod-like structure on the surface, which is the Cu-Sn alloy electrode used for the direct electrosynthesis of 3-aminophthalic acid.

[0014] In step (a) of this invention, the operation of preparing Cu-Sn alloy by electroplating can be carried out with reference to the methods disclosed in existing literature or manuals, such as the method for preparing Cu-Sn alloy by electroplating as recorded on page 325 of "Electroplating Process Manual, 2nd Edition" (China Machine Press), edited by Zeng Hualiang et al.

[0015] Preferably, the Sn mass fraction in the Cu-Sn alloy prepared by electroplating is 6%.

[0016] Preferably, in step (f), the Cu-Sn alloy treated in step (e) is placed in a 0.5-1 mol / L NaOH solution and kept in a vacuum oven at 75-80°C for 4.5-5 hours. Most preferably, the Cu-Sn alloy treated in step (e) is placed in a 1 mol / L NaOH solution and kept in a vacuum oven at 80°C for 5 hours.

[0017] Secondly, the present invention provides a method for the direct electrosynthesis of 3-aminophthalic acid, specifically implemented according to the following steps: 3-nitrophthalic acid, sulfuric acid, and a solvent are thoroughly mixed to obtain a cathode electrolyte, wherein the solvent is a mixture of DMF and deionized water with a volume ratio of 1:2-6, and the cathode electrolyte is added to a cathode storage tank; a sulfuric acid aqueous solution of a certain concentration is used as the anolyte, and the anolyte is added to an anolyte storage tank; the anolyte in the anolyte storage tank and the cathode electrode liquid in the cathode storage tank are pumped into the anode chamber and cathode chamber of a diaphragm electrolytic cell respectively via a peristaltic pump; the working electrode (cathode) is a Cu-Sn alloy electrode, and the counter electrode (anode) is a DSA-coated electrode (IrO2-Ta2O5) or a graphite electrode; the electrolysis power supply is turned on to carry out the reaction; the flow rates of the cathode electrolyte and the anolyte are controlled to be the same, with a flow rate of 50-150 ml / min, a reaction temperature of 40-80℃, and a current density of 80-140 mA / cm². 2 The reaction charge was 0.8 to 1.4 times the theoretical charge. After the reaction was completed, the reaction solution was removed and post-processed to obtain 3-aminophthalic acid.

[0018] In the cathode electrolyte, the initial molar ratio of 3-nitrophthalic acid to sulfuric acid is 1:3 to 7.

[0019] In this invention, sulfuric acid is used as the supporting electrolyte to provide an acidic environment. Preferably, the initial molar ratio of 3-nitrophthalic acid to sulfuric acid in the cathode electrolyte is 1:4 to 6, and most preferably 1:5.

[0020] In this invention, a mixed solution of DMF and deionized water is used as a solvent to ensure the solubility of 3-nitrophthalic acid and sulfuric acid in the solution, thereby promoting the electrolysis reaction. Preferably, the volume ratio of DMF to deionized water in the solvent is 1:3 to 6, more preferably 1:4 to 5, and most preferably 1:4.

[0021] In this invention, the anolyte is an aqueous solution of sulfuric acid prepared from sulfuric acid and deionized water. The sulfuric acid concentration is the same in both the anolyte and the cathode electrolyte. Preferably, the concentration of sulfuric acid is 0.5 to 1.5 mol / L, and more preferably 1 mol / L.

[0022] In this invention, the solution circulation in the storage tank and electrolytic cell is achieved via a peristaltic pump. The flow rates of the electrolyte at both the cathode and anode are 50–150 mL / min, preferably 90–120 mL / min, and most preferably 100 mL / min. The reaction current density is 80–140 mA / cm². 2 The preferred reaction current density is 100–130 mA / cm². 2 The optimal reaction current density is 120 mA / cm². 2The reaction temperature is 40–80℃, preferably 50–60℃, and most preferably 60℃. The reaction charge is 0.8–1.4 times the theoretical charge, preferably 1–1.2 times, and most preferably 1.2 times.

[0023] The reaction in the diaphragm electrolyzer of this invention is preferably carried out under the following conditions: reaction temperature of 60°C, electrolyte flow rate at both cathode and anode of 100 mL / min, and constant current electrolysis current density of 120 mA / cm². 2 The reaction charge is 1.2 times the theoretical charge.

[0024] The post-processing described in this invention is as follows: After the reaction is completed, the reaction solution is taken out, and after rotary evaporation, cooling and crystallization, filtration, and washing, 3-aminophthalic acid is obtained; specifically, the following steps are followed: After the reaction is completed, the reaction solution is rotary evaporated into a viscous oily liquid, and then placed in a low-temperature environment for refrigeration. After a large amount of solid precipitates out, it is taken out, filtered, repeatedly washed with mother liquor several times, rinsed with deionized water, and finally the solid is placed in an oven to dry to obtain the product.

[0025] Compared with the prior art, the beneficial effects of this invention are reflected in:

[0026] 1. Compared with the synthesis of 3-aminophthalic acid described in previous literature, the reaction conditions of this invention are simpler, the requirements for reaction equipment are lower, the synthesis can be carried out at a lower temperature, and the reaction efficiency is high and the reaction time is short.

[0027] 2. Compared with the high requirements for hydrogen source and catalyst performance in catalytic hydrogenation methods in recent literature, this invention uses cheaper "electrons" as a reducing agent, which reduces costs, has high reaction selectivity, and achieves green synthesis.

[0028] 3. This invention provides a method for preparing a Cu-Sn alloy with a highly catalytically active surface rod-like structure. The Cu-Sn alloy prepared by this method has a rod-like structure on its surface, which has a high specific surface area and good hydrophilicity. At the same time, Sn dissolves during electrolysis to further create pores and undergoes indirect electrosynthesis in the electrolyte. The residual Sn on the electrode surface catalytically reduces nitro groups, thereby achieving efficient synthesis of 3-aminophthalic acid and improving the yield of electrolytic synthesis of 3-aminophthalic acid. Attached Figure Description

[0029] Figure 1 The reaction route for the synthesis of 3-aminophthalic acid;

[0030] Figure 2 The liquid phase mass spectrum characterizing Example 15 at 0.5 times the flux is shown.

[0031] Figure 3EDS image of the Cu-Sn alloy electrode prepared in Example 4;

[0032] Figure 4 The image shows the AFM pattern of the Cu-Sn alloy electrode prepared in Example 4. Detailed Implementation

[0033] The following specific embodiments illustrate the technical solution of the present invention, but the scope of protection of the present invention is not limited thereto.

[0034] Examples 1-8

[0035] (a) Preparation of Cu-Sn alloy by electroplating method

[0036] The copper plate was placed in a pretreatment aqueous solution containing 100 g / L citric acid, 5 g / L copper sulfate, 10 ml / L sulfuric acid, 10 ml / L hydrochloric acid, and 50 ml / L ammonia (28%), and kept at room temperature for 60 seconds for material pretreatment.

[0037] Preparation of copper salt solution: Weigh 150g of citric acid, dissolve it in 500mL of water, add 120g of potassium hydroxide, then add 28g of basic copper carbonate to the potassium citrate solution, heat, and when the solution is clear and free of bubbles, cool, add 15g of potassium dihydrogen phosphate, filter, and obtain copper salt solution.

[0038] To prepare the tin salt solution: Take another container and dissolve 50g of potassium stannate in 200mL of dilute alkaline hot solution (add 3-5g of potassium hydroxide to the water). After complete dissolution, add 2mL of hydrogen peroxide, filter, and obtain the tin salt solution.

[0039] The cooled tin salt solution was slowly added to the copper salt solution with stirring, and then the solution volume was increased to 1L. The pH value was then adjusted to 9-10 with citric acid to prepare electrolyte ①.

[0040] The pretreated copper plate was used as the cathode, and the untreated copper plate as the anode. They were placed parallel to each other in a reactor containing electrolyte ①, and the current density was controlled between 0.4 and 0.6 A / cm² according to Table 1. 2 The electroplating time was 20-60 min to obtain Cu-Sn alloys with Sn mass fractions of 3% (Example 1), 4% (Example 2), 5% (Example 3), 6% (Example 4), 7% (Example 5), 8% (Example 6), 10% (Example 7), and 12% (Example 8).

[0041] Table 1

[0042]

[0043] (b) Immerse the Cu-Sn alloy obtained in step (a) in a 1 mol / L HCl solution and sonicate for 15 min. After completion, remove it and wash it with deionized water.

[0044] (c) Use #2 metallographic sandpaper to polish the surface of Cu-Sn alloy obtained in step (b), and then rinse the surface of Cu-Sn alloy with deionized water.

[0045] (d) Polish the surface of the Cu-Sn alloy obtained in step (c) to a mirror finish using Al2O3, and then rinse the surface of the Cu-Sn alloy with deionized water.

[0046] (e) Immerse the Cu-Sn alloy treated in step (d) in deionized water, sonicate for 15 minutes, and then remove and dry it.

[0047] (f) The Cu-Sn alloy treated in step (e) is placed in a 1 mol / L NaOH solution and kept in a vacuum oven at 80°C for 5 h. Then, the treated Cu-Sn alloy is thoroughly washed with anhydrous ethanol and deionized water, and dried to obtain a Cu-Sn alloy with a rod-like structure on the surface, which is the Cu-Sn alloy electrode used for the direct electrosynthesis of 3-aminophthalic acid.

[0048] Example 9

[0049] The conditions in step (f) are changed as follows: the Cu-Sn alloy treated in step (e) is placed in a 0.5 mol / L NaOH solution and kept in a vacuum oven at 60°C for 2 hours. Other preparation steps and conditions are the same as in Example 4, resulting in a Cu-Sn alloy with a rod-like structure on the surface, which is the Cu-Sn alloy electrode used for the direct electrosynthesis of 3-aminophthalic acid.

[0050] Example 10

[0051] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 1 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.2 mol / L 3-nitrophthalic acid, 1 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:4 was added to the cathode liquid storage tank. A 1 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then added to the anode liquid storage tank. The solution was heated to 40°C in a circulating water bath, with an electrolyte flow rate of 50 ml / min, and the current density for constant current electrolysis was set to 80 mA / cm². 2 The reaction was carried out at 1.2 times the theoretical charge. After the reaction was completed, the reaction solution (i.e., the cathode electrolyte) was analyzed by liquid chromatography-mass spectrometry. The results showed that the conversion rate of 3-nitrophthalic acid was 69% and the yield of 3-aminophthalic acid was 66%.

[0052] Example 11

[0053] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 2 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.05 mol / L 3-nitrophthalic acid, 0.5 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:4 was added to the cathode liquid storage tank. A 0.5 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then placed into the anode liquid storage tank. The solution was heated to 30°C in a circulating water bath, with an electrolyte flow rate of 120 ml / min, and the constant current electrolysis current density was set to 80 mA / cm². 2 With a theoretical charge of 1.2 times, the reaction solution was subjected to liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 46% and the yield of 3-aminophthalic acid was 44%.

[0054] Example 12

[0055] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 6 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.05 mol / L 3-nitrophthalic acid, 1 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:4 was added to the cathode liquid storage tank. A 1 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then added to the anode liquid storage tank. The solution was heated to 40°C in a circulating water bath, with an electrolyte flow rate of 120 ml / min, and the current density for constant current electrolysis was set to 100 mA / cm². 2 With a theoretical charge of 1.2 times, the reaction solution was analyzed by liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 40% and the yield of 3-aminophthalic acid was 38%.

[0056] Example 13

[0057] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 7 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.1 mol / L 3-nitrophthalic acid, 0.5 mol / L sulfuric acid, and a solvent volume ratio of DMF:water = 1:4 was added to the cathode liquid storage tank. The solution was then dissolved in a 0.5 mol / L sulfuric acid aqueous solution via ultrasonication and placed into the anode liquid storage tank. The temperature was raised to 60°C in a circulating water bath, the electrolyte flow rate was 120 ml / min, and the current density for constant current electrolysis was set to 100 mA / cm². 2 With a theoretical charge of 1.2 times, the reaction solution was analyzed by liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 50% and the yield of 3-aminophthalic acid was 48%.

[0058] Example 14

[0059] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 8 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.1 mol / L 3-nitrophthalic acid, 1.5 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:4 was added to the cathode liquid storage tank. A 1 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then added to the anode liquid storage tank. The solution was heated to 40°C in a circulating water bath, with an electrolyte flow rate of 120 ml / min, and the constant current electrolysis current density was set to 140 mA / cm². 2 With a theoretical charge of 1.2 times, the reaction solution was subjected to liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 60% and the yield of 3-aminophthalic acid was 46.1%.

[0060] Example 15: Best Practice

[0061] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 4 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.2 mol / L 3-nitrophthalic acid, 1 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:4 was added to the cathode liquid storage tank. A 1 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then added to the anode liquid storage tank. The solution was heated to 60°C in a circulating water bath, with an electrolyte flow rate of 120 ml / min, and the current density for constant current electrolysis was set to 120 mA / cm². 2 With a theoretical charge of 1.2 times, the reaction solution was analyzed by liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 77% and the yield of 3-aminophthalic acid was 72.9%. Figure 2 The electrolyte was analyzed by liquid chromatography-mass spectrometry (LC-MS) at 0.5 times the theoretical charge. The spectrum showed the presence of 3-nitrophthalic acid, 3-aminophthalic acid, and hydroxylamine compounds. It can be inferred that... Figure 1 The reaction mechanism.

[0062] Example 16

[0063] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 3 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.15 mol / L 3-nitrophthalic acid, 1 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:4 was added to the cathode liquid storage tank. A 0.5 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then placed into the anode liquid storage tank. The solution was heated to 40°C in a circulating water bath, with an electrolyte flow rate of 120 ml / min, and the current density for constant current electrolysis was set to 120 mA / cm². 2With a theoretical charge of 1.2 times, the reaction solution was analyzed by liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 62% and the yield of 3-aminophthalic acid was 59.5%.

[0064] Example 17

[0065] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 4 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.2 mol / L 3-nitrophthalic acid, 1.5 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:3 was added to the cathode liquid storage tank. The 1.5 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then placed into the anode liquid storage tank. The temperature was raised to 30°C in a circulating water bath, the electrolyte flow rate was 120 ml / min, and the current density for constant current electrolysis was set to 100 mA / cm². 2 With a theoretical charge of 1.2 times, the reaction solution was subjected to liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 70% and the yield of 3-aminophthalic acid was 67.2%.

[0066] Example 18

[0067] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 5 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.2 mol / L 3-nitrophthalic acid, 1 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:3 was added to the cathode liquid storage tank. A 1 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then added to the anode liquid storage tank. The solution was heated to 30°C in a circulating water bath, with an electrolyte flow rate of 120 ml / min, and the current density for constant current electrolysis was set to 100 mA / cm². 2 With a theoretical charge of 1.2 times, the reaction solution was subjected to liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 64% and the yield of 3-aminophthalic acid was 58.4%.

[0068] Example 19

[0069] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 9 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.2 mol / L 3-nitrophthalic acid, 2 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:4 was added to the cathode liquid storage tank. The 2 mol / L sulfuric acid aqueous solution was dissolved by ultrasonication and then placed into the anode liquid storage tank. The temperature was raised to 30°C in a circulating water bath, the electrolyte flow rate was 120 ml / min, and the current density for constant current electrolysis was set to 80 mA / cm². 2With a theoretical charge of 1.2 times, the reaction solution was analyzed by liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 68% and the yield of 3-aminophthalic acid was 60.3%.

[0070] Comparative Example 1: Using other organic solvents

[0071] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 4 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.2 mol / L 3-nitrophthalic acid, 1 mol / L sulfuric acid, and an organic solvent:water volume ratio of 1:4 was added to the cathode liquid storage tank. A 1 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then added to the anode liquid storage tank. The temperature was raised to 60°C in a circulating water bath, the electrolyte flow rate was 120 ml / min, and the current density for constant current electrolysis was set to 120 mA / cm². 2 The reaction was carried out at 1.2 times the theoretical charge. After the reaction was completed, the reaction solution was analyzed by liquid chromatography-mass spectrometry. The conversion rate of 3-nitrophthalic acid and the yield of 3-aminophthalic acid are shown in Table 2.

[0072] Table 2

[0073]

[0074] Comparative Example 2: Without DMF

[0075] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 4 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, 0.2 mol / L 3-nitrophthalic acid, 1 mol / L sulfuric acid, and solvent water were added to the cathode liquid storage tank. The 1 mol / L sulfuric acid aqueous solution was dissolved by ultrasonication and then placed into the anode liquid storage tank. The temperature was raised to 60°C in a circulating water bath, the electrolyte flow rate was 120 ml / min, and the current density for constant current electrolysis was set to 120 mA / cm². 2 The reaction was carried out at 1.2 times the theoretical charge. After the reaction was completed, the reaction solution was analyzed by liquid chromatography-mass spectrometry. The results showed that the conversion rate of 3-nitrophthalic acid was 0 and the yield of 3-aminophthalic acid was 0.

[0076] Comparative Example 3: No power supply

[0077] In an electrolysis apparatus using the Cu-Sn alloy electrode prepared in Example 4 as the cathode and the DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.2 mol / L 3-nitrophthalic acid, 1 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:4 was added. After ultrasonic dissolution with 1 mol / L sulfuric acid, the solution was placed in the anode and cathode storage tanks. The temperature was raised to 60°C in a circulating water bath, the electrolyte flow rate was 120 ml / min, and the current density for constant current electrolysis was set to 120 mA / cm². 2 Without applying electricity, the reaction solution was analyzed by liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 0 and the yield of 3-aminophthalic acid was 0.

[0078] Comparative Example 4: Using copper electrodes

[0079] In an electrolysis apparatus using a copper sheet as the cathode and a DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.2 mol / L 3-nitrophthalic acid, 1 mol / L sulfuric acid, and a solvent volume ratio of DMF:water = 1:4 was added to the cathode liquid storage tank. A 1 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then added to the anode liquid storage tank. The solution was heated to 60°C in a circulating water bath, with an electrolyte flow rate of 120 ml / min, and the constant current electrolysis current density was set to 120 mA / cm². 2 Without applying electricity, the reaction solution was analyzed by liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 70.7% and the yield of 3-aminophthalic acid was 58.6%.

[0080] Comparative Example 5: Cu-Sn alloy obtained by electroplating was used as an electrode

[0081] In an electrolytic device using a Cu-Sn alloy electrode prepared by electroplating as the cathode and a DSA-coated electrode (IrO2-Ta2O5) as the anode, a mixture of 0.2 mol / L 3-nitrophthalic acid, 1 mol / L sulfuric acid, and DMF:water in a volume ratio of 1:4 was added to the cathode liquid storage tank. A 1 mol / L sulfuric acid aqueous solution was ultrasonically dissolved and then added to the anode liquid storage tank. The device was heated to 60°C in a circulating water bath, with an electrolyte flow rate of 120 ml / min and a constant current electrolysis current density of 120 mA / cm². 2 With a theoretical charge of 1.2 times, the reaction solution was analyzed by liquid chromatography-mass spectrometry after the reaction was completed. The results showed that the conversion rate of 3-nitrophthalic acid was 73% and the yield of 3-aminophthalic acid was 65.7%.

Claims

1. A method for preparing a Cu-Sn alloy electrode for the direct electrosynthesis of 3-aminophthalic acid, characterized in that: The preparation method includes the following steps: (a) A Cu-Sn alloy was prepared by electroplating, wherein the mass fraction of Sn was 3-13%; (b) Immerse the Cu-Sn alloy obtained in step (a) in HCl solution, sonicate it, and then take it out and wash it with deionized water; (c) Use metallographic sandpaper of #1 to #7 to polish the surface of Cu-Sn alloy obtained in step (b), and then rinse the surface of Cu-Sn alloy with deionized water. (d) Polish the surface of the Cu-Sn alloy obtained in step (c) to a mirror finish using Al2O3 powder, and then rinse the surface of the Cu-Sn alloy with deionized water. (e) Immerse the Cu-Sn alloy treated in step (d) in deionized water, ultrasonically treat it, and then take it out and dry it. (f) The Cu-Sn alloy treated in step (e) is placed in a 0.5 ~ 2 mol / L NaOH solution and kept in a vacuum oven at 60 ~ 80℃ for 1 ~ 5 h. Then the treated Cu-Sn alloy is thoroughly washed with anhydrous ethanol and deionized water, and dried to obtain a Cu-Sn alloy with a rod-like structure on the surface, which is the Cu-Sn alloy electrode used for the direct electrosynthesis of 3-aminophthalic acid.

2. The preparation method according to claim 1, characterized in that: In step (f), the Cu-Sn alloy treated in step (e) is placed in a 0.5 ~ 1 mol / L NaOH solution and kept in a vacuum oven at 75 ~ 80 ℃ for 4.5 ~ 5 h.

3. The preparation method according to claim 2, characterized in that: In step (f), the Cu-Sn alloy treated in step (e) is placed in a 1 mol / L NaOH solution and kept in a vacuum oven at 80 °C for 5 h.

4. A method for the direct electrosynthesis of 3-aminophthalic acid, characterized in that: The method is implemented according to the following steps: 3-nitrophthalic acid, sulfuric acid, and a solvent are thoroughly mixed to obtain a cathode electrolyte. The solvent is a mixture of DMF and deionized water with a volume ratio of 1:2~6. The cathode electrolyte is added to a cathode storage tank. A sulfuric acid aqueous solution of a certain concentration is used as the anolyte, and the anolyte is added to an anode storage tank. The anolyte in the anode storage tank and the cathode electrode liquid in the cathode storage tank are pumped into the anode chamber and cathode chamber of the diaphragm electrolytic cell, respectively, via a peristaltic pump. The working electrode is a Cu-Sn alloy electrode prepared according to claim 1, and the counter electrode is a DSA-coated electrode or a graphite electrode. The electrolysis power supply is turned on to carry out the reaction. The flow rates of the cathode and anolyte are controlled to be the same, with a flow rate of 50~150 ml / min, a reaction temperature of 40~80 ℃, and a current density of 80~140 mA / cm². 2 The reaction flux was 0.8 to 1.4 times the theoretical flux. After the reaction was completed, the reaction solution was removed and post-processed to obtain 3-aminophthalic acid. In the cathode electrolyte, the initial molar ratio of 3-nitrophthalic acid to sulfuric acid is 1:3~7.

5. The method as described in claim 4, characterized in that: In the cathode electrolyte, the initial molar ratio of 3-nitrophthalic acid to sulfuric acid is 1:4~6.

6. The method as described in claim 5, characterized in that: In the cathode electrolyte, the initial molar ratio of 3-nitrophthalic acid to sulfuric acid is 1:

5.

7. The method as described in claim 4, characterized in that: In the solvent, the volume ratio of DMF to deionized water is 1:3~6.

8. The method as described in claim 7, characterized in that: In the solvent, the volume ratio of DMF to deionized water is 1:4~5.

9. The method as described in claim 8, characterized in that: In the solvent, the volume ratio of DMF to deionized water is 1:

4.

10. The method according to any one of claims 4-9, characterized in that: The anolyte and catholyte contain the same concentration of sulfuric acid, which is 0.5~1.5 mol / L.

11. The method as described in claim 10, characterized in that: The anolyte and catholyte contain the same concentration of sulfuric acid, which is 1 mol / L.

12. The method as described in claim 4, characterized in that: The flow rates of the electrolyte at both the cathode and anolyte were controlled at 50–150 mL / min; the reaction current density was 80–140 mA / cm². 2 The reaction temperature is 40~80 ℃; the reaction charge is 0.8~1.4 times the theoretical charge.

13. The method as described in claim 12, characterized in that: The flow rates of the electrolyte at both the cathode and anode are controlled to be 90~120 mL / min.

14. The method as described in claim 13, characterized in that: The flow rates of the electrolyte at both the cathode and anode were controlled at 100 mL / min.

15. The method as described in claim 12, characterized in that: The reaction current density is 100~130 mA / cm² 2 .

16. The method as described in claim 15, characterized in that: The reaction current density is 120 mA / cm² 2 .

17. The method as described in claim 12, characterized in that: The reaction temperature is 50~60 ℃.

18. The method as described in claim 17, characterized in that: The reaction temperature is 60 ℃.

19. The method as described in claim 12, characterized in that: The reaction charge is 1 to 1.2 times the theoretical charge.

20. The method as described in claim 19, characterized in that: The reaction charge is 1.2 times the theoretical charge.

21. The method as described in claim 5, characterized in that: The reaction in the diaphragm electrolyzer was carried out under the following conditions: reaction temperature 60℃, electrolyte flow rate at both cathode and anolyte 100 mL / min, and constant current electrolysis current density set to 120 mA / cm². 2 The reaction charge is 1.2 times the theoretical charge.

22. The method as described in claim 5, characterized in that: In the Cu-Sn alloy prepared in step (a), the mass fraction of Sn is 6%.

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