A method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential regulation

Abstract

A method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential regulation belongs to the field of organic electrocatalysis. In a three-electrode system, an electro-reduced copper nanowire catalyst (ER-Cu / CF) grown on copper foam is used as the cathode, a platinum sheet is used as the counter electrode, and an Ag / AgCl electrode is used as the reference electrode. The two poles of the electrolytic cell are separated by a nafion membrane to form an electrocatalytic reactor. In a neutral electrolyte containing nitro compounds, by adjusting the low direct current voltage, the electrocatalytic unsaturated nitro compounds are controllably stepwise reduced to obtain hydroxylamine intermediates, amino products, and fully reduced products with high selectivity and high yield. In the present invention, the selectivity and yield of the products are very high, it can be carried out at normal temperature and pressure, the operation is simple, green and safe, and the reaction controllability is high; it avoids problems such as low yield, poor selectivity, use of noble metal catalysts and toxic reagents, environmental pollution, and the need for high reaction temperature and pressure in other methods.

Description

Technical Field

[0001] The present invention belongs to the field of organic electrocatalysis, and relates to a method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential regulation. Background Art

[0002] Fine chemicals such as drug molecules, spices, and flavoring agents often have higher added values due to the complexity and difficulty of their synthesis. Such compounds often have multiple functional groups, and it is necessary to catalytically convert a certain functional group with high selectivity and high yield during the synthesis process. For example, in the multi-electron and multi-proton reduction process of a reducing group, how to control its reaction process to obtain a specific intermediate, or in the same compound, achieve controllable selective reduction of different functional groups. In organic synthesis, aromatic hydroxylamines, aromatic amines, aromatic alcohols, and aromatic nitrile compounds are important fine organic chemical intermediates, which are widely used in the synthesis of pesticides, pharmaceuticals, etc. For example, p-aminobenzaldehyde is used in the pharmaceutical industry to synthesize the sulfonamide antibacterial synergist trimethoprim (TMP), in the perfume industry to synthesize anisaldehyde and vanillin, and in the pesticide industry to synthesize p-chlorobenzaldehyde.

[0003] Hydroxylamine is an intermediate in the nitro reduction process. Commonly used methods for reducing aromatic nitro compounds to prepare aromatic hydroxylamines mainly include catalytic hydrogenation method, catalytic hydrogen transfer reduction method, metal reduction method, metal and borohydride reduction method, etc. These traditional methods use noble metal catalysts such as Pt / C and Pd / C, use hydrogen, hypophosphorous acid, hydrazine, etc. as hydrogen sources, or metal zinc powder as a reducing agent. Some need to add additives to stop the reduction of nitro at the hydroxylamine stage, generating wastewater, polluting the environment, and the reaction process is not easy to control, and good controllability cannot be achieved. Industrially, p-aminobenzaldehyde is synthesized by reducing p-nitrobenzaldehyde with a sulfide alkali process, using a large amount of sodium polysulfide or ferrous sulfate and other reducing agents, which will produce a large amount of wastewater; the second method is the disproportionation reduction of p-nitrotoluene with a sodium polysulfide solution, and the by-product p-aminotoluene needs to be removed, with low selectivity and yield. In addition, the product purification process will cause certain pollution to the environment, which does not meet the requirements of the development of society and the chemical industry; the catalytic hydrogenation process is relatively green, but requires high temperature and pressure, and has strict requirements for equipment. p-Aminobenzyl alcohol can be obtained by reducing p-nitrobenzaldehyde, using a half-sandwich ruthenium complex catalyst, with a long reaction time and a long experimental process.

[0004] In view of the deficiencies in the above methods, it is particularly important to develop a method for converting specific functional groups that is inexpensive, simple to operate, green and safe, has high reaction controllability, and high selectivity and high yield. The electroreduction method provides a direction and has certain practical significance for industrial production, etc. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and provide a method for electrocatalytically controllable stepwise reduction of unsaturated nitro compounds with potential regulation, that is, in a three-electrode system, in an H-type electrolytic cell, an electrolytic solution composed of neutral phosphate and p-nitrobenzaldehyde reaction substrate is used for electrochemically controllable stepwise reduction, and hydroxylamine intermediates, amino products and fully reduced products are obtained step by step with high selectivity and high yield. The system of the present invention has the advantages of high product selectivity and yield, mild reaction conditions, simple operation, green safety, high reaction controllability, etc., and has industrial application prospects.

[0006] The technical object of the present invention is achieved by the following technical solutions:

[0007] A method for electrocatalytically controllable stepwise reduction of unsaturated nitro compounds with potential regulation, using an electro-reduced copper nanowire catalyst grown on copper foam as the cathode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The two poles of the electrolytic cell are separated by a nafion membrane to form an electrocatalytic reactor. In a neutral electrolytic solution containing unsaturated nitro compounds, by adjusting the low direct current voltage, the electrocatalytically controllable stepwise reduction of unsaturated nitro compounds is carried out to obtain hydroxylamine intermediates, amino products and fully reduced products;

[0008] The preparation method of the electro-reduced copper nanowire catalyst grown on copper foam includes the following steps:

[0009] 1) Grow copper hydroxide nanowires on the copper foam substrate by chemical oxidation method. Put the freshly treated copper foam into an aqueous solution containing ammonium persulfate and sodium hydroxide. After reacting for 20 - 30 min, black precipitate is observed at the bottom of the beaker, and the red copper foam turns sky blue. Take it out and rinse it with ethanol and deionized water to wash away the residual drugs; the molar ratio of ammonium persulfate to sodium hydroxide in the aqueous solution is 1:15 - 1:20;

[0010] 2) Anneal the copper hydroxide nanowires and calcine them at 280 - 320 °C for 0.5 - 1.5 h to convert them into copper oxide nanowires;

[0011] 3) Electrochemically reduce the self-supporting copper oxide nanowires to self-supporting copper nanowires. Specifically: in a three-electrode system, in an alkaline KOH electrolytic solution, the self-supporting copper oxide nanowires are used as the cathode, a platinum sheet is used as the counter electrode, and a Hg / HgO electrode is used as the reference electrode. The two poles of the electrolytic cell are separated by a nafion membrane to form an electrocatalytic reactor. During the reduction process, Ar gas is continuously passed through the cathode. After CV scanning, rinse it with deionized water to obtain the electro-reduced copper nanowire catalyst supported on copper foam.

[0012] The unsaturated nitro compound is p-nitrobenzaldehyde or p-nitrobenzonitrile; the concentration of the unsaturated nitro compound in the electrolyte is 8-10 mM; the neutral electrolyte is a phosphate buffer solution with a volume ratio of water / 1,4-dioxane of (3-5):1.

[0013] The concentration of the alkaline electrolyte used for electrochemically reducing copper oxide nanowires is 0.5-1 M; the CV scanning range is 0 V vs. Hg / HgO to -2 V vs. Hg / HgO, and the number of cycles is 10-20.

[0014] When the unsaturated nitro compound is p-nitrobenzaldehyde, p-hydroxylamine benzaldehyde, p-aminobenzaldehyde, and p-aminobenzyl alcohol are obtained by stepwise reduction;

[0015] The process for obtaining p-hydroxylamine benzaldehyde by reduction is: constant potential electrolysis is carried out at a constant voltage of 0.2 to -0.1 V vs. RHE, and the reaction time is 0.5 to 6 h;

[0016] The process for obtaining p-aminobenzaldehyde by reduction is: constant potential electrolysis is carried out at a constant voltage of -0.1 to -0.15 V vs. RHE, and the reaction time is 5 to 7 h;

[0017] The process for obtaining p-aminobenzyl alcohol by reduction is: constant potential electrolysis is carried out at a constant voltage of -0.3 to -0.4 V vs. RHE, and the reaction time is 4 to 7 h.

[0018] When the unsaturated nitro compound is p-nitrobenzaldehyde, variable potential synthesis is used for stepwise reduction to obtain p-aminobenzaldehyde or p-aminobenzyl alcohol:

[0019] The process for obtaining p-aminobenzaldehyde by reduction is:

[0020] Electrolysis is carried out at a voltage of 0.2 to -0.1 V vs. RHE for 0.5 to 3 h; then the voltage is adjusted to -0.1 to -0.15 V vs. RHE for electrolysis, and the reaction time is 4 to 7 h;

[0021] The process for obtaining p-aminobenzyl alcohol by reduction is:

[0022] Electrolysis is carried out at a voltage of 0.2 to -0.1 V vs. RHE for 0.5 to 3 h; then the voltage is adjusted to -0.1 to -0.15 V vs. RHE for electrolysis, and the reaction time is 4 to 7 h; then the voltage is further adjusted to -0.3 to -0.4 V vs. RHE for electrolysis, and the reaction time is 4 to 7 h.

[0023] When the unsaturated nitro compound is p-nitrobenzonitrile, p-hydroxylamine benzonitrile, p-aminobenzonitrile, and p-aminobenzylamine are obtained by stepwise reduction;

[0024] The process for obtaining p-hydroxyaminobenzonitrile by reduction is as follows: Constant potential electrolysis is carried out at a constant voltage of 0.2~-0.1V vs. RHE, and the reaction time is 0.5~6h;

[0025] The process for obtaining p-aminobenzonitrile by reduction is as follows: Constant potential electrolysis is carried out at a constant voltage of -0.1~-0.3V vs. RHE, and the reaction time is 3~7h;

[0026] The process for obtaining p-aminobenzylamine by reduction is as follows: Constant potential electrolysis is carried out at a constant voltage of -0.5~-0.6V vs. RHE, and the reaction time is 4~7h.

[0027] When the unsaturated nitro compound is p-nitrobenzonitrile, variable potential synthesis is adopted for stepwise reduction to obtain p-aminobenzonitrile and p-aminobenzylamine;

[0028] The process for obtaining p-aminobenzonitrile by reduction is as follows:

[0029] Electrolysis is carried out at a voltage of 0.2~-0.1V vs.RHE for 0.5~3h; then the voltage is adjusted to -0.1~-0.3Vvs.RHE for electrolysis, and the reaction time is 4~7h;

[0030] The process for obtaining p-aminobenzylamine by reduction is as follows:

[0031] Electrolysis is carried out at a voltage of 0.2~-0.1V vs.RHE for 0.5~3h; then the voltage is adjusted to -0.1~-0.3Vvs.RHE for electrolysis, and the reaction time is 4~7h; then the voltage is further adjusted to -0.5~-0.6V vs. RHE for electrolysis, and the reaction time is 4~7h.

[0032] The diameter of the electrochemically reduced copper nanowires grown on copper foam is between 200~300nm, and the length is between 5~10μm.

[0033] Furthermore, the unsaturated nitro compound is dissolved in the neutral electrolyte by the cosolvent 1,4-dioxane. The neutral electrolyte is 0.5M phosphate buffer solution (volume ratio of water / 1,4-dioxane is 4 / 1).

[0034] Furthermore, the preparation method of the electrochemically reduced copper nanowires supported on copper foam includes the following steps:

[0035] 1) Grow cupric hydroxide nanowires on a copper foam substrate by chemical oxidation. Specifically, put freshly treated copper foam into 30 mL of aqueous solution containing 4 mmol of ammonium persulfate and 80 mmol of sodium hydroxide. After reacting for 30 min, black precipitate can be observed at the bottom of the beaker, and the red copper foam turns sky blue. Take it out and rinse with ethanol and deionized water to wash away the residual chemicals;

[0036] 2) Convert the cupric hydroxide nanowires into cupric oxide nanowires by annealing at 280 - 320 °C for 0.5 - 1.5 h;

[0037] 3) Electrochemically reduce self - supported cupric oxide nanowires to self - supported copper nanowires. Specifically, in a three - electrode system, in an alkaline KOH electrolyte, the self - supported cupric oxide nanowires serve as the cathode, a platinum sheet serves as the counter electrode, and a Hg / HgO electrode serves as the reference electrode. The two poles of the electrolytic cell are separated by a nafion membrane to form an electrocatalytic reactor. During the reduction process, Ar gas is continuously passed through the cathode. After CV scanning, rinse with deionized water to obtain a foam - copper - supported electrochemically reduced copper nanowire (ER - Cu / CF) catalyst.

[0038] Compared with the prior art, the beneficial effects achieved by the technical solution of the present invention are as follows:

[0039] (1) The present invention proposes a controllable step - by - step reduction of electrocatalytic unsaturated nitro compounds, which can obtain hydroxylamine intermediates, amino products, and fully reduced products with high selectivity and high yield in a system at normal temperature, normal pressure, green, and non - organic phase.

[0040] (2) For the catalytic system of the present invention, the electrocatalyst is simple and easy to prepare, the selectivity and yield of the products are very high, the reaction conditions are mild, it can be carried out at normal temperature and normal pressure, the operation is simple, green and safe, and the reaction controllability is high; it avoids problems such as low yield, poor selectivity, using noble metal catalysts and toxic reagents in other methods, polluting the environment, requiring high reaction temperature and pressure conditions, and dangerous and complex operations. Brief Description of the Drawings

[0041] Figure 1 It is a schematic diagram of a method for controllable step - by - step reduction of electrocatalytic unsaturated nitro compounds with potential regulation in the present invention.

[0042] Figure 2 It is an XRD characterization spectrum of the ER - Cu / CF nanowires used in the present invention. Among them, Figures a, b, and c are the XRD patterns of Cu(OH)2 / CF, CuO / CF, and ER - Cu / CF respectively.

[0043] Figure 3Low-magnification and high-magnification morphological characterization diagrams of the ER-Cu / CF nanowires used in the present invention. Among them, Figures a and d are SEM diagrams of Cu(OH)₂ / CF, Figures b and e are SEM diagrams of CuO / CF, and Figures c and f are SEM diagrams of ER-Cu / CF.

[0044] Figure 4 Product distribution diagram of the electroreduction of p-nitrobenzaldehyde to p-hydroxyaminobenzaldehyde and the curve diagrams of current and charge versus time in Example 2.

[0045] Figure 5 Product distribution diagram of the electroreduction of p-nitrobenzaldehyde to p-aminobenzaldehyde and the curve diagrams of current and charge versus time in Example 3.

[0046] Figure 6 Product distribution diagram of the electroreduction of p-nitrobenzaldehyde to p-aminobenzyl alcohol and the curve diagrams of current and charge versus time in Example 4.

[0047] Figure 7 Product distribution diagram of the electroreduction of p-nitrobenzonitrile to p-hydroxyaminobenzonitrile and the curve diagrams of current and charge versus time in Example 5.

[0048] Figure 8 Product distribution diagram of the electroreduction of p-nitrobenzonitrile to p-aminobenzonitrile and the curve diagrams of current and charge versus time in Example 6.

[0049] Figure 9 Product distribution diagram of the electroreduction of p-nitrobenzonitrile to p-aminobenzylamine and the curve diagrams of current and charge versus time in Example 7.

[0050] Figure 10 Product distribution diagram of the electroreduction of p-nitrobenzaldehyde to p-aminobenzyl alcohol at a variable potential in Example 8. Embodiment

[0051] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the following further elaborates on the present invention in conjunction with the accompanying drawings and embodiments.

[0052] 1) Grow copper hydroxide nanowires on the copper foam substrate by chemical oxidation method. Specifically: put the freshly treated copper foam into 30 mL of aqueous solution containing 4 mmol of ammonium persulfate and 80 mmol of sodium hydroxide. After reacting for 30 minutes, black precipitate can be observed at the bottom of the beaker, and the red copper foam turns sky blue. Take it out and rinse with ethanol and deionized water to wash away the residual chemicals;

[0053] 2) Convert the copper hydroxide nanowires into copper oxide nanowires by annealing at 300 °C for 1 hour;

[0054] 3) The self-supported copper oxide nanowires are reduced to self-supported copper nanowires electrochemically, specifically as follows: In a three-electrode system, in a 1 M alkaline KOH electrolyte solution, the self-supported copper oxide nanowires serve as the cathode, a platinum sheet serves as the counter electrode, and a Hg / HgO electrode serves as the reference electrode. The two electrodes of the electrolytic cell are separated by a nafion membrane to form an electrocatalytic reactor. During the reduction process, Ar gas is continuously passed through the cathode. After CV scanning, it is rinsed with deionized water to obtain a foam copper-supported electrochemically reduced copper nanowire (ER-Cu / CF) catalyst. The CV scanning range is 0 V vs. Hg / HgO to -2 V vs. Hg / HgO, and the number of cycles is 12.

[0055] The diameter of the electrochemically reduced copper nanowires grown on the foam copper is about 240 nm, and the length is between 5 and 10 μm.

[0056] Using an H-type electrolytic cell as the container, a nafion membrane connects the cathode chamber and the anode chamber of the electrolytic cell. 30 mL of 0.5 M neutral phosphate solution (volume ratio of water / 1,4-dioxane is 4 / 1) is added to each of the cathode chamber and the anode chamber. Then, 10 mM of p-nitrobenzaldehyde is added to the cathode chamber and continuously stirred with a magnetic stirrer at a rotation speed of 800 rpm. Ar gas is continuously passed through the cathode chamber during the entire electrolysis process. The prepared ER-Cu / CF is used as the working electrode, an Ag / AgCl electrode serves as the reference electrode and is fixed in the cathode chamber, and a platinum sheet serves as the counter electrode and is fixed in the anode chamber. It is connected to an electrochemical workstation, and a constant potential electrolysis is selected at 0.1 V vs. RHE (reversible hydrogen electrode).

[0057] Samples are taken in real time during the reaction process to monitor the reaction process. Standard samples are used to quantitatively analyze the reactants and products by the external standard method, and quantitative analysis is carried out by high-performance liquid chromatography. The curves of the product distribution, current, and charge changes with time during the electrolysis process are as Figure 4 shown. It can be seen from the figure that as the electrolysis time increases, p-nitrobenzaldehyde gradually converts to p-hydroxybenzaldehyde oxime. By quantitative analysis using liquid chromatography, when the reaction time in Example 2 is about 2 h, the conversion rate of p-nitrobenzaldehyde reaches 100%, the selectivity of p-hydroxybenzaldehyde oxime is 98%, and the yield is 98%. A small amount of p-hydroxybenzaldehyde oxime is converted to p-aminobenzaldehyde.

[0058] Using an H-type electrolytic cell as the container, a nafion membrane connects the cathode chamber and the anode chamber of the electrolytic cell. 30 mL of 0.5 M neutral phosphate solution (volume ratio of water / 1,4-dioxane is 4 / 1) is added to each of the cathode chamber and the anode chamber. Then, 10 mM of p-nitrobenzaldehyde is added to the cathode chamber, and it is continuously stirred with a magnetic stirrer at a rotation speed of 800 rpm. Ar gas is continuously passed through the cathode chamber throughout the electrolysis process. Using the prepared ER-Cu / CF as the working electrode, an Ag / AgCl electrode as the reference electrode is fixed in the cathode chamber, and a platinum sheet as the counter electrode is fixed in the anode chamber. It is connected to an electrochemical workstation, and constant potential electrolysis is carried out at -0.1 V vs. RHE.

[0059] Samples are taken in real time during the reaction process to monitor the reaction process. Standard samples are used to quantitatively analyze the reactants and products by the external standard method, and quantitative analysis is carried out by high performance liquid chromatography. The product distribution, and the curves of current and charge changing with time during the electrolysis process are as Figure 5 shown. It can be seen from the figure that as the electrolysis time increases, p-nitrobenzaldehyde gradually converts to p-hydroxyaminobenzaldehyde. After p-hydroxyaminobenzaldehyde experiences a maximum concentration, it gradually converts to p-aminobenzaldehyde, indicating that the nitro group in p-nitrobenzaldehyde can be completely reduced to an amino group after passing through the p-hydroxyaminobenzaldehyde intermediate, while the aldehyde group is basically not affected. The time is about 6 h, realizing the controllable stepwise reduction of the nitro group to an amino group. Quantitative analysis is carried out by liquid chromatography. In Example 3, the conversion rate of p-nitrobenzaldehyde reaches 100%, the selectivity for p-aminobenzaldehyde is 99%, and the yield is 99%.

[0060] The reduction process also shows that whether the substrate is p-nitrobenzaldehyde or p-hydroxyaminobenzaldehyde, it can be controllably and selectively electro-reduced to p-aminobenzyl alcohol.

[0061] Using an H-type electrolytic cell as the container, a nafion membrane connects the cathode chamber and the anode chamber of the electrolytic cell. 30 mL of 0.5 M neutral phosphate solution (volume ratio of water / 1,4-dioxane is 4 / 1) is added to each of the cathode chamber and the anode chamber. Then, 10 mM of p-nitrobenzaldehyde is added to the cathode chamber, and it is continuously stirred with a magnetic stirrer at a rotation speed of 800 rpm. Ar gas is continuously passed through the cathode chamber throughout the electrolysis process. Using the prepared ER-Cu / CF as the working electrode, an Ag / AgCl electrode as the reference electrode is fixed in the cathode chamber, and a platinum sheet as the counter electrode is fixed in the anode chamber. It is connected to an electrochemical workstation, and constant potential electrolysis is carried out at -0.3 V vs. RHE.

[0062] Samples are taken in real time during the reaction process to monitor the reaction process. Standard samples are used to quantitatively analyze the reactants and products by the external standard method, and quantitative analysis is carried out by high performance liquid chromatography. The product distribution, and the curves of current and charge changing with time during the electrolysis process are as Figure 6As shown in the figure. It can be seen from the figure that as the electrolysis time increases, p-nitrobenzaldehyde gradually converts to p-hydroxyaminobenzaldehyde, and at the same time, a small amount of p-aminobenzaldehyde and p-aminobenzyl alcohol are generated. As the reaction proceeds, the hydroxylamine group is gradually reduced to an amino group, and the aldehyde group is gradually reduced to an alcohol, indicating that at -0.3V vs. RHE, the nitro group in p-nitrobenzaldehyde is preferentially reduced. After passing through the p-hydroxyaminobenzaldehyde intermediate, it can be completely reduced to an amino group, and at the same time, the aldehyde group also starts to be reduced, finally obtaining the fully reduced product p-aminobenzyl alcohol, and the time is about 6h. Quantitative analysis was carried out by liquid chromatography. In Example 4, the conversion rate of p-nitrobenzaldehyde reached 100%, the selectivity for p-aminobenzyl alcohol was 99%, and the yield was 99%.

[0063] The reduction process also shows that regardless of whether the substrate is p-nitrobenzaldehyde, p-hydroxyaminobenzaldehyde, or p-aminobenzaldehyde, it can be further electro-reduced to p-aminobenzyl alcohol.

[0064] Using an H-type electrolytic cell as the container, a nafion membrane connects the cathode chamber and the anode chamber of the electrolytic cell. 30 mL of 0.5 M neutral phosphate solution (volume ratio of water / 1,4-dioxane is 4 / 1) is added to each of the cathode chamber and the anode chamber. Then, 10 mM p-nitrobenzonitrile is added to the cathode chamber and continuously stirred with a magnetic stirrer at a rotation speed of 800 rpm. Ar gas is continuously passed through the cathode chamber throughout the electrolysis process. The prepared ER-Cu / CF is used as the working electrode, the Ag / AgCl electrode is used as the reference electrode and fixed in the cathode chamber, and the platinum sheet is used as the counter electrode and fixed in the anode chamber. It is connected to an electrochemical workstation, and constant potential electrolysis is carried out at 0V vs. RHE.

[0065] Samples were taken in real time during the reaction process to monitor the reaction process. Standard samples were used to quantitatively analyze the reactants and products by the external standard method, and quantitative analysis was carried out by high-performance liquid chromatography. The product distribution, current, and charge vs. time curves during the electrolysis process are as Figure 7 shown. It can be seen from the figure that as the electrolysis time increases, p-nitrobenzonitrile gradually converts to p-hydroxyaminobenzonitrile. Quantitative analysis was carried out by liquid chromatography. In Example 5, when the reaction time was about 1.8 h, the conversion rate of p-nitrobenzonitrile reached 100%, the selectivity for p-hydroxyaminobenzonitrile was 95.7%, the yield was 95.7%, and a small amount of p-hydroxyaminobenzonitrile was reduced to p-aminobenzonitrile.

[0066] Using an H-type electrolytic cell as the container, a nafion membrane connects the cathode chamber and the anode chamber of the electrolytic cell. 30 mL of 0.5 M neutral phosphate solution (volume ratio of water / 1,4-dioxane is 4 / 1) is added to each of the cathode chamber and the anode chamber. Then, 10 mM of p-nitrobenzonitrile is added to the cathode chamber and continuously stirred with a magnetic stirrer at a speed of 800 rpm. Ar gas is continuously passed through the cathode chamber throughout the electrolysis process. The prepared ER-Cu / CF is used as the working electrode, the Ag / AgCl electrode is used as the reference electrode and fixed in the cathode chamber, and the platinum sheet is used as the counter electrode and fixed in the anode chamber. It is connected to an electrochemical workstation, and constant potential electrolysis is carried out at -0.1 V vs. RHE.

[0067] Samples are taken in real time during the reaction process to monitor the reaction process. Standard samples are used to quantitatively analyze the reactants and products by the external standard method, and quantitative analysis is carried out by high performance liquid chromatography. The curves of the product distribution, current and charge changes with time during the electrolysis process are as Figure 8 shown. It can be seen from the figure that as the electrolysis time increases, p-nitrobenzonitrile gradually converts to p-hydroxyaminobenzonitrile. After p-hydroxyaminobenzonitrile experiences a maximum concentration, it gradually converts to p-aminobenzonitrile, indicating that the nitro group in p-nitrobenzonitrile can be completely reduced to an amino group after passing through the p-hydroxyaminobenzonitrile intermediate, while the cyano group is basically not affected. The time is about 6 h, realizing the controllable stepwise reduction of the nitro group to an amino group. Quantitative analysis is carried out by liquid chromatography. In Example 6, the conversion rate of p-nitrobenzonitrile reaches 100%, the selectivity of p-aminobenzonitrile is 96.5%, and the yield is 96.5%. There is a small amount of p-hydroxyaminobenzonitrile product.

[0068] The reduction process also shows that whether the substrate is p-nitrobenzonitrile or p-hydroxyaminobenzonitrile, it can be controllably and selectively electro-reduced to p-aminobenzonitrile.

[0069] Using an H-type electrolytic cell as the container, a nafion membrane connects the cathode chamber and the anode chamber of the electrolytic cell. 30 mL of 0.5 M neutral phosphate solution (volume ratio of water / 1,4-dioxane is 4 / 1) is added to each of the cathode chamber and the anode chamber. Then, 10 mM of p-nitrobenzonitrile is added to the cathode chamber and continuously stirred with a magnetic stirrer at a speed of 800 rpm. Ar gas is continuously passed through the cathode chamber throughout the electrolysis process. The prepared ER-Cu / CF is used as the working electrode, the Ag / AgCl electrode is used as the reference electrode and fixed in the cathode chamber, and the platinum sheet is used as the counter electrode and fixed in the anode chamber. It is connected to an electrochemical workstation, and constant potential electrolysis is carried out at -0.5 V vs. RHE.

[0070] Samples are taken in real time during the reaction process to monitor the reaction process. Standard samples are used to quantitatively analyze the reactants and products by the external standard method, and quantitative analysis is carried out by high performance liquid chromatography. The curves of the product distribution, current and charge changes with time during the electrolysis process are as Figure 9As shown. It can be seen from the figure that with the increase of electrolysis time, p-nitrobenzonitrile gradually converts to p-hydroxyaminobenzonitrile, and a small amount of p-aminobenzonitrile and p-aminobenzylamine are generated. As the reaction proceeds, the hydroxylamine group is gradually reduced to an amino group, and the cyano group is gradually reduced to an amine, indicating that at -0.5V vs. RHE, the nitro group in p-nitrobenzonitrile is preferentially reduced. After passing through the p-hydroxyaminobenzonitrile intermediate, it can be completely reduced to an amino group, and at the same time, the cyano group also starts to be reduced, finally obtaining the fully reduced product p-aminobenzylamine, and the time is about 6h. Quantitative analysis was carried out by liquid chromatography. In Example 7, the conversion rate of p-nitrobenzonitrile reached 100%, the selectivity of p-aminobenzylamine was 92%, and the yield was 92%. There was still a small amount of p-aminobenzonitrile that was not converted.

[0071] The reduction process also shows that regardless of whether the substrate is p-nitrobenzonitrile, p-hydroxyaminobenzonitrile, or p-aminobenzonitrile, it can be further electro-reduced to p-aminobenzylamine.

[0072] Using an H-type electrolytic cell as the container, a nafion membrane connects the cathode chamber and the anode chamber of the electrolytic cell. 30 mL of 0.5 M neutral phosphate solution (volume ratio of water / 1,4-dioxane is 4 / 1) is added to each of the cathode chamber and the anode chamber. Then, 10 mM of p-nitrobenzaldehyde is added to the cathode chamber, and it is continuously stirred with a magnetic stirrer at a rotation speed of 800 rpm. Ar gas is continuously passed through the cathode chamber during the whole electrolysis process. Using the prepared ER-Cu / CF as the working electrode, an Ag / AgCl electrode as the reference electrode is fixed in the cathode chamber, and a platinum sheet as the counter electrode is fixed in the anode chamber. It is connected to an electrochemical workstation, and the potential is adjusted for electrolysis.

[0073] Samples were taken in real time during the reaction process to monitor the reaction process. The reactants and products were quantified by the external standard method using standard samples, and quantitative analysis was carried out by high performance liquid chromatography. The product distribution during the electrolysis process is as Figure 10 shown. First, constant potential electrolysis was carried out at 0.1V vs. RHE for 2h. With the increase of electrolysis time, p-nitrobenzaldehyde gradually converts to p-hydroxyaminobenzaldehyde. The conversion rate of p-nitrobenzaldehyde reaches 100%, the selectivity of p-hydroxyaminobenzaldehyde is 98%, and the yield is 98%. A small amount of p-hydroxyaminobenzaldehyde is converted to p-aminobenzaldehyde; then the electrolysis potential is increased, and constant potential electrolysis is carried out at -0.1V vs. RHE for about 5.5h. p-hydroxyaminobenzaldehyde is basically completely converted to p-aminobenzaldehyde. The selectivity of p-aminobenzaldehyde is 99%, and the yield is 99%; the electrolysis potential is further increased, and constant potential electrolysis is carried out at -0.3V vs. RHE for about 5h. The selectivity of p-aminobenzyl alcohol is 99%, and the yield is 99%.

Claims

1. A method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential regulation, characterized in that: Using the electrochemically reduced copper nanowire catalyst grown on copper foam as the cathode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode, with the two electrodes of the electrolytic cell separated by a nafion membrane to form an electrocatalytic reactor. In a neutral electrolyte containing unsaturated nitro compounds, by adjusting the direct current voltage, the electrocatalytic controllable stepwise reduction of unsaturated nitro compounds is carried out to obtain hydroxylamine intermediates, amino products, and fully reduced products; the unsaturated nitro compounds are p-nitrobenzaldehyde and p-nitrobenzonitrile; The preparation method of the electrochemically reduced copper nanowire catalyst grown on copper foam includes the following steps: 1) Grow copper hydroxide nanowires on the copper foam substrate by chemical oxidation. Put the freshly treated copper foam into an aqueous solution containing ammonium persulfate and sodium hydroxide. After reacting for 20 - 30 min, black precipitates are observed at the bottom of the beaker, and the red copper foam turns sky blue. Take it out and rinse it with ethanol and deionized water to wash away the residual drugs; the molar ratio of ammonium persulfate to sodium hydroxide in the aqueous solution is 1:15 - 1:20; 2) Convert the copper hydroxide nanowires into copper oxide nanowires by annealing, calcining at 280 - 320 °C for 0.5 - 1.5 h; 3) Electrochemically reduce the self-supporting copper oxide nanowires to self-supporting copper nanowires. Specifically: In a three-electrode system, in an alkaline KOH electrolyte, the self-supporting copper oxide nanowires are used as the cathode, a platinum sheet as the counter electrode, and a Hg / HgO electrode as the reference electrode. The two electrodes of the electrolytic cell are separated by a nafion membrane to form an electrocatalytic reactor. During the reduction process, Ar gas is continuously passed through the cathode. After CV scanning, rinse it with deionized water to obtain the electrochemically reduced copper nanowire catalyst supported on copper foam.

2. The method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential regulation according to claim 1, wherein The concentration of the unsaturated nitro compound in the electrolyte is 8 - 10 mM; the neutral electrolyte is a phosphate buffer solution, in which the volume ratio of water / 1,4-dioxane is (3 - 5):

1.

3. A method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential regulation according to claim 1, characterized in that, The concentration of the alkaline electrolyte used for electrochemically reducing copper oxide nanowires is 0.5 - 1 M; the CV scanning range is 0 V vs. Hg / HgO to -2 V vs. Hg / HgO, and the number of cycles is 10 - 20 cycles.

4. A method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential regulation according to claim 2, characterized in that: When the unsaturated nitro compound is p-nitrobenzaldehyde, p-hydroxybenzaldehyde, p-aminobenzaldehyde, and p-aminobenzyl alcohol are obtained by stepwise reduction; The process for obtaining p-hydroxybenzaldehyde by reduction is: Select a constant voltage of 0.2 - -0.1 V vs. RHE for potentiostatic electrolysis, and the reaction time is 0.5 - 6 h; The process for obtaining p-aminobenzaldehyde by reduction is: Select a constant voltage of -0.1 - -0.15 V vs. RHE for potentiostatic electrolysis, and the reaction time is 5 - 7 h; The process for obtaining p-aminobenzyl alcohol by reduction is: Select a constant voltage of -0.3 - -0.4 V vs. RHE for potentiostatic electrolysis, and the reaction time is 4 - 7 h.

5. According to the method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential adjustment described in claim 2, characterized in that: When the unsaturated nitro compound is p-nitrobenzaldehyde, the stepwise reduction to obtain p-aminobenzaldehyde or p-aminobenzyl alcohol is carried out by varying the potential synthesis: The process for reducing to obtain p-aminobenzaldehyde is: Electrolysis is carried out at a voltage of 0.2~-0.1V vs. RHE for 0.5~3h; then the voltage is adjusted to -0.1~-0.15V vs. RHE for electrolysis for 4~7h. The process for reducing to obtain p-aminobenzyl alcohol is: Electrolysis is carried out at a voltage of 0.2~-0.1V vs. RHE for 0.5~3h; then the voltage is adjusted to -0.1~-0.15V vs. RHE for electrolysis for 4~7h; and then the voltage is further adjusted to -0.3~-0.4V vs. RHE for electrolysis for 4~7h.

6. The method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential regulation according to claim 2, characterized in that: When the unsaturated nitro compound is p-nitrobenzonitrile, the stepwise reduction obtains p-hydroxyaminobenzonitrile, p-aminobenzonitrile and p-aminobenzylamine; The process for reducing to obtain p-hydroxyaminobenzonitrile is: Select a constant voltage of 0.2~-0.1V vs. RHE for constant potential electrolysis for 0.5~6h; The process for reducing to obtain p-aminobenzonitrile is: Select a constant voltage of -0.1~-0.3V vs. RHE for constant potential electrolysis for 3~7h; The process for reducing to obtain p-aminobenzylamine is: Select a constant voltage of -0.5~-0.6V vs. RHE for constant potential electrolysis for 4~7h.

7. A method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential regulation according to claim 2, characterized in that: When the unsaturated nitro compound is p-nitrobenzonitrile, the stepwise reduction to obtain p-aminobenzonitrile and p-aminobenzylamine is carried out by varying the potential synthesis; The process for reducing to obtain p-aminobenzonitrile is: Electrolysis is carried out at a voltage of 0.2~-0.1V vs. RHE for 0.5~3h; then the voltage is adjusted to -0.1~-0.3V vs. RHE for electrolysis for 4~7h; The process for reducing to obtain p-aminobenzylamine is: Electrolysis is carried out at a voltage of 0.2~-0.1V vs. RHE for 0.5~3h; then the voltage is adjusted to -0.1~-0.3V vs. RHE for electrolysis for 4~7h; and then the voltage is further adjusted to -0.5~-0.6V vs. RHE for electrolysis for 4~7h.

8. A method for controllable stepwise reduction of electrocatalytic unsaturated nitro compounds with potential regulation according to claim 3, characterized in that, The diameter of the electrochemically reduced copper nanowires grown on the copper foam is between 200~300nm, and the length is between 5~10μm.

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