Electro-catalysis system for synthesizing secondary amine products by coupling nitrile and aldehyde and application of electro-catalysis system

Abstract

The invention relates to the technical field of organic chemistry, in particular to an electro-catalysis system for synthesizing a secondary amine product by coupling nitrile and aldehyde and application of the electro-catalysis system. The electro-catalysis system comprises a reference electrode, an anode, a cathode loaded with a copper-based catalyst coating, an alkaline electrolyte and a reaction substrate which are arranged in an electrolytic tank, the copper-based catalyst contains bivalent copper; the cathode and the anode are connected with an external power supply through wires; relative to the potential of the standard hydrogen electrode, the reduction reaction potential of the electro-catalysis system is-1.0 to-0.3 V; the reaction current density of the electro-catalysis system is-20 to-300 mA / cm < 2 >, and the total reaction time is 5-20 hours; the reaction substrates comprise aldehyde organic matters and nitrile compounds. The application refers to the application of the electro-catalysis system in synthesis of secondary amine products. According to the invention, the electrochemical reduction rate of nitrile compounds can be improved, the electrochemical reduction rate of aldehyde organic matters can be inhibited, and the yield of synthesized secondary amine products can be further improved.

Description

Technical Field

[0001] This invention relates to the field of organic chemistry, and in particular to an electrocatalytic system for the coupling of nitrile and aldehyde to secondary amine products and its application. Background Technology

[0002] Secondary amines, possessing both high reactivity and structural diversity, play an irreplaceable role in pharmaceuticals, pesticides, materials science, and biochemistry. Reductive amination of carbonyl compounds using primary amines as nitrogen sources is one of the effective methods for producing secondary amines. Catalytic hydrogenation of nitrile compounds is a low-cost, atom-economical method for producing primary amines. Nitriles are widely available, with over 100 nitrile compounds directly obtainable from natural substances in terrestrial and marine environments. Furthermore, the industrial production of nitrile compounds is large-scale and inexpensive. Therefore, the direct catalytic hydrogenation of nitrile compounds to primary amines has attracted considerable attention. Among carbonyl compounds, aldehydes are more prone to cross-coupling due to their high electrophilic reactivity. Simultaneously, nitrile compounds are less expensive than primary amines as nitrogen sources for cross-coupling. Therefore, the synthesis of secondary amines through cross-coupling reactions of aldehydes and nitrile compounds is more economical.

[0003] However, the synthesis of secondary amines from aldehydes and nitriles using conventional thermocatalytic methods (see: Polidoro D, Espro C, Lazaro N, et al. Catalytic screening of the cascade reductive amination reaction of furfural and acetonitrile [J]. Catalysis Today, 2023, 423: 113890-113895.) requires not only large amounts of toxic reagents (such as acetonitrile solvents), expensive catalysts (such as ruthenium), and harsh reaction conditions (such as high pressure and high temperature), but also uncontrollable hydrogenation reactions that result in low yields of the synthesized secondary amines.

[0004] Given that electrochemical methods are widely used to synthesize various nitrogen-containing chemicals, and are green and safe, capable of being carried out mildly at room temperature and pressure, the electrocatalytic cross-coupling of aldehydes and nitriles to synthesize secondary amines is a very promising strategy. However, the electrochemical reducing power of aldehydes is much higher than that of nitriles, leading to the easy hydrogenation or self-coupling polymerization of aldehydes, which prevents them from coupling with the reduction products of nitriles to form secondary amines, ultimately resulting in a reduced yield of secondary amines.

[0005] Therefore, it is necessary to provide an electrocatalytic system and its application for the coupling of nitrile and aldehyde to synthesize secondary amine products to solve the problem of low yield of electrocatalytic cross-coupling of aldehyde organic compounds and nitrile compounds to synthesize secondary amine products in the prior art. Summary of the Invention

[0006] The purpose of this invention is to provide an electrocatalytic system for the coupling of nitrile aldehydes to form secondary amine products and its application. The specific technical solution is as follows: In a first aspect, the present invention provides an electrocatalytic system for the coupling of nitrile aldehydes to form secondary amine products, the electrocatalytic system comprising a reference electrode, an anode, a cathode supported on a copper-based catalyst coating, an alkaline electrolyte, and a reaction substrate disposed in an electrolytic cell; The copper-based catalyst is a copper-based catalyst containing divalent copper; The cathode and the anode are connected to an external power source via wires; The reduction reaction potential of the electrocatalytic system is -1.0 to -0.3 V relative to the potential of the standard hydrogen electrode; The reaction current density of the electrocatalytic system is -20 ~ -300 mA / cm². 2 The total reaction time is 5 to 20 hours. The reaction substrates include aldehydes and nitriles; in the alkaline electrolyte, the molar concentration of the aldehydes is 0.02 ~ 0.1 mol / L, and the molar concentration of the nitriles is 0.1 ~ 1 mol / L.

[0007] Optionally, the copper-based catalyst includes at least one of CuO, CuS, and copper-based catalysts doped with high-valence metals; In the copper-based catalyst doped with a high-valence metal, the high-valence metal includes any one of Fe, Co, Ni, Sn, and Ce.

[0008] Optionally, in the copper-based catalyst doped with high-valence metal, the molar percentage ratio of the high-valence metal to the divalent copper is 5%:95% ~ 30%:70%.

[0009] Optionally, the loading of the copper-based catalyst on the copper-based catalyst coating is 2~20 mg / cm³. 2 .

[0010] Optionally, the aldehyde organic compounds include at least one of furfural, benzaldehyde, pyridinaldehyde, butyraldehyde, and pentanal.

[0011] Optionally, the nitrile compound includes at least one of acetonitrile, propionitrile, butyronitrile, adiponitrile, and benzonitrile.

[0012] Optionally, the alkaline solute used in the alkaline electrolyte includes at least one of K2CO3, KOH, Na2CO3, and NaOH.

[0013] Optionally, in the alkaline electrolyte, the molar concentration of the alkaline solute is 0.5 to 2 mol / L.

[0014] In a second aspect, the present invention provides an application of the electrocatalytic system for the synthesis of secondary amine products by coupling nitrile aldehydes in the synthesis of secondary amine products.

[0015] Optionally, the yield of the synthesized secondary amine product is not less than 70%.

[0016] The application of the technical solution of the present invention has at least the following beneficial effects: (1) The electrocatalytic system for the coupling of nitrile aldehydes to secondary amine products provided by the present invention utilizes a copper-based catalyst containing divalent copper supported on the cathode. This catalyst can coordinate with nitrile compounds, adsorb a large amount of nitrile compounds, thereby increasing the electrochemical reduction rate of nitrile compounds and catalyzing the yield of the corresponding reduction products (such as...). Figure 2 Product I and Figure 2 In addition to product II, the copper-based catalyst containing divalent copper can inhibit the reduction of aldehydes to form carbon radicals, thereby reducing the self-coupling reaction activity of aldehydes and increasing the yield of secondary amine products formed by the coupling of aldehydes and nitrile compounds. That is, the present invention can improve the electrochemical reduction rate of nitrile compounds and inhibit the electrochemical reduction rate of aldehydes by using a copper-based catalyst containing divalent copper supported on the cathode, thereby increasing the yield of secondary amine products formed by the coupling of aldehydes and nitrile compounds. Furthermore, the alkaline electrolyte used in the electrocatalytic system of this invention can protect the stability of the reduction products of nitrile compounds, thereby helping to improve the yield of secondary amine products. Using a suitable reduction reaction potential in the electrocatalytic system can promote the reduction of nitrile compounds to form reduction products, thus ensuring efficient coupling with aldehydes to form secondary amine products. If the reduction reaction potential is too high, nitrile compounds are difficult to reduce to form reduction products; if the reduction reaction potential is too low, the water dissociation in the alkaline electrolyte will cause hydrogen evolution, and this reaction will dominate, forcing the secondary amine to... The synthesis efficiency of secondary amines decreases. Using appropriate reaction current density and total reaction time in the electrocatalytic system can promote the rapid and efficient synthesis of secondary amines. If the reaction current density is too low and the reaction time is too long, it will easily lead to the spontaneous decomposition of aldehyde organics, resulting in a reduction in the amount of aldehyde organics remaining, which in turn leads to a decrease in the yield of secondary amines. If the reaction current density is high and the reaction time is short, the hydrogen evolution reaction will occur due to the dissociation of water in the alkaline electrolyte, and this reaction will dominate, forcing a decrease in the Faraday efficiency of secondary amine synthesis, or even a decrease in the yield of secondary amines.

[0017] (2) In this invention, doping a suitable amount of high-valence metal into the copper-based catalyst can inhibit the reduction of divalent copper, which helps stabilize the activity of divalent copper, ensures the efficient synthesis of secondary amine products from aldehydes and nitriles, and improves the yield of secondary amine products. Furthermore, if the molar percentage of the high-valence metal is too low, Cu will be affected during the synthesis of secondary amine products. 2+ The reduction of Cu is difficult to suppress, i.e., Cu 2+ It is easily reduced by electroreduction, leading to a rapid decrease in activity; if the molar percentage of high-valence metals is too high, the inactive high-valence metals will hinder Cu. 2+ The expression of activity resulted in a significant decrease in the yield of secondary amine products.

[0018] (3) The aldehyde organic compounds selected in this invention include furfural, which is a biomass derivative extracted from lignocellulosic biomass and has the characteristic of abundant sources; the nitrile compounds selected in this invention include acetonitrile, which is a by-product of acrylonitrile production. Only a small portion of acetonitrile is recycled by the manufacturer, while most of acetonitrile is burned as fuel, producing a large amount of toxic nitrogen oxide gas; this invention selects acetonitrile and furfural as reaction substrates, and with the help of electrocatalysis, it can greenly synthesize high-value-added secondary amine products, namely ethyl-2-furan methylamine, and realize the value-added utilization of furfural, while avoiding the toxic gas produced by burning acetonitrile.

[0019] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is the XRD pattern of the copper-based catalyst CuO powder in Example 1; Figure 2 This is a schematic diagram of the reaction principle for the coupling of acetonitrile and furfural to form the secondary amine product ethyl-2-furanmethylamine. Figure 3 The image shows the 1H NMR spectrum of the electrocatalytic synthesis of ethyl-2-furanmethylamine using the electrocatalytic system in Example 1. Figure 4 The copper-based catalyst Cu in Example 2 1.8 Fe 0.2O 2.1 XRD pattern of the powder; Figure 5 The image shows the 1H NMR spectrum of the electrocatalytic synthesis of ethyl-2-furanmethylamine using the electrocatalytic system in Example 2. Figure 6a This is the CV curve of Fe2O3 in 1 M KOH solution; Figure 6b This is the CV curve of CuO in 1 M KOH solution; Figure 6c It is Cu 1.8 Fe 0.2 O 2.1 CV curve in 1 M KOH solution; Figure 7a This is the E-pH diagram for Cu. Figure 7b This is the E-pH diagram for Fe. Figure 8 The XRD pattern of Cu powder, a copper-based catalyst, in Comparative Example 1 is shown. Figure 9 The image shows the 1H NMR spectrum of the electrocatalytic synthesis of ethyl-2-furanmethylamine in the electrocatalytic system of Comparative Example 1. Figure 10 The cathode containing CuO is at -0.5 V. RHE In-situ synchrotron infrared spectrum (SR-FTIR) of electrolysis; Figure 11 The cathode containing Cu is at -0.5 V RHE In-situ synchrotron infrared spectrum (SR-FTIR) of electrolysis; Figure 12 The above is the 1H NMR spectrum of the electrocatalytic synthesis of ethyl-2-furanmethylamine in the electrocatalytic system of Comparative Example 2; Among them, Figure 6a ~ Figure 6c The “1 M KOH solution” in the figure represents a 1 mol / L KOH solution; the unit “mA cm” in the vertical axis -2 "Indicates mA / cm" 2 The unit "V vs. RHE" on the horizontal axis represents the potential relative to the standard hydrogen electrode, with the unit being V. exist Figure 10 and Figure 11 The "V" in the name RHE "" indicates the potential relative to the standard hydrogen electrode. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: This invention proposes an electrocatalytic system for the coupling of nitrile and aldehyde to form secondary amine products. The electrocatalytic system includes a reference electrode (specifically a Hg / HgO electrode), an anode (specifically a counter electrode made of commercially available RuIr loaded onto a Ti mesh), a cathode with a copper-based catalyst coating, an alkaline electrolyte, and a reaction substrate, all disposed in an electrolytic cell. The copper-based catalyst is a copper-based catalyst containing divalent copper; The cathode and the anode are connected to an external power source via wires; The reduction reaction potential of the electrocatalytic system is -1.0 ~ -0.3 V (specifically -0.5 V) relative to the potential of the standard hydrogen electrode. The reaction current density of the electrocatalytic system is -20 ~ -300 mA / cm². 2 (Specifically -90 mA / cm) 2 The total reaction time is 5 to 20 hours (specifically 8 hours). The reaction substrates include aldehydes and nitrile compounds; in the alkaline electrolyte, the aldehyde is furfural with a molar concentration of 0.02 ~ 0.1 mol / L (specifically 0.05 mol / L), and the nitrile is acetonitrile with a molar concentration of 0.1 ~ 1 mol / L (specifically 0.5 mol / L).

[0024] The copper-based catalyst is CuO powder, and its preparation method is as follows: 1.0 g of CuSO4·5H2O was dissolved in 100 mL of deionized water and stirred for 15 min. Then, 0.15 mol / L ammonia solution was added, and the mixture was stirred for another 15 min. Next, 1.2 mol / L NaOH solution was added. After reacting for 15 min, the mixture was placed in a constant temperature oven at 25 ℃ for three days. The black precipitate was collected by centrifugation and washed repeatedly with deionized water and ethanol. Then, the precipitate was placed in a freeze dryer for 12 h to obtain a dry black powder. Finally, the black powder was heated to 200 ℃ in air at a rate of 0.5 ℃ / min and calcined for 3 h. After cooling to room temperature, CuO powder was obtained.

[0025] Figure 1 This is the XRD pattern of CuO powder. See also... Figure 1 It is known that the copper-based catalyst CuO powder was successfully prepared.

[0026] The copper-based catalyst loading on the copper-based catalyst coating is 20 mg / cm³. 2 .

[0027] The method for loading the copper-based catalyst coating onto the cathode is as follows: 100 mg of copper-based catalyst powder (i.e., CuO powder) was added to a mixture of 2.0 mL of deionized water, 1.8 mL of isopropanol, and 200 μL of Nafion membrane solution (i.e., a 5% perfluorosulfonic acid resin solution). The mixture was then ultrasonically homogenized to obtain 4.0 mL of copper-based catalyst slurry. 800 μL of the slurry was then coated onto a 1 cm × 1 cm sheet of carbon paper and allowed to dry naturally to form the working electrode (i.e., the cathode).

[0028] The alkaline electrolyte uses KOH as the alkaline solute.

[0029] In the alkaline electrolyte, the molar concentration of the alkaline solute is 0.5 ~ 2 mol / L (specifically 1 mol / L).

[0030] In the electrocatalytic system described above, the reaction principle of the coupling of acetonitrile and furfural to form the secondary amine product ethyl-2-furanmethylamine is as follows: Figure 2 As shown, the copper-based catalyst containing divalent copper supported on the cathode can coordinate with acetonitrile, adsorb a large amount of acetonitrile, and thus increase the electrochemical reduction rate of acetonitrile, catalyzing the corresponding reduction products I and II. At the same time, the copper-based catalyst containing divalent copper can inhibit the reduction of furfural to form carbon free radicals, thereby reducing the self-coupling reaction activity of furfural. Furfural and the reduction product II of acetonitrile are coupled to form ethyl-2-furanimide (i.e., product III). Under the catalytic action of the copper-based catalyst containing divalent copper, ethyl-2-furanimide is further reduced to the secondary amine product ethyl-2-furanimide (i.e., product IV).

[0031] The solution after the coupling reaction of acetonitrile and furfural in the electrocatalytic system of Example 1 was collected and NMR was performed using methanol as an internal standard. Figure 3 This is the NMR spectrum of the electrocatalytic synthesis of ethyl-2-furanylamine using the electrocatalytic system in Example 1. Figure 3 It is known that the peak at 3.62 ppm is the peak of ethyl-2-furanmethylamine, while the peak at 3.25 ppm is the peak of methanol, the internal standard reagent of NMR. It is calculated that the yield of ethyl-2-furanmethylamine synthesized from Example 1 is about 72%.

[0032] Example 2: Unlike Example 1, the copper-based catalyst is a copper-based catalyst doped with a high-valence metal, specifically Cu. 1.8 Fe 0.2 O 2.1 Powder. Among which, Fe... 3+ With Cu 2+ The molar percentage ratio of Cu is 10%:90%. 1.8 Fe 0.2 O 2.1 The powder preparation method is as follows: 900 mg CuSO4·5H2O and 112 mg Fe2(SO4)3·9H2O were dissolved in 100 mL of deionized water and stirred for 15 min. Then, 0.15 mol / L ammonia solution was added, and the mixture was stirred for another 15 min. Finally, 1.2 mol / L NaOH solution was added. After reacting for 15 min, the mixture was placed in a constant temperature oven at 25 °C for three days. The black precipitate was collected by centrifugation and washed repeatedly with deionized water and ethanol. Then, the precipitate was freeze-dried for 12 h to obtain a dry black powder. Finally, the black powder was calcined in air at a rate of 0.5 °C / min to 200 °C for 3 h, and then cooled to room temperature to obtain Cu. 1.8 Fe 0.2 O 2.1 powder.

[0033] Figure 4 It is Cu 1.8 Fe 0.2 O 2.1 XRD pattern of the powder. See also Figure 4 It is known that the copper-based catalyst Cu 1.8 Fe 0.2 O 2.1 The powder was successfully prepared.

[0034] The solution after the coupling reaction of acetonitrile and furfural in the electrocatalytic system of Example 2 was collected and analyzed by NMR using methanol as an internal standard. Figure 5 This is the NMR spectrum of the electrocatalytic synthesis of ethyl-2-furanylamine using the electrocatalytic system in Example 2. Figure 5 It is known that the peak at 3.62 ppm is the peak of ethyl-2-furanmethylamine, while the peak at 3.25 ppm is the peak of methanol, the internal standard reagent of NMR. It is calculated that the yield of ethyl-2-furanmethylamine synthesized in Example 2 is about 98%.

[0035] Compared to Example 1, Example 2 shows that Cu is used. 1.8 Fe 0.2 O 2.1Powdered copper catalysts can improve the yield of ethyl-2-furanmethylamine synthesized from acetonitrile and furfural. This indicates that doping copper-based catalysts with an appropriate amount of high-valence metal Fe can inhibit the reduction of divalent copper, help stabilize the activity of divalent copper, ensure the efficient synthesis of secondary amine products from aldehydes and nitriles, and improve the yield of secondary amine products.

[0036] Additionally, regarding Cu in Example 2 1.8 Fe 0.2 O 2.1 Powder doping with high-valence metal Fe can inhibit the reduction of divalent copper, which helps stabilize the activity of divalent copper. This can also be demonstrated by the following data: First, CV testing using a rotating disk electrode was used to analyze why high-valent metal Fe can inhibit the reduction of divalent copper.

[0037] The CV testing method is as follows: Electrochemical cyclic voltammetry (CV) tests were conducted on the catalyst under test using a three-electrode testing system. The catalyst was drop-coated onto a glassy carbon electrode as the working electrode, a carbon rod as the counter electrode, and a Hg / HgO electrode as the reference electrode. The potential window set for the test was -0.3 V to 1.2 V (vs. RHE). The scanning process adopted a constant linear scan rate of 5 mV / s, and the scanning mode was "reverse-forward" cycle: first, a linear scan was performed from the starting potential of -1.2 V along the forward direction to the ending potential of -0.3 V, and then a linear scan was performed from -0.3 V along the reverse direction to the starting potential of -1.2 V, constituting one complete CV cycle. In the actual test, five consecutive scans were performed. The entire test process was carried out at room temperature (25±2℃), atmospheric pressure, and without inert gas protection (or: after purging with high-purity nitrogen for 30 min to remove oxygen). The electrolyte was a 1 mol / L KOH aqueous solution, and the rotation speed was set to 2400 rpm.

[0038] pass Figure 6a and Figure 6b Comparison revealed Fe 3+ The reduction peak potential (0.58 V) RHE ) compared to Cu 2+ The reduction peak potential (0.11 V) RHE Earlier, this indicates that Fe 3+ Cu 2+ It's easier to restore. Furthermore, through... Figure 6b and Figure 6c In comparison, Cu was also observed 1.8 Fe 0.2 O 2.1 Cu 2+ Peak reduction current (-4.6 mA / cm) 2 The peak value is much smaller than that of CuO (-33 mA / cm). 2These results directly confirm that Fe 3+ The introduction of Cu greatly slowed down 2+ The reduction rate, that is, the high-valence metal Fe can inhibit the reduction of divalent copper.

[0039] Secondly, the E-pH diagrams of Cu and Fe were used to analyze Cu. 1.8 Fe 0.2 O 2.1 The reason why powder doping with high-valence metal Fe can stabilize the activity of divalent copper.

[0040] The E-pH diagram, also known as the Pourbaix diagram, was first created by the Belgian scholar Marcel Pourbaix. It plots electrical potential (E) on the vertical axis and pH value on the horizontal axis, depicting the stable range or dominant region of various forms of elements in aqueous systems (metal ions, complex ions, solid hydroxides, oxides, and elements). The E-pH diagram is an equilibrium diagram calculated based on thermodynamic data (primarily the standard Gibbs free energy change) and the Nernst equation.

[0041] The E-pH diagram of Cu was generated using the thermodynamic software HSC Chemistry.

[0042] The E-pH diagram for Fe was generated using the thermodynamic software HSC Chemistry.

[0043] like Figure 7a As shown, in 1 M KOH (pH = 13.76) at -0.5 V RHE At the electrolysis potential, the thermodynamic form of Cu is Cu 0 ;like Figure 7b As shown, in 1 M KOH (pH = 13.76) at -0.5 V RHE At the electrolysis potential, the thermodynamic form of Fe is Fe. 3+ Therefore, when Fe 3+ Electrochemically reduced to Fe 2+ or Fe 0 At this electrolysis potential, Fe can also be spontaneously oxidized to form Fe. 3+ This avoids Fe 3+ In suppressing Cu 2+ During the reduction process, Cu itself is reduced and decreased, which in turn leads to Cu... 1.8 Fe 0.2 O 2.1 It can maintain high stability and ensure Cu 2+ Its activity is stable.

[0044] Comparative Example 1: Unlike Example 1, the copper-based catalyst CuO powder in Example 1 was replaced with Cu powder. The Cu powder was prepared as follows: First, CuO powder was prepared according to the method for preparing CuO powder in Example 1; Next, 100 mg of the prepared CuO powder was heated to 250 °C at a rate of 0.5 °C / min in a continuous Ar / H2 gas flow and held for 3 h; then, it was cooled to room temperature, and the black CuO powder turned into red Cu powder.

[0045] Figure 8 This is the XRD pattern of Cu powder. See also... Figure 8 It is known that the copper-based catalyst Cu powder was successfully prepared.

[0046] The solution after the coupling reaction of acetonitrile and furfural in the electrocatalytic system of Comparative Example 1 was collected and analyzed by NMR using methanol as an internal standard. Figure 9 The NMR spectrum is shown for the electrocatalytic synthesis of ethyl-2-furanylamine using the electrocatalytic system in Comparative Example 1. Figure 9 It is known that the peak at 3.62 ppm is the peak of ethyl-2-furanmethylamine, while the peak at 3.25 ppm is the peak of methanol, the internal standard reagent of NMR. It is calculated that the yield of ethyl-2-furanmethylamine synthesized from Comparative Example 1 is about 9%.

[0047] Compared to Example 1, as shown in Comparative Example 1, using Cu powder as a copper-based catalyst significantly reduced the yield of ethyl-2-furanmethylamine synthesized from acetonitrile and furfural. This indicates that Cu powder (i.e., zero-valent copper) cannot reverse the situation where the electrochemical reducing power of furfural is much higher than that of acetonitrile, thus leading to a significant decrease in the yield of ethyl-2-furanmethylamine synthesized from acetonitrile and furfural. Conversely, in Example 1, CuO powder was able to reverse the situation where the electrochemical reducing power of furfural was much higher than that of acetonitrile. Specifically, the copper-based catalyst containing divalent copper can coordinate with acetonitrile, adsorbing a large amount of acetonitrile, thereby increasing the electrochemical reduction rate of acetonitrile and catalyzing the yield of the corresponding reduction products (such as...). Figure 2 Product I and Figure 2 In addition to product II, the copper-based catalyst containing divalent copper can inhibit the reduction of furfural to form carbon free radicals, thereby reducing the activity of furfural self-coupling reaction, which in turn significantly increases the yield of acetonitrile and furfural coupled to synthesize ethyl-2-furanmethylamine.

[0048] Furthermore, the fact that CuO powder in Example 1 could reverse the electrochemical reducing power of furfural by a much higher rate than that of acetonitrile can also be demonstrated by the following data: See Figure 10 The cathode containing CuO is at -0.5 V. RHEThe in-situ synchrotron infrared spectrum (SR-FTIR) of the electrolytically extracted sample is located at 1662 cm⁻¹. -1 The peaks attributable to C=N or C=O stretching vibrations first increased and then decreased with increasing reaction time, indicating that acetonitrile was gradually reduced to form reduction products I and II. Subsequently, furfural coupled with acetonitrile reduction product II to form ethyl-2-furanimide (i.e., product III). Under the catalysis of CuO, ethyl-2-furanimide was further reduced to the secondary amine product ethyl-2-furanmamine (i.e., product IV). This demonstrates that CuO powder (i.e., divalent copper) can reverse the situation where the electrochemical reducing power of furfural is much higher than that of acetonitrile. Conversely, see [reference needed]. Figure 11 The cathode containing Cu is at -0.5 V. RHE The in-situ synchrotron infrared spectrum (SR-FTIR) of the electrolyzed sample is at 1646 cm⁻¹. -1 The stretching vibration peaks attributable to C=N or C=O gradually weakened with increasing reaction time, then slowly recovered, indicating that furfural was being rapidly consumed, followed by the slow formation of ethylamine. This demonstrates that Cu powder (i.e., zero-valent copper) could not reverse the fact that the electrochemical reducing power of furfural was much higher than that of acetonitrile.

[0049] Comparative Example 2: Unlike Example 1, the reduction reaction potential of the electrocatalytic system is -0.2 V.

[0050] The solution after the coupling reaction of acetonitrile and furfural in the electrocatalytic system of Comparative Example 2 was collected and analyzed by NMR using methanol as an internal standard. Figure 12 The image shows the NMR spectrum of the electrocatalytic synthesis of ethyl-2-furanylamine using the electrocatalytic system in Comparative Example 2. Figure 12 It is known that the peak at 3.62 ppm is the peak of ethyl-2-furanmethylamine, while the peak at 3.25 ppm is the peak of methanol, the internal standard reagent of NMR. It can be seen that the peak of ethyl-2-furanmethylamine is very low, indicating that the yield of ethyl-2-furanmethylamine synthesized from Comparative Example 2 is very low, and the yield cannot be calculated.

[0051] Compared to Example 1, as shown in Comparative Example 2, the reduction reaction potential of the electrocatalytic system is -0.2 V, which is significantly higher than the reduction reaction potential range of -1.0 to -0.3 V of the present invention. This results in a very low yield of ethyl-2-furanmethylamine produced by the coupling of acetonitrile and furfural. This is because an excessively high reduction reaction potential makes it difficult for acetonitrile to be reduced to form a reduction product, thus hindering its coupling with furfural to form ethyl-2-furanmethylamine. Therefore, the excessively high reduction reaction potential in Comparative Example 2 leads to a very low yield of ethyl-2-furanmethylamine, making it impossible to calculate the yield.

[0052] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. An electrocatalytic system for the coupling of nitrile and aldehyde to form secondary amine products, characterized in that, The electrocatalytic system includes a reference electrode, an anode, a cathode with a copper-based catalyst coating, an alkaline electrolyte, and a reaction substrate, all disposed in an electrolytic cell. The copper-based catalyst is a copper-based catalyst containing divalent copper; The cathode and the anode are connected to an external power source via wires; The reduction reaction potential of the electrocatalytic system is -1.0 to -0.3 V relative to the potential of the standard hydrogen electrode; The reaction current density of the electrocatalytic system is -20 ~ -300 mA / cm². 2 The total reaction time is 5 to 20 hours. The reaction substrates include aldehydes and nitriles; in the alkaline electrolyte, the molar concentration of the aldehydes is 0.02 ~ 0.1 mol / L, and the molar concentration of the nitriles is 0.1 ~ 1 mol / L.

2. The electrocatalytic system for the coupling of nitrile and aldehyde to form secondary amine products as described in claim 1, characterized in that, The copper-based catalyst includes at least one of CuO, CuS, and copper-based catalysts doped with high-valence metals; In the copper-based catalyst doped with a high-valence metal, the high-valence metal includes any one of Fe, Co, Ni, Sn, and Ce.

3. The electrocatalytic system for the coupling of nitrile and aldehyde to form secondary amine products as described in claim 2, characterized in that, In the copper-based catalyst doped with high-valence metals, the molar percentage ratio of the high-valence metals to the divalent copper is 5%:95% ~30%:70%.

4. The electrocatalytic system for the coupling of nitrile and aldehyde to form secondary amine products as described in claim 1, characterized in that, On the copper-based catalyst coating, the loading of the copper-based catalyst is 2~20 mg / cm³. 2 .

5. The electrocatalytic system for the coupling of nitrile and aldehyde to form secondary amine products as described in claim 1, characterized in that, The aldehydes include at least one of furfural, benzaldehyde, pyridinaldehyde, butyraldehyde, and pentanal.

6. The electrocatalytic system for the coupling of nitrile and aldehyde to form secondary amine products as described in claim 1, characterized in that, The nitrile compounds include at least one of acetonitrile, propionitrile, butyronitrile, adiponitrile, and benzonitrile.

7. The electrocatalytic system for the coupling of nitrile and aldehyde to form secondary amine products as described in claim 1, characterized in that, The alkaline electrolyte uses at least one of the following alkaline solutes: K2CO3, KOH, Na2CO3, and NaOH.

8. The electrocatalytic system for the coupling of nitrile and aldehyde to form secondary amine products as described in claim 7, characterized in that, In the alkaline electrolyte, the molar concentration of the alkaline solute is 0.5 ~ 2 mol / L.

9. The application of the electrocatalytic system for the coupling of nitrile aldehydes to secondary amine products as described in any one of claims 1 to 8 in the synthesis of secondary amine products.

10. The application of the electrocatalytic system for the coupling of nitrile and aldehyde to secondary amine products as described in claim 9 in the synthesis of secondary amine products, characterized in that, The yield of secondary amine products is not less than 70%.

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