Process for the synthesis of amines by reduction of nitro compounds in a flow membrane electrode electrolysis cell

Abstract

This invention discloses a method for synthesizing amino compounds from nitro compounds using a flow-through membrane electrode electrolysis cell. The method involves electrochemically catalyzing the reduction of nitro compounds to amino compounds in a constant-current electrolysis mode within the flow-through membrane electrode electrolysis cell. This invention increases the Faraday efficiency from 20% to over 70% while maintaining the same yield as existing batch membrane electrode reactors for reducing nitrobenzene, significantly reducing stationary energy consumption and enabling rapid, efficient, continuous, and large-scale production of nitrobenzene and its derivatives.

Description

Technical Field

[0001] This invention belongs to the field of organic chemical synthesis and relates to a method for synthesizing amino compounds by reducing nitro compounds using a flow membrane electrode electrolysis cell. Background Technology

[0002] The selective reduction of nitro compounds to amines is a key step in the preparation of pharmaceutical intermediates, dyes, agrochemicals, and polymers. Traditionally, the reduction of nitroaromatics mainly relies on the reduction of metals such as iron powder under acidic conditions. However, this method has poor atom economy, generates large amounts of sludge containing metal salts, has complex post-treatment processes, and is environmentally unfriendly, which seriously deviates from the requirements of current green chemistry and sustainable development.

[0003] Electrochemical synthesis, with its advantages of being clean, sustainable, and precisely controllable, offers a new strategy for nitro reduction. The applicant's earlier Chinese patent application, CN120776324A, discloses an electrochemical microreactor employing a multi-channel series electrolytic cell. This technology optimizes the flow channel thickness, uses a methanol / sulfuric acid aqueous solution as the electrolyte, and utilizes CuSn7Pb. 15 A cathode combined with an IrO2 / Ti anode successfully reduced nitrobenzene to aniline under constant current conditions, achieving a yield as high as 97% and a Faradaic efficiency of 85%. During the reaction, despite good electrochemical performance, excessively high substrate concentrations caused excessive membrane swelling, leading to solution leakage. Therefore, this system can only operate normally at low concentrations, posing a challenge for future industrial development.

[0004] Therefore, there is an urgent need in this field to develop a novel electrochemical reduction system and method for nitro compounds that can combine high Faradaic efficiency, high substrate concentration applicability, high selectivity, low catalyst cost, and good system durability, so as to achieve green, economical, and safe synthesis of amine compounds. Summary of the Invention

[0005] To address the problems of cumbersome processes, high energy consumption, significant pollution, inability to achieve continuous production, and high costs in traditional organic synthesis, this invention provides a method for synthesizing amino compounds by reducing nitro compounds using a flow-through membrane electrode electrolysis cell.

[0006] The technical solution of the present invention is as follows:

[0007] The method for synthesizing amino compounds from nitro compounds by reducing nitro compounds using a flow-through membrane electrode electrolysis cell specifically involves: in a flow-through membrane electrode electrolysis cell, electrochemically catalyzing the reduction of nitro compounds to amino compounds using a constant current electrolysis mode; the flow-through membrane electrode electrolysis cell is structurally composed of an anode, an anode chamber, an ion exchange membrane, a cathode chamber, a membrane electrode, and a hydrogenation reaction chamber, wherein the membrane electrode is a palladium foil membrane electrode or a hydrophilic membrane supported electrode, and the hydrophilic membrane supported electrode is composed of a supported palladium catalyst layer, a palladium black layer, and a hydrophilic membrane layer; the hydrogenation reaction chamber contains a nitro compound solution.

[0008] Furthermore, both the cathode and anode chambers of the flow-through membrane electrode electrolyzer contain an electrolyte solution, which is a conventional electrolyte solution used in flow-through membrane electrode electrolyzers, such as a 1-2 mol / L H2SO4 aqueous solution.

[0009] Furthermore, the flow rate of the electrolyte solution or the nitro compound solution is the same, which is 2.5~15 mL / min, preferably 5 mL / min.

[0010] Furthermore, the nitro compound solution is composed of nitro reactants and a proton solvent, wherein the proton solvent is preferably an alcohol solvent, such as methanol, ethanol, propanol, isopropanol, butanol, tert-butanol, etc., and more preferably methanol, ethanol or isopropanol.

[0011] In this invention, the nitro compound is an unsubstituted nitroaromatic hydrocarbon or a nitroaromatic hydrocarbon with one or more substituents R1. The aromatic hydrocarbon can be selected from benzene, naphthalene, quinoline, isoquinoline, indole, and benzimidazole. The substituent R1 is selected from C... 1-5 Alkyl, halogen, -CF3, -OC 1-5 Alkyl groups, etc. C 1-5 Alkyl, -OC 1-5 The alkyl group is either unsubstituted or has one or more substituents R2-substituted, where R2 can be selected from amino, carboxyl, etc. The halogen is F, Cl, Br, or I.

[0012] In some specific embodiments of the present invention, the nitro compound is... , , , , , , , , , , or .

[0013] In this invention, the anode of the flow membrane electrode electrolyzer is a conventionally used anode in the art, such as IrO2 / Ti.

[0014] In this invention, the palladium foil membrane electrode is a commonly used palladium foil membrane electrode in flow-through membrane electrode electrolysis cells. It consists of a palladium catalyst layer, a palladium black layer, and a palladium foil layer. It is prepared by first electrodepositing a palladium black precipitate layer on the surface of the palladium foil, and then ultrasonically spraying the palladium catalyst layer onto the surface of the palladium black layer.

[0015] In this invention, the hydrophilic membrane support electrode is prepared by first preparing a hydrophilic membrane scaffold, then depositing a palladium layer on the surface by magnetron sputtering, and finally ultrasonically spraying a palladium catalyst layer onto the surface of the palladium layer.

[0016] In this invention, the palladium foil layer of the palladium foil electrode or the hydrophilic membrane layer of the hydrophilic membrane support electrode is connected to the cathode chamber, and the supported palladium catalyst layer of the palladium foil electrode or the hydrophilic membrane support electrode is connected to the hydrogenation reaction chamber.

[0017] In this invention, the hydrophilic membrane is a common hydrophilic polymer membrane, selected from PVDF, PTFE or cellulose membrane, preferably a PVDF membrane, and more preferably a PVDF membrane with a pore size of 1μm.

[0018] In this invention, the palladium catalyst is a common palladium catalyst, selected from Pd / C, Pd / PDVB, and Pd 0.2 / CN、Pd 1.0 / CN、Pd 2.0 One or more of / CN and Pd / C3N4, preferably Pd / C.

[0019] Furthermore, the palladium catalyst has a surface loading of 0.03–0.3 mg / cm². 3 Preferably 0.05 mg / cm 3 .

[0020] Furthermore, the constant current density is 30~100 mA / cm². 2 Preferably 30 mA / cm 2 .

[0021] In this invention, the ion exchange membrane is a cation exchange membrane. Any cation exchange membrane can be selected based on the knowledge of those skilled in the art to achieve the purpose of this invention. Specifically, it can be a Nafion membrane. TM DIN-117 membrane, Nafion TM N324 membrane, Nafion TM NC500 membrane and other perfluorosulfonic acid type proton exchange membranes.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] This invention employs a flow-through membrane electrode electrolysis cell to reduce nitro aromatic compounds. By controlling the type of palladium catalyst in the palladium membrane electrode, the amount of palladium catalyst loaded, and the flow rates of the solutions in the cathode and anode chambers, the method achieves significant improvements. Compared to existing systems that directly reduce nitro compounds on the electrode surface, membrane electrode reduction is adaptable to high-concentration substrate environments (>500 mM). While maintaining the same yield, the Faraday efficiency is increased to 73%, significantly reducing stationary energy consumption. This enables rapid, efficient, continuous, and large-scale production of nitrobenzene and its derivatives, which is of great significance for the industrial production of amino aromatic compounds. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the flow membrane electrode electrolyzer of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will now be clearly and completely described in conjunction with the embodiments and accompanying drawings.

[0026] Figure 1 This is a schematic diagram of the system structure for synthesizing amino compounds from nitro compounds via electroreduction using a flow-through membrane electrode electrolysis cell according to the present invention. The flow-through membrane electrode electrolysis cell, from left to right, consists of an anode, an anode chamber, an ion exchange membrane, a cathode chamber, a membrane electrode, and a hydrogenation reaction chamber. It mainly comprises an anode, a membrane electrode, an electrode shell, two stainless steel end plates, two polytetrafluoroethylene gaskets, and a cation exchange membrane. The anode is IrO2 / Ti, and the membrane electrode is a palladium foil membrane electrode or a hydrophilic membrane-supported electrode. The cation exchange membrane is used to separate the electrolytes in the cathode and anode chambers. Three BT100-2J peristaltic pumps (China Baoding Rongbai Peristaltic Pump Manufacturing Co., Ltd.) are used to advance the anode electrolyte solution, cathode electrolyte solution, and reaction cell mixture into the corresponding sample cells.

[0027] The palladium foil electrode of this invention is prepared using existing conventional methods, specifically the following preparation methods:

[0028] (1) Preparation of the palladium black layer of the palladium foil electrode by electrodeposition: First, the commercially available palladium foil was cleaned with a mixed solvent (nitric acid: hydrogen peroxide: water = 1:2:2), and then dried. The dried palladium foil was fixed as the working electrode, and Ir / TiO2 was used as the other electrode of the electrolytic cell. A 1M HCl solution containing 15.9 mM PdCl2 was injected into the electrolytic cell. The electrodeposition process adopted a constant current mode (3.75 mA / cm). 2 The process is carried out when the total charge reaches 9.0 C (4.5 C / cm). 2 Stop when [the concentration reaches 0.05 mg / cm³]. At this point, a uniform dark black palladium black precipitate layer (3.0 ± 0.5 mg / cm³) will form. -2This yields a palladium foil electrode loaded with palladium black (Pd|Pd-black).

[0029] (2) Preparation of palladium foil electrode supported on palladium catalyst by ultrasonic spraying: Catalyst layers of different noble metal nanoparticles (Pd / PDVB, Pd / CN, Pd / C3N4 and Pd / C) were deposited on Pd|Pd-black film by ultrasonic spraying. For each powder, the prepared catalyst ink had a similar ionomer to carbon (I / C) weight ratio of ~0.6. Each catalyst powder was modulated with a polymer-carbon mass ratio of approximately 0.6 and a 5 wt% Nafion dispersion was used as a hydrophobic binder. The solvent used was a mixture of isopropanol and water with a volume ratio of 3:1, which yielded the best ink quality and uniform catalyst layer. After ultrasonicating the ink in an ultrasonic bath for at least 30 minutes, it was sprayed onto Pd|Pd-black film on a hot plate at 90°C using an air brush to finally obtain the palladium foil electrode.

[0030] The hydrophilic membrane-supported electrode of the present invention is prepared by the following steps:

[0031] (1) Fabrication of the hydrophilic membrane support: Two square masks (4 cm × 4 cm) were fabricated from a Capton substrate using a scalpel. A 2 cm × 2 cm square window was then cut in the middle of each mask. EpoxySet resin and hardener were thoroughly mixed at a 1:1 weight ratio to prepare an epoxy adhesive. This mixture was applied to one of the Capton masks, on which a hydrophilic polymer film (e.g., polytetrafluoroethylene, PVDF, or cellulose) was carefully laid. The second mask was then aligned and bonded on top using the same epoxy resin to form a sandwich structure. Finally, the entire assembly was cured in an oven at 60 °C for 12 hours to ensure complete curing of the epoxy resin.

[0032] (2) Preparation of palladium layer by magnetron sputtering: The palladium layer was deposited on the prepared hydrophilic film scaffold by DC magnetron sputtering. The deposition was carried out under vacuum to a base pressure of 3 × 10⁻⁶. -3 Deposition takes place in Torr's process chamber, with the argon working pressure maintained at 2 × 10⁻⁶. -3 Torr. Prior to deposition, the target was pre-sputtered for 20 minutes to remove surface contaminants. Palladium was then deposited at 100 W with a target-to-substrate distance of 10 cm. The deposition rate was 0.45 A / s, and the film thickness was approximately 1 μm. The mass of the deposited Pd was determined using an analytical balance by measuring the mass difference before and after deposition.

[0033] (3) The palladium catalyst was supported by ultrasonic spraying. The spraying process was similar to the process of preparing the palladium foil electrode, except that the palladium film was replaced by a hydrophilic membrane carrier.

[0034] In the course of this invention, the inventors first screened the types of catalysts in the palladium foil electrode using a batch electrolytic cell. The experiment involved either no catalyst or different palladium catalysts, and the reaction process was monitored. Experimental results showed that Pd / C, Pd / PDVB, and Pd... 0.2 / CN、Pd 1.0 / CN、Pd 2.0 Both Pd / C and Pd / C3N4 palladium catalysts can promote the reaction, and the catalysts are Pd / C and Pd... 1.0 / CN or Pd 2.0 The reaction is better with / CN. Preferably, the reaction is most effective when using Pd / C as a catalyst. To achieve the objectives of this invention, the inventors subsequently conducted electrochemical experiments using a flow electrolyzer, and based on the screening results of the batch electrolyzer, selected Pd / C as the palladium catalyst supported on the palladium film electrode.

[0035] According to the present invention, a flow-through membrane electrode electrolysis cell contains an ion exchange membrane for separating the cathode chamber and the anode chamber. Specifically, according to the reaction involved in the present invention, the ion exchange membrane of the electrochemical reactor is a cation exchange membrane. Any cation exchange membrane can be selected according to the knowledge of those skilled in the art, such as commercially available cation exchange membranes or domestically developed cation exchange membranes, all of which can achieve the purpose of the present invention. According to a specific embodiment of the present invention, the cation exchange membrane used in the present invention can be: Nafion TM DIN-117 membrane, Nafion TM N324 membrane, Nafion TM NC500 membrane and other perfluorosulfonic acid type proton exchange membranes.

[0036] This invention uses Faraday efficiency and yield to evaluate the extent of reaction progress. Faraday efficiency measures the degree of agreement between the actual electrochemical reaction occurring in the electrode reaction and the theoretically expected electrochemical reaction. A higher Faraday efficiency means that more charge is used for the target reaction, indicating good selectivity, high energy efficiency, and fewer side reactions in the electrochemical system. In practical applications such as batteries, water electrolysis for hydrogen production, and electrosynthesis, improving Faraday efficiency can reduce energy consumption, increase product purity, and improve production efficiency, which has significant economic and environmental implications.

[0037] The palladium catalyst of this invention is Pd / C, Pd / PDVB, or Pd 0.2 / CN、Pd 1.0 / CN、Pd 2.0 / CN or Pd / C3N4.

[0038] The Pd / PDVB catalyst used in this invention was prepared according to the literature (J. Am. Chem. Soc. 146(38) (2024)26379-26386.). Specifically: First, 9 g of divinylbenzene (DVB) and 1 g of polyvinylpyrrolidone (PVP) were dissolved in a mixed solution of 90 mL of ethyl acetate and 10 mL of ethanol, followed by the addition of 0.25 g of azobisisobutyronitrile (AIBN). After stirring at room temperature for 12 h, the mixture was transferred to a high-pressure reactor and hydrothermally reacted at 100 °C for 12 h. The resulting product was washed with ethanol and dried at 100 °C for 12 h to obtain the PDVB support. Subsequently, 1 g of PDVB was dispersed in 50 mL of 75% (v / v) aqueous ethanol solution and stirred at room temperature for 30 min to form a uniform suspension. 1.55 mL of Na2PdCl4 solution (Pd concentration of 0.188 mol·L⁻¹) was added to the suspension. -1 The reaction was continued at room temperature for 12 h, then stirred at 80 °C for 4 h to ensure complete reaction, yielding a solid intermediate. This solid was dried at 60 °C for 12 h, then reduced at 300 °C for 2 h in a 10% H₂ / Ar atmosphere, followed by purging at room temperature in a N₂ atmosphere for 1 h. To eliminate residual Na in the catalyst... + With Cl - To investigate the potential impact on catalytic performance, the sample was further washed with an aqueous ethanol solution (75% ethanol by volume) and then freeze-dried under vacuum to finally obtain the target catalyst, denoted as Pd / PDVB.

[0039] The Pd used in this invention x The / CN catalyst was prepared according to the literature (Catal. Lett. 153(8) (2023) 2398-2405.). Specifically, 0.5 g of urea and 3.0 g of glucose were first dissolved in 120 mL of deionized water and stirred at room temperature for 4 h. Then, the mixture was transferred to a 150 mL high-pressure reactor lined with polytetrafluoroethylene and hydrothermally reacted at 180 °C for 12 h. After the reaction, the mixture was naturally cooled to room temperature, and the nitrogen-doped carbon (CN) material was collected by centrifugation, washed repeatedly with deionized water, and dried overnight at 60 °C. Subsequently, 200 mg of the CN material prepared above was dispersed in a 1:1 mixture of ethanol and deionized water in 20 mL and stirred continuously for 12 h to form a uniform suspension. 1.89 μmol / mL of the solution was then added to the suspension. -1 The PdCl2 aqueous solution was stirred for 6 h, and then heated to 80 °C to allow the solvent to evaporate completely. The resulting solid precursor was thoroughly ground in an agate mortar to obtain a black powder. The powder was then subjected to programmed pyrolysis treatment in H2 at 5 °C·min. -1The temperature was increased to the set temperature (250-350 ℃) at a rising rate and held for 2 hours, then allowed to cool naturally to room temperature before grinding. The resulting product was denoted as Pd. x / CN, where x represents the mass fraction of Pd. Pd was prepared according to the above method. 0.2 / CN、Pd 1.0 / CN and Pd 2.0 Three different catalysts with varying loadings: / CN.

[0040] The Pd / C3N4 used in this invention was prepared according to the literature (RSC Advances 3(27) (2013) 10973-10982.). Specifically, 3 g of cyanamide and 7.5 g of Ludox-HS 40 silica sol were first mixed in an aqueous solution and stirred continuously in an oil bath at 80 °C while evaporating water overnight to obtain a white composite matrix. The matrix was calcined at 550 °C for 4 h and kept at a constant temperature for another 4 h to ensure that the matrix fully condensed to form polymeric C3N4. Subsequently, the matrix was treated with 4 M NH4HF2 solution for 2 days to remove silica. The reaction solution was separated by filtration, and the solid product was washed with water and ethanol in sequence to obtain a yellow solid, which was then dried in a vacuum oven at 80 °C overnight. 0.1 g of C3N4 support was dispersed in 10 mL of water and sonicated for 15 min to ensure full dispersion. 2 mL of PdCl2 aqueous solution was added for impregnation, and sonication was continued for another 15 min. Subsequently, 5 mL of 0.1% NaBH4 solution was added to the suspension to reduce PdCl2 in situ to Pd nanoparticles, which were then immediately deposited on the C3N4 surface. Finally, the Pd / C3N4 catalyst was obtained by vacuum filtration, washed with water multiple times, and dried at 70 °C.

[0041] In this invention, those skilled in the art can also prepare the aforementioned disclosed palladium catalyst by referring to preparation methods in other literature or publicly available information through publicly known means.

[0042] The reaction apparatus used in this invention can be self-made or purchased from Nanjing Qidaohui Microfluidic Technology Co., Ltd. The H-type electrolytic cell used in the batch electrolysis reaction was purchased from Shanghai Leton Industrial Co., Ltd.

[0043] In this invention, all reagents were of analytical grade. Nitrobenzene and its derivatives (99%) were purchased from Shanghai Titan Technology Co., Ltd. Various palladium salts and catalyst supports were purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd. PTFE and PVDF hydrophilic membranes of different pore sizes were purchased from Changzhou Jinchun Environmental Protection Co., Ltd. and JFE Engineering Co., Ltd., Tokyo, Japan, respectively. Cellulose membranes were purchased from Guangdong Xiansheng New Materials Co., Ltd.

[0044] The metal anode IrO2 / Ti (pure titanium TA1 substrate, IrO2 and Ta2O5 coating thicknesses of 15 μm and 25 μm respectively) was processed and customized by Suzhou Shushuertai Technology Co., Ltd. The palladium foil (99.9%, 25 μm thickness) was purchased from Xingtai Huiji Metal Materials Co., Ltd.

[0045] The post-processing and reaction yield determination methods used in this invention are as follows: A sample of the reaction solution is taken every 10 minutes, and the reaction progress is monitored by gas chromatography (GC). Once the required number of moles of electrons are introduced, the electrolysis reaction is stopped, and the solution in the hydrogenation reaction chamber is desolvated by vacuum distillation. The reaction yield is determined by gas chromatography using n-dodecane as an internal standard.

[0046] Unless otherwise specified, the experimental methods described in the following examples are generally performed under standard conditions or as recommended by the manufacturer.

[0047] Example 1

[0048] This embodiment provides a method for preparing corresponding amino compounds by reducing nitrobenzene in an intermittent electrolytic cell.

[0049] Experimental setup: The intermittent electrolysis experiment was conducted in a commercially available H-type electrolytic cell.

[0050] Experimental method: The H-type electrolytic cell device was used with a 1 cm⁻¹... 2 A platinum sheet is placed in the anode chamber as the anode, supporting the catalyst, and the catalyst layer area is 1 cm². 2 Palladium foil was used as the palladium foil membrane electrode. A stir bar was placed in the anode chamber, and 10 mL of 1 M H₂SO₄ aqueous solution was injected as the electrolyte. 1 mmol of nitrobenzene and 10 mL of ethanol (reactant concentration 100 mM) were added to the hydrogenation reaction chamber. The reaction solutions in both the anode and hydrogenation reaction chambers were stirred at room temperature. The experiment used 50 mA / cm². 2 Electrolysis was performed at a constant current density until a cumulative total of 24 F / mol of electrons was provided, at which point the reaction ended. After the reaction, n-dodecane was used as an internal standard, and the reaction progress was determined by gas chromatography.

[0051] The palladium catalysts investigated were: Pd / C, Pd / PDVB, and Pd. 0.2 / CN、Pd 1.0 / CN、Pd 2.0 / CN、Pd / C3N4.

[0052] The results are shown in Table 1.

[0053] Table 1

[0054] reactants Palladium catalyst Yield Nitrobenzene / 75% Nitrobenzene Pd / C 90% p-Nitroanisole / 12% p-Nitroanisole Pd / C 86% p-Nitroanisole Pd / PDVB 11% p-Nitroanisole <![CDATA[Pd 0.2 / CN]]> 25% p-Nitroanisole <![CDATA[Pd 1.0 / CN]]> 48% p-Nitroanisole <![CDATA[Pd 2.0 / CN]]> 40% p-Nitroanisole <![CDATA[Pd / C3N4]]> 22%

[0055] Note: " / " indicates that no palladium catalyst is added.

[0056] Table 1 shows that all the above-mentioned palladium catalysts can promote the reaction, and the catalysts are Pd / C and Pd. 1.0 / CN or Pd 2.0 The reaction is better with / CN, and the reaction is most effective when Pd / C is used as a catalyst.

[0057] To achieve the objectives of this invention, the inventors screened Pd / C as a catalyst for palladium foil electrodes using an intermittent electrolytic cell. Accordingly, in subsequent embodiments, Pd / C was used as the catalyst, and a flow electrolytic cell was employed for subsequent experiments.

[0058] Example 2

[0059] In this embodiment, a flow membrane electrode electrolysis cell was used to conduct the electrochemical reaction and to investigate the catalyst loading.

[0060] Experimental setup: The structure of the flow-through membrane electrode electrolyzer used is as follows: Figure 1 As shown, the electrolytic cell module is fabricated from a single piece of polytetrafluoroethylene (PTFE). The device contains three independent electrochemical chambers, which respectively house the IrO2 / Ti anode, the ion exchange membrane, and the palladium foil electrode. The anode chamber and the cathode chamber are separated by a Nafion-N117 membrane, effectively isolating the oxidative electrochemical process at the anode from the proton reduction reaction at the palladium cathode. The palladium foil electrode is sandwiched between the hydrogenation reaction chamber, which has a serpentine flow path, and the cathode chamber.

[0061] Experimental Method: p-Nitroanisole was dissolved in ethanol to prepare the hydrogenation reaction chamber solution. The solutions for the anode and cathode electrolytic cells were 1M sulfuric acid aqueous solutions. During the experiment, three peristaltic pumps were used to deliver the anode and cathode electrolytes to the electrolytic cells, with a flow rate of 5 mL / min in the cathode, anode, and hydrogenation reaction chambers. All three liquids returned to the collection bottle after passing through the electrode plates, forming an electrolyte circulation system. The reaction progress was monitored by thin-layer chromatography. After electrolysis, post-processing was performed, and the reaction yield was calculated.

[0062] In this embodiment, 1 mmol of nitrobenzyl ether was added to the hydrogenation reaction chamber solution, with a concentration of 100 mM. Electrolysis was performed at room temperature using a constant current electrolysis mode with a current density of 50 mA / cm². 2 The reaction was stopped after 12 F / mol of electrons were introduced. After post-processing, the yield of the reaction was calculated. The results are shown in Table 2.

[0063] Table 2

[0064] <![CDATA[Catalyst loading amount (mg / cm 2 ).]]> Yield (%) 0.03 86 0.05 93 0.10 93 0.15 92 0.20 82 0.30 80

[0065] The results showed that as the catalyst loading increased from 0.03 mg / cm³, the efficiency of the catalyst increased.2 Gradually increase to 0.3 mg / cm 2 The yield of the product showed a trend of first increasing and then decreasing. At a loading of 0.05 mg / cm³, the yield was... 2 The reaction reached its optimal point with a yield of 93%. Further increases in loading resulted in a corresponding increase in the content of the loaded material and binder on the membrane, leading to a decrease in yield.

[0066] Example 3

[0067] This embodiment is basically the same as Example 2, except that the substrate concentration was changed, as shown in Table 3. The catalyst loading used in this embodiment is 0.05 mg / cm³. 2 The reaction was stopped after the corresponding electrons were input, and the yield was calculated after post-processing. The results are shown in Table 3.

[0068] Table 3

[0069] Substrate concentration (mM) Yield (%) Faraday efficiency (%) 100 93 65 200 95 68 300 96 73 400 92 72 500 95 73

[0070] Experimental results showed that at low substrate concentrations, the yield was high but the Faraday efficiency was low. When the substrate concentration reached 300 mM, the yield of the target product reached 96%, and the Faraday efficiency was 73%. Further increasing the substrate concentration did not significantly change the yield or Faraday efficiency.

[0071] Example 4

[0072] This embodiment is largely the same as Example 2, except that the solvent of the substrate is changed, as shown in Table 4. The catalyst loading used in this embodiment is 0.05 mg / cm³. 2 The substrate concentration was 300 mM. The reaction was stopped after the corresponding electrons were introduced, and the yield was calculated after post-processing. The results are shown in Table 4.

[0073] Table 4

[0074] solvent Yield (%) Faraday efficiency (%) ethanol 96 73 methanol 95 70 tert-Butanol 80 62 Ethyl acetate 62 23 dichloromethane 71 52 Acetonitrile 79 44 n-Hexane 88 32

[0075] The results showed that when using proton solvents, the system maintained good proton transport capability while also exhibiting excellent substrate solubility; when ethanol was used as the solvent, the yield of the target product reached 96%, and the Faraday efficiency was 73%. In contrast, although aproton organic solvents could improve substrate solubility, they significantly reduced proton transport capability and increased side reactions, leading to a decrease in the overall reaction yield.

[0076] Example 5

[0077] This embodiment is largely the same as Embodiment 2, except that the current density is changed, as shown in Table 5. The catalyst loading used in this embodiment is 0.05 mg / cm³. 2The substrate concentration was 300 mM, and the solvent was ethanol. The reaction was stopped after the corresponding electrons were introduced. After post-processing, the reaction yield was calculated. The results are shown in Table 5.

[0078] Table 5

[0079] <![CDATA[Current density (mA / cm 2 )]]> Yield (%) efficiency(%) 30 96 76 50 96 73 70 92 60 100 81 42

[0080] Example 6

[0081] This embodiment is largely the same as Example 2, except that the substrate structure is changed, as shown in Table 6. The catalyst loading used in this embodiment is 0.05 mg / cm³. 2 The substrate concentration was 300 mM, and the solvent was ethanol. The reaction was stopped after the corresponding electrons were introduced. After post-processing, the reaction yield was calculated. The results are shown in Table 6.

[0082] Table 6

[0083] Nitrobenzene derivative structure Faraday efficiency (%) Yield (%) 73 97 61 96 71 95 82 86 70 95 76 93 61 91 61 95 66 93 60 85 68 82 65 66

[0084] As shown in Table 6, the method of the present invention is applicable to the reduction of various nitrobenzene derivatives. The yields of the reduction reactions of different nitrobenzene derivatives are all above 70%, with the highest reaching 97%. At the same time, the Faradaic efficiency of nitrobenzene derivatives is also high, with all Faradaic efficiencies above 70%.

[0085] Example 7

[0086] This embodiment is largely the same as Embodiment 2, except that the palladium foil electrode is replaced with a hydrophilic membrane-supported electrode, as shown in Table 7. The catalyst loading used in this embodiment is 0.05 mg / cm³. 2 The substrate concentration was 300 mM, and the solvent was ethanol. The reaction was stopped after the corresponding electrons were introduced. After post-processing, the reaction yield was calculated. The results are shown in Table 7.

[0087] Table 7

[0088] hydrophilic membrane Aperture (μm) Faraday efficiency (%) Yield (%) PVDF 0.45 53 71 PVDF 1 70 95 PVDF 3 / / PTFE 0.1 36 48 PTFE 0.5 50 66 PTFE 1 / / PTFE 2 / / cellulose membrane 0.1 / /

[0089] Note: " / " indicates that no target product was generated.

[0090] Experimental results show that PVDF has a better reaction when used as a hydrophilic membrane, with PVDF membranes with a pore size of 1 μm showing the best reaction effect.

[0091] Comparative Example 1

[0092] The reaction apparatus used in this comparative example is an intermittent membrane electrode reactor. The intermittent membrane electrode reactor mainly consists of an anode, a membrane electrode, and an H-type electrolytic cell.

[0093] The device is 1 cm2 A platinum sheet is placed as the anode in the anode chamber, and the catalyst layer area is 1 cm². 2 A palladium film was used as the cathode. A stir bar was placed in the anode chamber, and 10 mL of 1 M H₂SO₄ aqueous solution was injected as the electrolyte. 3 mmol of nitrobenzene and 10 mL of ethanol were added to the hydrogenation reaction chamber. The reaction solutions in both the anode and cathode chambers were stirred at room temperature. The experiment used 25 mA / cm². 2 Electrolysis was performed at a constant current density until a cumulative total of 24 F / mol of electrons was provided. After post-treatment of the reaction solution, n-tetradecane was added as an internal standard, and GC analysis yielded a yield of 95% and a Faraday efficiency of 20%.

[0094] In summary, this invention provides a method for reducing nitro compounds using an electrochemical microreactor. This method, based on an electrochemical continuous phase (under continuous mobile phase conditions), achieves rapid, efficient, continuous, and large-scale production of nitro compounds. This method can improve upon the industrialization problems of high pollution, low yield, and high cost in existing technologies, and is of great significance for the industrial production of amino compounds.

[0095] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing amino compounds by reducing nitro compounds using a flow-through membrane electrode electrolysis cell, characterized in that, Specifically, in a flow-through membrane electrode electrolyzer, a constant current electrolysis mode is used to electrochemically catalyze the reduction of nitro compounds to amino compounds. The flow-through membrane electrode electrolyzer consists of an anode, an anode chamber, an ion exchange membrane, a cathode chamber, a membrane electrode, and a hydrogenation reaction chamber. The membrane electrode is a palladium foil membrane electrode or a hydrophilic membrane supported electrode. The hydrophilic membrane supported electrode is composed of a supported palladium catalyst layer, a palladium black layer, and a hydrophilic membrane layer. The hydrogenation reaction chamber contains a nitro compound solution.

2. The method according to claim 1, characterized in that, The cathode and anode chambers of the flow-through membrane electrode electrolyzer both contain electrolyte solutions; the palladium foil membrane electrode consists of a supported palladium catalyst layer, a palladium black layer, and a palladium foil layer; the palladium foil layer of the palladium foil membrane electrode or the hydrophilic membrane layer of the hydrophilic membrane support electrode is connected to the cathode chamber, and the supported palladium catalyst layer of the palladium foil membrane electrode or the hydrophilic membrane support electrode is connected to the hydrogenation reaction chamber; the nitro compound solution consists of nitro reactants and a proton solvent, the proton solvent being an alcohol solvent; the flow rates of the electrolyte solution and the nitro compound solution are the same; the nitro compound is an unsubstituted or nitro aromatic hydrocarbon with one or more substituents R1.

3. The method according to claim 2, characterized in that, The palladium foil electrode was prepared by first electrodepositing a palladium black precipitate layer on the surface of a palladium foil, and then ultrasonically spraying a palladium catalyst layer onto the surface of the palladium black layer. The hydrophilic membrane support electrode was prepared by first fabricating a hydrophilic membrane scaffold, then depositing a palladium layer on its surface by magnetron sputtering, and finally ultrasonically spraying a palladium catalyst layer onto the surface of the palladium layer. The electrolyte solution was a 1-2 mol / L H2SO4 aqueous solution, the flow rate of the electrolyte solution or nitro compound solution was 2.5-15 mL / min, and the palladium catalyst loading per unit area was 0.03-0.3 mg / cm². 3 The constant current density is 30~100 mA / cm² 2 .

4. The method according to claim 1, characterized in that, The flow rate of the electrolyte solution or nitro compound solution was 5 mL / min, and the palladium catalyst surface loading was 0.05 mg / cm². 3 The constant current density is 30 mA / cm². 2 .

5. The method according to claim 2, characterized in that, The alcohol solvents are methanol, ethanol, propanol, isopropanol, butanol, or tert-butanol.

6. The method according to claim 2, characterized in that, The aromatic hydrocarbon is selected from benzene, naphthalene, quinoline, isoquinoline, indole, or benzimidazole, and the substituent R1 is selected from C. 1-5 Alkyl, halogen, -CF3 or -OC 1-5 alkyl.

7. The method according to claim 6, characterized in that, C 1-5 Alkyl, -OC 1-5 The alkyl group is either unsubstituted or substituted with one or more substituents R2, where R2 is selected from amino or carboxyl groups; the halogen is F, Cl, Br or I.

8. The method according to claim 1, characterized in that, Nitro compounds are , , , , , , , , , , or .

9. The method according to claim 1, characterized in that, The anode of the flow-through membrane electrode electrolyzer is IrO2 / Ti; the hydrophilic membrane is selected from PVDF, PTFE or cellulose membrane; and the palladium catalyst is selected from Pd / C, Pd / PDVB, Pd 0.2 / CN、Pd 1.0 / CN、Pd 2.0 One or more of / CN and Pd / C3N4; the ion exchange membrane is a cation exchange membrane.

10. The method according to claim 1, characterized in that, The hydrophilic membrane is a PVDF membrane with a pore size of 1 μm, and the cation exchange membrane is selected from Nafion. TM DIN-117 membrane, Nafion TM N324 membrane or Nafion TM NC500 membrane.

Images