Method for reducing nitro compound through electrochemical microreactor

Abstract

The invention discloses a method for reducing nitro compounds through an electrochemical microreactor. According to the method, nitrobenzene or a derivative thereof is subjected to electrochemical catalysis in a multi-channel series electrolytic tank in a constant-current electrolysis mode to be reduced to generate aniline or a corresponding aniline derivative. According to the method disclosed by the invention, the Faraday efficiency is improved from 40% to more than 80% under the condition that the yield of the nitrobenzene is kept unchanged compared with that of the existing electrochemical reduction nitrobenzene, so that the fixed energy consumption is greatly reduced, and rapid, efficient, continuous and large-scale production of the nitrobenzene and the derivatives thereof is realized.

Description

Technical Field

[0001] The invention belongs to the field of organic chemical synthesis and relates to a method for reducing nitro compounds through an electrochemical microreactor. Background Art

[0002] Aniline, as an extremely important organic chemical raw material, is widely used in many fields such as dyes, medicines, pesticides, and rubber additives. For a long time, the reduction of nitrobenzene to prepare aniline has been the key way to obtain aniline.

[0003] Traditional aniline preparation processes mainly include iron powder reduction, alkaline sulfide reduction, and catalytic hydrogenation reduction. The high reaction temperatures, pressurization, or use of hydrogen as a reducing agent used in these traditional processes all pose significant safety risks and also pose certain environmental risks. For example, literature reports suggest that nitrobenzene reacts with iron powder in the presence of hydrochloric acid to produce aniline, which can be produced on an industrial scale. However, this process produces excessive iron sludge, which poses significant challenges to environmental pollution control and sustainable development. As research deepens, these processes have gradually been replaced by transition metal / hydrogen source systems such as Pb / H2, Ni / NaBH4, and Rh / Et3SiH (Zeynizadeh, B.; Zahmatkesh, KJ Chin. Chem. Soc. 2003, 50, 267). However, when the nitro substrate contains groups that are susceptible to transition metal addition, such as halogens or trifluoromethanesulfonic acid, the formation of group-departing byproducts is inevitable, making the reaction selectivity uncontrollable.

[0004] The electroreduction method uses nitrobenzene as the raw material and reduces nitrobenzene to aniline through an electrochemical process. Compared with traditional methods, the electroreduction method has significant advantages. The electroreduction method has mild reaction conditions, does not require high temperature and high pressure, and does not use large amounts of chemical reagents, avoiding the waste residue, wastewater and other pollutants generated by traditional methods, achieving clean production from the source and better meeting environmental protection requirements. Therefore, in-depth research and development of the process of preparing aniline by electroreduction of nitrobenzene has important practical significance and broad application prospects. However, to date, industrial electrosynthesis equipment is still mainly based on batch reactors and trough flow reactors. The non-steady-state operation of these reactors will cause significant energy loss, and mass transfer limitations will cause the reactant concentration to continue to decrease during the reaction, while product accumulation will lead to an increase in local concentration gradients, which will aggravate overpotential losses. These inherent defects make the overall energy efficiency of batch electrochemical reactors generally 40-60% lower than that of continuous systems (Org. Process Res. Dev. 2024, 28, 1474-1485). Current research trends show that the development of modular continuous hybrid systems is a more promising approach. Summary of the Invention

[0005] In order to solve the problems of traditional organic synthesis such as complicated process, high energy consumption, large pollution, inability to produce continuously and high cost, the present invention provides a method for reducing nitro compounds by using an electrochemical microreactor.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for reducing nitro compounds by an electrochemical microreactor comprises: using a multi-channel series electrolytic cell as an electrochemical reduction microreactor, and adopting a constant current electrolysis mode in the multi-channel series electrolytic cell to electrochemically catalyze the reduction of nitrobenzene or its derivatives to generate aniline or the corresponding aniline derivatives; the multi-channel series electrolytic cell comprises an electrode, a cathode chamber, an anode chamber and a cation exchange membrane, and the flow channel plate has a thickness of 0.5-2 mm; the cathode chamber and the anode chamber both contain an electrolyte solution; the cathode chamber also contains nitrobenzene or its derivatives and a cosolvent, the volume ratio of the electrolyte solution to the cosolvent is 4:1, the electrolyte solution is a 1-2 mol / L H2SO4 aqueous solution, and the cosolvent is methanol; the flow rates of the solutions in the cathode chamber and the anode chamber are independently 25-50 mL / min.

[0008] The nitrobenzene derivatives of the present invention are nitrobenzene substituted by one or more substituents, wherein the substituents are selected from C 1-5 Alkyl, halogen, -CF3, -CH=CH2, -COCH3, -NH2, -OH, etc., halogen is F, Cl, Br or I. In some embodiments, the nitrobenzene derivative is

[0009] The multi-channel series electrolytic cell of the present invention uses IrO2 / Ti as the anode electrode, CuSn7Pb 15 as cathode electrode.

[0010] The cation exchange membrane of the present invention is used to separate the cathode chamber and the anode chamber of the multi-channel series electrolytic cell. According to the knowledge of those skilled in the art, any cation exchange membrane can be selected to achieve the purpose of the present invention. Specifically, it can be Nafion TM DIN-117 membrane, Nafion TM N324 membrane, Nafion TM NC500 membrane and other perfluorosulfonic acid type proton exchange membranes.

[0011] In some embodiments, the constant current density is 25-40 mA / cm 2 , preferably 30mA / cm 2 .

[0012] In some embodiments, the flow rates of the solutions in the cathode chamber and the anode chamber are the same. Preferably, the flow rates of the solutions in the cathode chamber and the anode chamber are both 25 mL / min.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] The method of the present invention adopts a multi-channel series electrolytic cell as an electrochemical microreactor. By regulating the thickness of the flow channel plate, the type of co-solvent, the ratio of the co-solvent to the electrolyte solution, the flow rate of the solution in the cathode chamber and the anode chamber, etc., the Faradaic efficiency is increased from 40% to more than 80% while maintaining the yield of existing electrochemical reduction of nitrobenzene. The fixed energy consumption is greatly reduced, and the rapid, efficient, continuous and large-scale production of nitrobenzene and its derivatives is achieved, which is of great significance for the industrial production of aniline compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of the multi-channel series electrolytic cell of the present invention;

[0016] Figure 2 This is a physical picture of the large multi-channel series electrolytic cell of the present invention. DETAILED DESCRIPTION

[0017] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings.

[0018] Figure 1 The present invention schematically shows the system structure of the electroreduction of nitro compounds by a multi-channel series electrolytic cell. The multi-channel series electrolytic cell is made with reference to the research of Noel (J.Flow Chem.2018,8,157-165). The multi-channel series electrolytic cell mainly consists of electrodes, electrode housings, two stainless steel end plates, two polytetrafluoroethylene gaskets and a cation exchange membrane. The anode of the electrode is IrO2 / Ti and the cathode is CuSn7Pb 15 The cation exchange membrane was used to separate the two half-cell electrolytes. Two BT100-2J peristaltic pumps (Rongbai Peristaltic Pump Manufacturing Co., Ltd., Baoding, China) were used to push the anolyte solution and the cathode solution mixture into the sample cell, respectively. A constant current electrolysis model was used at room temperature.

[0019] Figure 2The structure of the large multi-channel series electrolytic cell of the present invention is an enlarged version of the multi-channel series electrolytic cell, which is composed of five flow channels with dimensions of 1 mm (thickness) × 8.5 mm (width) × 160 mm (length) running in series. Eight screws are used to compress between two stainless steel end plates (8×6M×600mm screws) to provide a large axial stress. The bolted connection ensures the filling structure and provides airtightness for the reaction part in the battery. In order to introduce the liquid into the reactor, we used a combination of a stainless steel ferrule and a feed screw (316L, 1 / 8-Φ6 flat bottom), which enables the reaction mixture to be evenly injected on the electrode.

[0020] According to the present invention, the electrochemical reactor 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. According to the cognition of those skilled in the art, any cation exchange membrane can be selected, such as a commercially available cation exchange membrane or a self-developed cation exchange membrane, 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.

[0021] The present invention uses Faradaic efficiency and yield to evaluate the degree of reaction progress. Faradaic efficiency is used to measure the degree of conformity between the electrochemical reaction actually occurring in the electrode reaction and the electrochemical reaction expected to occur in theory. A higher Faradaic efficiency means that more charge is used for the target reaction, indicating that the electrochemical system has good selectivity, high energy utilization efficiency, and few side reactions. In practical applications such as batteries, water electrolysis to produce hydrogen, and electrosynthesis, improving Faradaic efficiency can reduce energy consumption, improve product purity and production efficiency, and has important economic and environmental significance.

[0022] During the course of the present invention, the inventors found that in the cathode reaction cell, less co-solvent will cause the reactants to be unable to dissolve in the system, resulting in lower Faraday electron efficiency, lower yield and longer reaction time. An appropriate amount of methanol as a co-solvent can enhance the solubility and dispersibility of the substrate, thereby improving the Faraday efficiency of the reaction. However, excessive use of co-solvent may lead to the formation of semi-reduction products, thereby reducing the selectivity of the reaction. Therefore, the volume ratio of the co-solvent and the electrolyte aqueous solution is 1: (1 to 4), preferably, the volume ratio of the co-solvent and the electrolyte aqueous solution is 1: 4.

[0023] The reaction device used in the present invention can be homemade or purchased from Nanjing Qidaohui Microfluidics Technology Co., Ltd.

[0024] In an embodiment of the present invention, the cation exchange membrane Nafion TM DIN-117 was purchased from Suzhou Shengernuo Technology Co., Ltd.

[0025] The post-treatment and reaction yield determination methods used in the present invention include: taking a sample of the reaction solution every 10 minutes and monitoring the reaction progress by gas chromatography (GC). When the required number of electron moles has been introduced, the electrolysis reaction is stopped, the cathode reaction solution is transferred to a separatory funnel, and the reaction solution is neutralized with a 10% sodium hydroxide solution to a pH greater than 10. The resulting mixture is extracted three times with 30 mL of ethyl acetate. The reaction yield is determined by crude gas chromatography using n-dodecane as an internal standard.

[0026] The chemical raw materials used in the following examples are all commercially available or prepared according to existing technologies. Experimental methods in the following examples where specific conditions are not specified are generally performed under conventional conditions or conditions recommended by the manufacturers.

[0027] Example 1

[0028] This embodiment provides a method for preparing aniline by reducing nitrobenzene through an electrochemical microreactor, wherein the structure of the multi-channel series electrolytic cell used is as follows: Figure 1 As shown, it mainly consists of an electrode, an electrode shell, two stainless steel end plates, two polytetrafluoroethylene gaskets and a cation exchange membrane. The anode of the electrode is IrO2 / Ti and the cathode is CuSn7Pb 15 The cation exchange membrane can be used to separate the two half-cell electrolytes.

[0029] The cathode chamber consisted of nitrobenzene (5 mmol, concentration 200 mmol / L) and a mixed solution of 1 mol / L aqueous sulfuric acid / MeOH (volume ratio 4:1, 25 mL). The anode chamber contained 1 M H2SO4 (50 mL).

[0030] At room temperature, the constant current electrolysis mode was adopted with a constant current density of 30 mA / cm 2 Two BT100-2J peristaltic pumps were used to push the anolyte and cathode solution mixtures into the sample cells, respectively. The flow rates in the cathode and anode chambers were 25 mL / min. The reaction was terminated after the input of 8 F / mol of electrons. The reaction solution was post-processed and analyzed by GC, yielding a calculated 97% yield and a Faradaic efficiency of 85%.

[0031] Example 2

[0032] This example is essentially the same as Example 1, except that a constant current electrolysis mode was used, and the current density and flow channel plate thickness were varied, as shown in Table 1. The reaction was terminated after inputting 8 F / mol of electrons, and the reaction yield was calculated after post-processing. The results are shown in Table 1.

[0033] Table 1

[0034] Example Thickness of flow channel plate / mm <![CDATA[电流密度mA / cm 2 ]]> Yield (%) 2-1 3 25 78 2-2 2 25 84 2-3 1 25 91 2-4 1 30 96 2-5 0.5 35 93 2-6 0.5 40 89

[0035] Example 3

[0036] This example is essentially the same as Example 1, except that the flow rates in the cathode and anode chambers were varied, as shown in Table 2. The reaction was stopped after the corresponding electrons were input, and the reaction yield was calculated after post-processing. The results are shown in Table 2.

[0037] Table 2

[0038] Example Flow rate mL / min Yield (%) Faraday efficiency (%) 3-1 3 89 53 3-2 5 76 40 3-3 15 84 50 3-4 25 95 81 3-5 30 92 79 3-6 50 91 78

[0039] Example 4

[0040] This example is substantially the same as Example 1, except that the cathode chamber contains nitrobenzene (9.4 mmol, 1.15 g, 200 mmol / L), a mixed solution of 2M H2SO4 solution and a cosolvent (47 mL), and the anode chamber contains 1M H2SO4 (50 mL). The type of cosolvent in the cathode chamber and the ratio of the cosolvent to the H2SO4 solution are adjusted as shown in Table 3. The flow rate in the cathode and anode chambers is 25 mL / min. At room temperature, a constant current electrolysis mode is used with a current density of 30 mA / cm 2 The reaction was stopped after inputting 12F / mol of electrons, and the reaction yield was calculated after post-processing. The results are shown in Table 3.

[0041] In this embodiment, reduction by-products may be produced during the reduction of nitrobenzene. The reaction formula is as follows:

[0042]

[0043] Table 3

[0044] Serial number The ratio of cosolvent and electrolyte solution Yield (%) By-product content (%) Faraday efficiency (%) 1 <![CDATA[EtOH:H2O=1:1]]> 23 - 12 2 [CAT] t-BuOH:H20 = 1:1 4 - 2 3 <![CDATA[MeCN:H2O=1:1]]> 22 - 11 4 <![CDATA[DMF:H2O=1:1]]> 16 - 8 5 <![CDATA[EA:H2O=1:1]]> 14 - 7 6 <![CDATA[MeOH:H2O=1:1]]> 52 22 26 7 MeOH:H2O = 2:1 43 38 22 8 <![CDATA[MeOH:H2O=3:1]]> 26 48 13 9 <![CDATA[MeOH:H2O=1:2]]> 59 N 30 10 <![CDATA[MeOH:H2O=1:3]]> 72 N 36 11 <![CDATA[MeOH:H2O=1:4]]> 86 N 43

[0045] Note: “-” means the content was not detected; “N” means the content was not detected, that is, the detected content was 0.

[0046] From the sequence numbers 1 to 6 in Table 3, it can be seen that when methanol, ethanol and acetonitrile are selected as the co-solvent, the yield is good, and methanol is preferably used as the co-solvent.

[0047] As shown in Table 3, from No. 6 to No. 11, overuse of the cosolvent can result in formation of the semi-reduction product, thus reducing the selectivity of the reaction. Therefore, the volume ratio of the cosolvent to the aqueous electrolyte is preferably 1: (1-4), and more preferably 1:4.

[0048] Example 4

[0049] This example is substantially the same as Example 1, except that the cathode chamber contains a mixed solution of nitrobenzene (9.4 mmol, 1.15 g, 200 mmol / L), aqueous sulfuric acid and methanol (volume ratio 4:1, 47 mL), the anode chamber contains 1 M H2SO4(50 mL), and the concentration of the aqueous sulfuric acid in the cathode chamber is adjusted as shown in Table 4. The flow rate of the cathode chamber and the anode chamber is 25 mL / min. The reaction is stopped after 7 F of electrons are input at a constant current density of 30 mA / cm2at room temperature. The yield is calculated after post-treatment. The results are shown in Table 4. 2

[0050] Table 4

[0051] Example Sulfuric acid concentration (mol / L) Yield (%) efficiency(%) 4-1 0.5 82 70 4-2 1 88 75 4-3 2 86 74 4-4 3 83 71 4-5 4 80 69

[0052] Example 5

[0053] This example is substantially the same as Example 1. The cathode chamber contains a mixed solution of nitrobenzene derivatives (5 mmol, concentration 200 mmol / L) and 1 M aqueous sulfuric acid / MeOH (volume ratio 4:1, 25 mL) as shown in Table 5. The anode chamber contains 1 M H2SO4(50 mL). The reaction is stopped after 8 F of electrons are input at a constant current density of 30 mA / cm2at room temperature. The yield and the Faraday efficiency are calculated after post-treatment and GC detection. The results are shown in Table 5. 2

[0054] Table 5

[0055]

[0056]

[0057] As shown in Table 5, the method of the present application is applicable to reduction of various nitrobenzene derivatives, and the yield of the reduction reaction of different nitrobenzene derivatives is all above 70%, and the yield of Example 5-4 is as high as 98%. Meanwhile, the Faraday efficiency of the nitrobenzene derivatives is also high, for example, the Faraday efficiency of Examples 5-4, 5-7 and 5-12 is all above 80%.

[0058] Example 6 ​​

[0059] The present embodiment provides a method for preparing 3-aminotrifluorotoluene by reducing 3-nitrotrifluorotoluene through an electrochemical microreactor. The present embodiment adopts a large multi-channel series electrolytic cell, and the electrolytic device of the large multi-channel series electrolytic cell is as shown in Figure 2 The large multi-channel series electrolytic cell is composed of 5 channels, with the size of 1 mm (high) x 8.5 mm (wide) x 160 mm (long), and is operated in series. The electrochemical reduction process is tested by using a constant current instrument.

[0060] The cathode chamber is composed of a mixed solution of 3-nitrotrifluorotoluene (19.1 g, 0.1 mol) and 1 mol / L sulfuric acid aqueous solution / MeOH (volume ratio of 4:1, 500 mL). The anode chamber contains 1M H2SO4 (500 mL). At room temperature, a constant current electrolysis mode is adopted, and the constant current is 2.16 A (regarded as a constant current density of 30 mA / cm 2 ). The flow rate of the cathode chamber and the anode chamber is 25 mL / min. The reaction is stopped after inputting 8F / mol electrons, and the reaction solution is post-treated and detected by GC, and the yield is calculated to be 95%, and the faradic efficiency is 72%.

[0061] The above results show that the method of the present embodiment can realize the scale-up (about 20 g) reaction of nitrobenzene derivatives, and provides a reference significance for the industrial production of reducing nitrobenzene derivatives.

[0062] Comparative Example 1

[0063] The reaction device adopted in the present comparative example is a serpentine flow channel electrolytic cell. The serpentine flow channel electrolytic cell is mainly composed of an electrode, an electrode shell, two stainless steel end plates, two polytetrafluoroethylene gaskets and a cation exchange membrane. The anode in the electrode is IrO2 / Ti, and the cathode is CuSn7Pb 15 . The cation exchange membrane can be used to separate the electrolytes of the two half cells. And the serpentine flow channel in the flow cell contains a long 11x2 mm, wide 80 mm, and deep 1 mm serpentine flow channel.

[0064] The cathode chamber is composed of a mixed solution of nitrobenzene (5 mmol, with a concentration of 200 mmol / L) and 1 mol / L sulfuric acid aqueous solution / MeOH (volume ratio of 4:1, 25 mL). The anode chamber contains 1M H2SO4 (50 mL). At room temperature, a constant current electrolysis mode is adopted, and the constant current density is 30 mA / cm 2 . The flow rate of the cathode chamber and the anode chamber is 25 mL / min. The reaction is stopped after inputting 8F / mol electrons, and the reaction solution is post-treated and detected by GC, and the yield is calculated to be 88%, and the faradic efficiency is 53%.

[0065] Comparative Example 2

[0066] The reaction device used in the present comparative example is a tank type flow electrolytic cell. The structure of the tank type electrolytic cell is described in the paper published by the inventor (Chem. Eng. Sci. 310 (2025) 121473). Specifically, the tank type reactor contains two half cells, each of which contains an electrode with an active surface area of 64 square centimeters, and IrO2 / Ti is used as the anode electrode, and CuSn7Pb 15 is used as the cathode electrode. The cation exchange membrane can be used to separate the electrolytes of the two half cells, and specifically the ion exchange membrane is SIN-D117 membrane. The two sides of the ion exchange membrane are fixed by polytetrafluoroethylene washers with a thickness of 1 mm, and there are no flow channels on the washers to guide the flow of liquid. Two BT100-2J peristaltic pumps are used to push the anode electrolyte solution and the cathode solution mixture into the sample cell, respectively.

[0067] The cathode chamber is composed of a mixture of nitrobenzene (5 mmol, with a concentration of 200 mmol / L) and 1 mol / L aqueous sulfuric acid / MeOH (volume ratio of 4:1, 25 mL). The anode chamber contains 1M H2SO4 (50 mL). The constant current electrolysis model is used at room temperature. The constant current density is 30 mA / cm 2 . The flow rate of the cathode chamber and the anode chamber is 25 mL / min. The reaction is stopped after inputting 8F / mol of electrons, and the reaction solution is treated and detected by GC to calculate the yield of 80% and the Faraday efficiency of 48%.

[0068] In summary, the present application provides a method for reducing nitro compounds by an electrochemical microreactor, which realizes rapid, efficient, continuous and scaled production of nitro compounds on the basis of electrochemical continuous phase (under the condition of continuous flow phase). The method of the present application can improve the problems of pollution, low yield and high cost in the prior art, and has important significance for the industrial production of amines.

[0069] The above describes the embodiments of the present application. However, the present application is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for reducing nitro compounds by an electrochemical microreactor, characterized in that: include: A multi-channel series electrolytic cell is used as an electrochemical reduction microreactor, and a constant current electrolysis mode is adopted in the multi-channel series electrolytic cell to electrochemically catalyze the reduction of nitrobenzene or its derivatives to produce aniline or the corresponding aniline derivatives. The multi-channel series electrolytic cell includes electrodes, a cathode chamber, an anode chamber and a cation exchange membrane, and the flow channel plate has a thickness of 0.5-2 mm. The cathode chamber and the anode chamber both contain an electrolyte solution. The cathode chamber also contains nitrobenzene or its derivatives and a cosolvent, and the volume ratio of the electrolyte solution to the cosolvent is 4:

1. The electrolyte solution is a 1-2 mol / L H2SO4 aqueous solution, and the cosolvent is methanol. The flow rates of the solutions in the cathode chamber and the anode chamber are independently 25-50 mL / min.

2. The method according to claim 1, characterized in that Nitrobenzene derivatives are nitrobenzene substituted by one or more substituents selected from C 1-5 Alkyl, halogen, -CF3, -CH=CH2, -COCH3, -NH2 or -OH, halogen is F, Cl, Br or I.

3. The method according to claim 1, characterized in that Nitrobenzene derivatives are 、 、 、 、 、 、 、 、 、 、 、 、 or .

4. The method according to claim 1, wherein The multi-channel series electrolytic cell uses IrO2 / Ti as the anode electrode and CuSn7Pb 15 as cathode electrode.

5. The method according to claim 1, wherein Cation exchange membrane is Nafion TM DIN-117 membrane, Nafion TM N324 membrane or Nafion TM NC500 membrane.

6. The method according to claim 1, wherein Constant current density is 25~40 mA / cm 2 .

7. The method according to claim 1, wherein The constant current density is 30 mA / cm 2 .

8. The method according to claim 1, characterized in that The flow rates of the solutions in the cathode and anode chambers are the same.

9. The method according to claim 1, characterized in that The flow rate of the solutions in the cathode and anode chambers was 25 mL / min.

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