A method for preparing FCAA by electrochemical oxidation of FCA by anode and cathode

Abstract

The present invention provides a method for preparing 2-methyl-4-acetoxy-2-butenoic acid (FCAA) by electrochemical oxidation of 2-methyl-4-acetoxy-2-butenal (FCA) by coordinated cathode and anode, wherein an electrode supporting oxygen reduction reaction is used as cathode, a metal catalytic electrode is used as anode, and an ionic liquid is used as an electrolyte solvent. The raw material FCA is pre-oxidized to FCA at the anode. . Intermediate, oxygen undergoes only one electron oxygen reduction reaction at the cathode, generating reactive oxygen species ROS in situ to achieve FCA . The intermediate is oxidized to produce FCAA. The method of the present invention does not require an ion exchange membrane, has a wide electrochemical window, eliminates the problem of oxygen evolution at the anode, and does not require the addition of a supporting electrolyte in the system. Furthermore, the ionic liquid has high stability and low volatility, resulting in almost no loss, making it environmentally friendly and economically low.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical intermediate preparation, and particularly relates to a method for preparing 2-methyl-4-acetoxy-2-butenoic acid by electrochemically oxidizing 2-methyl-4-acetoxy-2-butenal in coordination with anodes and cathodes. Background Art

[0002] 2-Methyl-4-acetoxy-2-butenal (FCA) is an important intermediate in the synthesis of vitamin A. When a VA device is producing VA, a large amount of FCA intermediates are often generated. FCA intermediates can not only be used in the synthesis of VA devices, but also for carotenoid projects based on the VA industry chain, its oxidation product 2-methyl-4-acetoxy-2-butenoic acid (FCAA) is an important starting point for the synthesis of intermediates, from which different synthetic sub-fragments can be extended to synthesize different carotenoids.

[0003] Therefore, how to efficiently realize the conversion from FCA to FCAA is a very important link in the VA device derivative industry chain.

[0004] Currently, the main methods for oxidizing FCA to FCAA are chemical oxidation and electrochemical oxidation. For example, CN102863367A discloses a method for preparing FCAA by oxidation of FCA using inorganic oxidants such as H2O2 and NaClO2 in the presence of a buffer. Because the reaction is violent and has significant exothermic and oxidative effects, low temperatures must be maintained throughout the process. This is accompanied by quenching of the oxidant and the treatment of large amounts of Cl-containing inorganic salt wastewater. The post-treatment and corrosion of the three wastes are very unfavorable, and do not meet current low-carbon and environmentally friendly chemical industry requirements.

[0005] Conventional electrochemical oxidation methods involve oxidation on the anode surface, which is a violent oxidation process and results in low selectivity. Indirect oxidation using the cathode to reduce oxygen to generate ROS is a very mild method that greatly improves selectivity. However, a diaphragm must be applied to prevent direct oxidation reactions at the anode, which leads to the problem of oxygen evolution at the anode and very low current efficiency.

[0006] Therefore, there is still a need to optimize the electrochemical system to solve the aforementioned problems. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for oxidizing FCA to prepare FCAA by synergistically generating ROS in situ through electrochemical in situ reaction at a modified metal catalytic anode and a cathode in an ionic liquid, thereby greatly improving the current efficiency while meeting high yield and high selectivity.

[0008] In order to achieve the above object of the invention, the present invention adopts the following technical solutions:

[0009] A method for preparing 2-methyl-4-acetoxy-2-butenoic acid (FCAA) by electrochemical oxidation of 2-methyl-4-acetoxy-2-butenal (FCA) using anode and cathode, wherein an electrode supporting oxygen reduction reaction is used as a cathode, a metal catalytic electrode is used as an anode, and an ionic liquid is used as an electrolyte solution to form an electrochemical reaction system, wherein the raw material FCA is electrochemically oxidized to produce FCAA.

[0010] In a specific embodiment, the cathode is a modified graphite felt carbon material gas diffusion electrode.

[0011] In a specific embodiment, the modification method of the modified graphite felt carbon material gas diffusion electrode is:

[0012] 1) Soak the graphite felt electrode in deionized water, then place it in a mixed dilute sulfuric acid / nitric acid solution, heat it to boiling, keep boiling for 30-60 minutes, remove it, wash it with deionized water until the washing solution is no longer acidic, let it stand, and dry it;

[0013] 2) Connect the acid-boiled graphite felt to the electrochemical workstation and keep it at the anode potential of 1.5-3.0V vsAg / Ag + A cyclic voltammetry scan was performed with a scanning number of >500. After the cyclic voltammetry scan was completed, the electrode was taken out to obtain a modified graphite felt carbon material gas diffusion electrode.

[0014] In a specific embodiment, the metal catalytic electrode of the anode is selected from a modified titanium ruthenium mesh (TiO2 / RuO3 / Ti / Ru) electrode.

[0015] In a specific embodiment, the modification method of the modified titanium ruthenium mesh (TiO2 / RuO3 / Ti / Ru) electrode is:

[0016] 1) ultrasonically treating the titanium ruthenium mesh electrode with an ethanol aqueous solution to clean the surface, then pickling it in a dilute sulfuric acid solution, washing it with deionized water at room temperature until the washing solution is no longer acidic, letting it stand, and drying it;

[0017] 2) The dried titanium ruthenium mesh is placed in a sodium sulfate aqueous solution and connected to an electrochemical workstation to maintain a constant potential oxygen evolution electrolysis at an anode potential of 2.0-3.0 V. The electrode is then removed, dried, and calcined in a muffle furnace under a nitrogen atmosphere, preferably at a calcination temperature of 200-250° C. and a calcination time of 2-3 h. After removal, the mesh is cooled and allowed to stand for 8-12 h, and then cut for later use.

[0018] In a specific embodiment, the ionic liquid used as the electrolyte solution is selected from any one or more of [Bmim]BF4, [Emim]BF4, [Emim]SO4, and [Bmim]SO4.

[0019] In a specific embodiment, the oxygen flow rate is 0.2-1 mL / min, and the stirring rate is 100-250 rpm.

[0020] In a specific embodiment, the cathode potential is -1.5 to -1.8 V vs Ag / Ag + .

[0021] In a specific embodiment, the temperature of the electrochemical reaction is 20-40° C., and the time of the electrochemical reaction is 1-3 hours.

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

[0023] 1) Compared with the chemical method, the method of the present invention does not require the addition of an external chemical oxidant, and does not require the addition of a quenching agent after the reaction, thereby saving raw material costs and improving product purity. At the same time, the introduction of halogen oxidants is avoided, and the three waste environmental problems and corrosion problems are reduced.

[0024] 2) The electrochemical reaction conditions of the method of the present invention are mild and the reaction risk is low.

[0025] 3) When the method of the present invention uses an ionic liquid system, the selectivity of the FCAA product is greater than 99%. At the same time, the synergistic effect of the cathode and anode accelerates the reaction rate. The conversion rate of the method reached 98% in 1 hour. Compared with the water system, the current efficiency increased from 54% to 96%, greatly reducing current loss. This is a very green, environmentally friendly and economical FCA oxidation method. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described below, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0027] A method for preparing 2-methyl-4-acetoxy-2-butenoic acid (FCAA) by electrochemical oxidation of 2-methyl-4-acetoxy-2-butenal (FCA) via anode and cathode, wherein an electrode supporting oxygen reduction reaction is used as a cathode, a metal catalytic electrode is used as an anode, and an ionic liquid is used as an electrolyte solution to form an electrochemical reaction system. The raw material FCA is initially oxidized to FCA at the anode. . The oxygen introduced undergoes an oxygen reduction reaction at the cathode, generating reactive oxygen species (ROS) in situ to achieve the FCA . Further oxidation of the intermediate generates FCAA.

[0028] The electrochemical oxidation FCA method of the present invention adopts ionic liquid as the electrolyte solvent of the electrochemical system, and uses a modified metal catalytic electrode as the anode and a carbon material gas diffusion electrode that can generate an oxygen reduction reaction with the addition of oxygen as the cathode, thereby achieving the FCA oxidation technical effect with high selectivity, high yield and high current efficiency.

[0029] The inventors of this application speculate that the principle may be that the modified metal catalytic anode adjusts its oxidation ability, so that FCA is oxidized to free radical molecules FCA on the surface. . Intermediate, while the added oxygen undergoes oxygen reduction cathode reaction at the cathode, O2 obtains 1e - Generate reactive oxygen species (O - , O . etc.) attack FCA . The intermediate is further oxidized to generate FCAA. Because the use of a water system is avoided, the problem of oxygen evolution at the anode is solved, and the current efficiency is greatly improved. At the same time, because the electrochemical window of the ionic liquid is wide, a higher potential can be applied, and the electrolysis efficiency is also greatly accelerated.

[0030] Specifically, the method for preparing FCA by electrochemical oxidation of the present invention comprises the following steps:

[0031] 1. Preparation of cathode carbon material modified graphite felt:

[0032] 1) Soak the graphite felt electrode in deionized water at room temperature (20-30°C), then place it in a mixed dilute sulfuric acid / nitric acid solution (concentration of 5-10wt%), heat it to boiling, maintain boiling for 30-60 minutes, remove it, wash it with deionized water at room temperature until the washing solution is no longer acidic, let it stand, and dry it at 50-60°C, 0.01-0.03mPa for 8-12 hours;

[0033] 2) Connect the acid-boiled graphite felt to the electrochemical workstation and keep it at the anode potential of 1.5-3.0V vsAg / Ag + Cyclic voltammetry scanning was performed with a scanning number of 500-800. After the cyclic voltammetry scanning was completed, the electrode was taken out to obtain a modified graphite felt carbon material gas diffusion electrode, which was cut into small pieces of 1 cm*1 cm for future use.

[0034] After acid-boiling modification, a large number of oxygen-containing functional groups can be modified on the carbon fiber surface, increasing its affinity for oxygen-containing substances. After CV etching, the surface of the graphite felt fiber will have a large number of cracks and rough surfaces, which increases the effective surface area of ​​the electrode, making it more fully exposed to dissolved oxygen and improving the oxygen reduction reaction (ORR) effect.

[0035] 2. Preparation of modified metal catalytic anode:

[0036] 1) The titanium ruthenium mesh electrode was ultrasonically treated with a 10-20 wt% ethanol aqueous solution for 10-20 minutes to clean the surface, and then the electrode was pickled in a 10-20 wt% dilute sulfuric acid solution for 30-45 minutes. After the pickling, the electrode was washed with deionized water at room temperature (20-30° C.) until the washing solution was no longer acidic, and the electrode was allowed to stand and dried.

[0037] 2) The dried titanium ruthenium mesh is placed in a 1wt%-2wt% sodium sulfate aqueous solution and connected to an electrochemical workstation to maintain an anode potential of 2.0-3.0V for constant potential oxygen evolution electrolysis for 2-3 hours. The electrode is then removed, dried, and calcined in a muffle furnace under a nitrogen atmosphere, preferably at a calcination temperature of 200-250°C and a calcination time of 2-3 hours. After removal, the mesh is cooled and allowed to stand for 8-12 hours, and then cut into 1cm*1cm pieces for later use.

[0038] Ultrasonic cleaning and acid washing remove the uniform oxide film on the electrode surface, creating numerous cracks and rough surfaces on the metal surface, increasing the electrode's effective surface area. Electrolytic oxygen evolution is then used to achieve uneven oxidation within and on the surface, lowering its oxidizing capacity. Finally, calcination in a nitrogen atmosphere finalizes the crystal lattice and increases electrode stability.

[0039] 3. Pretreatment before experiment:

[0040] Assemble the electrode system (cathode, anode, reference electrode Ag / Ag + ), add ionic liquid and raw materials into the system. First, start stirring at a stirring rate of 100-250rpm / min, then introduce oxygen near the cathode at an oxygen flow rate of 0.2-1mL / min, and wait for saturation after 10-20min of oxygen flow, maintaining the oxygen flow rate, and applying a cathode potential of -1.5~-1.8V vsAg / Ag + The reaction temperature is 20-40°C and the reaction time is 1-3 hours.

[0041] The cathode electrode, where the oxygen reduction reaction occurs, is not particularly limited in form, but is preferably a gas diffusion electrode, and various carbon electrode materials can be used. Furthermore, it can be modified to further increase the effective area of ​​the electrode and its affinity for oxygen-containing species, which is preferred.

[0042] The oxidation reaction electrode serving as the anode is not particularly limited in form, but is preferably a modified metal catalytic electrode, and various metals can be used. It can also be modified to further increase the effective area of ​​the electrode and to adjust the oxidizing properties downward, which is preferred.

[0043] The electrolyte solvent is preferably an ionic liquid. Various types of ionic liquids can be used. The selected ionic liquid must meet the following two requirements: 1) good solubility in the raw materials; and 2) low viscosity. Imidazolium ionic liquids (e.g., one or more selected from [Bmim]BF4, [Emim]BF4, [Emim]SO4, and [Bmim]SO4) are preferably used as the organic solvent of the present invention.

[0044] In the electrochemical oxidation reaction of FCA of the present invention, the electrochemical reaction conditions are as follows: the cathode potential is -1.5 to -1.8 V vs Ag / Ag + , for example -1.5V, -1.6V, -1.7V, -1.8V vs Ag / Ag + The temperature of the electrochemical reaction is 20-40°C, such as 20°C, 25°C, 30°C, 35°C, 40°C, etc. The time of the electrochemical reaction is 1-3 hours, such as 1h, 1.5h, 2h, 2.5h, 3h, etc. It is further preferred to use a cathode potential of -1.6 to -1.8V vs Ag / Ag + , the reaction temperature is 20-30°C, and the electrochemical reaction time is in the range of 1-2 hours.

[0045] In this specification, unless otherwise specified, percentages are by mass and temperatures are in degrees Celsius (°C).

[0046] The present invention is further explained below by more specific examples, but does not constitute any limitation.

[0047] The FCA raw materials come from the company's VA device, and can also be purchased from outside (Zhejiang Medicine). The ionic liquid is purchased commercially (Aladdin), and the unmodified electrodes are purchased commercially (Shanghai Chenhua) and processed by ourselves before use.

[0048] The chemical structures of the FCA raw materials and FCAA products used in the following examples are shown below:

[0049]

[0050] The FCA conversion, selectivity, and purity in the examples were determined as follows:

[0051] Degradation rate evaluation was performed using a gas chromatograph: Agilent 7820A gas chromatograph, DB-5 capillary column, injection volume: 0.2 μl. The test method is as follows:

[0052] Inlet temperature: 240 °C, initial column temperature 60 °C, hold for 2 min, then increase to 200 °C at a rate of 15 °C / min, hold for 10 min, total running time is 21.33 min.

[0053] First, a series of FCA and FCAA standard substances with standard concentrations were prepared and a calibration curve was established using gas chromatography to compare peak area and concentration. Then, the electrochemical reaction product was tested and the concentrations of the reactants and products were calculated by substituting the concentrations into the calibration curve. The reaction conversion rate and selectivity were then calculated.

[0054] Preparation Example 1

[0055] The modification method of the modified graphite felt carbon material gas diffusion electrode is:

[0056] 1) Soak the graphite felt electrode in deionized water at 25°C, then place it in a mixed dilute sulfuric acid / nitric acid solution (concentration: 5 wt%), heat to boiling, maintain boiling for 30 minutes, remove it, and wash it with deionized water at 20°C until the washing solution is no longer acidic. Then, let it stand and dry it at 50°C, 0.01 mPa for 8 hours;

[0057] 2) Connect the acid-boiled graphite felt to the electrochemical workstation and keep it at the anode potential of 1.5V vs Ag / Ag + A cyclic voltammetry scan was performed with 500 scan cycles. After the cyclic voltammetry scan was completed, the electrode was taken out to obtain a modified graphite felt carbon material gas diffusion electrode, which was cut into small pieces of 1 cm*1 cm for later use.

[0058] Preparation Example 2

[0059] 1) Soak a graphite felt electrode in deionized water at 25°C, then place it in a mixed dilute sulfuric acid / nitric acid solution (concentration: 10 wt%), heat to boiling, maintain boiling for 60 minutes, remove it, and wash it with deionized water at 30°C until the washing solution is no longer acidic. Then, let it stand and dry it at 60°C, 0.03 mPa for 12 hours;

[0060] 2) Connect the acid-boiled graphite felt to the electrochemical workstation and keep it at the anode potential of 3.0 V vs Ag / Ag + A cyclic voltammetry scan was performed with a scanning number of 800. After the cyclic voltammetry scan was completed, the electrode was taken out to obtain a modified graphite felt carbon material gas diffusion electrode, which was cut into small pieces of 1 cm*1 cm for later use.

[0061] Preparation Example 3

[0062] 1) The titanium ruthenium mesh electrode was ultrasonically treated with a 10 wt % ethanol aqueous solution for 10 minutes to clean the surface, and then it was pickled in a 10 wt % dilute sulfuric acid solution for 30 minutes. After the pickling, it was washed with deionized water at room temperature (20-30° C.) until the washing solution was no longer acidic, and then allowed to stand and dried.

[0063] 2) The dried titanium ruthenium mesh was placed in a 1 wt% sodium sulfate aqueous solution and connected to an electrochemical workstation to maintain a constant potential oxygen evolution electrolysis at an anode potential of 2.0 V for 2 h. The electrode was then removed, dried, and calcined in a muffle furnace under a nitrogen atmosphere at a temperature of 200°C for 2 h. After removal, the mesh was cooled and allowed to stand for 8 h, and then cut into 1 cm*1 cm pieces for later use.

[0064] Preparation Example 4

[0065] 1) The titanium ruthenium mesh electrode was ultrasonically treated with a 20 wt % ethanol aqueous solution for 20 minutes to clean the surface, and then it was pickled in a 20 wt % dilute sulfuric acid solution for 45 minutes. After the pickling, it was washed with deionized water at room temperature (20-30° C.) until the washing solution was no longer acidic, and then allowed to stand and dried;

[0066] 2) The dried titanium ruthenium mesh was placed in a 2 wt% sodium sulfate aqueous solution and connected to an electrochemical workstation to maintain a constant potential oxygen evolution electrolysis at an anode potential of 3.0 V for 1 h. The electrode was then removed, dried, and calcined in a muffle furnace under a nitrogen atmosphere, preferably at a calcination temperature of 250°C and a calcination time of 3 h. After removal, the mesh was cooled and allowed to stand for 12 h, and then cut into 1 cm*1 cm pieces for later use.

[0067] Example 1

[0068] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 1 was used as the cathode, the modified metal catalytic electrode prepared in Preparation Example 3 was used as the anode, and the Ag / Ag + A three-electrode system was established, with the electrode serving as the reference electrode. 0.6 g of [Bmim]BF450 was weighed and added to an electrolytic cell. 25.6 g of FCA was weighed and added to the cell, allowing it to completely dissolve. An oxygen flow rate of 0.8 mL was maintained near the cathode, and the stirring speed was 250 rpm. Aeration was performed for 20 minutes to fully saturate the system with oxygen. Under a continuous oxygen atmosphere maintained at 25°C, constant-potential electrolysis was performed at a cathode potential of -1.6 V for 1 hour. Analysis by gas chromatography (GC) revealed an FCA conversion of 98.2%, a selectivity of >99%, and a current efficiency of 96.1%.

[0069] Example 2

[0070] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 2 was used as the cathode, the modified metal catalytic electrode prepared in Preparation Example 4 was used as the anode, and the Ag / Ag +A three-electrode system was established, with the electrode serving as the reference electrode. 0.3 g of [Emim]BF4500 was weighed and added to an electrolytic cell. 25.6 g of FCA was weighed and added to the cell, allowing it to completely dissolve. The oxygen flow rate near the cathode was adjusted to 0.8 mL, and the stirring speed was 250 rpm. Aeration was performed for 20 minutes to fully saturate the system with oxygen. Under a continuous oxygen atmosphere maintained at 25°C, constant-potential electrolysis was performed at a cathode potential of -1.6 V for 1 hour. Analysis by gas chromatography (GC) revealed an FCA conversion of 97.8%, a selectivity of >99%, and a current efficiency of 95.7%.

[0071] Example 3

[0072] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 1 was used as the cathode, the modified metal catalytic electrode prepared in Preparation Example 4 was used as the anode, and the Ag / Ag + A three-electrode system was established, with the electrode serving as the reference electrode. 0.3 g of [Emim]BF4500 was weighed and added to an electrolytic cell. 25.6 g of FCA was weighed and added to the cell, allowing it to completely dissolve. The oxygen flow rate near the cathode was adjusted to 0.4 mL, and the stirring speed was 250 rpm. Aeration was performed for 20 minutes to fully saturate the system with oxygen. Under a continuous oxygen atmosphere maintained at 25°C, constant-potential electrolysis was performed at a cathode potential of -1.6 V for 1 hour. Analysis by gas chromatography (GC) revealed an FCA conversion of 92.1%, a selectivity of >99%, and a current efficiency of 89.6%.

[0073] Example 4

[0074] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 2 was used as the cathode, the modified metal catalytic electrode prepared in Preparation Example 3 was used as the anode, and the Ag / Ag + A three-electrode system was established, with the electrode serving as the reference electrode. 0.3 g of [Emim]BF4500 was weighed and added to an electrolytic cell. 25.6 g of FCA was weighed and added to the cell, allowing it to completely dissolve. The oxygen flow rate near the cathode was adjusted to 1.0 mL, and the stirring speed was 250 rpm. Aeration was performed for 20 minutes to fully saturate the system with oxygen. Under a continuous oxygen atmosphere maintained at 25°C, constant-potential electrolysis was performed at a cathode potential of -1.6 V for 1 hour. Analysis by gas chromatography (GC) revealed an FCA conversion of 98.1%, a selectivity of >99%, and a current efficiency of 96.0%.

[0075] Example 5

[0076] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 1 was used as the cathode, the modified metal catalytic electrode prepared in Preparation Example 3 was used as the anode, and the Ag / Ag +A three-electrode system was established, with the electrode serving as the reference electrode. 0.3 g of [Emim]BF4500 was weighed and added to an electrolytic cell. 25.6 g of FCA was weighed and added to the cell, allowing it to completely dissolve. The oxygen flow rate near the cathode was adjusted to 0.8 mL, and the stirring speed was 200 rpm. Aeration was performed for 20 minutes to fully saturate the system with oxygen. Under a continuous oxygen atmosphere maintained at 25°C, constant-potential electrolysis was performed at a cathode potential of -1.6 V for 1 hour. Analysis by gas chromatography (GC) revealed an FCA conversion of 89.2%, a selectivity of >99%, and a current efficiency of 85.3%.

[0077] Example 6

[0078] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 1 was used as the cathode, the modified metal catalytic electrode prepared in Preparation Example 4 was used as the anode, and the Ag / Ag + A three-electrode system was established, with the electrode serving as the reference electrode. 0.6 g of [Bmim]SO₄ ...

[0079] Example 7

[0080] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 2 was used as the cathode, the modified metal catalytic electrode prepared in Preparation Example 4 was used as the anode, and the Ag / Ag + A three-electrode system was established, with the electrode serving as the reference electrode. 0.6 g of [Bmim]SO₄ ...

[0081] Example 8

[0082] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 1 was used as the cathode, the modified metal catalytic electrode prepared in Preparation Example 4 was used as the anode, and the Ag / Ag +A three-electrode system was established, with the electrode serving as the reference electrode. 0.6 g of [Bmim]BF450 was weighed and added to an electrolytic cell. 25.6 g of FCA was weighed and added to the cell, allowing it to completely dissolve. An oxygen flow rate of 0.8 mL was maintained near the cathode, and the stirring speed was 250 rpm. Aeration was performed for 20 minutes to fully saturate the system with oxygen. The system was then maintained at 40°C, with a continuous oxygen atmosphere, and potentiostatic electrolysis was performed at a cathode potential of -1.6 V for 1 hour. Analysis by gas chromatography (GC) revealed an FCA conversion of 98.0%, a selectivity of >99%, and a current efficiency of 96.1%.

[0083] Comparative Example 1

[0084] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 1 was used as the cathode, the unmodified metal catalytic electrode was used as the anode, and the Ag / Ag + A three-electrode system was established, with the electrode serving as the reference electrode. 0.6 g of [Bmim]BF450 was weighed and added to an electrolytic cell. 25.6 g of FCA was weighed and added to the cell, allowing it to completely dissolve. An oxygen flow rate of 0.8 mL was maintained near the cathode, and the stirring speed was 250 rpm. Aeration was performed for 20 minutes to fully saturate the system with oxygen. Under a continuous oxygen atmosphere maintained at 25°C, constant-potential electrolysis was performed at a cathode potential of -1.6 V for 1 hour. Analysis by gas chromatography (GC) revealed an FCA conversion of 84.3%, a selectivity of 61%, and a current efficiency of 65.1%.

[0085] Comparative Example 2

[0086] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 1 was used as the cathode, the modified metal catalytic electrode prepared in Preparation Example 3 was used as the anode, and the Ag / Ag + A three-electrode system was established, with the electrode serving as the reference electrode. 0.6 g of [Bmim]BF450 was weighed and added to an electrolytic cell. 25.6 g of FCA was weighed and added to the cell, allowing it to completely dissolve. A nitrogen flow rate of 0.8 mL was maintained near the cathode, and the stirring speed was 250 rpm. Aeration was performed for 20 minutes to fully saturate the system with nitrogen. Under a continuous nitrogen atmosphere maintained at 25°C, constant-potential electrolysis was performed at a cathode potential of -1.6 V for 1 hour. Analysis by gas chromatography (GC) revealed an FCA conversion of 11.3%, a selectivity of 32.5%, and a current efficiency of 3.6%.

[0087] Comparative Example 3

[0088] Following the method in the literature (Pi Shiqing, Jiang Hongying, Zhai Dewei, et al. Synthesis of β-apo-8'-carotene ethyl ester [J]. Journal of Chemical Engineering of Colleges and Universities, 2014, 28(6):5.), FCA was oxidized by chemical oxidation:

[0089] C5 aldehyde and methanol were added to a 3L jacketed reactor, cooled to 0°C, and 1.1 eq of H2O2 was added, followed by 2 eq of sodium dihydrogen phosphate solution as a buffer. The reaction was maintained at 0°C with stirring at 250 rpm. Another oxidant, NaClO2, was slowly added dropwise for 2.5 hours. The reaction was allowed to react for 3 hours. After the reaction was completed, sodium sulfite was added for quenching. The pH was then adjusted to a strongly acidic state to precipitate FCAA from the aqueous phase. The product FCAA was extracted and stripped using ethyl acetate 3-5 times to obtain the FCA conversion rate of 96.5% and the selectivity of 98.2%.

[0090] Comparative Example 4

[0091] Weigh 100.6 g of acetonitrile solution and add it to 403.7 g of deionized water to prepare a 20% acetonitrile / water solution; weigh 0.21 g of Na2SO4 solid and add it to the above solution to a concentration of about 400 ppm.

[0092] In a diaphragm electrolyzer equipped with a perfluorosulfonic acid cation exchange membrane, the modified graphite felt electrode prepared in Preparation Example 1 was used as the cathode, the platinum sheet electrode was used as the anode, and the Ag / Ag + A three-electrode system was established, with the electrode as the reference electrode. The above-prepared solution was added. 25.5 g of FCA was weighed and added to the cathode of the electrolytic cell, allowing it to completely dissolve. An oxygen flow rate of 0.8 mL was maintained near the cathode, and the stirring speed was 250 rpm. Aeration was performed for 20 minutes to fully saturate the system with oxygen. Under a continuous oxygen atmosphere maintained at 25°C, constant-potential electrolysis was performed at a cathode potential of -1.2 V for 2 hours. Analysis by gas chromatography (GC) revealed an FCA conversion of 98.1%, a selectivity of >99%, and a current efficiency of 41%.

[0093] Comparative Example 5

[0094] Weigh 100.6 g of acetonitrile solution and add it to 403.7 g of deionized water to prepare a 20% acetonitrile / water solution; weigh 0.21 g of Na2SO4 solid and add it to the above solution to a concentration of about 400 ppm.

[0095] In the electrolytic cell, the modified graphite felt electrode prepared in Preparation Example 1 was used as the cathode, the modified metal catalytic electrode prepared in Preparation Example 3 was used as the anode, and the Ag / Ag +A three-electrode system was established, with the electrode as the reference electrode. The above-prepared solution was added. 25.5 g of FCA was weighed and added to the electrolytic cell, allowing it to completely dissolve. An oxygen flow rate of 0.8 mL was maintained near the cathode, and the stirring speed was 250 rpm. Aeration was performed for 20 minutes to fully saturate the system with oxygen. Under a continuous nitrogen atmosphere, the system was maintained at 25°C and electrolysis was performed at a cathode potential of -1.6 V for 1 hour. Analysis by gas chromatography (GC) revealed an FCA conversion of 69.7%, a selectivity of >99%, and a current efficiency of 37.1%.

[0096] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. Those skilled in the art will appreciate that, based on the teachings of this specification, modifications or adjustments may be made to the present invention. Such modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing 2-methyl-4-acetoxy-2-butenoic acid by electrochemical oxidation of 2-methyl-4-acetoxy-2-butenal by anode and cathode, characterized in that: An electrochemical reaction system is formed by using an electrode supporting oxygen reduction reaction as a cathode, a metal catalytic electrode as an anode, and an ionic liquid as an electrolyte solution. The raw material 2-methyl-4-acetoxy-2-butenal is electrochemically oxidized to produce 2-methyl-4-acetoxy-2-butenoic acid. The cathode is a modified graphite felt carbon material gas diffusion electrode, and the metal catalytic electrode of the anode is selected from a modified titanium ruthenium mesh (TiO2 / RuO3 / Ti / Ru) electrode.

2. The method according to claim 1, wherein The modification method of the modified graphite felt carbon material gas diffusion electrode is: 1) Soak the graphite felt electrode in deionized water, then place it in a mixed dilute sulfuric acid / nitric acid solution, heat it to boiling, keep boiling for 30-60 minutes, remove it, wash it with deionized water until the washing solution is no longer acidic, let it stand, and dry it; 2) Connect the acid-boiled graphite felt to the electrochemical workstation and keep it at an anode potential of 1.5-3.0Vvs Ag / Ag + A cyclic voltammetry scan was performed with a scanning number of >500. After the cyclic voltammetry scan was completed, the electrode was taken out to obtain a modified graphite felt carbon material gas diffusion electrode.

3. The method according to claim 1, wherein The modification method of the modified titanium ruthenium mesh (TiO2 / RuO3 / Ti / Ru) electrode is: 1) Clean the surface of the titanium ruthenium mesh electrode with ethanol / water ultrasonic treatment, then place it in a dilute acid solution for pickling. After the pickling is completed, wash it with deionized water at room temperature until the washing solution is no longer acidic, let it stand, and dry it; 2) The dried titanium ruthenium mesh was placed in a sodium sulfate aqueous solution and connected to an electrochemical workstation to maintain an anode potential of 2.0-3.0 V for constant potential oxygen evolution electrolysis for 2 hours. The electrode was then removed, dried, and calcined in a muffle furnace under a nitrogen atmosphere. After removal, the mesh was cooled and allowed to stand for 8-12 hours before being cut for later use.

4. The method according to claim 3, wherein In step 2), the calcination temperature is 200-250° C. and the calcination time is 2-3 hours.

5. The method according to claim 1, wherein The ionic liquid used as the electrolyte solution is selected from any one or two or more of [Bmim]BF4, [Emim]BF4, [Emim]SO4, and [Bmim]SO4.

6. The method according to claim 1, wherein The raw material 2-methyl-4-acetoxy-2-butenal is initially oxidized to a 2-methyl-4-acetoxy-2-butenal intermediate at the anode. The introduced oxygen undergoes an oxygen reduction reaction at the cathode, generating reactive oxygen species (ROS) in situ to further oxidize the 2-methyl-4-acetoxy-2-butenal intermediate to produce 2-methyl-4-acetoxy-2-butenoic acid.

7. The method according to claim 6, wherein The oxygen flow rate is 0.2-1 mL / min, and the stirring rate is 100-250 rpm.

8. The method according to claim 1, wherein Cathode potential is -1.5~-1.8V vs Ag / Ag + .

9. The method according to claim 1 or 8, wherein: The temperature of the electrochemical reaction is 20-40° C., and the time of the electrochemical reaction is 1-3 hours.

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