Preparation method of epoxidized olefin based on organic electrochemical synthesis

Abstract

The embodiment of the invention discloses a preparation method of epoxidized olefin based on organic electrochemical synthesis, and is characterized in that the method comprises the following steps: adding an electrolyte containing corresponding anions into a closed pressurized electrolytic tank according to a reaction path selected by an epoxidation reaction of olefin; and performing an epoxidation reaction of olefin in the closed pressurized electrolytic tank under electro-catalysis so as to perform an epoxidation reaction with target selectivity and obtain epoxidized olefin with target yield. According to the embodiment of the invention, the epoxidation reaction under the electro-catalysis of the olefin is carried out in the closed pressurized environment, the loss caused by the volatilization of the olefin and the solvent is effectively reduced, the yield is improved, and the corresponding anions are added into the electrolytic tank for carrying out the epoxidation reaction according to the selected oxidation path of the olefin epoxidation; therefore, optimization of selectivity and yield of the epoxidation reaction of olefin is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic electrochemical synthesis, and in particular to a preparation method of epoxidized olefins based on organic electrochemical synthesis. BACKGROUND

[0002] Epoxides are important intermediates in organic synthesis, widely used in fine chemicals, pharmaceuticals, materials and other fields. Traditional methods of olefin epoxidation usually use strong oxidants such as peroxy acid, hydrogen peroxide / catalyst system, hypochlorite, etc. These methods often have problems such as harsh reaction conditions, low atom economy, environmental pollution, etc. In recent years, electrochemical methods have attracted widespread attention in the field of organic synthesis due to their mild reaction conditions, controllable reactions, and environmental friendliness.

[0003] Electrochemically driven olefin epoxidation mainly includes two pathways: direct oxidation and indirect oxidation. Direct oxidation usually generates active oxygen species on the anode surface, which then reacts with the olefin substrate to form epoxides; indirect oxidation involves the reaction of an oxidizing agent or oxidizing precursor generated by electrochemistry with the olefin. However, existing electrochemical epoxidation methods still face problems such as low selectivity and low efficiency.

[0004] Therefore, it is of great scientific value and application prospect to develop an efficient and highly selective electrochemical olefin epoxidation method. SUMMARY

[0005] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a preparation method of epoxidized olefins based on organic electrochemical synthesis, which is efficient, highly selective, and improves the yield of electrochemical olefin epoxidation.

[0006] Specifically, the present application provides a preparation method of epoxidized olefins based on organic electrochemical synthesis, which comprises:

[0007] adding an electrolyte containing corresponding anions to a closed and pressurized electrolytic cell according to the reaction pathway selected for the epoxidation reaction of the olefin;

[0008] carrying out the epoxidation reaction of the olefin under electrocatalysis in the closed and pressurized electrolytic cell to perform the target selective epoxidation reaction and obtain the epoxidized olefin with the target yield.

[0009] In one embodiment of the above-mentioned preparation method of epoxidized olefins based on organic electrochemical synthesis, adding an electrolyte containing corresponding anions to a closed and pressurized electrolytic cell according to the reaction pathway selected for the epoxidation reaction of the olefin comprises:

[0010] adding an electrolyte containing BF4 -electrolyte of an anionic conductive salt;

[0011] adding an electrolyte of an anionic conductive salt into the closed pressurized electrolytic cell according to the indirect oxidation pathway selected for the epoxidation reaction of the olefin - electrolyte of an anionic conductive salt.

[0012] In one embodiment of the above-mentioned method for preparing epoxidized olefin based on organic electrochemical synthesis, the method further comprises:

[0013] monitoring the concentration of the target anion in the epoxidation reaction of the olefin in real time during the epoxidation reaction of the olefin under the electrocatalysis;

[0014] adjusting the proportion of the target anion in the electrolyte based on the concentration of the target anion.

[0015] In one embodiment of the above-mentioned method for preparing epoxidized olefin based on organic electrochemical synthesis, the monitoring the concentration of the target anion in the epoxidation reaction of the olefin in real time comprises:

[0016] monitoring the concentration of the target anion in the epoxidation reaction of the olefin in real time based on electrochemical-Raman combined use.

[0017] In one embodiment of the above-mentioned method for preparing epoxidized olefin based on organic electrochemical synthesis, the epoxidation reaction of the olefin in the electrolytic cell under the electrocatalysis comprises:

[0018] producing hydrogen peroxide at the cathode of the electrolytic cell based on the two-electron reduction reaction of oxygen;

[0019] carrying out the epoxidation reaction of the olefin at the anode of the electrolytic cell under the electrocatalysis based on the hydrogen peroxide.

[0020] In one embodiment of the above-mentioned method for preparing epoxidized olefin based on organic electrochemical synthesis, the cathode of the electrolytic cell is selected from one or more of carbon materials, modified noble metals, and modified alloys.

[0021] In one embodiment of the above-mentioned method for preparing epoxidized olefin based on organic electrochemical synthesis, the anode of the electrolytic cell is selected from one or more of platinum, gold, palladium, tin, platinum alloy, gold alloy, palladium alloy, and tin alloy.

[0022] In one embodiment of the above-mentioned method for preparing epoxidized olefin based on organic electrochemical synthesis, the electrolyte further comprises water and an organic solvent;

[0023] The volume ratio of the water to the organic solvent is (10:90) to (50:50).

[0024] In one embodiment of the above described process for the preparation of epoxidized olefins based on organic electrochemical synthesis, the organic solvent is selected from one or more of acetonitrile, methanol, ethanol, tetrahydrofuran.

[0025] In one embodiment of the above described process for the preparation of epoxidized olefins based on organic electrochemical synthesis, the pressure in the closed pressurized environment is between 0.5 and 5 bar;

[0026] The reaction temperature of the epoxidation reaction is between 25 and 40 °C and the current density in the electrocatalysis is between 5 and 50 mA / cm 2 .

[0027] The above described one or more embodiments of the present application have at least one or more of the following beneficial effects: the epoxidation reaction of the olefins is carried out in a closed pressurized environment under electrocatalysis, effectively reducing the loss caused by the volatilization of the olefins and the solvent, increasing the yield, and adding the corresponding anion in the electrolytic cell in which the epoxidation reaction is carried out according to the selected oxidation path of the epoxidation of the olefins, so as to achieve the selectivity of the epoxidation reaction of the olefins and the optimization of the yield.

[0028] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0029] The disclosure of the present application will become more fully understood from the detailed description, taken in conjunction with the accompanying drawings, in which like reference numerals refer to like elements in the several views. It will be readily understood to those skilled in the art that the present application is not limited to the embodiments described and that many modifications and other embodiments could be made without departing from the scope of the present application. For example, the present application as described is applicable to a variety of olefins and solvents. In addition, similar reference numerals denote similar parts throughout the various drawings. In addition, elements of the drawings can not be to scale as elements have been enlarged to more clearly depict and describe the figures.

[0030] Figure 1 is a schematic diagram of the direct and indirect oxidation reaction mechanisms of the olefins;

[0031] Figure 2 is a graph of the yield and potential difference of different anion electrolytes in the indirect oxidation system;

[0032] Figure 3 is a graph of the yield and capacitance change of different anion electrolytes in the direct oxidation system;

[0033] Figure 4 is an in situ ATR-SEIRAS spectrum in the indirect oxidation system;

[0034] Figure 5 is a stability test graph of different anion electrolytes in the direct oxidation system;

[0035] Figure 6 is a schematic diagram of the electrolytic cell designed in the present application. DETAILED DESCRIPTION

[0036] Some embodiments of the present application will be described below with reference to the accompanying drawings. Those skilled in the art will understand that these embodiments are only used to explain the technical principles of the present application and are not intended to limit the protection scope of the present application.

[0037] As described in the background, the existing electrochemical driven olefin epoxidation has two paths of direct oxidation and indirect oxidation, but both paths have the problems of low selectivity and low efficiency, therefore, it is urgent to develop an efficient and high-selectivity electrochemical olefin epoxidation method.

[0038] To solve the above problems, the present application creatively proposes a preparation method of epoxidized olefin based on organic electrochemical synthesis, which implements the epoxidation reaction of olefin under electrocatalysis in a closed and pressurized environment, effectively reduces the loss caused by the volatilization of olefin and solvent, improves the yield, and adds corresponding anions in the electrolytic cell according to the selected oxidation path of olefin epoxidation, so as to realize the selectivity of the epoxidation reaction of olefin and the optimization of the yield.

[0039] The present application will be specifically described below through specific embodiments.

[0040] Specifically, the present application provides a preparation method of epoxidized olefin based on organic electrochemical synthesis, which comprises:

[0041] S1, adding corresponding anions into a closed and pressurized electrolytic cell according to the selected reaction path of the epoxidation reaction of olefin.

[0042] S2, implementing the epoxidation reaction of olefin under electrocatalysis in the closed and pressurized electrolytic cell, so as to perform the epoxidation reaction of the target selectivity and obtain the epoxidized olefin of the target yield.

[0043] In the present application, the olefin is selected from one or more of cyclopentene, cyclohexene, cycloheptene, cyclooctene, 1-pentene, 1-hexene, 1-heptene, 1-octene, and styrene.

[0044] The epoxidation path of olefin includes two ways: indirect oxidation path and direct oxidation path. Referring to Figure 1 As shown in the figure, the two ways have significant differences in reaction mechanism, reaction area and influencing factors:

[0045] Indirect oxidation pathway: This pathway contains two key steps. First, hydrogen peroxide is generated in situ at the cathode of the electrolytic cell through the oxygen reduction reaction (ORR). Subsequently, the generated hydrogen peroxide H2O2 is oxidized at the anode of the electrolytic cell to generate active oxygen species. These active oxygen species are mainly distributed in the OHP or outer layer region, and react with olefin molecules in the electrolyte of the electrolytic cell to generate epoxide compounds. In this pathway, the reaction occurs in the region outside the electrode surface, and the active species needs to diffuse from the hydrophilic environment to the hydrophobic-hydrophilic interface region to react with the olefin, so the interface characteristics have a significant impact on the reaction efficiency.

[0046] Direct oxidation pathway: In this pathway, water molecules are directly oxidized at the anode surface of the electrolytic cell to generate adsorbed active oxygen species. This active oxygen species is strongly adsorbed on the electrode surface to form an IHP plane. The olefin molecules must penetrate the double layer formed by the anions to contact the active oxygen species on the electrode surface to occur the epoxidation reaction. In this pathway, the reaction occurs on the electrode surface, and the mass transfer process of the olefin molecules has a decisive influence on the reaction rate.

[0047] As shown in Figure 2 , the hydrophobicity of the anion has a significant impact on the indirect oxidation pathway of the olefin. In the acetonitrile / water mixed solvent system, the anion forms a double layer in the interface region, and its hydrophobicity directly affects the concentration distribution of the active species and the olefin molecules at the interface. The TFSI - anion has both hydrophilic and hydrophobic characteristics, and can most effectively disperse the hydrophilic H2O2 and its oxidation products and the hydrophobic olefin molecules, creating a microenvironment at the interface that is conducive to the reaction of the two. Specifically, the TFSI - molecule contains hydrophobic CF3 and hydrophilic SO2 groups, and can form a microphase separation structure at the interface, while providing suitable reaction space for the hydrophilic active oxygen species and the hydrophobic olefin molecules. While the electrolyte based on TFSI - anion performs best in a mixed solvent of 70% acetonitrile and 30% water, with a cyclooctene epoxidation yield of 66.91%, which is about 18.87% higher than the lowest yield of FSI - system.

[0048] As shown in Figure 3 , for the direct oxidation pathway, the size of the anion is a key factor affecting the reaction efficiency. In this pathway, the olefin molecules need to penetrate the double layer formed by the anions to contact the active oxygen species on the electrode surface. The larger the size of the anion, the more "crowded" the double layer formed, and the more difficult it is for the olefin molecules to penetrate. BF4 - is the smallest in size among the anions studied, forming a relatively thin and low-density double layer, which is conducive to the penetration of the olefin molecules and the contact with the active oxygen species on the electrode surface. In contrast, TFSI -The anion size is the largest, and the double layer formed has the strongest blocking effect on olefin molecules. The experimental results show that in the direct oxidation pathway, the order of the anion effect is BF4 - (17.3%)>PF6 - (14.7%)>ClO4 - (14.2%)>CF3SO3 - (12.6%)>FSI - (10.8%)>TFSI - (10.2%), which is highly consistent with the increasing order of anion size.

[0049] like Figure 4 As shown in Figure 2, in situ ATR-SEIRAS spectroscopy analysis further confirmed the regulatory effect of anion characteristics on the reaction interface. - The spectrum of the system shows that as the potential increases, the CH3CN peak intensity increases while the H2O peak intensity decreases, indicating that a more hydrophobic environment is formed in the interface area, which is conducive to the enrichment of hydrophobic olefin molecules; at the same time, the C=C stretching vibration peak shows a significant negative peak, indicating that the consumption rate of olefins at the interface increases. In contrast, FSI - These features are not obvious in the system, indicating that its interface regulation ability is weak. This result is highly consistent with the results of electrochemical analysis and yield determination.

[0050] like Figure 5 As shown in Figure 2, in the direct oxidation system, the electrochemical stability and interfacial capacitance characteristics of different anion electrolytes also have significant differences. - The system exhibits excellent stability in a wide potential window, and the interfacial capacitance value changes more with potential, indicating that the electrode surface can more effectively adsorb and desorb olefin molecules and their reaction intermediates. The analysis results of the capacitance-potential curve show that small-sized anions (such as BF4 - The double-layer structure formed by the olefin molecules is more conducive to the penetration of olefin molecules and their reaction with surface active oxygen species. In summary, for different reaction pathways, anions with different characteristics should be selected to obtain the best catalytic effect.

[0051] Anion selected from BF4 - PF6 - 、ClO4 - CF3SO3 - 、FSI - TFSI -correspondingly, the conductive salt in the electrolyte is selected from one or more of LiBF4, LiPF6, LiClO4, LiCF3SO3, LiFSI, LiTFSI, NaBF4, NaPF6, NaClO4, NaCF3SO3, NaFSI, NaTFSI, KBF4, KPF6, KClO4, KCF3SO3, KFSI, KTFSI.

[0052] In some embodiments, the reaction path selected according to the epoxidation reaction of the olefin adds to the closed pressurized electrolytic cell an electrolyte containing a corresponding anion, including:

[0053] According to the direct oxidation path selected according to the epoxidation reaction of the olefin, an electrolyte containing a conductive salt with BF4 - anion is added to the closed pressurized electrolytic cell.

[0054] According to the indirect oxidation path selected according to the epoxidation reaction of the olefin, an electrolyte containing a conductive salt with TFSI - anion is added to the closed pressurized electrolytic cell.

[0055] The indirect oxidation path preferably has an amphiphilic TFSI - anion, while the direct oxidation path preferably has a small size BF4 - anion.

[0056] In some embodiments, the method further comprises:

[0057] In the process of implementing the epoxidation reaction of the olefin under electrocatalysis, the concentration of the target anion in the epoxidation reaction of the olefin is monitored in real time;

[0058] The proportion of the target anion in the electrolyte is adjusted based on the concentration of the target anion.

[0059] Specifically, when the indirect oxidation path is selected, the concentration of TFSI - anion in the reaction process is monitored in real time; when the direct oxidation path is selected, the concentration of BF4 - anion in the reaction process is monitored in real time.

[0060] Preferably, the concentration of the target anion in the epoxidation reaction of the olefin is monitored in real time by electrochemical-Raman combined real-time monitoring of the concentration of the target anion in the epoxidation reaction of the olefin.

[0061] Specifically, the electrochemical impedance spectroscopy / differential pulse voltammetry is combined with the in-situ Raman spectroscopy technology, the electrochemical signals are collected in the electrolytic cell to reflect the electrochemical behaviors of ions at the electrode interface and the characteristics of the double electric layer, and the Raman spectrum signals provide the characteristic vibration fingerprints of each anion molecule, then the multi-element correction algorithm is used for data fusion processing of the two signals, so that the real-time quantitative monitoring of the concentrations of various anions such as TFSI - , FSI - , BF4 - , ClO4 - , CF3SO3 - , PF6 - , etc. in the electrolyte is realized. The monitoring accuracy and reliability are improved through the weighted fusion algorithm, and continuous ion concentration change information can be provided in the process of electrocatalytic olefin epoxidation reaction.

[0062] In another embodiment, the approximate concentration of the target anion in the current electrolyte can also be obtained according to the real-time pH value of the electrolyte.

[0063] In some embodiments, the epoxidation reaction of the olefin under electrocatalysis in the electrolytic cell comprises:

[0064] Preparation of hydrogen peroxide at the cathode of the electrolytic cell based on the two-electron reduction reaction of oxygen;

[0065] Carrying out the epoxidation reaction of the olefin under electrocatalysis at the anode of the electrolytic cell based on the hydrogen peroxide.

[0066] Through the in-situ generation of hydrogen peroxide by the cathode oxygen reduction reaction, combined with the anode epoxidation reaction, the efficient epoxidation process of the olefin is realized, and the safety hidden danger caused by the direct addition of hydrogen peroxide is avoided.

[0067] In some embodiments, the cathode of the electrolytic cell is selected from one or more of carbon materials, modified noble metals, and modified alloys.

[0068] The selection of the cathode material is crucial for the generation of hydrogen peroxide. Pure platinum and other noble metals usually tend to directly reduce oxygen to water through a four-electron path, which is not conducive to the generation of hydrogen peroxide. Carbon materials or specially modified noble metal alloys (such as Pt-Hg and Au-Hg) can effectively promote the two-electron reduction path of oxygen, and are more suitable as the cathode material of the present application.

[0069] In some embodiments, the anode of the electrolytic cell is selected from one or more of platinum, gold, palladium, tin, platinum alloy, gold alloy, palladium alloy, and tin alloy.

[0070] The anode adopts one or more of platinum, gold, palladium, tin, platinum alloy, gold alloy, palladium alloy, and tin alloy, which has high activity and can effectively promote the activation of hydrogen peroxide and the epoxidation of olefin.

[0071] In some embodiments, the electrolyte further comprises water and an organic solvent.

[0072] The volume ratio of the water to the organic solvent is (10:90) to (50:50). Alternatively, the volume ratio of the water to the organic solvent can be 10:90, 15:85, 22:78, 30:70, 36:64, 40:60, 43:57, 50:50, or any ratio within the range of the above volume ratio values. Preferably, the volume ratio of the water to the organic solvent is 20:80.

[0073] In some embodiments, the organic solvent is selected from one or more of acetonitrile, methanol, ethanol, and tetrahydrofuran.

[0074] Preferably, the organic solvent is acetonitrile. Acetonitrile not only has excellent electrochemical stability, but also can participate in the epoxidation reaction process as an oxygen source or oxidant to promote the formation of specific intermediates.

[0075] In some embodiments, the pressure in the closed and pressurized environment is 0.5 to 5 bar. Alternatively, the pressure in the closed and pressurized environment can be 0.5 bar, 1 bar, 1.5 bar, 2 bar, 2.5 bar, 3 bar, 3.5 bar, 4 bar, 4.5 bar, 5 bar, or any value within the range of the above pressure values.

[0076] The reaction temperature of the epoxidation reaction is 25 to 40 °C. Alternatively, the reaction temperature of the epoxidation reaction can be 25 °C, 30 °C, 35 °C, 40 °C, or any value within the range of the above temperature values. The current density in the electrocatalysis is 5 to 50 mA / cm 2 Alternatively, the current density in the electrocatalysis can be 5 mA / cm 2 , 10 mA / cm 2 , 15 mA / cm 2 , 20 mA / cm 2 , 25 mA / cm 2 , 30 mA / cm 2 , 35 mA / cm 2 , 40 mA / cm 2 , 45 mA / cm 2 , 50 mA / cm 2 , or any value within the range of the above current density values.

[0077] The present application also provides an electrolytic cell for implementing the above method, comprising: a closed and pressurized reaction chamber, which is divided into an anode chamber and a cathode chamber by a separator, an anode for oxygen reduction reaction for olefin epoxidation reaction is installed in the anode chamber, and a cathode is installed in the cathode chamber.

[0078] The closed reaction chamber can withstand a maximum pressure of 5 bar.

[0079] The cathode is made of carbon materials, specially modified noble metals or alloys, preferably, the cathode is made of one or more of carbon paper, carbon cloth, graphite felt, carbon nanotubes or surface modified Pt-Hg, Au-Hg alloys.

[0080] The anode is made of one or more of platinum, gold, palladium, tin or their alloys.

[0081] The separator is provided with micro-channels to allow the directional migration of hydrogen peroxide generated on the cathode from the cathode chamber to the anode chamber.

[0082] The distance between the cathode and the anode is 0.1-0.3 cm, preferably 0.2 cm, to significantly reduce Ohmic loss and improve mass transfer efficiency; the anode and the cathode are fixed by electrode supports to ensure that the electrode distance remains stable during long-term operation.

[0083] The electrolytic cell is equipped with a control system for controlling the reaction temperature and current density; this system can monitor and adjust the temperature fluctuations in the electrolytic cell in real time, ensuring that the reaction is carried out within the optimal temperature range, while the current density can be automatically adjusted according to the substrate conversion to maximize energy utilization efficiency.

[0084] Both the cathode chamber and the anode chamber are connected to a solution circulation system to enhance mass transfer and increase local hydrogen peroxide concentration; this solution circulation system is equipped with a micro-pump and a flow controller, which can accurately adjust the circulation rate (10-20 mL / min) according to the reaction requirements, achieving efficient exchange of reactants and products; the anode chamber and the cathode chamber are connected to a micro-pump through a pipeline, and the flow controller is installed on the pipeline. In addition, an inter-chamber circulation pump is also provided to drive the liquid to circulate between the anode chamber and the cathode chamber.

[0085] Among them, the liquid circulation flow rate in the cathode chamber is 15-25 mL / min to promote oxygen dissolution and hydrogen peroxide generation; the liquid circulation flow rate in the anode chamber is 10-20 mL / min to promote the mixing reaction of hydrogen peroxide and olefins; the liquid circulation flow rate between the cathode chamber and the anode chamber is 5-10 mL / min to control the directional migration of hydrogen peroxide from the cathode to the anode.

[0086] The cathode chamber is also connected to a cathode chamber aeration system that provides pure oxygen or oxygen-rich gas to the cathode, which can enhance the oxygen reduction reaction rate; this system is equipped with a precision gas flow meter and a gas diffusion device to ensure uniform distribution of oxygen on the cathode surface.

[0087] The electrolytic cell is designed as a quasi-single-chamber flow-through structure, which optimizes the material transfer efficiency, is particularly suitable for large-scale production under closed and pressurized conditions, and has higher material transfer efficiency and production capacity. The flow-through structure adopts parallel electrode arrangement, the electrode spacing is accurately controlled, the circulation system is connected with the external storage tank, continuous feeding and product collection are facilitated, and industrialized scale-up production is suitable.

[0088] The application will be further described below through specific examples, but the protection scope of the application is not limited thereto.

[0089] Example 1: Electrochemical epoxidation of cyclooctene under indirect oxidation pathway:

[0090] (1) Electrolytic cell design: A closed and pressurized quasi-single-chamber electrolytic cell is used, the operating pressure is 2.0 bar, the cathode uses high specific surface area porous carbon material (area 5 cm x 5 cm) or surface modified Pt-Hg, Au-Hg alloy, the anode uses nano-structured platinum or gold catalyst (area 5 cm x 5 cm), the distance between the cathode and the anode is 0.2 cm, which is partially separated by a special separator, and the separator is provided with a microchannel to allow material exchange without generating significant membrane resistance, pure oxygen is introduced into the cathode area, and a gas recirculation system is provided to maintain the gas pressure.

[0091] (2) Electrolyte preparation: A mixture of 0.1M LiTFSI in acetonitrile / water (7:3, v / v) is used in the entire electrolytic cell, and 60mM cyclooctene is added.

[0092] (3) Electrolysis conditions: At room temperature, a constant current density of 10 mA / cm 2 for 3 hours.

[0093] (4) Product analysis: After the electrolysis is completed, the anode chamber solution is taken out and analyzed by GC-MS and 1H NMR, the yield of the product cyclooctene oxide is 66.91%, and the selectivity is greater than 95%.

[0094] Example 2: Electrochemical epoxidation of cyclooctene under direct oxidation pathway:

[0095] (1) Electrolytic cell design: A closed and pressurized single-chamber electrolytic cell is used, the operating pressure is 2.0 bar, the working electrode is a platinum sheet (1 cm x 2 cm), the counter electrode is a graphite rod, and the reference electrode is an Ag / AgCl electrode. The electrolytic cell is equipped with a pressure monitoring and safety release system to ensure that the reaction is carried out under constant pressure and effectively prevents the volatilization of olefins and solvents.

[0096] (2) Electrolyte preparation: A mixture of 0.1M LiBF in acetonitrile / water (7:3, v / v) is used, and 60mM cyclooctene is added.

[0097] (3) Electrolysis conditions: constant potential of 2.91 V vs. RHE was applied at room temperature for 3 h.

[0098] (4) Product analysis: after electrolysis, the solution was taken out and analyzed by GC-MS and 1H NMR. The yield of product cyclooctene oxide was 17.3% with a selectivity of more than 90%.

[0099] Example 3: Effect of anion on indirect oxidation pathway:

[0100] According to the improved quasi-single-chamber design method, the LiTFSI in the electrolyte was replaced by an equal amount of LiBF4, LiPF6, LiCIO4, LiCF3SO3, and LiFSI under the condition of closed pressurization (2.0 bar), and other conditions remained unchanged to measure the yield of cyclooctene oxide. The results showed that the yield changed with the anion as follows: TFSI - (66.91%) > BF4 - (61.22%) > CF3SO3 - (60.14%) > PF6 - (56.65%) > CIO4 - (48.12%) > FSI - (48.04%). This trend is related to the amphiphilic characteristics of the anion, and TFSI - has the strongest amphiphilic property, which can most effectively disperse the solvent domain and active species.

[0101] Example 4: Effect of anion on direct oxidation pathway:

[0102] According to the method of Example 2, the LiBF4 in the electrolyte was replaced by an equal amount of LiPF6, LiCIO4, LiCF3SO3, LiFSI, and LiTFSI, and other conditions remained unchanged to measure the yield of cyclooctene oxide. The results showed that the yield changed with the anion as follows: BF4 - (17.3%) > PF6 - (14.7%) > CIO4 - (14.2%) > CF3SO3 - (12.6%) > FSI - (10.8%) > TFSI - (10.2%). This trend is negatively correlated with the size of the anion, and smaller BF4 - is beneficial to the penetration of olefin molecules through the double electric layer to react with surface active oxygen species.

[0103] Example 5: Effect of acetonitrile / water ratio on reaction performance:

[0104] The method of Example 1 was followed to determine the yield of epoxy cyclooctane by adjusting the volume ratio of acetonitrile / water to 50:50, 70:30 and 90:10, respectively. The results showed that the yield was highest (66.91%) at a ratio of 70:30, and too high or too low would result in a decrease in yield. This is because the appropriate ratio of mixed solvents can balance the solubility of hydrophilic reactants (H2O2) and hydrophobic reactants (cyclooctene), promoting their effective collision at the interface.

[0105] Example 6: Substrate expansion study:

[0106] The method of Example 1 was followed to perform electrochemical epoxidation reactions with different olefins as substrates, with the following results:

[0107] Cyclopentene: yield >99%, selectivity >99%;

[0108] Cyclohexene: yield 51.2%, selectivity 98.3%;

[0109] Cycloheptene: yield 93.7%, selectivity >99%;

[0110] 4-Hydroxycyclooctene: yield 91.6%, selectivity 91.6%;

[0111] 3-Methylcyclohexene: yield 71.7%, selectivity 85.2%;

[0112] 1-Hexene: yield 77.2%, selectivity 96.2%;

[0113] 1-Heptene: yield 47.2%, selectivity >99%;

[0114] 1-Octene: yield 53.7%, selectivity >99%;

[0115] Styrene: yield 52.5%, selectivity 77.9%.

[0116] The results show that the method has good applicability to both cyclic olefins and linear olefins, and especially exhibits excellent yield and selectivity for cyclic olefins.

[0117] Example 7: This example provides a new type of closed pressurized flow-through electrolytic cell, with the following specific structure:

[0118] (1) Closed pressurized design: The entire electrolytic cell is made of pressure-resistant stainless steel material, with a design working pressure of 5 bar, equipped with a pressure gauge and a safety release valve, and low-boiling point olefins (such as cyclopentene, 1-hexene, etc.) and volatile solvents (such as acetonitrile) can participate in the reaction under stable conditions.

[0119] (2) Quasi-single chamber structure: The electrolytic cell adopts an innovative quasi-single chamber design, which fundamentally solves the problems of large membrane resistance, easy damage of the membrane, and difficulty of hydrogen peroxide permeating through the proton exchange membrane. The cathode and anode are located in the same reaction chamber but are partially separated by a special separator, which is provided with a carefully designed network of micro-channels, allowing hydrogen peroxide to migrate from the cathode region to the anode region in a targeted manner while reducing substrate interference. The distance between the cathode and the anode is optimized to 0.1-0.3 cm, preferably 0.2 cm, significantly reducing the solution resistance and improving the energy efficiency.

[0120] (3) Electrode materials and layout:

[0121] The cathode uses high specific surface area porous carbon material (area 5 cm x 5 cm) or surface modified Pt-Hg, Au-Hg alloy, which is specially treated to selectively promote the two-electron reduction of oxygen to hydrogen peroxide, avoiding the four-electron reduction path. The anode uses nanostructured platinum or gold catalyst (area 5 cm x 5 cm) with high activity, which can effectively promote the activation of hydrogen peroxide and olefin epoxidation. The electrodes are arranged in a three-dimensional manner to form a "sandwich" structure, increasing the reaction area and optimizing the mass transfer path of the reactants.

[0122] (4) Microfluidic channel design: The electrolytic cell is designed with a precise microfluidic channel network, completely replacing the traditional proton exchange membrane, solving the problem of hydrogen peroxide permeating through the membrane, while maintaining the relative independence of the electrode area. The network includes: oxygen diffusion channels in the cathode region to ensure uniform distribution of oxygen and improve the two-electron reduction efficiency; hydrogen peroxide directional migration channels that use concentration gradients and fluid dynamics principles to guide the efficient migration of hydrogen peroxide from the cathode region to the anode region; reactant mixing channels in the anode region to optimize the contact efficiency of olefins and hydrogen peroxide in local areas; the size and shape of the channels are precisely designed to ensure efficient mass transfer while maintaining the electrochemical independence of the electrode area.

[0123] (5) Circulation system: equipped with a precise micro-pump to control: cathode region circulation, circulation flow rate 15-25 mL / min, promoting oxygen dissolution and hydrogen peroxide generation; anode region circulation, circulation flow rate 10-20 mL / min, promoting hydrogen peroxide and olefin mixing reaction; inter-regional circulation, flow rate 5-10 mL / min, controlling the directional migration of hydrogen peroxide from the cathode to the anode;

[0124] (6) Hydrogen peroxide enrichment zone design: A special hydrogen peroxide enrichment zone is designed near the anode, made of hydrophilic material, which can adsorb and enrich hydrogen peroxide, increase the local concentration, and enhance the epoxidation reaction efficiency.

[0125] (7) Temperature and pressure control system:

[0126] Temperature control accuracy ±0.5℃, working temperature range 25-40℃;

[0127] Pressure control range 0.5-5 bar, accuracy ±0.1 bar;

[0128] Equipped with safety protection system, automatically stop the reaction when the pressure or temperature exceeds the set range.

[0129] (8) Online monitoring system:

[0130] Hydrogen peroxide concentration online monitoring probe, real-time monitoring of hydrogen peroxide generation rate;

[0131] Dissolved oxygen concentration monitoring, optimizing oxygen flow rate;

[0132] Electrochemical parameter monitoring, including current, voltage and electrode potential;

[0133] Under the same reaction conditions (0.1 M LiTFSI with tetrabutylammonium salt complex electrolyte, 80 mM cyclooctene, acetonitrile / water = 80:20, v / v, 30℃, 15 mA / cm 2 Current density, 1.5 bar pressure), the product yield and purity of cyclooctene oxide of the new sealed pressurized flow electrolysis cell are significantly improved, and the electrical energy consumption is reduced by about 40%.

[0134] The electrolysis cell provided by the embodiment has the following advantages:

[0135] (1) The problem of olefin and solvent evaporation is completely solved by the sealed and pressurized design;

[0136] (2) The quasi-single-chamber design eliminates the problem of membrane resistance while maintaining the relative independence of the reaction area;

[0137] (3) The microfluidic channel and intelligent circulation system realize the efficient directional migration of hydrogen peroxide;

[0138] (4) The compact electrode arrangement greatly reduces the solution resistance;

[0139] (5) The accurate control of temperature and pressure ensures that the reaction is carried out under the best conditions.

[0140] Most importantly, the design takes into account the needs of laboratory research and industrial expansion at the same time, adopts the modular design concept, and can be flexibly expanded according to the production capacity demand.

[0141] In the description of the application, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. The illustrative description of the above terms in the specification does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0142] In addition, the terms "first", "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0143] Although the embodiments of the application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the application.

Claims

1. A method for preparing epoxidized olefins based on organic electrochemical synthesis, characterized in that: The method comprises: adding an electrolyte containing corresponding anions into a sealed pressurized electrolytic cell according to a reaction path selected for the epoxidation reaction of the olefin; The epoxidation reaction of olefins is carried out under electrocatalysis in the sealed pressurized electrolytic cell to carry out the epoxidation reaction with target selectivity and obtain the epoxidized olefin with target yield.

2. The method for preparing epoxidized olefins based on organic electrochemical synthesis according to claim 1, characterized in that: The adding of the corresponding anions into the sealed pressurized electrolytic cell according to the reaction path selected for the epoxidation reaction of the olefin comprises: According to the direct oxidation pathway selected for the epoxidation reaction of the olefin, an electrolyte containing a conductive salt of BF4- anions is added to a sealed pressurized electrolytic cell; According to the indirect oxidation route selected for the olefin epoxidation reaction, an electrolyte containing a conductive salt of TFS I- anions is added to a sealed pressurized electrolytic cell.

3. The method for preparing epoxidized olefins based on organic electrochemical synthesis according to claim 1 or 2, characterized in that: The method further comprises: During the electrocatalytic epoxidation of the olefin, the concentration of the target anion in the epoxidation of the olefin is monitored in real time; The type and proportion of the corresponding anions in the electrolyte are adjusted based on the concentration of the target anions.

4. The method for preparing epoxidized olefins based on organic electrochemical synthesis according to claim 3, characterized in that: The real-time monitoring of the concentration of the target anion in the epoxidation reaction of the olefin comprises: The concentration of target anions in the epoxidation reaction of the olefins was monitored in real time based on electrochemical-Raman coupling.

5. The method for preparing epoxidized olefins based on organic electrochemical synthesis according to claim 1, characterized in that: The epoxidation reaction of olefins carried out in an electrolytic cell under electrocatalysis comprises: producing hydrogen peroxide at the cathode of the electrolytic cell based on a two-electron reduction reaction of oxygen; The epoxidation reaction of olefins is carried out under electrocatalysis based on the hydrogen peroxide at the anode of the electrolytic cell.

6. The method for preparing epoxidized olefins based on organic electrochemical synthesis according to claim 5, characterized in that: The cathode of the electrolytic cell is selected from one or more of carbon materials, modified precious metals, and modified alloys.

7. The method for preparing epoxidized olefins based on organic electrochemical synthesis according to claim 5, characterized in that: The anode of the electrolytic cell is selected from one or more of platinum, gold, palladium, tin, platinum alloy, gold alloy, palladium alloy, and tin alloy.

8. The method for preparing epoxidized olefins based on organic electrochemical synthesis according to claim 1, characterized in that: The electrolyte further includes water and an organic solvent, and the volume ratio of the water to the organic solvent is (10:90) to (50:50).

9. The method for preparing epoxidized olefins based on organic electrochemical synthesis according to claim 8, characterized in that: The organic solvent is selected from one or more of acetonitrile, methanol, ethanol and tetrahydrofuran.

10. The method for preparing epoxidized olefins based on organic electrochemical synthesis according to claim 1, characterized in that: The pressure in the closed pressurized environment is 0.5 to 5 bar; The reaction temperature of the epoxidation reaction is 25-40° C., and the current density in the electrocatalysis is 5-50 mA / cm 2 .

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