A method for preparing vinyl ethylene carbonate

Abstract

This invention relates to the field of chemical synthesis technology, specifically disclosing a method for preparing vinyl ethylene carbonate. The method uses glycidyl as a starting material, first converting it to glycidaldehyde via a mild oxidation reaction with high selectivity. Then, using a cross-linked imidazole polymeric ionic liquid as a catalyst, glycidaldehyde undergoes an atom-economical cycloaddition reaction with carbon dioxide to construct a cyclic carbonate intermediate. Finally, under catalytic conditions, a condensation reaction introduces a vinyl functional group to obtain the vinyl ethylene carbonate product. This invention uses widely available, low-toxicity, and inexpensive glycidyl instead of highly toxic raw materials, and utilizes greenhouse gas carbon dioxide as a carbonyl source for resource utilization. The process route is highly atom-economical, the reaction conditions are mild, and the catalyst is easy to separate, recover, and recycle, effectively solving the prominent problems of high raw material toxicity, expensive catalysts, and difficult byproduct treatment in traditional preparation techniques.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, and in particular to a method for preparing vinyl ethylene carbonate. Background Technology

[0002] Vinyl ethylene carbonate (VEC) is a functional organic compound containing both vinyl and carbonate groups. It possesses excellent reactivity and chemical stability. Its molecular structure allows it to participate in free radical polymerization reactions and promote the formation of a stable solid electrolyte interphase (SEI) film during the charging and discharging process of lithium-ion batteries, thus holding an important position in the field of electrolyte additives. VEC has a wide range of applications, serving as a solvent, polymer additive, and organic synthesis intermediate for the synthesis of functionalized polymers, lactones, and other fine chemical products. However, in current industrial applications, its core application is concentrated in the field of lithium-ion battery electrolytes. Typically, only 1% to 5% of VEC needs to be added to lithium-ion battery electrolytes to form a dense and stable SEI film on the negative electrode surface. This effectively prevents solvent co-intercalation, inhibits electrolyte decomposition, and significantly improves battery cycle performance, high-temperature storage performance, and safety. This has significant practical implications for the development of core areas relying on lithium-ion batteries, such as new energy vehicles, energy storage, and consumer electronics, and is one of the key supports for promoting the high-quality development of the lithium battery industry.

[0003] Currently, the commonly used methods for preparing vinyl ethylene carbonate (VEC) in this field are mainly divided into three categories, each with varying degrees of shortcomings, making it difficult to meet the actual needs of industrial-scale production. Among these, the direct cyclization method of haloolefins is a relatively common route. This method uses 3,4-dichlorobutene as a raw material. Under inert gas protection, 3,4-dichlorobutene is dissolved in an organic solvent with an inorganic base and a specific metal ligand catalyst, and the reaction is carried out at 80-85°C for 8-12 hours. After the reaction, high-purity VEC is obtained by filtration, concentration to remove the solvent, and vacuum distillation, with a yield of approximately 90%. However, the inorganic salt byproducts generated during this route require additional post-processing and separation, increasing the process steps and production costs. Furthermore, the catalyst system used is relatively complex, containing phosphine ligands and palladium salts, resulting in high catalyst costs.

[0004] Transesterification is another commonly used preparation route. This method uses halogenated hydrocarbons or aromatic hydrocarbons as solvents and organic amines as initiators and acid-binding agents. 3,4-Butenediol reacts with solid phosgene at 0–10°C, yielding a crude product with a purity of up to 98% and a yield exceeding 70%. However, the solid phosgene used in this route is highly toxic, posing a serious threat to the safety of operators and generating large amounts of organic amine hydrochloride byproducts. Furthermore, waste treatment is difficult and costly, resulting in significant safety hazards and environmental pressures.

[0005] The direct synthesis of epoxides from CO2 is a preparation route that has attracted attention in recent years. This method uses vinyl ethylene oxide and CO2 as raw materials, reacting them under the catalysis of porous carbon catalyzed by hydroxyimidazolium phenolic resin to produce VEC. The reaction conditions are a temperature of 100-140℃ and a pressure of 1-3 MPa, with a product yield of over 80%. However, the preparation process of the catalyst used in this method is complex and the production cycle is long, resulting in high catalyst costs. Furthermore, the use of toxic reagents such as chloromethyl ether and organic solvents in the preparation process not only increases the safety risks of the production process but also increases the pressure on environmental treatment, which is not conducive to achieving large-scale and green production.

[0006] Therefore, developing a simple, low-cost, safe, environmentally friendly, and large-scale VEC preparation method has become a research hotspot and urgent need in this field. Summary of the Invention

[0007] In view of the problems that existing technologies for preparing vinyl ethylene carbonate generally have, such as complicated process steps, high cost of catalysts or raw materials, high risk of using highly toxic substances, or difficulty in handling by-products, this invention provides a method for preparing vinyl ethylene carbonate.

[0008] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: This invention provides a method for preparing vinyl ethylene carbonate, comprising the following steps: S1, glycidyl ether and an oxidizing agent are oxidized in an organic solvent to obtain glycidaldehyde; S2, the glycidaldehyde and carbon dioxide are subjected to a cycloaddition reaction under the catalysis of the cross-linked imidazole polymeric ionic liquid shown in formula (I) to obtain the cyclic carbonate intermediate shown in formula (II); S3, the cyclic carbonate intermediate and the aliphatic aldehyde undergo a condensation reaction under catalytic conditions to obtain vinyl ethylene carbonate as shown in formula (Ⅲ); .

[0009] Compared to existing technologies, the method for preparing vinyl ethylene carbonate provided by this invention uses glycidyl ether, which is widely available, inexpensive, and has low toxicity, as a starting material. First, glycidyl ether is selectively converted to glycidaldehyde through a mild oxidation reaction. Then, using a cross-linked imidazole polymeric ionic liquid as a catalyst, glycidaldehyde undergoes an atom-economical cycloaddition reaction with carbon dioxide to prepare a cyclic carbonate intermediate. Finally, a vinyl functional group is introduced through a condensation reaction to successfully obtain the vinyl ethylene carbonate product. This three-step reaction process features mild reaction conditions and high selectivity, effectively improving the yield and purity of VEC.

[0010] In the S2 cycloaddition reaction, the cross-linked imidazole polymeric ionic liquid shown in formula (Ⅰ) is used as a catalyst. This catalyst has high catalytic activity and excellent selectivity, which can efficiently promote the cycloaddition reaction of glycidaldehyde and CO2, achieve an atom-economical reaction, and reduce the occurrence of side reactions. At the same time, CO2 participates in the cycloaddition step as a reactant, which not only realizes the resource utilization of greenhouse gases and reduces the cost of reaction raw materials, but also endows the skeleton of cyclic carbonate intermediates with abundant oxygen functional groups, effectively improving the activity of the subsequent S3 condensation reaction, and thus significantly improving the yield and purity of the final VEC product.

[0011] In summary, this invention effectively solves the problems commonly found in existing vinyl ethylene carbonate preparation technologies, such as high toxicity of raw materials, expensive catalysts, difficult treatment of by-products, and harsh process conditions. It provides a practical and feasible new process for the large-scale, clean, and low-cost production of vinyl ethylene carbonate, with good prospects for industrial application and significant socio-economic benefits.

[0012] As a specific embodiment of the present invention, the preparation method of the vinyl ethylene carbonate specifically includes the following steps: S1, glycidyl ether and oxidant are oxidized in an organic solvent to obtain glycidyl aldehyde reaction solution; anhydrous diethyl ether is added to the glycidyl aldehyde reaction solution for dilution, the solution is allowed to stand to precipitate chromium salt, filtered, and the filtrate is concentrated under reduced pressure to obtain glycidyl aldehyde. S2, the glycidaldehyde and carbon dioxide undergo a cycloaddition reaction under the catalysis of a cross-linked imidazole polymeric ionic liquid to obtain a cyclic carbonate intermediate reaction solution; dichloromethane is added to the cyclic carbonate intermediate reaction solution, mixed evenly, the cross-linked imidazole polymeric ionic liquid is removed by filtration, dichloromethane is removed from the obtained filtrate, and distillation is carried out under vacuum conditions to collect the fraction at 110℃~120℃ to obtain the cyclic carbonate intermediate; S3, the cyclic carbonate intermediate and the aliphatic aldehyde undergo a condensation reaction under catalytic conditions to obtain a VEC reaction solution; a saturated sodium chloride solution is added to the VEC reaction solution, and the solution is extracted with ethyl acetate. The extract is then subjected to vacuum distillation to obtain vinyl ethylene carbonate. The specific synthetic route is as follows:

[0013] Furthermore, in S1, the oxidant is pyridinium chlorochromate.

[0014] Using pyridinium chlorochromate as an oxidant can selectively oxidize the primary hydroxyl groups in glycidyl ether to aldehyde groups, effectively avoiding the problem of over-oxidation and formation of carboxylic acid byproducts that is easily caused by traditional strong oxidants, thus ensuring the purity and yield of the intermediate glycidaldehyde. Meanwhile, the reaction conditions of this oxidant are mild, the operation is safe, and the chromium salt byproduct generated after the reaction is a solid precipitate, which can be efficiently separated simply by settling and filtration, without complex post-processing steps. This significantly simplifies the operation process, reduces separation costs, and is more conducive to quality control and process integration in industrial-scale production.

[0015] Further, in S1, the organic solvent is at least one of dichloromethane, acetonitrile, or ethyl acetate.

[0016] The aforementioned solvents exhibit excellent solubility for both glycidyl ether and pyridinium chlorochromate oxidants, ensuring a homogeneous reaction system that promotes thorough oxidation and highly selective conversion. Furthermore, these solvents possess suitable chemical inertness, minimizing the likelihood of side reactions under oxidizing conditions. Their low boiling points facilitate rapid removal after the reaction via vacuum concentration, effectively reducing the interference of residual solvents on subsequent steps, simplifying post-processing, and enhancing the feasibility of continuous processing and product purity.

[0017] Further, in S1, the molar ratio of glycidol to oxidant is 1:1.2 to 1:2.0.

[0018] Preferably, in S1, the molar ratio of glycidol to oxidant is 1:1.2 to 1:1.5.

[0019] The above-mentioned proportion of oxidant ensures that the oxidative conversion of hydroxyl groups to aldehyde groups is sufficient and complete, effectively improving the reaction conversion rate and glycidaldehyde yield; at the same time, it avoids the risk of side reactions caused by excessive oxidant, which may lead to further oxidation of aldehyde groups to carboxylic acids.

[0020] Furthermore, in S1, the oxidation reaction is carried out at a temperature of 25°C to 30°C for a reaction time of 2 hours to 6 hours.

[0021] Preferably, in S1, the oxidation reaction takes 2 to 4 hours.

[0022] Within this temperature range, the oxidizing activity of pyridinium chlorochromate is moderate, effectively inhibiting violent reactions and byproduct formation caused by local overheating or temperature fluctuations.

[0023] Further, in S1, the volume ratio of the anhydrous diethyl ether to the organic solvent is 1:1 to 1.5:1, preferably 1:1 to 1.2:1.

[0024] Furthermore, in S2, the pressure of carbon dioxide gas during the cycloaddition reaction is maintained at 1 MPa to 3 MPa.

[0025] Preferably, in S2, the pressure of carbon dioxide gas during the cycloaddition reaction is maintained at 1.5 MPa to 2.5 MPa.

[0026] Furthermore, in S2, the amount of the cross-linked imidazole polymeric ionic liquid added is 1% to 5% of the mass of glycidaldehyde.

[0027] The amount of catalyst added above can ensure the efficient catalytic conversion of glycidaldehyde and carbon dioxide cycloaddition reaction under the premise of low catalyst cost.

[0028] Furthermore, in S2, the temperature of the addition reaction is 50℃~100℃, and the reaction time is 4h~8h.

[0029] Preferably, in S2, the temperature of the addition reaction is 70℃~90℃, and the reaction time is 4h~6h.

[0030] This temperature and time range is lower than the high-temperature conditions (100℃~140℃) and reaction time (approximately 10h) required for the traditional direct synthesis of epoxides-CO2, effectively reducing production energy consumption. Within this mild temperature range, the cross-linked imidazole polymeric ionic liquid provided by this invention maintains excellent catalytic activity, ensuring that glycidaldehyde and carbon dioxide undergo sufficient atom-economical cycloaddition. The catalytic efficiency and reaction selectivity are not affected by the mild reaction conditions, effectively reducing side reactions and ensuring the full progress of the cycloaddition reaction, thus guaranteeing atom economy and product conversion.

[0031] As a specific embodiment of the present invention, the preparation method of the cross-linked imidazole polymeric ionic liquid includes the following steps: S2-1, 1-vinylimidazole is reacted with 1,4-dichlorobenzyl to obtain an ionic liquid monomer; S2-2, an initiator and an organic solvent are added to the ionic liquid monomer to carry out a polymerization reaction, yielding the cross-linked imidazole polymeric ionic liquid. The reaction route is as follows:

[0032] This preparation method uses 1-vinylimidazolium and 1,4-dichlorobenzyl as raw materials, and the target catalyst can be obtained through a two-step reaction of quaternization and polymerization. The process is simple and the raw materials are readily available. The resulting cross-linked imidazolium-based polymeric ionic liquid is an insoluble solid and exists heterogeneously in the reaction system. After the reaction, it can be quickly separated from the product by filtration, making the operation simple. This catalyst can be recycled multiple times while maintaining stable activity, significantly reducing the cost per batch of catalysis. It combines high catalytic efficiency with excellent reusability, making it economical and practical.

[0033] Further, in S2-1, the molar ratio of 1-vinylimidazole to 1,4-dichlorobenzyl is 2:1 to 3:1.

[0034] Preferably, in S2-1, the molar ratio of 1-vinylimidazole to 1,4-dichlorobenzyl is 2.1:1 to 2.5:1.

[0035] Furthermore, in S2-1, the reaction temperature is 75℃~85℃, and the reaction time is 20h~30h.

[0036] Furthermore, in S2-2, the initiator is azobisisobutyronitrile.

[0037] Furthermore, in S2-2, the amount of the initiator added is 0.5% to 2% of the mass of the ionic liquid monomer.

[0038] Preferably, in S2-2, the amount of initiator added is 1% to 1.5% of the mass of the ionic liquid monomer.

[0039] Furthermore, in S2-2, the organic solvent is petroleum ether, and its volume ratio with the ionic liquid monomer is 2:1 to 5:1.

[0040] Preferably, in S2-2, the organic solvent is petroleum ether, and its volume ratio with the ionic liquid monomer is 3:1 to 4:1.

[0041] Furthermore, in S2-2, the specific steps of the polymerization reaction are as follows: first react at 60℃~70℃ for 1h~3h, then react at 70℃~80℃ for 1h~3h, and finally react at 80℃~90℃ for 1h~3h.

[0042] Furthermore, in S3, the fatty aldehyde is formaldehyde or acetaldehyde.

[0043] Furthermore, in S3, the molar ratio of the cyclic carbonate intermediate to the aliphatic aldehyde is 1:1 to 1:5.

[0044] Furthermore, in S3, the catalyst is a mixture of triethylamine and glacial acetic acid in a molar ratio of 1:0.5 to 1:1.

[0045] Preferably, in S3, the molar ratio of triethylamine to glacial acetic acid is 1:0.8 to 1:1.

[0046] The synergistic effect of triethylamine and glacial acetic acid can efficiently promote the condensation reaction under mild conditions, significantly improve the reaction selectivity, and effectively inhibit side reactions such as product polymerization or decomposition, thereby improving the yield and purity of vinyl ethylene carbonate.

[0047] Furthermore, in S3, the molar ratio of the cyclic carbonate intermediate to the aliphatic aldehyde is 1:1 to 1:5.

[0048] Preferably, in S3, the molar ratio of the cyclic carbonate intermediate to the aliphatic aldehyde is 1:1 to 1:2.

[0049] Further, in S3, the molar ratio of triethylamine to the cyclic carbonate intermediate is 0.05:1 to 0.2:1.

[0050] Preferably, in S3, the molar ratio of triethylamine to the cyclic carbonate intermediate is 0.08:1 to 0.12:1.

[0051] Furthermore, in S3, the temperature of the condensation reaction is 60℃~100℃, and the reaction time is 3h~5h.

[0052] Preferably, in S3, the temperature of the condensation reaction is 80℃~100℃.

[0053] In summary, this invention provides a method for preparing vinyl ethylene carbonate. The method uses glycidyl ether as a starting material, firstly converting it to glycidaldehyde via a mild oxidation reaction with high selectivity. Then, using a cross-linked imidazole polymeric ionic liquid as a catalyst, glycidaldehyde undergoes an atom-economical cycloaddition reaction with carbon dioxide to construct a cyclic carbonate intermediate. Finally, under catalytic conditions, a condensation reaction introduces a vinyl functional group to obtain the vinyl ethylene carbonate product. This invention uses widely available, low-toxicity, and inexpensive glycidyl ether to replace highly toxic raw materials, and utilizes greenhouse gas carbon dioxide as a carbonyl source for resource utilization. The process route is highly atom-economical, the reaction conditions are mild, and the catalyst is easy to separate, recover, and recycle. It effectively solves the prominent problems of high raw material toxicity, expensive catalysts, and difficult byproduct treatment in traditional preparation techniques, significantly improving product yield and purity. The prepared VEC product has high purity and high yield, meeting the application requirements of high-end fields such as lithium-ion battery electrolytes, and can be widely used in core areas relying on lithium-ion batteries, such as new energy vehicles, energy storage, and consumer electronics. This method provides a practical new approach for the large-scale, clean, and low-cost production of vinyl ethylene carbonate, and has good prospects for industrial application in fields such as lithium-ion battery electrolyte additives. Attached Figure Description

[0054] Figure 1 The glycidaldehyde prepared in Example 6 of this invention 1 H NMR spectrum; Figure 2 The cyclic carbonate intermediate prepared in Example 6 of this invention 1 H NMR spectrum; Figure 3 The vinyl ethylene carbonate prepared in Example 6 of this invention 1 H NMR spectrum. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0056] To better illustrate the present invention, further examples are provided below.

[0057] Example 1 This embodiment provides a method for preparing a cross-linked imidazole polymeric ionic liquid, comprising the following steps: Step a: Mix 1-vinylimidazole and 1,4-dichlorobenzyl in a molar ratio of 2.5:1, heat to 80°C, and react for 24 h to obtain the ionic liquid monomer; Step b: Add 1.5% (by mass) of azobisisobutyronitrile to the ionic liquid monomer, mix thoroughly, then add petroleum ether at a volume ratio of 3:1 (petroleum ether to ionic liquid monomer). First, react at 65°C for 2 hours, then at 75°C for 2 hours, and finally at 85°C for 2 hours. After the reaction is complete, precipitate, filter, wash, and dry to obtain the cross-linked imidazole polymeric ionic liquid. The reaction route is as follows:

[0058] Example 2 This embodiment provides a method for preparing a cross-linked imidazole polymeric ionic liquid, comprising the following steps: Step a: Mix 1-vinylimidazole and 1,4-dichlorobenzyl in a molar ratio of 3:1, heat to 75°C, and react for 30 h to obtain the ionic liquid monomer; Step b: Add 0.5% (by mass) of azobisisobutyronitrile to the ionic liquid monomer, mix thoroughly, then add petroleum ether at a volume ratio of 2:1 (petroleum ether to ionic liquid monomer). First, react at 70°C for 1 hour, then at 80°C for 1 hour, and finally at 90°C for 1 hour. After the reaction is complete, precipitate, filter, wash, and dry to obtain the cross-linked imidazole polymeric ionic liquid. The reaction route is as follows:

[0059] Example 3 This embodiment provides a method for preparing a cross-linked imidazole polymeric ionic liquid, comprising the following steps: Step a: Mix 1-vinylimidazole and 1,4-dichlorobenzyl in a molar ratio of 2:1, heat to 85°C, and react for 20 h to obtain the ionic liquid monomer; Step b: Add 2% (by mass) of azobisisobutyronitrile to the ionic liquid monomer, mix thoroughly, then add petroleum ether at a volume ratio of 5:1 (petroleum ether to ionic liquid monomer). First, react at 60°C for 3 hours, then at 70°C for 3 hours, and finally at 80°C for 1 hour. After the reaction, precipitate, filter, wash, and dry to obtain the cross-linked imidazole polymeric ionic liquid. The reaction route is as follows:

[0060] Example 4 This embodiment provides a method for preparing vinyl ethylene carbonate, comprising the following steps: S1, under nitrogen protection, 100 mL of dichloromethane, 13.5 g of pyridine chlorochromate and 3.70 g of glycidyl ether were added to a three-necked flask. The mixture was stirred at 30 °C for 2 h. After the reaction was complete, 110 mL of anhydrous diethyl ether was added to the reaction solution to dilute it. The mixture was stirred for 10 min to allow the chromium salt to fully precipitate. After standing, the solid was removed by vacuum filtration. The filtrate was collected and the solvent was removed by rotary evaporation under reduced pressure at 30 °C and 0.06 MPa to obtain 3.54 g of glycidyl ether.

[0061] S2, add the glycidaldehyde prepared in the above steps to the reaction vessel, and add 0.086g of the cross-linked imidazole polymeric ionic liquid prepared in Example 1. Seal the reaction vessel, check the air tightness, introduce CO2 to replace the air in the vessel three times, and then introduce CO2 to the initial pressure of 1.0MPa. React at 50°C for 8 hours. After the reaction is completed, cool the reaction vessel to room temperature, slowly release the remaining CO2, transfer the reaction solution to a beaker, add 30mL of dichloromethane, remove the cross-linked imidazole polymeric ionic liquid by vacuum filtration, collect the filtrate, and perform rotary evaporation on the obtained filtrate at 40°C and 0.06MPa vacuum to remove the solvent and obtain crude cyclic carbonate intermediate. Transfer the crude cyclic carbonate intermediate to a distillation flask, heat it under a vacuum of 0.5mmHg, and collect the fraction at 110~120°C to obtain 5.65g of pure cyclic carbonate intermediate.

[0062] S3. The cyclic carbonate intermediate prepared in the above steps was added to a three-necked flask, along with 7.91 g of formaldehyde solution (37 wt%), 0.40 g of triethylamine, and 0.21 g of glacial acetic acid. The mixture was magnetically stirred in an oil bath at 90 °C for 4 h. After the reaction was completed, the reaction system was cooled to room temperature, and 20 mL of saturated sodium chloride solution was added to the system. The mixture was then extracted with ethyl acetate. The supernatant was collected and transferred to a vacuum distillation apparatus. Vacuum distillation was performed in an oil bath at 100 °C and a vacuum degree of 0.02 MPa. The distillate was collected to obtain a colorless and transparent solution, which is the high-purity VEC product. The product weighed 5.54 g, with a yield of 98.05% and a purity of 99.37%.

[0063]

[0064] Example 5 This embodiment provides a method for preparing vinyl ethylene carbonate, comprising the following steps: S1, under nitrogen protection, 100 mL of acetonitrile, 14.3 g of pyridine chlorochromate and 3.70 g of glycidyl aldehyde were added to a three-necked flask and stirred at 25 °C for 4 h. After the reaction was complete, 120 mL of anhydrous diethyl ether was added to the reaction solution to dilute it and stirred for 10 min to allow the chromium salt to be fully precipitated. After standing, the solid was removed by suction filtration and the filtrate was collected. The solvent was removed by rotary evaporation under reduced pressure at 30 °C and 0.06 MPa to obtain 3.47 g of glycidyl aldehyde. S2, add the glycidaldehyde prepared in the above steps to the reaction vessel, and add 0.035g of the cross-linked imidazole polymeric ionic liquid prepared in Example 1. Seal the reaction vessel, check the air tightness, introduce CO2 to replace the air in the vessel three times, and then introduce CO2 to the initial pressure of 3.0MPa. React at 70℃ for 6h. After the reaction is completed, cool the reaction vessel to room temperature, slowly release the remaining CO2, transfer the reaction solution to a beaker, add 50mL of dichloromethane, remove the cross-linked imidazole polymeric ionic liquid by vacuum filtration, collect the filtrate, and perform rotary evaporation on the obtained filtrate at 40℃ and 0.06MPa vacuum to remove the solvent and obtain crude cyclic carbonate intermediate. Transfer the crude cyclic carbonate intermediate to a distillation flask, heat it under a vacuum of 0.5mmHg, and collect the fraction at 110~120℃ to obtain 5.56g of pure cyclic carbonate intermediate. S3. The cyclic carbonate intermediate prepared in the above steps was added to a three-necked flask, along with 11.62 g of formaldehyde solution (37 wt%), 0.25 g of triethylamine, and 0.11 g of glacial acetic acid. The mixture was magnetically stirred in an oil bath at 100 °C for 3 h. After the reaction was completed, the reaction system was cooled to room temperature, and 20 mL of saturated sodium chloride solution was added to the system. The mixture was then extracted with ethyl acetate. The supernatant was collected and transferred to a vacuum distillation apparatus. Vacuum distillation was performed in an oil bath at 100 °C and a vacuum degree of 0.02 MPa. The distillate was collected to obtain a colorless and transparent solution, which is the high-purity VEC product. The product weighed 5.42 g, with a yield of 95.95% and a purity of 99.12%.

[0065] Example 6 This embodiment provides a method for preparing vinyl ethylene carbonate, comprising the following steps: S1, under nitrogen protection, 100 mL of ethyl acetate, 16.2 g of pyridine chlorochromate and 3.70 g of glycidaldehyde were added to a three-necked flask and stirred at 25 °C for 2 h. After the reaction was complete, 100 mL of anhydrous diethyl ether was added to the reaction solution to dilute it, and the mixture was stirred for 10 min to allow the chromium salt to be fully precipitated. After standing, the solid was removed by suction filtration, and the filtrate was collected. The solvent was removed by rotary evaporation under reduced pressure at 30 °C and 0.06 MPa to obtain 3.60 g of glycidaldehyde. S2, add the glycidaldehyde prepared in the above steps to the reaction vessel, and add 0.072g of the cross-linked imidazole polymeric ionic liquid prepared in Example 1. Seal the reaction vessel, check the air tightness, introduce CO2 to replace the air in the vessel three times, and then introduce CO2 to the initial pressure of 2.0MPa. React at 80℃ for 4h. After the reaction is completed, cool the reaction vessel to room temperature, slowly release the remaining CO2, transfer the reaction solution to a beaker, add 40mL of dichloromethane, remove the cross-linked imidazole polymeric ionic liquid by vacuum filtration, collect the filtrate, and perform rotary evaporation on the obtained filtrate at 40℃ and 0.06MPa vacuum to remove the solvent and obtain crude cyclic carbonate intermediate. Transfer the crude cyclic carbonate intermediate to a distillation flask, heat it under a vacuum of 0.5mmHg, and collect the fraction at 110~120℃ to obtain 5.77g of pure cyclic carbonate intermediate. S3. The cyclic carbonate intermediate prepared in the above steps was added to a three-necked flask, along with 4.03 g of formaldehyde solution (37 wt%), 0.49 g of triethylamine, and 0.30 g of glacial acetic acid. The mixture was magnetically stirred in an oil bath at 80 °C for 3 h. After the reaction was completed, the reaction system was cooled to room temperature, and 20 mL of saturated sodium chloride solution was added to the system. The mixture was then extracted with ethyl acetate. The supernatant was collected and transferred to a vacuum distillation apparatus. Vacuum distillation was performed in an oil bath at 100 °C and a vacuum degree of 0.02 MPa. The distillate was collected to obtain a colorless and transparent solution, which is the high-purity VEC product. The product weighed 5.63 g, with a yield of 99.65% and a purity of 99.87%.

[0066] Example 7 This embodiment provides a method for preparing vinyl ethylene carbonate, comprising the following steps: S1, under nitrogen protection, 100 mL of dichloromethane, 21.5 g of pyridine chlorochromate and 3.70 g of glycidyl ether were added to a three-necked flask. The mixture was stirred at 25 °C for 3 h. After the reaction was complete, 150 mL of anhydrous diethyl ether was added to the reaction solution to dilute it. The mixture was stirred for 10 min to allow the chromium salt to precipitate. After standing, the solid was removed by vacuum filtration. The filtrate was collected and the solvent was removed by rotary evaporation under reduced pressure at 30 °C and 0.06 MPa to obtain 3.53 g of glycidyl ether. S2, add the glycidaldehyde prepared in the above steps to the reaction vessel, and add 0.176g of the cross-linked imidazole polymeric ionic liquid prepared in Example 1. Seal the reaction vessel, check the air tightness, introduce CO2 to replace the air in the vessel three times, and then introduce CO2 to the initial pressure of 2.5MPa. React at 100℃ for 4h. After the reaction is completed, cool the reaction vessel to room temperature, slowly release the remaining CO2, transfer the reaction solution to a beaker, add 45mL of dichloromethane, remove the cross-linked imidazole polymeric ionic liquid by vacuum filtration, collect the filtrate, and perform rotary evaporation on the obtained filtrate at 40℃ and 0.06MPa vacuum to remove the solvent and obtain crude cyclic carbonate intermediate. Transfer the crude cyclic carbonate intermediate to a distillation flask, heat it under a vacuum of 0.5mmHg, and collect the fraction at 110~120℃ to obtain 5.65g of pure cyclic carbonate intermediate. S3. The cyclic carbonate intermediate prepared in the above steps was added to a three-necked flask, along with 5.36 g of acetaldehyde solution (40 wt%), 0.98 g of triethylamine, and 0.30 g of glacial acetic acid. The mixture was magnetically stirred in an oil bath at 60 °C for 5 h. After the reaction was completed, the reaction system was cooled to room temperature, and 20 mL of saturated sodium chloride solution was added to the system. The mixture was then extracted with ethyl acetate. The supernatant was collected and transferred to a vacuum distillation apparatus. Vacuum distillation was performed in an oil bath at 100 °C and a vacuum degree of 0.02 MPa. The distillate was collected to obtain a colorless and transparent solution, which is the high-purity VEC product. The product weighed 5.36 g, with a yield of 94.87% and a purity of 99.03%.

[0067] Comparative Example 1 This comparative example provides a method for preparing vinyl ethylene carbonate, which differs from Example 6 only in that the oxidation reaction in step S1 is omitted, and a cycloaddition reaction is directly carried out with glycidyl. The specific preparation method is as follows: S1, 3.70 g glycidyl ether was added to the reaction vessel, along with 0.072 g of the cross-linked imidazole polymeric ionic liquid prepared in Example 1. The reaction vessel was sealed, and the airtightness was checked. CO2 was introduced to replace the air in the vessel three times. Then, CO2 was introduced until the initial pressure was 2.0 MPa. The reaction was carried out at 80°C for 4 hours. After the reaction was completed, the reaction vessel was cooled to room temperature, and the remaining CO2 was slowly released. The reaction solution was transferred to a beaker, and 40 mL of dichloromethane was added. The cross-linked imidazole polymeric ionic liquid was removed by vacuum filtration. The filtrate was collected, and the obtained filtrate was subjected to rotary evaporation at 40°C and 0.06 MPa vacuum to remove the solvent, yielding a crude cyclic carbonate intermediate. The crude cyclic carbonate intermediate was transferred to a distillation flask and heated under a vacuum of 0.5 mmHg. The fraction at 110~120°C was collected to obtain 1.92 g of pure cyclic carbonate intermediate. S2, the cyclic carbonate intermediate prepared in the above steps was added to a three-necked flask, along with 1.34 g of formaldehyde solution (37 wt%), 0.16 g of triethylamine, and 0.10 g of glacial acetic acid. The mixture was magnetically stirred in an oil bath at 80 °C for 3 h. After the reaction was completed, the reaction system was cooled to room temperature, and 20 mL of saturated sodium chloride solution was added to the system. The mixture was then extracted with ethyl acetate. The supernatant was collected and transferred to a vacuum distillation apparatus. Vacuum distillation was performed in an oil bath at 100 °C and a vacuum degree of 0.02 MPa. The distillate was collected to obtain a colorless and transparent solution, which was the VEC product. The product weighed 1.16 g, with a yield of 20.53% and a purity of 48.50%.

[0068] Comparative Example 2 This comparative example provides a method for preparing vinyl ethylene carbonate, which differs from Example 6 only in that no catalyst is added in S2. The specific steps are as follows: S1, the same as in Example 6, will not be described again here; S2, add the glycidaldehyde prepared in the above steps to the reaction vessel, seal the reaction vessel, check the air tightness, introduce CO2 to replace the air in the vessel three times, then introduce CO2 to the initial pressure of 2.0 MPa, react at 80℃ for 4 hours, after the reaction is completed, cool the reaction vessel to room temperature, slowly release the remaining CO2, transfer the reaction solution to a distillation flask, heat under a vacuum of 0.5 mmHg, collect the fraction at 110~120℃, and obtain 1.38 g of pure cyclic carbonate intermediate; S3. The cyclic carbonate intermediate prepared in the above steps was added to a three-necked flask, along with 0.96 g of formaldehyde solution (37 wt%), 0.12 g of triethylamine, and 0.071 g of glacial acetic acid. The mixture was magnetically stirred in an oil bath at 80 °C for 3 h. After the reaction was completed, the reaction system was cooled to room temperature, and 20 mL of saturated sodium chloride solution was added to the system. The mixture was then extracted with ethyl acetate. The supernatant was collected and transferred to a vacuum distillation apparatus. Vacuum distillation was performed in an oil bath at 100 °C and a vacuum degree of 0.02 MPa. The distillate was collected to obtain a colorless and transparent solution, which was the VEC product. The product weighed 1.07 g, with a yield of 18.94% and a purity of 39.07%.

[0069] Comparative Example 3 This comparative example provides a method for preparing vinyl ethylene carbonate, which differs from Example 6 only in that the cross-linked imidazole polymeric ionic liquid catalyst in S2 is replaced with a PILs-XSS catalyst. The specific steps are as follows: S1, the same as in Example 6, will not be repeated here; S2, add the glycidaldehyde prepared in the above steps to the reaction vessel, add 0.072g of PILs-XSS catalyst, seal the reaction vessel, check the air tightness, introduce CO2 to replace the air in the vessel three times, then introduce CO2 to the initial pressure of 2.0MPa, react at 80℃ for 4h. After the reaction is completed, cool the reaction vessel to room temperature, slowly release the remaining CO2, transfer the reaction solution to a beaker, add 40mL of dichloromethane, remove the cross-linked imidazole polymeric ionic liquid by vacuum filtration, collect the filtrate, and perform rotary evaporation on the obtained filtrate at 40℃ and 0.06MPa vacuum to remove the solvent, and obtain crude cyclic carbonate intermediate. Transfer the crude cyclic carbonate intermediate to a distillation flask, heat at a vacuum of 0.5mmHg, collect the fraction at 110~120℃, and obtain 2.76g of pure cyclic carbonate intermediate. S3. The cyclic carbonate intermediate prepared in the above steps was added to a three-necked flask, along with 1.93 g of formaldehyde solution (37 wt%), 0.23 g of triethylamine, and 0.14 g of glacial acetic acid. The mixture was magnetically stirred in an oil bath at 80 °C for 3 h. After the reaction was completed, the reaction system was cooled to room temperature, and 20 mL of saturated sodium chloride solution was added to the system. The mixture was then extracted with ethyl acetate. The supernatant was collected and transferred to a vacuum distillation apparatus. Vacuum distillation was performed in an oil bath at 100 °C and a vacuum degree of 0.02 MPa. The distillate was collected to obtain a colorless and transparent solution, which was the VEC product. The product weighed 2.61 g, with a yield of 46.19% and a purity of 83.01%.

[0070] The preparation method of the above-mentioned PILs-XSS catalyst includes the following steps: 1-Ethyleneimidazolium (18.82 g), 1,2-dibromoethane (18.79 g), and acrylamide (7.11 g) were added to a three-necked flask and reacted at 80 °C for 6 h to obtain an ionic liquid monomer. Then, 2,2-azobisisobutyronitrile (0.22 g) was added as an initiator and stirred thoroughly until homogeneous. The mixture was then added to a three-necked flask containing petroleum ether and subjected to nitrogen protection throughout the reaction. The reaction was carried out under magnetic stirring: first at 65 °C for 2 h, then at 75 °C for 2 h, and then at 85 °C for 2 h. After the reaction was completed, the mixture was precipitated, filtered, washed, and dried to obtain the PILs-XSS catalyst.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing vinyl ethylene carbonate, characterized in that, Includes the following steps: S1, glycidyl ether and an oxidizing agent are oxidized in an organic solvent to obtain glycidaldehyde; S2, the glycidaldehyde and carbon dioxide are subjected to a cycloaddition reaction under the catalysis of the cross-linked imidazole polymeric ionic liquid shown in formula (I) to obtain the cyclic carbonate intermediate shown in formula (II); S3, the cyclic carbonate intermediate and the aliphatic aldehyde undergo a condensation reaction under catalytic conditions to obtain vinyl ethylene carbonate as shown in formula (Ⅲ); 。 2. The method for preparing vinyl ethylene carbonate as described in claim 1, characterized in that, In S1, the oxidant is pyridinium chlorochromate; and / or In S1, the organic solvent is at least one of dichloromethane, acetonitrile, or ethyl acetate; and / or In S1, the molar ratio of glycidol to oxidant is 1:1.2 to 1:2.

0.

3. The method for preparing vinyl ethylene carbonate as described in claim 1 or 2, characterized in that, In S1, the oxidation reaction is carried out at a temperature of 25°C to 30°C for 2 hours to 6 hours.

4. The method for preparing vinyl ethylene carbonate as described in claim 1, characterized in that, In S2, the pressure of carbon dioxide gas during the cycloaddition reaction is maintained at 1 MPa to 3 MPa; and / or In S2, the amount of the cross-linked imidazole polymeric ionic liquid added is 1% to 5% of the mass of glycidaldehyde.

5. The method for preparing vinyl ethylene carbonate as described in claim 1 or 4, characterized in that, In S2, the cycloaddition reaction is carried out at a temperature of 50℃~100℃ for a reaction time of 4h~8h.

6. The method for preparing vinyl ethylene carbonate as described in claim 1 or 4, characterized in that, In S2, the preparation method of the cross-linked imidazole polymeric ionic liquid includes the following steps: S2-1, 1-vinylimidazole is reacted with 1,4-dichlorobenzyl to obtain an ionic liquid monomer; S2-2, an initiator and an organic solvent are added to the ionic liquid monomer to carry out a polymerization reaction, thereby obtaining the cross-linked imidazole polymeric ionic liquid.

7. The method for preparing vinyl ethylene carbonate as described in claim 6, characterized in that, In S2-1, the molar ratio of 1-vinylimidazole to 1,4-dichlorobenzyl is 2:1 to 3:1; and / or In S2-1, the reaction temperature is 75℃~85℃ and the reaction time is 20h~30h.

8. The method for preparing vinyl ethylene carbonate as described in claim 6, characterized in that, In S2-2, the initiator is azobisisobutyronitrile; and / or In S2-2, the amount of initiator added is 0.5% to 2% of the mass of the ionic liquid monomer; and / or In S2-2, the organic solvent is petroleum ether, and its volume ratio to the ionic liquid monomer is 2:1 to 5:1; and / or In S2-2, the specific steps of the polymerization reaction are as follows: first react at 60℃~70℃ for 1h~3h, then react at 70℃~80℃ for 1h~3h, and finally react at 80℃~90℃ for 1h~3h.

9. The method for preparing vinyl ethylene carbonate according to claim 1, characterized in that, In S3, the fatty aldehyde is formaldehyde or acetaldehyde; and / or In S3, the catalyst is a mixture of triethylamine and glacial acetic acid in a molar ratio of 1:0.5 to 1:

1.

10. The method for preparing vinyl ethylene carbonate as described in claim 9, characterized in that, In S3, the molar ratio of the cyclic carbonate intermediate to the aliphatic aldehyde is 1:1 to 1:5; and / or In S3, the molar ratio of triethylamine to the cyclic carbonate intermediate is 0.05:1 to 0.2:1; and / or In S3, the temperature of the condensation reaction is 60℃~100℃, and the reaction time is 3h~5h.

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