A bipyridine-based multifunctional ionic liquid and its preparation method and application

Abstract

Disclosed are bipyridyl-based multifunctional ionic liquids, their preparation methods, and applications. The bipyridyl-based multifunctional ionic liquids of the present invention are designated as [C2H4]2O[Py]2ZnBr2Cl2, [C2H4]2O[MeOPy]2ZnBr2Cl2, and [C2H4]2O[EOPy]2ZnBr2Cl2, respectively. The present invention also includes preparation methods and applications of the bipyridyl-based multifunctional ionic liquids. The cations of the bipyridyl-based multifunctional ionic liquid of the present invention contain bipyridyl cationic groups with different ether groups, which are characterized by lower price, better biodegradability and biocompatibility; Zn metal has the characteristics of low toxicity and high abundance, and is suitable for constructing structurally diverse, low-cost, and environmentally friendly ionic liquids; the catalyst is applied to the cycloaddition reaction of CO2 and epoxy substrates at room temperature and pressure to prepare cyclic carbonates. The catalyst of the present invention has very mild CO2 catalytic conversion conditions, is low-cost, highly efficient, and environmentally friendly, and has the characteristics of green enzyme-like catalytic conversion, can avoid the addition of solvents and additives, has low energy consumption, and can significantly reduce the production cost of cyclic carbonates.

Description

Technical Field

[0001] The present invention relates to a multifunctional ionic liquid and a preparation method and application thereof, in particular to a bipyridine-based multifunctional ionic liquid and a preparation method and application thereof. Background Art

[0002] Global climate change caused by the greenhouse effect has become a major environmental issue that requires high attention. World industrialization and the extensive use of fossil fuels have led to a sharp increase in carbon dioxide concentrations. Therefore, the resulting global warming and climate change have become serious challenges facing the world [Chemical Engineering Journal 493(2024)152345 and Nature Communications 15(2024)1-9]. Carbon capture and utilization (CCU) is an effective method to reduce carbon dioxide emissions into the atmosphere [Science of The Total Environment 948(2024)174873]. Using CO2 as a cheap and readily available C1 resource, a variety of high-value-added products can be catalytically prepared. Among them, the process of cyclization of epoxides with CO2 to form cyclic carbonates has 100% atom economy and has always attracted the attention of scientific researchers. As a highly soluble, low-toxic, green, environmentally friendly, and biodegradable compound, cyclic carbonate has broad application prospects. It can be widely used as a polar aprotic solvent, lithium battery electrolyte, fuel additive, and chemical raw material for synthesizing dimethyl carbonate, polycarbonate, and resin. It has broad market demand and high added value.

[0003] To date, homogeneous and heterogeneous catalytic systems, such as ionic liquids, metal-organic frameworks, and polyionic liquids, have been developed to generate cyclic carbonates. However, obtaining high yields of cyclic carbonates usually requires additional nucleophilic co-catalysts and relatively harsh conditions such as high temperature and high pressure. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a new bipyridyl multifunctional ionic liquid and its preparation method and application. The bipyridyl multifunctional ionic liquid can be used as a catalyst to prepare cyclic carbonates under very mild conditions of normal temperature and pressure.

[0005] Furthermore, the bipyridyl multifunctional ionic liquid can be used as a catalyst to prepare cyclic carbonates under very mild enzyme-like conditions at room temperature and pressure.

[0006] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0007] The bipyridyl multifunctional ionic liquid of the present invention has any of the following three structural formulas:

[0008]

[0009] They were named [C2H4]2O[Py]2ZnBr2Cl2, [C2H4]2O[MeOPy]2ZnBr2Cl2 and [C2H4]2O[EOPy]2ZnBr2Cl2 respectively.

[0010] The preparation method of the bipyridyl multifunctional ionic liquid of the present invention comprises the following steps: dissolving a pyridine compound in ethyl acetate under an inert atmosphere, stirring uniformly, adding 2,2'-dibromodiethyl ether dropwise, reacting under reflux at a certain temperature for a period of time, removing the ethyl acetate by distillation under reduced pressure, adding an organic solvent with relatively low polarity, stirring, filtering, removing the organic solvent by distillation under reduced pressure from the filtrate, and drying to obtain a bipyridyl bromide salt; mixing the bipyridyl bromide salt with ZnCl2, stirring at a certain temperature until a uniform viscous liquid is obtained; and drying the obtained viscous liquid to remove impurities to obtain a bipyridyl multifunctional ionic liquid.

[0011] By adopting the above technical solution, bipyridine-based multifunctional ionic liquids can be prepared. The method is simple, low-cost, easy and controllable to operate, and easy to scale up.

[0012] Preferably, the pyridine compound is at least one of pyridine, 2-methoxypyridine or 2-ethoxypyridine.

[0013] Preferably, the molar ratio of the raw materials is: pyridine compound: 2,2'-dibromodiethyl ether = 2-2.2: 1-1.1. Bispyridinium bromide: ZnCl2 = 1-1.05: 1-1.05. By adopting the above technical solution, a higher yield can be obtained.

[0014] Preferably, after adding 2,2'-dibromodiethyl ether, the mixture is refluxed at 80-90°C for 24-48 hours.

[0015] Preferably, the organic solvent with relatively low polarity is at least one of ethyl acetate, toluene, acetone, and dichloromethane. By adopting the above technical solution, a better washing effect can be achieved.

[0016] Preferably, the inert atmosphere is a nitrogen atmosphere. The drying method adopted after the filtrate is distilled under reduced pressure to remove the organic solvent is vacuum drying. By adopting the above technical solution, a better protection or drying effect can be obtained at a lower cost. The use of other inert atmospheres or drying methods is also feasible.

[0017] Preferably, the bispyridinium bromide is mixed with ZnCl2 and stirred at 80-120°C for 20-30 hours until a uniform viscous liquid is obtained.

[0018] Preferably, the obtained viscous liquid is dried in an oven at 50-70°C overnight to remove impurities.

[0019] The present invention uses the bipyridyl multifunctional ionic liquid as a catalyst for synthesizing cyclic carbonates from carbon dioxide and epoxides. By adopting the above technical solution, the production cost of cyclic carbonates is greatly reduced.

[0020] Preferably, the bipyridyl multifunctional ionic liquid is mixed with an epoxy compound as a catalyst, and the reaction is carried out for more than 24 hours (preferably 24 hours) under the conditions of a carbon dioxide pressure of 0.1 to 0.12 MPa and a temperature of 25 to 60°C.

[0021] By adopting the above technical solution, a better catalytic effect is achieved.

[0022] Preferably, the molar ratio of the bipyridyl multifunctional ionic liquid to the epoxy compound is 0.5-3.2%, more preferably 2.5-3.0%, that is, the amount of the bipyridyl multifunctional ionic liquid is equivalent to 0.5-3.2% of the amount of the epoxy compound.

[0023] By adopting the above technical solution, a better catalytic effect is achieved.

[0024] Preferably, the epoxy compound is at least one of epichlorohydrin, epibromohydrin, tert-butyl glycidyl ether, glycidyl phenyl ether, and epoxystyrene.

[0025] By adopting the above technical solution, a good catalytic effect is achieved in producing cyclic carbonates. For other epoxy compounds with similar structures, the bipyridyl multifunctional ionic liquid also has a good catalytic effect.

[0026] The present invention provides a method for preparing a novel multifunctional ionic liquid containing ether-based bipyridyl groups. These liquids exhibit low toxicity, excellent biocompatibility and solubility, and are readily biodegradable. Their application in the CO2 cycloaddition reaction to synthesize cyclic carbonates aligns with the requirements of green carbon science and sustainable development, enhancing the performance of ionic liquids in absorbing and converting CO2 while avoiding the use of solvents and co-catalysts. Based on the versatility and rich designability of ether-functionalized ionic liquids, novel green ionic liquid catalytic materials suitable for the mild, enzyme-like catalytic conversion of CO2 into high-value-added cyclic carbonates at ambient temperature and pressure have been developed. This overcomes the harsh conditions typically required for ionic liquid-catalyzed CO2 conversion, demonstrating significant scientific value and promising industrial applications.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention provides a novel bipyridine Zn-based ionic liquid;

[0029] (2) The cation of the ionic liquid used in this method is a bipyridine group containing a diethyl ether group. The introduction of the ether group greatly increases the intermolecular free volume, facilitates mass transfer between adjacent molecules, reduces the viscosity of the ionic liquid, and significantly increases its absorption selectivity for CO2. At the same time, the Zn metal in the anion of the ionic liquid has the characteristics of high sustainability and low toxicity, making it easy to construct a new type of ionic liquid with diverse structures and low cost;

[0030] (3) A novel bipyridine multifunctional Zn-based ionic liquid with a unique structure is used as a novel catalytic material for the cycloaddition reaction of CO2 with epoxy substrates to prepare cyclic carbonates. Compared with conventional catalytic materials, the CO2 catalytic conversion conditions of the present invention are simple, easy to control, and efficient, and avoid the addition of external solvents and additives. The reaction conditions are very mild (0.1-0.12MPa CO2 pressure, 25-60°C), and the energy consumption is low, thereby greatly reducing the production cost of cyclic carbonates. Moreover, ionic liquids containing different side chains can significantly regulate the room temperature and pressure enzymatic conversion of CO2 by ether-functionalized ionic liquids, which has important scientific value and industrial application prospects.

[0031] The cations of the bipyridyl-based multifunctional ionic liquid of the present invention contain bipyridyl cationic groups with different ether groups. Compared with common imidazole ionic liquids, it has the characteristics of lower price, better biodegradability and biocompatibility. Zn metal has the characteristics of low toxicity and high abundance, which is suitable for constructing structurally diverse, low-cost, and environmentally friendly ionic liquids. The novel bipyridyl-based multifunctional Zn-based ionic liquid with unique structure is used as a new and efficient catalytic material for the cycloaddition of CO2 and epoxy substrates to prepare cyclic carbonates at room temperature and pressure. Compared with conventional catalytic materials, the catalyst of the present invention has very mild CO2 catalytic conversion conditions, low price, high efficiency and environmentally friendly, and has the characteristics of green enzyme-mimicking catalytic conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the FT-IR graph of the bipyridyl multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2 of Example 1 of the present invention;

[0033] Figure 2 The present invention is Example 1 of the bipyridyl multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2 1 HNMR spectrum;

[0034] Figure 3 The chlorinated cyclic carbonate synthesized in Example 4 of the present invention 1 H NMR spectrum;

[0035] Figure 4This is a line graph showing the effect of the amount of the bipyridine multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2 used in Example 5 of the present invention on the catalytic effect of the epoxide cycloaddition;

[0036] Figure 5 This is a line graph showing the effect of time on the cycloaddition reaction of epoxides catalyzed by the bipyridine multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2 according to Example 5 of the present invention;

[0037] Figure 6 The brominated cyclic carbonate synthesized in Example 6 of the present invention 1 H NMR spectrum. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0039] The raw materials used in the examples of the present invention were all obtained through conventional commercial channels.

[0040] Example 1

[0041] The bipyridyl multifunctional ionic liquid catalyst prepared in this embodiment has the following structural formula:

[0042] Expressed by [C2H4]2O[Py]2ZnBr2Cl2.

[0043] Preparation method of [C2H4]2O[Py]2ZnBr2Cl2 ionic liquid in this embodiment:

[0044] Under nitrogen, pyridine was dissolved in ethyl acetate and stirred until homogeneous. 2,2'-dibromodiethyl ether was added dropwise and stirred until homogeneous (molar ratio of pyridine: 2,2'-dibromodiethyl ether = 2:1). The mixture was refluxed at 80°C for 48 hours, and the ethyl acetate was removed by vacuum distillation. The mixture was washed three times with ethyl acetate and stirred. The filtrate was then vacuum distilled to remove the organic solvent and dried at 80°C for 24 hours to obtain the bispyridinium bromide salt. The bispyridinium bromide salt ionic liquid was then mixed with ZnCl2 (molar ratio of bispyridinium bromide: ZnCl2 = 1:1) and added to a round-bottom flask. The mixture was stirred at 100°C for 24 hours until a uniform viscous liquid was obtained. The viscous liquid was then dried in an oven at 60°C overnight to remove impurities, yielding the bispyridyl-based multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2.

[0045] Figure 1 This is the FT-IR graph of the bipyridyl multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2 of Example 1 of the present invention;

[0046] Figure 2The present invention is Example 1 of the bipyridyl multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2 1 HNMR spectrum.

[0047] Example 2

[0048] The bipyridyl multifunctional ionic liquid catalyst prepared in this embodiment has the following structural formula:

[0049] Expressed by [C2H4]2O[MeOPy]2ZnBr2Cl2.

[0050] Preparation method of [C2H4]2O[MeOPy]2ZnBr2Cl2 ionic liquid in this embodiment:

[0051] Under nitrogen, 2-methoxypyridine was dissolved in ethyl acetate and stirred uniformly. 2,2'-dibromodiethyl ether was added dropwise and mixed thoroughly (molar ratio of 2-methoxypyridine: 2,2'-dibromodiethyl ether = 2:1). The mixture was refluxed at 80°C for 48 hours, and the ethyl acetate was removed by vacuum distillation. The mixture was washed three times with ethyl acetate and stirred. The filtrate was then distilled under reduced pressure to remove the organic solvent and dried at 80°C for 24 hours to obtain the bispyridinium bromide salt. The bispyridinium bromide salt ionic liquid was then mixed with ZnCl2 (molar ratio of bispyridinium bromide: ZnCl2 = 1:1) and added to a round-bottom flask. The mixture was stirred at 100°C for 24 hours until a uniform viscous liquid was obtained. The viscous liquid was then dried in an oven at 60°C overnight to remove impurities, yielding the bispyridyl-based multifunctional ionic liquid [C2H4]2O[MeOPy]2ZnBr2Cl2.

[0052] Example 3

[0053] The bipyridyl multifunctional ionic liquid catalyst prepared in this embodiment has the following structural formula:

[0054] Expressed by [C2H4]2O[EOPy]2ZnBr2Cl2.

[0055] Preparation method of [C2H4]2O[EOPy]2ZnBr2Cl2 ionic liquid in this embodiment:

[0056] Under nitrogen, 2-ethoxypyridine was dissolved in ethyl acetate and stirred uniformly. 2,2'-dibromodiethyl ether was added dropwise and mixed uniformly (molar ratio of 2-ethoxypyridine: 2,2'-dibromodiethyl ether = 2:1). The mixture was refluxed at 80°C for 48 hours. The ethyl acetate was removed by vacuum distillation, and the mixture was washed three times with ethyl acetate. The filtrate was stirred and the organic solvent was removed by vacuum distillation. The mixture was then dried at 80°C for 24 hours to obtain the bispyridinium bromide salt. The bispyridinium bromide salt ionic liquid was mixed with ZnCl2 (molar ratio of bispyridinium bromide: ZnCl2 = 1:1) and added to a round-bottom flask. The mixture was stirred at 100°C for 24 hours until a uniform viscous liquid was obtained. The viscous liquid was then dried in an oven at 60°C overnight to remove impurities, yielding the bispyridyl-based multifunctional ionic liquid [C2H4]2O[EOPy]2ZnBr2Cl2.

[0057] Example 4

[0058] Epoxide cycloaddition catalyzed by bipyridyl-based multifunctional ionic liquids [C2H4]2O[Py]2ZnBr2Cl2, [C2H4]2O[MeOPy]2ZnBr2Cl2, and [C2H4]2O[EOPy]2ZnBr2Cl2:

[0059] A bipyridyl multifunctional ionic liquid was used as a catalyst and added to a 25 mL side-mouth flask with epichlorohydrin. After mixing, 0.1 MPa CO2 was introduced and the mixture was reacted at 25°C for 24 hours. The catalyst addition amount was 16 mg (3 mol% of the amount of epichlorohydrin). After the reaction, the selectivity and yield of cyclic carbonate were calculated and the results are summarized in Table 1. The H NMR spectrum of the obtained product chlorocyclic carbonate was consistent with the theoretical value (e.g. Figure 3 ), proving that the pure target product was obtained.

[0060] Table 1 Effect of bipyridyl-based multifunctional ionic liquids on the synthesis of cyclic carbonates from carbon dioxide and epoxides

[0061]

[0062] Bispyridine Zn-based ionic liquids with different side chains on the pyridine group have good catalytic effects on the cycloaddition reaction of epoxy compounds; among them, the bispyridine Zn-based ionic liquid [C2H4]2O[Py]2ZnBr2Cl2 without side chains on the pyridine group and epichlorohydrin are added to a 25mL branched flask, mixed and then introduced with 0.1MPa CO2. The reaction is carried out at 25°C for 24 hours. When the catalyst addition amount is 16mg (3mol%), the catalytic effect is optimal, providing high yield (93%) and high selectivity (99%).

[0063] Example 5

[0064] Further study on the cycloaddition of epoxides catalyzed by the multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2 of the bipyridine family:

[0065] (1) Effect of catalyst dosage on reaction

[0066] The catalyst and epichlorohydrin were added to a 25 mL side-mouth flask, mixed, and then 0.1 MPa CO2 was introduced. The catalyst addition amount was 10, 12, 14, 16, and 18 mg (1.5-3.5 mol%). The reaction temperature was 25°C and the reaction time was 24 h. After the reaction was completed, the selectivity and yield of the chlorocyclic carbonate were calculated. The results are as follows: Figure 4 As shown in the figure, when the catalyst dosage increases from 10 mg to 16 mg, the catalyst active sites increase, and the yield of chlorocyclic carbonate increases from 89% to 93%. When the catalyst dosage is further increased, the yield and selectivity show a downward trend. Excessive catalyst dosage will cause mass transfer difficulties, which is not conducive to the reaction.

[0067] (2) Effect of reaction time on reaction

[0068] The catalyst and epichlorohydrin were added to a 25 mL side-mouth flask, mixed, and then 0.1 MPa CO2 was introduced. The reaction time was 18-28 hours and the reaction temperature was 25°C. The amount of catalyst added was 16 mg (3 mol%). After the reaction was completed, the selectivity and yield of the chlorocyclic carbonate were calculated. The results are as follows: Figure 5 As shown, within a reaction time of 18 to 24 hours, the yield of the chlorocyclic carbonate was significantly improved (89% to 93%). As the main reaction proceeded more and more deeply, the selectivity of the chlorocyclic carbonate was also improved (97% to 99%). When the reaction time exceeded 26 hours, the conversion rate and selectivity did not change significantly, indicating that the reaction was almost completed within 26 hours, with a yield and selectivity of 94% and 97%, respectively.

[0069] In summary, the cycloaddition of epoxides catalyzed by the bipyridine multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2 is preferably carried out as follows: the catalyst and epichlorohydrin are added to a 25 mL side-mouth flask, mixed, and then 0.1 MPa CO2 is introduced at 25°C for 26 hours. The catalyst addition amount is 16 mg (3 mol%). The yield of the obtained product, chlorocyclic carbonate, reaches 94%, and the nuclear magnetic resonance hydrogen spectrum is consistent with the theoretical value, proving that a pure target product is obtained.

[0070] Example 6

[0071] The cycloaddition of various epoxides catalyzed by the bipyridine multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2 was performed by adding the catalyst [C2H4]2O[Py]2ZnBr2Cl2 and the epoxide to a 25 mL side-mouth flask. After mixing, 0.1 MPa of CO2 was introduced. The catalyst was added in an amount of 16 mg (3 mol%). The reaction was carried out at 25-60°C for 26 h. The selectivity and yield of the cyclic carbonate were calculated and summarized in Table 2. The H NMR spectrum of the synthesized brominated cyclic carbonate is shown in Table 2. Figure 6 shown.

[0072] Table 2 Effect of different epoxide cycloadditions catalyzed by the bipyridine-based multifunctional ionic liquid [C2H4]2O[Py]2ZnBr2Cl2

[0073]

Claims

1. A bipyridyl multifunctional ionic liquid, characterized in that: Having any of the following structural formulas:

2. The method for preparing the bipyridyl multifunctional ionic liquid according to claim 1, characterized in that: The method comprises the following steps: dissolving a pyridine compound in ethyl acetate under an inert atmosphere, stirring uniformly, adding 2,2'-dibromodiethyl ether dropwise, reacting under reflux at a certain temperature for a period of time, removing the ethyl acetate by distillation under reduced pressure, adding an organic solvent with relatively low polarity, stirring, filtering, removing the organic solvent by distillation under reduced pressure from the filtrate, and drying to obtain a bipyridinium bromide salt; mixing the bipyridinium bromide salt with ZnCl2, stirring at a certain temperature until a uniform viscous liquid is obtained; and drying the obtained viscous liquid to remove impurities to obtain a bipyridyl-based multifunctional ionic liquid.

3. The method for preparing a bipyridyl multifunctional ionic liquid according to claim 2, wherein: The pyridine compound is at least one of pyridine, 2-methoxypyridine or 2-ethoxypyridine.

4. The method for preparing a bipyridyl multifunctional ionic liquid according to claim 2 or 3, wherein: The molar ratio of the raw materials is: pyridine compound: 2,2'-dibromodiethyl ether = 2-2.2: 1-1.1, and bispyridinium bromide: ZnCl2 = 1-1.05: 1-1.

05.

5. The method for preparing a bipyridyl multifunctional ionic liquid according to claim 2 or 3, wherein: After adding 2,2'-dibromodiethyl ether, reflux the mixture at 80-90°C for 24-48 hours.

6. The method for preparing a bipyridyl multifunctional ionic liquid according to claim 2 or 3, characterized in that: The organic solvent with relatively low polarity is at least one of ethyl acetate, toluene, acetone, and dichloromethane.

7. The method for preparing a bipyridyl multifunctional ionic liquid according to claim 2 or 3, characterized in that: The inert atmosphere is a nitrogen atmosphere; and / or, the drying method adopted after the filtrate is distilled under reduced pressure to remove the organic solvent is vacuum drying; and / or, bipyridinium bromide and ZnCl2 are mixed and stirred at 80-100°C for 20-30 hours until a uniform viscous liquid is obtained; and / or, the obtained viscous liquid is dried in an oven at 50-70°C overnight to remove impurities.

8. Use of the bipyridyl multifunctional ionic liquid according to claim 1 or the bipyridyl multifunctional ionic liquid prepared by the preparation method of the bipyridyl multifunctional ionic liquid according to any one of claims 2 to 7, characterized in that: As a catalyst for the synthesis of cyclic carbonates from carbon dioxide and epoxides.

9. The use of the bipyridyl multifunctional ionic liquid according to claim 8, characterized in that: The bipyridyl multifunctional ionic liquid is used as a catalyst and mixed with an epoxy compound, and reacted for more than 24 hours under the conditions of a carbon dioxide pressure of 0.1 to 0.12 MPa and a temperature of 25 to 60° C.

10. Use of the bipyridyl multifunctional ionic liquid according to claim 8 or 9, characterized in that: The molar ratio of the bipyridyl multifunctional ionic liquid to the epoxy compound is 0.5-3.2%; and / or the epoxy compound is at least one of epichlorohydrin, epibromohydrin, tert-butyl glycidyl ether, glycidyl phenyl ether, and epoxystyrene.

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