Multi-point pyrazole ionic liquid, preparation method thereof and method for catalytically synthesizing cyclic carbonate

Abstract

The invention provides a multi-point pyrazole ionic liquid, a preparation method thereof and a method for catalytically synthesizing cyclic carbonate, belongs to the technical field of green catalysis, and aims to solve the technical problems that a homogeneous catalyst is low in activity and reaction conditions are not mild enough. The method for preparing the cyclic carbonate through catalysis of the multi-site pyrazole ionic liquid and the imgabs0 # comprises the following steps that the multi-site pyrazole ionic liquid and an epoxy compound are mixed and then subjected to a cycloaddition reaction in a carbon dioxide atmosphere, and after the reaction is finished, treatment is conducted to obtain the cyclic carbonate. According to the method, different substituent groups and bridging groups are introduced, so that multiple hydrogen supply sites and halogen anions are constructed to synergistically activate the ring opening of the epoxy compound, and the cyclic carbonate (the yield reaches 99.0%) is prepared by efficiently catalyzing the epoxide under mild reaction conditions (the temperature is less than or equal to 90 DEG C and less than or equal to 1.0 MPa). The synthesis method has the advantage of mild reaction conditions, and the catalyst has good cycle stability and substrate applicability.

Description

Technical Field

[0001] The present invention belongs to the technical field of green catalysis, and particularly relates to an ionic liquid catalyst. Background Art

[0002] The conversion of carbon dioxide into high-value products is the main route for the resource utilization of CO2 while alleviating CO2 emissions. Cyclic carbonates are mostly used in the production of electrolytes for lithium-ion batteries and have become high-demand high-value products in recent years. The new route of ethylene oxide-induced activation of CO2 cycloaddition to synthesize cyclic carbonates is expected to efficiently activate CO2. However, the catalytic activity of traditional catalysts is low, making the reaction process often carried out under high temperature and high pressure. Therefore, the development of efficient catalysts is the key to realizing the efficient conversion of CO2 under mild conditions.

[0003] Currently, the homogeneous catalysts used in the cycloaddition reaction mainly include organic catalysts, ionic liquids (CN111362901A), transition metal complexes (CN107827857A, CN107827858A, CN111215148A), and composite catalysts (CN111393402A, CN107715918B), etc. However, organic catalysts are prone to decomposition and have poor catalytic activity, and metal-based catalysts are prone to metal deposition, which affects the product quality.

[0004] Ionic liquid is a new type of green medium composed of anions and cations, with characteristics such as adjustable structural properties and stable structure that are not easily decomposed. It shows unique advantages in the reaction of catalyzing the synthesis of cyclic carbonates from CO2 and epoxides. (CN 114539202A) discloses an imidazole-based ionic liquid as the active component. By regulating the anions, cations, and end-group groups, high-efficiency generation of carbonates from CO2 and epoxides is achieved under the condition of adding a co-catalyst chloride salt, with a conversion rate of 99%. However, a breakthrough in catalysis under mild conditions (<100 °C) has not yet been achieved. This is mainly because the aggregation effect of ionic liquids reduces the contact and collision probability between reaction molecules and the active sites of ionic liquids, resulting in difficulty in fully exerting the catalytic activity and low catalytic efficiency of ionic liquids. Summary of the Invention

[0005] Aiming at the technical problems of low activity of homogeneous catalysts and insufficiently mild reaction conditions, the present invention provides a multi-site pyrazole ionic liquid, its preparation method, and a method for catalytic synthesis of cyclic carbonates. By introducing different substituents and bridging groups, multi-hydrogen-donating sites and halogen anions are constructed to synergistically activate the ring-opening of epoxides, achieving efficient catalysis for the preparation of cyclic carbonates under mild reaction conditions (≤90 °C, ≤1.0 MPa) (the yield reaches 99.0%). This synthesis method has the advantage of mild reaction conditions, and the catalyst has good cycle stability and substrate applicability.

[0006] To achieve the above object, the technical solution of the present invention is implemented as follows:

[0007] A multi-site pyrazole ionic liquid has the following structural formula:

[0008]

[0009] L = CH2OH, CH2OCH2, Ph, or (CH2) i , i = 1, 2, 3, 4, 5, 6;

[0010] F = H, COOH or OH, X = Cl or Br.

[0011] The multi-site pyrazole ionic liquid is one of 2,2'-(2-hydroxypropane-1,3-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([PROPz-COOH]Br2), 2,2'-(2-hydroxypropane-1,3-diyl)bis(5-carboxy-1-methyl-1H-pyrazolium) dichloride ([PROPz-COOH]Cl2), 2,2'-(oxybis(ethane-2,1-diyl))bis(5-carboxy-1-methylpyrazolium) dibromide ([EEPz-COOH]Br2), 2,2'-(oxybis(ethane-2,1-diyl))bis(5-carboxy-1-methylpyrazolium) dichloride ([EEPz-COOH]Cl2), 2,2'-(1,4-phenylenebis(methylene))bis-(5-hydroxy-1-methylpyrazolium) dibromide ([MBPz-COOH]Br2), 2,2'-(1,4-phenylenebis(methylene))bis(5-hydroxy-1-methylpyrazolium) dichloride ([MBPz-COOH]Cl2), 2,2'-(hexane-1,6-diyl)bis(5-carboxy-1-methylpyrazolium) dichloride ([C6Pz-COOH]Cl2, 2,2'-(hexane-1,6-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C6Pz-COOH]Br2, 2,2'-(pentane-1,5-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C5Pz-COOH]Br2, 2,2'-(butane-1,4-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C4Pz-COOH]Br2, 2,2'-(propane-1,3-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C3Pz-COOH]Br2, 2,2'-(ethane-1,2-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C2Pz-COOH]Br2, 2,2'-(methane-1,2-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C1Pz-COOH]Br2).

[0012] The specific structure is as follows:

[0013]

[0014] A preparation method of a multi-site pyrazole ionic liquid,

[0015] The general formula of the synthesis reaction is:

[0016] It includes the following steps: dispersing and dissolving a substituted pyrazole monomer and a dihalo monomer in a solvent, and then reacting to obtain it.

[0017] The pyrazole monomer is one of 1-methylpyrazole, 1-methylpyrazole-5-carboxylic acid or 1-methylpyrazole-5-hydroxy.

[0018] The dihalo monomer is one of 1,6-dibromohexane, 1,5-dibromopentane, 1,4-dibromobutane, 1,3-dibromopropane, 1,2-dibromoethane, 1,1-dibromomethane, 1,3-dibromo-2-propanol, 1,3-dichloro-2-propanol, 1,4-bis(bromomethyl)benzene, 1,4-bis(chloromethyl)benzene, bis(2-bromoethyl) ether or bis(2-chloroethyl) ether.

[0019] The molar ratio of the substituted pyrazole monomer to the dihalo monomer is 1:1 to 3:1.

[0020] The solvent is acetonitrile, and the dosage is 1 to 10 times the total volume of the pyrazole monomer and the dihalo monomer.

[0021] Preferably, the general formula of the synthesis reaction of the multi-site pyrazole ionic liquid is:

[0022]

[0023] A method for catalytically preparing cyclic carbonates with a multi-site pyrazole ionic liquid, which includes the following steps: mixing the multi-site pyrazole ionic liquid with an epoxide and performing a cycloaddition reaction in a carbon dioxide atmosphere, and obtaining a cyclic carbonate after the reaction is completed through treatment.

[0024] The structural formula of the epoxide is:

[0025]

[0026] In the formula, R = CH3, CH2Cl, CH2=CHOCH2, HOCH2, CH3CH2 or Ph.

[0027] Preferably, the reaction general formula is:

[0028]

[0029] R is an epoxide substituent: one or more of C1-C2 alkyl groups (CH3CH2, CH3), cyclohexyl, haloalkyl (CH2Cl), hydroxyalkyl (HOCH2), allyl methylene ether group (CH2=CHOCH2), or aromatic group (Ph); the amount of the ionic liquid is 1.0-3.0 mol% of the molar amount of the epoxide, preferably 2.0-3.0%. The reaction temperature is 50-130°C, preferably 90-130°C. The reaction pressure is 0.1-2.5 MPa, preferably 1.0-1.5 MPa. The reaction time is 0.75-9.0 h, preferably 5.0-9.0 h.

[0030] Advantages of the present invention:

[0031] (1) The present invention adopts a pyrazolium cation rich in multi-hydrogen bond donors and acceptors, separates multiple sites through a bridging group, adjusts the substituents on the cation and the bridging groups between cations, and designs and synthesizes a series of multi-site pyrazolium ionic liquid catalysts with multi-site centers, which is beneficial to multi-site cooperative catalysis, greatly promotes the reaction of CO2 and epoxides, and realizes the high-efficiency generation of cyclic carbonates under mild conditions (<100°C).

[0032] (2) Compared with other ionic liquids, the ionic liquid catalyst in the present invention has less dosage, high catalytic activity, mild reaction conditions, simple preparation, and good recycling performance, and can solve the problems existing in homogeneous catalysts in many aspects. Specific embodiments

[0033] The technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] Example 1

[0035] Synthesis of multi-site pyrazolium ionic liquid 2,2'-(2-hydroxypropane-1,3-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([PROPz-COOH]Br2):

[0036] 0.1 moL of 1-methylpyrazole-5-carboxylic acid was added to CH3CN (100 mL) in a three-necked flask and stirred at room temperature. Then, 0.1 moL of 1,3-dibromo-2-propanol was added, and the mixture was refluxed for 30 hours under N2 protection. At the end of the reaction, the remaining solvent was evaporated using a rotary evaporator. The residue was washed with a mixed solution of methanol and ethyl acetate and purified by centrifugation to remove impurities. Then, a pure white solid ([PROPz-COOH]Br2) was obtained and dried in a vacuum oven at 60 °C for 20 hours.

[0037] Example 2

[0038] Synthesis of multi-site pyrazole ionic liquid 2,2'-(2-hydroxypropane-1,3-diyl)bis(5-carboxy-1-methyl-1H-pyrazolium) dichloride ([PROPz-COOH]Cl2):

[0039] 0.1 moL of 1-methylpyrazole-5-carboxylic acid was added to CH3CN (100 mL) in a three-necked flask and stirred at room temperature. Then, 0.1 moL of 1,3-dichloro-2-propanol was added, and the mixture was refluxed for 30 hours under N2 protection. At the end of the reaction, the remaining solvent was evaporated using a rotary evaporator. The residue was washed with a mixed solution of methanol and ethyl acetate and purified by centrifugation to remove impurities. Then, a pure white solid ([PROPz-COOH]Br2) was obtained and dried in a vacuum oven at 60 °C for 20 hours.

[0040] Example 3

[0041] Synthesis of multi-site pyrazole ionic liquid 2,2'-(oxybis(ethane-2,1-diyl))bis(5-carboxy-1-methylpyrazolium) dibromide ([EEPz-COOH]Br2):

[0042] 0.3 moL of 1-methylpyrazole-5-carboxylic acid was added to CH3CN (200 mL) in a three-necked flask and stirred at room temperature. Then, 0.1 moL of bis(2-bromoethyl) ether was added, and the mixture was refluxed for 30 hours under N2 protection. At the end of the reaction, the remaining solvent was evaporated using a rotary evaporator. The residue was washed with a mixed solution of methanol and ethyl acetate and purified by centrifugation to remove impurities. Then, a pure white solid ([EEPz-COOH]Br2) was obtained and dried in a vacuum oven at 60 °C for 20 hours.

[0043] Example 4

[0044] Synthesis of multi-site pyrazole ionic liquid 2,2'-(oxybis(ethane-2,1-diyl))bis(5-carboxy-1-methylpyrazolium) dichloride ([EEPz-COOH]Cl2)

[0045] 0.1 moL of 1 - methylpyrazole - 5 - carboxylic acid was added to CH3CN (100 mL) in a three - necked flask and stirred at room temperature. Then 0.1 moL of bis(2 - chloroethyl) ether was added and the reaction was refluxed for 30 hours under N2 protection. At the end of the reaction, the remaining solvent was evaporated using a rotary evaporator. The residue was washed with a mixed solution of methanol and ethyl acetate and purified by centrifugation to remove impurities. Then a pure white solid ([EEPz - COOH]Cl2) was obtained and dried in a vacuum oven at 60 °C for 20 hours.

[0046] Example 5

[0047] Synthesis of multi - site pyrazole ionic liquid 2,2'-(1,4 - phenylenebis(methylene))bis-(5 - hydroxy - 1 - methylpyrazolium) dibromide ([MBPz - COOH]Br2):

[0048] 0.1 moL of 1 - methylpyrazole - 5 - carboxylic acid was added to CH3CN (100 mL) in a three - necked flask and stirred at room temperature. Then 0.1 moL of 1,4 - bis(bromomethyl)benzene was added and the reaction was refluxed for 30 hours under N2 protection. At the end of the reaction, the remaining solvent was evaporated using a rotary evaporator. The residue was washed with a mixed solution of methanol and ethyl acetate and purified by centrifugation to remove impurities. Then a pure white solid ([MBPz - COOH]Br2) was obtained and dried in a vacuum oven at 60 °C for 20 hours.

[0049] Example 6

[0050] Synthesis of multi - site pyrazole ionic liquid 2,2'-(1,4 - phenylenebis(methylene))bis(5 - hydroxy - 1 - methylpyrazolium) dichloride ([MBPz - COOH]Cl2):

[0051] 0.1 moL of 1 - methylpyrazole - 5 - carboxylic acid was added to CH3CN (100 mL) in a three - necked flask and stirred at room temperature. Then 0.1 moL of 1,4 - bis(chloromethyl)benzene was added and the reaction was refluxed for 30 hours under N2 protection. At the end of the reaction, the remaining solvent was evaporated using a rotary evaporator. The residue was washed with a mixed solution of methanol and ethyl acetate and purified by centrifugation to remove impurities. Then a pure white solid ([MBPz - COOH]Cl2) was obtained and dried in a vacuum oven at 60 °C for 20 hours.

[0052] Example 7

[0053] Synthesis of multi-site pyrazole ionic liquid 2,2'-(hexane-1,6-diyl)bis(5-carboxy-1-methylpyrazolium) dichloride ([C6Pz-COOH]Cl2):

[0054] 0.1 moL of 1-methylpyrazole-5-carboxylic acid was added to CH3CN (100 mL) in a three-necked flask and stirred at room temperature. Then 0.1 moL of 1,6-dibromohexane was added and the reaction was refluxed for 30 hours under N2 protection. At the end of the reaction, the remaining solvent was evaporated using a rotary evaporator. The residue was washed with a mixed solution of methanol and ethyl acetate and purified by centrifugation to remove impurities. Then a pure white solid ([C6Pz-COOH]Cl2) was obtained and dried in a vacuum oven at 60 °C for 20 hours.

[0055] Example 8

[0056] Synthesis of multi-site pyrazole ionic liquid 2,2'-(hexane-1,6-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C6Pz-COOH]Br2):

[0057] 0.1 moL of 1,6-dibromohexane was mixed with 0.1 moL of 1-methylpyrazole in acetonitrile (100 mL) and the mixture was stirred at room temperature for 1 hour. Then under nitrogen protection, the mixture was stirred at 80 °C for 48 hours. After the reaction was completed, the remaining solvent was evaporated using a rotary evaporator, and the resulting residue was washed with ethyl acetate to remove impurities using a high-speed centrifuge. Finally, it was dried in a vacuum oven at 60 °C for 24 hours.

[0058] Example 9

[0059] Synthesis of multi-site pyrazole ionic liquid 2,2'-(pentane-1,5-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C5Pz-COOH]Br2):

[0060] 0.1 moL of 1,5-dibromopentane was mixed with 0.1 moL of 1-methylpyrazole in acetonitrile (100 mL) and the mixture was stirred at room temperature for 1 hour. Then under nitrogen protection, the mixture was stirred at 80 °C for 48 hours. After the reaction was completed, the remaining solvent was evaporated using a rotary evaporator, and the resulting residue was washed with ethyl acetate to remove impurities using a high-speed centrifuge. Finally, it was dried in a vacuum oven at 60 °C for 24 hours.

[0061] Example 10

[0062] Synthesis of multi-site pyrazole ionic liquid 2,2'-(butane-1,4-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C4Pz-COOH]Br2):

[0063] 0.1 moL of 1,4-dibromobutane and 0.1 moL of 1-methylpyrazole were mixed in acetonitrile (100 mL), and the above mixture was stirred at room temperature for 1 hour. Then, under nitrogen protection, the mixture was stirred at 80 °C for 48 hours. After the reaction was completed, the remaining solvent was evaporated using a rotary evaporator, and the resulting residue was washed with ethyl acetate to remove impurities using a high-speed centrifuge. Finally, it was dried in a vacuum oven at 60 °C for 24 hours.

[0064] Example 11

[0065] Synthesis of multi-site pyrazole ionic liquid 2,2'-(propane-1,3-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C3Pz-COOH]Br2):

[0066] 0.1 moL of 1,3-dibromopropane and 0.1 moL of 1-methylpyrazole were mixed in acetonitrile (100 mL), and the above mixture was stirred at room temperature for 1 hour. Then, under nitrogen protection, the mixture was stirred at 80 °C for 48 hours. After the reaction was completed, the remaining solvent was evaporated using a rotary evaporator, and the resulting residue was washed with ethyl acetate to remove impurities using a high-speed centrifuge. Finally, it was dried in a vacuum oven at 60 °C for 24 hours.

[0067] Example 12

[0068] Synthesis of multi-site pyrazole ionic liquid 2,2'-(ethane-1,2-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C2Pz-COOH]Br2):

[0069] 0.1 moL of 1,2-dibromoethane and 0.1 moL of 1-methylpyrazole were mixed in acetonitrile (100 mL), and the above mixture was stirred at room temperature for 1 hour. Then, under nitrogen protection, the mixture was stirred at 80 °C for 48 hours. After the reaction was completed, the remaining solvent was evaporated using a rotary evaporator, and the resulting residue was washed with ethyl acetate to remove impurities using a high-speed centrifuge. Finally, it was dried in a vacuum oven at 60 °C for 24 hours.

[0070] Example 13

[0071] Synthesis of multi-site pyrazole ionic liquid 2,2'-(methane-1,2-diyl)bis(5-carboxy-1-methylpyrazolium) dibromide ([C1Pz-COOH]Br2):

[0072] Mix 0.1 moL of 1,1-dibromomethane with 0.1 moL of 1-methylpyrazole in acetonitrile (100 mL) and stir the above mixture at room temperature for 1 hour. Then, under nitrogen protection, stir the mixture at 80 °C for 48 hours. After the reaction is completed, evaporate the remaining solvent using a rotary evaporator, and then wash the resulting residue with ethyl acetate to remove impurities using a high-speed centrifuge. Finally, dry it in a vacuum oven at 60 °C for 24 hours.

[0073] Example 14

[0074] A method for catalytic preparation of cyclic carbonates using a multi-site pyrazole ionic liquid, comprising the following steps:

[0075] Into a 25 mL stainless steel autoclave equipped with a magnetic stirrer, add 30 mmol of propylene oxide and the ionic liquid catalyst [C6Pz-COOH]Br2 (2% of the molar amount of propylene oxide) respectively, maintain a CO2 pressure of 1.0 MPa, maintain the temperature of the autoclave at 90 °C, react at 90 °C for 8 h, after the reaction is completed, cool the autoclave to room temperature, slowly release the remaining CO2 in the autoclave, take out the reaction solution and analyze the yield and selectivity by Agilent 6820 gas chromatography (GC) to obtain the product propylene carbonate, the yield of propylene carbonate is 98.8%, and the selectivity is 99.9%.

[0076] Example 15

[0077] A method for catalytic preparation of cyclic carbonates using a multi-site pyrazole ionic liquid, comprising the following steps:

[0078] Into a 25 mL stainless steel autoclave equipped with a magnetic stirrer, add 30 mmol of propylene oxide and the ionic liquid catalyst [PROPz-COOH]Br2 (2% of the molar amount of propylene oxide) respectively, maintain a CO2 pressure of 1.0 MPa, maintain the temperature of the autoclave at 90 °C, react at 90 °C for 8 h, after the reaction is completed, cool the autoclave to room temperature, slowly release the remaining CO2 in the autoclave, take out the reaction solution and analyze the yield and selectivity by Agilent 6820 gas chromatography (GC) to obtain the product propylene carbonate, the yield of propylene carbonate is 99.0%, and the selectivity is 99.9%.

[0079] Example 16

[0080] A method for catalytic preparation of cyclic carbonates using a multi-site pyrazole ionic liquid, comprising the following steps:

[0081] Into a 25 mL stainless steel autoclave equipped with a magnetic stir bar, 30 mmol of styrene oxide and the [PROPz-COOH]Br2 ionic liquid catalyst (2% of the molar amount of styrene oxide) were added respectively. CO2 at 1.0 MPa was maintained, and the temperature of the autoclave was maintained at 80 °C. The reaction was carried out at 80 °C for 5 h. After the reaction, the autoclave was cooled to room temperature, and the remaining CO2 in the autoclave was slowly vented. The reaction solution was taken out and analyzed for yield and selectivity by Agilent 6820 gas chromatography (GC) to obtain the product styrene carbonate. The yield of styrene carbonate was 88.4%, and the selectivity was 99.8%.

[0082] Example 17

[0083] A method for preparing cyclic carbonates catalyzed by a multi-site pyrazole ionic liquid, comprising the following steps:

[0084] Into a 25 mL stainless steel autoclave equipped with a magnetic stir bar, 30 mmol of styrene oxide and the [MBPz-COOH]Br2 ionic liquid catalyst (2% of the molar amount of styrene oxide) were added respectively. CO2 at 1.0 MPa was maintained, and the temperature of the autoclave was maintained at 80 °C. The reaction was carried out at 80 °C for 5 h. After the reaction, the autoclave was cooled to room temperature, and the remaining CO2 in the autoclave was slowly vented. The reaction solution was taken out and analyzed for yield and selectivity by Agilent 6820 gas chromatography (GC) to obtain the product styrene carbonate. The yield of styrene carbonate was 76.5%, and the selectivity was 99.8%.

[0085] Example 18

[0086] A method for preparing cyclic carbonates catalyzed by a multi-site pyrazole ionic liquid, comprising the following steps:

[0087] Into a 25 mL stainless steel autoclave equipped with a magnetic stir bar, 30 mmol of styrene oxide and the [EEPz-COOH]Br2 ionic liquid catalyst (2% of the molar amount of styrene oxide) were added respectively. CO2 at 1.0 MPa was maintained, and the temperature of the autoclave was maintained at 80 °C. The reaction was carried out at 80 °C for 5 h. After the reaction, the autoclave was cooled to room temperature, and the remaining CO2 in the autoclave was slowly vented. The reaction solution was taken out and analyzed for yield and selectivity by Agilent 6820 gas chromatography (GC) to obtain the product styrene carbonate. The yield of styrene carbonate was 77.7%, and the selectivity was 99.9%.

[0088] Example 19

[0089] A method for preparing cyclic carbonates catalyzed by a multi-site pyrazole ionic liquid, comprising the following steps:

[0090] Into a 25 mL stainless-steel high-pressure reactor equipped with a magnetic stir bar, 30 mmol of styrene oxide and the [PROPz-COOH]Br2 ionic liquid catalyst (2% of the molar amount of styrene oxide) were added respectively. CO2 was maintained at 1.0 MPa, and the temperature of the reactor was maintained at 80 °C. The reaction was carried out at 80 °C for 5 h. After the reaction, the reactor was cooled to room temperature, and the remaining CO2 in the reactor was slowly vented. The reaction solution was taken out and analyzed for yield and selectivity by Agilent 6820 gas chromatography (GC) to obtain the product styrene carbonate. The yield of styrene carbonate was 93.7%, and the selectivity was 99.9%.

[0091] Example 20

[0092] A method for preparing cyclic carbonates catalyzed by a multi-site pyrazole ionic liquid, comprising the following steps:

[0093] Into a 25 mL stainless-steel high-pressure reactor equipped with a magnetic stir bar, 30 mmol of styrene oxide and the [C6Pz-COOH]Br2 ionic liquid catalyst (2% of the molar amount of styrene oxide) were added respectively. CO2 was maintained at 1.5 MPa, and the temperature of the reactor was maintained at 120 °C. The reaction was carried out at 120 °C for 3 h. After the reaction, the reactor was cooled to room temperature, and the remaining CO2 in the reactor was slowly vented. The reaction solution was taken out and analyzed for yield and selectivity by Agilent 6820 gas chromatography (GC) to obtain the product styrene carbonate. The yield of styrene carbonate was 74.6%, and the selectivity was 99.9%.

[0094] Examples 21 - 34

[0095] The preparation method was the same as that of Example 20, only the ionic liquid catalyst was changed, and other conditions remained unchanged. The specific results are shown in Table 1 below, where 1 - 15 represent Examples 20 - 34.

[0096] Table 1

[0097]

[0098] Example 35

[0099] A method for preparing cyclic carbonates catalyzed by a multi-site pyrazole ionic liquid, comprising the following steps:

[0100] Into a 25 mL stainless steel high-pressure reactor equipped with a magnetic stir bar, 30 mmol of styrene oxide and the [PROPz-COOH]Br2 ionic liquid catalyst (1% of the molar amount of styrene oxide) were added respectively. CO2 was maintained at 0.1 MPa, and the temperature of the reactor was maintained at 50 °C. The reaction was carried out at 50 °C for 9 h. After the reaction was completed, the reactor was cooled to room temperature, and the remaining CO2 in the reactor was slowly vented. The reaction solution was taken out and analyzed for yield and selectivity by Agilent 6820 gas chromatography (GC) to obtain the product styrene carbonate. The yield of styrene carbonate was 89.1%, and the selectivity was 99.7%.

[0101] Example 36

[0102] A method for catalytic preparation of cyclic carbonates by a multi-site pyrazole ionic liquid, comprising the following steps:

[0103] Into a 25 mL stainless steel high-pressure reactor equipped with a magnetic stir bar, 30 mmol of styrene oxide and the [PROPz-COOH]Br2 ionic liquid catalyst (3% of the molar amount of styrene oxide) were added respectively. CO2 was maintained at 2.5 MPa, and the temperature of the reactor was maintained at 130 °C. The reaction was carried out at 130 °C for 0.75 h. After the reaction was completed, the reactor was cooled to room temperature, and the remaining CO2 in the reactor was slowly vented. The reaction solution was taken out and analyzed for yield and selectivity by Agilent 6820 gas chromatography (GC) to obtain the product styrene carbonate. The yield of styrene carbonate was 82.4%, and the selectivity was 99.9%.

[0104] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multi-site pyrazole ionic liquid, characterized in that, The structural formula is as follows: L = CH2OH, CH2OCH2 or Ph, or (CH2) i , where i = 1, 2, 3, 4, 5 or 6; F = H, COOH or OH, and X = Cl or Br.

2. The preparation method of the multi-site pyrazole ionic liquid according to claim 1, characterized in that, It includes the following steps: It is prepared by dispersing and dissolving the substituted pyrazole monomer and the dihalo monomer in a solvent and then reacting.

3. The preparation method of the multi-site pyrazole ionic liquid according to claim 2, wherein, The pyrazole monomer is one of 1-methylpyrazole, 1-methylpyrazole-5-carboxylic acid or 1-methylpyrazole-5-ol.

4. The preparation method of the multi-site pyrazole ionic liquid according to claim 3, wherein, The dihalo monomer is one of 1,6-dibromohexane, 1,5-dibromopentane, 1,4-dibromobutane, 1,3-dibromopropane, 1,2-dibromoethane, 1,1-dibromomethane, 1,3-dibromo-2-propanol, 1,3-dichloro-2-propanol, 1,4-bis(bromomethyl)benzene, 1,4-bis(chloromethyl)benzene, bis(2-bromoethyl) ether or bis(2-chloroethyl) ether.

5. The preparation method of the multi-site pyrazole ionic liquid according to claim 5, wherein, The molar ratio of the substituted pyrazole monomer to the dihalo monomer is 1 to 3:

1.

6. The preparation method of the multi-site pyrazole ionic liquid according to claim 4, characterized in that, The solvent is acetonitrile, and the amount used is 1 to 10 times the total volume of the substituted pyrazole monomer and the dihalo monomer.

7. The method for catalytic preparation of cyclic carbonate by multi-site pyrazole ionic liquid as claimed in claim 1, characterized in that, It includes the following steps: The multi-site pyrazole ionic liquid and the epoxide are mixed and then subjected to a cycloaddition reaction in a carbon dioxide atmosphere. After the reaction is completed, the cyclic carbonate is obtained through treatment.

8. The method for catalytic preparation of cyclic carbonates by multi-site pyrazolium ionic liquid according to claim 7, characterized in that, The structural formula of the epoxide is: In the formula, R = CH3, CH2Cl, CH2=CHOCH2, HOCH2, CH3CH2 or Ph.

9. The method for catalytic preparation of cyclic carbonates by multi-site pyrazolium ionic liquids according to claim 7, wherein The multi-site pyrazole ionic liquid accounts for 1.0 to 3.0 mol% of the epoxide.

10. The method for catalytic preparation of cyclic carbonates with multi-site pyrazolium ionic liquids according to claim 7, characterized in that, The temperature of the cycloaddition reaction is 50 to 130 °C, the time is 0.75 to 9.0 h, and the pressure is 0.1 to 2.5 MPa.

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