B-l dicationic ionic liquid, method for preparing the same, and method for preparing carboxylate ester using the same

Abstract

The application belongs to the technical field of olefin hydroesterification and its catalyst, and particularly relates to B-L double acid type ionic liquid and a preparation method thereof, and a method for preparing carboxylic acid ester by simultaneously using the same as an auxiliary agent and a solvent. The preparation method of the B-L double acid type ionic liquid comprises the following steps: mixing a zwitterion precursor A and a zwitterion precursor B, performing suction filtration, washing and drying after the reaction is completed to obtain zwitterion solid powder; after the zwitterion solid powder is dissolved in methanol, acid is added dropwise, and B acid type ionic liquid is obtained through reaction; L acid is added dropwise into the B acid type ionic liquid, and B-L double acid type ionic liquid is obtained through stirring reaction, washing and drying. The B-L double acid type ionic liquid provided in the application is used as an auxiliary agent and a solvent in the preparation of organic carboxylic acid ester, has a small amount, has small corrosion to equipment, is easy to separate, can be reused, and has good catalytic activity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of olefin hydroesterification and its catalyst, and particularly relates to a B-L double acid type ionic liquid and a preparation method thereof, and a method for preparing carboxylic acid ester by using the same as an assistant and a solvent. BACKGROUND

[0002] Carboxylic acid esters and their derivatives are valuable compounds in the chemical industry, which can be used as universal intermediates for producing medicines (non-steroidal anti-inflammatory drugs such as ibuprofen and naproxen), surfactants and perfumes, etc. Due to the atom economy and the universality of raw materials (olefins, alcohols and CO), transition metal-catalyzed olefin hydroesterification is one of the most effective methods for synthesizing these high-value products. So far, transition metals including Rh, Ru, Ni, Co and Pd have been studied in olefin hydroesterification reactions. Among the existing catalytic systems, homogeneous catalytic systems composed of palladium, phosphine ligands and acids have attracted widespread attention due to their good substrate adaptability and excellent catalytic performance, such as PdCl2 / PPh3 / CuCl2, [Pd(dtbpx)(dba)], [Pd(PPh3)2(olefin)], [PdCl2(dppp)] and the like. However, these catalytic systems still have serious problems in practical application, such as the difficulty in separation and reuse of the catalyst. In order to overcome these problems, widely used methods include supported transition metal complexes, biphasic systems and metal-oxide systems.

[0003] At present, Acids are usually used as assistants and initiators for olefin hydroesterification and hydroxylation reactions. In industry, soluble acids such as hydrochloric acid, heteropoly acid, oxalic acid and p-toluenesulfonic acid (p-TsOH) are commonly used. In recent years, polymer sulfonic acid resins, acidic ionic liquids and the like have also been applied to the reaction as acidic assistants. In particular, ionic liquids (ILs) have been widely used in various transition metal-centered catalytic reactions. ILs have low coordination ability and similar polarity to organic solvents, so selecting appropriate ILs can make the metal center more stable. In addition, ILs are non-volatile and adjustable, which makes ILs an ideal solvent for catalytic recycling, achieving the recycling and reuse of catalysts in catalytic recycling, and successfully solving the problem of separation and reuse of olefin hydroesterification catalysts.

[0004] CN102531890A discloses a method for preparing organic carboxylic acid ester by olefin hydroesterification reaction, using terminal olefin, CO and alcohol as reactants, in the presence of a catalyst composed of a palladium compound, a monodentate phosphine ligand or a bidentate phosphine ligand, an acidic ionic liquid and an organic solvent, controlling the reaction pressure to be 1.0-10.0 MPa and the reaction temperature to be 50-150 DEG C, to generate organic carboxylic acid ester with one more carbon than the olefin. An ionic liquid acidic ionic liquid is used to replace methanesulfonic acid to perform hydroesterification reaction to reduce the corrosion to the reactor, but there are still problems of large usage amount, strong corrosion to the equipment, unstable reaction and low reaction activity. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the deficiencies of the prior art, and provide a B-L double acid type ionic liquid which is used as an additive and a solvent in the preparation of organic carboxylic acid ester, has a small usage amount, has a small corrosion to the equipment, has a product easy to separate, can be reused, and has good catalytic activity.

[0006] The preparation method of the B-L double acid type ionic liquid comprises the following steps:

[0007] (1) mixing zwitterionic precursor A and zwitterionic precursor B, after the reaction is completed, performing suction filtration, washing and drying to obtain zwitterionic solid powder;

[0008] (2) dissolving the zwitterionic solid powder in methanol, and then adding acid dropwise to obtain B acid type ionic liquid by reaction;

[0009] (3) adding L acid dropwise to the B acid type ionic liquid, stirring and reacting, and then washing and drying to obtain B-L double acid type ionic liquid.

[0010] The zwitterionic precursor A in step (1) is one of 1-methylimidazole, benzimidazole, triphenylphosphine and pyridine; and the zwitterionic precursor B is propylsulfonic acid lactone or butylsulfonic acid lactone.

[0011] The molar ratio of the zwitterionic precursor A to the zwitterionic precursor B in step (1) is (1-5):(0.5-1).

[0012] The reaction temperature in step (1) is 40-90 DEG C, and the reaction time is 2-12 h.

[0013] The solvent used for washing in step (1) is one of toluene, diethyl ether, n-hexane, nonane, methanol and deionized water, and the drying temperature is 60-120 DEG C.

[0014] The molar ratio of the zwitterionic solid powder to the acid in step (2) is (1-5):(1-100). The acid is preferably hydrochloric acid.

[0015] The reaction temperature of step (2) is 30-80℃, and the reaction time is 1-12h.

[0016] The L acid of step (3) is one of AlCl3, SnCl2, FeCl3, and ZnCl2.

[0017] The molar ratio of the B acid type ionic liquid to the L acid of step (3) is (1-5):(0.1-10).

[0018] The solvent used for washing of step (3) is one of toluene, n-hexane, cyclohexane, and ethylbenzene, and the drying temperature is 60-120℃ for 2-6h.

[0019] The B-L double acid type ionic liquid is prepared by the method for preparing the B-L double acid type ionic liquid.

[0020] The method for preparing carboxylic acid ester by using the B-L double acid type ionic liquid comprises the following steps: mixing a Pd compound, a B-L double acid type ionic liquid, a phosphine ligand, and an alcohol, charging an end alkene, pressurizing, and heating to react to obtain the carboxylic acid ester; the molar ratio of the Pd compound to the phosphine ligand is (1-4):(1-100) in terms of the molar amount of Pd; and the molar ratio of the Pd compound to the B-L double acid type ionic liquid is (0.1-1):(0.1-0.5) in terms of the molar amount of Pd. The heating is to 50-180℃, preferably 80-120℃, the reaction pressure is controlled to be 1-10 MPa, preferably 1-5 MPa, and the reaction time is controlled to be 2-10h.

[0021] The alcohol is one of methanol, ethanol, ethylene glycol, and glycerol, and simultaneously serves as a solvent of the reaction system.

[0022] The Pd compound is one of palladium acetate (Pd(OAc)2), palladium chloride (PdCl2), palladium acetylacetonate, and allyl palladium chloride.

[0023] The phosphine ligand is one of monodentate phosphine ligands or bidentate phosphine ligands, such as triphenylphosphine (PPh3), tri-n-butylphosphine, tricyclohexylphosphine, 1,2-bis[(di-tert-butylphosphine)methyl]benzene, and 1,4-bis(diphenylphosphino)butane.

[0024] The end alkene is one of ethylene, propylene, butylene, butadiene, and styrene, and the mass purity of the end alkene is 90%-100%.

[0025] The gas used for pressurizing is CO or a mixed gas of CO and N2, and the mass purity of the gas used is 90%-100%.

[0026] Specifically, the method for preparing carboxylic acid ester by using the B-L double acid type ionic liquid comprises the following steps:

[0027] (1) Put the zwitterion precursor A and the zwitterion precursor B into a 100 mL round-bottom flask, stir the reaction at 40-90℃ for 2-12h, perform suction filtration, repeatedly wash to remove non-ionic residues, and vacuum dry at 60-120℃ to obtain zwitterion solid powder.

[0028] (2) Put the zwitterion solid powder into a flask, dissolve it with methanol, drop in HCl, and stir the reaction at 30-80℃ for 1-12h to obtain B acid type ionic liquid.

[0029] (3) Drop in the methanol solution of L acid into the B acid type ionic liquid, stir the reaction for 4-6h, wash, and dry at 60-120℃ for 2-6h to obtain B-L double acid type ionic liquid.

[0030] (4) In a 250ml high-pressure reaction kettle, sequentially add a Pd compound, a B-L double acid type ionic liquid, a phosphine ligand, and an alcohol, seal the reaction kettle, fill the reaction kettle with terminal olefin, replace the reaction kettle with CO or a mixture of CO and N2 for 3 times, then fill the reaction kettle with CO or a mixture of CO and N2 until the pressure of the reaction kettle is 1-10MPa, slowly increase the temperature to 50-180℃ by a temperature controller, and react for 2-10h, then cool to room temperature, unload the kettle, and quantitatively analyze the obtained carboxylate by Agilent 6890.

[0031] The present application uses terminal olefin, CO and alcohol as reactants to generate organic carboxylate with more than one carbon under the action of a catalyst composed of a Pd compound, a phosphine ligand and a B-L double acid type ionic liquid. The B-L double acid type ionic liquid used as a catalyst in the present application can significantly improve the acidity of the ionic liquid and further reduce the use amount of the ionic liquid and the corrosion of the equipment, on the one hand, due to the electron-withdrawing effect of the Lewis acid site, and on the other hand, due to the strong electronic synergistic effect between the Lewis acid composed of a metal salt and the active site Pd, which can significantly improve the reaction activity and stability of the catalyst.

[0032] Compared with the prior art, the present application has the beneficial effects that:

[0033] (1) The method for preparing carboxylate by using B-L double acid type ionic liquid in the present application has mild reaction conditions, wide application range of raw materials and high product selectivity.

[0034] (2) The B-L double acid type ionic liquid prepared by using the present application as a catalyst does not add acid additives in the catalyst system, and the acid in the B-L double acid type ionic liquid synergistically acts with the Lewis acid site to improve the dissociation of hydrogen protons, and has small corrosion to the equipment.

[0035] (3) The B-L double acid type ionic liquid prepared by the application can improve the adsorption capacity of Pd to reactants by the interaction between Lewis acid of metal salt and active site Pd, thereby improving the reaction activity and selectivity of the catalyst.

[0036] (4) The method for preparing carboxylic acid ester by using the B-L double acid type ionic liquid can adjust the proportion of B-L acid sites according to the requirements of the reaction, and optimize the reaction results by using the adjustable advantage of the structure of the B-L double acid type ionic liquid. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The infrared spectrum of the B-L double acid type ionic liquid prepared for Example 1.

[0038] Figure 2 The nuclear magnetic resonance spectrum of the B-L double acid type ionic liquid in Example 1 before and after coordination with AlCl3. 1 H spectrum. DETAILED DESCRIPTION

[0039] The application will be further described below in combination with specific examples.

[0040] The following examples and comparative examples, the mass purity of the alcohol is 90%-100%, the mass purity of CO or CO and N2 mixed gas is 90%-100%, and other chemical reagents used are commercially available products, and the equipment used is existing equipment.

[0041] Example 1

[0042] The method for preparing carboxylic acid ester by using the B-L double acid type ionic liquid comprises the following steps:

[0043] (1) 0.2 mol of 1-methylimidazole and 0.2 mol of butylsulfonic acid lactone are put into a 100 mL round-bottom flask, stirred at 40℃ for 12 h, filtered, and the obtained white solid is repeatedly washed with diethyl ether to remove non-ionic residues, and dried at 80℃ under vacuum to obtain a zwitterionic solid powder.

[0044] (2) 1 mol of the zwitterionic solid powder is put into a flask, dissolved with methanol, and 1 mol of HCl is added dropwise, stirred at 60℃ for 6 h to obtain a B acid type ionic liquid.

[0045] (3) 0.01 mol of AlCl3 methanol solution is added dropwise to 0.5 mol of the B acid type ionic liquid, stirred for 4 h, washed with toluene, and dried at 100℃ under vacuum for 6 h to obtain a B-L double acid type ionic liquid.

[0046] (4) In a 250 ml high-pressure reactor, 0.05 mol of PdCl2, 0.05 mol of the above-mentioned B-L double acid type ionic liquid, 0.5 mol of PPh3, 100 mL of methanol were sequentially added, the reactor was closed, 0.08 mol of styrene was filled, the reactor was replaced with CO for 3 times, CO was filled again until the pressure of the reactor was 4 MPa, the temperature was slowly increased to 100°C by the temperature controller, and the reaction was carried out for 4 h. After cooling to room temperature, the reactor was unloaded, and the obtained carboxylate was quantitatively analyzed by Agilent 6890. The conversion rate of styrene was 99%, and the selectivity of the product methyl phenylpropionate was 95%.

[0047] By Figure 1 It can be seen that after testing the B-L double acid type ionic liquid by using a Bruker infrared spectrometer, 3151 cm -1 belongs to the stretching vibration of C-H on the methyl group of the imidazole ring; 2946 cm -1 belongs to the stretching vibration of C-H on the methylene group in the propyl sulfonic acid group; 1574 cm -1 belongs to the stretching vibration of -C=N- on the imidazole ring; 1459 cm -1 belongs to the bending vibration of C-H on the methylene group; 1185 cm -1 belongs to the asymmetric stretching vibration of S=O on the sulfonate; 1041 cm -1 belongs to the symmetric stretching vibration of S=O. Thus, the synthesis of the amphoteric B-L double acid type ionic liquid is proved.

[0048] By Figure 2 It can be seen that by using 600 MHz for 1H spectrum testing, the coordination of AlCl3 will cause the displacement of H in the ionic liquid to change, and then the displacement occurs.

[0049] Example 2

[0050] The method for preparing carboxylate by using B-L double acid type ionic liquid comprises the following steps:

[0051] (1) 2 mol of triphenylphosphine and 0.2 mol of butyl sulfonic acid lactone were put into a 100 mL round-bottom flask, and stirred at 60°C for 8 h. Filtration was performed, and the obtained white solid was repeatedly washed with toluene to remove non-ionic residues, and vacuum dried at 60°C to obtain an amphoteric ionic solid powder.

[0052] (2) 0.1 mol of the amphoteric ionic solid powder was taken into a flask and dissolved with methanol, and 10 mol of HCl was added dropwise. The reaction was stirred at 60°C for 6 h to obtain a B acid type ionic liquid.

[0053] (3) To 0.01 mol of B acid type ionic liquid, 0.05 mol of FeCl3methanol solution was added dropwise, and the reaction was stirred for 6 h. The product was washed with toluene and dried at 60°C under vacuum for 6 h to obtain B-L double acid type ionic liquid.

[0054] (4) In a 250 ml high-pressure reactor, 0.005 mol of Pd(OAc)2, 0.01 mol of B-L double acid type ionic liquid, and 0.5 mmol of tri-n-butylphosphine were sequentially added, and 100 mL of ethanol was added. The reactor was sealed, and the reactor was replaced with 0.1 mol of ethylene three times with a mixture of CO and N2. The reactor was filled with a mixture of CO and N2to a pressure of 5 MPa, and the temperature was slowly increased to 110°C by a temperature controller. The reaction was carried out for 8 h, and the reactor was cooled to room temperature. The obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890. The conversion rate of ethylene was 97%, and the selectivity of the product methyl propionate was 96%.

[0055] Repeatability: After the reaction solution was evaporated by a rotary evaporator to remove methyl propionate and methanol, the repeatability of the B-L double acid type ionic liquid catalyst was evaluated under the same reaction conditions as in Example 2. The reaction was carried out for 8 h, and the reactor was cooled to room temperature. The reaction liquid was quantitatively analyzed by Agilent 6890. The conversion rate of ethylene was 97%, and the selectivity of the product methyl propionate was 96%. The reaction was repeated 10 times. The conversion rates of ethylene were 97%, 96%, 96%, 96%, 95%, 96%, 95%, and 95%, respectively, and the selectivities of the product methyl propionate were 96%, 96%, 96%, 96%, 95%, 95%, 95%, and 95%, respectively.

[0056] Example 3

[0057] The method for preparing carboxylic acid ester using B-L double acid type ionic liquid includes the following steps:

[0058] (1) 0.4 mol of pyridine and 0.2 mol of propenesulfonic acid lactone were placed in a 100 mL round-bottom flask, and the reaction was stirred at 80°C for 6 h. Filtration was performed, and the obtained white solid was repeatedly washed with methanol to remove non-ionic residues. The product was dried at 80°C under vacuum to obtain zwitterionic solid powder.

[0059] (2) 0.1 mol of zwitterionic solid powder was placed in a flask and dissolved with methanol. 0.02 mol of HCl was added dropwise, and the reaction was stirred at 30°C for 12 h to obtain B acid type ionic liquid.

[0060] (3) To 0.05 mol of B acid type ionic liquid, 0.5 mol of SnCl2methanol solution was added dropwise, and the reaction was stirred for 6 h. The product was washed with n-hexane and dried at 120°C for 2 h to obtain B-L double acid type ionic liquid.

[0061] (4) In a 250 ml high-pressure reactor, 0.002 mol of acetylacetone palladium, 0.01 mol of the above-mentioned B-L double acid type ionic liquid, 0.4 mmol of 1,4-bis(diphenylphosphine)butane, 100 mL of ethylene glycol were sequentially added, the reactor was closed, 0.08 mol of propylene was filled, the reactor was replaced with CO for 3 times, CO was filled again until the pressure of the reactor was 2 MPa, the temperature was slowly increased to 180°C by the temperature controller, and the reaction was carried out for 2 h. After cooling to room temperature, the reactor was unloaded, and the obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890. The conversion rate of propylene was 94%, and the selectivity of the product methyl butyrate was 98%.

[0062] Example 4

[0063] A method for preparing a carboxylic acid ester using a B-L double acid type ionic liquid, comprising the following steps:

[0064] (1) 1 mol of benzimidazole and 0.2 mol of propylsulfonate lactone were placed in a 100 mL round-bottom flask, stirred at 90°C for 2 h, and filtered. The obtained white solid was repeatedly washed with nonane to remove non-ionic residues, and dried at 120°C under vacuum to obtain a zwitterionic solid powder.

[0065] (2) 0.1 mol of the zwitterionic solid powder was placed in a flask, dissolved with methanol, and 1 mol of HCl was added dropwise. The reaction was stirred at 80°C for 1 h to obtain a B acid type ionic liquid.

[0066] (3) 0.05 mol of a ZnCl2 methanol solution was added dropwise to 0.01 mol of the B acid type ionic liquid, stirred for 6 h, washed with cyclohexane, and dried at 100°C under vacuum for 4 h to obtain a B-L double acid type ionic liquid.

[0067] (4) In a 250 ml high-pressure reactor, 0.004 mmol of allyl palladium chloride, 0.01 mmol of the above-mentioned B-L double acid type ionic liquid, 0.001 mmol of 1,2-bis[(di-tert-butylphosphine)methyl]benzene, and 100 mL of glycerol were sequentially added. The reactor was closed, 0.08 mol of butene was filled, the reactor was replaced with CO for 3 times, CO was filled again until the pressure of the reactor was 1 MPa, the temperature was slowly increased to 50°C by the temperature controller, and the reaction was carried out for 10 h. After cooling to room temperature, the reactor was unloaded, and the obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890. The conversion rate of butene was 96%, and the selectivity of the product methyl pentanoate was 98%.

[0068] Comparative Example 1

[0069] A method for preparing a carboxylic acid ester, comprising the following steps:

[0070] 0.2 mol of 1-methylimidazole and 0.2 mol of butylsulfone lactone were put into a 100 mL round-bottom flask, stirred at 40°C for 10 h, and the white solid zwitterion was repeatedly washed with diethyl ether to remove non-ionic residues and dried at 80°C under vacuum.

[0071] 0.1 mol of the zwitterion was put into a flask, dissolved with methanol, and 0.1 mol of an HCl solution was added dropwise, followed by stirring at 60°C for 6 h. Then, 0.01 mol of an AlCl3 methanol solution was added to 0.1 mol of the B acid type ionic liquid, and stirring was continued for 4 h. After washing with toluene, the B-L double acid type ionic liquid was obtained by drying at 100°C under vacuum for 6 h.

[0072] In a 250 mL high-pressure reaction kettle, 0.05 mmol of PdCl2, 0.5 mmol of the B-L double acid type ionic liquid, and 0.5 mmol of PPh3 were sequentially added, 100 mL of methanol was added, 0.08 mol of styrene was added, the reaction kettle was closed, the reaction kettle was replaced with CO for 3 times, CO was filled into the reaction kettle to a pressure of 4 MPa, the temperature was slowly increased to 100°C by a temperature controller, and reaction was performed for 4 h. After cooling to room temperature, the reaction kettle was unloaded, and the obtained liquid was subjected to quantitative analysis by Agilent 6890. The conversion rate of styrene was 80%, and the selectivity of the product methyl benzoate was 75%.

[0073] Comparative Example 2

[0074] A method for preparing a carboxylic acid ester, comprising the steps of:

[0075] 0.2 mol of 1-methylimidazole and 0.2 mol of butylsulfone lactone were put into a 100 mL round-bottom flask, stirred at 40°C for 10 h, and the white solid zwitterion was repeatedly washed with diethyl ether to remove non-ionic residues and dried at 80°C under vacuum.

[0076] 0.1 mol of the zwitterion was put into a flask, dissolved with methanol, and 0.1 mol of an HCl solution was added dropwise, followed by stirring at 60°C for 6 h. Then, 0.01 mol of an AlCl3 methanol solution was added to 0.1 mol of the B acid type ionic liquid, and stirring was continued for 4 h. After washing with toluene, the B-L double acid type ionic liquid was obtained by drying at 100°C under vacuum for 6 h.

[0077] In a 250ml high-pressure reactor, 0.5mmol of PdCl2, 0.01mmol of B-L double acid ionic liquid, 0.5mmol of PPh3, 100ml of methanol, 0.08mol of styrene were sequentially added, the reactor was closed, the reactor was replaced with CO for 3 times, CO was filled into the reactor to a pressure of 4MPa, the temperature was slowly increased to 100℃ by a temperature controller, the reaction was carried out for 4h, the reactor was cooled to room temperature, and the obtained liquid was analyzed by Agilent 6890, the conversion rate of styrene was 68%, and the selectivity of the product methyl phenylpropionate was 85%.

[0078] Comparative Example 3

[0079] A method for preparing a carboxylic acid ester, comprising the following steps:

[0080] In a 250ml high-pressure reactor, 0.05mmol of Pd(OAc)2, 0.05mmol of methane sulfonic acid, 0.4mmol of 1,2-bis[(di-tert-butylphosphine)methyl]benzene, 100ml of methanol were sequentially added, the reactor was closed, the reactor was replaced with CO for 3 times, 0.2mol of ethylene was filled, CO gas was filled into the reactor to a pressure of 3MPa, the temperature was slowly increased to 80℃ by a temperature controller, the reaction was carried out for 6h, the reactor was cooled to room temperature, and the obtained liquid was analyzed by Agilent 6890, the conversion rate of ethylene was 82%, and the selectivity of the product methyl propionate was 90%.

[0081] Comparative Example 4

[0082] A method for preparing a carboxylic acid ester, comprising the following steps:

[0083] 0.2mol of 1-methylimidazole and 0.2mol of butyl sulfonic acid lactone were loaded into a 100ml round-bottom flask, stirred at 80℃ for 10h, the white solid zwitterion was repeatedly washed with diethyl ether to remove non-ionic residues, and dried at 80℃ under vacuum.

[0084] 0.1mol of the zwitterion was loaded into a flask, dissolved with methanol, 0.2mol of HCl solution was added dropwise, stirred at 60℃ for 6h, washed with toluene, and dried at 100℃ under vacuum for 6h to obtain the B acid ionic liquid.

[0085] In a 250ml high-pressure reactor, 0.02mmol of PdCl2, 0.5mmol of B acid type ionic liquid, 0.5mmol of PPh3, 100mL of methanol, 0.4mol of ethylene were sequentially added, the reactor was closed, the reactor was replaced with CO for 3 times, then CO was filled into the reactor to a pressure of 2MPa, the temperature was slowly increased to 80℃ by a temperature controller, the reaction was carried out for 3h, then the reactor was cooled to room temperature, the reactor was unloaded, and the reaction liquid was quantitatively analyzed by Agilent 6890, the ethylene conversion rate was 80%, and the selectivity of the product methyl phenylpropionate was 93%.

[0086] Repeatability: after the reaction, methyl propionate, methanol and the like were evaporated by a rotary evaporator, the repeatability of the catalyst was tested under the same reaction conditions as those of Comparative Example 3, the reaction was carried out for 3h, then the reactor was cooled to room temperature, the reactor was unloaded, and the reaction liquid was quantitatively analyzed by Agilent 6890. The ethylene conversion rate was 70%, and the selectivity of the product methyl phenylpropionate was 85%.

[0087] Of course, the above only describes the preferred embodiments of the present application and should not be considered as limiting the scope of the embodiments of the present application. The present application is also not limited to the above examples, and equivalent changes and improvements made by those skilled in the art within the scope of the present application should also be included in the scope of the present application.

Claims

1. A method for preparing a carboxylic acid ester using a B-L double acid type ionic liquid, characterized by: The method comprises the following steps: mixing a Pd compound, a B-L double acid ionic liquid, a phosphine ligand and an alcohol, filling an end alkene, pressurizing, heating and reacting to obtain a carboxylic acid ester; the molar ratio of the Pd compound to the phosphine ligand is (1-4):(1-100) in terms of the molar amount of Pd; the molar ratio of the Pd compound to the B-L double acid ionic liquid is (0.1-1):(0.1-0.5) in terms of the molar amount of Pd; The preparation method of the B-L double acid ionic liquid is characterized in that it comprises the following steps: (1) mixing a zwitterion precursor A and a zwitterion precursor B, reacting at 40-90 DEG C for 2-12 h, after completion, performing suction filtration, washing and drying to obtain a zwitterion solid powder; the zwitterion precursor A is one of 1-methyl imidazole, benzimidazole, triphenyl phosphine and pyridine; the zwitterion precursor B is propyl sulfonic acid lactone or butyl sulfonic acid lactone; the molar ratio of the zwitterion precursor A to the zwitterion precursor B is (1-5):(0.5-1); (2) dissolving the zwitterion solid powder in methanol, then adding an acid dropwise, and reacting to obtain a B acid ionic liquid; (3) adding L acid dropwise into the B acid ionic liquid, stirring and reacting, and then washing, drying to obtain a B-L double acid ionic liquid; the L acid is one of AlCl3, SnCl2, FeCl3 and ZnCl2; the molar ratio of the B acid ionic liquid to the L acid is (1-5):(0.1-10).

2. The method for preparing carboxylic acid ester using B-L double acid type ionic liquid according to claim 1, characterized in that: The molar ratio of the zwitterion solid powder in step (2) to the acid is (1-5):(1-100).

3. The method for preparing carboxylic acid ester using B-L double acid type ionic liquid according to claim 1, characterized in that: The reaction temperature in step (2) is 30-80 DEG C, and the reaction time is 1-12 h.

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