B-L double-acid ionic liquid, preparation method thereof and method for preparing carboxylic ester by adopting B-L double-acid ionic liquid

Abstract

The invention belongs to the technical field of olefin hydroesterification reaction and catalysts thereof, and particularly relates to a B-L double-acid ionic liquid and a preparation method thereof, and a method for preparing carboxylic ester by adopting the B-L double-acid ionic liquid as an auxiliary agent and a solvent at the same time. The preparation method of the B-L double-acid type ionic liquid comprises the following steps: mixing a zwitterionic precursor A and a zwitterionic precursor B, and after the reaction is completed, carrying out suction filtration, washing and drying to obtain zwitterionic solid powder; dissolving the zwitterionic solid powder in methanol, dropwise adding acid, and reacting to obtain a B acid type ionic liquid; dropwise adding L acid into the B acid type ionic liquid, stirring for reaction, washing and drying to obtain the B-L double-acid type ionic liquid. The B-L double-acid type ionic liquid provided by the invention is also used as an auxiliary agent and a solvent in the preparation of organic carboxylic ester, the dosage is small, the corrosion to equipment is small, the product is easy to separate, and the B-L double-acid type ionic liquid can be reused and has good catalytic activity.

Description

Technical Field

[0001] The invention belongs to the technical field of olefin hydroesterification reaction and catalysts thereof, and specifically relates to BL bis-acid type ionic liquid and a preparation method thereof, and a method for preparing carboxylic acid ester by using the BL bis-acid type ionic liquid as an auxiliary agent and a solvent. Background Art

[0002] Carboxylates and their derivatives are a class of valuable compounds in the chemical industry, and can be used as general intermediates in the production of drugs (non-steroidal anti-inflammatory drugs such as ibuprofen and naproxen), surfactants, and perfumes. Due to the atom economy and the universality of the raw materials (olefins, alcohols, and CO), transition metal-catalyzed olefin hydroesterification is one of the most effective methods for synthesizing these high-value products. To date, 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, phosphorus ligands, and acids have attracted widespread attention due to their good substrate adaptability and excellent catalytic performance, such as PdCl 2 / PPh 3 / CuCl 2 、[Pd(dtbpx)(dba)]、[Pd(PPh 3 ) 2 (olefin)], [PdCl 2 (dppp)] and other catalyst systems. However, these catalytic systems still have serious problems in practical application, such as difficulty in catalyst separation and reuse. In order to overcome these problems, the widely used methods include supported transition metal complexes, dual-phase systems and metal-oxide systems.

[0003] at present, Acids are usually used as additives and initiators for olefin hydroesterification and hydroxylation reactions. In industry, soluble acids such as hydrochloric acid, heteropolyacids, oxalic acid and p-toluenesulfonic acid (p-TsOH) are usually used. Acidic ionic liquids are also used as acidic additives in the reaction. In particular, ionic liquids (ILs) have been used in a variety of transition metal-centered catalytic reactions. ILs have low coordination ability and polarity similar to organic solvents, so choosing suitable ILs can make the metal center more stable. In addition, ILs are non-volatile and adjustable, which makes ILs an ideal solvent for catalytic cycles, realizing the recovery and reuse of catalysts in catalytic cycles, and can successfully solve the difficult problem of separating and reusing catalysts for olefin hydroesterification reactions.

[0004] CN102531890A discloses a method for preparing organic carboxylic acid esters by hydroesterification of olefins, wherein terminal olefins, CO and alcohols are used as reactants, and in the presence of an organic solvent and under the action of a catalyst composed of a palladium compound, a monodentate phosphine ligand or a bidentate phosphine ligand, and an acidic ionic liquid, the reaction pressure is controlled at 1.0 to 10.0 MPa and the reaction temperature is controlled at 50 to 150° C. to generate an organic carboxylic acid ester having one more carbon than the olefin. Ionic liquid acidic ionic liquid is used to replace methanesulfonic acid for hydroesterification reaction to reduce corrosion to the reactor, but there are still problems such as large usage, strong corrosion to equipment, unstable reaction, and low reaction activity. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a BL bis-acid type ionic liquid which can be used as an auxiliary agent and a solvent in the preparation of organic carboxylic acid esters, has a small dosage, is less corrosive to equipment, is easy to separate the product, is reusable, and has good catalytic activity.

[0006] The preparation method of the BL bis-acid type ionic liquid of the present invention comprises the following steps:

[0007] (1) mixing a zwitterion precursor A and a zwitterion precursor B, and after the reaction is completed, filtering, washing, and drying to obtain a zwitterion solid powder;

[0008] (2) dissolving the zwitterionic solid powder in methanol, adding acid dropwise to react to obtain a B acid-type ionic liquid;

[0009] (3) Add L acid dropwise to the B acid type ionic liquid, stir to react, wash and dry to obtain the BL bis acid type ionic liquid.

[0010] The zwitterion precursor A in step (1) is one of 1-methylimidazole, benzimidazole, triphenylphosphine and pyridine; the zwitterion precursor B is propane sultone or butyl sultone.

[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 of step (1) is 40-90°C and the reaction time is 2-12h.

[0013] The solvent used for washing in step (1) is one of toluene, ether, n-hexane, nonane, methanol and deionized water, and the drying temperature is 60-120°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°C, and the reaction time is 1-12h.

[0016] The L acid in step (3) is AlCl 3 SnCl 2 、FeCl 3 、ZnCl 2 One of them.

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

[0018] The washing solvent used in step (3) is one of toluene, n-hexane, cyclohexane and ethylbenzene, and the drying temperature is 60-120° C. and the drying time is 2-6 hours.

[0019] A BL bis-acid type ionic liquid is prepared by the preparation method of the BL bis-acid type ionic liquid.

[0020] The method for preparing carboxylic acid ester by using BL bis-acid type ionic liquid comprises the following steps: mixing a Pd compound, a BL bis-acid type ionic liquid, a phosphine ligand and an alcohol, charging a terminal olefin, pressurizing, and heating to react to obtain a carboxylic acid ester; the molar ratio of the Pd compound based on the molar amount of Pd to the phosphine ligand based on the molar amount of P is (1-4): (1-100); the molar ratio of the Pd compound based on the molar amount of Pd to the BL bis-acid type ionic liquid is (0.1-1): (0.1-0.5). The temperature is raised to 50-180°C, preferably 80-120°C, the reaction pressure is controlled at 1-10MPa, preferably 1-5MPa; and the reaction time is controlled at 2-10h.

[0021] The alcohol is one of methanol, ethanol, ethylene glycol and propylene glycol, and is also used as the solvent of the reaction system.

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

[0023] The phosphine ligand is a monodentate phosphine ligand or a bidentate phosphine ligand, such as triphenylphosphine (PPh 3 ), one of tri-n-butylphosphine, tricyclohexylphosphine, 1,2-bis[(di-tert-butylphosphino)methyl]benzene, and 1,4-bis(diphenylphosphino)butane.

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

[0025] The gas used for pressurization is CO or CO and N2 The mixed gas uses a gas with a purity of 90% to 100%.

[0026] Specifically, the method for preparing carboxylic acid ester using BL diacid type ionic liquid comprises the following steps:

[0027] (1) The zwitterion precursor A and the zwitterion precursor B are placed in a 100 mL round-bottom flask, stirred and reacted at 40-90° C. for 2-12 h, filtered, repeatedly washed to remove non-ionic residues, and vacuum dried at 60-120° C. to obtain a zwitterion solid powder.

[0028] (2) The zwitterionic solid powder is placed in a flask, dissolved in methanol, HCl is added dropwise, and the mixture is stirred at 30-80° C. for 1-12 h to obtain a B acid-type ionic liquid.

[0029] (3) Add a methanol solution of L acid to the B acid type ionic liquid, stir and react for 4-6 hours, wash, and dry at 60-120° C. for 2-6 hours to obtain a BL bis-acid type ionic liquid.

[0030] (4) In a 250 ml high pressure reactor, add Pd compound, BL bis-acid ionic liquid, phosphine ligand, and alcohol in sequence, seal the reactor, fill in terminal olefins, and react with CO or CO and N 2 The reactor was replaced three times with mixed gas, and then filled with CO or CO and N 2 The mixed gas is added to the reactor to a pressure of 1-10 MPa, and the temperature is slowly raised to 50-180°C by a temperature controller for reaction for 2-10 hours. The mixture is cooled to room temperature, the reactor is unloaded, and the obtained carboxylic acid ester is quantitatively analyzed by Agilent 6890.

[0031] The present invention uses terminal olefins, CO and alcohol as reactants, and generates an organic carboxylic acid ester with one more carbon under the action of a catalyst composed of a Pd compound, a phosphine ligand and a BL di-acidic ionic liquid. The present invention uses BL di-acidic ionic liquid as a catalyst. On the one hand, the electron-withdrawing effect of the Lewis acid site can significantly improve the Acidity can further reduce the usage of ionic liquids and the corrosiveness to equipment; on the other hand, the Lewis acid composed of metal salts has a strong electronic synergistic effect with the active site Pd, which can significantly improve the reaction activity and stability of the catalyst.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The method of preparing carboxylic acid esters by using BL bis-acid ionic liquids has mild reaction conditions, a wide range of raw material applications, and high product selectivity.

[0034] (2) The BL di-acid type ionic liquid prepared by the present invention is used as a catalyst, and no acid auxiliary agent is added to the catalyst system. The acid works synergistically with Lewis acid sites to enhance the dissociation of hydrogen protons and is less corrosive to equipment.

[0035] (3) By using the BL bis-acid ionic liquid prepared by the present invention, the Lewis acid of the metal salt interacts with the active site Pd, thereby improving the adsorption capacity of Pd for reactants, thereby improving the reaction activity and selectivity of the catalyst.

[0036] (4) The present invention adopts the method of preparing carboxylic acid esters using BL bis-acid type ionic liquids. By taking advantage of the adjustable structure of BL bis-acid type ionic liquids, the ratio of BL acid sites can be adjusted according to the requirements of the reaction to optimize the reaction results. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the infrared spectrum of the BL diacid-type ionic liquid prepared in Example 1.

[0038] Figure 2 The BL double acid type ionic liquid in Example 1 is in AlCl 3 NMR of the changes before and after coordination 1 H spectrum. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with specific embodiments.

[0040] In the following examples and comparative examples, the alcohol has a purity of 90% to 100%, CO or CO and N 2 The quality purity of the mixed gas is 90%-100%, other chemical reagents used are from commercial products, and the equipment used is existing equipment.

[0041] Example 1

[0042] The method for preparing carboxylic acid ester using BL bis-acid type ionic liquid comprises the following steps:

[0043] (1) 0.2 mol of 1-methylimidazole and 0.2 mol of butane sultone were placed in a 100 mL round-bottom flask, stirred and reacted at 40° C. for 12 h, and then filtered. The obtained white solid was repeatedly washed with ether to remove non-ionic residues, and vacuum dried at 80° C. to obtain a zwitterionic solid powder.

[0044] (2) 1 mol of zwitterionic solid powder was placed in a flask, dissolved with methanol, 1 mol of HCl was added dropwise, and the mixture was stirred at 60° C. for 6 h to obtain a B acid-type ionic liquid.

[0045] (3) Add 0.01 mol of AlCl to 0.5 mol of B acid ionic liquid. 3 The methanol solution was stirred for reaction for 4 h, washed with toluene, and dried under vacuum at 100 °C for 6 h to obtain BL bis-acid ionic liquid.

[0046] (4) In a 250 ml autoclave, add 0.05 mol of PdCl 2 , 0.05 mol of the above BL di-acid ionic liquid, 0.5 mol of PPh 3 , 100mL of methanol, the reactor was sealed, 0.08mol of styrene was charged into it, the reactor was replaced with CO for 3 times, CO was then charged into the reactor until the pressure of the reactor was 4MPa, the temperature was slowly raised to 100°C by a temperature controller, the reaction was carried out for 4h, the reaction was cooled to room temperature, the reactor was unloaded, and the obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890, the styrene conversion rate was 99%, and the selectivity of the product methyl phenylpropionate was 95%.

[0047] Depend on Figure 1 It can be seen that after testing the BL di-acid ionic liquid using a Bruker infrared spectrometer, the 3151 cm -1 The position is attributed to the stretching vibration of CH on the imidazole ring methyl group; 2946cm -1 Assigned to the stretching vibration of CH on the methylene group in the sulfonic acid propyl group; 1574cm -1 The position is attributed to the stretching vibration of -C=N- on the imidazole ring; 1459cm -1 The 1185cm-1 is attributed to the bending vibration of CH on the methylene group; -1 The position is attributed to the asymmetric stretching vibration of S=O on the sulfonate; 1041cm -1 The position is assigned to the S=O symmetric stretching vibration. This confirms the synthesis of the amphoteric BL diacid type ionic liquid.

[0048] Depend on Figure 2 It can be seen that the 1H NMR spectrum test at 600 MHz shows that AlCl 3 The coordination of will cause the displacement of H in the ionic liquid to change, and then the displacement will occur.

[0049] Example 2

[0050] The method for preparing carboxylic acid ester using BL bis-acid type ionic liquid comprises the following steps:

[0051] (1) 2 mol of triphenylphosphine and 0.2 mol of butane sultone were placed in a 100 mL round-bottom flask, stirred and reacted at 60° C. for 8 h, and then filtered. The obtained white solid was repeatedly washed with toluene to remove non-ionic residues, and vacuum dried at 60° C. to obtain a zwitterionic solid powder.

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

[0053] (3) Add 0.05 mol of FeCl to 0.01 mol of B acid ionic liquid. 3 The methanol solution was stirred for reaction for 6 h, washed with toluene, and dried under vacuum at 60 °C for 6 h to obtain BL bis-acid ionic liquid.

[0054] (4) In a 250 ml autoclave, add 0.005 mol of Pd(OAc) 2 , 0.01 mol of BL bis-acid ionic liquid, 0.5 mmol of tri-n-butylphosphine, 100 mL of ethanol, sealed the reactor, charged with 0.1 mol of ethylene, and heated with CO and N 2 The reactor was replaced three times with the mixed gas, and then filled with CO and N 2 The mixed gas was added to the reactor to a pressure of 5 MPa, and the temperature was slowly raised to 110°C controlled by a temperature controller for reaction for 8 hours. The reactor was cooled to room temperature, and the obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890. The ethylene conversion rate was 97%, and the selectivity of the product methyl propionate was 96%.

[0055] Repeatability: After evaporating methyl propionate and methanol from the reacted solution using a rotary evaporator, the repeatability of the BL double acid ionic liquid catalyst was evaluated using the same reaction conditions as in Example 2. The reaction was carried out for 8 hours, cooled to room temperature, and the reactor was unloaded. The liquid obtained by the reaction was quantitatively analyzed by Agilent 6890, and the ethylene conversion was 97%, and the selectivity of the product methyl propionate was 96%. The reaction was repeated 10 times, and the ethylene conversions were 97%, 96%, 96%, 95%, 96%, 95%, and 95%, respectively, and the selectivities of the product methyl propionate were 96%, 96%, 96%, 96%, 95%, 95%, 95%, respectively.

[0056] Example 3

[0057] The method for preparing carboxylic acid ester using BL bis-acid type ionic liquid comprises the following steps:

[0058] (1) 0.4 mol of pyridine and 0.2 mol of propane sultone were placed in a 100 mL round-bottom flask, stirred and reacted at 80° C. for 6 h, and then filtered. The obtained white solid was repeatedly washed with methanol to remove non-ionic residues, and vacuum dried at 80° C. to obtain a zwitterionic solid powder.

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

[0060] (3) Add 0.5 mol of SnCl to 0.05 mol of B acid ionic liquid. 2 The methanol solution was stirred for reaction for 6 h, washed with n-hexane, and dried at 120 °C for 2 h to obtain BL bis-acid ionic liquid.

[0061] (4) In a 250 ml autoclave, 0.002 mol of palladium acetylacetonate, 0.01 mol of the above-mentioned BL bis(diphenylphosphino)butane, 0.4 mmol, and 100 mL of ethylene glycol were added in sequence. The autoclave was sealed, and 0.08 mol of propylene was charged. The autoclave was replaced with CO for 3 times, and then CO was charged until the pressure of the autoclave was 2 MPa. The temperature was slowly raised to 180° C. by a temperature controller to react for 2 h. The autoclave was cooled to room temperature, and the autoclave was unloaded. The obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890. The propylene conversion rate was 94%, and the selectivity of the product methyl butyrate was 98%.

[0062] Example 4

[0063] The method for preparing carboxylic acid ester using BL bis-acid type ionic liquid comprises the following steps:

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

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

[0066] (3) Add 0.05 mol of ZnCl to 0.01 mol of B acid ionic liquid. 2 The methanol solution was stirred for reaction for 6 h, washed with cyclohexane, and dried in vacuum at 100 °C for 4 h to obtain BL bis-acid ionic liquid.

[0067] (4) In a 250 ml high-pressure reactor, 0.004 mmol of allylpalladium chloride, 0.01 mmol of the above-mentioned BL bis-acid type ionic liquid, 0.001 mmol of 1,2-bis[(di-tert-butylphosphino)methyl]benzene, and 100 mL of propylene glycol were added in sequence. The reactor was sealed and charged with 0.08 mol of butene. The reactor was replaced with CO for 3 times, and then CO was charged until the pressure of the reactor reached 1 MPa. The temperature was slowly raised to 50° C. by a temperature controller to react for 10 h. The reactor was cooled to room temperature and the reactor was unloaded. The obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890. The butene conversion rate was 96%, and the selectivity of the product methyl valerate was 98%.

[0068] Comparative Example 1

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

[0070] 0.2 mol of 1-methylimidazole and 0.2 mol of butane sultone were placed in a 100 mL round-bottom flask and stirred at 40°C for 10 h. The white solid zwitterion was repeatedly washed with ether to remove non-ionic residues and dried in vacuo at 80°C.

[0071] Take 0.1 mol of zwitterion into a flask, dissolve it with methanol, add 0.1 mol of HCl solution, stir at 60 °C for 6 h, then add 0.01 mol of AlCl 3 Methanol solution, continued stirring for 4 h, washed with toluene, and dried under vacuum at 100 °C for 6 h to obtain BL bis-acid ionic liquid.

[0072] In a 250 ml autoclave, 0.05 mmol of PdCl 2 , 0.5mmol of BL diacid type ionic liquid, 0.5mmol of PPh 3 , 100mL of methanol, 0.08mol of styrene was added, the reactor was sealed, the reactor was replaced with CO for 3 times, and CO was then filled in until the pressure of the reactor was 4MPa. The temperature was slowly raised to 100°C by a temperature controller, and the reaction was carried out for 4h. The reaction was cooled to room temperature, the reactor was unloaded, and the liquid obtained by the reaction was quantitatively analyzed by Agilent 6890. The styrene conversion rate was 80%, and the selectivity of the product methyl phenylpropionate was 75%.

[0073] Comparative Example 2

[0074] A method for preparing a carboxylic acid ester comprises the following steps:

[0075] 0.2 mol of 1-methylimidazole and 0.2 mol of butane sultone were placed in a 100 mL round-bottom flask and stirred at 40°C for 10 h. The white solid zwitterion was repeatedly washed with ether to remove non-ionic residues and dried in vacuo at 80°C.

[0076] Take 0.1 mol of zwitterion into a flask, dissolve it with methanol, add 0.1 mol of HCl solution, stir at 60 °C for 6 h, then add 0.01 mol of AlCl 3 Methanol solution, continued stirring for 4 h, washed with toluene, and dried under vacuum at 100 °C for 6 h to obtain BL bis-acid ionic liquid.

[0077] In a 250 ml autoclave, 0.5 mmol of PdCl 2 , 0.01mmol of BL diacid ionic liquid, 0.5mmol of PPh 3 , 100 ml of methanol, add 0.08 mol of styrene, close the reactor, replace the reactor with CO 3 times, and then fill CO to the reactor pressure of 4 MPa. Control the temperature slowly to 100 ° C by the temperature controller, react for 4 hours, cool to room temperature, unload the reactor, and quantitatively analyze the liquid obtained by the reaction using Agilent 6890. The styrene conversion rate is 68%, and the selectivity of the product methyl phenylpropionate is 85%.

[0078] Comparative Example 3

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

[0080] In a 250ml high pressure reactor, 0.05 mmol of Pd(OAc) 2 , 0.05mmol methanesulfonic acid, 0.4mmol 1,2-bis[(di-tert-butylphosphino)methyl]benzene, 100mL methanol, closed the reactor, replaced the reactor with CO 3 times, flushed with 0.2mol ethylene, and then filled with CO gas until the pressure of the reactor was 3MPa. The temperature was slowly raised to 80°C by the temperature controller, reacted for 6h, cooled to room temperature, unloaded, and the liquid obtained by the reaction was quantitatively analyzed by Agilent 6890. The ethylene conversion rate 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 comprises the following steps:

[0083] 0.2 mol of 1-methylimidazole and 0.2 mol of butane sultone were placed in a 100 mL round-bottom flask and stirred at 80 °C for 10 h. The white solid zwitterion was repeatedly washed with ether to remove non-ionic residues and dried in vacuo at 80 °C.

[0084] Take 0.1 mol of zwitterion and put it into a flask, dissolve it with methanol, add 0.2 mol of HCl solution, stir at 60°C for 6 hours, wash with toluene, and vacuum dry at 100°C for 6 hours to obtain B acid ionic liquid.

[0085] In a 250 ml autoclave, 0.02 mmol of PdCl 2 , 0.5mmol of B acid ionic liquid, 0.5mmol of PPh 3 , 100mL of methanol, add 0.4mol of ethylene, close the reactor, replace the reactor with CO 3 times, and then fill CO to the reactor pressure of 2MPa. Control the temperature slowly to 80°C by the temperature controller, react for 3h, cool to room temperature, unload the reactor, and quantitatively analyze the liquid obtained by the reaction using Agilent 6890. The ethylene conversion rate is 80%, and the selectivity of the product methyl phenylpropionate is 93%.

[0086] Repeatability: After the reaction, methyl propionate, methanol and other substances were evaporated using a rotary evaporator. The catalyst repeatability was tested using the same reaction conditions as in Comparative Example 3. The reaction was continued for 3 hours, cooled to room temperature, and the reactor was unloaded. The liquid obtained by the reaction was quantitatively analyzed using an Agilent 6890. The ethylene conversion rate was 70%, and the selectivity of the product methyl phenylpropionate was 85%.

[0087] Of course, the above contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of the embodiments of the present invention. The present invention is not limited to the above examples, and equal changes and improvements made by ordinary technicians in the technical field within the essential scope of the present invention should all fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing a BL bis-acid type ionic liquid, characterized in that: The following steps are involved: (1) mixing a zwitterion precursor A and a zwitterion precursor B, and after the reaction is completed, filtering, washing, and drying to obtain a zwitterion solid powder; (2) dissolving the zwitterionic solid powder in methanol, adding acid dropwise to react to obtain a B acid-type ionic liquid; (3) Add L acid dropwise to the B acid type ionic liquid, stir to react, wash and dry to obtain the BL bis acid type ionic liquid.

2. The method for preparing the BL bis-acid type ionic liquid according to claim 1, characterized in that: The zwitterion precursor A in step (1) is one of 1-methylimidazole, benzimidazole, triphenylphosphine and pyridine; the zwitterion precursor B is propane sultone or butyl sultone.

3. The method for preparing the BL bis-acid type ionic liquid according to claim 2, characterized in that: The molar ratio of the zwitterionic precursor A to the zwitterionic precursor B in step (1) is (1-5):(0.5-1).

4. The method for preparing the BL bis-acid type ionic liquid according to claim 1, characterized in that: The reaction temperature of step (1) is 40-90°C and the reaction time is 2-12h.

5. The method for preparing the BL bis-acid type ionic liquid according to claim 1, characterized in that: The molar ratio of the zwitterionic solid powder to the acid in step (2) is (1-5):(1-100).

6. The method for preparing the BL bis-acid type ionic liquid according to claim 1, characterized in that: The reaction temperature of step (2) is 30-80°C, and the reaction time is 1-12h.

7. The method for preparing the BL bis-acid type ionic liquid according to claim 1, characterized in that: The L acid in step (3) is one of AlCl3, SnCl2, FeCl3, and ZnCl2.

8. The method for preparing the BL bis-acid type ionic liquid according to claim 1, characterized in that: The molar ratio of the B acid type ionic liquid to the L acid in step (3) is (1-5):(0.1-10).

9. A BL bis-acid type ionic liquid, characterized in that: The BL di-acid type ionic liquid is prepared by the preparation method of any one of claims 1 to 8.

10. A method for preparing carboxylic acid esters using the BL diacid type ionic liquid according to claim 9, characterized in that: The method comprises the following steps: mixing a Pd compound, a BL bis-acid type ionic liquid, a phosphine ligand and an alcohol, charging a terminal olefin, applying pressure, and reacting at a high temperature to obtain a carboxylate; the molar ratio of the Pd compound based on the molar amount of Pd to the phosphine ligand based on the molar amount of P is (1-4):(1-100); the molar ratio of the Pd compound based on the molar amount of Pd to the BL bis-acid type ionic liquid is (0.1-1):(0.1-0.5).

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