Preparation method of ionic liquid

Abstract

The invention relates to a preparation method of an ionic liquid, which comprises the following steps: (1) reacting mixed powder of oxalic acid metal salt and boric acid in hexamethyldisiloxane at 90-120 DEG C for 24-36 hours, and filtering the obtained reaction liquid to obtain a reaction mother solution and a solid 1; (2) washing the solid 1 with dimethyl carbonate and / or methyl ethyl carbonate, drying, mixing with ethyl acetate and / or acetonitrile, filtering the mixture to obtain filtrate and a solid 2, and performing rotary evaporation on the filtrate to obtain bis (oxalato) boric acid metal salt; and (3) reacting the bis (oxalato) boric acid metal salt and onium salt in water at 50-60 DEG C, and separating and drying the obtained reaction liquid to obtain the quaternary ammonium onium / pyridinium bis (oxalato) borate ionic liquid. The ionic liquid prepared by the method is colorless and high in purity, and the method is easy to obtain raw materials, simple to operate, low in cost and suitable for industrial popularization.

Description

Technical Field

[0001] The present invention belongs to the technical field of antistatic agents, and particularly relates to a preparation method of an ionic liquid. Background Art

[0002] With the rapid growth of the touch screen market, the application scenarios of antistatic optical films are becoming more and more extensive. Due to its excellent antistatic performance and relatively simple usage method, antistatic agents have become important additives in the production of optical films. Among them, bis(oxalato)borate ionic liquids have high thermal stability, can maintain antistatic performance under high temperature conditions, are suitable for the production of optical films that require high temperature processing, and their application in optical films does not affect their transparency, which can meet the strict requirements of optical films for optical properties. Quaternary ammonium / pyridinium bis(oxalato)borate ionic liquids have important application value as antistatic agents in fields such as optical films.

[0003] The preparation of quaternary ammonium / pyridinium bis(oxalato)borate ionic liquids involves the preparation of bis(oxalato)borate and the ion exchange reaction of bis(oxalato)borate with quaternary ammonium salts / pyridinium salts. It has been found that the purity of bis(oxalato)borate directly affects the performance of quaternary ammonium / pyridinium bis(oxalato)borate ionic liquids. In the prior art, bis(oxalato)borate can be prepared by different reactions. For example, trimethylchlorosilane reacts with oxalic acid first and then with lithium tetrafluoroborate to obtain lithium bis(oxalato)borate, and this reaction will produce harmful gas fluorosilane, which is harmful to people and instruments. Another example is that boron trifluoride·dimethyl carbonate complex, oxalic acid and lithium fluoride react to obtain lithium bis(oxalato)borate, and the raw material boron trifluoride·dimethyl carbonate complex used in this reaction is highly harmful and HF gas will be produced during the reaction process. Another example is that lithium bicarbonate, boric acid and oxalic acid react to form lithium bis(oxalato)borate. This method does not produce harmful gases, but it will produce water. Lithium bis(oxalato)borate is easily decomposed by water, and additional water removal operations are required to ensure the purity of lithium bis(oxalato)borate, and the operation is cumbersome. During the ion exchange reaction, bis(oxalato)borate is unstable and prone to produce by-products, which affect the performance of quaternary ammonium / pyridinium bis(oxalato)borate ionic liquids. In addition, improving the utilization rate of raw materials and reducing production costs are also important goals in the industrial production of quaternary ammonium / pyridinium bis(oxalato)borate ionic liquids. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a quaternary ammonium / pyridinium bis(oxalato)borate ionic liquid that is colorless, has high purity and is more suitable for industrial production.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A preparation method of an ionic liquid, which comprises the following steps:

[0007] (1) The mixed powder of metal oxalate and boric acid reacts in hexamethyldisiloxane at 90 - 120 °C for 24 - 36 h. The resulting reaction solution is filtered to obtain a reaction mother liquor and solid 1;

[0008] (2) The solid 1 is washed with dimethyl carbonate and / or ethyl methyl carbonate and dried, then mixed with ethyl acetate and / or acetonitrile. The resulting mixture is filtered to obtain a filtrate and solid 2. The filtrate is rotary evaporated to obtain metal bis(oxalato)borate;

[0009] (3) The metal bis(oxalato)borate and the onium salt react in water at 50 - 60 °C. The resulting reaction solution is separated by liquid - liquid extraction and dried to obtain the ionic liquid. The cation of the onium salt is an alkyl - substituted quaternary ammonium cation or a pyridinium cation, and the anion is a chloride ion.

[0010] In an embodiment of the present invention, the metal oxalate is selected from lithium oxalate, sodium oxalate or potassium oxalate.

[0011] In an embodiment of the present invention, the onium salt is selected from the compound shown in formula (I) or the compound shown in formula (II),

[0012]

[0013] wherein, R1 is an alkane with 4 - 10 carbon atoms, and R2 is a methyl group.

[0014] In an embodiment of the present invention, in step (1), the molar ratio of the metal oxalate to boric acid in the feed is 1:(3 - 5), and the reaction temperature is 100 - 120 °C.

[0015] In an embodiment of the present invention, in step (1), the molar ratio of boric acid to hexamethyldisiloxane in the feed is 1:(2.25 - 3).

[0016] In an embodiment of the present invention, in step (3), the metal bis(oxalato)borate is mixed with deionized water at 0 - 5 °C to form an aqueous solution of metal bis(oxalato)borate. The aqueous solution of metal bis(oxalato)borate is mixed with an aqueous solution of the onium salt and then reacts at 50 - 60 °C for 2 - 4 h.

[0017] In an embodiment of the present invention, in step (3), the molar ratio of the metal bis(oxalato)borate to the onium salt in the feed is (1.2 - 1.5):1.

[0018] In an embodiment of the present invention, the preparation method further includes step (4). Step (4) includes mixing the reaction mother liquor with concentrated sulfuric acid and reacting at 70 - 90 °C for 4 - 8 h. The resulting reaction solution is subjected to vacuum distillation to obtain hexamethyldisiloxane. The obtained hexamethyldisiloxane can be recycled to the next batch of raw materials.

[0019] Furthermore, the addition amount of the concentrated sulfuric acid is 0.5% - 1.5% of the mass of the reaction mother liquor.

[0020] In an embodiment of the present invention, step (4) further includes mixing the solid 2 with an aqueous oxalic acid solution, reacting at 50 - 60°C for 2 - 4 h, subjecting the obtained reaction solution to rotary evaporation to obtain a mixture of boric acid and metal oxalate, and drying and grinding to obtain a mixed powder of metal oxalate and boric acid. The obtained mixed powder of metal oxalate and boric acid can be recycled into the next batch of raw materials.

[0021] Furthermore, the molar ratio of the white solid to the oxalic acid in the feed is 1:(0.9 - 1.2).

[0022] The present invention also provides an antistatic agent, which is an ionic liquid prepared by the above preparation method.

[0023] The present invention also provides the application of the above antistatic agent in an optical film.

[0024] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0025] The present invention adopts a new synthesis route. First, under specific reaction conditions, using boric acid, lithium oxalate, and hexamethyldisiloxane, bis(oxalato)borate metal salt is synthesized by the "one-pot method", and high-purity bis(oxalato)borate metal salt is obtained through the selected separation method. Then, under another specific reaction condition, bis(oxalato)borate metal salt reacts with quaternary ammonium salt / pyridinium salt in water through an ion exchange reaction to obtain quaternary ammonium / pyridinium bis(oxalato)borate ionic liquid. Compared with the existing preparation methods, the method for preparing quaternary ammonium / pyridinium bis(oxalato)borate ionic liquid by the method of the present invention is colorless and has high purity. No toxic gases containing F or Cl are generated throughout the preparation process, and the by-products generated can be recycled. The recycling operation is safe and simple, green and environmentally friendly. The method of the present invention has easily available raw materials, simple operation, easy control, low preparation cost, and is suitable for industrial promotion. Description of the Drawings

[0026] Figure 1 1H NMR spectrum of the ionic liquid (TBMA-BOB) in Example 1;

[0027] Figure 2 11B NMR spectrum of the ionic liquid (TBMA-BOB) in Example 1;

[0028] Figure 3 13C NMR spectrum of the ionic liquid (TBMA-BOB) in Example 1;

[0029] Figure 4 1H NMR spectrum of the ionic liquid (4MHP-BOB) in Example 2;

[0030] Figure 5 11B NMR spectrum of the ionic liquid (4MHP-BOB) in Example 2;

[0031] Figure 6 13C NMR spectrum of the ionic liquid (4MHP-BOB) in Example 2. Detailed implementation manners

[0032] The present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples. The implementation conditions adopted in the examples can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry.

[0033] Unless otherwise specified, the raw materials used in the following examples and comparative examples are all commercially available products.

[0034] The operations without special instructions in the following examples and comparative examples are carried out at room temperature.

[0035] The reaction equation of the quaternary ammonium / pyridinium bis(oxalato)borate of the present invention is as follows:

[0036]

[0037] where M is Li or Na or K

[0038]

[0039] where R1 is an alkane with 4 to 10 carbon atoms; R2 is a methyl group, which can be at the 2 or 3 or 4 position of the pyridine ring; M is Li or Na or K.

[0040] The main reaction equation for by-product recovery is as follows:

[0041]

[0042] where M is Li or Na or K.

[0043] In the following examples and comparative examples, the detection methods for bis(oxalato)borate are as follows: purity is detected by liquid chromatography (IC); water content is detected by the Karl Fischer method using a KF furnace; solvent residue is detected by gas chromatography (GC); metal ions are detected by ion chromatography (ICP). The detection methods for ionic liquids are as follows: purity is detected by the weight loss method, with the non-volatile matter being the product and the detection temperature being 105 °C; chloride ion content is detected by potentiometric titration; water content is detected by the Karl Fischer method using a KF furnace; metal ions are detected by ion chromatography (ICP); colority is detected by the general method for the determination of colority of chemical reagents in GB / T 605-2006.

[0044] Example 1

[0045] This embodiment provides a method for preparing an ionic liquid, which includes the following steps:

[0046] (1) Add 5 mol of lithium oxalate and 17.5 mol of boric acid into a mortar and grind them into powder. Put 52.5 mol of hexamethyldisiloxane and the above solid powder into a reaction kettle, and stir and react at 100 °C for 36 h. After the reaction is completed, filter to obtain the reaction mother liquor and white solid 1 respectively.

[0047] (2) Add 26.5 mol of dimethyl carbonate to white solid 1, stir and wash for 1 h, filter, remove the filtrate, repeat the washing twice in this way, and put the washed white solid 1 into an oven at 80 °C for drying for 4 h. Add 36.2 mol of ethyl acetate to the dried white solid 1, stir and mix for 2 h, then filter to obtain a colorless filtrate and white solid 2 respectively. Rotate evaporate the filtrate (temperature is 90 °C) to obtain the crude product, and deeply dry the crude product in an oven at 100 °C to obtain 413.8 g of lithium bis(oxalato)borate (LiBOB).

[0048] (3) Dissolve 1.8 mol of tri-n-butylmethylammonium chloride (TBMA-Cl) in 23.6 mol of deionized water. Dissolve the obtained lithium bis(oxalato)borate (LiBOB) in 46.0 mol of deionized water (0 - 5 °C), and filter. Mix the tri-n-butylmethylammonium chloride aqueous solution and the lithium bis(oxalato)borate aqueous solution, and stir and react at 50 °C for 4 h. After the reaction is completed, separate the liquid, add 132.3 mol of deionized water to the lower layer material for washing twice, and obtain 595.3 g of ionic liquid (TBMA-BOB) through vacuum drying and filtration.

[0049] (4) Drop 0.9 mol of concentrated sulfuric acid into the reaction mother liquor obtained by filtration in step (1), react at 70 °C for 8 h, and perform vacuum distillation to obtain hexamethyldisiloxane, which can be recycled to the next batch of raw materials. Add an appropriate amount of oxalic acid aqueous solution to white solid 2 in step (2) (white solid 2 is lithium borate, and oxalic acid is added in an equimolar amount to lithium borate), react at 50 °C for 2 h, rotate evaporate the reaction solution (temperature is 110 °C) to obtain a mixed crude product of boric acid and lithium oxalate, and then deeply dry it in an oven at 110 °C (about 80% of lithium oxalate and boric acid are recovered), which can be recycled to the next batch of raw materials.

[0050] The test results of LiBOB obtained in step (2) are as follows: Purity: 99.90%; Moisture: 54 ppm; Solvent residue: 534 ppm; Metal ion content, Al: not detected; Ca: not detected; Cr: not detected; Cu: 0.2 ppm; Fe: 0.1 ppm; K: not detected; Na: 0.2 ppm; Ni: 0.1 ppm; Pb: not detected; Zn: 0.1 ppm.

[0051] The test results of the TBMA-BOB obtained in step (3) are as follows: purity: 99.67%; moisture: 256 ppm; chloride ion content: 1.6 ppm; chromaticity: 30 APHA; metal ion content, Al: not detected; Ca: not detected; Cr: 0.1 ppm; Cu: not detected; Fe: 0.1 ppm; K: not detected; Na: not detected; Ni: not detected; Pb: not detected; Zn: not detected.

[0052] The nuclear magnetic resonance spectrum of the TBMA-BOB obtained in step (3) is shown in Figures 1 to 3 .

[0053] Example 2

[0054] This example provides another method for preparing an ionic liquid, which includes the following steps:

[0055] (1) Add 5 mol of potassium oxalate and 17.5 mol of boric acid to a mortar and grind them into a powder. Put 39.4 mol of hexamethyldisiloxane and the above solid powder into a reaction kettle, and stir and react at 120 °C for 24 h. After the reaction is completed, filter to obtain the reaction mother liquor and white solid 1 respectively.

[0056] (2) Add 33.7 mol of dimethyl carbonate to white solid 1, stir and wash for 1 h, filter, remove the filtrate, repeat the washing twice according to this, and put the washed white solid 1 into an oven at 80 °C to dry for 4 h. Add 39.8 mol of ethyl acetate to the dried white solid 1, stir and mix for 2 h, then filter to obtain a colorless filtrate and white solid 2 respectively. Rotate evaporate the filtrate (temperature is 90 °C) to obtain a crude product, and deeply dry the crude product in an oven at 100 °C to obtain 468.3 g of potassium bis(oxalato)borate (KBOB).

[0057] (3) Dissolve 1.4 mol of N-hexyl-4-methylpyridinium chloride (4MHP-Cl) in 32.8 mol of deionized water. Dissolve the obtained potassium bis(oxalato)borate (KBOB) in 52.0 mol of deionized water (0 - 5 °C), and filter. Mix the N-hexyl-4-methylpyridinium chloride aqueous solution and the potassium bis(oxalato)borate aqueous solution, and stir and react at 50 °C for 4 h. After the reaction is completed, separate the liquid, add 91.6 mol of deionized water to the lower layer material for washing twice, and obtain 412.1 g of ionic liquid (4MHP-BOB) through vacuum drying and filtration.

[0058] (4) Add 0.9 mol of concentrated sulfuric acid dropwise to the reaction mother liquor obtained by filtration in step (1), react at 90 °C for 4 h, and perform vacuum distillation to obtain hexamethyldisiloxane, which can be recycled to the next batch of raw materials. Add the white solid 2 in step (2) to an appropriate amount of oxalic acid aqueous solution, react at 50 °C for 2 h, rotary evaporate the reaction solution (temperature is 110 °C) to obtain a crude product of boric acid and potassium oxalate, and then perform deep drying in an oven at 110 °C to obtain a mixed solid of boric acid and potassium oxalate, which can be recycled to the next batch of raw materials.

[0059] The test results of KBOB obtained in step (2) are as follows: Purity: 99.94%; Moisture: 26 ppm; Solvent residue: 412 ppm; Metal ion content, Al: not detected; Ca: not detected; Cr: not detected; Cu: not detected; Fe: 0.1 ppm; K: 17.3%; Na: 0.3 ppm; Ni: not detected; Pb: not detected; Zn: not detected.

[0060] The test results of 4MHP - BOB obtained in step (3) are as follows: Purity: 99.36%; Moisture: 162 ppm; Chloride ion content: 3.4 ppm; Chromaticity: 50 APHA; Metal ion content, Al: not detected; Ca: not detected; Cr: 0.1 ppm; Cu: not detected; Fe: 0.1 ppm; K: 0.9 ppm; Na: 0.2 ppm; Ni: not detected; Pb: not detected; Zn: 0.1 ppm.

[0061] The nuclear magnetic resonance spectrum of 4MHP - BOB obtained in step (3) is shown in Figures 4 to 6 .

[0062] Example 3

[0063] This example provides another preparation method of ionic liquid, including the following steps:

[0064] (1) Add 5 mol of sodium oxalate and 17.5 mol of boric acid to a mortar and grind them into powder. Charge 52.5 mol of hexamethyldisiloxane and the above solid powder into a reaction kettle, and stir and react at 110 °C for 30 h. After the reaction is completed, filter to obtain a reaction mother liquor and a white solid 1 respectively.

[0065] (2) Add 25.2 mol of ethyl methyl carbonate to the white solid 1, stir and wash for 1 h, filter to remove the filtrate, repeat the washing twice in this way, and put the washed white solid 1 into an oven at 80 °C for drying for 4 h. Add 85.4 mol of acetonitrile to the dried white solid 1, stir and mix for 2 h, then filter to obtain a colorless filtrate and a white solid 2 respectively. Rotary evaporate the filtrate (temperature is 90 °C) to obtain a crude product, and perform deep drying of the crude product in an oven at 100 °C to obtain 444.3 g of sodium bis(oxalato)borate (NaBOB).

[0066] (3) Dissolve 1.4 mol of trioctylmethylammonium chloride (TOMA-Cl) in 31.7 mol of deionized water. Dissolve the obtained sodium bis(oxalato)borate (NaBOB) in 49.4 mol of deionized water (0 - 5 °C), and filter. Mix the trioctylmethylammonium chloride aqueous solution with the sodium bis(oxalato)borate aqueous solution, and stir and react at 50 °C for 4 h. After the reaction is completed, separate the liquid layers, add 138.3 mol of deionized water to the lower-layer material and wash twice. Obtain 622.2 g of ionic liquid (TOMA-BOB) by vacuum drying and filtration.

[0067] (4) Dropwise add 0.9 mol of concentrated sulfuric acid to the reaction mother liquor obtained by filtration in step (1), react at 80 °C for 6 h, and perform vacuum distillation to obtain hexamethyldisiloxane, which can be recycled to the next batch of raw materials. Add the white solid 2 in step (2) to an appropriate amount of oxalic acid aqueous solution, react at 50 °C for 2 h, rotate and evaporate the reaction solution (temperature is 110 °C) to obtain a crude mixture of boric acid and sodium oxalate, and then perform deep drying in an oven at 110 °C to obtain a solid mixture of boric acid and sodium oxalate, which can be recycled to the next batch of raw materials.

[0068] The test results of the NaBOB obtained in step (2) are as follows: Purity: 99.93%; Moisture: 23 ppm; Solvent residue: 312 ppm; Metal ion content, Al: 0.1 ppm; Ca: not detected; Cr: not detected; Cu: not detected; Fe: 0.1 ppm; K: 0.1 ppm; Na: 10.9%; Ni: not detected; Pb: not detected; Zn: not detected.

[0069] The test results of the TOMA-BOB obtained in step (3) are as follows: Purity: 99.90%; Moisture: 351 ppm; Chloride ion content: 5.8 ppm; Chromaticity: 80 APHA; Metal ion content, Al: 0.1 ppm; Ca: not detected; Cr: not detected; Cu: not detected; Fe: not detected; K: 0.1 ppm; Na: 0.8 ppm; Ni: 0.1 ppm; Pb: not detected; Zn: not detected.

[0070] Example 4

[0071] This example provides another method for preparing an ionic liquid, which includes the following steps:

[0072] (1) Add 1 mol of lithium oxalate, 3.5 mol of boric acid, and the mixed solid recovered from step (4) of Example 1 into a mortar, and grind into a powder. Put 52.5 mol of hexamethyldisiloxane (about 81.4% of the hexamethyldisiloxane recovered from step (4) of Example 1) and the above powder into a reaction kettle, and stir and react at 120 °C for 36 h. After the reaction is completed, filter to obtain the reaction mother liquor and white solid 1 respectively.

[0073] (2) Add 30.6 mol of ethyl methyl carbonate to the white solid 1, stir and wash for 1 h, filter, remove the filtrate, repeat the washing twice according to this method, and put the washed white solid 1 into an oven at 80 °C for drying for 4 h. Add 36.2 mol of ethyl acetate to the dried white solid 1, stir and mix for 2 h, then filter to obtain a colorless filtrate and a white solid 2 respectively. Rotate evaporate the filtrate (temperature is 90 °C) to obtain a crude product, and deeply dry the crude product in an oven at 100 °C to obtain 405.0 g of lithium bis(oxalato)borate (LiBOB).

[0074] (3) Dissolve 1.5 mol of N-octyl-3-methylpyridinium chloride (3MOP-Cl) in 34.4 mol of deionized water. Dissolve the obtained lithium bis(oxalato)borate (LiBOB) in 45.0 mol of deionized water (0 - 5 °C), and filter. Mix the N-octyl-3-methylpyridinium chloride aqueous solution with the lithium bis(oxalato)borate aqueous solution, and stir and react at 60 °C for 3 h. After the reaction is completed, separate the liquid, add 96.2 mol of deionized water to the lower layer material for washing twice, and obtain 433.1 g of ionic liquid (3MOP-BOB) through vacuum drying and filtration.

[0075] (4) Dropwise add 0.9 mol of concentrated sulfuric acid to the reaction mother liquor obtained by filtration in step (1), react at 90 °C for 4 h, and carry out vacuum distillation to obtain hexamethyldisiloxane, which can be recycled to the next batch of raw materials. Add an appropriate amount of oxalic acid aqueous solution to the white solid 2 in step (2), react at 50 °C for 2 h, rotate evaporate the reaction solution (temperature is 110 °C) to obtain a crude mixture of boric acid and lithium oxalate, and then deeply dry it in an oven at 110 °C to obtain a solid mixture of boric acid and lithium oxalate, which can be recycled to the next batch of raw materials.

[0076] The test results of LiBOB obtained in step (2) are as follows: purity: 99.92%; moisture: 31 ppm; solvent residue: 237 ppm; metal ion content, Al: 0.1 ppm; Ca: 0.1 ppm; Cr: 0.2 ppm; Cu: 0.1 ppm; Fe: 0.1 ppm; K: 0.1 ppm; Na: 0.2 ppm; Ni: 0.1 ppm; Pb: not detected; Zn: 0.1 ppm.

[0077] The test results of 3MOP-BOB obtained in step (3) are as follows: purity: 99.34%; moisture: 504 ppm; chloride ion content: 0.7 ppm; chromaticity: 60 APHA; metal ion content, Al: not detected; Ca: not detected; Cr: not detected; Cu: not detected; Fe: not detected; K: 0.1 ppm; Na: 0.1 ppm; Ni: not detected; Pb: not detected; Zn: not detected.

[0078] Example 5

[0079] (1) Add 5 mol of potassium oxalate and 17.5 mol of boric acid into a mortar and grind them into powder. Put 39.4 mol of hexamethyldisiloxane and the above solid powder into a reaction kettle, and stir and react at 90 °C for 36 h. After the reaction is completed, filter to obtain the reaction mother liquor and white solid 1 respectively.

[0080] (2) Add 37.3 mol of dimethyl carbonate to white solid 1, stir and wash for 1 h, filter, remove the filtrate, repeat the washing twice in this way, and put the washed white solid 1 into an oven at 80 °C and dry for 4 h. Add 38.2 mol of ethyl acetate to the dried white solid 1, stir and mix for 2 h, then filter to obtain a colorless filtrate and white solid 2 respectively. Rotate evaporate the filtrate (temperature is 90 °C) to obtain the crude product, and deeply dry the crude product in an oven at 100 °C to obtain 335.5 g of potassium bis(oxalato)borate (KBOB).

[0081] (3) Dissolve 1.2 mol of tributylmethylammonium chloride (TBMA-Cl) in 23.6 mol of deionized water. Dissolve the obtained potassium bis(oxalato)borate (KBOB) in 37.3 mol of deionized water (0 - 5 °C), and filter. Mix the tributylmethylammonium chloride aqueous solution and the potassium bis(oxalato)borate aqueous solution, and stir and react at 60 °C for 4 h. After the reaction is completed, separate the liquid, add 132.3 mol of deionized water to the lower layer material and wash twice, and obtain 379.2 g of ionic liquid (TBMA-BOB) through vacuum drying and filtration.

[0082] The test results of KBOB obtained in step (2) are as follows: Purity: 99.92%; Moisture: 67 ppm; Solvent residue: 435 ppm; Metal ion content, Al: 0.1 ppm; Ca: 0.2 ppm; Cr: 0.1 ppm; Cu: 0.1 ppm; Fe: 0.1 ppm; K: 17.3%; Na: 0.2 ppm; Ni: 0.1 ppm; Pb: 0.2 ppm; Zn: 0.1 ppm.

[0083] The test results of TBMA-BOB obtained in step (3) are as follows: Purity: 99.88%; Moisture: 556 ppm; Chloride ion content: 1.6 ppm; Chromaticity: 40 APHA; Metal ion content, Al: not detected; Ca: not detected; Cr: not detected; Cu: not detected; Fe: 0.1 ppm; K: not detected; Na: not detected; Ni: not detected; Pb: not detected; Zn: not detected.

[0084] Comparative Example 1

[0085] Add 5 mol of potassium oxalate and 17.5 mol of boric acid into a mortar and grind them into powder. Put 39.4 mol of hexamethyldisiloxane and the above solid powder into a reaction kettle. Stir and react at 30 °C for 36 h. After the reaction is completed, filter to obtain the reaction mother liquor and white solid 1 respectively. Add 29.2 mol of dimethyl carbonate to white solid 1, stir and wash for 1 h, and then filter. Wash twice. After the washing is completed, put white solid 1 into an oven at 80 °C and dry for 4 h. Add 39.8 mol of ethyl acetate to the dried white solid 1, stir and mix for 2 h, and then filter to obtain a colorless filtrate and white solid 2 respectively. After rotary evaporation of the filtrate (temperature is 90 °C), it is found that no product precipitates. The subsequent operations cannot be carried out.

[0086] Comparative Example 2

[0087] This comparative example provides another preparation method of ionic liquid, including the following steps:

[0088] (1) Add 5 mol of lithium oxalate and 17.5 mol of boric acid into a mortar and grind them into powder. Put 52.5 mol of hexamethyldisiloxane and the above solid powder into a reaction kettle, and stir and react at 120 °C for 24 h. After the reaction is completed, filter to obtain the reaction mother liquor and white solid 1 respectively.

[0089] (2) Add 23.6 mol of dimethyl carbonate to white solid 1, stir and wash for 1 h, filter, remove the filtrate, repeat washing twice according to this, and put the washed white solid 1 into an oven at 80 °C and dry for 4 h. Add 36.2 mol of ethyl acetate to the dried white solid 1, stir and mix for 2 h, and then filter to obtain a colorless filtrate and white solid 2 respectively. Rotary evaporate the filtrate (temperature is 90 °C) to obtain the crude product, and deeply dry the crude product in an oven at 100 °C to obtain 386.1 g of lithium bis(oxalato)borate (LiBOB).

[0090] (3) Dissolve 1.3 mol of N-octyl-3-methylpyridinium chloride (3MOP-Cl) in 29.8 mol of deionized water. Dissolve the obtained lithium bis(oxalato)borate (LiBOB) in 42.9 mol of deionized water (0 - 5 °C), and filter. Mix the N-octyl-3-methylpyridinium chloride aqueous solution with the lithium bis(oxalato)borate aqueous solution, and stir and react at 100 °C for 4 h. After the reaction is completed, separate the liquid, add 53.8 mol of deionized water to the lower layer material and wash twice, and obtain 242.3 g of ionic liquid (3MOP-BOB) through vacuum drying and filtration.

[0091] The test results of LiBOB obtained in step (2) are as follows: purity: 99.94%; moisture: 24 ppm; solvent residue: 312 ppm; metal ion content, Al: not detected; Ca: not detected; Cr: not detected; Cu: not detected; Fe: not detected; K: not detected; Na: not detected; Ni: not detected; Pb: not detected; Zn: not detected.

[0092] The test results of 3MOP-BOB obtained in step (3) are as follows: purity: 99.23%; moisture: 104 ppm; chloride ion content: 1.2 ppm; metal ion content, Al: not detected; Ca: not detected; Cr: not detected; Cu: 0.1 ppm; Fe: 0.1 ppm; K: not detected; Na: not detected; Ni: not detected; Pb: 0.1 ppm; Zn: 0.2 ppm. The color is reddish brown.

[0093] Comparative Example 3

[0094] (1) Add 5 mol of lithium oxalate and 17.5 mol of boric acid into a mortar and grind them into powder. Put 52.5 mol of hexamethyldisiloxane and the above solid powder into a reaction kettle, and stir and react at 120 °C for 24 h. After the reaction is completed, filter to obtain the reaction mother liquor and white solid 1 respectively.

[0095] (2) Add 37.6 mol of ethyl methyl carbonate to white solid 1, stir and wash for 1 h, filter, remove the filtrate, repeat the washing twice in this way, and put the washed white solid 1 into an oven at 80 °C to dry for 4 h. Add 44.5 mol of ethyl acetate to the dried white solid 1, stir and mix for 2 h, then filter to obtain a colorless filtrate and white solid 2 respectively. Rotate evaporate the filtrate (temperature is 90 °C) to obtain the crude product, and deeply dry the crude product in an oven at 100 °C to obtain 369.4 g of lithium bis(oxalato)borate (LiBOB).

[0096] (3) Dissolve 1.5 mol of N-octyl-3-methylpyridinium chloride (3MOP-Cl) in 34.4 mol of deionized water. Dissolve the obtained lithium bis(oxalato)borate (LiBOB) in 41.0 mol of deionized water (0 - 5 °C), and filter. Mix the N-octyl-3-methylpyridinium chloride aqueous solution with the lithium bis(oxalato)borate aqueous solution, and stir and react at 70 °C for 4 h. After the reaction is completed, separate the liquid, add 96.2 mol of deionized water to the lower layer material and wash twice, and obtain 287.0 g of ionic liquid (3MOP-BOB) through vacuum drying and filtration.

[0097] The test results of LiBOB obtained in step (2) are as follows: purity: 99.78%; moisture: 76 ppm; solvent residue: 563 ppm; metal ion content, Al: not detected; Ca: 0.1 ppm; Cr: not detected; Cu: not detected; Fe: 0.1 ppm; K: 0.1 ppm; Na: 0.2 ppm; Ni: 0.1 ppm; Pb: not detected; Zn: not detected.

[0098] The test results of 3MOP-BOB obtained in step (3) are as follows: purity: 99.49%; moisture: 672 ppm; chloride ion content: 1.1 ppm; chromaticity: 100 APHA; metal ion content, Al: not detected; Ca: not detected; Cr: not detected; Cu: not detected; Fe: not detected; K: not detected; Na: not detected; Ni: not detected; Pb: not detected; Zn: not detected.

[0099] Comparative Example 4

[0100] This comparative example provides another preparation method of ionic liquid, including the following steps:

[0101] (1) Add 5 mol of sodium oxalate and 17.5 mol of boric acid into a mortar and grind them into powder. Put 52.5 mol of hexamethyldisiloxane and the above solid powder into a reaction kettle, and stir and react at 120 °C for 8 h. After the reaction is completed, filter to obtain the reaction mother liquor and white solid 1 respectively.

[0102] (2) Add 26.5 mol of dimethyl carbonate to white solid 1, stir and wash for 1 h, filter, remove the filtrate, repeat the washing twice in this way, and put the washed white solid 1 into an oven at 80 °C to dry for 4 h. Add 85.4 mol of acetonitrile to the dried white solid 1, stir and mix for 2 h, then filter to obtain a colorless filtrate and white solid 2 respectively. Rotate evaporate the filtrate (temperature is 90 °C) to obtain the crude product, and deeply dry the crude product in an oven at 100 °C to obtain 55.6 g of sodium bis(oxalato)borate (NaBOB).

[0103] (3) Dissolve 0.2 mol of trioctylmethylammonium chloride (TOMA-Cl) in 5.0 mol of deionized water. Dissolve the obtained sodium bis(oxalato)borate (NaBOB) in 6.2 mol of deionized water (0 - 5 °C), and filter. Mix the trioctylmethylammonium chloride aqueous solution and the sodium bis(oxalato)borate aqueous solution, and stir and react at 50 °C for 4 h. After the reaction is completed, separate the liquid, add 19.8 mol of deionized water to the lower layer material and wash twice, and obtain 89.1 g of ionic liquid (TOMA-BOB) through vacuum drying and filtration.

[0104] The test results of the NaBOB obtained in step (2) are as follows: purity: 98.92%; moisture: 76 ppm; solvent residue: 618 ppm; metal ion content, Al: not detected; Ca: 0.1 ppm; Cr: not detected; Cu: 0.1 ppm; Fe: 0.1 ppm; K: 0.3 ppm; Na: 10.8%; Ni: not detected; Pb: not detected; Zn: not detected.

[0105] The test results of the TOMA-BOB obtained in step (3) are as follows: purity: 98.44%; moisture: 453 ppm; chloride ion content: 7.9 ppm; chromaticity: 120 APHA; metal ion content, Al: not detected; Ca: not detected; Cr: not detected; Cu: not detected; Fe: 0.1 ppm; K: 0.1 ppm; Na: 1.3 ppm; Ni: not detected; Pb: not detected; Zn: not detected.

[0106] The ionic liquids of Examples 1 to 5 above can be used as antistatic agents for optical films, which can eliminate the influence of static electricity and have a chromaticity ≤ 80 APHA, and basically have no color influence on the optical film. Among them, Example 1 has the highest purity and the lowest chromaticity, and while eliminating the influence of static electricity, it does not affect the performance of the optical film at all.

[0107] In Comparative Example 1, since the reaction temperature was too low during the synthesis of KBOB, the reaction could not proceed, resulting in no precipitation of KBOB and unable to carry out subsequent operations.

[0108] In Comparative Example 2, since the reaction temperature during the synthesis of 3MOP-BOB was too high, the product yield was low and the chromaticity was unqualified. Analyzing the reason, it was that the high reaction temperature caused LiBOB to decompose rapidly in the aqueous phase and did not participate in the subsequent reaction. The product turned red during the reaction at high temperature, and it was very difficult to fade the red color by decolorization operation, and it could not be used as an antistatic agent material for polarizing film in the future.

[0109] In Comparative Example 3, the reaction temperature during the synthesis of 3MOP-BOB was slightly higher, resulting in an increase in the chromaticity of the ionic liquid. Analyzing the reason, it may be due to the discoloration phenomenon of the N-octyl-3-methylpyridinium group.

[0110] The yield and purity of Comparative Example 4 were on the low side. Analyzing the reason, it may be that the reaction time for the synthesis of NaBOB was too short, resulting in incomplete reaction. There were more raw materials remaining after the incomplete reaction, increasing the difficulty of purification, and a small amount of raw materials would be introduced into the ionic liquid product, resulting in a decrease in product purity and an increase in chromaticity.

[0111] The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It is not intended to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of an ionic liquid, characterized in that: It includes the following steps: (1) A mixed powder of metal oxalate and boric acid reacts in hexamethyldisiloxane at 90 - 120 °C for 24 - 36 h. The obtained reaction solution is filtered to obtain a reaction mother liquor and solid 1; (2) The solid 1 is washed with dimethyl carbonate and / or ethyl methyl carbonate and dried, then mixed with ethyl acetate and / or acetonitrile. The obtained mixture is filtered to obtain a filtrate and solid 2. The filtrate is rotary evaporated to obtain metal bis(oxalato)borate; (3) The metal bis(oxalato)borate and an onium salt react in water at 50 - 60 °C. The obtained reaction solution is separated by liquid-liquid extraction and dried to obtain the ionic liquid. The cation of the onium salt is an alkyl-substituted quaternary ammonium cation or a pyridinium cation, and the anion is a chloride ion.

2. The preparation method according to claim 1, characterized in that: The metal oxalate is selected from lithium oxalate, sodium oxalate or potassium oxalate, and / or the onium salt is selected from the compound shown in formula (I) or the compound shown in formula (II), wherein, R1 is an alkane with 4 - 10 carbon atoms, and R2 is a methyl group.

3. The preparation method according to claim 1, wherein: In the step (1), the molar ratio of the metal oxalate to boric acid in the feed is 1:(3 - 5), and the reaction temperature is 100 - 120 °C.

4. The preparation method according to claim 1, characterized in that: In the step (1), the molar ratio of boric acid to hexamethyldisiloxane in the feed is 1:(2.25 - 3).

5. The preparation method according to claim 1, characterized in that: In the step (3), the metal bis(oxalato)borate is mixed with deionized water at 0 - 5 °C to form an aqueous solution of metal bis(oxalato)borate. The aqueous solution of metal bis(oxalato)borate is mixed with an aqueous solution of the onium salt and then reacts at 50 - 60 °C for 2 - 4 h.

6. The preparation method according to claim 1, characterized in that: In the step (3), the molar ratio of the metal bis(oxalato)borate to the onium salt in the feed is (1.2 - 1.5):

1.

7. The preparation method according to claim 1, characterized in that: The preparation method further includes step (4). The step (4) includes mixing the reaction mother liquor with concentrated sulfuric acid and reacting at 70 - 90 °C for 4 - 8 h. The obtained reaction solution is subjected to vacuum distillation to obtain hexamethyldisiloxane.

8. The preparation method according to claim 7, characterized in that: The step (4) further includes mixing the solid 2 with an aqueous oxalic acid solution and reacting at 50 - 60 °C for 2 - 4 h. The obtained reaction solution is rotary evaporated to obtain a mixture of boric acid and metal oxalate, which is dried and ground to obtain a mixed powder of metal oxalate and boric acid.

9. An antistatic agent, which is an ionic liquid prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the antistatic agent according to claim 9 in an optical film.

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