Preparation method of N-alkyl-4-methylpyridinium salt antistatic agent

Abstract

The invention relates to a preparation method of N-alkyl-4-methylpyridinium salt ionic liquid, which comprises the following steps: reacting 4-methylpyridine and 1-chloroalkane in water to obtain reaction liquid, separating the reaction liquid, and decolorizing the reaction liquid to obtain an aqueous solution of N-alkyl-4-methylpyridinium salt; and mixing the aqueous solution of the N-alkyl-4-methylpyridine chloride salt with a premix of metal salt and water to react, and performing liquid separation, water washing and drying on the obtained reaction liquid to obtain the colorless N-alkyl-4-methylpyridinium ionic liquid. According to the method, 4-methylpyridine, 1-chloroalkane and metal salt are adopted as raw materials and react in water in the whole process, a solvent does not need to be replaced, and technological operation is simplified. At a proper temperature, the conversion rate of 4-methylpyridine is high, a colorless intermediate is obtained through physical activated carbon decoloration, and the influence on the color of a final product is avoided. Unreacted 1-chloroalkane can be separated and reused in a simple liquid separation mode, and the utilization rate of raw materials is high.

Description

Technical Field

[0001] The invention belongs to the technical field of antistatic agents, and specifically relates to a preparation method of an N-alkyl-4-methylpyridinium antistatic agent. Background Art

[0002] Static electricity can cause serious harm to products and production, and antistatic agents have been widely studied and used in the field of eliminating static electricity. The representative of cationic antistatic agents is a quaternary ammonium salt compound that can provide a stable ammonium cation group. Quaternization enhances the hydrophilicity of the polymer, allowing the polymer to better absorb moisture in the air, promotes the transfer of charge, and has a very obvious antistatic effect. The optical film in CN106003940B is added with an antistatic agent N-octyl-4-methylpyridinium hexafluorophosphate, showing the practicality of N-alkyl-4-methylpyridinium salt ionic liquid as an antistatic agent.

[0003] Regarding the preparation of N-alkyl-4-methylpyridinium salt ionic liquid, CN100577667C adopts the reaction of N-trimethylsilyl tris(pentafluoroethyl)phosphazene, trifluoromethyl trifluoroboric acid, hydrogen fluoride, potassium fluoride and N-alkyl-4-methylpyridinium chloride, and can obtain N-alkyl-4-methylpyridinium hexafluorophosphate by separation. It does not introduce the source or preparation method of N-alkyl-4-methylpyridinium chloride, and its method for obtaining the product is more complicated than the ion exchange method, which is not suitable for the process of synthesizing only N-alkyl-4-methylpyridinium hexafluorophosphate.

[0004] Antistatic agents used in optical films such as polarizers not only need to be of high purity, but also need to have no effect on the color of the optical film products, that is, the N-alkyl-4-methylpyridinium salt ionic liquid is required to be colorless. How to improve the quality of N-alkyl-4-methylpyridinium salt while simplifying the preparation process is a key issue that needs to be overcome in the development of N-alkyl-4-methylpyridinium salt antistatic agents. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a colorless N-alkyl-4-methylpyridinium salt ionic liquid which can be used as an antistatic agent and has a simple process, does not require the use of multiple solvents, has a high raw material utilization rate, is high in purity, and can be used as an antistatic agent.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing an N-alkyl-4-methylpyridinium salt ionic liquid, the preparation method comprising the following steps:

[0008] (1) reacting 4-methylpyridine and 1-chloroalkane in water, and separating and decolorizing the reaction solution to obtain an aqueous solution of N-alkyl-4-methylpyridine chloride;

[0009] (2) The aqueous solution of N-alkyl-4-methylpyridinium chloride described in step (1) is mixed with a premix of a metal salt and water for reaction, and the obtained reaction solution is separated, washed with water, and dried to obtain a colorless N-alkyl-4-methylpyridinium ionic liquid.

[0010] Preferably, the reaction temperature of the reaction in step (1) is 110-140°C, for example, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C.

[0011] Preferably, the reaction time of the reaction in step (1) is 4 to 24 h, for example 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h.

[0012] Preferably, the reaction in step (1) is carried out in a reactor, and the pressure in the reactor is less than 0.50 MPa.

[0013] Preferably, the 1-chloroalkane in step (1) is a monochlorinated straight-chain alkane having 4 to 12 carbon atoms, and the chlorine atom is substituted on the carbon atom No. 1 of the alkane molecule.

[0014] Preferably, in step (1), the molar ratio of the 4-methylpyridine to the 1-chloroalkane is 1:1.05-1.2, for example, 1:1.05, 1:1.08, 1:1.1, 1:1.12, 1.15, 1:1.2.

[0015] Preferably, the decolorization in step (1) adopts activated carbon decolorization, and the decolorization time is 3 to 5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours.

[0016] Preferably, in the liquid separation operation in step (1), the lower layer is the N-alkyl-4-methylpyridine chloride solution, and the upper layer is 1-chloroalkane, which can be used as the raw material for the next batch of material synthesis reaction.

[0017] Preferably, the cation of the metal salt in step (2) is potassium ion, sodium ion or lithium ion, and the anion is hexafluorophosphate ion, bis(fluorosulfonyl)imide ion or bis(trifluoromethylsulfonyl)imide ion.

[0018] Preferably, the metal salt and water are mixed in a weight ratio of 0.8 to 1.2:1 to form a premix.

[0019] Preferably, the molar amount of the metal salt in step (2) is 1.02 to 1.2 times the molar amount of 4-methylpyridine in step (1), for example, 1.02 times, 1.05 times, 1.08 times, 1.1 times, 1.12 times, 1.15 times, or 1.2 times.

[0020] Preferably, the reaction in step (2) is carried out under stirring.

[0021] Preferably, the reaction time of the reaction in step (2) is 1 to 5 h, for example, 1 h, 2 h, 3 h, 4 h, 5 h.

[0022] The preparation method of N-alkyl-4-methylpyridinium salt ionic liquid specifically comprises the following steps:

[0023] (1) 4-methylpyridine and 1-chloroalkane are mixed with water and added into a reaction kettle for reaction at 110-140° C. After the reaction is completed, the mixture is allowed to stand and the liquid is separated. The upper layer liquid is the unreacted 1-chloroalkane (which can be recycled for the next batch of materials). The lower layer liquid is taken, and activated carbon is added to the lower layer liquid for decolorization for 3-5 hours, and then filtered to obtain N-alkyl-4-methylpyridine chloride salt solution;

[0024] (2) The N-alkyl-4-methylpyridinium chloride solution obtained above is mixed with a premix of a metal salt and water, stirred for 1 to 5 hours, and then allowed to stand for separation. The lower layer is taken, washed twice with water, and dried under reduced pressure to obtain a colorless liquid, which is the N-alkyl-4-methylpyridinium salt ionic liquid.

[0025] The present invention also provides an antistatic agent, which is the N-alkyl-4-methylpyridinium salt ionic liquid prepared by the above preparation method.

[0026] The present invention also provides application of the antistatic agent in an optical film.

[0027] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0028] The preparation method of the N-alkyl-4-methylpyridinium salt antistatic agent of the present invention adopts 4-methylpyridine, 1-chloroalkane and metal salt as raw materials, and the two-step reaction is carried out in the water phase, and there is no need to change the solvent, thereby simplifying the process operation. Under a suitable temperature, the conversion rate of 4-methylpyridine is high, and the colorless intermediate N-alkyl-4-methylpyridinium chloride salt is obtained by physical activated carbon decolorization, thereby avoiding affecting the color of the final product. The unreacted 1-chloroalkane can be separated and applied by a simple liquid separation method, and the raw material utilization rate is high. No toxic products are generated during the reaction process of the present invention, and the entire reaction process is safe and environmentally friendly, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the NMR image of the N-hexyl-4-methylpyridinium salt of Examples 1 to 3;

[0030] Figure 2 This is the NMR image of the N-octyl-4-methylpyridinium salt of Example 4. DETAILED DESCRIPTION

[0031] The present invention is further described below in conjunction with the examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry.

[0032] The 1-chloroalkane described herein refers to an alkane molecule in which a chlorine atom is substituted on the first carbon atom (carbon atom No. 1) of the alkane molecule.

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

[0034] The water used in the following examples and comparative examples is all high-purity water. KPF6 is the full name of potassium hexafluorophosphate, KFSI is the full name of potassium bis(trifluoromethylsulfonyl)imide, and KTFSI is the full name of potassium bis(trifluoromethylsulfonyl)imide.

[0035] The step (1) of the following examples and comparative examples was carried out in a reactor, and the pressure in the reactor was less than 0.50 MPa.

[0036] Taking the preparation of N-hexyl-4-methylpyridinium salt of Examples 1 to 3 as an example, the reaction equation is as follows:

[0037]

[0038] In the following examples and comparative examples, the moisture content was detected by Karl Fischer method; the chloride ion content was detected by potentiometric titration; the 4-methylpyridine was detected by gas chromatography (GC); and the metal ion content was detected by inductively coupled plasma (ICP).

[0039] Example 1

[0040] This embodiment provides a method for preparing an ionic liquid (N-hexyl-4-methylpyridinium hexafluorophosphate), comprising the following steps:

[0041] (1) 5 mol 4-methylpyridine, 5.5 mol 1-chlorohexane and 1.1 L water were mixed and added to a reaction kettle, and reacted at 130°C for 8 h. After standing and liquid separation, the upper layer was unreacted 1-chlorohexane (which could be recycled for the next batch of materials). 25.6 g activated carbon was added to the lower layer for decolorization. After decolorization for 4 h, filter pressing was performed to obtain 2014.4 g N-hexyl-4-methylpyridine chloride salt solution. The chlorine content was 8.8% according to potentiometric titration. The conversion rate of 4-methylpyridine was calculated to be 99.5%.

[0042] (2) The N-hexyl-4-methylpyridinium chloride solution obtained above was mixed with a premix (2 kg KPF6 and water were mixed in a weight ratio of 1:1), stirred for 2 h, and then allowed to stand for separation. The lower layer was removed, washed twice with 3 L of water, and dried under negative pressure at -0.99 MPa and 120° C. to obtain 1422.3 g of a colorless oily liquid, namely N-hexyl-4-methylpyridinium hexafluorophosphate, with a purity of 99.5% and a total yield of 88.0%.

[0043] The test results of the obtained N-hexyl-4-methylpyridinium hexafluorophosphate are as follows:

[0044] Moisture: 304ppm;

[0045] Chloride ion content: 2.04ppm;

[0046] 4-Methylpyridine residue: Not detected;

[0047] Metal ion content, Al: not detected; Ca: 0.2ppm; Cr: 0.2ppm; Cu: not detected; Fe: 0.1ppm; K: not detected; Na: 0.1ppm; Ni: not detected; Pb: not detected; Zn: not detected.

[0048] Example 2

[0049] This embodiment provides a method for preparing an ionic liquid (N-hexyl-4-methylpyridine bis(fluorosulfonyl)imide salt), comprising the following steps:

[0050] (1) 5 mol 4-methylpyridine, 5.5 mol 1-chlorohexane and 1.1 L water were mixed and added to a reaction kettle, and reacted at 120°C for 18 hours. After standing and liquid separation, the upper layer was unreacted 1-chlorohexane (which could be recycled for the next batch of materials). 25.5 g activated carbon was added to the lower layer for decolorization. After decolorization for 4 hours, filter pressing was performed to obtain 2026.7 g N-hexyl-4-methylpyridine chloride salt solution. The chlorine content was 8.6% according to the potentiometric titration method. The conversion rate of 4-methylpyridine was calculated to be 98.9%.

[0051] (2) The N-hexyl-4-methylpyridine chloride solution obtained above was mixed with a premix of 2.2 kg of KFSI (bis(fluorosulfonyl)imide potassium salt) and water in a weight ratio of 1:1, stirred for 2 h, and then allowed to stand for separation. The lower layer was removed, washed twice with 3 L of water, and dried under negative pressure at -0.99 MPa and 120° C. to obtain 1566.3 g of a colorless liquid, i.e., N-hexyl-4-methylpyridine bis(fluorosulfonyl)imide salt, with a purity of 99.6% and a total yield of 87.4%.

[0052] The test results of the obtained N-hexyl-4-methylpyridine bis(fluorosulfonyl)imide salt are as follows:

[0053] Moisture: 617ppm;

[0054] Chloride ion content: 6.05ppm;

[0055] 4-Methylpyridine residue: Not detected;

[0056] Metal ion content, Al: not detected; Ca: 0.1ppm; Cr: 0.1ppm; Cu: not detected; Fe: 0.2ppm; K: not detected; Na: 0.4ppm; Ni: 0.1ppm; Pb: not detected; Zn: not detected.

[0057] Example 3

[0058] This embodiment provides a method for preparing an ionic liquid (N-hexyl-4-methylpyridine bis(trifluorosulfonyl)imide salt), comprising the following steps:

[0059] (1) 5 mol of 4-methylpyridine, 6 mol of 1-chlorohexane (part of which is unreacted 1-chlorohexane from Example 1 and Example 2) and 1.2 L of water were mixed and added to a reaction kettle, and reacted at 130° C. for 8 h. After standing and liquid separation, the upper layer was unreacted 1-chlorohexane (which could be recycled for the next batch of materials). 25.6 g of activated carbon was added to the lower layer for decolorization. After decolorization for 4 h, filter pressing was performed to obtain 2004.9 g of N-hexyl-4-methylpyridine chloride salt solution. The chlorine content was 8.8% as determined by potentiometric titration. The conversion rate of 4-methylpyridine was 99.2% as calculated.

[0060] (2) The N-hexyl-4-methylpyridine chloride solution obtained above was mixed with a premix (3.3 kg of KTFSI and water were mixed in a weight ratio of 1:1), stirred for 2 h, and then allowed to stand for separation. The lower layer was taken, washed twice with 3 L of water, and dried under negative pressure at -0.99 MPa and 120° C. to obtain 1888.8 g of a colorless liquid, namely N-hexyl-4-methylpyridine bistrifluorosulfonyl imide salt, with a purity of 99.9% and a total yield of 82.4%.

[0061] The test results of the obtained N-hexyl-4-methylpyridine bis(trifluorosulfonyl)imide salt are as follows:

[0062] Moisture: 715ppm;

[0063] Chloride ion content: 1.93ppm;

[0064] 4-Methylpyridine residue: Not detected;

[0065] Metal ion content, Al: not detected; Ca: 0.1ppm; Cr: 0.2ppm; Cu: not detected; Fe: 0.2ppm; K: not detected; Na: 0.2ppm; Ni: not detected; Pb: not detected; Zn: not detected.

[0066] Example 4

[0067] This embodiment provides a method for preparing an ionic liquid (N-octyl-4-methylpyridinium hexafluorophosphate), comprising the following steps:

[0068] (1) 5 mol 4-methylpyridine, 5.5 mol 1-chlorooctane and 1.28 L water were mixed and added to a reactor, and reacted at 130° C. for 8 h. After the reaction was completed, the upper layer was unreacted 1-chlorooctane (which could be recycled for the next batch of materials) after standing and separating. 30.8 g activated carbon was added to the lower layer for decolorization. After decolorization for 4 h, filter press was performed to obtain 2412.6 g N-octyl-4-methylpyridine chloride salt solution. The chlorine content was 7.3% according to the potentiometric titration method. The conversion rate of 4-methylpyridine was calculated to be 99.3%.

[0069] (2) The N-octyl-4-methylpyridinium chloride solution obtained above was mixed with a premix (2 kg KPF6 and water were mixed in a weight ratio of 1:1), stirred for 2 h, and then allowed to stand for separation. The lower layer was removed, washed twice with 3.3 L of water, and dried under negative pressure at -0.99 MPa and 120° C. to obtain 1496.6 g of colorless liquid, i.e., N-octyl-4-methylpyridinium hexafluorophosphate, with a purity of 99.1% and a total yield of 85.2%.

[0070] The test results of the obtained N-octyl-4-methylpyridinium hexafluorophosphate are as follows:

[0071] Moisture: 523ppm;

[0072] Chloride ion content: 4.01ppm;

[0073] 4-Methylpyridine residue: Not detected;

[0074] Metal ion content, Al: not detected; Ca: 0.1ppm; Cr: 0.1ppm; Cu: not detected; Fe: 0.2ppm; K: not detected; Na: 0.3ppm; Ni: not detected; Pb: not detected; Zn: not detected.

[0075] Example 5

[0076] This embodiment provides a method for preparing an ionic liquid (N-dodecyl-4-methylpyridinium hexafluorophosphate), comprising the following steps:

[0077] (1) 5 mol 4-methylpyridine, 5.5 mol 1-chlorododecane and 1.6 L water were mixed and added to a reaction kettle, and reacted at 140° C. for 8 h. After the reaction was completed, the mixture was allowed to stand and the liquid was separated. The upper layer was unreacted 1-chlorododecane (which could be recycled for the next batch of materials). 32.1 g activated carbon was added to the lower layer for decolorization. After decolorization for 4 h, the mixture was filtered to obtain 2946.3 g N-dodecyl-4-methylpyridine chloride salt solution. The chlorine content was 5.9% as determined by potentiometric titration. The conversion rate of 4-methylpyridine was 97.6% as calculated.

[0078] (2) The N-dodecyl-4-methylpyridinium chloride solution obtained above was mixed with a premix (2 kg KPF6 and water in a weight ratio of 1:1), stirred for 2 h, and then allowed to stand for separation. The lower layer was removed, washed twice with 3.8 L of water, and dried under negative pressure at -0.99 MPa and 120° C. to obtain 1703.0 g of colorless liquid, i.e., N-dodecyl-4-methylpyridinium hexafluorophosphate, with a purity of 98.9% and a total yield of 83.6%.

[0079] The test results of the obtained N-dodecyl-4-methylpyridinium hexafluorophosphate are as follows:

[0080] Moisture: 458ppm;

[0081] Chloride ion content: 5.12ppm;

[0082] 4-Methylpyridine residue: Not detected;

[0083] Metal ion content, Al: not detected; Ca: 0.1ppm; Cr: 0.2ppm; Cu: not detected; Fe: 0.8ppm; K: not detected; Na: 0.3ppm; Ni: 0.2ppm; Pb: not detected; Zn: not detected.

[0084] Comparative Example 1

[0085] This comparative example provides a method for preparing an ionic liquid (N-hexyl-4-methylpyridinium hexafluorophosphate), comprising the following steps:

[0086] (1) 5 mol 4-methylpyridine, 5.5 mol 1-chlorohexane and 1.1 L water were mixed and added to a reaction kettle, and reacted at 105°C for 24 hours. After standing and liquid separation, the upper layer was unreacted 1-chlorohexane. 25.6 g activated carbon was added to the lower layer for decolorization. After decolorization for 4 hours, filter pressing was performed to obtain 1601.8 g N-hexyl-4-methylpyridine chloride salt solution. The chlorine content was 3.8% according to the potentiometric titration method. The conversion rate of 4-methylpyridine was 34.6% by calculation.

[0087] (2) The N-hexyl-4-methylpyridinium chloride solution obtained above was mixed with a premix (2 kg KPF6 and water were mixed in a weight ratio of 1:1), stirred for 2 h, and then allowed to stand for separation. The lower layer was removed, washed twice with 3 L of water, and dried under negative pressure at -0.99 MPa and 120° C. to obtain 504.3 g of a reddish brown liquid, i.e., N-hexyl-4-methylpyridinium hexafluorophosphate, with a purity of 96.7% and a total yield of 31.2%.

[0088] The test results of the obtained N-hexyl-4-methylpyridinium hexafluorophosphate are as follows:

[0089] Moisture: 714ppm;

[0090] Chloride ion content: 23.4ppm;

[0091] 4-Methylpyridine residue: 874ppm;

[0092] Metal ion content, Al: not detected; Ca: 0.1ppm; Cr: 0.1ppm; Cu: not detected; Fe: 0.2ppm; K: 0.1ppm; Na: 0.2ppm; Ni: not detected; Pb: not detected; Zn: not detected.

[0093] Comparative Example 2

[0094] This comparative example provides a method for preparing an ionic liquid (N-hexyl-4-methylpyridinium hexafluorophosphate), comprising the following steps:

[0095] (1) 5 mol of 4-methylpyridine, 5 mol of 1-chlorohexane and 1 L of water were mixed and added to a reaction kettle, and reacted at 130° C. for 8 h. After standing and liquid separation, the upper layer was unreacted 1-chlorohexane. 25.6 g of activated carbon was added to the lower layer for decolorization. After decolorization for 4 h, filter pressing was performed to obtain 1991.2 g of N-hexyl-4-methylpyridine chloride salt solution. The chlorine content was 8.6% as determined by potentiometric titration. The conversion rate of 4-methylpyridine was calculated to be 96.4%.

[0096] (2) The N-hexyl-4-methylpyridinium chloride solution obtained above was mixed with a premix (2 kg KPF6 and water in a weight ratio of 1:1), stirred for 2 h, and then allowed to stand for separation. The lower layer was removed, washed twice with 3 L of water, and dried under negative pressure at -0.99 MPa and 120° C. to obtain 1286.6 g of yellow liquid, i.e., N-hexyl-4-methylpyridinium hexafluorophosphate, with a purity of 98.9% and a total yield of 79.6%.

[0097] The test results of the obtained N-hexyl-4-methylpyridinium hexafluorophosphate are as follows:

[0098] Moisture: 345ppm;

[0099] Chloride ion content: 13.2ppm;

[0100] 4-Methylpyridine residue: 297ppm;

[0101] Metal ion content: Al: 0.1ppm; Ca: 0.3ppm; Cr: 0.1ppm; Cu: not detected; Fe: 0.2ppm; K: 0.1ppm; Na: 0.1ppm; Ni: not detected; Pb: not detected; Zn: not detected.

[0102] Comparative Example 3

[0103] This comparative example provides a method for preparing an ionic liquid (N-hexyl-4-methylpyridinium hexafluorophosphate), comprising the following steps:

[0104] (1) 5 mol of 4-methylpyridine, 5.5 mol of 1-bromohexane and 15.6 mol of ethyl acetate were added to a reaction kettle and reacted at 80° C. for 12 h. The reaction solution was concentrated and dried under reduced pressure to obtain 1365.5 g of N-hexyl-4-methylpyridine bromide (viscous liquid). The bromide ion content was 28.7% according to IC detection. The conversion rate of 4-methylpyridine was calculated to be 98.2%.

[0105] The N-hexyl-4-methylpyridinium bromide obtained above was mixed with 25.6 g of activated carbon and 1.5 L of water, decolorized for 4 hours and filtered, and the liquid was separated after filtering. The upper layer was the N-hexyl-4-methylpyridinium bromide solution, and the lower layer was the unreacted 1-bromohexane.

[0106] (2) The N-hexyl-4-methylpyridinium chloride solution obtained above was mixed with a premix (2 kg KPF6 and water were mixed in a weight ratio of 1:1), stirred for 2 h, and then allowed to stand for separation. The lower layer was removed, washed twice with 3 L of water, and dried under negative pressure at -0.99 MPa and 120° C. to obtain 1377.1 g of light red liquid, i.e., N-hexyl-4-methylpyridinium hexafluorophosphate, with a purity of 99.3% and a total yield of 85.2%.

[0107] The test results of the obtained N-hexyl-4-methylpyridinium hexafluorophosphate are as follows:

[0108] Moisture: 316ppm;

[0109] Bromide ion content: 1.32ppm;

[0110] 4-Methylpyridine residue: Not detected;

[0111] Metal ion content, Al: not detected; Ca: 0.1ppm; Cr: 0.2ppm; Cu: not detected; Fe: 0.1ppm; K: 0.1ppm; Na: 0.1ppm; Ni: not detected; Pb: not detected; Zn: not detected.

[0112] In the above-mentioned Examples 1 to 5, 4-methylpyridine and 1-chloroalkane are reacted in water, and the N-alkyl-4-methylpyridine chloride solution obtained by separation and activated carbon decolorization can be directly mixed with the aqueous solution of the metal salt for stirring reaction, and then separated, decolorized with activated carbon and dried to obtain the N-alkyl-4-methylpyridinium salt. At a suitable reaction temperature, the conversion rate of 4-methylpyridine can reach more than 97.5%, and the unreacted 1-chloroalkane can be separated by the separation method and recycled for the next batch of materials, thereby improving the utilization rate of raw materials. The prepared N-alkyl-4-methylpyridinium salt has high purity, high yield, low metal ion content, and is colorless.

[0113] The ionic liquids of the above embodiments 1 to 5 can be used as antistatic agents. When used in optical films, they can eliminate static electricity effects and have no effect on the color of the optical film, and will not affect the performance of the optical film.

[0114] The reaction of Comparative Examples 1 and 2 is incomplete, resulting in residual 4-picoline, and excessive 4-picoline can react with oxygen to generate colored substances. After the substance enters the product, the product color also has this color. The depth of the color of the substance changes according to the unreacted 4-picoline content, and it is difficult to remove the color by general physical decolorization methods. Comparative Example 3 is the synthetic route of N-hexyl-4-picoline bromide, and the generated product has a light red color, which is affected by bromide ions, and a subsequent decolorization process is required (this type of color problem is difficult to remove the color by an activated carbon decolorization method), which is much more complicated than the synthetic route of N-hexyl-4-picoline chloride.

[0115] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used 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 included in the protection scope of the present invention.

Claims

1. A method for preparing an N-alkyl-4-methylpyridinium salt ionic liquid, characterized in that: The preparation method comprises the following steps: (1) reacting 4-methylpyridine and 1-chloroalkane in water, and separating and decolorizing the reaction solution to obtain an aqueous solution of N-alkyl-4-methylpyridine chloride; (2) The aqueous solution of N-alkyl-4-methylpyridinium chloride described in step (1) is mixed with a premix of a metal salt and water for reaction, and the obtained reaction solution is separated, washed with water, and dried to obtain a colorless N-alkyl-4-methylpyridinium ionic liquid.

2. The preparation method according to claim 1, characterized in that: The reaction temperature of the reaction in step (1) is 110 to 140° C., and / or the reaction time of the reaction in step (1) is 4 to 24 hours, and / or the reaction in step (1) is carried out in a reactor with a pressure of less than 0.50 MPa.

3. The preparation method according to claim 1, characterized in that: The 1-chloroalkane in step (1) is a chlorinated straight-chain alkane having 4 to 12 carbon atoms, wherein the chlorine atom is substituted on the carbon atom No. 1 of the alkane molecule; and / or, the molar ratio of the 4-methylpyridine to the 1-chloroalkane in step (1) is 1:1.05 to 1.

2.

4. The preparation method according to claim 1, characterized in that: The decolorization in step (1) adopts activated carbon decolorization, and the decolorization time is 3 to 5 hours.

5. The preparation method according to claim 1, characterized in that: In the liquid separation operation in step (1), the lower layer is the N-alkyl-4-methylpyridine chloride solution, and the upper layer is 1-chloroalkane, which can be used as the raw material for the next batch of material synthesis reaction.

6. The preparation method according to claim 1, characterized in that: In step (2), the cation of the metal salt is potassium ion, sodium ion or lithium ion, and the anion is hexafluorophosphate ion, bis(fluorosulfonyl)imide ion or bis(trifluoromethylsulfonyl)imide ion; and / or, the metal salt and water are mixed in a weight ratio of 0.8 to 1.2:1 to form the premix.

7. The preparation method according to claim 1, characterized in that: The molar amount of the metal salt in step (2) is 1.02 to 1.2 times the molar amount of the 4-methylpyridine in step (1).

8. The preparation method according to claim 1, characterized in that: The reaction in step (2) is carried out under stirring, and / or the reaction time of the reaction in step (2) is 1 to 5 hours. 9 . An antistatic agent, which is an N-alkyl-4-methylpyridinium salt 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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