CN109734668B - Synthesis method of tetrafluoroborate ionic liquid - Google Patents
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Abstract
The invention discloses a method for synthesizing tetrafluoroborate ionic liquid, which comprises the following steps: dispersing a quaternized substrate and alkyl halide in a molar ratio of 1: 1-7 in a solvent, and irradiating by adopting ultraviolet light at 30-50 ℃ with the illumination intensity of 10-1000W/m2Irradiating for 8-12 h to obtain a quaternary ammonium salt solution; uniformly mixing a quaternary ammonium salt solution and tetrafluoroborate, and irradiating by adopting ultraviolet light at the temperature of 35-45 ℃ with the illumination intensity of 10-1000W/m2Irradiating for 16-20 h to obtain a mixed solution; and filtering the mixed solution to obtain a filtrate, heating and concentrating the filtrate, and removing the solvent to obtain the tetrafluoroborate ionic liquid. The invention adopts the ultraviolet irradiation and heating mode to synthesize the tetrafluoroborate ionic liquid, and has high yield and reaction rate.
Description
Technical Field
The invention relates to a method for synthesizing tetrafluoroborate ionic liquid, in particular to a method for synthesizing tetrafluoroborate ionic liquid with N, N' -disubstituted imidazole cation.
Background
The ionic liquid has great breakthrough in the aspect of being an environment-friendly solvent, is called as a green solvent, generally consists of organic cations with larger volume and inorganic or organic anions with smaller volume, and is molten at room temperature or low temperature. Compared with the traditional organic solvent and electrolyte, the ionic liquid has the following advantages: almost no vapor pressure exists, so that the problem of environmental pollution caused by volatile organic substances is solved; the method has a large stable temperature range, good chemical stability and a wide electrochemical stable potential window; low melting point and high polarity, and has good solubility for various organic substances, water and inorganic substances. In addition, different requirements are realized by reasonably designing anions and cations, so that the anions and the cations have unique properties. The ionic liquid is used under normal pressure, not only can reduce the cost, but also can reduce the pollution of organic solvents to the environment and the harm to human beings, and has wide application in the fields of organic synthesis, biocatalysis, electrochemistry, gas dissolution and the like.
There are two main methods for synthesizing ionic liquids, direct synthesis and two-step synthesis. The direct synthesis method synthesizes the ionic liquid by one step through acid-base neutralization reaction or quaternization reaction, the operation is simple, and the product is easy to purify. When it is difficult to obtain the target ionic liquid by the direct synthesis method, a two-step synthesis method is used. Generally, firstly, a quaternary ammonium halide salt containing target cations is obtained through quaternization, then, the target anions are used for replacing halogen ions, an organic solvent is used for extracting ionic liquid for multiple times, and finally, the solvent is removed in vacuum to obtain the target ionic liquid. It should be noted that in the two-step synthesis, the step of replacing the halide ion with the target anion is a reaction rate determining step, and the reaction is generally slow and incomplete. If halogen ions remain in the target ionic liquid, the application and the characterization of physicochemical characteristics of the ionic liquid are influenced. Therefore, increasing the reaction rate of this step and ensuring that the reaction is complete are key to achieving high quality and high yield of ionic liquids.
Document 1 ("preparation of 1-methyl-3-aminoethylimidazole tetrafluoroborate under microwave radiation", shanghai institute of applied technology (nature science edition), 9 months in 2013, 13(3), pages 182-185) discloses a method for synthesizing tetrafluoroborate ionic liquid by microwave radiation. Firstly, obtaining brominated 1-methyl-3-aminoethyl imidazole by microwave radiation (the radiation power is 400W, and the radiation time is 10 min); then microwave radiation (the radiation power is 450W, and the radiation time is 30min) is adopted to obtain the 1-methyl-3 aminoethyl imidazole tetrafluoroborate. Document 2 ("microwave radiation one-pot synthesis of 1-carboxymethyl-3-methylimidazolium tetrafluoroborate ionic liquid", synthetic chemistry, 9.2007, 15(6), page 763-764) discloses a method for directly synthesizing 1-carboxymethyl-3-methylimidazolium tetrafluoroborate ionic liquid by using microwave intermittent radiation. Document 3 ("microwave water bath synthesis of room temperature ionic liquid 1-butyl-3-methylimidazole tetrafluoroborate", sichuan chemical industry, 2010, 13(6), pages 10 to 12) discloses a method for synthesizing 1-butyl-3-methylimidazole tetrafluoroborate ionic liquid in a short time by using a microwave water bath method.
Disclosure of Invention
The invention aims to provide a method for synthesizing tetrafluoroborate ionic liquid, which has high yield and high reaction rate. The purpose of the invention is realized by the following technical scheme.
In one aspect, the invention provides a method for synthesizing tetrafluoroborate ionic liquid, which comprises the following steps:
(1) dispersing a quaternized substrate and alkyl halide in a solvent, wherein the molar ratio of the quaternized substrate to the alkyl halide is 1: 1-7, irradiating by adopting ultraviolet light at the temperature of 30-50 ℃, and the illumination intensity is 10-1000W/m2Irradiating for 8-12 h to obtain a quaternary ammonium salt solution;
(2) uniformly mixing the quaternary ammonium salt solution and tetrafluoroborate, wherein the molar ratio of the quaternary ammonium substrate to the tetrafluoroborate is 1: 1-7, and irradiating by adopting ultraviolet light at 35-45 ℃ with the illumination intensity of 10-1000W/m2Irradiating for 16-20 h to obtain a mixed solution containing tetrafluoroborate ionic liquid;
(3) and (3) further processing the mixed solution obtained in the step (2) to obtain the tetrafluoroborate ionic liquid.
According to the synthesis method of the present invention, preferably, the quaternized substrate is selected from a tertiary amine, an N-substituted imidazole, or an N-substituted pyridine.
According to the synthesis method of the present invention, preferably, the alkyl halide is selected from one of methyl bromide, methyl iodide, ethyl chloride, ethyl bromide, 1-chloropropane, 2-bromopropane, 1-iodopropane or 2-bromo-2-methylpropane.
According to the synthesis method of the present invention, preferably, the solvent is selected from one or more of methanol, ethanol, acetone, dichloromethane, tetrahydrofuran, dioxane or acetonitrile.
According to the synthesis method of the present invention, preferably, the tetrafluoroborate is selected from sodium tetrafluoroborate or potassium tetrafluoroborate.
According to the synthesis method of the invention, preferably, the cation of the tetrafluoroborate ionic liquid is selected from one of quaternary ammonium salt cation shown in formula (I), N' -disubstituted imidazole cation shown in formula (II) or N-substituted pyridine cation shown in formula (III),
wherein R1-R7 are the same or different and are respectively and independently selected from C1-C6 alkyl, C2-C6 heteroalkyl, C3-C6 cycloalkyl, C1-C6 alkoxy, C1-C6 alkylthio or aryl.
According to the synthesis method of the invention, preferably, the cation of the tetrafluoroborate ionic liquid is an N, N' -disubstituted imidazole cation shown as a formula (II).
According to the synthesis method of the invention, preferably, the illumination intensity of the ultraviolet light in the step (1) is 50-800W/m2The irradiation time is 9-11 h; the illumination intensity of the ultraviolet light in the step (2) is 50-800W/m2The irradiation time is 17-19 h; the illumination intensity of the ultraviolet light in the step (1) and the step (2) is the same.
According to the synthesis method of the present invention, preferably, the step (3) comprises the following processes: filtering the mixed solution obtained in the step (2) to obtain a filtrate, concentrating the filtrate at 50-70 ℃, and removing the solvent to obtain the tetrafluoroborate ionic liquid.
In another aspect, the present invention provides a method for synthesizing tetrafluoroborate ionic liquid, comprising the following steps:
(1) dispersing a quaternized substrate and alkyl halide in a solvent, wherein the molar ratio of the quaternized substrate to the alkyl halide is 1: 1-4; at the temperature of 30-35 ℃, the illumination intensity is 50-800W/m2Irradiating by using ultraviolet light for 9-11 hours to obtain a quaternary ammonium salt solution;
(2) uniformly mixing the quaternary ammonium salt solution obtained in the step (1) with sodium tetrafluoroborate, and mixing the quaternary ammonium substrate with the quaternary ammonium borate solutionThe molar ratio of the sodium tetrafluoroborate is 1: 1-4, and the illumination intensity is 50-800W/m at 38-43 DEG C2Irradiating the ultraviolet light for 17-19 hours to obtain a mixed liquid containing tetrafluoroborate ionic liquid;
(3) filtering the mixed solution obtained in the step (2) to obtain a filtrate, concentrating the filtrate at 55-65 ℃, and removing the solvent to obtain the tetrafluoroborate ionic liquid.
The invention adopts a heating and ultraviolet irradiation method to synthesize the tetrafluoroborate ionic liquid, and has higher yield and faster reaction rate. According to the preferred technical scheme, the invention can obtain the tetrafluoroborate ionic liquid with higher conductivity and refractive index.
Detailed Description
The present invention will be further described with reference to the following specific examples, but the scope of the present invention is not limited thereto.
The quaternization substrate of the invention refers to a substance which can react with a halide to generate a quaternary ammonium salt, and generally comprises tertiary amines, N-substituted imidazoles or N-substituted pyridines.
< preparation of quaternary ammonium salt solution >
Dispersing a quaternized substrate and alkyl halide in a molar ratio of 1: 1-7 in a solvent, and irradiating with ultraviolet light at 30-50 ℃ at an illumination intensity of 10-1000W/m2And (4) irradiating for 8-12 h to obtain a quaternary ammonium salt solution.
The quaternized substrate in the present invention is selected from a tertiary amine represented by formula (a), an N-substituted imidazole represented by formula (b), or an N-substituted pyridine represented by formula (c), preferably an N-substituted imidazole represented by formula (b),
wherein R1-R4 are the same or different and are respectively and independently selected from C1-C6 alkyl, C2-C6 heteroalkyl, C3-C6 cycloalkyl, C1-C6 alkoxy, C1-C6 alkylthio or aryl. The selection of such electron rich groups may facilitate the reaction of the quaternized substrate with the alkyl halide to form the quaternary ammonium salt.
In the present invention, the C1-C6 alkyl group may include, but is not limited to, a straight chain alkyl group or a branched chain alkyl group; preferably C1-C3 alkyl, more preferably C1-C3 straight chain alkyl. Examples of C1-C6 alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, hexyl and the like.
In the present invention, the C2-C6 heteroalkyl group may include, but is not limited to, a straight or branched heteroalkyl group; preferably C2-C5 heteroalkyl, more preferably C2-C3 heteroalkyl. The heteroalkyl group in the present invention refers to a group formed by substituting a carbon atom on an alkyl chain with another heteroatom.
In the present invention, the C3-C6 cycloalkyl group may include substituted cycloalkyl groups and unsubstituted cycloalkyl groups; preferably C5-C6 cycloalkyl, more preferably C5 cycloalkyl. Specific examples of C3-C6 cycloalkyl groups of the present invention include, but are not limited to: cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, 3-methylcyclopentyl, 3-methylcyclohexyl, and 3-ethylcyclohexyl, with cyclopentyl and cyclohexyl being preferred.
In the present invention, the C1-C6 alkoxy group may include, but is not limited to, a linear alkoxy group or a branched alkoxy group; preferably C1-C3 alkoxy, more preferably C1-C3 straight chain alkoxy. Examples of C1-C6 alkoxy include, but are not limited to, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, n-pentoxy, isopentoxy, neopentoxy, hexoxy, and the like.
In the present invention, C1-C6 alkylthio may include, but is not limited to, straight or branched alkylthio; preferably C1-C3 alkylthio, more preferably C1-C3 straight chain alkylthio. Examples of C1-C6 alkylthio include, but are not limited to, methylthio, ethylthio, n-propylthio, isopropylthio, n-butylthio, isobutylthio, tert-butylthio, n-pentylthio, isopentylthio, neopentylthio, hexylthio, and the like.
In the present invention, aryl means a substituted or unsubstituted monocyclic or bicyclic compound containing at least one aromatic ring. The substituent on the aryl is selected from but not limited to C1-C6 alkyl, C2-C6 heteroalkyl, C3-C6 cycloalkyl or C1-C6 alkoxy, and examples of each substituent are the same as those described above and are not repeated here.
According to a preferred embodiment of the invention, R1 to R4 are each independently selected from C1-C3 alkyl, C2-C3 heteroalkyl, C1-C3 alkoxy or C1-C3 alkylthio. The quaternary ammonium salt cation which can be stably formed by selecting the electron donor and the substituent with smaller occupied space position is beneficial to improving the generation rate and the yield of the tetrafluoroborate ionic liquid.
The alkyl halide in the invention is a monohalide obtained by substituting one hydrogen atom in the alkane by a halogen element, wherein the halogen element is one of chlorine, bromine or iodine, and the alkane is C1-C6 alkane, preferably C1-C4 alkane. Examples of C1-C4 alkanes include, but are not limited to, methane, ethane, propane, n-butane, or isobutane. Examples of the alkyl halide include, but are not limited to, methyl bromide, methyl iodide, ethyl chloride, ethyl bromide, 1-chloropropane, 2-bromopropane, 1-iodopropane or 2-bromo-2-methylpropane, and ethyl chloride or methyl bromide is more preferable.
According to an embodiment of the present invention, the solvent is selected from one or more of methanol, ethanol, acetone, dichloromethane, tetrahydrofuran, dioxane or acetonitrile, preferably one or more of methanol, ethanol or acetone, more preferably ethanol or acetone.
In the present invention, the molar ratio of the quaternized substrate to the alkyl halide is 1:1 to 7, preferably 1:1 to 4, and more preferably 1:1 to 1.5. The reaction temperature is 30-50 ℃, preferably 30-35 ℃. The illumination intensity is 10-1000W/m2Preferably 50 to 800W/m2Further preferably 60 to 750W/m2More preferably 70 to 680W/m2. The irradiation time is 8-12 h, preferably 9-11 h, and more preferably 10 h. The heating mode in the invention is selected from water bath heating, oil bath heating or electric heating, and the like, and preferably the water bath heating can ensure that the reaction is heated uniformly and avoid partial carbonization. The heating apparatus of the present invention may employ a heating cycle device known in the art, and will not be described herein.
< preparation of a liquid mixture containing tetrafluoroborate Ionic liquid >
Uniformly mixing the quaternary ammonium salt solution obtained in the step (1) with tetrafluoroborate. The molar ratio of the quaternized substrate to the tetrafluoroborate is 1: 1-7. At the temperature of 35-45 ℃, the illumination intensity is 10-1000W/m2The ultraviolet light is irradiated for 16-19 hours to obtain a mixed liquid containing the tetrafluoroborate ionic liquid. In the present invention, the tetrafluoroborate salt is preferably sodium tetrafluoroborate or potassium tetrafluoroborate.
In the invention, the molar ratio of the quaternization substrate to the tetrafluoroborate required for preparing the quaternary ammonium salt solution is 1: 1-7, preferably 1: 1-4, and more preferably 1: 1-1.5. The temperature of the prepared mixed solution is 35-45 ℃, preferably 38-43 ℃, and more preferably 40 ℃. The illumination intensity is 10-1000W/m2Preferably 50 to 800W/m2Further preferably 60 to 750W/m2More preferably 70 to 680W/m2. The irradiation time is 16-20 h, preferably 17-19 h, and more preferably 17.5-18.5 h. The heating mode adopted in the step (2) is water bath heating, oil bath heating or electric heating, and the like, preferably water bath heating, so that the reaction can be uniformly heated, and partial carbonization is avoided. The heating apparatus of the present invention may employ a heating cycle device known in the art, and will not be described herein.
< purification of tetrafluoroborate Ionic liquid mixture >
And (3) filtering the mixed solution obtained in the step (2) to obtain a filtrate, heating the obtained filtrate to 50-70 ℃, and removing the solvent to obtain the tetrafluoroborate ionic liquid. In the present invention, the conventional operations in the art are adopted for filtering the mixed solution, and the filtering operation and the used apparatuses are all those known in the art and will not be described herein again.
The cation of the tetrafluoroborate ionic liquid is selected from quaternary ammonium salt cation shown in formula (I), N' -disubstituted imidazole cation shown in formula (II) or N-substituted pyridine cation shown in formula (III). Preferably, the cation is an N, N' -disubstituted imidazolium cation.
In the present invention, R1 to R4 are the same as the groups R1 to R4 described above, and are not described herein again. R5-R7 are respectively and independently selected from C1-C6 alkyl, C2-C6 heteroalkyl, C3-C6 cycloalkyl, C1-C6 alkoxy, C1-C6 alkylthio or aryl.
In the present invention, the C1-C6 alkyl group may include, but is not limited to, a straight chain alkyl group or a branched chain alkyl group; preferably C1-C3 alkyl, more preferably C1-C3 straight chain alkyl. Examples of C1-C6 alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, hexyl and the like. C2-C6 heteroalkyl can include, but is not limited to, straight or branched chain heteroalkyl; preferably C2-C5 heteroalkyl, more preferably C2-C3 heteroalkyl. The heteroalkyl group in the present invention refers to a group formed by substituting a carbon atom on an alkyl chain with another heteroatom. The heteroatom is preferably O or S. C3-C6 cycloalkyl can include substituted cycloalkyl and unsubstituted cycloalkyl; preferably C5-C6 cycloalkyl, more preferably C5 cycloalkyl. Specific examples of C3-C6 cycloalkyl groups of the present invention include, but are not limited to: cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, 3-methylcyclopentyl, 3-methylcyclohexyl, and 3-ethylcyclohexyl, with cyclopentyl and cyclohexyl being preferred. C1-C6 alkoxy can include, but is not limited to, straight or branched chain alkoxy; preferably C1-C3 alkoxy, more preferably C1-C3 straight chain alkoxy. Examples of C1-C6 alkoxy include, but are not limited to, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, n-pentoxy, isopentoxy, neopentoxy, hexoxy, and the like. C1-C6 alkylthio can include, but is not limited to, straight or branched alkylthio; preferably C1-C3 alkylthio, more preferably C1-C3 straight chain alkylthio. Examples of C1-C6 alkylthio include, but are not limited to, methylthio, ethylthio, n-propylthio, isopropylthio, n-butylthio, isobutylthio, tert-butylthio, n-pentylthio, isopentylthio, neopentylthio, hexylthio, and the like. Aryl represents a substituted or unsubstituted monocyclic or bicyclic compound containing at least one aromatic ring. The substituent on the aryl is selected from but not limited to C1-C6 alkyl, C2-C6 heteroalkyl, C3-C6 cycloalkyl or C1-C6 alkoxy, and the examples of each substituent are the same as above and are not repeated here.
According to a preferred embodiment of the invention, R5 to R7 are each independently selected from C1-C3 alkyl, C2-C3 heteroalkyl, C1-C3 alkoxy or C1-C3 alkylthio. The quaternary ammonium salt cation can be stabilized by selecting the electron donor and the group with smaller occupied space position, and the generation rate and the yield of the tetrafluoroborate ionic liquid are improved.
In the present invention, the temperature required for removing the solvent is 50 to 70 ℃, preferably 55 to 65 ℃, and more preferably 58 to 62 ℃. In a preferred embodiment of the present invention, the solvent may be removed by heating under atmospheric pressure, by vacuum evaporation, or by heating under vacuum evaporation, preferably by vacuum evaporation. The volatilization rate of the solvent is accelerated, and the volatilization efficiency is improved.
According to a preferred embodiment of the present invention, the method for synthesizing the tetrafluoroborate ionic liquid comprises the following steps:
(1) dispersing a quaternized substrate and alkyl halide in a solvent, wherein the molar ratio of the quaternized substrate to the alkyl halide is 1: 1-4; at the temperature of 30-35 ℃, the illumination intensity is 50-800W/m2Irradiating by using ultraviolet light for 9-11 hours to obtain a quaternary ammonium salt solution;
(2) uniformly mixing the quaternary ammonium salt solution obtained in the step (1) with sodium tetrafluoroborate, wherein the molar ratio of the quaternary ammonium substrate to the sodium tetrafluoroborate is 1: 1-4, and the illumination intensity is 50-800W/m at 38-43 DEG C2Irradiating the ultraviolet light for 17-19 hours to obtain a mixed liquid containing tetrafluoroborate ionic liquid;
(3) filtering the mixed solution obtained in the step (2) to obtain a filtrate, concentrating the filtrate at 55-65 ℃, and removing the solvent to obtain the tetrafluoroborate ionic liquid.
According to one embodiment of the invention, the method for synthesizing the tetrafluoroborate ionic liquid comprises the following steps:
(1) uniformly dispersing 1-methylimidazole and chloroethane in a molar ratio of 1:1 in ethanol, heating to 35 ℃ by using a circulating heating device, and then adopting illumination intensity of 75W/m2Or 600W/m2Is irradiated for 10 hours to obtain the quaternary phosphonium chloride of 1-ethyl-3-methylimidazoleAn ammonium salt solution;
(2) uniformly mixing the quaternary ammonium salt solution obtained in the step (1) with sodium tetrafluoroborate, wherein the molar ratio of the 1-methylimidazole to the sodium tetrafluoroborate is 1:1, heating to 40 ℃, and then, adopting illumination intensity of 75W/m2Or 600W/m2The ultraviolet light is irradiated for 18 hours, and the mixed liquid contains tetrafluoroborate ionic liquid;
(3) and (3) filtering the mixed solution obtained in the step (2) to obtain a filtrate, concentrating the filtrate at 60 ℃, and removing ethanol to obtain the 1-ethyl-3-methylimidazole tetrafluoroborate ionic liquid.
The test methods used in the examples and comparative examples are described below:
method for determining yield of quaternary ammonium salt solution: subjecting the quaternary ammonium salt solution to a nuclear magnetic resonance apparatus1Analysis of the H NMR spectrum if1An absorption peak at 7ppm in the H NMR spectrum indicates incomplete reaction, otherwise it indicates complete reaction.
The method for measuring the yield of the ionic liquid comprises the following steps: and carrying out thermogravimetric analysis on the ionic liquid by adopting a thermogravimetric analyzer (TGA) to obtain the actual concentration of the ionic liquid, and converting the actual concentration with the theoretical yield to further obtain the yield of the ionic liquid.
Conductivity test method: the ionic liquid was tested for conductivity using a conductivity meter model CON 150 from Thermo Eutech.
The method for testing the refractive index comprises the following steps: the refractivity of the ionic liquid was measured by a refractometer manufactured by the company ATAGO.
Example 1
(1) Uniformly dispersing 1-methylimidazole and chloroethane in a molar ratio of 1:1 in ethanol, heating to 35 ℃ by using a circulating heating device, and stirring under the condition of illumination intensity of 600W/m2The ultraviolet light is used for irradiating for 10 hours to obtain the quaternary ammonium salt solution of the 1-ethyl-3-methylimidazole chloride, and the yield is 100 percent;
(2) uniformly mixing the quaternary ammonium salt solution obtained in the step (1) with sodium tetrafluoroborate (the molar ratio of 1-methylimidazole to sodium tetrafluoroborate is 1:1), heating to 40 ℃, and stirringUnder the condition, the illumination intensity is 600W/m2The ultraviolet light is irradiated for 18 hours, and the mixed liquid contains tetrafluoroborate ionic liquid;
(3) and (3) filtering the mixed solution obtained in the step (2) for 2 times to obtain a filtrate, concentrating the filtrate at 60 ℃, and removing ethanol to obtain the 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid with the yield of 94%. The properties of the resulting ionic liquid are shown in table 1.
Comparative example 1
(1) Uniformly dispersing 1-methylimidazole and chloroethane in a molar ratio of 1:1 in ethanol, heating to 35 ℃ by using a circulating heating device, and stirring for 24 hours to obtain yellow viscous quaternary ammonium salt solution, wherein the yield is 98%;
(2) uniformly mixing the quaternary ammonium salt solution and sodium tetrafluoroborate (the molar ratio of 1-methylimidazole to sodium tetrafluoroborate is 1:1), heating to 40 ℃, and stirring for 48 hours to obtain a mixed solution containing tetrafluoroborate ionic liquid;
(3) and (3) filtering the mixed solution obtained in the step (2) for 2 times to obtain a filtrate, concentrating the filtrate at 60 ℃, and removing ethanol to obtain the 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid with the yield of 89%. The properties of the resulting ionic liquid are shown in table 1.
Comparative example 2
(1) Uniformly dispersing 1-methylimidazole and chloroethane in a molar ratio of 1:1 in ethanol, heating to 35 ℃ by using a circulating heating device, and simultaneously carrying out auxiliary heating for 12 hours by using microwaves with the radiation intensity of 150W under the stirring condition to obtain yellow viscous quaternary ammonium salt solution, wherein the yield is 99%;
(2) uniformly mixing the quaternary ammonium salt solution and sodium tetrafluoroborate (the molar ratio of 1-methylimidazole to sodium tetrafluoroborate is 1:1), heating to 40 ℃, and performing auxiliary heating for 24 hours by using microwaves with the radiation intensity of 150W under the stirring condition to obtain a mixed solution containing tetrafluoroborate ionic liquid;
(3) and (3) filtering the mixed solution obtained in the step (2) for 2 times to obtain a filtrate, concentrating the filtrate at 60 ℃, and removing ethanol to obtain the 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid with the yield of 91%. The properties of the resulting ionic liquid are shown in table 1.
TABLE 1
As can be seen from Table 1, the method of the present invention can improve the yield of the ionic liquid and improve the synthesis efficiency of the ionic liquid. In addition, the conductivity and the refractive index of the obtained ionic liquid are also improved.
Example 2
(1) Uniformly dispersing 1-methylimidazole and chloroethane in a molar ratio of 1:1 in ethanol, heating to 35 ℃ by using a circulating heating device, and then adopting illumination intensity of 75W/m2The solution is irradiated by ultraviolet light and stirred for 10 hours to obtain a quaternary ammonium salt solution of 1-ethyl-3-methylimidazole chloride, and the yield is 100 percent;
(2) uniformly mixing the quaternary ammonium salt solution obtained in the step (1) with sodium tetrafluoroborate (the molar ratio of 1-methylimidazole to sodium tetrafluoroborate is 1:1), heating to 40 ℃, and then adopting illumination intensity of 75W/m2The ultraviolet light is irradiated and stirred for 18 hours to obtain a mixed solution containing tetrafluoroborate ionic liquid;
(3) and (3) filtering the mixed solution obtained in the step (2) for 2 times to obtain a filtrate, concentrating the filtrate at 60 ℃, and removing ethanol to obtain the 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid with the yield of 93%. The properties of the resulting ionic liquid are shown in table 2.
TABLE 2
The present invention is not limited to the above-described embodiments, and any variations, modifications, and substitutions which may occur to those skilled in the art may be made without departing from the spirit of the invention.
Claims (5)
1. A method for synthesizing tetrafluoroborate ionic liquid is characterized by comprising the following steps:
(1) dispersing a quaternized substrate and alkyl halide in a solvent, wherein the molar ratio of the quaternized substrate to the alkyl halide is 1: 1-4, irradiating by adopting ultraviolet light at the temperature of 30-50 ℃, and the illumination intensity is 70-680W/m2Irradiating for 9-11 h to obtain a quaternary ammonium salt solution; wherein the alkyl halide is ethyl chloride or methyl bromide; the quaternization substrate is N-substituted imidazole shown as a formula (b),
wherein R4 is selected from C1-C6 alkyl, C2-C6 heteroalkyl, C3-C6 cycloalkyl, C1-C6 alkoxy, C1-C6 alkylthio or aryl;
(2) uniformly mixing the quaternary ammonium salt solution and tetrafluoroborate, wherein the molar ratio of the quaternary ammonium substrate to the tetrafluoroborate is 1: 1-4, irradiating by using ultraviolet light at 35-45 ℃, and the illumination intensity is 70-680W/m2Irradiating for 17-19 h to obtain a mixed solution containing tetrafluoroborate ionic liquid;
(3) filtering the mixed solution obtained in the step (2) to obtain a filtrate, concentrating the filtrate at 50-70 ℃, and removing the solvent to obtain the tetrafluoroborate ionic liquid.
2. The synthesis method according to claim 1, wherein the solvent is selected from one or more of methanol, ethanol, acetone, dichloromethane, tetrahydrofuran, dioxane or acetonitrile.
3. A synthesis method according to claim 2, characterized in that the tetrafluoroborate is chosen from sodium tetrafluoroborate or potassium tetrafluoroborate.
4. The synthesis method as claimed in claim 3, wherein the cation of the tetrafluoroborate ionic liquid is an N, N' -disubstituted imidazole cation shown in formula (II),
wherein R4 is selected from C1-C6 alkyl, C2-C6 heteroalkyl, C3-C6 cycloalkyl, C1-C6 alkoxy, C1-C6 alkylthio or aryl; r6 is ethyl or methyl.
5. The method of claim 1, wherein the ultraviolet light in step (1) and step (2) is irradiated at the same intensity.
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