Water-soluble ionic liquid and preparation method thereof

Abstract

The invention discloses a water-soluble ionic liquid and a preparation method thereof, the ionic liquid is 1, 3-bis (2-ethoxyl) imidazole lactate, the ionic liquid is composed of cation 1, 3-bis (2-ethoxyl) imidazole cation ([DHEIM] +) and anion lactate (2-hydracrylate, [Lactate]-), the purity of the ionic liquid is greater than or equal to 99%, and the pH value of the ionic liquid is greater than or equal to 7. The thermal decomposition temperature of the ionic liquid in a nitrogen atmosphere is greater than or equal to 200 DEG C. The invention relates to the technical field of ionic liquid preparation, the ionic liquid is mutually soluble with water in any proportion at 25 DEG C, and the solubility is greater than 500g / 100mL water. The water-soluble ionic liquid is suitable for a high-water-content reaction or separation system, has a wider application range, and is suitable for industrial production. The preparation method disclosed by the invention is simple in process, mild in reaction condition and free of harsh equipment; by optimizing the raw material molar ratio, complete reaction is ensured, and the raw material utilization rate is increased; the whole process does not generate toxic and harmful wastes, conforms to the green chemical development concept, and is easy for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to the field of ionic liquid preparation technology, specifically to a water-soluble ionic liquid and its preparation method. Background Technology

[0002] Ionic liquids are salt compounds composed of organic cations and inorganic / organic anions that are liquid at room temperature. They possess outstanding characteristics such as low vapor pressure, high chemical stability, and strong designability, showing broad application prospects in various fields such as catalysis, gas absorption, bioseparation, and electrolyte materials. Among them, water-soluble ionic liquids, due to their combination of the inherent advantages of ionic liquids and excellent water compatibility, are widely used in aqueous solution systems as reaction media, separation and extraction agents, and solvents for bioactive substances.

[0003] However, some existing water-soluble ionic liquids suffer from insufficient thermal stability, with thermal decomposition temperatures below 200℃, limiting their application in medium- and high-temperature reaction systems. Some preparation processes are complex, requiring stringent reaction conditions, making it difficult to achieve product purity above 99%, and residual impurities (such as chloride ions and unreacted raw materials) affect application performance. Furthermore, some ionic liquids have limited miscibility with water, with solubility below 500 g / 100 mL of water, failing to meet the requirements for high-concentration aqueous solutions. Simultaneously, existing preparation methods involve cumbersome impurity removal processes, especially for inorganic impurities such as chloride ions, which are difficult to completely remove, hindering the industrial application of these products. Therefore, developing a water-soluble ionic liquid with high purity, high thermal stability, excellent water solubility, and a simple preparation process has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a water-soluble ionic liquid and its preparation method, thereby addressing the aforementioned problems in the prior art.

[0005] To achieve the above objectives, the main technical solution adopted by the present invention includes: The present invention provides a water-soluble ionic liquid, wherein the ionic liquid is 1,3-bis(2-hydroxyethyl)imidazolium lactate, which is composed of the cation 1,3-bis(2-hydroxyethyl)imidazolium cation ([DHEIM]+) and the anion lactate (2-hydroxypropionate, [Lactate]-). Furthermore, the purity of the ionic liquid is ≥99%.

[0006] Through recrystallization, multi-stage filtration, and vacuum drying in subsequent preparation processes, unreacted raw materials, byproducts, and solvent residues are effectively removed, ensuring that the product meets the stringent requirements of precision chemicals, biomedicine, and other scenarios with strict impurity content requirements. Furthermore, the thermal decomposition temperature of the ionic liquid under a nitrogen atmosphere is ≥200℃.

[0007] The stable combination of hydroxyethyl and imidazole rings in its molecular structure enhances its thermal stability, making it suitable for medium- and high-temperature reaction systems and applications requiring long-term storage. Furthermore, the ionic liquid is miscible with water in any proportion at 25°C, and its solubility is >500g / 100mL water.

[0008] The hydroxyethyl group in the cation has strong hydrophilicity and works synergistically with the lactate anion to give the product excellent water solubility, making it suitable for reaction or separation systems with high water content. This invention also provides a method for preparing the above-mentioned water-soluble ionic liquid, comprising the following steps: S1. Preparation of intermediate [DHEIM]Cl: Imidazole, 2-chloroethanol, and acetonitrile were mixed and refluxed at 80-85°C for 12-16 h under nitrogen protection. After the reaction was completed, acetonitrile was removed by vacuum distillation, and the mixture was recrystallized from anhydrous ethanol and dried under vacuum to obtain [DHEIM]Cl. Further, in step S1, the molar ratio of 2-chloroethanol to imidazole was 2.2:1.

[0009] An excess of 20% 2-chloroethanol ensures that both N atoms in the imidazole molecule undergo complete alkylation, avoiding the formation of monosubstituted byproducts and improving the yield and purity of the intermediate [DHEIM]Cl. Furthermore, in step S1, the vacuum drying conditions are 60℃, 0.09MPa, and drying time is 8h.

[0010] This condition can completely remove residual anhydrous ethanol during recrystallization without decomposing intermediates, thus preventing the solvent from interfering with subsequent ion exchange reactions. S2. Preparation of the target product via ion exchange reaction: [DHEIM]Cl was dissolved in deionized water, sodium lactate was added, and the mixture was stirred at room temperature for 24 h. The NaCl precipitate was removed by filtration. The filtrate was concentrated under reduced pressure, dissolved and filtered with anhydrous ethanol, concentrated again under reduced pressure, and dried under vacuum to obtain 1,3-bis(2-hydroxyethyl)imidazolium lactate. Furthermore, in step S2, the molar ratio of sodium lactate to [DHEIM]Cl is 1.1:1. An excess of 10% sodium lactate can promote the forward ion exchange reaction, ensuring the [DHEIM]Cl... ﹢ Completely convert to the target product, reducing intermediate residues. Furthermore, in step S2, the stirring rate is 300-500 rpm. This rate allows the reaction system to be fully mixed, avoiding incomplete reactions caused by excessively high local concentrations, while also preventing splashing or energy waste caused by excessively fast stirring. Furthermore, in step S2, after filtering to remove the NaCl precipitate, the precipitate is washed twice with a small amount of deionized water. The washing solution can be combined with the filtrate for further treatment to recover the [DHEIM] adsorbed on the precipitate surface. ﹢ This will increase the overall yield of the target product. Furthermore, in step S2, the anhydrous ethanol dissolution and filtration step is used to remove trace amounts of unreacted NaCl. Since the solubility of NaCl in anhydrous ethanol is extremely low (<0.1g / 100mL), while the target product can be completely dissolved in anhydrous ethanol, the impurities and the product can be efficiently separated by filtration. Furthermore, in step S2, the vacuum drying conditions are 70°C, 0.09 MPa, and 12 h. These conditions can completely remove residual water and anhydrous ethanol from the filtrate, avoiding the impact of solvent residue on product purity and performance stability.

[0011] The beneficial effects of this invention are: 1. The water-soluble ionic liquid of this invention has a purity of ≥99% and extremely low impurity content, which can meet the requirements of high-end fields such as precision chemicals and biomedicine; the thermal decomposition temperature is ≥200℃, and the thermal stability is excellent, which broadens its application scenarios in medium and high temperature systems; it is miscible with water in any proportion at 25℃, with a solubility of >500g / 100mL water, making it suitable for reaction or separation systems with high water content and with a wider range of applications.

[0012] 2. The preparation method of the present invention is simple. The reflux temperature in step S1 is 80-85℃, and the reaction in step S2 is at room temperature. The reaction conditions are mild and do not require demanding equipment. By optimizing the molar ratio of raw materials, the reaction is ensured to be complete and the utilization rate of raw materials is improved. The combined post-treatment process of recrystallization, ethanol dissolution and filtration, and multiple washing can efficiently remove the by-product NaCl and unreacted raw materials, ensuring that the purity of the product reaches more than 99%. The entire process generates no toxic or harmful waste, which is in line with the concept of green chemical development and is easy to scale up for industrial production.

[0013] 3. This ionic liquid combines the structural tunability of imidazole ionic liquids with the biocompatibility of lactate, and has excellent water solubility, making it promising for applications in catalytic synthesis, extraction of bioactive substances, and separation and purification of aqueous solutions. Detailed Implementation

[0014] The present invention will be further described below with reference to the embodiments. Example

[0015] A water-soluble ionic liquid, characterized in that the ionic liquid is 1,3-bis(2-hydroxyethyl)imidazolium lactate, composed of the cation 1,3-bis(2-hydroxyethyl)imidazolium ([DHEIM)). ﹢ ) and the anionic lactate (2-hydroxypropionate, [Lactate])- The ionic liquid is composed of 99% purity, has a thermal decomposition temperature of ≥200℃ under a nitrogen atmosphere, is miscible with water in any proportion at 25℃, and has a solubility of >500g / 100mL water.

[0016] A method for preparing water-soluble ionic liquids includes the following steps: S1. Imidazole, 2-chloroethanol and acetonitrile were mixed, with a molar ratio of 2-chloroethanol to imidazole of 2.2:1. The mixture was refluxed at 80°C for 12 h under nitrogen protection. After the reaction was completed, the acetonitrile was removed by vacuum distillation. The mixture was then recrystallized from anhydrous ethanol and dried under vacuum at 60°C and 0.09 MPa for 8 h to obtain [DHEIM]Cl. S2. Dissolve [DHEIM]Cl in deionized water, add sodium lactate (molar ratio of sodium lactate to [DHEIM]Cl 1.1:1), stir at room temperature for 24 h at a stirring rate of 300 rpm, filter to remove the generated NaCl precipitate, wash the precipitate twice with a small amount of deionized water, concentrate the filtrate under reduced pressure, dissolve and filter in anhydrous ethanol, concentrate again under reduced pressure and dry under vacuum at 70℃ and 0.09 MPa for 12 h to obtain 1,3-bis(2-hydroxyethyl)imidazolium lactate. Example

[0017] A water-soluble ionic liquid, characterized in that the ionic liquid is 1,3-bis(2-hydroxyethyl)imidazolium lactate, composed of the cation 1,3-bis(2-hydroxyethyl)imidazolium ([DHEIM)). ﹢ ) and the anionic lactate (2-hydroxypropionate, [Lactate]) - The ionic liquid is composed of 99% purity, has a thermal decomposition temperature of ≥200℃ under a nitrogen atmosphere, is miscible with water in any proportion at 25℃, and has a solubility of >500g / 100mL water.

[0018] A method for preparing water-soluble ionic liquids includes the following steps: S1. Imidazole, 2-chloroethanol and acetonitrile were mixed, with a molar ratio of 2-chloroethanol to imidazole of 2.2:1. The mixture was refluxed at 82°C for 14 h under nitrogen protection. After the reaction was completed, the acetonitrile was removed by vacuum distillation. The mixture was then recrystallized from anhydrous ethanol and dried under vacuum at 60°C and 0.09 MPa for 8 h to obtain [DHEIM]Cl. S2. Dissolve [DHEIM]Cl in deionized water, add sodium lactate (molar ratio of sodium lactate to [DHEIM]Cl 1.1:1), stir at room temperature for 24 h at a stirring rate of 400 rpm, filter to remove the generated NaCl precipitate, wash the precipitate twice with a small amount of deionized water, concentrate the filtrate under reduced pressure, dissolve and filter in anhydrous ethanol, concentrate again under reduced pressure and dry under vacuum. The vacuum drying conditions are 70℃, 0.09 MPa and drying time is 12 h to obtain 1,3-bis(2-hydroxyethyl)imidazolium lactate. Example

[0019] A water-soluble ionic liquid, characterized in that the ionic liquid is 1,3-bis(2-hydroxyethyl)imidazolium lactate, composed of the cation 1,3-bis(2-hydroxyethyl)imidazolium ([DHEIM)). ﹢ ) and the anionic lactate (2-hydroxypropionate, [Lactate]) - The ionic liquid is composed of 99% purity, has a thermal decomposition temperature of ≥200℃ under a nitrogen atmosphere, is miscible with water in any proportion at 25℃, and has a solubility of >500g / 100mL water.

[0020] A method for preparing water-soluble ionic liquids includes the following steps: S1. Imidazole, 2-chloroethanol and acetonitrile were mixed, with a molar ratio of 2-chloroethanol to imidazole of 2.2:1. The mixture was refluxed at 80-85℃ for 16 h under nitrogen protection. After the reaction was completed, the acetonitrile was removed by vacuum distillation. The mixture was recrystallized by anhydrous ethanol and dried under vacuum at 60℃ and 0.09 MPa for 8 h to obtain [DHEIM]Cl. S2. Dissolve [DHEIM]Cl in deionized water, add sodium lactate (molar ratio of sodium lactate to [DHEIM]Cl 1.1:1), stir at room temperature for 24 h at a stirring rate of 500 rpm, filter to remove the generated NaCl precipitate, wash the precipitate twice with a small amount of deionized water, concentrate the filtrate under reduced pressure, dissolve and filter in anhydrous ethanol, concentrate again under reduced pressure and dry under vacuum at 70℃ and 0.09 MPa for 12 h to obtain 1,3-bis(2-hydroxyethyl)imidazolium lactate.

[0021] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A water-soluble ionic liquid, characterized in that, The ionic liquid is 1,3-bis(2-hydroxyethyl)imidazolium lactate, composed of the cation 1,3-bis(2-hydroxyethyl)imidazolium ([DHEIM)). ﹢ ) and the anionic lactate (2-hydroxypropionate, [Lactate]) - )composition.

2. The water-soluble ionic liquid according to claim 1, characterized in that, The purity of the ionic liquid is ≥99%.

3. The water-soluble ionic liquid according to claim 1, characterized in that, The thermal decomposition temperature of the ionic liquid under a nitrogen atmosphere is ≥200℃.

4. The water-soluble ionic liquid according to claim 1, characterized in that, The ionic liquid is miscible with water in any proportion at 25°C, and its solubility is >500g / 100mL water.

5. A method for preparing a water-soluble ionic liquid as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Imidazole, 2-chloroethanol and acetonitrile are mixed and refluxed at 80-85℃ for 12-16h under nitrogen protection. After the reaction is completed, the acetonitrile is removed by vacuum distillation, recrystallized by anhydrous ethanol and dried under vacuum to obtain [DHEIM]Cl. S2. Dissolve [DHEIM]Cl in deionized water, add sodium lactate, stir and react at room temperature for 24 h, filter to remove the generated NaCl precipitate, concentrate the filtrate under reduced pressure, dissolve and filter in anhydrous ethanol, concentrate again under reduced pressure and dry under vacuum to obtain 1,3-bis(2-hydroxyethyl)imidazolium lactate.

6. The method for preparing a water-soluble ionic liquid according to claim 5, characterized in that, In step S1, the molar ratio of 2-chloroethanol to imidazole is 2.2:

1.

7. The method for preparing a water-soluble ionic liquid according to claim 5, characterized in that, In step S1, the vacuum drying conditions are 60℃, 0.09MPa, and drying time is 8h.

8. The method for preparing a water-soluble ionic liquid according to claim 5, characterized in that, In step S2, the molar ratio of sodium lactate to [DHEIM]Cl is 1.1:

1.

9. The method for preparing a water-soluble ionic liquid according to claim 5, characterized in that, In step S2, the stirring rate is 300-500 rpm; the vacuum drying conditions are 70℃, 0.09 MPa, and the drying time is 12 h.

10. The method for preparing a water-soluble ionic liquid according to claim 5, characterized in that, In step S2, after filtering to remove the NaCl precipitate, the precipitate is washed twice with a small amount of deionized water; the anhydrous ethanol dissolution and filtration step is used to remove trace amounts of unreacted NaCl.