Method for producing crystals of ionic liquids and crystals of ionic liquids

Abstract

This invention provides a simple method for producing crystals of highly pure ionic liquids. [Solution] A method for producing crystals of an ionic liquid, comprising a crystallization step of dehydrating a liquid ionic liquid to generate crystals of the ionic liquid.

Description

[Technical Field]

[0001] This disclosure relates to a method for producing crystals of ionic liquids and to crystals of ionic liquids. [Background technology]

[0002] Ionic liquids are substances that exist as liquids at or near room temperature and are known as a third type of liquid, possessing characteristics distinct from water or organic solvents. Numerous examples have been reported of ionic liquids exhibiting superior functions not found in water or organic solvents.

[0003] For example, ionic liquids have almost no vapor pressure, which is an advantage when used as a solvent because they do not cause solvent loss due to evaporation or environmental problems. On the other hand, a disadvantage of ionic liquids, which have almost no vapor pressure, is that it is difficult to separate high-boiling point impurities and by-products contained in the ionic liquid by distillation of the ionic liquid.

[0004] Known methods for purifying ionic liquids include, for example, a method of obtaining the ionic liquid as a high-boiling product after distillation of a composition containing the ionic liquid (Patent Document 1), a method of recovering the ionic liquid using an ion exchange membrane (Patent Document 2), a method of recovering the ionic liquid by adding a poor solvent to the ionic liquid and causing crystallization (Patent Documents 3, 4), and separation of the ionic liquid by extraction (Patent Document 5). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2023-176945 [Patent Document 2] Japanese Patent Publication No. 2015-96255 [Patent Document 3] Japanese Patent Publication No. 2010-184902 [Patent Document 4] Japanese Patent Publication No. 2008-133248 [Patent Document 5] International Publication No. 2023-176944 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] As mentioned above, various methods for purifying ionic liquids have been proposed, such as those described in Patent Documents 1 to 5.

[0007] However, the method described in Patent Document 1, for example, is prone to problems such as discoloration and decomposition of the ionic liquid due to high heat. Also, the method described in Patent Document 2, for example, has the problem of a low processing capacity due to the high viscosity of the ionic liquid. Furthermore, the methods described in Patent Documents 3 and 4, for example, require the use of organic solvents as poor solvents and also require large-scale cooling equipment. In addition, the method described in Patent Document 5, for example, has the problem of not being able to reach a high limit of achievable ionic liquid purity and increasing costs and solvent usage due to the need for a multi-stage purification process.

[0008] Under these circumstances, the primary objective of this disclosure is to provide a simple method for producing crystals of high-purity ionic liquids. Furthermore, this disclosure also aims to provide novel crystals of ionic liquids. [Means for solving the problem]

[0009] The inventors of this disclosure have diligently studied to solve the above-mentioned problems. As a result, they have found that by dehydrating a liquid ionic liquid, crystals of the ionic liquid are generated, and that crystals of a high-purity ionic liquid can be easily obtained.

[0010] This disclosure is the result of further consideration based on these findings. Specifically, this disclosure provides inventions in the following embodiments.

[0011] Item 1. A method for producing crystals of an ionic liquid, comprising a crystallization step of dehydrating a liquid ionic liquid to produce crystals of the ionic liquid. Item 2. The method for producing crystals of an ionic liquid according to Item 1, wherein a shearing force is applied to the liquid ionic liquid in the crystallization step. Item 3. The method for producing crystals of an ionic liquid according to Item 1 or 2, wherein the liquid ionic liquid is dehydrated until the water content of the liquid ionic liquid becomes 5% by mass or less. Item 4. The method for producing crystals of an ionic liquid according to any one of Items 1 to 3, wherein the liquid ionic liquid is dehydrated until the water content of the liquid ionic liquid becomes 0.5% by mass or less. Item 5. The method for producing crystals of an ionic liquid according to any one of Items 1 to 4, wherein the temperature condition in the crystallization step is 15°C or higher. Item 6. The method for producing crystals of an ionic liquid according to any one of Items 1 to 5, wherein the melting point of the crystals of the ionic liquid is 30°C or higher. Item 7. The liquid ionic liquid contains a 1-R-3-R'-imidazolium skeleton as a cation component, where R and R' are each independently an alkyl group, an allyl group, a vinyl group, or a benzyl group, and contains a dimethyl phosphate group, a carboxy group having 1 to 6 carbon atoms, or a hydrogen sulfate ion as an anion component. The method for producing crystals of an ionic liquid according to any one of Items 1 to 6. Item 8. The method for producing crystals of an ionic liquid according to Item 7, wherein the liquid ionic liquid contains a carboxy group having 1 to 6 carbon atoms as the anion component. Item 9. The method for producing crystals of an ionic liquid according to any one of Items 1 to 8, wherein the liquid ionic liquid contains 1-alkyl-3-methylimidazolium acetate or 1-alkenyl-3-methylimidazolium acetate. Item 10. A step of preparing crystals of an ionic liquid according to any one of Items 1 to 9, and a crystallization step of bringing a solution containing a liquid ionic liquid into contact with the crystals of the ionic liquid to form crystals of the liquid ionic liquid. A method for producing crystals of an ionic liquid, comprising the above steps. Item 11. A crystal of an ionic liquid substantially composed of only 1-alkyl-3-methylimidazolium acetate or only 1-alkenyl-3-methylimidazolium acetate. Item 12. A crystal of an ionic liquid substantially composed of only 1-ethyl-3-methylimidazolium acetate, only 1-allyl-3-methylimidazolium acetate, or only 1-vinyl-3-methylimidazolium acetate.

Advantages of the Invention

[0012] According to the present disclosure, a simple method for producing a crystal of an ionic liquid with high purity can be provided. Further, according to the present disclosure, a novel crystal of an ionic liquid can be provided.

Brief Description of the Drawings

[0013] [Figure 1] It is a photograph of the solidified product obtained in Example 1. [Figure 2] It is a 1H-NMR spectrum of the solidified product obtained in Example 1. [Figure 3] It is a 13C-NMR spectrum of the solidified product obtained in Example 1. [Figure 4] It is an XRD diffraction pattern of the solidified product obtained in Example 1. [Figure 5] It is a photograph of the solidified product obtained in Example 2. [Figure 6] It is a DSC curve of the solidified product obtained in Example 2. [Figure 7] It is an XRD diffraction pattern of the solidified product obtained in Example 1. [[ID=!]]

Modes for Carrying Out the Invention

[0014] Each configuration and their combinations in each embodiment are examples, and within the scope not departing from the gist of the present disclosure, addition, omission, substitution, and other changes of the configuration can be made as appropriate. The present disclosure is not limited by the embodiments.

[0015] In the numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Alternatively, the upper and lower limits, upper and lower limits, or lower and lower limits described separately may be combined to form numerical ranges. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples.

[0016] [Method for producing crystals of ionic liquids] The present disclosure's method for producing crystals of an ionic liquid is characterized by comprising a crystallization step of dehydrating a liquid ionic liquid to produce crystals of the ionic liquid. By having this configuration, the present disclosure's method for producing crystals of an ionic liquid can suitably produce crystals of an ionic liquid with high purity. The present disclosure's method for producing crystals of an ionic liquid will be described in detail below.

[0017] In the crystallization process, which generates crystals from an ionic liquid, the liquid ionic liquid is dehydrated.

[0018] From the viewpoint of suitably exhibiting the effects of the present invention, the dehydration of the liquid ionic liquid is carried out until the water content of the ionic liquid is preferably about 5% by mass or less, more preferably about 2% by mass or less, even more preferably about 1% by mass or less, even more preferably about 0.5% by mass or less, and even more preferably about 0.2% by mass or less. The lower limit of this water content is, for example, about 0.0% by mass. The water content of the ionic liquid is a value measured by the Hiranuma Trace Water Measurement Device AQ-2200.

[0019] The method for dehydrating a liquid ionic liquid is not particularly limited, but preferably, it is a method of evaporating the water from the ionic liquid under reduced pressure (for example, vacuum drying).

[0020] The temperature conditions for dehydrating the ionic liquid are set appropriately according to the pressure conditions, type of liquid ionic liquid, purity, water content, etc., as described later. However, from the viewpoint of suitably exhibiting the effects of the present invention, the temperature is preferably about 15°C or higher, more preferably about 30°C or higher, even more preferably about 40°C or higher, and also preferably about 100°C or lower, more preferably about 80°C or lower, and even more preferably about 50°C or lower. Preferred ranges include about 30-100°C, about 30-80°C, about 30-50°C, about 40-100°C, about 40-80°C, and about 40-50°C.

[0021] Furthermore, the pressure conditions for dehydrating the ionic liquid using this method are appropriately set according to the temperature conditions, the type, purity, and water content of the liquid ionic liquid, but from the viewpoint of suitably exhibiting the effects of the present invention, the pressure is preferably about 100 Pa or less, more preferably about 50 Pa or less, and even more preferably about 10 Pa or less. The lower limit is, for example, about 0.4 Pa, and preferred ranges include about 0.4 to 100 Pa, about 0.4 to 50 Pa, and about 0.4 to 10 Pa.

[0022] In the manufacturing method disclosed herein, it is preferable to apply a shear force to the liquid ionic liquid during the crystallization step. Applying a shear force to the liquid ionic liquid promotes the crystallization of the dehydrated liquid ionic liquid, making it possible to rapidly generate crystals. Furthermore, by using dehydration and shear force in combination, it can be said that crystals of the ionic liquid are more easily formed even if the water content of the ionic liquid is relatively high, compared to the case where crystals of the ionic liquid are formed by dehydration alone without applying a shear force.

[0023] Shear force is most effectively applied to a dehydrated liquid ionic liquid. The shear force may be applied while dehydrating the liquid ionic liquid, or it may be applied after the liquid ionic liquid has been dehydrated to reach the predetermined moisture content as described above.

[0024] There are no particular limitations on the method of applying shear force to a liquid ionic liquid. Examples include shaking the liquid ionic liquid, stirring the liquid ionic liquid, or placing the liquid ionic liquid between two flat plates and sliding one plate horizontally relative to the other. Only one method of applying shear force may be used, or two or more methods may be used in combination.

[0025] The temperature conditions for applying shear force to a liquid ionic liquid are exemplified by the same temperatures used for dehydrating the ionic liquid as described above.

[0026] The duration for applying shear force is not particularly limited and can be set appropriately depending on temperature conditions, pressure conditions, type of liquid ionic liquid, water content, timing of shear force application (during dehydration, after dehydration), etc., and should be continued until crystals of the ionic liquid are formed. Examples of shear force application durations include 1 minute or more, 30 minutes or more, 60 minutes or more, as well as 1 minute or less, 30 seconds or less, and 1 second or less.

[0027] The crystallization process is preferably carried out in a dry air or inert gas environment. This is because if the crystallization process is carried out in an atmosphere with a high moisture content, the liquid ionic liquid will absorb moisture from the atmosphere, making crystallization difficult. The moisture content of the inert gas in the crystallization process is preferably 30 ppm or less, more preferably 10.7 ppm or less, and even more preferably 5.3 ppm or less.

[0028] Suitable inert gases include, for example, nitrogen and argon.

[0029] In the crystallization process, the liquid ionic liquid may be dehydrated, and if necessary, shear force may be applied, followed by standing until crystals of the ionic liquid are formed. The standing time may be, for example, 10 days or more, or 30 days or less.

[0030] The temperature at which crystals of an ionic liquid are formed from a dehydrated liquid ionic liquid is not particularly limited and can be set appropriately depending on the type, purity, and water content of the liquid ionic liquid. Preferably, it is -25°C or higher, more preferably about 4°C or higher, and even more preferably about 10°C or higher. Also, preferably about 50°C or lower, more preferably about 40°C or lower, and even more preferably about 35°C or lower. Preferred ranges include approximately -25 to 50°C, approximately -25 to 40°C, approximately -25 to 35°C, approximately 4 to 50°C, approximately 4 to 40°C, approximately 4 to 35°C, approximately 10 to 50°C, approximately 10 to 40°C, and approximately 10 to 35°C.

[0031] In this disclosure, the crystalline nature of the ionic liquid is determined by the clear observation of crystalline structure peaks through X-ray diffraction (XRD) measurements.

[0032] In the method for producing crystals of ionic liquids according to this disclosure, the liquid ionic liquid used as a raw material is not particularly limited as long as it can be crystallized by the method of this disclosure. In this specification, "ionic liquid" means a substance that is a salt composed of a cationic component and an anionic component and exists as a liquid or supercooled liquid at around room temperature (approximately 10 to 40°C). Ionic liquids have almost no vapor pressure. The following are specific examples of ionic liquids to which the method for producing crystals of ionic liquids according to this disclosure can be employed.

[0033] (Ionic liquid) <Cationic components> Examples of cationic components of ionic liquids include imidazolium cations, pyridinium cations, pyrrolidinium cations, piperidinium cations, quaternary ammonium cations, and quaternary phosphonium cations, among which imidazolium cations are preferred.

[0034] Examples of the imidazolium cations mentioned above include the cation represented by formula (1) below. The cation represented by formula (1) also includes its tautomers and cations represented by structural formulas that are in resonance with formula (1).

[0035] [ka]

[0036] In formula (1), R 1 and R 3 R is the same or different substituted or unsubstituted alkyl group, alkenyl group, alkoxyalkyl group, or substituted or unsubstituted phenyl group, 2 , R 4 , and are, either identical or different, a hydrogen atom, a substituted or unsubstituted alkyl group, an alkenyl group, an alkoxyalkyl group, or a substituted or unsubstituted phenyl group.

[0037] R 1 ~R 5Examples of the substituted or unsubstituted alkyl group include linear or branched alkyl groups having 1 to 20 (preferably 1 to 10, more preferably 2 to 6, still more preferably 2 to 4) carbon atoms, such as methyl group, ethyl group, n-propyl group, isopropyl group, butyl group, hexyl group, octyl group, etc. A sulfo group may be bonded to the end of these alkyl groups. Examples of the alkenyl group include linear or branched alkenyl groups having 2 to 20 (preferably 2 to 10, more preferably 2 to 6, still more preferably 2 to 4) carbon atoms, such as vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 2-butenyl group, 1-pentenyl group, 2-pentenyl group, 1-hexenyl group, 2-hexenyl group, 1-octenyl group, etc. Examples of the alkoxyalkyl group include linear or branched alkoxyalkyl groups having 2 to 20 (preferably 2 to 10, more preferably 2 to 6, still more preferably 2 to 4) carbon atoms, such as methoxymethyl group, ethoxymethyl group, 1-methoxyethyl group, 2-methoxyethyl group, 1-ethoxyethyl group, 2-ethoxyethyl group, etc. Further, examples of the substituted or unsubstituted phenyl group include phenyl groups which may be substituted with 1 to 2 groups selected from a hydroxyl group, a halogen atom, a lower alkoxy group, a lower alkenyl group, a methylsulfonyloxy group, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted amino group, a substituted or unsubstituted phenyl group, a substituted or unsubstituted phenoxy group, and a substituted or unsubstituted pyridyl group.

[0038] R 1 and R 3 are preferably an alkyl group, an alkenyl group, or a substituted or unsubstituted phenyl group, more preferably a linear alkyl group having 1 to 6 carbon atoms. Also 1 and R 3 One of them is preferably a linear alkyl group having 1 to 4 carbon atoms and the other is preferably a linear alkyl group having 2 to 6 carbon atoms, and it is particularly preferable that the number of carbon atoms of these alkyl groups is different. R 2 、R 4 and R 5It is preferably a hydrogen atom, an alkyl group, an alkenyl group, or a substituted or unsubstituted phenyl group, and more preferably a hydrogen atom or an alkyl group.

[0039] The imidazolium cation comprises a 1-R-3-R'-imidazolium skeleton, where R and R' are preferably independently an alkyl group, an allyl group, a vinyl group, or a benzyl group. R is preferably ethyl, and R' is preferably methyl. The imidazolium cation is particularly preferably 1-ethyl-3-methylimidazolium cation.

[0040] <Anionic components> The anionic component in the ionic liquid is not particularly limited as long as it constitutes the ionic liquid together with the aforementioned cationic component. However, from the viewpoint of suitably exhibiting the effects of the present invention, it is preferable that it contains a dimethyl phosphate anion, a carbon-1 to carbon-6 carboxylate anion, or a bisulfate ion.

[0041] As the liquid ionic liquid, commercially available products can be used, or they can be manufactured using known techniques.

[0042] The ionic liquid is obtained by arbitrarily combining the above-mentioned cationic component and the above-mentioned anionic component. For example, an ionic liquid containing an imidazolium cation as the cationic component is preferred. Furthermore, an ionic liquid containing a carboxylic acid anion having 1 to 6 carbon atoms as the anionic component is preferred.

[0043] Specific examples of ionic liquids to which the method for producing crystals of the ionic liquids of this disclosure is preferable include 1-alkyl-3-methylimidazolium acetate and 1-alkenyl-3-methylimidazolium acetate. The alkyl group is preferably methyl, ethyl, propyl, butyl, or pentyl, and 1-ethyl-3-methylimidazolium acetate is particularly preferred as a specific compound. The alkenyl group is preferably allyl or vinyl, and 1-allyl-3-methylimidazolium acetate and 1-vinyl-3-methylimidazolium acetate are particularly preferred as specific compounds.

[0044] In the method for producing crystals of an ionic liquid according to the present disclosure, the purity of the liquid ionic liquid used as a raw material is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 60% by mass or more, from the viewpoint of suitably exhibiting the effects of the present invention.

[0045] Furthermore, the water content of the liquid ionic liquid used as a raw material is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 0.5% by mass or less. Note that commercially available liquid ionic liquids may absorb moisture from the air and have a water content of 2% by mass or more. In the manufacturing method of this disclosure, the water content is reduced to the aforementioned level (for example, 5% by mass or less) to generate the crystallinity of the ionic liquid.

[0046] In the method for producing crystals of an ionic liquid according to this disclosure, it is preferable that a poor solvent for the ionic liquid is not required, and that a poor solvent is substantially not used. A poor solvent for an ionic liquid is a solvent that does not readily dissolve the ionic liquid, and examples include polar aprotic organic solvents and low-polarity organic solvents. Examples of polar aprotic organic solvents include dimethyl sulfoxide and N,N-dimethylformamide. Examples of low-polarity organic solvents include hydrocarbon solvents such as toluene and hexane, ether solvents such as tetrahydrofuran and 1,4-dioxane, and chloroform.

[0047] "Substantially using no poor solvent" means that the amount of poor solvent used in the method for producing crystals of an ionic liquid according to this disclosure is, for example, 100 parts by mass or less, based on 100 parts by mass of liquid ionic liquid, preferably 50 parts by mass or less, preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 0 parts by mass.

[0048] The method for producing crystals of an ionic liquid according to this disclosure may also include a crystallization step in which crystals of an ionic liquid are prepared using the aforementioned dehydration method, and the ionic liquid crystals are brought into contact with a solution containing a liquid ionic liquid to generate crystals of a liquid ionic liquid. Hereinafter, this method will be referred to as the method for producing crystals of an ionic liquid according to the second aspect of this disclosure.

[0049] In the second embodiment of the method for producing crystals of an ionic liquid, the aforementioned crystals of the ionic liquid are used as seed crystals and brought into contact with a solution containing liquid ionic liquid, thereby generating crystals of liquid ionic liquid.

[0050] As in the second embodiment, when using an ionic liquid crystal as a seed crystal, the type of liquid ionic liquid (cationic and anionic components), purity, and water content of the raw material into which the seed crystal is brought into contact are the same as those of the ionic liquid raw material described above, and the same ionic liquid can be used as the raw material in the second embodiment as well.

[0051] In a second embodiment, the solution containing the liquid ionic liquid may also contain a solvent in addition to the liquid ionic liquid. Examples of solvents include water, methanol, ethanol, propanol, and dichloromethane. The solution may contain only one type of solvent or two or more types. As mentioned above, in the method for producing crystals of the ionic liquid according to this disclosure, it is not necessary to use a poor solvent for the ionic liquid, and it is preferable to substantially avoid using a poor solvent.

[0052] In the second embodiment, the content of the liquid ionic liquid in the solution containing the liquid ionic liquid is preferably 1% by mass or more, more preferably 20% by mass or more, and even more preferably 50% by mass or more, from the viewpoint of suitably exhibiting the effects of the present invention. The solution containing the liquid ionic liquid may be substantially composed of only the liquid ionic liquid and water. Here, "substantially" means that the total proportion of these contained in the solution is 99.0% by mass or more, more preferably 99.5% by mass or more, and more preferably 100% by mass or more.

[0053] In the crystallization step of the second embodiment, it is not necessary to perform the dehydration described above, but dehydration may be performed in the same manner as described above.

[0054] In the crystallization step of the second embodiment, it is preferable to apply a shear force to the mixture of the solution containing the liquid ionic liquid and the ionic liquid crystals. The type of shear force, time, temperature conditions, etc., are the same as described above. Furthermore, in the crystallization step of the second embodiment, it is preferable to carry out the crystallization step in a dry inert gas environment, and the preferred moisture content of the inert gas is the same as described above.

[0055] Furthermore, in the crystallization step of the second embodiment, the liquid ionic liquid may be left to stand until ionic liquid crystals are formed from the liquid ionic liquid.

[0056] In the crystallization step of the second embodiment, the temperature at which crystals of the ionic liquid are formed from a solution of the liquid ionic liquid is not particularly limited and can be set appropriately depending on the type of solvent, the type, purity, and water content of the liquid ionic liquid, but is preferably 10°C or higher, more preferably about 15°C or higher, even more preferably about 20°C or higher, and also preferably about 50°C or lower, more preferably about 40°C or lower, and even more preferably about 35°C or lower. Preferred ranges include about 10-50°C, about 10-40°C, about 10-35°C, about 15-50°C, about 15-40°C, about 15-35°C, about 20-50°C, about 20-40°C, and about 20-35°C.

[0057] The melting point of the ionic liquid crystal produced by the method for producing the ionic liquid crystal of this disclosure is preferably about 0°C or higher, more preferably about 10°C or higher, and even more preferably about 30°C or higher. In this disclosure, the melting point of the ionic liquid crystal means the extrapolation start temperature at the melting endothermic peak of the DSC curve. The extrapolation start temperature is the temperature at the intersection of a straight line extending from the low-temperature baseline to the high-temperature side and a tangent line drawn at the point where the slope of the curve on the low-temperature side of the melting peak is maximum. The melting point of the ionic liquid crystal is a value measured by differential scanning calorimetry (DSC) as specified in JIS K 7121-1987.

[0058] The water content of the ionic liquid crystals produced by the method for producing ionic liquid crystals of this disclosure is preferably about 2% by mass or less, more preferably about 0.5% by mass or less, even more preferably about 0.1% by mass or less, with a lower limit of 0.0% by mass. Furthermore, the purity of the ionic liquid crystals produced by the method for producing ionic liquid crystals of this disclosure is preferably about 99% by mass or more, more preferably about 99.5% by mass or more, and even more preferably about 99.9% by mass or more. The water content and purity of the ionic liquid crystals are values ​​measured by elemental analysis and mass spectrometry, respectively.

[0059] [Crystals of ionic liquids] The ionic liquid crystals of this disclosure are ionic liquid crystals composed substantially of 1-alkyl-3-methylimidazolium acetate or 1-alkenyl-3-methylimidazolium acetate. Here, "substantially composed of 1-alkyl-3-methylimidazolium acetate" means that the content of 1-alkyl-3-methylimidazolium acetate in the ionic liquid crystal is, for example, 95% by mass or more, preferably 98% by mass or more, more preferably 99% by mass or more, even more preferably 99.5% by mass or more, and even more preferably 99.8% by mass or more. Similarly, "substantially composed of 1-alkenyl-3-methylimidazolium acetate" means that the content of 1-alkenyl-3-methylimidazolium acetate in the ionic liquid crystal is, for example, 95% by mass or more, preferably 98% by mass or more, more preferably 99% by mass or more, even more preferably 99.5% by mass or more, and even more preferably 99.8% by mass or more.

[0060] In 1-alkyl-3-methylimidazolium acetate, the alkyl group is preferably methyl, ethyl, propyl, butyl, or pentyl. A particularly preferred specific example of 1-alkyl-3-methylimidazolium acetate is 1-ethyl-3-methylimidazolium acetate. The alkenyl group is preferably allyl or vinyl, and specific compounds such as 1-allyl-3-methylimidazolium acetate and 1-vinyl-3-methylimidazolium acetate are particularly preferred.

[0061] As stated above, in this disclosure, the crystalline nature of the ionic liquid can be determined by X-ray diffraction (XRD) measurement, which clearly shows peaks of the crystalline structure. Similarly, the crystalline nature of 1-alkyl-3-methylimidazolium acetate and 1-alkenyl-3-methylimidazolium acetate can also be determined by XRD.

[0062] The method for producing the crystals of the ionic liquid of this disclosure (crystals of the ionic liquid substantially composed of only 1-alkyl-3-methylimidazolium acetate or only 1-alkenyl-3-methylimidazolium acetate) is not particularly limited as long as the crystals of the ionic liquid are produced. A preferred method for producing the crystals of the ionic liquid is the method of production of this disclosure described above [Method for producing crystals of ionic liquid]. [Examples]

[0063] The present disclosure will be explained in more detail below with reference to examples.

[0064] (Example 1) Liquid 1-ethyl-3-methylimidazolium acetate (hereinafter referred to as [C2mim]OAc) was heated and vacuum-dried under conditions of 60-80°C and 0.4-5 Pa to reduce the moisture content to 0.14% by mass.

[0065] [ka]

[0066] The dried [C2mim]OAc was immediately transferred to a glove box under a dry nitrogen atmosphere at room temperature and stored in a vial. After standing for one month, shear force was applied by opening and closing the vial, and it was confirmed that the [C2mim]OAc inside the vial had solidified (see photograph in Figure 1). The melting point of the solidified [C2mim]OAc (solidified material) was measured by differential scanning calorimetry (DSC) as specified in JIS K 7121-1987, and the melting point was 43.6°C. Furthermore, the decomposition temperature of the solidified [C2mim]OAc was measured by thermogravimetric analysis (TG), and the decomposition temperature was 227°C.

[0067] In previous reports (DOI: 10.1039 / b818061j), the melting point of [C2mim]OAc was not found to be between -50°C and 200°C, and was thought to be below room temperature. Therefore, it was considered possible that the solidified material obtained in Example 1 was not pure [C2mim]OAc due to decomposition during vacuum drying or long-term storage. Thus, the nuclear magnetic resonance (NEM) of the solidified material obtained in Example 1 was investigated. 1 H-NMR and 13 The chemical structure was confirmed by 13C-NMR (C-NMR) spectroscopy. From the obtained NMR spectrum, it was revealed that the chemical structure of the solidified product obtained in Example 1 was [C2mim]OAc, indicating very high purity. 1 H-NMR and 13 The 1C-NMR spectra are shown in Figures 2 and 3, respectively. Furthermore, elemental analysis and mass spectrometry confirmed that the solidified material was high-purity [C2mim]OAc. The results of the elemental and mass spectrometry analyses are shown in Table 1.

[0068] The results from Example 1 revealed that [C2mim]OAc exists as a solid at room temperature (25°C) and has a melting point of approximately 43°C.

[0069] Furthermore, the crystal structure of the solidified material obtained in Example 1 was confirmed using wide-angle XRD. As a result, the XRD peaks were particularly sharp, indicating that [C2mim]OAc is highly crystalline. The obtained XRD diffraction pattern is shown in Figure 4.

[0070] [Table 1]

[0071] Furthermore, when the solidified [C2mim]OAc obtained in Example 1 was left in the air, its high hygroscopicity caused the solid to begin liquefying, and after 2 hours, most of the solid had liquefied (see photograph in Figure 5).

[0072] Next, 200 mg of the solidified [C2mim]OAc obtained in Example 1 was mixed with 1 mg of water, and the process of stirring was repeated. As a result, the solidified material liquefied after a total of 4 mg of water had been added. This result indicates that crystallization of liquid [C2mim]OAc proceeds as long as the water content is at least 2% by mass or less.

[0073] (Example 2) In a glove box under a dry nitrogen atmosphere, 50 mg of the solidified [C2mim]OAc obtained in Example 1 was used as a seed crystal and added to 500 μl of the liquid 1-ethyl-3-methylimidazolium acetate (1-Ethyl-3-methylimidazolium acetate, 95%, manufactured by IOLITEC) used in Example 1 at room temperature (25°C). When the resulting mixture was left to stand, the entire mixture, including the liquid [C2mim]OAc, solidified within 30 minutes (see photograph in Figure 5).

[0074] The solidified [C2mim]OAc obtained in Example 2 was subjected to differential scanning calorimetry (DSC) as specified in JIS K 7121-1987, and the melting point of the solidified [C2mim]OAc was found to be 43.6°C (see the DSC curve in Figure 6).

[0075] Furthermore, XRD measurements of the solidified [C2mim]OAc obtained in Example 2 showed that the solid exhibited high crystallinity. Specifically, characteristic peaks were observed around the scattering vectors q=0.83, 0.92, 0.98, 1.10, 1.26, and 1.37 (|q|=q=4πλsinθ). The obtained XRD diffraction pattern is shown in Figure 7.

[0076] Furthermore, the solidified [C2mim]OAc obtained in Example 2 1 H and 13 The 1C NMR spectrum showed that the purity of [C2mim]OAc was very high.

Claims

1. A method for producing crystals of an ionic liquid, comprising a crystallization step of dehydrating a liquid ionic liquid to generate crystals of the ionic liquid.

2. A method for producing crystals of an ionic liquid according to claim 1, wherein a shear force is applied to the liquid ionic liquid in the crystallization step.

3. A method for producing crystals of an ionic liquid according to claim 1 or 2, comprising dehydrating the liquid ionic liquid until the water content of the liquid ionic liquid becomes 5% by mass or less.

4. A method for producing crystals of an ionic liquid according to claim 1 or 2, comprising dehydrating the liquid ionic liquid until the water content of the liquid ionic liquid becomes 0.5% by mass or less.

5. A method for producing crystals of an ionic liquid according to claim 1 or 2, wherein the temperature condition in the crystallization step is 15°C or higher.

6. A method for producing crystals of an ionic liquid according to claim 1 or 2, wherein the melting point of the crystals of the ionic liquid is 30°C or higher.

7. The aforementioned liquid ionic liquid is The cationic component contains a 1-R-3-R'-imidazolium skeleton. R and R' are each independently an alkyl group, an allyl group, a vinyl group, or a benzyl group. The anionic component includes a dimethyl phosphate group, a carboxyl group having 1 to 6 carbon atoms, or a bisulfate ion. A method for producing crystals of an ionic liquid according to claim 1 or 2.

8. The method for producing crystals of an ionic liquid according to claim 7, wherein the liquid ionic liquid contains a carboxyl group having 1 to 6 carbon atoms as the anionic component.

9. A method for producing crystals of an ionic liquid according to claim 1 or 2, wherein the liquid ionic liquid comprises 1-alkyl-3-methylimidazolium acetate or 1-alkenyl-3-methylimidazolium acetate.

10. A step of preparing crystals of the ionic liquid according to claim 1 or 2, A crystallization step involves bringing a solution containing a liquid ionic liquid into contact with crystals of the ionic liquid to generate crystals of the liquid ionic liquid, A method for producing crystals of an ionic liquid, comprising the following:

11. A crystal of an ionic liquid substantially composed solely of 1-alkyl-3-methylimidazolium acetate or 1-alkenyl-3-methylimidazolium acetate.

12. A crystal of an ionic liquid substantially composed of only 1-ethyl-3-methylimidazolium acetate, only 1-allyl-3-methylimidazolium acetate, or only 1-vinyl-3-methylimidazolium acetate.

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