Deep eutectic solvent

Abstract

To provide a novel deep eutectic solvent.SOLUTION: A deep eutectic solvent comprises a compound represented by formula (1) in the figure and a quaternary ammonium salt. In formula (1), R1 represents a carboxyl group or a hydroxyalkyl group, and R2, R3, R4, R5 and R6 each independently represent a hydrogen atom, an alkyl group, an aryl group, or -OR7, and R7 represents a hydrogen atom, an alkyl group, or an aryl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to deep eutectic solvents. [Background technology]

[0002] In recent years, the use of deep eutectic solvents has been studied as a new organic fluid to replace ionic liquids. For example, Patent Document 1 discloses an optical wavelength conversion element in which organic photosensitizer molecules and organic luminescent molecules are dissolved or dispersed in a deep eutectic solvent, as well as a solar cell, a photocatalyst, and the like that use the same. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-180277 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure aims to provide novel deep eutectic solvents. [Means for solving the problem]

[0005] The present disclosure provides, for example, the following [1] to [6]. [1] A deep eutectic solvent comprising a compound represented by the following formula (1) and a quaternary ammonium salt: [ka] [In formula (1), R 1 represents a carboxy group or a hydroxyalkyl group, R 2 , R 3 , R 4 , R 5 and R 6 are each independently a hydrogen atom, an alkyl group, an aryl group, or -OR 7indicates, R 7 represents a hydrogen atom, an alkyl group, or an aryl group. [2] R 1 The deep eutectic solvent according to [1], wherein the hydroxyalkyl group is a hydroxyalkyl group. [3] R 1 The deep eutectic solvent according to [1], wherein is a carboxy group. [4] R 2 , the R 3 , the R 4 , the R 5 and the above R 6 The deep eutectic solvent according to any one of [1] to [3], wherein at least one of the groups is a hydroxy group. [5] The deep eutectic solvent according to any one of [1] to [4], wherein the quaternary ammonium salt is a compound represented by the following formula (2-1): [ka] [In formula (2-1), R 11 , R 12 , R 13 and R 14 each independently represents an alkyl group, an alkenyl group, an aryl group, or a hydroxyalkyl group; X - indicates an anion.] [6] The deep eutectic solvent according to [5], wherein the anion is a halide ion. [Effects of the Invention]

[0006] According to the present disclosure, novel deep eutectic solvents are provided. DETAILED DESCRIPTION OF THE INVENTION

[0007] Preferred embodiments of the present disclosure will be described in detail below.

[0008] The deep eutectic solvent of this embodiment contains a compound represented by formula (1) and a quaternary ammonium salt. [ka]

[0009] In formula (1), R 1 represents a carboxyl group or a hydroxyalkyl group, and R 2 , R 3 , R 4 , R 5 and R 6 are each independently a hydrogen atom, an alkyl group, an aryl group, or -OR 7 indicates R 7 represents a hydrogen atom, an alkyl group, or an aryl group.

[0010] In this embodiment, the compound represented by formula (1) functions as a hydrogen bond donor, and the quaternary ammonium salt functions as a hydrogen bond acceptor. Therefore, the deep eutectic solvent of this embodiment exhibits a melting point lower than the melting points of the compound represented by formula (1) and the quaternary ammonium salt, and can be suitably used as a deep eutectic solvent. In other words, the deep eutectic solvent of this embodiment can be said to contain the compound represented by formula (1), which is a hydrogen bond donor, and the quaternary ammonium salt, which is a hydrogen bond acceptor.

[0011] The compound represented by formula (1) (hereinafter also referred to as a hydrogen bond donor) and the quaternary ammonium salt (hereinafter also referred to as a hydrogen bond acceptor) will be described in detail below.

[0012] <Hydrogen bond donor> The hydrogen bond donor of this embodiment is a compound represented by formula (1). The compound represented by formula (1) is R 1 is a carboxy group or a hydroxyalkyl group, and therefore functions as a hydrogen bond donor. The deep eutectic solvent of this embodiment may contain one or more hydrogen bond donors.

[0013] In formula (1), R 1The hydroxyalkyl group in the formula (I) may be, for example, a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 or 2 carbon atoms (i.e., a hydroxymethyl group or a hydroxyethyl group), or a hydroxyalkyl group having 1 carbon atom (i.e., a hydroxymethyl group).

[0014] R 2 ~R 6 The alkyl group in R may be, for example, an alkyl group having 1 to 8 carbon atoms, or may be an alkyl group having 1 to 4 carbon atoms. 2 ~R 6 The alkyl group in may be, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, or the like.

[0015] R 2 ~R 6 The aryl group in R may be, for example, an aryl group having 6 to 20 carbon atoms, or may be an aryl group having 6 to 10 carbon atoms. 2 ~R 6 The aryl group in may be, for example, a phenyl group, a tolyl group (o-tolyl group, m-tolyl group, p-tolyl group), a naphthyl group (1-naphthyl group, 2-naphthyl group), or the like.

[0016] R 7 The alkyl group in R may be, for example, an alkyl group having 1 to 8 carbon atoms, or may be an alkyl group having 1 to 4 carbon atoms. 2 ~R 6 The alkyl group in may be, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, or the like.

[0017] R 7 The aryl group in R may be, for example, an aryl group having 6 to 20 carbon atoms, or may be an aryl group having 6 to 10 carbon atoms. 2 ~R 6The aryl group in may be, for example, a phenyl group, a tolyl group (o-tolyl group, m-tolyl group, p-tolyl group), a naphthyl group (1-naphthyl group, 2-naphthyl group), or the like.

[0018] R 2 ~R 6 At least one of R is preferably a hydroxy group. 2 ~R 6 Among these, it is preferred that one or two of them are hydroxy groups, and it is more preferred that one of them is a hydroxy group.

[0019] R 2 ~R 6 Among them, R 4 is preferably a hydroxy group.

[0020] R 2 ~R 6 At least one of them is -OR 7 It is preferable that R 2 ~R 6 One or the other is -OR 7 and one is -OR 7 It is more preferable that:

[0021] R 2 ~R 6 Among them, R 3 and R 5 At least one of the following is -OR 7 Preferably, R 3 and R 5 Either one of them is -OR 7 It is more preferable that:

[0022] An example of the compound represented by formula (1) is a compound represented by formula (1-1). [ka]

[0023] In formula (1-1), R 2 ~R6 has the same meaning as above.

[0024] By using the compound represented by formula (1-1), a deep eutectic solvent having a melting point of about 50 to 130°C can be obtained.

[0025] R in formula (1-1) 2 ~R 6 Examples and preferred ranges of are R in formula (1) 2 ~R 6 The examples and preferred ranges may be the same as those given above.

[0026] Examples of compounds represented by formula (1-1) include ferulic acid, isoferulic acid, coumaric acid (o-coumaric acid, p-coumaric acid, m-coumaric acid), sinapic acid, cinnamic acid, 3,4-hydroxycinnamic acid, 2,4-hydroxycinnamic acid, and 3,4,5-hydroxycinnamic acid.

[0027] Examples of the compound represented by formula (1) include compounds represented by formula (1-2). [ka]

[0028] In formula (1-2), R 2 ~R 6 is the same as above, and R 8 represents an alkanediyl group.

[0029] By using the compound represented by formula (1-2), a deep eutectic solvent that does not crystallize even at extremely low temperatures of -20°C or lower (that is, having a melting point of -20°C or lower) can be obtained.

[0030] R in formula (1-2) 2 ~R 6 Examples and preferred ranges of are R in formula (1) 2 ~R 6 The examples and preferred ranges may be the same as those given above.

[0031] R 8The alkanediyl group in the formula (I) may be, for example, an alkanediyl group having 1 to 4 carbon atoms, preferably an alkanediyl group having 1 to 2 carbon atoms, and more preferably a methylene group. Examples of the alkanediyl group include a methylene group, an ethylene group, a 1,3-propanediyl group, and a 1,4-butanediyl group.

[0032] Examples of the compound represented by formula (1-2) include compounds in which the carboxy group (-COH) of the compound exemplified as the compound represented by formula (1-1) is converted to a hydroxymethyl group (-CHOH). Examples of the compound represented by formula (1-2) include coniferyl alcohol, sinapyl alcohol, p-hydroxycinnamic alcohol, 3,4-hydroxycinnamic alcohol, and 3,4,5-hydroxycinnamic alcohol.

[0033] <Hydrogen bond acceptor> The hydrogen bond acceptor of this embodiment is a quaternary ammonium salt. The deep eutectic solvent of this embodiment may contain one or more types of hydrogen bond acceptors.

[0034] The quaternary ammonium salt may have a quaternary ammonium cation and an anion.

[0035] The quaternary ammonium cation may have, for example, a nitrogen atom and four organic groups bonded to the nitrogen atom, such as an alkyl group, an alkenyl group, an aryl group, an arylalkyl group, or a hydroxyalkyl group.

[0036] The alkyl group in the organic group may be, for example, an alkyl group having 1 to 24 carbon atoms, an alkyl group having 1 to 18 carbon atoms, an alkyl group having 1 to 12 carbon atoms, an alkyl group having 1 to 6 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or an alkyl group having 1 to 3 carbon atoms, or may be an alkyl group having 1 carbon atom (i.e., a methyl group). Examples of the alkyl group in the organic group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-hexyl group, an n-heptyl group, and an n-octyl group.

[0037] The alkenyl group in the organic group may be, for example, an alkenyl group having 4 to 24 carbon atoms, or an alkenyl group having 7 to 22 carbon atoms. Examples of the alkenyl group in the organic group include a cis-9-hexadecen-1-yl (palmitoleyl) group, a trans-9-octadecenyl (elaidyl) group, a cis-9-octadecenyl (oleyl) group, a cis,cis-9,12-octadecadienyl (linolenyl) group, and a (9E,12E,15E)-octadeca-9,12,15-trienyl (elaidolinolenyl) group.

[0038] The aryl group in the organic group may be, for example, an aryl group having 6 to 20 carbon atoms, or an aryl group having 6 to 10 carbon atoms. The aryl group in the organic group may be, for example, a phenyl group, a tolyl group (o-tolyl group, m-tolyl group, p-tolyl group), a naphthyl group (1-naphthyl group, 2-naphthyl group), etc.

[0039] The arylalkyl group in the organic group may be, for example, a group in which the above-mentioned alkyl group is substituted with an aryl group. Examples of the alkyl group and the aryl group may be the same as those described above. Examples of the arylalkyl group in the organic group include a benzyl group.

[0040] The number of carbon atoms in the hydroxyalkyl group in the organic group may be, for example, 1 or more, 2 or more, or 3 or more. The number of carbon atoms in the hydroxyalkyl group in the organic group may be, for example, 8 or less, 6 or less, 4 or less, or 3 or less.

[0041] The organic group is preferably an alkyl group or a hydroxyalkyl group.

[0042] At least one of the organic groups is preferably a hydroxyalkyl group, and more preferably one of the organic groups is a hydroxyalkyl group.

[0043] The anion is not particularly limited and may be appropriately selected from known anions as anions in quaternary ammonium salts. Examples of the anion include halide ions (e.g., chloride ions, bromide ions, or iodide ions). Among these, halide ions are preferred, and chloride ions are more preferred, from the viewpoints of easy availability and low environmental impact.

[0044] The quaternary ammonium salt may be, for example, a compound represented by the following formula (2-1): [ka]

[0045] In formula (2-1), R 11 , R 12 , R 13 and R 14 each independently represents an alkyl group, an alkenyl group, an aryl group, an arylalkyl group, or a hydroxyalkyl group; X - indicates an anion.

[0046] R 11 ~R 14The examples and preferred ranges of the alkyl group, alkenyl group, aryl group, arylalkyl group, and hydroxyalkyl group in the above may be the same as the examples and preferred ranges of the alkyl group, alkenyl group, aryl group, arylalkyl group, and hydroxyalkyl group in the above organic group.

[0047] X - The examples and preferred ranges of the anion in may be the same as the examples and preferred ranges of the anion described above.

[0048] Examples of the compound represented by formula (2-1) include choline chloride, choline iodide, tetrabutylammonium chloride, tributylmethylammonium chloride, and benzyltributylammonium chloride.

[0049] The compound represented by formula (2-1) may be, for example, a compound represented by the following formula (2-1-1). [ka]

[0050] In formula (2-1-1), X - is the same as above, and R 15 represents an alkanediyl group, and R 16 , R 17 and R 18 each independently represents an alkyl group, an alkenyl group, an aryl group, an arylalkyl group, or a hydroxyalkyl group.

[0051] X in formula (2-1-1) - Examples and suitable ranges of the anion may be the same as the examples and suitable ranges of the anion described above.

[0052] R in formula (2-1-1) 15 The number of carbon atoms in the alkanediyl group in R may be, for example, 1 or more, 2 or more, or 3 or more. 15The number of carbon atoms in the alkanediyl group may be, for example, 8 or less, 6 or less, 4 or less, or 3 or less. Examples of the alkanediyl group include a methylene group, an ethylene group, a 1,3-propanediyl group, and a 1,4-butanediyl group.

[0053] R in formula (2-1-1) 16 ~R 18 The examples and suitable ranges of the alkyl group, alkenyl group, aryl group, arylalkyl group, and hydroxyalkyl group in the above may be the same as the examples and suitable ranges of the alkyl group, alkenyl group, aryl group, arylalkyl group, and hydroxyalkyl group in the above organic group.

[0054] In formula (2-1-1), R 16 ~R 18 is preferably an alkyl group, more preferably a methyl group or an ethyl group, and even more preferably a methyl group.

[0055] Examples of the compound represented by formula (2-1-1) include choline chloride, choline iodide, oleylbis(2-hydroxyethyl)methylammonium chloride, and alkylbis(2-hydroxyethyl)methylammonium chloride.

[0056] The quaternary ammonium salt may be, for example, a compound represented by the following formula (2-2). [ka]

[0057] In formula (2-2), R 21 represents an alkanediyl group, and R 22 , R 23 and R 24 R each independently represents an alkyl group, an alkenyl group, an aryl group, an arylalkyl group, or a hydroxyalkyl group. 21 and R 22 may be bonded to each other to form a ring. 21The alkanediyl group may have a substituent.

[0058] R 21 Examples and preferred ranges of the alkanediyl group in R 15 The examples and preferred ranges of the alkanediyl group in

[0059] R 21 Examples of the substituent that the alkanediyl group in the formula (I) may have include a hydroxy group.

[0060] R 22 , R 23 and R 24 The examples and suitable ranges of the alkyl group, alkenyl group, aryl group, arylalkyl group, and hydroxyalkyl group in the above may be the same as the examples and suitable ranges of the alkyl group, alkenyl group, aryl group, arylalkyl group, and hydroxyalkyl group in the above organic group.

[0061] Examples of the compound represented by formula (2-2) include carnitine, trimethylglycine, and proline betaine.

[0062] In the deep eutectic solvent of this embodiment, the ratio of the hydrogen bond donor to the total of the hydrogen bond donor and the hydrogen bond acceptor may be, for example, 5 mol% or more, 10 mol% or more, or 15 mol% or more. Also, the ratio of the hydrogen bond donor to the total of the hydrogen bond donor and the hydrogen bond acceptor may be, for example, 95 mol% or less, 90 mol% or less, or 85 mol% or less.

[0063] When the hydrogen bond donor is a compound represented by formula (1-1), the ratio of the hydrogen bond donor to the total of the hydrogen bond donor and the hydrogen bond acceptor may be 80 mol % or less, 70 mol % or less, 60 mol % or less, 50 mol % or less, or 45 mol % or less, which tends to lower the melting point of the deep eutectic solvent.

[0064] When the hydrogen bond donor is a compound represented by formula (1-2), the ratio of the hydrogen bond donor to the total of the hydrogen bond donor and the hydrogen bond acceptor is not particularly limited. When the hydrogen bond donor is a compound represented by formula (1-2), the deep eutectic solvent exhibits an extremely low melting point (e.g., a melting point of −20° C. or less) regardless of the mixing ratio. Therefore, when the hydrogen bond donor is a compound represented by formula (1-2), it can be suitably used as a deep eutectic solvent even if the blending ratio of the hydrogen bond donor and the hydrogen bond acceptor is biased to one side. From this perspective, when the hydrogen bond donor is a compound represented by formula (1-2), the ratio of the hydrogen bond donor to the total of the hydrogen bond donor and the hydrogen bond acceptor may be, for example, 50 mol% or less, 40 mol% or less, 30 mol% or less, or 25 mol% or less. Furthermore, when the hydrogen bond donor is a compound represented by formula (1-2), the ratio of the hydrogen bond donor to the total of the hydrogen bond donor and the hydrogen bond acceptor may be, for example, 50 mol % or more, 60 mol % or more, or 70 mol % or more.

[0065] The deep eutectic solvent of this embodiment may or may not further contain components other than the compound represented by formula (1) and the quaternary ammonium salt. That is, the deep eutectic solvent of this embodiment may be a deep eutectic solvent whose main components are the compound represented by formula (1) and the quaternary ammonium salt (for example, the total of the compound represented by formula (1) and the quaternary ammonium salt is 90 mass% or more, 95 mass% or more, or 99 mass% or more), or may be a deep eutectic solvent consisting of the compound represented by formula (1) and the quaternary ammonium salt.

[0066] In the deep eutectic solvent of this embodiment, the hydrogen bond donor may be derived from biomass. Examples of biomass-derived hydrogen bond donors include ferulic acid, isoferulic acid, coumaric acid (o-coumaric acid, p-coumaric acid, m-coumaric acid), sinapic acid, cinnamic acid, 3,4-hydroxycinnamic acid, and 3,4,5-hydroxycinnamic acid. Examples of biomass-derived hydrogen bond donors include compounds in which the carboxyl group (—COH) in the above-mentioned biomass-derived compounds has been converted to a hydroxymethyl group (—CHOH), such as coniferyl alcohol, sinapyl alcohol, p-hydroxycinnamic alcohol, 3,4-hydroxycinnamic alcohol, and 3,4,5-hydroxycinnamic alcohol.

[0067] In the deep eutectic solvent of this embodiment, the hydrogen bond acceptor may be derived from biomass. Examples of the biomass-derived hydrogen bond acceptor include choline chloride.

[0068] The use of the deep eutectic solvent of this embodiment is not particularly limited. The deep eutectic solvent of this embodiment can be suitably used, for example, as an extraction solvent, a reaction solvent, an electrical material, etc. The deep eutectic solvent of this embodiment can also be suitably used as a substitute for an ionic liquid.

[0069] Although the preferred embodiments have been described above, the present disclosure is not limited to the above embodiments. [Example]

[0070] The present disclosure will be explained in more detail below with reference to examples, but is not limited to these examples.

[0071] (Examples 1-1 to 1-27) Ferulic acid and choline chloride were placed in a mortar in the mixing ratio shown in Table 1, mixed, and then heated until liquid. After heating, the mixture was transferred to a 20 mL Erlenmeyer flask and dried under reduced pressure at 50°C for one day to remove moisture. A small amount of the sample was then placed in a melting point analyzer, and a cover glass was placed over it to measure the melting point. The results are shown in Table 1. In Table 1, "HBD / HBA" indicates the molar ratio of ferulic acid to choline chloride (ferulic acid / choline chloride). In Table 1, "HBD content" indicates the proportion (mol %) of ferulic acid relative to the total of ferulic acid and choline chloride. In Table 1, "Tm" indicates the melting point measured using a melting point analyzer.

[0072] (Comparative Example 1-1) The melting point of choline chloride was measured using a melting point analyzer, and the results are shown in Table 1.

[0073] (Comparative Example 1-2) The melting point of ferulic acid was measured using a melting point analyzer, and the results are shown in Table 1.

[0074] [Table 1]

[0075] (Examples 2-1 to 2-5) Coniferyl alcohol and choline chloride were placed in a mortar in the mixing ratio shown in Table 2 and mixed. After mixing, the mixture was transferred to a 20 mL Erlenmeyer flask and dried under reduced pressure at 50°C for 1 day to remove moisture. It was then cooled in a freezer at -28°C. It was confirmed that none of Examples 2-1 to 2-5 crystallized at -28°C, and had a melting point of -28°C or lower. In Table 2, "HBD / HBA" indicates the molar ratio of coniferyl alcohol to choline chloride (coniferyl alcohol / choline chloride). In Table 2, "HBD content" indicates the proportion (mol %) of coniferyl alcohol relative to the total of coniferyl alcohol and choline chloride. In Table 2, "Tm" indicates the melting point measured using a melting point analyzer (however, if measurement using a melting point analyzer was not possible and crystallization was not confirmed visually at -28°C, it is recorded as "<-28").

[0076] (Comparative Example 2-1) The melting point of coniferyl alcohol was measured using a melting point analyzer, and the results are shown in Table 2.

[0077] [Table 2]

[0078] (Example 3-1) A deep eutectic solvent was obtained in the same manner as in Example 1-1, except that the molar ratio of ferulic acid to choline chloride was 1:1. The ionic conductivity of the obtained deep eutectic solvent was measured by the following method. The results are shown in Table 3.

[0079] <Measurement of ionic conductivity> A BioLogic SP-150 was used as the measurement device. A 100 μm thick Teflon sheet with 6 mm diameter holes was placed on a stainless steel plate, and the sample was placed in the holes. Another stainless steel plate was placed on top of that, and finally, it was wrapped with imide tape and fixed with a clip to obtain a measurement sample. The obtained measurement sample was left to stand at 80°C for 1 hour, and the ionic conductivity at 80°C was measured. Next, the measurement sample was cooled by 10°C, left to stand for 30 minutes, and the ionic conductivity was measured, and this process was repeated up to 30°C.

[0080] [Table 3]

[0081] Example 4-1 A deep eutectic solvent was obtained in the same manner as in Example 2-1, except that the molar ratio of phenyl alcohol to choline chloride was 1:1. The ionic conductivity of the obtained deep eutectic solvent was measured in the same manner as in Example 3-1. The results are shown in Table 4.

[0082] Furthermore, when the deep eutectic solvent of Example 4-1 was subjected to thermogravimetry by the following method, the thermal decomposition onset temperature was 257°C. Furthermore, when differential scanning calorimetry was performed by the following method, the glass transition temperature was -13°C.

[0083] <Thermogravimetry> The measurement device used was a Hitachi High-Tech TG / DTA7200. The measurement temperature range was 30°C to 450°C, and the heating rate was 10°C / min.

[0084] <Differential scanning calorimetry> The measurement device used was a Hitachi High-Tech DSC7020. Measurements were performed with a first temperature rise from 30°C to 120°C, a first temperature drop from 120°C to -120°C, and a second temperature rise from -120°C to 120°C. The temperature rise and drop rates were both 10°C / min. The glass transition temperature was determined from the DSC curve during the second temperature rise.

[0085] [Table 4]

Claims

1. A deep eutectic solvent comprising a compound represented by the following formula (1) and a quaternary ammonium salt: 【Chemical 1】 [In formula (1), R １ represents a carboxy group or a hydroxyalkyl group, R ２ , R ３ , R ４ , R ５ and R ６ are each independently a hydrogen atom, an alkyl group, an aryl group, or —OR ７ indicates, R ７ represents a hydrogen atom, an alkyl group, or an aryl group.

2. The R １ is a hydroxyalkyl group.

3. The R １ is a carboxy group.

4. The R ２ , the R ３ , the R ４ , the R ５ and the R ６ The deep eutectic solvent according to any one of claims 1 to 3, wherein at least one of the groups is a hydroxy group.

5. The deep eutectic solvent according to any one of claims 1 to 3, wherein the quaternary ammonium salt is a compound represented by the following formula (2-1): 【Chemistry 2】 [In formula (2-1), R １１ , R １２ , R １３ and R １４ each independently represents an alkyl group, an aryl group, or a hydroxyalkyl group; X － indicates an anion.]

6. 6. The deep eutectic solvent of claim 5, wherein the anion is a halide ion.

Images