JP2006232713A - New method for synthesizing ionic liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method for capable of producing an N-alkyl-substituted imidazoline tetrafluoroborate which is noncombustible, nonvolatile and useful as a solvent in various chemical reactions, etc., by using an inexpensive raw materials in a good efficiency. <P>SOLUTION: This N-alkyl-substituted imidazoline tetrafluoroborate is produced by reacting an N-alkyl-substituted imidazoline with a trialkyloxonium tetrafluoroborate in an ether solvent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a novel method for the synthesis of ionic liquid N, N'-dialkyl substituted imidazolium tetrafluoroborate.

  An ionic liquid is a salt that is in a liquid state near room temperature, and is also called a room temperature molten salt.

  Ionic liquids are attracting attention in the electrochemical field because of their high ionic conductivity. Ionic liquids are safe and reusable due to their non-flammable and non-volatile characteristics, and are expected to be used as substitutes for volatile organic compounds that have been considered problematic in recent years (Green Solvent). In addition, the ionic liquid has characteristics as a new medium that is completely different from water and organic solvents, and is an interesting material as an extraction solvent and reaction solvent that have not existed before.

The ionic liquid is conventionally produced from an organic cation and an inorganic or organic anion. As the cationic species, alkylammonium, alkylphosphonium, N, N′-dialkyl-substituted imidazolium, N-alkylpyridinium, and the like are used. Examples of the anion species include chlorinated anions of aluminum, tetrafluoroborate anions (BF ₄ ⁻ ), and hexafluorophosphate anions.

  N, N'-dialkyl-substituted imidazolium salts have higher ionic dissociation ability than other organic cation salts such as quaternary ammonium, and are expected to be widely used as electrolytes.

Conventionally, an ionic liquid using a cation (EMI) of an N, N′-dialkyl-substituted imidazolium salt has been proposed which uses a double ion of Cl ⁻ and AlCl ₃ as an anion. However, these compounds are difficult to handle because they easily react with moisture in the air and decompose.

Therefore, in Non-Patent Document 1, an attempt is made to apply various counter ions to the N, N′-dialkyl-substituted imidazolium salt cation. That is, using 1-ethyl-3-methyl-imidazolium cation, a salt composed of each anion such as NO ₃ ⁻ , NO ₂ ⁻ , BF ₄ ⁻ , CH ₃ CO ₃ ⁻ and SO ₄ ²⁻ is synthesized as an anion. I'm investigating their physical properties.

  Due to these many attempts, many of the N, N′-dialkyl-substituted imidazolium salts whose anions are tetrafluoroborate anions exhibit a liquid state at room temperature and exist stably in air. For this reason, application in many fields has been expected as an ionic liquid.

  Non-Patent Document 1 and conventional N.I. N'-dialkyl substituted imidazolium salts are N.I. This was an ion exchange method represented by the following general formula using N'-dialkyl-substituted imidazolium salt as a raw material.

（式中、Ｒ_１はアルキル基、Ｒ_２は水素原子又はアルキル基、Ｒ_３はアルキル基、Ｘは一価の金属又はＮＨ_４ ^＋を表す。）
例えば、下記のような合成法が報告されている。

(In the formula, R ₁ represents an alkyl group, R ₂ represents a hydrogen atom or an alkyl group, R ₃ represents an alkyl group, and X represents a monovalent metal or NH ₄ ⁺ .)
For example, the following synthesis methods have been reported.

  Non-Patent Document 1 is based on iodine salt of 1-ethyl-3-methyl-imidazolium (EMI) and silver tetrafluoroborate.

の反応が示されている。

The reaction is shown.

In this case, the target product (EMIBF ₄ ) is dissolved in the alcohol, and the alcohol as the solvent must be removed by evaporation.

  Non-Patent Document 2 uses 1,2-dimethyl-3-propylimidazolium (DMPI) as a cation and is synthesized by the following reaction.

ＬｉＣｌをろ別し、アセトニトリルを蒸発させて目的物（ＤＭＰＩＢＦ_４）を得ている。

LiCl was filtered off and acetonitrile was evaporated to obtain the target product (DMPIBF ₄ ).

  Furthermore, in Non-Patent Document 3, 1-ethyl-3-methylimidazolium chloride (EMICl) was used. It is synthesized by the reaction shown below.

この場合、ＮＨ_４Ｃｌをろ別し、アセトンを蒸発させて目的物（ＥＭＩＢＦ_４）を得ている。

In this case, NH ₄ Cl is filtered off, and acetone is evaporated to obtain the target product (EMIBF ₄ ).

  Furthermore, Non-Patent Document 4 synthesizes the body 1-butyl-3-methyl-imidazolium by the reaction shown below.

この場合、ＮａＣｌをろ別し、アセトンを蒸発させて目的物（ＢＭＩＢＦ_４）を得ている。

In this case, NaCl is filtered off and acetone is evaporated to obtain the target product (BMIBF ₄ ).

As described above, the synthesis method of N, N′-dialkyl-substituted imidazolium tetrafluoroborate by the conventional ion exchange method is that the raw material is expensive, the reaction requires 3 to 7 days, Li ⁺ and X ^- such pairs removal of ions that tend to remain as difficult impurities, such as there is a problem, therefore N currently available, N'- dialkyl substituted imidazolium tetrafluoroborate is expensive and the purity is sufficiently Often not.
“Air and Water Stable 1-Ethyl-3-methylimidazolium Based Ionic Liquids” J. et al. S. Wilkes, M.M. J. et al. Zawortko, J .; Chem. Soc. , Chem. Commun. 1992, pp. 965. “The Intrinsic Anodic Stableness of Several Anions Compiling Solvent-Free Ionic Liquids” V. R. Koch, L.M. A. Dominey, C.I. Nanjundiah, M.M. J. et al. Ondrechen, J. et al. Electrochem. Soc. , Vol. 143, pp. 798 (1996). “The Room Temperature Ionic Liquid 1-Ethyl-3-methylimidazolium Tetrafluoro-borate: Electrochemical Couples and Physical Properties” J. et al. Fuller, R.M. T. T. et al. Carlin, R.M. A. Osteryon, J .; Electrochem. Soc. , Vol. 148, pp. 3881 (1997). “The Use of New Ionic Liquids in Two-phase Catalytic Hydrolysis Reaction by Rhodium Complexes”, P.M. A. Suarez, J. et al. E. L. Dullius, S.M. Einloft, R.A. F. de Souza, J .; Dupont, Polyhedron, Vol. 15, pp. 1217 (1996).

An object of the present invention is to eliminate the above-mentioned problems of the conventional synthesis method of N, N′-dialkyl-substituted imidazolium tetrafluoroborate.
That is, an object of the present invention is to provide a synthesis method capable of easily producing N, N′-dialkyl-substituted imidazolium tetrafluoroborate. It is another object of the present invention to provide a method for synthesizing N, N′-dialkyl-substituted imidazolium tetrafluoroborate having a high purity. Furthermore, an object of the present invention is to provide a synthesis method capable of synthesizing N, N′-dialkyl-substituted imidazolium tetrafluoroborate at a low cost.

  When the present inventors reacted N-alkyl-substituted imidazoline with trialkyloxonium tetrafluoroborate in a solvent, N, N′-dialkyl-substituted imidazolium tetrafluoroborate is produced with high purity. The present invention has been completed.

  This reaction is shown by the following formula.

（式中、Ｒ_１は、炭素数１〜１０のアルキルを示す。Ｒ_２は、水素又は炭素数１〜１０のアルキル基を示す。Ｒ_３は、炭素数１〜１０のアルキル基を示す。）
生成するＮ，Ｎ’−ジアルキル置換イミダゾリウム四フッ化ホウ酸塩は、溶媒から二層に分離し、容易に回収可能である。
このＮ，Ｎ’−ジアルキル置換イミダゾリウム四フッ化ホウ酸塩の生成反応には原理的に対イオンの混入はない。したがって、対イオンの除去を要しない。
このＮ，Ｎ’−ジアルキル置換イミダゾリウム四フッ化ホウ酸塩の生成反応は、一段階反応であり、要する時間は、２０時間以内である。

(In the formula, _{R 1,} .R ₂ represents an alkyl having 1 to 10 carbon atoms, .R ₃ represent a hydrogen or an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms. )
The resulting N, N′-dialkyl-substituted imidazolium tetrafluoroborate can be separated from the solvent in two layers and easily recovered.
In principle, there is no counter ion contamination in the formation reaction of this N, N′-dialkyl-substituted imidazolium tetrafluoroborate. Therefore, it is not necessary to remove counter ions.
This N, N′-dialkyl-substituted imidazolium tetrafluoroborate production reaction is a one-step reaction and takes 20 hours or less.

  The starting N-alkyl substituted imidazoline is readily available on the market. Compared to expensive N, N'-dialkyl substituted imidazolines, it is very inexpensive.

  The starting material trialkyloxonium tetrafluoroborate is readily available on the market.

The starting N-alkyl-substituted imidazoline is represented by the following general formula (1).
General formula (1)

（式中、Ｒ_１は、炭素数１〜１０のアルキルを示す。Ｒ_２は、水素又は炭素数１〜１０のアルキル基を示す。）
原料の四フッ化ホウ酸トリアルキルオキソニウムは、下記一般式（２）で示される。
一般式（２）

(In the formula, _{R 1,} .R ₂ represents an alkyl having 1 to 10 carbon atoms, represents hydrogen or an alkyl group having 1 to 10 carbon atoms.)
The starting material trialkyloxonium tetrafluoroborate is represented by the following general formula (2).
General formula (2)

（式中、Ｒ_３は、炭素数１〜１０のアルキル基を示す。）
生成物のＮ，Ｎ’−ジアルキル置換イミダゾリウム四フッ化ホウ酸塩は、下記一般式（３）で示される。

(In the formula, R ₃ represents an alkyl group having 1 to 10 carbon atoms.)
The product N, N′-dialkyl-substituted imidazolium tetrafluoroborate is represented by the following general formula (3).

  The following general formula (3)

（式中、Ｒ_１は、炭素数１〜１０のアルキルを示す。Ｒ_２は、水素又は炭素数１〜１０のアルキル基を示す。Ｒ_３は、炭素数１〜１０のアルキル基を示す。）

(In the formula, _{R 1,} .R ₂ represents an alkyl having 1 to 10 carbon atoms, .R ₃ represent a hydrogen or an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms. )

The method for synthesizing the N, N'-dialkyl-substituted imidazolium tetrafluoroborate of the present invention is easy to synthesize. The synthesis method of the present invention can synthesize N, N′-dialkyl-substituted imidazolium tetrafluoroborate having high purity. Furthermore, the synthesis method of the present invention can synthesize N, N'-dialkyl-substituted imidazolium tetrafluoroborate at a low cost.

Ionic liquids tetrafluoroboric acid 1-ethyl-3-methyl - imidazolium _{(R 1 = CH 3 CH 2} -, R 2 = H-, R 3 = CH 3 -) Synthesis tetrafluoride of (EMIBF ₄₎ 10 g of trimethyloxonium borate (CH ₃ ) ₃ OBF ₄ (Wako Pure Chemical Industries, Ltd.) was dissolved in about 100 ml of diethyl ether and stirred with a magnetic stirrer. 6.51 g of 1-ethylimidazole (Kanto Chemical) was added dropwise thereto, and further stirred for about 20 hours. The product was separated into two phases. After discarding the supernatant, the lower phase was washed with diethyl ether and dried at 50 ° C. under reduced pressure for 2 hours to obtain a product. The product weight was 13.1 g. About 5 μl of the product was dissolved in deuterated chloroform and measured by ¹ H-NMR to confirm the structure and purity of the product. The ¹ H-NMR spectrum of the product is shown in FIG. From this, it can be seen that the product is almost entirely the target product EMIBF ₄ .

Synthesis of ionic liquid 1,3-dimethyl-imidazolium tetrafluoroborate (R ₁ = R ₃ = CH _3- , R ₂ = H-) (DMIB ₄ ) Trimethyloxonium tetrafluoroborate (CH ₃ ) ₃ OBF ₄ (Wako pure Chemical) 10 g was dissolved in diethyl ether 100 ml, and stirred with a magnetic stirrer. Thereto was added dropwise 5.62 g of 1-methylimidazole (Kanto Chemical), and the mixture was further stirred for about 20 hours. The product was separated into two phases. After discarding the supernatant, the lower phase was washed with diethyl ether and dried at 50 ° C. under reduced pressure for 2 hours to obtain a product. The product weight was 13.2 g. About 5 μl of the product was dissolved in deuterated chloroform and measured by ¹ H-NMR to confirm the structure and purity of the product. The ¹ H-NMR spectrum of the product is shown in FIG. From this it can be seen that the product is almost all of the target product DMIBF ₄ .

¹ H-NMR spectrum of the product of Example 1 ¹ H-NMR spectrum of the product of Example 2

Claims (1)

The N-alkyl-substituted imidazoline of the following general formula (1) is reacted with a trialkyloxonium tetrafluoroborate of the following general formula (2) to give an N, N′-dialkyl-substituted imidazolium 4 of the following general formula (3) A method for producing a fluorinated borate.

(In the formula, _{R 1,} .R ₂ represents an alkyl having 1 to 10 carbon atoms, represents hydrogen or an alkyl group having 1 to 10 carbon atoms.)

(In the formula, R ₃ represents an alkyl group having 1 to 10 carbon atoms.)

(In the formula, _{R 1,} .R ₂ represents an alkyl having 1 to 10 carbon atoms, .R ₃ represent a hydrogen or an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms. )

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