JP2006298901A - Method for refining n-alkyl-n'-alkylimidazolium salt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of efficiently refining an N-alkyl-N'-alkylimidazolium salt even in such a case wherein the salt has aqueous inorganic anions. <P>SOLUTION: The refining method comprises extracting and removing a remaining imidazolium halide salt using an alcohol after obtaining the N-alkyl-N'-alkylimidazolium salt by the reaction of formula (1) [wherein R and R' are each 1-15C alkyl or alkenyl which may have a substituent; R1, R2 and R3 are each H, 1-15C alkyl, alkenyl, formyl, carboxy or its ester which may have a substituent, cyano or halogen; M is an alkali metal; A is PF<SB>6</SB>, BF<SB>4</SB>or (CF<SB>3</SB>SO<SB>2</SB>)<SB>2</SB>N; and X is halogen]. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for purifying N-alkyl-N′-alkylimidazolium salts.

Conventionally, an ionic liquid has been produced from an organic cation and an inorganic anion. Examples of the organic cation include N-alkyl-N′-alkylimidazolium and N-alkylpyridinium, and examples of the inorganic anion include PF ₆ and BF ₄ are generally known.

As a method for producing such an ionic liquid, for example, in producing an N-alkyl-N′-alkylimidazolium salt, a corresponding imidazolium halogen salt and the N-alkyl-N′-alkylimidazolium salt are used. There is known a method of reacting an alkali metal salt containing an anion having an anion, followed by washing with a hydrocarbon solvent and then washing with water (see, for example, Patent Document 1). Such imidazolium halogen is also known. As a method for purifying a salt, it is described in literature (for example, see Patent Document 2) that it is dissolved in chloroform and purified through a column of activated alumina.
JP 2003-313171 A JP 2002-3478 A

However, when the present inventors examined the above method in detail, in the method described in Patent Document 1, when the inorganic anion is aqueous, for example, BF ₄ or the like, it is dissolved in water and purified. It became difficult, and it was found that the purification efficiency was low even when the method of Patent Document 2 was applied.
Therefore, there is a demand for a method that can efficiently purify even an imidazolium salt having an aqueous inorganic anion.

〔Ｒ，Ｒ'は炭素数１〜１５の置換基を有していても良いアルキル基及びアルケニル基、Ｒ１，Ｒ２，Ｒ３はそれぞれ水素、炭素数１〜１５の置換基を有していても良いアルキル基、アルケニル基、ホルミル基、カルボキシル基およびそのエステル、シアノ基、ハロゲンを示し、Ｍはアルカリ金属、ＡはＰＦ₆、ＢＦ₄または（ＣＦ₃ＳＯ₂）₂Ｎ、Ｘはハロゲンである。〕
また、本発明においては、アルコールが炭素数３〜１０のアルコールであること、アルコールの使用量が得られたＮ−アルキル−Ｎ'−アルキルイミダゾリウム塩に対して１〜１５倍（重量基準）であること、原料のイミダゾリウムハロゲン塩が、下記（２）式の反応により得られたものであること、等が好ましい実施態様である。

〔Ｒ、Ｒ'、Ｒ１、Ｒ２、Ｒ３、Ｘは（１）式と同じ〕 However, as a result of intensive studies in view of the present situation, the present inventors have obtained an N-alkyl-N′-alkylimidazolium salt by the reaction of the following formula (1), and then the remaining imidazolium halogen salt: The present invention has been completed by finding that the above-mentioned object can be achieved by extraction and removal of alcohol using alcohol.

[R and R ′ may have an alkyl group and an alkenyl group which may have a substituent of 1 to 15 carbon atoms, and R 1, R 2 and R 3 may have a substituent of 1 to 15 carbon atoms, respectively. A good alkyl group, alkenyl group, formyl group, carboxyl group and its ester, cyano group, halogen, M is alkali metal, A is PF ₆ , BF ₄ or (CF ₃ SO ₂ ) ₂ N, X is halogen . ]
In the present invention, the alcohol is an alcohol having 3 to 10 carbon atoms, and the amount of alcohol used is 1 to 15 times (weight basis) with respect to the obtained N-alkyl-N′-alkylimidazolium salt. It is preferable that the raw material imidazolium halide salt is obtained by the reaction of the following formula (2).

[R, R ′, R1, R2, R3, and X are the same as in formula (1)]

  Since the method for purifying an N-alkyl-N′-alkylimidazolium salt of the present invention performs extraction with alcohol, even an imidazolium salt having an aqueous inorganic anion can be efficiently purified.

〔Ｒ、Ｒ'は炭素数１〜１５の置換基を有していても良いアルキル基及びアルケニル基、Ｒ１，Ｒ２，Ｒ３はそれぞれ水素、炭素数１〜１５の置換基を有していても良いアルキル基、アルケニル基、ホルミル基、カルボキシル基およびそのエステル、シアノ基、ハロゲンを示し、Ｍはアルカリ金属、ＡはＰＦ₆、ＢＦ₄または（ＣＦ₃ＳＯ₂）₂Ｎ、Ｘはハロゲンである。〕 Hereinafter, the present invention will be specifically described.
The N-alkyl-N′-alkylimidazolium salt obtained in the present invention is obtained by the reaction represented by the following formula (1), and the imidazolium halogen salt as a raw material is specifically N-ethyl- N'-methylimidazolium bromide, N-butyl-N'-methylimidazolium bromide, N-butyl-N'-methylimidazolium chloride and the like can be used.

[R and R ′ may have an alkyl group and an alkenyl group which may have a substituent of 1 to 15 carbon atoms, and R1, R2 and R3 may have hydrogen and a substituent of 1 to 15 carbon atoms, respectively. A good alkyl group, alkenyl group, formyl group, carboxyl group and its ester, cyano group, halogen, M is alkali metal, A is PF ₆ , BF ₄ or (CF ₃ SO ₂ ) ₂ N, X is halogen . ]

〔Ｒ、Ｒ'、Ｒ１、Ｒ２、Ｒ３、Ｘは（１）式と同じ〕 In addition, although there is no restriction | limiting in particular in manufacturing such an imidazolium halogen salt of a raw material, Usually, it was obtained by reaction of following (2) Formula at the point of the ease of raw material acquisition, and shortening of reaction time. It is preferable.

[R, R ′, R1, R2, R3, and X are the same as in formula (1)]

  In obtaining the imidazolium halide salt as a raw material by the above formula (2), an alkyl halide equivalent to imidazole is added to a solvent (acetonitrile, ethyl acetate, acetone, etc.), and 0 to 100 ° C. (more preferably The reaction is carried out at 50 to 80 ° C. for 10 to 40 hours, followed by concentration to obtain the desired imidazolium halide salt. In the above, when the reaction temperature is less than 0 ° C., the reaction may not proceed sufficiently. On the other hand, when the reaction temperature exceeds 100 ° C., coloring is not preferable.

  An N-alkyl-N′-alkylimidazolium salt is produced by the reaction of the above formula (1) using the imidazolium halogen salt of the raw material obtained by the above method, etc. As production conditions, an alkali metal salt of a counter anion equivalent to an imidazolium halogen salt is added to a solvent (acetonitrile, ethyl acetate, acetone, etc.), and 0 to 100 ° C. (more preferably 40 to 60 ° C.) Then, the reaction is carried out for 3 to 20 hours (more preferably 5 to 10 hours), followed by filtration and then concentration to obtain the desired N-alkyl-N′-alkylimidazolium salt. In the above, when the reaction temperature is less than 0 ° C., the reaction may not proceed sufficiently. On the other hand, when the reaction temperature exceeds 100 ° C., coloring is not preferable.

Thus, the target N-alkyl-N′-alkylimidazolium salt is obtained, but at this time, an unreacted imidazolium halogen salt remains.
In the present invention, the greatest feature is to purify the N-alkyl-N′-alkylimidazolium salt by extracting and removing the remaining imidazolium halogen salt using an alcohol. The method will be described below.

The alcohol used in the present invention is not particularly limited, and examples thereof include methanol, ethanol, isopropanol, n-butanol, hexanol, octanol and the like, but the number of carbon atoms is 3 to 10 in terms of solubility of imidazole halogen salts. The alcohol is preferred.
The amount of alcohol used is 1 to 15 times (more preferably 5 to 8 times) (weight basis, the same shall apply hereinafter) relative to the N-alkyl-N′-alkylimidazolium salt obtained in the above formula (1). If the amount used is less than 1 time, the effect of the present invention may not be sufficiently obtained. On the other hand, if it exceeds 15 times, the dissolution loss of the product increases, which is not preferable.

In purification, the N-alkyl-N′-alkylimidazolium salt and alcohol obtained above are usually shaken sufficiently at 0 to 100 ° C. (more preferably 15 to 30 ° C.) for 5 to 30 minutes (stirring). If the temperature is less than 0 ° C., sufficient purification may not be achieved. Conversely, if the temperature exceeds 100 ° C., it is not preferable because it causes coloring. Furthermore, if the time is less than 5 minutes, sufficient purification may not be performed. Conversely, if the time exceeds 30 minutes, the improvement of the effect is not recognized, which is not preferable.
After shaking (stirring), leave to stand, remove the alcohol layer and repeat the above purification again (preferably once or more in total), thereby purifying the N-alkyl-N′-alkylimidazolium salt By removing the remaining solvent by a method such as vacuum drying, a highly pure N-alkyl-N′-alkylimidazolium salt can be obtained.

  Hereinafter, the method of the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the following, “%” and “parts” refer to weight basis unless otherwise specified.

Example 1
A reaction vessel was charged with 11 g of 1-methylimidazole, 15 g of ethyl bromide and 11 g of acetonitrile, reacted at 40 ° C. for 10 hours, and then concentrated to obtain 25 g of N-ethyl-N′-methylimidazolium bromide salt. .
Next, 18 g of NaBF ₄ and 34 g of acetone were added to 25 g of the obtained N-ethyl-N′-methylimidazolium bromide salt, reacted at 50 ° C. for 6 hours, filtered, and the filtrate was concentrated. Thus, a mixed solution of 27 g of N-ethyl-N′-methylimidazolium tetrafluoroborate and residual N-ethyl-N′-methylimidazolium bromide salt was obtained. The obtained mixed solution and 100 g of isopropanol were put into a separating funnel, sufficiently stirred and allowed to stand, and then separated into an N-ethyl-N′-methylimidazolium tetrafluoroborate layer and an isopropanol layer. The layer of -ethyl-N'-methylimidazolium tetrafluoroborate was removed. This operation was repeated three times, and the resulting N-ethyl-N′-methylimidazolium tetrafluoroborate layer was vacuum dried to obtain 19 g of N-ethyl-N′-methylimidazolium tetrafluoroborate. It was. The yield at this time was 70%.
When the obtained N-ethyl-N′-methylimidazolium tetrafluoroborate was measured by capillary electrophoresis, the remaining Br form was 100 ppm or less, which was the detection limit.

Example 2
In Example 1, instead of NaBF _4, except that a KPF ₆ was used 24g went were obtained in the same manner as N- ethyl -N'- methylimidazolium hexafluorophosphate 25 g. The yield at this time was 75%.
When the obtained N-ethyl-N′-methylimidazolium hexafluorophosphoric acid was measured by capillary electrophoresis, the remaining Br form was 100 ppm or less, which was the detection limit.

Example 3
In Example 1, it replaced with isopropanol and carried out similarly except having used n-butanol, and obtained 18.8g of N-ethyl-N'-methylimidazolium tetrafluoroborate. The yield at this time was 73%.
When the obtained N-ethyl-N′-methylimidazolium tetrafluoroborate was measured by capillary electrophoresis, the remaining Br body was 100 ppm or less of the detection limit.

Example 4
In Example 1, N-butyl-N′-methylimidazolium tetrafluoroborate was used in the same manner except that the reaction was carried out at 60 ° C. for 16 hours using 17.8 g of butyl bromide instead of ethyl bromide. 19 g was obtained. The yield at this time was 70%.
When the obtained N-butyl-N′-methylimidazolium tetrafluoroborate was measured by capillary electrophoresis, the remaining Br body was 100 ppm or less of the detection limit.

Comparative Example 1
In Example 1, it replaced with isopropanol and performed similarly except having used acetone, However, N-ethyl-N'-methylimidazolium tetrafluoroborate melt | dissolves and it can refine | purify into a homogeneous solution. could not.

Since the purification method of the present invention performs extraction with alcohol, even an imidazolium salt having an aqueous inorganic anion can be efficiently purified, and is a very useful method for purification of imidazole-based ionic liquids. is there.

Claims (4)

N-alkyl-N′-alkylimidazolium salt is obtained by the reaction of the following formula (1), and then the remaining imidazolium halogen salt is extracted and removed using alcohol: N-alkyl-N′- A method for purifying alkylimidazolium salts.

[R and R ′ may have an alkyl group and an alkenyl group which may have a substituent of 1 to 15 carbon atoms, and R 1, R 2 and R 3 may have a substituent of 1 to 15 carbon atoms, respectively. A good alkyl group, alkenyl group, formyl group, carboxyl group and its ester, cyano group, halogen, M is alkali metal, A is PF ₆ , BF ₄ or (CF ₃ SO ₂ ) ₂ N, X is halogen . ]   The method for purifying an N-alkyl-N'-alkylimidazolium salt according to claim 1, wherein the alcohol is an alcohol having 3 to 10 carbon atoms.   The N-alkyl-N 'according to claim 1 or 2, wherein the amount of alcohol used is 1 to 15 times (by weight) with respect to the obtained N-alkyl-N'-alkylimidazolium salt. -Method for purifying alkylimidazolium salts. The method for purifying an N-alkyl-N'-alkylimidazolium salt according to any one of claims 1 to 3, wherein the starting imidazolium halide salt is obtained by a reaction of the following formula (2): .

[R, R ′, R1, R2, R3, and X are the same as in formula (1)]