JP2010270077A - Ionic liquid and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new ionic liquid that is noncombustible and has low viscosity, and a method for producing the same. <P>SOLUTION: The ionic liquid is represented by formula (I) [wherein a plurality of Rs are each independently alkyl]. The method for producing the ionic liquid represented by formula (I) comprises reacting an ionic compound of a cyclic phosphazene having a specific structure with a salt represented by formula (III): A<SP>+</SP>PF<SB>6</SB><SP>-</SP>[wherein A<SP>+</SP>is monovalent cation] in an organic solvent. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a novel ionic liquid and a method for producing the same, and more particularly to a novel non-flammable and low-viscosity ionic liquid and a method for producing the ionic liquid in a high yield.

  Since the report by Wilkes et al. In 1992, an ionic liquid has attracted attention as a substance that is liquid at room temperature and has excellent ionic conductivity. In the ionic liquid, the cation and the anion are combined by electrostatic attraction, the number of ion carriers is very large, and the viscosity is relatively low, so that the ion mobility is high even at room temperature. It has the characteristic that the property is very high. In addition, since the ionic liquid is composed only of cations and anions, the boiling point is high (above 300 ° C.) and the temperature range in which the liquid state can be maintained is very wide. Furthermore, since the ionic liquid has almost no vapor pressure, its flammability is low and its thermal stability is very excellent.

  Because of these various advantages, application of ionic liquids to electrolytes of non-aqueous electrolyte secondary batteries and electric double layer capacitors has recently been studied (see Patent Documents 1 and 2). When an ionic liquid is used as the electrolytic solution of the multilayer capacitor, the ionic liquid also functions as an ion source for forming an electric double layer, and thus there is an advantage that it is not necessary to add a supporting electrolyte separately. However, since the ionic liquid is a liquid at room temperature, it usually contains an organic group and has a risk of combustion.

  In contrast, JP 2007-153868 (Patent Document 3) reports a novel substance having a structure in which an amine is bonded to a cyclic phosphazene compound as an ionic liquid with a very low risk of combustion. However, a reaction mixture obtained by simply mixing a cyclic phosphazene compound and an amine is unstable in air and electrically unstable.

JP 2004-111294 A JP 2004-146346 A JP 2007-153868 A

  As described above, the ionic liquid has low flammability, and its application to the electrolyte of non-aqueous electrolyte secondary batteries and electric double layer capacitors has been studied, but the ionic liquid itself is flame retardant. It has not yet been shown to be nonflammable. Moreover, when applying an ionic liquid to electrolyte solution, it is desired that it is low viscosity from a viewpoint of ionic conductivity.

  Accordingly, an object of the present invention is to solve the above-described problems of the prior art and provide a novel non-flammable, low-viscosity ionic liquid and a method for producing the same.

  As a result of intensive studies to achieve the above object, the present inventor has found that a novel substance having a structure in which a tertiary amine is bonded to a cyclic phosphazene compound and ion-exchanged with a hexafluorophosphate ion has an ionic property and is incombustible. And the viscosity is low, and after ion exchange, further filtering, centrifuging, and purifying with activated carbon, it has been found that a highly luminescent ionic liquid can be produced in high yield. It came to complete.

［式中、Ｒはそれぞれ独立してアルキル基である］で表されることを特徴とする。 That is, the ionic liquid of the present invention has the following general formula (I):

[Wherein, each R is independently an alkyl group].

  In the ionic liquid of the present invention, R in the general formula (I) is preferably an alkyl group having 1 to 8 carbon atoms.

［式中、Ｒはそれぞれ独立してアルキル基である］で表されるイオン性化合物と下記一般式(III)：
Ａ⁺ＰＦ₆ ^- ・・・ (III)
［式中、Ａ⁺は一価の陽イオンを表す］で表される塩とを反応させて、下記一般式(I)：

［式中、Ｒはそれぞれ独立してアルキル基である］で表されるイオン液体を生成させる工程（Ａ）と、
前記工程（Ａ）で得られる反応混合物を濾過して、Ａ⁺Ｃｌ^-（式中、Ａ⁺は上記と同義である）を除去する工程（Ｂ）と、
前記工程（Ｂ）で得られる濾液を遠心分離して上澄み液を採取する工程（Ｃ）と、
前記工程（Ｃ）で得られる上澄み液に活性炭を加えて反応副生物を除去する工程（Ｄ）と
を含むことを特徴とする。この方法によれば、発光性の高いイオン液体を高い収率で製造できる。 The method for producing an ionic liquid of the present invention includes
In an organic solvent, the following general formula (II):

[Wherein R is independently an alkyl group] and the following general formula (III):
_{^{A + PF 6 - ··· (III}} )
[Wherein A ⁺ represents a monovalent cation] is reacted with a salt represented by the following general formula (I):

A step (A) of producing an ionic liquid represented by the formula: wherein each R is independently an alkyl group;
Filtering the reaction mixture obtained in the step (A) to remove A ⁺ Cl ⁻ (wherein A ⁺ is as defined above) (B),
(C) collecting the supernatant by centrifuging the filtrate obtained in the step (B);
A step (D) of adding activated carbon to the supernatant obtained in the step (C) to remove reaction by-products. According to this method, an ionic liquid having high luminescence can be produced with a high yield.

  In the method for producing an ionic liquid of the present invention, the organic solvent is preferably a halogenated hydrocarbon, particularly preferably chloroform.

  In a preferred example of the method for producing an ionic liquid of the present invention, the concentration of the ionic compound represented by the general formula (II) in the organic solvent is in the range of 1 to 5 mol / L, and the general formula ( The concentration of the salt represented by III) in the organic solvent is in the range of 1.5 to 7.5 mol / L.

  According to the present invention, it is possible to provide a novel ionic liquid which is nonflammable and has a low viscosity. In addition, according to the present invention, an ionic liquid that is nonflammable, has a low viscosity, and has a high light emitting property can be produced in a high yield.

The present invention is described in detail below. The ionic liquid of the present invention is represented by the above general formula (I). The ionic liquid of the formula (I) is a kind of cyclic phosphazene compound having a plurality of phosphorus-nitrogen double bonds and has an ionic substituent, and thus has ionicity. And since it has a phosphazene skeleton, it decomposes | disassembles at the time of combustion, generate | occur | produces nitrogen gas, phosphate ester, etc., and since this nitrogen gas, phosphate ester, etc. suppress the progress of combustion, the danger of combustion is low. In the ionic liquid, fluorine functions as a scavenger for active radicals in the unlikely event of combustion, further reducing the risk of combustion. Further, the ionic liquid contains an alkyl group and produces a carbide (char) during combustion, and has an oxygen blocking effect. Furthermore, PF ₆ ⁻ in the ionic liquid further reduces the risk of combustion. As a result of combining these actions, the ionic liquid of formula (I) exhibits nonflammability. Further, the ionic liquid of formula (I) has a low viscosity, and the viscosity at 25 ° C. is usually 50 to 70 mPa · s, preferably 50 to 60 mPa · s. Surprisingly, the ionic liquid of the present invention exhibits luminescence.

  R in the general formula (I) is each independently an alkyl group, preferably an alkyl group having 1 to 8 carbon atoms. When the number of carbon atoms in the alkyl group exceeds 8, the viscosity increases. Here, as the alkyl group in R, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, s-butyl group, t-butyl group, various pentyl groups, various hexyl groups, various heptyls Group, various octyl groups and the like. In the formula (I), each R may be the same or different.

The ionic substituent of the ionic liquid of formula (I) is formed by bonding —N ⁺ R ₃ and PF ₆ ^— mainly by electrostatic attraction. Therefore, the compound of formula (I) has ionicity.

  The ionic liquid of formula (I) comprises, for example, a step (A) of reacting an ionic compound represented by the general formula (II) with a salt represented by the general formula (III) in an organic solvent. It can be generated via. According to this method, the ionic liquid of formula (I) can be obtained in high yield.

  As the organic solvent used in the reaction of the ionic compound of the general formula (II) and the salt represented by the general formula (III), a halogenated hydrocarbon is preferable, and among the halogenated hydrocarbons, chloroform is preferable. In addition, the organic solvent to be used may be only 1 type, and 2 or more types of mixtures may be sufficient as it.

  In the general formula (II), each R is independently an alkyl group, and examples of the alkyl group in R of the formula (II) include those exemplified in the section of the alkyl group in R of the formula (I). be able to.

In the general formula (III), A ⁺ is a monovalent cation, and examples of the monovalent cation in A ⁺ in the formula (III) include K ⁺ , Ag ⁺ , and Li ⁺ . Specific examples of the salt of the formula (III) include KPF ₆ , AgPF ₆ , LiPF _{6 and the} like.

  In the reaction of the ionic compound of the formula (II) and the salt of the formula (III), the amount of the salt of the formula (III) used is preferably in the range of 1 to 1.5 mol per 1 mol of the ionic compound of the formula (II). . The concentration of the ionic compound of formula (II) in the organic solvent is preferably in the range of 1 to 5 mol / L, and the concentration of the salt of formula (III) in the organic solvent is in the range of 1.5 to 7.5 mol / L. Is preferred. If the concentration of the ionic compound of formula (II) in the organic solvent is in the range of 1 to 5 mol / L, the solid substance insoluble in the organic solvent may occupy the volume in the solvent and inhibit the reaction. Few. On the other hand, if the concentration of the salt of the formula (III) in the organic solvent is excessively about 1.5 times the concentration of the ionic compound of the formula (II), that is, in the range of 1.5 to 7.5 mol / L, Ligand substitution reaction with chloride ions is carried out smoothly.

  The reaction temperature in the reaction between the ionic compound of formula (II) and the salt of formula (III) is not particularly limited, but is preferably in the range of room temperature to 50 ° C., and the reaction proceeds sufficiently even at room temperature. Further, the reaction pressure is not particularly limited, and the reaction can be performed under atmospheric pressure.

After the step (A), the reaction mixture obtained in the step (A) is filtered to remove a salt represented by A ⁺ Cl ⁻ (wherein A ⁺ is as defined above) ( It is preferable to carry out B). Here, in the step (B), the filtration method is not particularly limited, and may be filtered under a normal pressure or a reduced pressure using a known filter medium. The salt to be removed in the step (B) depends on the salt of the formula (III) to be used, KCl is removed when the potassium salt is used, AgCl is removed when the silver salt is used, and lithium When the salt is used, LiCl is removed.

  Here, as a result of examination by the present inventors, it was found that the reaction product obtained by distilling off the organic solvent from the filtrate obtained in the step (B) contains by-products and has a low emission quantum yield. . Therefore, it is preferable to purify the reaction product through the step (C) and the step (D) described in detail below.

  That is, after the step (B), it is preferable to perform a step (C) of collecting the supernatant by centrifuging the filtrate obtained in the step (B). In the step (C), the centrifugation method is not particularly limited, and can be carried out by a usual method using a known centrifuge. In addition, the rotational speed in centrifugation is not specifically limited, However, The range of 9000-12000 rpm is preferable.

  Moreover, after the said process (C), it is preferable to perform the process (D) which adds activated carbon to the supernatant liquid obtained at the said process (C), and removes a reaction byproduct. The activated carbon used in the step (D) is not particularly limited, and known activated carbon can be used. The amount of the activated carbon used is not particularly limited, but is preferably in the range of 1 g to 5 g per 1 g of the ionic liquid of the formula (I).

  After the step (D), for example, the activated carbon is removed by filtration, and the organic solvent used is distilled off to isolate the ionic liquid of formula (I). In addition, since the reaction product obtained by distilling off the organic solvent from the filtrate obtained in the above step (B) contains by-products, it has low luminescence but is purified through the steps (C) and (D). The ionic liquid of the formula (I) thus obtained has a feature of high luminescence.

で表される環状ホスファゼン化合物と、下記一般式(V)：
ＮＲ₃ ・・・ (V)
［式中、Ｒはそれぞれ独立してアルキル基である］で表される３級のアミンとを反応させることで、上記一般式(II)で表されるイオン性化合物を製造することができる。 The method for producing the ionic compound represented by the general formula (II) used as a starting material is not particularly limited, and for example, in an organic solvent, the following chemical formula (IV):

A cyclic phosphazene compound represented by the following general formula (V):
NR ₃ ... (V)
An ionic compound represented by the above general formula (II) can be produced by reacting with a tertiary amine represented by the formula [wherein each R is independently an alkyl group].

  As the organic solvent used in the reaction of the cyclic phosphazene compound of the formula (IV) and the tertiary amine of the formula (V), aromatic hydrocarbons, ester compounds and ether compounds are preferred. Here, toluene is preferable among aromatic hydrocarbons, ethyl acetate is preferable among ester compounds, and diethyl ether is preferable among ether compounds. These organic solvents may be used individually by 1 type, and 2 or more types may be mixed and used for them.

The cyclic phosphazene compound represented by the above general formula (IV) is, for example, a commercially available cyclic phosphazene compound represented by (NPCl ₂ ) ₃ as a starting material, fluorinated all chlorine with a fluorinating agent, After introducing an alkoxy group, an amine group or the like into the target chlorine substitution site, chlorination with a chlorinating agent such as HCl or phosgene, or a commercially available phosphazene compound represented by (NPCl ₂ ) ₃ It is possible to synthesize by a method of adding a necessary amount of a fluorinating agent after calculating the equivalent amount of fluorine to be introduced.

  In the general formula (V), each R is independently an alkyl group, and examples of the alkyl group in R of the formula (V) include those exemplified in the section of the alkyl group in R of the formula (I). be able to.

  Specific examples of the tertiary amine represented by the general formula (V) include aliphatics such as trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trioctylamine, butyldimethylamine, and hexyldimethylamine. A tertiary amine is mentioned.

  In the reaction of the cyclic phosphazene compound of formula (IV) with the tertiary amine of formula (V), the amount of amine of formula (V) used is in the range of 1 to 1.5 mol per mole of cyclic phosphazene compound of formula (IV). Is preferred. The concentration of the cyclic phosphazene compound of formula (IV) in the organic solvent is preferably in the range of 1 to 5 mol / L, and the concentration of the amine of formula (V) in the organic solvent is 1 to 5 mol / L. A range is preferred. If the concentration of the cyclic phosphazene compound of the formula (IV) in the organic solvent is in the range of 1 to 5 mol / L, it is easily soluble in the organic solvent, and the concentration of the amine of the formula (V) in the organic solvent is If it is the range of 1-5 mol / L, the produced | generated ionic compound (solid) will precipitate rapidly in a solvent, and reaction will not be inhibited.

  In addition, the reaction temperature in the reaction of the cyclic phosphazene compound of the formula (IV) and the amine of the formula (V) is not particularly limited, and the reaction proceeds sufficiently even at room temperature, but the range of 15 ° C to 50 ° C Can be controlled. If the reaction is fast, it is effective to lower the temperature in a timely manner. If the reaction is slow, the reaction rate can be increased by raising the temperature. However, when the temperature exceeds 50 ° C., the phosphazene compound that is a raw material is likely to volatilize, so that the reaction is preferably performed at 50 ° C. or less. Further, the reaction pressure is not particularly limited, and the reaction can be performed under atmospheric pressure. The reaction between the cyclic phosphazene compound of the formula (IV) and the amine of the formula (V) is preferably performed in an inert gas atmosphere such as nitrogen so that moisture does not enter the reaction system from the outside. By performing the reaction under an inert gas atmosphere, by-production of amine hydrochloride can be suppressed.

  The above-described ionic liquid of the present invention has a melting point of 50 ° C. or lower, preferably a melting point of 25 ° C. or lower, is nonflammable and has a low viscosity. Therefore, the ionic liquid of the present invention can be used as an electrolytic solution for electric double layer capacitors, an electrolytic solution for lithium ion batteries, an electrolytic solution for dye-sensitized solar cells, and the like. In addition, the ionic liquid of the present invention surprisingly has a high light emitting property and emits light even at a high temperature. For example, a light emitting material under a high temperature condition, a polymer or a resin material that requires a high temperature process, and the like. It is also useful as an agent for imparting light-emitting properties.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

で表わされる化合物［即ち、上記一般式(I)で表され、３つのＲの総てがｎ-プロピル基である化合物］であることを確認した。 (Production Example 1)
In a three-necked flask equipped with a reflux condenser, 1.5 mL (0.01 mol) of a cyclic phosphazene compound represented by the above chemical formula (IV) and tri-n-propylamine [that is, represented by the above general formula (V), Amine in which all three R's are n-propyl groups] 1.1 mL (0.01 mol) was dissolved in 30 mL of dehydrated diethyl ether, stirred at 20 ° C. for 1 hour, and then the diethyl ether was distilled off with an evaporator. Thus, an ionic compound represented by the above general formula (II), in which all three Rs are n-propyl groups, was obtained. After dissolving 1.0 g (0.0024 mol) of the ionic compound in 30 mL of chloroform, 0.3 g (0.0016 mol) of KPF ₆ was added and stirred at room temperature for 2 hours, whereby KCl precipitated. The precipitated KCl was separated by filtration, and the filtrate was further centrifuged at 12000 rpm for 30 minutes using a centrifuge, and the supernatant was collected. Next, the obtained supernatant was dissolved in 30 mL of chloroform, 1.0 g of activated carbon was further added, and the mixture was stirred for 1 hour to remove coloring components. Next, the activated carbon was removed by filtration, chloroform was removed by an evaporator, and further, drying was performed at 150 ° C. for 24 hours under reduced pressure using a vacuum pump to obtain 0.85 g of liquid (yield 60%). When the obtained liquid was dissolved in deuterated chloroform and analyzed by ¹ H-NMR and ¹³ C-NMR, the liquid was represented by the following chemical formula (a):

It was confirmed that the compound represented by the above formula [that is, a compound represented by the above general formula (I), in which all three R's are n-propyl groups].

[Spectral data (400 MHz, CDCl ₃ , δ / ppm)]
¹ H-NMR: δ = 1.0065 ・ ・ ・ H _A ,
δ = 1.8032 ... H _B ,
δ = 2.9441 ・ ・ ・ H _C
^{· 13 C-NMR: δ =} 11.0417 ··· C D,
δ = 16.8205... C _E ,
δ = 54.0364 ・ ・ ・ C _F

(Production Example 2)
The filtrate obtained by removing KCl by filtration in the same manner as in Production Example 1 was dried for 24 hours at 150 ° C. under reduced pressure with a vacuum pump without being subjected to centrifugation and activated carbon treatment, and 0.92 g (yield) 72%). When the obtained liquid was analyzed by ¹ H-NMR and ¹³ C-NMR, it was confirmed that the liquid was a compound represented by the above chemical formula (a).

で表わされる化合物［即ち、上記一般式(I)で表され、３つのＲの総てがｎ-ブチル基である化合物］であることを確認した。 (Production Example 3)
In a three-necked flask equipped with a reflux condenser, 1.5 mL (0.01 mol) of the cyclic phosphazene compound represented by the above chemical formula (IV) and tri-n-butylamine [that is, represented by the above general formula (V), 3 Amine in which all Rs are n-butyl groups] 1.72 mL (0.01 mol) was dissolved in 30 mL of dehydrated dimethyl ether, stirred at 20 ° C. for 3 hours, and then dimethyl ether was distilled off with an evaporator. An ionic compound represented by the general formula (II), in which all three R's are n-butyl groups, was obtained. After dissolving 1.0 g (0.0021 mol) of the ionic compound in 30 mL of chloroform, 0.3 g (0.0016 mol) of KPF ₆ was added and stirred at room temperature for 2 hours, whereby KCl precipitated. The precipitated KCl was separated by filtration, and the filtrate was further centrifuged at 12000 rpm for 30 minutes using a centrifuge, and the supernatant was collected. Next, the obtained supernatant was dissolved in 30 mL of chloroform, 1.0 g of activated carbon was further added, and the mixture was stirred for 1 hour to remove coloring components. Next, the activated carbon was removed by filtration, chloroform was removed by an evaporator, and further drying was performed at 150 ° C. for 24 hours under reduced pressure using a vacuum pump to obtain 0.85 g of liquid (yield 70%). When the obtained liquid was dissolved in deuterated chloroform and analyzed by ¹ H-NMR and ¹³ C-NMR, the liquid was represented by the following chemical formula (b):

[That is, a compound represented by the above general formula (I), in which all three R's are n-butyl groups].

[Spectral data (400 MHz, CDCl ₃ , δ / ppm)]
¹ H-NMR: δ = 0.9716 ... H _A ,
δ = 1.3773 ・ ・ ・ H _B ,
δ = 1.7063 ・ ・ ・ H _C ,
δ = 2.9103 ・ ・ ・ H _D
・¹³ C-NMR: δ = 13.44639... C _E ,
δ = 20.0661 ... C _F ,
δ = 25.5267 ... C _G ,
δ = 52.3325 ・ ・ ・ C _H

(Production Example 4)
The filtrate obtained by removing KCl by filtration in the same manner as in Production Example 3 was dried at 150 ° C. for 24 hours under reduced pressure with a vacuum pump without being subjected to centrifugation and activated carbon treatment, and 0.97 g of liquid (yield) 80%). When the obtained liquid was analyzed by ¹ H-NMR and ¹³ C-NMR, it was confirmed that the liquid was a compound represented by the above chemical formula (b).

で表わされる化合物［即ち、上記一般式(I)で表され、３つのＲの総てがｎ-オクチル基である化合物］であることを確認した。 (Production Example 5)
In a three-necked flask equipped with a reflux condenser, 1.5 mL (0.01 mol) of the cyclic phosphazene compound represented by the above chemical formula (IV) and tri-n-octylamine [that is, represented by the above general formula (V), Amine in which all three Rs are n-octyl groups] 4.38 mL (0.01 mol) was dissolved in 30 mL of dehydrated dimethyl ether, stirred at 20 ° C. for 3 hours, and then dimethyl ether was distilled off with an evaporator. An ionic compound represented by the above general formula (II), in which all three Rs are n-octyl groups, was obtained. After dissolving 1.0 g (0.0016 mol) of the ionic compound in 30 mL of chloroform, 0.3 g (0.0016 mol) of KPF ₆ was added and stirred at room temperature for 2 hours, whereby KCl precipitated. The precipitated KCl was separated by filtration, and the filtrate was further centrifuged at 12000 rpm for 30 minutes using a centrifuge, and the supernatant was collected. Next, the obtained supernatant was dissolved in 30 mL of chloroform, 1.0 g of activated carbon was further added, and the mixture was stirred for 1 hour to remove coloring components. Next, the activated carbon was removed by filtration, chloroform was removed by an evaporator, and further, drying was performed at 150 ° C. for 24 hours under reduced pressure using a vacuum pump to obtain 0.65 g of liquid (yield 55%). When the obtained liquid was dissolved in deuterated chloroform and analyzed by ¹ H-NMR and ¹³ C-NMR, the liquid was represented by the following chemical formula (c):

[That is, a compound represented by the above general formula (I), in which all three R's are n-octyl groups].

[Spectral data (400 MHz, CDCl ₃ , δ / ppm)]
・¹ H-NMR: δ = 0.8810... H _A ,
δ = 1.2888 ... H _B ,
δ = 1.6464 ・ ・ ・ H _C ,
δ = 2.7867 ・ ・ ・ H _D
^{· 13 C-NMR: δ =} 14.0130 ··· C F,
δ = 22.5538 ・ ・ ・ C _G ,
δ = 24.2536 ・ ・ ・ C _H ,
δ = 27.0082 C _I ,
δ = 29.0753 ... C _J ,
δ = 31.6761 ・ ・ ・ C _K ,
δ = 52.8870 ・ ・ ・ C _L

(Production Example 6)
The filtrate obtained by removing KCl by filtration in the same manner as in Production Example 5 was dried for 24 hours at 150 ° C. under reduced pressure with a vacuum pump without being subjected to centrifugation and activated carbon treatment, and 0.77 g of liquid (yield) 65%). When the obtained liquid was analyzed by ¹ H-NMR and ¹³ C-NMR, it was confirmed that the liquid was a compound represented by the above chemical formula (c).

<Evaluation of ionic liquid>
The safety of the ionic liquids obtained in the above Production Examples 1 to 6 was evaluated by the following methods, and the viscosity and luminescence quantum yield were further measured by the following methods. The results are shown in Table 1. For comparison, see 1-methyl-3-butylimidazolium hexafluorophosphate ([bmim] PF ₆ , A. Paul, PKMandel and A. Samanta, Chem. Phys. Lett., 402, 375-379 (2005). ) Was also evaluated and measured. The results are shown in Table 1.

<Evaluation of safety>
The safety of ionic liquids was evaluated from the combustion behavior of flames ignited in an atmospheric environment by the method of arranging UL94HB method of UL (Underwriting Laboratory) standard. At that time, ignitability, combustibility, formation of carbides, and secondary ignition phenomena were also observed. Specifically, based on the UL test standard, an incombustible quartz fiber was impregnated with 1.0 mL of an ionic liquid, and a 127 mm × 12.7 mm test piece was produced. Here, when the test flame does not ignite the test piece (burning length: 0 mm), it is “non-flammable”, and when the ignited flame does not reach the 25 mm line and the fallen object is not ignited, “difficult” “Flammability”, “Self-extinguishing” when the ignited flame is extinguished in the 25-100 mm line and no fallen objects are ignited, “Flammability” when the ignited flame exceeds the 100 mm line It was evaluated.

<Measurement of viscosity>
Using a viscometer [R-type viscometer Model RE500-SL, manufactured by Toki Sangyo Co., Ltd.] at room temperature (25 ° C.), 1 rpm, 2 rpm, 3 rpm, 5 rpm, 7 rpm, 10 rpm, 20 Measure the viscosity at 120 rpm for each rotation speed of rpm and 50 rpm, use the rotation speed when the indicated value is 50-60% as the analysis condition, and measure the viscosity at that time to determine the viscosity of the ionic liquid. Asked.

<Measurement of luminescence quantum yield>
The luminescence quantum yield of the ionic liquid was measured as a relative value of the fluorescence quantum yield of 4-aminophthalimide. The excitation wavelength was 360 nm, each ionic liquid was dissolved in methanol at a concentration of 0.1 mol / L, and the measurement was performed at room temperature (25 ° C.). The results are shown in Table 1.

  From Table 1, it can be seen that the ionic liquid of the present invention is nonflammable and has a low viscosity, whereas the ionic liquid of Comparative Example 1 shows only self-extinguishing properties and has a high viscosity.

  It can also be seen that the ionic liquids synthesized in Production Examples 1, 3 and 5 have improved emission quantum yields compared to the ionic liquids synthesized in Production Examples 2, 4 and 6. This is considered to be due to the apparent decrease in quantum yield due to light scattering by impurities, etc., unless activated carbon treatment is performed.

Claims (7)

The following general formula (I):

An ionic liquid represented by the formula: wherein each R is independently an alkyl group.   2. The ionic liquid according to claim 1, wherein R is an alkyl group having 1 to 8 carbon atoms. In an organic solvent, the following general formula (II):

[Wherein R is independently an alkyl group] and the following general formula (III):
_{^{A + PF 6 - ··· (III}} )
[Wherein A ⁺ represents a monovalent cation] is reacted with a salt represented by the following general formula (I):

A step (A) of producing an ionic liquid represented by the formula: wherein each R is independently an alkyl group;
Filtering the reaction mixture obtained in the step (A) to remove A ⁺ Cl ⁻ (wherein A ⁺ is as defined above) (B),
(C) collecting the supernatant by centrifuging the filtrate obtained in the step (B);
And a step (D) of adding activated carbon to the supernatant obtained in the step (C) to remove reaction byproducts, and a method for producing the ionic liquid represented by the general formula (I).   The method for producing an ionic liquid according to claim 3, wherein the organic solvent is a halogenated hydrocarbon.   The method for producing an ionic liquid according to claim 4, wherein the organic solvent is chloroform.   The method for producing an ionic liquid according to claim 3, wherein the concentration of the ionic compound represented by the general formula (II) in the organic solvent is in the range of 1 to 5 mol / L.   The method for producing an ionic liquid according to claim 3, wherein the concentration of the salt represented by the general formula (III) in the organic solvent is in the range of 1.5 to 7.5 mol / L.