JP6083643B2 - Ionic liquid having silsesquioxane structure and method for producing the same - Google Patents

Description

  The present invention relates to an ionic liquid having a silsesquioxane structure and a method for producing the same.

  In recent years, ionic liquids have characteristics such as non-volatility, flame retardancy, ionic conductivity, and high thermal stability. Therefore, ionic liquids have been used as electrolytes for capacitors, lithium ion batteries, dye-sensitized solar cells, fuel cells, etc. It is expected (see Non-Patent Document 1).

As a definition of an ionic liquid, “a salt having a melting point (T _m ) near room temperature (100 ° C. or lower) and consisting only of ions” is generally accepted (see Non-Patent Document 2). However, it is not necessarily limited to those having T _m below 100 ° C. In amorphous ionic liquids, T _m does not exist and only a glass transition point (T _g ) is reported. ing. For example, 1-butyl-3-methylimidazolium tetrafluoroborate, which is an amorphous ionic liquid, exhibits T _g at −85 ° C., but T _m does not exist (see Non-Patent Document 3). This is considered to be due to the influence of the bulky substituent, but such an ionic liquid becomes a so-called “liquid” that exhibits fluidity at T _g or higher. Further, it is reported that an ionic liquid composed of 1-ethyl-3-methylimidazolium cation and phosphate derivative anion ([(MeO) (R) PO ₂ ]) does not show T _m but only T _g is observed. (See Non-Patent Document 4). Therefore, the ionic liquid can also be defined as “a“ salt ”composed of only a cation and an anion that shows a“ liquid ”state near room temperature (100 ° C. or less)”.

  Cations used in ionic liquids include quaternary ammonium, imidazolium, and pyridinium. On the other hand, anions include halogens such as bromide ions and triflate, borons such as tetraphenylborate, and phosphoruss such as hexafluorophosphate. and so on.

In general, there are relatively few salts consisting of inorganic ions that become ionic liquids at room temperature, and many ionic liquids are composed of organic ions, either or both of cations and anions. However, the development of ionic liquids that contain more inorganic components (for example, materials having a siloxane (Si-O-Si) bond as a skeleton) is expected to improve durability, heat resistance, and flame retardancy, and thus a safer electrolyte The use as is expected. For example, in the case of an electrolyte for a lithium ion battery or a capacitor for use in automobiles, the flame retardant property is very important for minimizing damage in the event of an accident. In view of the above background, recently, a carboxylate anion in the side chain of cage-type octasilsesquioxane (hereinafter referred to as “SQ”), which is a Si—O—Si bond skeleton material, and imidazo in the counter ion. It has been reported that those having a lithium cation exhibit the properties of an ionic liquid having _Tm near room temperature (see Non-Patent Document 5).

  However, since the cage-type octa SQ ionic liquid requires a multi-step reaction and a complicated purification process, the development of a simpler method for synthesizing an ionic liquid having an SQ structure is required.

  On the other hand, the present inventors have made a ladder-type poly SQ by hydrolyzing / condensing (sol-gel reaction) an amino group-containing organic trialkoxysilane, which is a raw material of SQ, in an acid aqueous solution (Patent Document). 1, Non-Patent Document 6, Non-Patent Document 7, Non-Patent Document 8) and cage-type oligo SQ (Non-Patent Document 9) report that cationic SQ soluble in a solvent having a regular structure can be obtained. doing. Furthermore, it has been found that an anionic ladder-type poly SQ soluble in a solvent can also be synthesized by sol-gel reaction of a cyano group-containing organic trialkoxysilane in an aqueous base solution (Non-patent Document 10).

Japanese Patent No. 4559596

Ishikawa, Shoji, Capacitor for Future Energy Society, Kay Dee Neobook, Chapter 3, p. 83-88, 2007 State-of-the-art Material System One Point Ionic Liquid, The Society of Polymer Science, Kyoritsu Publishing, 2012 T. Nishida et al., Journal of Fluorine Chemistry, vol.120, p.135-141, 2003 H. Ohno et al., Green Chemistry, vol.10, p.44-46, 2008 Y. Chujo et al., Journal of the American Chemical Society, vol.132, p.17649-17651, 2010 Y. Kaneko et al., Chemistry of Materials, vol.16, p.3417-3423, 2004 Y. Kaneko et al., Polymer, vol.46, p.1828-1833, 2005 Y. Kaneko et al., International Journal of Polymer Science, Article ID 684278, 2012 Y. Kaneko et al., Journal of Materials Chemistry, vol.22, p.14475-14478, 2012 Y. Kaneko et al., Polymer, vol.53, p.6021-6026, 2012

  An object of the present invention is to provide an ionic liquid having an SQ structure that can be easily manufactured and a method for manufacturing the ionic liquid.

As a result of intensive studies to achieve the above object, the inventor of the present invention is an ion having a regular structure as long as it is an organic trialkoxysilane having a substituent capable of becoming an ion during the reaction. Therefore, by examining the sol-gel reaction using various organic trialkoxysilanes, it has been thought that the synthesis of SQ as an ionic liquid is possible. And the monomer in the synthetic method of cationic SQ (patent document 1, nonpatent literature 6, nonpatent literature 7, nonpatent literature 8, nonpatent literature 9) already reported by the present inventors contains a quaternary ammonium salt. It has been found that an ionic liquid having an SQ skeleton can be obtained by making an organic trialkoxysilane an aqueous trifluoromethanesulfonimide (TFSI: (CF ₃ SO ₂ ) ₂ NH) solution as an acid catalyst.

  The ionic liquid according to the present invention is characterized in that the structural formula is represented by the following chemical formula 1.

However, the case where n = 1 and R = H is excluded.

The method for producing an ionic liquid according to the present invention includes a step of causing a sol-gel reaction of an organic trialkoxysilane containing a quaternary ammonium salt using an aqueous trifluoromethanesulfonimide solution as a catalyst. By the method for producing an ionic liquid according to the present invention, the ionic liquid represented by Chemical Formula 1 is obtained.

  According to the present invention, an ionic liquid having an SQ structure can be easily produced.

It is a figure which shows the manufacturing method of an ionic liquid. It is a figure which shows the result of a < ¹ > H NMR (nuclear magnetic resonance) spectrum measurement. It is a figure which shows the result of EDX (energy dispersive X-ray analysis). It shows the results of ²⁹ Si NMR spectroscopy. It is a figure which shows the result of a XRD (X-ray diffraction) measurement. It is a figure which shows the change of the fluidity | liquidity of a sample. It is a figure which shows the result of DSC (differential scanning calorie | heat amount) measurement.

As a result of diligent research to synthesize an ionic liquid having an SQ skeleton, the present inventor has developed a quaternary ammonium salt-containing organic trialkoxysilane as a monomer in the ionic SQ synthesis method already invented by the present inventors. , catalysts using TFSI solution is superacid sol - by simple means that gel reaction has been found to be able to synthesize amorphous of SQ ionic liquids indicating a T _g in the vicinity of room temperature.

Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. The structural formula of the ionic liquid according to the embodiment of the present invention is represented by the above chemical formula 1. That is, this ionic liquid has a 3- (trimethylammonium) propyl group in the side chain. The counter ion of the ionic liquid is composed of TFSI anion ((CF ₃ SO ₂ ) ₂ N ⁻ ).

  This ionic liquid can be manufactured as follows. FIG. 1 is a diagram illustrating a method for producing an ionic liquid.

  First, a quaternary ammonium salt-containing organic trialkoxysilane is prepared as a raw material (monomer). As the quaternary ammonium salt-containing organic trialkoxysilane, for example, trimethyl [3- (triethoxysilyl) propyl] ammonium chloride (TMTESPAC) is used. Moreover, a TFSI aqueous solution is prepared as a catalyst. Next, an aqueous TFSI solution is added to TMTESPAC and stirred. For example, the concentration of the TFSI aqueous solution is 0.5 mol / L, and the molar ratio of TFSI to TMTESPAC (amount of TFSI (mol) / amount of TMTESPAC (mol)) is 1.5. For example, stirring is performed at room temperature for 2 hours ((a) in FIG. 1). Thereafter, the viscous product phase-separated from the aqueous solution is isolated by decantation and washed with water ((b) in FIG. 1). Further, drying is performed under reduced pressure ((c) in FIG. 1). Subsequently, it is dissolved in methanol ((d) in FIG. 1). Then, for example, it is evaporated and dried in an open system at 60 ° C. ((e) in FIG. 1), and further heated in an oven at 150 ° C. ((f) in FIG. 1). Dissolution in methanol and subsequent heating are treatments for removing water slightly contained in the product even after drying under reduced pressure.

  By such a method, a sol-gel reaction of a quaternary ammonium salt-containing organic trialkoxysilane occurs, and an ionic liquid represented by the above chemical formula 1 can be produced.

  And this ionic liquid has Si-O-Si bond as a skeleton, and it can be further improved in durability, heat resistance and flame retardancy than conventional ionic liquids, as supported by experiments described later. Therefore, it is extremely suitable for an electrolyte such as a capacitor, a lithium ion battery, a dye-sensitized solar cell, and a fuel cell in applications requiring higher safety.

  Next, an experiment conducted by the inventor will be described. The conditions and the like in this experiment are examples adopted for confirming the feasibility of the present invention, and the present invention is not limited to these examples.

(First experiment)
In the first experiment, first, 9.0 mL (4.5 mmol) 0.5 mol / L TFSI aqueous solution was added to 0.9181 g (3.0 mmol) TMTESPAC in a glass container, and the mixture was stirred at room temperature for 2 hours. Thereafter, the viscous product phase-separated from the aqueous solution was isolated by decantation, washed 10 times with 10 mL of water, and then dried under reduced pressure. Furthermore, in order to remove water slightly contained in the product, 2 mL of methanol was added and dissolved, and heated in an open system until the solvent evaporated (about 60 ° C.). Thereafter, the SQ ionic liquid was obtained by heating in an oven at 150 ° C. for 2 hours (yield: 1.0412 g, 2.40 mmol unit, yield: 80%). Then, a part of the SQ ionic liquid was sampled and measured by ¹ H nuclear magnetic resonance (NMR) spectrum using an ECX-400 spectrometer manufactured by JEOL, and energy dispersive X-ray analysis (EDX) using an XL-30 E-SEM manufactured by Philips. , ²⁹ Si NMR spectrum measurement by ECX-400 spectrometer manufactured by JEOL, molecular weight measurement by static light scattering by DLS-8000 spectrophotometer manufactured by Otsuka Electronics, and X-ray diffraction (XRD) measurement by X'Pert Pro diffractometer (manufactured by PANallytical) A structural analysis was performed.

FIG. 2 shows the results of ¹ H NMR spectrum measurement. As shown in FIG. 2, the peak derived from the ethoxy group (—CH ₂ CH ₃ ) in the TMTESPAC monomer and the sulfonimide group (—NH) in the TFSI catalyst disappeared. From this, it was confirmed that no raw material remained in the product.

  FIG. 3 shows the results of EDX. As shown in FIG. 3, the peak derived from chlorine (Cl) (around 2.6 keV and 2.8 keV) is not observed, and the element number ratio of silicon (Si) and sulfur (S) is about 1: 2 (1 .00: 2.04). This confirmed that the product was composed of equimolar quaternary ammonium cations and TFSI anions.

FIG. 4 shows the results of ²⁹ Si NMR spectrum measurement. As shown in FIG. 4, a T ³ peak (−67.1 ppm) representing a Si atom having three siloxane bonds and a T ² peak (−59.5 ppm) representing a Si atom having two siloxane bonds were observed. . Furthermore, the weight average molecular weight (M _w ) was calculated to be 1800 by the Jim plot method by static light scattering measurement. That is, it was suggested that this product was an oligomer in which monomers were connected by a siloxane bond.

  FIG. 5 shows the results of XRD measurement. As shown in FIG. 5, no diffraction peak was observed, and it was confirmed to be amorphous. From the above results, it was confirmed that the product was amorphous oligo SQ.

  The above measurement confirmed that the product was an amorphous oligo SQ. Next, in order to confirm that this product exhibits the properties of an ionic liquid, the following operation was performed and visually observed. . First, the sample bottle containing the product was heated in an oven at 100 ° C. in a horizontal state, and then returned to room temperature. Next, the sample bottle was left to stand for 15 minutes in a tilted state in a water bath having a constant temperature every 5 ° C. When this operation was performed at each temperature, it was confirmed that the product exhibited fluidity at about 35 ° C. or higher as shown in FIG.

In addition, DSC (differential scanning calorimetry) measurement of the SQ ionic liquid produced as described above was also performed. The result is shown in FIG. When DSC measurement of the product was performed in the range of −100 ° C. to 150 ° C., an endothermic peak was observed around 13.5 ° C. as shown in FIG. Since the baseline is shifted down in heating process, the endothermic peak was suggested that derived from T _g. Also, T _m was not observed. This is because the product is amorphous.

  The monomer (TMTESPAC) and the catalyst (TFSI) used for the synthesis were both solids, and no peak due to water evaporation was observed near 100 ° C. from DSC measurement. It was confirmed that it was not a so-called “solution” dissolved in From the above results, it was suggested that the product obtained this time was an ionic liquid.

Moreover, the reason why the difference between T _g (13.5 ° C.) and the temperature (about 35 ° C.) that showed fluidity by visual observation was that this SQ ionic liquid is highly viscous, and therefore has a temperature of T _g or higher. This is probably because the fluidity could not be shown immediately.

Claims (4)

An ionic liquid characterized in that the structural formula is represented by the following chemical formula 1.
However, the case where n = 1 and R = H is excluded. Trifluoromethane sulfonimide aqueous solution as a catalyst, sol quaternary ammonium salt-containing organic trialkoxysilanes - have a process to produce a gel reactions, the manufacture of ionic liquids, characterized in that to obtain an ionic liquid according to claim 1 Method.   The method for producing an ionic liquid according to claim 2, wherein the organic trialkoxysilane containing a quaternary ammonium salt is trimethyl [3- (triethoxysilyl) propyl] ammonium chloride.   4. The method for producing an ionic liquid according to claim 2, further comprising a step of removing water contained after the sol-gel reaction after the step of causing the sol-gel reaction. 5.