JP2008208083A - Fullerene derivative and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fullerene derivative electrolyte soluble in organic solvents and easily and uniformly miscible and dispersible with a binder polymer for producing a proton conductive membrane free from deionization exchange reaction by an electrophilic substitution reaction by proton attack even under a high-temperature acidic condition and to provide a method for producing the electrolyte. <P>SOLUTION: The invention provides a fullerene derivative having a phosphonic acid ester group -PO(OR)<SB>2</SB>(R is a 1-5C alkyl group or a phenyl group) bonded to the derivative and essentially free from bonded organic compound, preferably a fullerene derivative having a sulfonic acid group -SO<SB>3</SB>M (M is H or an alkali metal ion) bonded together with the above group. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fullerene derivative useful for an electrolyte of a proton conductive membrane used in a polymer electrolyte fuel cell and a method for producing the same.

  Conventionally, a perfluorosulfonic acid resin membrane (manufactured by DuPont, trade name Nafion membrane) has been used as an electrolyte membrane that governs the performance of a polymer electrolyte fuel cell. An electrolyte membrane based on a hydrocarbon polymer has been studied. This membrane has a structure in which a sulfonic acid group is directly bonded to an aromatic ring. However, as described in Non-Patent Document 1, when the membrane is used for a long time under acidic conditions of 100 ° C. or higher, the desulfonic acid group reaction gradually increases. There are defects that arise and degrade performance. The mechanism is that protons attack the aromatic ring to cause an electrophilic substitution reaction, and a method for directly bonding a sulfonic acid group to a substrate different from the aromatic ring is required.

  As an electrolyte useful for solving this problem, a fullerene derivative in which a sulfonic acid group is directly bonded to fullerene is disclosed in Patent Document 1, but dimethylformamide used as a reaction solvent is also bonded during the sulfonation reaction, and the target product There was a problem that could not be obtained. For this reason, Patent Document 2 and Patent Document 3 disclose a method of bonding a fullerene and a sulfonic acid group of a substrate with a hydrocarbon-based or fluorine-based spacer molecule. There was a drawback that the exchange capacity could not be increased.

The present inventor uses K ₂ SO ₃ as a sulfonating reagent and uses a specific reaction solvent (dimethylacetamide + water) to directly bond a sulfonic acid group to fullerene without bonding of the reaction solvent. Successful. However, the sulfonated fullerene thus obtained is water-soluble and hardly soluble in an organic solvent, and it has been difficult to uniformly mix and disperse it in an organic solvent-soluble binder polymer. The present inventor further studied and solved this problem by making the phosphonic acid ester group coexist with the sulfonic acid group and making it soluble in an organic solvent.

  Conventionally, phosphonated fullerenes are generally disclosed in Patent Document 2 and the like, but a specific production method is not described, and a direct bond type chemical structure is not specified. Patent Document 4 generally shows a direct bond type structure, but does not show a specific manufacturing method thereof. A coexistence type of a sulfonic acid group and a phosphonic acid group is also included in the general formula of Patent Document 4, but the coexistence type of the sulfonic acid group and the phosphonic acid ester group of the present invention is not shown.

The present inventor has used LiPO as phosphonate reagent _(OR) 2 (R is alkyl or phenyl _C 1 -C _5), by using dioxane as the reaction solvent, without binding of the reaction solvent, The present invention has been completed by successfully obtaining a direct-linked phosphonate esterified fullerene. The phosphonate ester group of the fullerene derivative mixed and dispersed with the binder polymer is converted to a phosphonic acid group by hydrolysis if necessary, and contributes to proton conduction like the sulfonic acid group. A fullerene derivative having a single group bonded thereto is also useful in the present invention.

JP 2002-326984 A JP 2005-093417 A Japanese Patent Laying-Open No. 2005-068124 JP-A-2005-194304 Supervised by Kyoji Kimoto, “Development of electrolyte membrane for PEFC”, CMC Publishing, published in December 2005, P.A. 30

  In the present invention, in order to produce a proton conducting membrane that does not cause deion exchange reaction by electrophilic substitution reaction by proton attack even under high temperature acidic conditions, it is soluble in an organic solvent that is easy to mix and disperse uniformly with a binder polymer. It is an object of the present invention to provide a fullerene derivative electrolyte and a method for producing the same.

また、部分構造Ｘ−Ｃ−Ｃ−Ｈ（Ｘはホスホン酸エステル基又はスルホン酸基）を１〜１２個含む前記フラーレン誘導体も本発明である。
また、反応溶媒としてジオキサンを用い、フラーレン又はスルホン酸化フラーレンとホスホン酸エステル化試薬ＬｉＰＯ（ＯＲ）_２（ＲはＣ_１〜Ｃ_５のアルキル基又はフェニル基）を反応させることを特徴とする、前記フラーレン誘導体の製造方法も本発明である。 In order to achieve the above-described object, the present invention provides a phosphonic acid ester group —PO (OR) ₂ (wherein R is a C ₁ -C ₅ alkyl group or phenyl group) and an organic compound is substantially bonded. The fullerene derivative is preferably a fullerene derivative in which a sulfonic acid group —SO ₃ M (M is H or an alkali metal ion) is bonded at the same time.
The fullerene derivative in which the number of bonds m of the phosphonic acid ester group and the number of bonds n of the sulfonic acid group are in the following ranges is also the present invention.

Moreover, the fullerene derivative containing 1 to 12 partial structures XC-C-H (X is a phosphonic acid ester group or a sulfonic acid group) is also the present invention.
In addition, using dioxane as a reaction solvent, fullerene or sulfonated fullerene and phosphonate esterification reagent LiPO (OR) ₂ (R is a C _{1 to} C ₅ alkyl group or phenyl group) are reacted, A method for producing a fullerene derivative is also the present invention.

  By using the fullerene derivative of the present invention, it is possible to produce a proton conducting membrane that does not cause a deion exchange group reaction due to an electrophilic substitution reaction caused by proton attack on an aromatic ring. Since the fullerene derivative of the present invention is soluble in an organic solvent, it can be easily mixed and dispersed uniformly in a binder polymer as an electrolyte. The fullerene derivative of the present invention can also be used as a lithium battery electrolyte, a bioacid solid acid catalyst, a medical material, or a raw material for medicine.

本発明のフラーレン誘導体は、反応方法に由来してＸ−Ｃ−Ｃ−Ｈ（Ｘはホスホン酸エステル基又はスルホン酸基）という部分構造を１〜１２個含む。上記のフラーレン誘導体は、精製して官能基の種類と数が実質的に単一なフラーレン誘導体でもよく、また官能基の種類と数が異なるフラーレン誘導体の混合物でも構わない。 The present invention is a fullerene derivative to which a phosphonic acid ester group —PO (OR) ₂ (R is a C _{1 to} C ₅ alkyl group or phenyl group) is bonded and an organic compound is not substantially bonded, It is a fullerene derivative in which a sulfonic acid group —SO ₃ M (M is H or an alkali metal ion) is simultaneously bonded. The number of bonds m of phosphonic acid ester groups and the number of bonds n of sulfonic acid groups are usually in the following range from the number of five-membered rings contained in the raw material fullerene, but the total number of functional groups (m + n) is larger depending on the reaction conditions. It is also possible to do.

The fullerene derivative of the present invention includes 1 to 12 partial structures of XC-C-H (X is a phosphonic acid ester group or a sulfonic acid group) derived from the reaction method. The fullerene derivative may be purified to be a fullerene derivative having substantially a single type and number of functional groups, or a mixture of fullerene derivatives having different types and numbers of functional groups.

The fullerene derivative of the present invention comprises a fullerene such as C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , and C ₈₄ as a substrate, a sulfonated reagent K ₂ SO ₃ or a phosphonate esterifying reagent LiPO using a specific organic solvent. (OR) It can be produced by reacting with ₂ . The reaction is usually carried out for 10 to 200 hours at a normal pressure or under pressure using a reaction temperature of 50 to 200 ° C.
According to the study of the present inventor, it was found by measuring the infrared absorption spectrum of the product that the reaction result of the fullerene and the sulfonating reagent varies greatly as shown in Table 1 depending on the organic solvent used. In the case of the solvent bond shown in Table 1, the organic compound derived from the reaction solvent binds to the fullerene, so that a complex peak appears in the infrared absorption spectrum and can be easily distinguished from the product of the target reaction showing a simple spectrum. Can do. By the way, DMF is (CH ₃ ) ₂ NCOH, DMAc is (CH ₃ ) ₂ NCOCH ₃ and belongs to the same amide solvent. It is a surprising discovery that is quite different.

※（特許文献１の実施例参照，溶媒はＤＭＦ）

* (Refer to Examples in Patent Document 1, solvent is DMF)

反応後のＳＯ_３Ｋ型は、必要により、イオン交換法でＳＯ_３Ｈ型や他のアルカリ金属イオン型に変換することが可能である。 Here, one reason for adding water to the organic solvent is to increase the solubility of the sulfonating reagent in the organic solvent. Another reason for adding water is that, as will be described below, the carbanion produced during the reaction is stabilized by extracting protons from the water before combining with the solvent molecules.

The SO ₃ K type after the reaction can be converted into an SO ₃ H type or other alkali metal ion type by an ion exchange method if necessary.

この中にフラーレン又は上記の方法で製造されたスルホン酸基ＳＯ_３Ｋが結合したフラーレン誘導体を加えてホスホン酸エステル化反応を行うが、溶媒としてジメチルホルムアミドを用いると溶媒結合が生じるので、ジオキサンを用いる必要があることが生成物の赤外吸収スペクトル分析から判明した。この場合、同じ環状エーテル系のテトラヒドロフランを使用することも可能であるが、沸点が低いため反応温度が低くなるので、ジオキサンを用いることが好ましい。 Next, the phosphonic acid esterification reaction will be described. Phosphonate esterification reagent LiPO (OR) ₂ (R is a C ₁ -C ₅ alkyl group or phenyl group) is prepared by the following reaction using an aprotic polar organic solvent and usually at 25-100 ° C. The

A fullerene or a fullerene derivative to which a sulfonic acid group SO ₃ K produced by the above method is bonded is added to this to carry out a phosphonic acid esterification reaction. When dimethylformamide is used as a solvent, solvent bonding occurs. It was found from the infrared absorption spectrum analysis of the product that it was necessary to use it. In this case, it is possible to use the same cyclic ether-based tetrahydrofuran, but it is preferable to use dioxane because the reaction temperature is lowered because the boiling point is low.

本発明においては、反応中間体として生じるカルバニオンが溶媒と結合する前にプロトンを引き抜いて安定化するように、スルホン化反応時の水の添加やホスホン酸エステル化反応時のジオキサンの使用が行われる。

本発明に係わるフラーレン誘導体においては、Ｘのβ位にプロトンが結合した上記の部分構造が主に含まれるが、一部の部分構造で、Ｈの代わりに水酸基ＯＨやカルボン酸基ＣＯ_２Ｈが結合していても、有機化合物ではないので構わない。また次式のように、２個のＸがフラーレンに付加する際に２重結合が生成するため、プロトンが結合していない部分構造が含まれていても、有機化合物が結合しないので構わない。

The carbanion produced during the phosphonic acid esterification reaction is stabilized by extracting a proton from the solvent dioxane.

In the present invention, water is added during the sulfonation reaction and dioxane is used during the phosphonate esterification reaction so that the carbanion produced as a reaction intermediate is extracted and stabilized before binding to the solvent. .

The fullerene derivative according to the present invention mainly includes the above partial structure in which a proton is bonded to the β-position of X. In some partial structures, a hydroxyl group OH or a carboxylic acid group CO ₂ H is substituted for H. Even if they are bonded, they are not organic compounds. Further, as shown in the following formula, a double bond is generated when two Xs are added to the fullerene, and therefore, even if a partial structure to which no proton is bonded is included, the organic compound may not be bonded.

One method for producing a proton conducting membrane using the fullerene derivative of the present invention includes a hydroalcoholic solution of perfluorosulfonic acid resin (manufactured by DuPont, trade name Nafion resin) as a binder polymer, and a fullerene derivative of the present invention. A tetrahydrofuran solution is mixed and a film is formed by a casting method, or a reinforcing material such as a glass fiber nonwoven fabric or a stretched porous polytetrafluoroethylene film is applied and impregnated and dried.
In the above method, a fluorinated resin such as polyvinylidene fluoride or a hydrocarbon resin such as polyethersulfone, polyetheretherketone, or polyimide can be used as a binder polymer instead of perfluorosulfonic acid resin. In that case, the resin and the fullerene derivative of the present invention are dissolved and mixed in an organic solvent such as dimethylformamide, dimethylacetamide, tetrahydrofuran, etc. to form a film by a casting method, or a glass fiber nonwoven fabric or a stretched porous polytetrafluoroethylene film. A film can be formed by coating and impregnating the reinforcing material and drying.

Since the fullerene derivative of the present invention is water-insoluble when the ratio of the sulfonic acid group / phosphonic acid ester group is sufficiently small, the membrane obtained by the above method is immersed in an aqueous hydrochloric acid solution at room temperature to obtain SO _{3 of} the sulfonic acid group. A proton conducting membrane can be obtained by converting K to SO ₃ H. However, when hydrolyzing the phosphonic acid ester group and converting it to a phosphonic acid group to contribute to proton conduction, or when reducing the possibility of physical extrusion during long-term use, Na ₂ S, HO— It is preferable to crosslink and insolubilize using a bifunctional compound such as C ₆ H ₄ —OH or HS—C ₆ H ₄ —SH. In this case, the following three methods are possible for crosslinking.
1) Add a cross-linking agent to the organic solvent solution of the fullerene derivative of the present invention and heat and stir. Add the cross-linked material to the organic solvent solution of the binder polymer and vigorously stir and mix with a homogenizer. A film is formed by applying and impregnating a reinforcing material such as a glass fiber nonwoven fabric or a stretched porous polytetrafluoroethylene film and drying.
2) A crosslinking agent is added to the organic solvent solution of the fullerene derivative and binder polymer of the present invention, and after crosslinking by heating and stirring, a film is formed by a casting method, or a glass fiber nonwoven fabric or a stretched porous polytetrafluoroethylene film is used. A film is formed by coating and impregnating the reinforcing material and drying.
3) A crosslinking agent is added to the organic solvent solution of the fullerene derivative and the binder polymer of the present invention, and a film is formed by a casting method, or a reinforcing material such as a glass fiber nonwoven fabric or a stretched porous polytetrafluoroethylene film is coated and impregnated. After film formation, heating is performed to remove the solvent and simultaneously perform crosslinking.

It is preferable to remove the cross-linking agent remaining in the film after the above-described three types of film formation by thoroughly washing with water or methanol. The phosphonic acid ester group PO (OR) ₂ in the membrane can be converted into the phosphonic acid group PO (OH) ₂ by hydrolysis in hydrochloric acid / methanol. During this operation, the coexisting sulfonic acid group SO ₃ K is converted to the SO ₃ H type, so that a proton conductive membrane having a sulfonic acid group and a phosphonic acid group can be obtained.
Examples are shown below, but the present invention is not limited thereto.

690 mg of diethyl phosphite HPO (OEt) ₂ and 200 ml of dioxane were placed in a 300 ml three-necked flask, and 40 mg of LiH was added. When heated and stirred at 80 ° C., H ₂ was generated and eventually the solution became transparent. Thus, 720 mg of fullerene C ₆₀ was added, and the mixture was heated and stirred at 80 ° C. for 4 days. After completion of the reaction, the solvent was removed by drying, the residue was extracted with (ethanol + THF), the solid content was filtered off, and the filtrate (ethanol + THF) was removed by drying, and then the infrared absorption spectrum was measured with KBr. _C 2 _H 5 to 2926cm ^-1, to 1209cm ^-1 P = O, appear absorption of PO-C to 1043 ^-1, it was confirmed that a phosphonic acid ester group PO _{(OEt) 2} is bonded (See FIG. 1).
In order to further confirm the structure, 1 g of trimethylsilyl bromide was added to 500 mg of this phosphonate esterified fullerene, and the ester exchange was carried out overnight at room temperature, followed by hydrolysis with water. After drying the obtained product was measured with infrared absorption spectrum in _KBr, absorption of C 2 _{H 5} is lost, OH to 3348cm ^-1, to 1184cm ^-1 P = O. Absorption of P—O—C appeared at 1074 cm ⁻¹ . The obtained phosphonated fullerene was subjected to P analysis by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy), and the results of elemental analysis of C, H, O by combustion method were C73.9%, P10.6. %, H1.4%, and O15.5%, and it was confirmed that about 3 to 4 phosphonic acid groups PO (OH) ₂ and H were bonded. Furthermore, when the sample was dissolved in D ₂ O and NMR was measured, a peak presumed to be a β-position proton was confirmed. The yield of the phosphonated fullerene obtained was approximately 35% on a fullerene basis.

(Comparative Example 1)
In Example 1, the same operation was performed using dimethylformamide instead of dioxane, and the infrared absorption spectrum of the product was measured. As a result, many peaks appeared, and it was confirmed that the solvent dimethylformamide was bound. (See FIG. 2).

In a 300 ml three-necked flask, 720 mg of fullerene C ₆₀ and 200 ml of dimethylacetamide were placed. To this was added 790 mg of potassium sulfite K ₂ SO ₃ (5 mol of fullerene) dissolved in 10 ml of water, and the mixture was heated and stirred at 80 ° C. for 4 days. After completion of the reaction, the solvent was removed by drying and the residue was extracted with ethanol. The solid was filtered off, after which the filtrate ethanol was removed by drying, The infrared absorption spectrum was measured using a KBr, SO ₂ stretch to 1117cm ^-1, a peak of CS stretch to 619cm ^-1 appeared (Fig. 3). Moreover, S, K analysis was performed by ICP-AES, and the results of elemental analysis of C, H, O by the combustion method were C57.5%, S11.4%, K14.7%, H0.55%, O 13.0%, and it was confirmed that about 4 to 5 sulfonic acid groups SO ₃ K and H were bonded. Furthermore, when the sample was dissolved in D ₂ O and NMR was measured, a peak presumed to be a β-position proton was confirmed. The yield of the sulfonated fullerene obtained was approximately 30% on a fullerene basis.
When the same operation as in Example 1 was performed using the above sulfonated fullerene as a raw material, absorption of a sulfonic acid group and a phosphonic acid ester group appeared in the infrared absorption spectrum, and both were confirmed to coexist. It was. Moreover, it was confirmed by P analysis using ICP-AES that about two phosphonate ester groups were bonded, and it was hardly soluble in water.

(Comparative Example 2)
In Example 2, dimethylformamide was used in place of dimethylacetamide to carry out sulfonation with K ₂ SO ₃ , and when the infrared absorption spectrum of the product was measured, many peaks appeared, and the solvent dimethylformamide was bound. (See FIG. 4).

(Usage example 1)
In a 50 ml beaker, 20 g of 5% Nafion solution (Aldrich, EW = 1100) was added, and about 2 phosphonate ester groups PO (OEt) ₂ obtained in Example 2 and about 4 to 5 sulfones were obtained. A solution prepared by dissolving 500 mg of a fullerene derivative having an acid group SO ₃ K bonded thereto in 5 ml of tetrahydrofuran was added. After stirring with a homogenizer, the resulting solution was applied onto a 100-micron glass fiber nonwoven fabric (manufactured by Japan Vilene Co., Ltd.) using a brush and impregnated in the gaps. This operation was repeated 10 times and then dried at 100 ° C. to obtain a translucent film. The membrane was immersed in a 1 N aqueous hydrochloric acid solution at room temperature overnight to convert the sulfonic acid group SO ₃ K into SO ₃ H to obtain a proton conductive membrane.

(Usage example 2)
0.5 g of the phosphonate esterified fullerene obtained in Example 1 was reacted with 0.12 g of Na ₂ S · 9H ₂ O in 150 g of dimethylacetamide at 80 ° C. for 3 days to crosslink and insolubilize. This was filtered out, 500 mg was weighed and added to 20 g of a 5% Nafion solution (Aldrich, EW = 1100) in a 50 ml beaker, and stirred with a homogenizer. The obtained dispersion was applied onto a 100-micron glass fiber nonwoven fabric (manufactured by Nippon Vilene Co., Ltd.) using a brush and impregnated in the gaps. This operation was repeated 10 times and then dried at 100 ° C. to obtain a translucent film. The membrane was heated in 1N hydrochloric acid / methanol at 90 ° C. overnight to hydrolyze the phosphonate ester group to obtain a proton conducting membrane.

2 is a graph showing an infrared absorption spectrum of a fullerene derivative obtained in Example 1. FIG. 4 is a diagram showing an infrared absorption spectrum of a fullerene derivative obtained in Comparative Example 1. FIG. 2 is a graph showing an infrared absorption spectrum of a fullerene derivative obtained in Example 2. FIG. 6 is a graph showing an infrared absorption spectrum of a fullerene derivative obtained in Comparative Example 2. FIG.

Claims (5)

A fullerene derivative to which a phosphonic acid ester group —PO (OR) ₂ (R is a C _{1 to} C ₅ alkyl group or phenyl group) is bonded and an organic compound is not substantially bonded. The fullerene derivative according to claim 1, wherein a sulfonic acid group —SO ₃ M (M is H or an alkali metal ion) is bonded thereto. The fullerene derivative according to claim 1 or 2, wherein the number of bonds m of the phosphonic acid ester group and the number of bonds n of the sulfonic acid group are in the following ranges.

  The fullerene derivative according to any one of claims 1 to 3, comprising 1 to 12 partial structures XC-C-H (X is a phosphonic acid ester group or a sulfonic acid group). 2. Dioxane is used as a reaction solvent, and fullerene or sulfonated fullerene is reacted with a phosphonic esterification reagent LiPO (OR) ₂ (R is a C _{1 to} C ₅ alkyl group or phenyl group). The manufacturing method of the fullerene derivative in any one of -4.

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