JP2010037277A - Method for producing chemically modified fullerene - Google Patents

Abstract

【選択図】なしA chemically modified fullerene having a phosphonic acid group or a sulfonic acid group, which is useful for producing a proton conductive membrane for a fuel cell, is produced at low cost.
SOLUTION: In the case of a sulfonation reagent K ₂ SO ₃ (dimethylacetamide + water), the phosphonation reagent LiPO (OR) ₂ (R is a C _{1 to} C ₅ alkyl group or phenyl group) is called dioxane. A specific reaction solvent is selected, and fullerene and K ₂ SO ₃ or LiPO (OR) ₂ are dispersed in the solvent, and the reaction temperature of 20 to 200 ° C. is used for 10 to 200 hours under normal pressure or pressure. by reacting, in a method of producing a chemically modified fullerene containing 1-12 a partial structure of the following, a manufacturing method of the raw material of the fullerene, characterized in that it comprises a mixture of C ₆₀ and C _70.
[Chemical 1]

[Selection figure] None

Description

  The present invention relates to a method for producing chemically modified fullerene useful for producing a proton conducting membrane used in a polymer electrolyte fuel cell.

Conventionally, a perfluorosulfonic acid resin membrane (trade name Nafion membrane manufactured by DuPont) has been used as an electrolyte membrane that governs the performance of a polymer electrolyte fuel cell. However, since the membrane is expensive, an electrolyte membrane based on a hydrocarbon polymer has recently been studied.
The electrolyte membrane based on this hydrocarbon polymer has a structure in which a sulfonic acid group is directly bonded to an aromatic ring. However, when it is used for a long time under an acidic condition of 100 ° C. or higher, a desulfonic acid group reaction gradually occurs and the performance is improved. There is a defect that deteriorates (for example, see Non-Patent Document 1). 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, chemically modified fullerene in which a sulfonic acid group is directly bonded to fullerene is disclosed (for example, see Patent Document 1). However, dimethylformamide used as a reaction solvent is also bonded during the sulfonation reaction, and there is a problem that the target product cannot be obtained.
In order to cope with this problem, a method of bonding a fullerene and a sulfonic acid group of a substrate with a hydrocarbon-based or fluorine-based spacer molecule is disclosed (for example, see Patent Document 2 and Patent Document 3). However, the manufacturing method is complicated and the ion exchange capacity cannot be increased.

The present inventor uses K ₂ SO ₃ as a sulfonating reagent and uses a specific reaction solvent (dimethylacetamide + water) to bond a sulfonic acid group directly to fullerene without bonding of the reaction solvent. Successful (see Patent Document 4).
In addition, by using LiPO (OEt) ₂ as a phosphonation reagent and using dioxane as a reaction solvent, a direct bond type phosphonation fullerene was successfully obtained without binding of the reaction solvent (see Patent Document 4). .

JP 2002-326984 A JP 2005-093417 A Japanese Patent Laying-Open No. 2005-068124 Japanese Patent No. 3984280 Supervised by Kyoji Kimoto, “Development of electrolyte membrane for PEFC”, CMC Publishing, published in December 2005, P.C. 30

The raw material fullerene used in Patent Document 4 is an organic solvent containing soot containing C ₆₀ and C ₇₀ mixed fullerene obtained by heating a carbon rod by a resistance heating method, an arc discharge method, a laser method or the like. extracted obtain a mixed fullerene based on a mixture of C ₆₀ and C _70, since it separates the C ₆₀ and C ₇₀ by high performance liquid chromatography, it is relatively expensive.

  An object of the present invention is to provide an inexpensive method for producing a chemically modified fullerene used for producing a proton conducting membrane.

In order to achieve the above object, the present invention provides a sulfonated reagent K ₂ SO ₃ (dimethylacetamide + water), a phosphonating reagent LiPO (OR) ₂ (R is a C ₁ -C ₅ alkyl group or In the case of a phenyl group), a specific reaction solvent called dioxane is selected, and fullerene and K ₂ SO ₃ or LiPO (OR) ₂ are dispersed in the solvent, followed by reaction at 20 to 200 ° C. under normal pressure or pressure. reacted 10-200 hours with the temperature, to a process for the preparation of chemically modified fullerenes containing 1-12 a partial structure of the following, characterized in that the material of the fullerene containing a mixture of C ₆₀ and C ₇₀ production Is the method.

In addition, the above production method in which C ₆₀ contained in the raw material fullerene is in the range of 50 to 90%, C _{70 in} the range of 40 to 10%, and higher order fullerene in the range of 10% or less is also the present invention.
Further, the carbon rod for example a resistance heating method, arc discharge method, and extracted with an organic solvent from soot obtained by heating by a laser method or the like, the above-described production using fullerenes containing mixtures of C ₆₀ and C ₇₀ as a raw material The method is also the present invention.
Further, the carbon rod for example a resistance heating method, arc discharge method, a mixed fullerene containing C ₆₀ and C ₇₀ in soot obtained by heating by a laser method or the like, the above-mentioned used as the raw material without extraction with an organic solvent The manufacturing method is also the present invention.

  The method of the present invention makes it possible to produce chemically modified fullerenes having a sulfonic acid group or a phosphonic acid group, which are useful for producing a proton conductive membrane for a fuel cell, at low cost.

The present invention is a method for producing a chemically modified fullerene containing 1 to 12 of the following partial structures at low cost.

In this case, the sulfonic acid group and the phosphonic acid group may coexist, and the insolubilization necessary when the proton conducting membrane contains the chemically modified fullerene can be performed by using metal ion crosslinking of the phosphonic acid group. . The polyvalent metal ions used for crosslinking include cerium ions, manganese ions, calcium ions, platinum ions, etc., but it is possible to use cerium ions and manganese ions that have the function of removing OH radicals that cause oxidative degradation of the film. preferable.
The total number of functional groups is usually in the range of 1 to 12, but can be increased depending on the reaction conditions. The chemically modified fullerene may be a chemically modified fullerene having a substantially single functional group after purification, or a mixture of chemically modified fullerenes having different functional groups.

In the present invention, the sulfonating reagent K ₂ SO ₃ is (dimethylacetamide + water), and the phosphonating reagent LiPO (OR) ₂ (R is a C _{1 to} C ₅ alkyl group or phenyl group) is dioxane. The specific reaction solvent is selected, and fullerene and K ₂ SO ₃ or LiPO (OR) ₂ are dispersed in the solvent, and the reaction temperature is 20 to 200 ° C. under normal pressure or pressure, and 10 to 200. It is produced by reacting for a period of time, hydrolyzing the phosphonate group of the chemically modified fullerene obtained, and performing ion exchange if necessary.
In this case, simple fullerenes purified by high performance liquid chromatography such as C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , C _{84 and the} like can also be used as raw materials. However, in the present invention, the fullerene containing a mixture of C ₆₀ and C _70, be used as a raw material without performing a separation operation by high performance liquid chromatography, it is possible to realize a cost reduction of chemical modification fullerene products preferred. Generally, the composition of the mixed fullerene after extraction with an organic solvent _{C 60} is 50 to _{90% C 70} is 40 to 10%, in the range higher fullerenes less 10%, particularly the use of this mixture fullerene material preferable.
Incidentally, the carbon rod for example a resistance heating method, arc discharge method, and extracted with an organic solvent from soot obtained by heating by a laser method or the like, by using the fullerene containing a mixture of C ₆₀ and C ₇₀ as a raw material, product Can significantly reduce the cost of chemically modified fullerene. Further, the carbon rod for example a resistance heating method, arc discharge method, a mixed fullerene containing C ₆₀ and C ₇₀ in soot obtained by heating by a laser method or the like, by using the reaction materials without extraction with an organic solvent Further, it is possible to further reduce the cost as compared with the above method.

In the present invention, the chemically modified fullerene reacts with a sulfonating reagent K ₂ SO ₃ or a phosphonating reagent LiPO (OR) ₂ (R is a C _{1 to} C ₅ alkyl group or phenyl group) using a specific organic solvent. Can be manufactured. 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 inventor's research, it has been found by measuring the infrared absorption spectrum of the product that the reaction result between the fullerene and the sulfonating reagent or phosphonating reagent varies greatly depending on the organic solvent used.

The table below shows the reaction results of fullerene and a sulfonating reagent.
In the case of the solvent bond in the table, since the organic compound derived from the reaction solvent binds to the fullerene, a complex peak appears in the infrared absorption spectrum, and it 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 shown in the following formula, 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 to the SO ₃ H type by an ion exchange method, if necessary.

The phosphonating reagent LiPO (OR) ₂ (R is a C _{1 to} C ₅ alkyl group or phenyl group) used in the present invention uses an aprotic polar organic solvent and is usually the following conditions at 25 to 100 ° C. Prepared by reaction.

Phosphonation reaction is carried out by adding fullerene to this, but when dimethylformamide is used as a solvent, solvent bonding occurs, and it was found from the infrared absorption spectrum analysis of the product that dioxane must be used.
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.

The carbanion produced during the phosphonation reaction is stabilized by extracting a proton from the alkyl group of the phosphonate ester or the dioxane of the solvent.

In particular, the ethyl group of the phosphonic acid ester tends to cause a proton abstraction reaction in the next reaction, and is useful for preventing the carbanion produced during the reaction from binding to the solvent.

The phosphonic acid ester group obtained by the phosphonation reaction is reacted with trimethylsilyl bromide by a known method for transesterification, and then hydrolyzed by adding water to convert it to the phosphonic acid group PO (OH) ₂ . be able to. The hydrolysis of the phosphonic acid ester group can also be performed in hot concentrated hydrochloric acid.
It is also possible to synthesize a chemically modified fullerene in which a phosphonic acid group and a sulfonic acid group coexist by introducing the phosphonic acid ester group by the above-mentioned method and then performing the sulfonation reaction. In this case, it is also possible to reverse the reaction sequence and first attach the sulfonic acid group and then introduce the phosphonate ester group.

  Examples are shown below, but the present invention is not limited thereto.

Diethyl phosphite HPO (OEt) ₂ (690 mg) and dioxane (200 ml) were placed in a 300 ml three-necked flask, and LiH (40 mg) was added. When heated and stirred at 80 ° C., H ₂ was generated and eventually the solution became transparent. Therefore, a mixed fullerene having a C ₆₀ of 77%, a C ₇₀ of 22% and a higher fullerene of 1% (MTR, Fullrenes, C −60, C-70) was added, and the mixture was stirred with heating at 80 ° C. for 4 days.
After completion of the reaction, the solvent was removed by drying, and the residue was extracted with (ethanol + THF). The solid was filtered off, after which the filtrate of the (ethanol + THF) was removed by drying, it was measured infrared absorption spectrum in KBr, _C 2 _H 5 to 2926cm ^-1, to 1209cm ^-1 P = O, 1043cm ^-1 P—O—C absorption was observed, and it was confirmed that the phosphonate ester group PO (OEt) ₂ was bonded.

1 g of trimethylsilyl bromide was added to 500 mg of this phosphonate esterified mixed 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, the 1074Cm ^-1 Absorption of PO-C appeared.
The obtained phosphonated mixed fullerene was subjected to P analysis by ICP-AES and subjected to elemental analysis of C, H, O by combustion method, and about 3 to 4 phosphonic acid groups PO (OH) ₂ and H were bonded. It was confirmed that The yield of the resulting phosphonated mixed fullerene was approximately 35% on a fullerene basis.

A solution of 500 mg of the phosphonated mixed fullerene obtained above in 5 ml of water was placed in a 50 ml beaker, and a solution of 180 mg of cerium chloride heptahydrate CeCl ₃ · 7H ₂ O in 10 ml of water was added thereto. The resulting precipitate was filtered, washed and dried to obtain 400 mg of a phosphonated mixed fullerene crosslinked with cerium ions.

(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. It was.

20 g of a 5% Nafion solution (Aldrich, EW = 1100) was placed in a 50 ml beaker, and 400 mg of the cerium ion crosslinked phosphonated mixed fullerene obtained in Example 1 was added. After stirring for 30 minutes with a homogenizer, the obtained dispersion was applied onto a 100-micron glass fiber nonwoven fabric (manufactured by Nippon Vileen 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 proton conducting membrane.
The membrane was immersed in water overnight, and the change in the P analysis value was measured using ICP-AES. There was no difference between before and after the immersion, and it was confirmed that the phosphonated mixed fullerene was not eluted.

Three-necked flask 300 _{ml, C 60} is _{77% C 70} 22%, higher fullerenes 1% mixed fullerenes (MTR Co., Fullerenes, C-60, C -70) was charged 720mg dimethylacetamide 200ml . 790 mg of potassium sulfite K ₂ SO ₃ was dissolved in 10 ml of water and added thereto, followed by heating and stirring 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 the 1117Cm ^-1, appeared peaks of CS stretch to 619cm ^-1. In addition, as a result of performing S, K analysis by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) and elemental analysis of C, H, O by combustion method, sulfonic acid groups SO ₃ K and H are 4-5. It was confirmed that about one was connected. The yield of the resulting sulfonated mixed fullerene was approximately 30% on a fullerene basis.

When the same operation as in Example 1 was performed using the above sulfonated mixed fullerene as a raw material, absorption of sulfonic acid groups and phosphonic acid groups appeared in the infrared absorption spectrum, and it was confirmed that both coexisted. It was. When P analysis was performed by ICP-AES, it was estimated that about two phosphonic acid groups were bonded.
In a 50 ml beaker, the solution obtained by dissolving 500 mg (phosphonated + sulfonated) mixed fullerene obtained above in 5 ml water was added, and a solution obtained by dissolving 150 mg manganese nitrate hexahydrate in 10 ml water was added and stirred. The resulting precipitate was filtered, washed and dried to obtain a mixed fullerene (phosphonated + sulfonated) crosslinked with manganese ions.

(Comparative Example 2)
In Example 3, the same operation was carried out using dimethylformamide instead of dimethylacetamide, 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. It was done.

  In Example 2, instead of the cerium ion cross-linked phosphonated mixed fullerene, the same operation was performed using the manganese ion cross-linked (phosphonated + sulfonated) mixed fullerene obtained in Example 3, and the proton conducting membrane containing manganese ions was used. Got.

In Example 1, the soot containing a mixed fullerene of C ₆₀ and C ₇₀ obtained by the resistance heating method was treated in the same manner by using a raw material, to obtain a phosphonated mixed fullerenes.

Claims (4)

In the case of the sulfonating reagent K ₂ SO ₃ (dimethylacetamide + water), in the case of the phosphonating reagent LiPO (OR) ₂ (R is a C _{1 to} C ₅ alkyl group or phenyl group), a specific reaction solvent called dioxane And fullerene and K ₂ SO ₃ or LiPO (OR) ₂ are dispersed in the solvent, and reacted at normal pressure or under pressure using a reaction temperature of 20 to 200 ° C. for 10 to 200 hours, In a method for producing a chemically modified fullerene containing 1 to 12 of the following partial structures:
Production method the raw material of fullerene characterized in that it comprises a mixture of C ₆₀ and C _70.

_{C 60} is 50-90% contained in the raw material _{fullerene, C 70} is 40 to 10%, higher fullerenes is in the range of 10% or less, the production method according to claim 1. And extracted with an organic solvent from soot obtained by heating a carbon rod, using a fullerene comprising a mixture of C ₆₀ and C ₇₀ as a raw material, production method according to claim 1 or 2. The mixture fullerenes containing C ₆₀ and C ₇₀ in soot obtained by heating the carbon rod, use the raw material without extraction with an organic solvent, the production method according to claim 1.