JP2002124436A - Electrolytic solution for electrolytic capacitor and electrolytic capacitor using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide electrolytic solution for an electrolytic capacitor whose are voltage and electric conductivity are both high and which deteriorates less at a high temperature by providing tricarboxylic acid which is useful as solute of electrolytic solution for an electrolytic capacitor, and an electrolytic capacitor using the electrolytic solution. SOLUTION: Electrolytic solution for an electrolytic capacitor is prepared by performing Foehnton oxidization for 4 to 14C cycloalkanone in the presence of unsaturated dicarboxylic-acid ester expressed by a formula (1) and then dissolving tricarboxylic acid obtained by hydrolysis, the tricarboxylic acid and/or its salt in solvent. The electrolytic solution is used in the capacitor. (In the formula, R1 expresses an alkyl group which can have a 1 to 5C branch).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel tricarboxylic acid, an electrolytic solution for an electrolytic capacitor using the same, and an electrolytic capacitor.

[0002]

2. Description of the Related Art Electrolytic capacitors are characterized by having a large capacitance while being small, and are often used for low-frequency filters and bypasses. Generally, an electrolytic capacitor has a structure in which an anode foil and a cathode foil are wound via a separator, and this is housed in a case and sealed (FIG. 1). A valve metal such as aluminum or tantalum having an insulating oxide film formed thereon as a dielectric layer is used for the anode foil, and an etched aluminum foil is generally used for the cathode foil. The separator interposed between the anode and the cathode is impregnated with an electrolytic solution to prevent a short circuit between the two electrodes, and functions as a true cathode. For this reason, the electrolytic solution is an important component that greatly affects the characteristics of the electrolytic capacitor.

[0003] Various electrolytic solutions have been proposed and used in the past. For example, an electrolytic solution in which boric acid or ammonium borate as an electrolyte is dissolved in ethylene glycol or the like is used particularly for capacitors such as capacitors for medium and high pressure. However, this type of electrolyte has a problem that ethylene glycol and boric acid cause an esterification reaction to generate water. For this reason, when the temperature is 100 ° C. or higher, the water vapor pressure becomes extremely high, and the aluminum of the electrode easily reacts.

In order to improve such disadvantages, electrolytic solutions using adipic acid or sebacic acid as a solute have been proposed. However, they have an extremely high electric conductivity but a low spark voltage. Further, there is also an example in which a long-chain fatty acid dibasic acid is used as a solute (see
Japanese Patent Application Laid-Open No. 85356/85) has a disadvantage that the solubility in a solvent is low, and crystals are deposited when left for a long time or operated at a low temperature. For this reason, it was not possible to provide an electrolytic capacitor having high electric conductivity even by using these solutes.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve these problems of the prior art. That is, in the present invention, both the spark voltage and the electrical conductivity are high,
Further, an object of the present invention is to provide an electrolytic solution for an electrolytic capacitor in which crystals are not easily deposited even when the device is left at a low temperature for a long period of time and an electrolytic capacitor using the same. Another object of the present invention is to provide an electrolytic solution for an electrolytic capacitor which can be stably supplied industrially and can be manufactured at low cost, and an electrolytic capacitor using the same.

[0006]

As a result of intensive studies to solve these problems, the present inventors have found that a tricarboxylic acid derived from a specific cycloalkanone and an unsaturated dicarboxylic acid ester is unknown in the literature. A new compound,
It has been found that an excellent electrolytic solution having the desired effect can be obtained by using the tricarboxylic acid and / or its salt, and the present invention has been completed.

That is, the present invention provides a cycloalkanone having a total of 4 to 14 carbon atoms represented by the following general formula (1):

Embedded image (Wherein, R ¹ represents an alkyl group having 1 to 5 carbon atoms which may have a branch), which is obtained by Fenton oxidation in the presence of an unsaturated dicarboxylic acid ester compound represented by the following formula, followed by hydrolysis: It provides a tricarboxylic acid. Further, a composition containing a plurality of tricarboxylic acids obtained by this reaction is also included in the scope of the present invention. As the cycloalkanone as a starting material for the reaction, for example, cyclohexanone and 3,3,5-trimethylcyclohexanone can be preferably used.

The present invention also provides an electrolytic solution for an electrolytic capacitor in which the tricarboxylic acid and / or its salt obtained by the above reaction is dissolved in a solvent. In a preferred embodiment of the present invention, one or more solvents selected from the group consisting of ethylene glycol and γ-butyrolactone are used as the solvent. Further, the present invention also provides an electrolytic capacitor using the above electrolytic solution.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a tricarboxylic acid, an electrolytic solution and an electrolytic capacitor of the present invention will be described in detail in order. The tricarboxylic acid of the present invention has a total carbon number of 4-1.
This compound is obtained by subjecting cycloalkanone No. 4 to Fenton oxidation in the presence of the unsaturated dicarboxylic acid ester represented by the above general formula (1), followed by hydrolysis. The tricarboxylic acid of the present invention is a novel compound provided for the first time by the present inventors.

The cycloalkanone having 4 to 14 carbon atoms used as a starting material for the tricarboxylic acid synthesis reaction of the present invention includes cyclobutanone, 2-methylcyclobutanone,
3-methylcyclobutanone, 2-ethylcyclobutanone, 3-ethylcyclobutanone, 2-n-propylcyclobutanone, 3-n-propylcyclobutanone, 2-isopropylcyclobutanone, 3-isopropylcyclobutanone, 2-n-butylcyclobutanone, 3-n- Butylcyclobutanone, 2-isobutylcyclobutanone, 3
-Isobutylcyclobutanone, 2-tert-butylcyclobutanone, 3-tert-butylcyclobutanone,
2-n-pentylcyclobutanone, 3-n-pentylcyclobutanone, 2-tert-amylcyclobutanone,
3-tert-amylcyclobutanone, cyclopentanone, 2-methylcyclopentanone, 3-methylcyclopentanone, 2-ethylcyclopentanone, 3-ethylcyclopentanone, 2-n-propylcyclopentanone,
3-n-propylcyclopentanone, 2-isopropylcyclopentanone, 3-isopropylcyclopentanone, 2-n-butylcyclopentanone, 3-n-butylcyclopentanone, 2-isobutylcyclopentanone,
3-isobutylcyclopentanone, 2-tert-butylcyclopentanone, 3-tert-butylcyclopentanone, 2-n-pentylcyclopentanone, 3-n-
Pentylcyclopentanone, 2-tert-amylcyclopentanone, 3-tert-amylcyclopentanone, cyclohexanone, 2-methylcyclohexanone,
3-methylcyclohexanone, 4-methylcyclohexanone, 2-ethylcyclohexanone, 3-ethylcyclohexanone, 4-ethylcyclohexanone, 2-n-propylcyclohexanone, 3-n-propylcyclohexanone, 4-n-propylcyclohexanone, 2-isopropylcyclohexanone , 3-isopropylcyclohexanone, 4-isopropylcyclohexanone, 2-n
-Butylcyclohexanone, 3-n-butylcyclohexanone, 4-n-butylcyclohexanone, 2-isobutylcyclohexanone, 3-isobutylcyclohexanone, 4-isobutylcyclohexanone, 2-tert-
Butylcyclohexanone, 3-tert-butylcyclohexanone, 4-tert-butylcyclohexanone,
2-n-pentylcyclohexanone, 3-n-pentylcyclohexanone, 4-n-pentylcyclohexanone, 2-tert-amylcyclohexanone, 3-te
rt-amylcyclohexanone, 4-tert-amylcyclohexanone, 2,3-dimethylcyclohexanone, 2,4-dimethylcyclohexanone, 2,5-dimethylcyclohexanone, 3,4-dimethylcyclohexanone, 3,5-dimethylcyclohexanone, 2,3 -Diethylcyclohexanone, 2,4-diethylcyclohexanone, 2,5-diethylcyclohexanone, 3,4-
Diethylcyclohexanone, 3,5-diethylcyclohexanone, 2,3,4-trimethylcyclohexanone,
2,3,5-trimethylcyclohexanone, 3,4,5
-Trimethylcyclohexanone, 3,3,5-trimethylcyclohexanone, 2,4,5-trimethylcyclohexanone, 2,3,4-triethylcyclohexanone,
2,3,5-triethylcyclohexanone, 3,4,5
-Triethylcyclohexanone, 2,4,5-triethylcyclohexanone, 2,3,4,5-tetramethylcyclohexanone, 2,3,4,5-tetraethylcyclohexanone, cycloheptanone, 2-methylcycloheptanone, 3-methyl Cycloheptanone, 4-methylcycloheptanone, 2-ethylcycloheptanone, 3-ethylcycloheptanone, 4-ethylcycloheptanone, 2
-N-propylcycloheptanone, 3-n-propylcycloheptanone, 4-n-propylcycloheptanone,
2-isopropylcycloheptanone, 3-isopropylcycloheptanone, 4-isopropylcycloheptanone, 2-n-butylcycloheptanone, 3-n-butylcycloheptanone, 4-n-butylcycloheptanone,
2-isobutylcycloheptanone, 3-isobutylcycloheptanone, 4-isobutylcycloheptanone, 2-
tert-butylcycloheptanone, 3-tert-butylcycloheptanone, 4-tert-butylcycloheptanone, 2-n-pentylcycloheptanone, 3-n
-Pentylcycloheptanone, 4-n-pentylcycloheptanone, 2-tert-amylcycloheptanone,
3-tert-amylcycloheptanone, 4-tert
-Amylcycloheptanone.

As the cycloalkanone, cyclohexanone and alkyl-substituted cyclohexanone are preferably used. In the reaction, one kind of cycloalkanone may be selected and used, or two or more kinds of cycloalkanone may be used in combination.

In the Fenton oxidation referred to in the present specification, a cycloalkanone is reacted with hydrogen peroxide, and the compound represented by the general formula (1)
Is a reaction to form a tricarboxylic acid ester by the action of a reducing metal catalyst in the presence of the unsaturated dicarboxylic acid ester. In the following description, the step of reacting hydrogen peroxide is referred to as “first step”, and the step of reacting the reducing metal catalyst is referred to as “second step”. The hydrolysis step performed after the Fenton oxidation is referred to as “third step”.

The first step is usually carried out by adding hydrogen peroxide to cycloalkanone in alcohol.
Alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, te
It is preferable to use rt-butanol or the like. The most preferred alcohol is methanol. These alcohols are preferably anhydrous. The reaction of the first step is preferably performed in an acid catalyst. Examples of the acid catalyst include sulfuric acid, hydrochloric acid, phosphoric acid, and trifluoroacetic acid, and among them, sulfuric acid or phosphoric acid is preferably used.

The amount of hydrogen peroxide used in the first step is
Preferably 0.8 to 1. 1 mole of cycloalkanone.
It is 3 mol, more preferably 0.9 to 1.2 mol, most preferably 1.0 to 1.1 mol. The amount of the alcohol used is preferably from 3 to 70 per mole of cycloalkanone.
Mol, more preferably 10 to 40 mol. The amount of the acid catalyst to be used is preferably 0.04 to 0.1 mol, more preferably 0.05 to 0.1 mol per mol of cycloalkanone.
08 mol. The reaction in the first step is preferably performed under cooling, and particularly preferably at a temperature in the range of -20 to 10C. The reaction time is preferably 5 minutes to 1 hour, more preferably 10 minutes to 30 minutes.

Although not wishing to be bound by any theory, it is believed that the reaction in the first step produces an alkoxycycloalkane peroxide and becomes a reactant in the next second step. It is preferable that the alkoxycycloalkane peroxide generated by the reaction of the first step is subjected to the reaction of the second step without isolation.

The second step is a step of reacting the product of the first step with a reducing metal catalyst in the presence of an unsaturated dicarboxylic acid ester. The unsaturated dicarboxylic acid ester used in the second step has a structure represented by the general formula (1), wherein R ¹ represents an alkyl group having 1 to 5 carbon atoms which may have a branch. Specific examples of R ¹ include methyl, ethyl, n
-Propyl, isopropyl, n-butyl, isobutyl,
Examples include tert-butyl, n-pentyl, neopentyl, and amyl.

As the unsaturated dicarboxylic acid ester represented by the general formula (1), methyl 2-methyleneglutarate,
Ethyl 2-methyleneglutarate, n-propyl 2-methyleneglutarate, isopropyl 2-methyleneglutarate, n-butyl 2-methyleneglutarate, isobutyl 2-methyleneglutarate, tert-2-methyleneglutarate
t-butyl can be mentioned. One of these unsaturated dicarboxylic acid esters may be used alone, or two or more thereof may be used in combination.

In the reaction of the second step, an unsaturated dicarboxylic acid ester is added to the reaction mixture obtained in the first step, and the reducing metal catalyst is added as it is with stirring, or the reducing metal catalyst is added to the reaction mixture in the first step. It is preferable to carry out by dropping a suspension or a homogeneous solution as much as possible dissolved in the alcohol used in the step. The suspension or the homogeneous solution is preferably prepared by suspending or dissolving in a 2 to 4 times amount of alcohol with respect to the reducing metal catalyst. If nitrogen gas is present in the preparation, the reaction of the second step can be performed efficiently. The amount of the unsaturated dicarboxylic acid ester used is preferably from 1 to 1 per mole of cycloalkanone.
0 mol, more preferably 1.1 to 5 mol.

Examples of the reducing metal catalyst include sulfates, chlorides, ammonium salts and hydrates of metals such as iron, copper, cobalt, titanium and tin. Among them, ferrous salts are used. Is preferred. Examples of the ferrous salt include ferrous sulfate, ferrous chloride, ammonium ferrous sulfate, and hydrates thereof. Among them, ferrous sulfate is particularly preferable because it can be recovered by reduction with sulfuric acid and iron after the reaction, and can be advantageously reused. In the second step, two or more reducing metal catalysts may be used in combination. The amount of the reducing metal catalyst used in the second step is
Preferably 0.8 to 1. 1 mole of cycloalkanone.
It is 3 mol, more preferably 0.9 to 1.2 mol, most preferably 1.0 to 1.1 mol.

The reaction in the second step is preferably performed under cooling, more preferably at a temperature in the range of -20 to 10 ° C, and particularly preferably at a temperature in the range of -10 to 5 ° C. . The reaction time is preferably 0.1 to 5 hours, more preferably 0.3 to 2 hours. In order to decompose the alkoxycycloalkane peroxide which may remain after the reaction, it is preferable to add an acid such as sulfuric acid.

After completion of the second step, the reaction solution may be subjected to a post-treatment such as removal of the reducing metal catalyst used, and then subjected to the reaction of the third step as it is as the reaction mixture, or may be further purified. To the third step. When purifying,
By appropriately selecting purification conditions, a single compound may be isolated, or a mixture of a plurality of compounds may be obtained.
When a mixture of a plurality of compounds is obtained, the ratio of components can be adjusted by utilizing the chemical or physical properties of each component. However, when the purpose is to prepare an electrolytic solution for an electrolytic capacitor, it is necessary to subject the product obtained in the second step to the third step without changing the ratio of the tricarboxylic acid ester in the spark voltage or the solubility. It is preferable from the point of view.

The tricarboxylic acid ester obtained in the second step is converted into a tricarboxylic acid by ester hydrolysis in the third step. The method of ester hydrolysis is performed using any of the methods well known to those skilled in the art. For example, hydrolysis can be performed by adding an acid or an alkali. The reaction solution obtained in the third step may be subjected to post-treatment and purified in the same manner as the reaction solution obtained in the second step. When the purpose is to prepare an electrolytic solution for an electrolytic capacitor, it is preferable that the ratio of tricarboxylic acid in the product obtained in the third step is not changed.

The tricarboxylic acid of the present invention can be produced by carrying out the above three-step production method. However, the production method of the tricarboxylic acid of the present invention is not limited to the above three-step method. Absent. That is, any compound having the same structure as the tricarboxylic acid produced by the above three-step production method is included in the scope of the present invention regardless of the production method. For example, tricarboxylic acids synthesized by appropriately combining synthesis reactions known to those skilled in the art, and even tricarboxylic acids extracted from appropriate natural resources or artificial materials, tricarboxylic acids produced by the method comprising the above three steps As long as it has the same structure as described above, it is included in the scope of the present invention.

The tricarboxylic acids of the present invention are all excellent in chemical stability. For this reason, it exists stably even during long-term storage or high temperature, and its chemical and physical properties can be maintained. Further, the tricarboxylic acid of the present invention has high solubility in alcoholic solvents such as ethylene glycol. Further, when used as an electrolytic solution for an electrolytic capacitor, there is an excellent advantage that spark voltage and electric conductivity are increased. Therefore, by using the tricarboxylic acid of the present invention, it is possible to provide an electrolytic capacitor that has a low loss, a high rated voltage, and is less likely to precipitate crystals even when left at rest for a long period of time.

When an electrolytic solution for an electrolytic capacitor is produced using the tricarboxylic acid of the present invention, only one of the tricarboxylic acids of the present invention may be selected and used alone, or two or more may be used in combination. May be. When two or more kinds are used in combination, it is preferable to use the same without changing the ratio of the tricarboxylic acid in the product obtained by the above three steps as described above.

The salt of the tricarboxylic acid of the present invention can also be used in the electrolytic solution for electrolytic capacitors. The method for forming the salt is not particularly limited, and can be performed according to a method well-known to those skilled in the art. Usually, it is an ammonium salt. For example, triethylmethylammonium salt, diethyldimethylammonium salt, triisopropylmethylammonium salt, dimethyldiisopropylammonium salt, dibutyldimethylammonium salt, ethyldimethylisopropylammonium salt, dimethylallylammonium salt, diallylmethylammonium salt and the like can be used. In addition, as salts other than ammonium salts, for example, quaternary salts of cyclic amidine compounds, quaternary phosphonium salts, and N, N-alkylenetetrahydrooxazinium compound salts can be used. These salts may be used in combination of two or more in the electrolytic solution for electrolytic capacitors.

The solvent used in the electrolytic solution for an electrolytic capacitor of the present invention can be selected and used without any particular limitation as long as it can dissolve the tricarboxylic acid of the present invention. Solvents that can be used in the electrolytic solution of the present invention include, for example, ethylene glycol, diethylene glycol, propylene glycol, glycerin, 1,4-
Alcohols such as butanediol, methylcellosolve and ethylcellosolve; lactones such as γ-butyrolactone; carbonates such as ethylene carbonate and propylene carbonate; methylformamide, dimethylformamide, ethylformamide, diethylformamide, methylacetamide, dimethylacetamide Amides such as, ethylacetamide and diethylacetamide;
Examples thereof include nitriles such as acetonitrile; oxides such as dimethyl sulfoxide; sulfolane and N-methylpyrrolidone. Among them, ethylene glycol and γ-
Butyrolactone is preferred. One of these solvents may be used alone, or two or more thereof may be used in combination as a mixed solvent. Further, the electrolytic solution for an electrolytic capacitor of the present invention may contain water, but when water is used, the content is 30% by weight or less, preferably 10% by weight or less of the electrolytic solution.

The composition ratio of the solute and the solvent in the electrolytic solution for an electrolytic capacitor of the present invention is not particularly limited, but it is particularly preferable that the weight ratio is in the range of 5:95 to 30:70. Further, components other than the above-mentioned solute and solvent can be added to the electrolytic solution for an electrolytic capacitor of the present invention, if necessary.

The present invention also provides an electrolytic capacitor using the electrolytic solution for an electrolytic capacitor. The structure and material of the electrolytic capacitor of the present invention are not particularly limited as long as the electrolytic solution for the electrolytic capacitor is used. Therefore, all cases where the electrolytic solution for an electrolytic capacitor of the present invention is used for a conventionally used electrolytic capacitor or a newly proposed electrolytic capacitor are included in the scope of the present invention.

As a typical configuration example of the electrolytic capacitor of the present invention, a wound element structure shown in FIG. 1 can be exemplified. In this example, a cathode foil (2) is arranged so as to face the anode foil (1), and is wound with a separator (3) interposed therebetween. This is placed in an outer case made of aluminum (6), and the case is sealed with a sealing material (5) such as a phenol laminate, polypropylene, or polyphenylene sulfide via packing such as butyl rubber, ethylene propylene rubber, or silicone rubber. This makes it an electrolytic capacitor. The electrolytic solution for an electrolytic capacitor of the present invention is used for a separator (3) sandwiched between an anode foil and a cathode foil. Kraft paper, manila paper, or the like is generally used for the separator, but the separator is not particularly limited thereto.
The electrolytic capacitor of the present invention is characterized in that both the spark voltage and the electrical conductivity are high, and that the crystal is unlikely to precipitate even during operation at a low temperature even when left for a long time.

[0031]

The present invention will be described more specifically with reference to the following examples. The materials, usage amounts, ratios, operations, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples.

Example 1 50 ml of anhydrous methanol was placed in a flask equipped with a stirrer, cooled to 5 ° C., and 4.91 g of cyclohexanone and 0.29 g of concentrated sulfuric acid were added. 0.72 g was added dropwise, and 8
The reaction was continued while stirring at 10 ° C. for 10 minutes. 10.33 g of methyl 2-methyleneglutarate was dissolved in this reaction solution, and ferrous sulfate (heptahydrate) 14.7 was dissolved under a nitrogen stream.
4 g was gradually added while maintaining the reaction temperature at -20 to -5 ° C, and the reaction was carried out for 45 minutes. After the reaction, 50% sulfuric acid aqueous solution 1
0 ml was added and methanol was distilled off with an evaporator.
Extracted with diethyl ether. The diethyl ether layer was washed with water and dried, and the diethyl ether was distilled off to obtain 15.9 g of trimethyl tricarboxylate. The obtained trimethyl tricarboxylate was analyzed by gas chromatography, and as a result, it was confirmed that at least three or more kinds of the mixtures had a molecular weight of 302.

The tricarboxylic acid trimethyl ester mixture was dissolved in methyl alcohol (50 ml), and a 50% aqueous solution of sodium hydroxide (10.4 g) was added thereto. The mixture was heated to reflux for hydrolysis to give a tricarboxylic acid mixture (9.5).
3 g were obtained. The resulting mixture is mixed with ethylene glycol 3
The solution was dissolved in 8.12 g, and ammonia was blown into the solution to obtain a 20% by weight ammonium salt ethylene glycol solution. The pH of the solution was 6.61.

The water concentration of this solution was adjusted to about 1%, and the performance as an electrolyte was evaluated. First, the conductivity at 25 ° C. was measured, and then the low-temperature solubility was evaluated based on the presence or absence of solid precipitation when cooled to −20 ° C., −40 ° C., and −70 ° C. X, and when it was dissolved without precipitation, it was marked as ○). Further, the wound element shown in FIG. 1 was impregnated with an electrolytic solution, and a voltage value at which a spike or scintillation was first observed in a voltage-time rising curve when a constant current of 3 mA was applied was recorded as a spark voltage. The specifications of the aluminum electrolytic capacitor element used were a rated voltage of 550 WV and a capacitance of 10 μF.
Table 1 summarizes the measurement results of the conductivity and the spark voltage and the evaluation results of the low-temperature solubility.

Example 2 50 ml of anhydrous methanol was placed in a flask equipped with a stirrer, cooled to 5 ° C.
7.71 g of rt butyl cyclohexanone and concentrated sulfuric acid 0.1 g.
4. Add 29 g and stir while stirring 30% aqueous hydrogen peroxide.
72 g was added dropwise, and the reaction was continued while stirring at 8 ° C. for 10 minutes. Ethyl 2-methyleneglutarate (11.89 g) was dissolved in the reaction solution, and ferrous sulfate (heptahydrate) (14.74 g) was added under a nitrogen stream at a reaction temperature of -20 to -5 ° C.
, And reacted for 45 minutes. After the reaction, 10 ml of a 50% aqueous sulfuric acid solution was added, methanol was distilled off by an evaporator, and the mixture was extracted with diethyl ether. The diethyl ether layer was washed with water and dried, and the diethyl ether was distilled off.
0.31 g was obtained. As a result of analysis by gas chromatography, it was confirmed that the obtained tricarboxylic acid diethylmethyl ester was a mixture of at least three or more kinds, and all had a molecular weight of 386.

This mixture of diethyl methyl tricarboxylate was dissolved in 50 ml of methyl alcohol, and a 50% aqueous solution of 12.26 g of sodium hydroxide was added thereto, followed by hydrolysis by heating under reflux to obtain 13.6 g of a mixture of tricarboxylic acids. This mixture is mixed with ethylene glycol 5
The solution was dissolved in 4.4 g, and ammonia was blown into the solution to obtain a 20% by weight ammonium salt solution of ethylene glycol. The pH of the solution was 6.65. An electrolytic solution was prepared in the same manner as in Example 1, the electrical conductivity and the spark voltage were measured, and the low-temperature solubility was evaluated. The results are shown in Table 1.

Example 3 50 ml of anhydrous methanol was placed in a flask equipped with a stirrer and cooled to 5 ° C.
7.01 g of 5-trimethylcyclohexanone and 0.29 g of concentrated sulfuric acid were added, and while stirring, 5.72 g of 30% aqueous hydrogen peroxide was added dropwise. The reaction was continued for 10 minutes while maintaining the temperature at 8 ° C. Ethyl 2-methyleneglutarate (11.89 g) was dissolved in the reaction solution, and ferrous sulfate (heptahydrate) (14.74 g) was added thereto under a nitrogen stream at a reaction temperature of -20 to -5.
While maintaining the temperature at ° C, the mixture was gradually added and reacted for 45 minutes. After the reaction, 10 ml of a 50% aqueous sulfuric acid solution was added, methanol was distilled off by an evaporator, and the mixture was extracted with diethyl ether.
The diethyl ether layer was washed with water and dried, and the diethyl ether was distilled off to obtain 18.07 g of diethyl methyl tricarboxylate. As a result of analysis by gas chromatography, it was confirmed that the obtained trimethyl carboxylate was a mixture of at least three or more kinds, and all had a molecular weight of 372.

This mixture of diethylmethyl tricarboxylate was dissolved in 50 ml of methyl alcohol, and a 50% aqueous solution of 11.38 g of sodium hydroxide was added thereto, followed by hydrolysis by heating under reflux to obtain 7.8 g of a mixture of tricarboxylic acids. This mixture is mixed with ethylene glycol 3
The resultant was dissolved in 1.2 g, and ammonia was blown into the solution to obtain a 20% by weight ammonium salt solution of ethylene glycol. The pH of the solution was 6.63. An electrolytic solution was prepared in the same manner as in Example 1, the electrical conductivity and the spark voltage were measured, and the low-temperature solubility was evaluated. The results are shown in Table 1.

Comparative Example 1 An electrolytic solution was prepared in the same manner as in Example 1 using an ethylene glycol solution of an ammonium salt of adipic acid (10% by weight), and the electric conductivity and the spark voltage were measured. Are shown in Table 1.

[0040]

[Table 1]

[0041]

The results in Table 1 show that the electrolytic capacitor of the present invention has high electric conductivity and high spark voltage. Therefore, by using the present invention, it is possible to provide an electrolytic capacitor having a lower loss and a higher rated voltage. Further, the electrolytic capacitor of the present invention also has an advantage that it is difficult to precipitate crystals even when the capacitor is left for a long period of time or during operation at a low temperature.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structural example of an electrolytic capacitor.

[Explanation of symbols]

 1: anode foil 2: cathode foil 3: separator 4: lead wire 5: sealing material 6: outer case

Claims (7)

[Claims] 1. A tricarboxylic acid obtained by subjecting a cycloalkanone having a total of 4 to 14 carbon atoms to Fenton oxidation in the presence of an unsaturated dicarboxylic acid ester represented by the general formula (1), followed by hydrolysis. Embedded image (Wherein, R ¹ represents an alkyl group having 1 to 5 carbon atoms which may have a branch) 2. The tricarboxylic acid according to claim 1, wherein the cycloalkanone is cyclohexanone or 3,3,5-trimethylcyclohexanone. 3. A plurality of tricarboxylic acids obtained by subjecting a cycloalkanone having a total of 4 to 14 carbon atoms to Fenton oxidation in the presence of an unsaturated dicarboxylic acid ester represented by the general formula (1), and then hydrolyzing the cyclocarboxylic acid. A composition comprising: Embedded image (Wherein, R ¹ represents an alkyl group having 1 to 5 carbon atoms which may have a branch) 4. The composition according to claim 3, wherein said cycloalkanone is cyclohexanone or 3,3,5-trimethylcyclohexanone. 5. An electrolytic solution for an electrolytic capacitor obtained by dissolving the tricarboxylic acid and / or its salt according to claim 1 in a solvent. 6. The method according to claim 1, wherein the solvent is ethylene glycol and γ-
The electrolytic solution for an electrolytic capacitor according to claim 5, which is one or more solvents selected from the group consisting of butyrolactone. 7. An electrolytic capacitor using the electrolytic solution for an electrolytic capacitor according to claim 5 or 6.