JPH0696569B2 - Method for producing 2-furancarboxylic acid - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing 2-furancarboxylic acid.

Conventional technology and its problems 2-furancarboxylic acid is generally a pharmaceutical intermediate, fragrance,
Raw materials for agricultural chemicals and resins, and their derivatives are also useful substances used for various purposes.

Conventionally, as a method for producing 2-furancarboxylic acid, for example, alkali hydroxide such as sodium hydroxide and furfural are dropped in parallel in the presence of a metal oxide catalyst such as silver, platinum, or palladium, and oxygen or air is used. How to oxidize (Or
ganic Syntheses coll Vol.4 p.493-496), a method in which alkali hydroxide and furfural are added in parallel and sodium hypochlorite is used as an oxidizing agent (Japanese Patent Publication No. 25-1130).
No.), method by the Cannizzaro reaction (Organic Synthe
ses coll Vol.1 p.276-280) etc. are known. However, in these conventional production methods, the reaction is always performed in the presence of an alkali hydroxide such as sodium hydroxide (pH is not adjusted in the conventional method, and the pH of the reaction system is not adjusted).
It has become strongly alkaline over 11.5), and the Cannizzaro reaction progresses as a side reaction (or main reaction).
Furfuryl alcohol is produced as a by-product in addition to furancarboxylic acid. By the way, since 2-furancarboxylic acid is mainly used as an intermediate for medicines and agricultural chemicals as described above,
Used as a high-purity single item. Therefore, in the conventional method, the furfuryl alcohol must be removed after the 2-furancarboxylic acid is produced. As a method for removing furfuryl alcohol, for example, a solvent extraction method,
The steam distillation method and the like are known. However, in the solvent extraction method, furfuryl alcohol cannot be completely removed because it is well soluble in water. On the other hand, the furfuryl alcohol cannot be completely removed even by the steam distillation method, which is industrially expensive and is not preferable. Further, the obtained 2-furancarboxylic acid has a drawback that it is colored by furfuryl alcohol.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to provide a method for producing 2-furancarboxylic acid from furfural with high selectivity without producing furfuryl alcohol as a by-product. It is to provide a method for producing 2-furancarboxylic acid with high yield and high purity by further increasing the exchange rate of furfural as a raw material.

Means for Solving the Problems The object of the present invention is achieved by the following method for producing 2-furancarboxylic acid.

When furfural is oxidized with oxygen in the presence of a metal oxide catalyst to synthesize 2-furancarboxylic acid, an alkali metal salt is further present in the reaction system and the pH of the reaction system is adjusted to 9%.
The method for producing 2-furancarboxylic acid is characterized in that the oxidation reaction is carried out while maintaining the range of 1 to 11.5, and an alkali metal hydroxide is present together with an alkali metal salt in the reaction system and the pH of the reaction system is 9 to 11.5. The method for producing 2-furancarboxylic acid is characterized in that the oxidation reaction is carried out while maintaining the above range.

According to the research conducted by the present inventor, when furfural is oxidized with oxygen in the presence of a metal oxide catalyst to synthesize 2-furancarboxylic acid, an alkali metal salt is further present in the reaction system, and It was found that by carrying out the oxidation reaction while maintaining the pH at 9 to 11.5, 2-furancarboxylic acid can be selectively obtained without the by-product of furfuryl alcohol. Further, alkali hydroxide is present in the reaction system together with an alkali metal salt, and the above pH range, that is, pH 9
When the oxidation reaction is carried out in the range of up to 11.5, the conversion rate of the furfural starting material is significantly improved while maintaining the above selectivity, and therefore 2-furancarboxylic acid can be obtained with high selectivity and high yield. Was found.

In the present invention, the metal oxide catalyst may be any known metal oxide catalyst used in this type of reaction, for example, a main catalyst selected from oxides of silver, gold, platinum, palladium and the like. Examples thereof include a co-catalyst selected from oxides of copper, iron, nickel and the like and having catalytic activity in the alkaline region. Among them, silver oxide-copper oxide catalysts are preferable. The ratio of silver oxide to copper oxide in this catalyst is not particularly limited and may be appropriately selected. Usually, the molar ratio (silver oxide / copper oxide) is about 1/100 to 1/1. . The catalyst is prepared according to a known method, for example, by dropping an aqueous solution of a mixture of copper sulfate pentahydrate and silver nitrate into a 5 wt% NaOH solution heated to 80 ° C. in a hot water bath to form an oxide. After that, it can be obtained by leaving it to stand and performing washing. Further, the catalyst is, for example, after completion of the synthesis of 2-furancarboxylic acid, passed through a catalyst and washed with water,
Then, it can be reused by suspending it in a 5% by weight aqueous NaOH solution heated to 80 ° C. in a hot water bath and further repeating washing with water and drying. Thus, the catalyst can be used semi-permanently if it is regenerated, which is economical. The amount of the metal oxide catalyst used is not particularly limited and may be appropriately selected,
Usually, it may be about 2.5 to 10 parts by weight with respect to 100 parts by weight of furfural.

As the alkali metal salt, any known salt can be used, and examples thereof include sodium carbonate, sodium monohydrogen phosphate, potassium carbonate, sodium acetate and the like. The amount of the alkali metal salt used is not particularly limited and may be appropriately selected so that the pH of the reaction system is in the range of 9 to 11.5, but is usually about 0.5 to 2.0 mol per 1 mol of furfural. In the present invention, the alkali metal salt is used in the form of an aqueous solution. The concentration of the alkali metal salt in the aqueous solution is not particularly limited as long as it satisfies the above-mentioned usage amount, but normally, the one dissolved in the minimum amount of water, that is, the saturated state may be used.

In the present invention, in order to further improve the conversion rate of furfural to 2-furancarboxylic acid, alkali hydroxide may be used together with the alkali metal salt. Even when alkali hydroxide is used in combination, it is necessary to keep the pH of the reaction system within the range of 9 to 11.5.

Known alkali hydroxides can be used, and examples thereof include sodium hydroxide, lithium hydroxide, potassium hydroxide, and calcium hydroxide. The amount of alkali hydroxide used is such that the cation equivalent ratio of alkali hydroxide and alkali metal salt (alkali hydroxide / alkali metal salt) is about 25/75 to 75/25, preferably about 70/30 to 75/25. It should be so. The equivalent ratio of alkali hydroxide is 75
If it exceeds, it tends to be difficult to control the pH of the reaction system,
On the other hand, if it is less than 25, the reaction rate becomes slow and the reaction time becomes long, which is not preferable. In the present invention, alkali hydroxide is used in the form of an aqueous solution. The concentration of the alkali hydroxide in the aqueous solution is not particularly limited and may be appropriately selected within the range satisfying the above cation equivalent ratio, but is usually the same as the case of the alkali metal salt alone, that is, the saturated state is used. do it.

In addition, in the present invention, when alkali hydroxide is added in an amount of 0.9 equivalent or more, particularly about 0.9 to 1.1 equivalent to 1 equivalent of furfural as a raw material after satisfying the above cation equivalent ratio,
2-furancarboxylic acid can be obtained in a higher yield. If it exceeds 1.1 equivalents, there is no particular advantage, and the post-treatment tends to be complicated, and if it is less than 0.9 equivalents, unreacted furfural tends to remain.

The reaction in the present invention needs to be carried out while maintaining the pH of the reaction system within the range of 9 to 11.5. If the pH exceeds 11.5, furfuryl alcohol may be produced as a by-product. On the other hand, if the pH is less than 9, the reaction is difficult to proceed and the yield of 2-furancarboxylic acid decreases.

The reaction may be carried out usually in an aqueous system according to a known method.
Specifically, for example, in an aqueous solution containing a metal oxide catalyst,
Along with furfural, a method of concurrently dropping an alkali metal salt or an alkali metal salt and alkali hydroxide so that the pH of the reaction system falls within the above-specified range, an aqueous solution containing a metal oxide catalyst and furfural, and the pH of the reaction system is Examples thereof include a method of dropping an alkali metal salt or an alkali metal salt and an alkali hydroxide so as to fall within the above-specified range, but the method is not limited thereto, and any method capable of controlling pH within the above-specified range may be used. Good. In the above method, when the alkali metal salt and the alkali hydroxide are used in combination, an aqueous solution containing the alkali hydroxide and the alkali metal salt may be added dropwise, and the alkali hydroxide aqueous solution and the alkali metal salt aqueous solution are separately prepared. You may drop. In the present invention, it is necessary to add a known oxidizing agent such as oxygen to the reaction system. Oxygen may be supplied using an introduction pipe, but oxygen in the air may be used as it is for air oxidation. The reaction temperature is usually about 20 to 65 ° C, preferably about 50 to 60 ° C. If the temperature exceeds 65 ° C, the reaction becomes violent and the reaction control becomes difficult, which is not preferable. The reaction is difficult to proceed below 20 ° C. The reaction time may be appropriately selected according to the amount of the alkali metal salt aqueous solution, the alkali hydroxide aqueous solution, the metal oxide catalyst, etc. used, but it is usually about 4 to 6 hours, preferably 4.5.
It should be about 5.5 hours. After completion of the reaction, according to a known method, for example, the obtained reaction aqueous solution is passed over and the solution is treated with sulfuric acid or the like to precipitate 2-furancarboxylic acid,
High-purity crystals can be obtained by subsequent passing, but may be recrystallized with water, benzene, or the like. still,
In the above reaction, when furfural does not completely react and remains partially unreacted, for example, a solvent extraction method,
Furfural and 2- by a known method such as steam distillation method
It can be easily separated from furancarboxylic acid.

EFFECTS OF THE INVENTION According to the present invention, a production method capable of selectively obtaining 2-furancarboxylic acid from furfural without by-producing furfuryl alcohol, and 2-furancarboxylic acid without impairing the selectivity. There is provided a production method capable of obtaining a high purity and a high yield. Further, since the reaction and operation of the production method are simple, they are suitable for industrial scale-up.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to these examples.
In the examples, all parts and% are by weight unless otherwise specified.

Example 1 In a 1-volume flask equipped with a condenser, a stirrer, two dropping funnels, a thermometer and an oxygen introducing tube, 400 ml of water and a silver oxide-copper oxide catalyst (AgNO ₃ / CuSO ₄ 5H ₂ O = 0.013 / 0.107 molar ratio) 10 parts was added and the temperature was raised to 60 ° C. with stirring. Start blowing oxygen (flow rate 1.0 l / min) and furfural 9
6 parts (1.0 mol) for 3 hours and sodium hydroxide 30.0
Parts (0.75 mol) and sodium carbonate 13.25 parts (0.125 mol)
150 parts of an alkaline aqueous solution containing and was added dropwise from another dropping funnel over 3.5 hours. Further, 50 parts of an alkaline aqueous solution having the same composition was added and the reaction was carried out for a total of 5.5 hours. During the reaction
The reaction temperature was 60 ° C., and the pH was measured at any time using a pH meter and kept at 11.0-11.1. The reaction was monitored by liquid chromatography. After the reaction is complete, cool to room temperature,
The liquid and the catalyst were separated by filtration. The obtained liquid
The mixture was treated with 30% sulfuric acid, cooled overnight, and then dried to obtain 95 parts (yield 85%) of 2-furancarboxylic acid having a white powder and a melting point of 130 to 131 ° C.

Example 2 The procedure of Example 1 was repeated except that sodium hydrogen phosphate was used instead of sodium carbonate in the alkaline aqueous solution, and the pH was adjusted to 10.5 to 10.8. White powder, melting point 130-131
93 parts of 2-furan carboxylic acid (yield 83%) were obtained.

Example 3 As Example 1, except that 150 parts of an aqueous alkali solution containing 106 parts (1 mol) of sodium carbonate were used, the pH was adjusted to 9.1, and unreacted furfural was removed by steam distillation after completion of the reaction. The same operation was performed, and 16 parts of 2-furancarboxylic acid having a white powder and a melting point of 130 to 131 ° C (yield
14%).

In the above Examples 1 to 3, furfuryl alcohol was not produced as a by-product at all.

Comparative Example 1 The same operation as in Example 1 was carried out except that as the alkaline aqueous solution, 150 parts containing 40 parts (1 mol) of sodium hydroxide was used. The pH at this time was 12.5. Analysis by liquid chromatography revealed that 2-furancarboxylic acid was 84% and furfuryl alcohol was 16% in the reaction solution. Extraction was performed with toluene and 1,2-dichloroethane, and steam distillation was performed.
Furfuryl alcohol cannot be completely removed,
The obtained 2-furancarboxylic acid was brown crystals.

Claims (5)

[Claims] 1. When synthesizing 2-furancarboxylic acid by oxidizing furfural with oxygen in the presence of a metal oxide catalyst, an alkali metal salt is further present in the reaction system and the pH of the reaction system is 9 to 11.5. A method for producing 2-furancarboxylic acid, which comprises carrying out an oxidation reaction while maintaining the range. 2. The production method according to claim 1, wherein the oxidation reaction is carried out in the presence of an alkali hydroxide together with an alkali metal salt. 3. The method according to claim 1, wherein the metal oxide catalyst is silver oxide-copper oxide. 4. The method according to claim 1 or 2, wherein the alkali metal salt is sodium carbonate or sodium dihydrogen phosphate. 5. The production method according to claim 2, wherein the alkali hydroxide is sodium hydroxide or potassium hydroxide.