JPH11228502A - Preparation of pyruvic acid ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a pyruvic acid ester by which the pyruvic acid ester is industrially produced without using a catalyst such as bromine and further without requiring a high grade drainage treatment by oxidizing a lactic acid ester with chlorine under irradiation of light in an organic solvent. SOLUTION: A lactic acid ester of 1 pt.wt. in an aromatic compound-based or halogenated aliphatic hydrocarbon-based organic solvent, preferably benzonitrile, monochlorobenzene or dichlorobenzene, of 5-50 pts.wt. is oxidized by chlorine gas of 1.2-1.7 mol equivalent based on the lactic acid ester under irradiation of light such as the light of a halogen lamp to provide the objective pyruvic acid ester in the method for producing the pyruvic acid ester.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a pyruvate ester, and more particularly, to a method for producing a pyruvate ester which is free of wastewater containing water-soluble organic substances and which is easy to treat a waste liquid and is suitable for industrialization. About the method.

[0002]

2. Description of the Related Art Pyruvate is used as an intermediate in the production of many chemicals such as fragrances, food additives, and electronic materials. In addition, pyruvate is an intermediate in the metabolic pathway of biological substances. Therefore, it is attracting attention as a raw material when producing various physiologically active substances, and is also important as a raw material for producing pharmaceuticals and the like.In recent years, it has also been used as a solvent and the like in the production of semiconductors and the like. As a result, there is a tendency that the demand for these compounds is extremely important and is increasing.

[0003] As a method for producing this pyruvate ester, several methods have been conventionally proposed. Typically, a lactate ester which is industrially available at low cost is used as a raw material, and lactate dehydrogenase or lactate is used. Oxidatively using a microorganism having a dehydrogenase, or by chemical oxidation using an oxidizing agent such as potassium permanganate or hydrogen peroxide, or by catalytic catalytic oxidation using a noble metal catalyst such as palladium. Methods for dehydrogenation are known.

[0004] However, both of these methods have high B
A large amount of OD wastewater, lack of selectivity for oxidation reaction, or incomplete oxidation reaction. However, there is a problem that an excessive burden is required for post-processing and the like.

Therefore, a first method of oxidizing a lactate ester in bromine water under light irradiation (Ciusa, Atti Accad. Naz. Li
ncei Cl. Sci. Fis. Mat. Nat. Rend., 25, (6), p637
(1937)) and a second method of oxidizing a lactate ester in an aqueous solution of hydrogen peroxide in the presence of a catalytic amount of bromine (Japanese Patent Application Laid-Open No.
No. 42554) and a third method of oxidizing a lactate ester with chlorine or hypochlorite by irradiating light in the presence of a catalytic amount of bromine or a bromine compound and water (JP-A-5-33920).
No. 8) has been proposed.

However, since all of these methods use water as a solvent or as a means for dissolving an oxidizing agent, the lactic acid ester as a raw material and the pyruvic acid ester formed during the reaction undergo hydrolysis. As a result, the yield decreases, or wastewater containing soluble organic substances and salts is generated, and furthermore, the reaction uses bromine as a catalyst. Costly waste liquid treatment such as treatment is inevitably required.

Further, in the first and second methods, bromine and hydrogen peroxide used as an oxidizing agent are expensive and not economical, and in the third method, they are used as an oxidizing agent. Hydrochloric acid is by-produced from chlorine and hypochlorite, but hydrogen bromide from bromine used as a catalyst is mixed into the by-product hydrochloric acid as an impurity, and this by-product hydrochloric acid cannot be industrially recovered. There is also.

[0008]

Therefore, the present inventors have used a commercially available lactic acid ester as a raw material and a relatively inexpensive oxidizing agent without using a catalyst such as bromine. Moreover, as a result of intensive studies on a method capable of producing a pyruvate ester that does not require advanced wastewater treatment, the lactic acid ester is oxidized with chlorine under light irradiation in an organic solvent, so that a high yield is obtained. The present inventors have found that a pyruvate can be produced industrially advantageously, and have completed the present invention.

Therefore, an object of the present invention is to use a lactate ester as a raw material, a relatively inexpensive oxidizing agent without using a catalyst such as bromine, and eliminate the need for advanced wastewater treatment.
Moreover, it is an object of the present invention to provide a method for producing a pyruvate ester, which can industrially produce a pyruvate ester in a high yield.

[0010]

That is, the present invention is a method for producing pyruvate, which oxidizes lactate with chlorine in an organic solvent under light irradiation. And, preferably, the organic solvent is an aromatic compound-based solvent or a halogenated aliphatic hydrocarbon-based solvent having a halogen atom in the molecule, and more preferably, the organic solvent is benzonitrile, Monochlorobenzene or dichlorobenzene.

In the present invention, the lactic acid ester used as a raw material may be a commercially available lactic acid ester or a lactic acid ester produced by a known method. Preferably, the alkyl group ester-bonded to lactic acid is a methyl group, Those having 1 to 4 carbon atoms such as ethyl group, n-propyl group, iso-propyl group, n-butyl group and tert-butyl group are used.

The chlorine used as the oxidizing agent may be a commercially available product or a product produced by a known method. When using chlorine, a high-concentration chlorine gas may be directly introduced into the reaction system. Alternatively, it may be introduced after being diluted with an inert gas such as nitrogen gas to a concentration that can be easily handled. The amount of chlorine used is preferably 1.2 to 1.7 molar equivalents with respect to the lactic acid ester. If the amount of chlorine used is less than 1.2 molar equivalents to the lactate ester, unreacted lactate ester remains in the reaction mixture,
Since the boiling point of this lactate ester is relatively close to the boiling point of the target pyruvate ester, a high degree of distillation purification is required when recovering the pyruvate ester from the reaction mixture, and also causes a decrease in yield, On the other hand, when it is more than 1.7 molar equivalents, chlorination by-products are formed, which causes a decrease in yield.

In the present invention, an organic solvent is used as a reaction solvent. As this organic solvent, it is preferable that it be inert to lactate and chlorine and dissolve these lactate and chlorine. As such an organic solvent, from the viewpoint of a general photo-chlorinated solvent,
Preferably aromatic solvents and halogenated hydrocarbon solvents having a halogen atom in the molecule and the like, specifically,
Examples include aromatic compound solvents such as benzene, benzonitrile, nitrobenzene, monochlorobenzene, dichlorobenzene, and trichlorobenzene, and halogenated aliphatic hydrocarbon solvents such as dichloromethane, chloroform, carbon tetrachloride, dichloroethane, and trichloroethane. . Further, from the viewpoint of stability under reaction conditions, benzonitrile, monochlorobenzene, or dichlorobenzene is more preferable.

The amount of the organic solvent to be used is preferably in the range of 5 to 50 parts by weight per 1 part by weight of the lactic acid ester. The problem is that the yield is reduced, and conversely,
If it exceeds 50 parts by weight, there is a problem that it is not economical from the viewpoint of volumetric efficiency.

In the present invention, the reaction is carried out by dissolving a lactate ester in an organic solvent, and irradiating the light with a halogen lamp such as a fluorescent lamp, an incandescent lamp or a high-pressure mercury lamp, and converting the chlorine into chlorine gas with stirring. The reaction is preferably performed while maintaining the reaction temperature in the range of -10 to 80C, more preferably in the range of 0 to 50C, and even more preferably in the range of 10 to 40C. In order to lower the reaction temperature industrially below −10 ° C., a cooling device is required, which is not economical, and when it exceeds 80 ° C., the yield decreases due to an increase in by-products such as chlorinated products.

The progress of the reaction is preferably determined by measuring the lactate ester in the reaction system over time by means such as gas chromatography, and the conversion of the lactate ester is 5.0% or less, preferably 1.0% or less. React until And
After completion of the reaction, an inert gas such as nitrogen is preferably introduced into the reaction system to remove chlorine remaining in the reaction mixture to the outside of the system. The reaction mixture thus obtained is separated and purified by a conventional method such as distillation under reduced pressure to obtain a target pyruvate.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below based on examples.

Example 1 A reaction vessel equipped with a condenser, an exhaust gas elimination device, and a cooling device was charged with 425 g (2.89 mol) of o-dichlorobenzene and 23.6 g (0.20 mol) of ethyl lactate. The reaction temperature was maintained at 30 ° C. under irradiation, chlorine gas was introduced at a rate of 0.06 g / min with stirring, and the oxidation reaction of ethyl lactate was carried out while bubbling the reaction system.

During this oxidation reaction step, the reaction mixture is sampled with time from the reaction system, and the concentration of ethyl lactate in the reaction mixture is measured by gas chromatography, and the concentration of ethyl lactate becomes 1.0% or less. At this point, the reaction was terminated. The reaction time until the end of the reaction is 6 hours,
The amount of chlorine used was 21.6 g (0.30 mol), and the chlorine utilization was 67%.

After completion of the reaction, nitrogen gas was introduced into the reaction system in place of chlorine gas, and the reaction mixture was bubbled for about 10 minutes to drive off excess chlorine from the reaction mixture.
As a result of analyzing the obtained reaction mixture by gas chromatography, the reaction yield to ethyl pyruvate was 90%, and the remaining ethyl lactate was 0.5%. Further, 457 g of the obtained reaction mixture was purified by distillation under normal pressure by a conventional method,
18.5 g of ethyl pyruvate having a purity of 99.2% (0.1
6 mol, 79.0%).

Example 2 A reaction vessel equipped with a condenser, an exhaust gas elimination device, and a cooling device was charged with 425 g (3.78 mol) of monochlorobenzene and 23.6 g (0.20 mol) of ethyl lactate, and irradiated with a high-pressure mercury lamp. The reaction temperature was maintained at 10 ° C., and chlorine gas was introduced at a rate of 0.06 g / min with stirring to perform an oxidation reaction of ethyl lactate while bubbling the reaction system.

During this oxidation reaction step, the reaction mixture is sampled with time from the reaction system, and the concentration of ethyl lactate in the reaction mixture is measured by gas chromatography, and the concentration of ethyl lactate becomes 1.0% or less. At this point, the reaction was terminated. The reaction time until the completion of the reaction was 6.5 hours, the amount of chlorine used was 23.4 g (0.33 mol), and the chlorine utilization was 61%.

After the completion of the reaction, nitrogen gas was introduced into the reaction system instead of chlorine gas, and the reaction mixture was bubbled for about 10 minutes to drive off excess chlorine from the reaction mixture.
As a result of analyzing the obtained reaction mixture by gas chromatography, the reaction yield to ethyl pyruvate was 80%, and the remaining ethyl lactate was 0.5%. Further, 460 g of the obtained reaction mixture was purified by distillation under normal pressure by a conventional method,
17.0 g of ethyl pyruvate having a purity of 99.3% (0.1
5 mol, 72.6%).

Example 3 425 g (4.12 mol) of benzonitrile was placed in a reaction vessel equipped with a condenser, an exhaust gas elimination device, and a cooling device.
And 23.6 g (0.20 mol) of ethyl lactate,
The reaction temperature was maintained at 10 ° C. under irradiation with a high-pressure mercury lamp, and chlorine gas was introduced at a rate of 0.06 g / min with stirring to perform an oxidation reaction of ethyl lactate while bubbling the reaction system.

During this oxidation reaction step, the reaction mixture is sampled with time from the reaction system, and the concentration of ethyl lactate in the reaction mixture is measured by gas chromatography, and the concentration of ethyl lactate becomes 1.0% or less. At this point, the reaction was terminated. The reaction time until the end of the reaction is 6 hours,
The amount of chlorine used was 21.6 g (0.30 mol), and the chlorine utilization was 67%.

After completion of the reaction, nitrogen gas was introduced into the reaction system in place of chlorine gas, and the reaction mixture was bubbled for about 10 minutes to drive off excess chlorine from the reaction mixture.
As a result of analyzing the obtained reaction mixture by gas chromatography, the reaction yield to ethyl pyruvate was 75%, and the remaining ethyl lactate was 0.5%. Further, 458 g of the obtained reaction mixture was purified by distillation under normal pressure by a conventional method,
16.2 g of ethyl pyruvate having a purity of 99.1% (0.1
4 mol, 69.8%).

Example 4 A reaction vessel equipped with a condenser, an exhaust gas elimination device, and a cooling device was charged with 425 g (2.89 mol) of o-dichlorobenzene and 20.8 g (0.20 mol) of methyl lactate. The reaction temperature was maintained at 30 ° C. under irradiation, chlorine gas was introduced at a rate of 0.06 g / min under stirring, and the methyl lactate oxidation reaction was performed while bubbling the reaction system.

During this oxidation reaction step, the reaction mixture is sampled over time from the reaction system, and the concentration of methyl lactate in the reaction mixture is measured by gas chromatography. At this point, the reaction was terminated. The reaction time until the end of the reaction is 6 hours,
The amount of chlorine used was 21.6 g (0.30 mol), and the chlorine utilization was 67%.

After completion of the reaction, nitrogen gas was introduced into the reaction system in place of chlorine gas, and the reaction mixture was bubbled for about 10 minutes to drive off excess chlorine from the reaction mixture.
As a result of analyzing the obtained reaction mixture by gas chromatography, the reaction yield to methyl pyruvate was 80%, and the remaining methyl lactate was 0.4%. Further, 453 g of the obtained reaction mixture was distilled and purified under normal pressure by a conventional method,
15.3 g of methyl pyruvate having a purity of 99.2% (0.1
5 mol, 74.9%).

Comparative Example 1 118.1 g (1.00 mol) of ethyl lactate was placed in a reaction vessel equipped with a condenser, an exhaust gas elimination device, and a cooling device.
The reaction was maintained at a reaction temperature of 30 ° C. under irradiation with a high-pressure mercury lamp, and a chlorine gas was introduced at a rate of 0.40 g / min with stirring to perform an oxidation reaction of ethyl lactate while bubbling the reaction system. The reaction was carried out for 5 hours, and the amount of chlorine used was 1
20.0 g (1.69 mol).

After completion of the reaction, nitrogen gas was introduced into the reaction system in place of chlorine gas, and the reaction mixture was bubbled for about 10 minutes to drive off excess chlorine from the reaction mixture.
Analysis of the resulting reaction mixture by gas chromatography showed that the conversion of ethyl lactate was 90%, but the reaction yield to ethyl pyruvate was 6%, and the remaining 94%.
% Were various by-products such as chlorinated products.

[0032]

According to the method of the present invention, a lactate ester which is industrially available at a low cost is used as a raw material, a relatively inexpensive oxidizing agent is used without using a catalyst such as bromine, etc. The pyruvate can be produced industrially advantageously without the need for wastewater treatment.

Claims (3)

[Claims] 1. A process for producing a pyruvate ester, comprising oxidizing a lactate ester with chlorine in an organic solvent under light irradiation. 2. The method for producing a pyruvate according to claim 1, wherein the organic solvent is an aromatic compound solvent or a halogenated aliphatic hydrocarbon solvent having a halogen atom in the molecule. 3. The method for producing a pyruvate according to claim 1, wherein the organic solvent is benzonitrile, monochlorobenzene, or dichlorobenzene.