JPS6411011B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing pyruvate ester, which comprises oxygen-oxidizing lactic acid ester in the presence of a catalyst. Pyruvate ester and pyruvic acid obtained by hydrolyzing the same are extremely useful compounds as synthetic intermediates in various organic synthesis reactions, or as raw materials for fermentation and enzymatic reactions.

Conventionally, pyruvic acid has been produced by reacting sodium cyanide and acetyl chloride to synthesize acetyl cyanide and hydrolyzing it, or by carbonizing tartaric acid in the presence of potassium hydrogen sulfate. However, the method using acetyl cyanide has a low yield, and the method using tartaric acid as a raw material has the disadvantages that the raw material is expensive and the yield is low.

Reflecting the above circumstances, interest has been focused on a method of producing pyruvate ester by oxidatively dehydrogenating lactic acid ester as a raw material. Conventionally proposed methods include (i) a method in which lactic acid ester is oxidized with oxygen in the liquid phase in the presence of a noble metal catalyst such as platinum or palladium (Japanese Patent Application Laid-open No. 138514/1983); (ii) a method in which lactic acid ester is Oxygen oxidation method in the gas phase in the presence of metal oxides of group b and group b of the periodic table (Japanese Patent Publication No. 38-3662, Japanese Patent Publication No. 56-19854)
Publication No.) etc. However, method (i) above requires an expensive noble metal catalyst, has the disadvantages of slow reaction rate, and does not necessarily have a sufficient selectivity to pyruvate ester. In addition, the method (ii) above has the disadvantage that the selectivity to pyruvate ester is not necessarily sufficient and the life of the catalyst is short. Measures to solve the drawbacks of method (ii) are also being considered, for example,
Publication No. 54-21982 discloses that when ammonium metavanadate is deposited together with oxalic acid and water on a carrier having a specific pKa value and then calcined, a catalyst with excellent performance in terms of selectivity, yield, and life can be obtained. is listed. However, the production of pyruvate ester according to the description in JP-A No. 54-21982 requires time and effort to prepare the catalyst, and because it is a gas phase reaction, it is difficult to control the production scale of pyruvate ester. There are some drawbacks such as:

The present inventors conducted intensive studies to develop a method for producing pyruvate ester suitable for industrial implementation using lactic acid ester as a starting material. The present inventors have discovered that pyruvate ester can be produced in high yield by oxygen oxidation at 90 to 170° C. while keeping the concentration of pyruvate ester in the liquid not to exceed about 5 mol/mol/liter, and have completed the present invention.
This method has many advantages such as low equipment cost, excellent operational stability, adaptability to any production scale, extremely high reaction selectivity, and long catalyst activity life because the reaction is carried out in the liquid phase. It has advantages.

There are no particular limitations on the lactic acid ester used as a starting material in the method of the present invention, and examples include methyl lactate, ethyl lactate, n-propyl lactate, and n-butyl lactate. Lactic acid esters can be produced by known methods. For example, methyl lactate is produced industrially by hydrolyzing acetaldehyde cyanohydrin with sulfuric acid and esterifying the resulting lactic acid amide/sulfate with methanol. In addition, this product hydroformylates vinyl acetate to α-acetoxypropionaldehyde, which is oxidized to α-acetoxypropionic acid, and then the α-acetoxypropionaldehyde.
-It can also be easily produced by reacting acetoxypropionic acid with methanol.

There are several types of tungsten oxide used as a catalyst in the method of the present invention, depending on their oxidation number, but they are easy to obtain, have catalytic activity,
When various points such as reaction selectivity are comprehensively judged, tungsten trioxide (WO ₃ ) is most preferably used. Tungsten oxide is commercially produced and can be easily obtained.
Precipitate obtained by igniting ammonium tungstate or adding nitric acid to ammonium tungstate solution according to the method described on pages 382-383 (February 25, 1962, published by Chijinshokan Co., Ltd.) It can also be produced by washing and drying. The catalyst can also be supported on a carrier such as silica, alumina, or activated carbon.
Catalysts are generally used in terms of metal oxides relative to the reaction mixture in consideration of reaction rate and reaction selectivity.
It is used in proportions of 0.5 to 10 weight percent.

The reaction according to the method of the present invention needs to be carried out under conditions in which the concentration of pyruvate ester in the reaction mixture does not exceed about 5 mol/, preferably 4 mol/, which results in a high reaction selectivity. can be achieved. It is undesirable for the concentration of pyruvate ester in the reaction mixture to exceed about 5 mol/mole because the pyruvate ester causes undesirable side reactions under the reaction conditions. Methods for adjusting the concentration of pyruvate ester in the reaction mixture include controlling the average residence time of the reaction mixture by adjusting the supply rate of lactate ester according to the reaction rate, and controlling the concentration of the pyruvate ester produced. A general method can be applied, such as carrying out the reaction while continuously or intermittently distilling a portion out of the reaction system (reactive distillation method).

The reaction according to the method of the present invention is carried out by bringing a mixture containing a catalyst and a lactic acid ester into contact with an oxygen-containing gas. In this case, it is advantageous to use the raw material lactic acid ester, the product pyruvate ester, or a mixture thereof as the reaction solvent, but other ester solvents such as methyl acetate, ethyl acetate, Butyl acetate, methyl propionate, dimethyl succinate, etc. can also be used in combination. In the method of the present invention, the reaction mixture and the oxygen-containing gas may be brought into contact with each other in a stirred reaction tank with stirring, or in a bubble column type reaction tank using a gas flow. As the oxygen-containing gas, oxygen gas and a mixed gas of nitrogen and oxygen in any proportion are generally used. The reaction is generally carried out under pressures from atmospheric to 10 atmospheres. The reaction temperature is 90-170℃, preferably
Selected from the range of 100 to 150℃. Reaction temperature is 90℃
Below 170℃, the reaction rate will be slow.
Exceeding this is not preferable because the selectivity to pyruvate esters will drop significantly. Pyruvate ester can be obtained in high purity by conventional fractional distillation from the reaction mixture after the catalyst has been removed by sedimentation, filtration, centrifugation, etc. When the reaction is carried out by a reactive distillation method, the pyruvic acid ester can be obtained in high purity by subjecting the distillate to a fractional distillation operation.

The method of the present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 In a 200 ml four-necked flask equipped with a thermometer, reflux condenser, stirring device, oxygen gas inlet, and off-gas sampling port, 2 g of WO ₃ "99.9% purity, manufactured by Kishida Chemical Co., Ltd." and 40 ml of methyl lactate were added. I prepared it. While stirring the contents of the flask at room temperature at a rotation speed of 750 rpm, oxygen gas was injected at 10/20% from the oxygen gas inlet.
hr. for 15 minutes to replace the inside of the system. Thereafter, the four-necked flask was immersed in an oil bath maintained at 130°C, and when the temperature inside the reactor reached 115°C, the contents were stirred at a rotational speed of 750 rpm and oxygen gas was introduced at a flow rate of 10/hr. The reaction was started while introducing Three hours after the start of the reaction, the reaction was stopped and the reaction mixture was analyzed by gas chromatography. As a result, the conversion rate of methyl lactate was 33%, and the selectivity to methyl pyruvate was 93%. The concentration of methyl pyruvate at the end of the reaction was 3.2 mol/ml. Carbon dioxide, methane, acetic acid, methanol, methyl acetate, methyl formate, etc. were observed as by-products.

Example 2 The reaction mixture obtained in Example 1 was allowed to stand at room temperature for 30 minutes to precipitate the catalyst, and the supernatant liquid was separated by decantation. Into the same four-necked flask as used in Example 1, 40 ml of methyl lactate was newly charged, and the reaction was then carried out under the same operations and conditions as in Example 1. The reaction and the separation of the catalyst from the reaction mixture were repeated 10 times in total according to the above procedure. As a result, the third
The conversion rates of methyl lactate in the 1st, 6th, and 10th reactions were 35%, 33%, and 32%, respectively, and no decrease in catalyst activity was observed due to repeated reaction and catalyst separation operations. In addition, the 3rd and 6th
The selectivity to methyl pyruvate in the 1st and 10th reactions was 93%, 91%, and 92%, respectively.

Example 3 The same conditions and operations as in Example 1 were used, except that the amount of methyl lactate used was 10 ml and dimethyl succinate was used as the reaction solvent, and the oil bath temperature was changed to 160 ° C. and the reaction time was changed to 2 hours. The reaction was carried out by The temperature inside the reactor at the start of the reaction is
The temperature was 135°C, and the concentration of methyl pyruvate at the end of the reaction was 1.2 mol/. Analysis of the reaction mixture by gas chromatography revealed that the conversion rate of methyl lactate was 48% and the selectivity to methyl pyruvate was 90%.

Example 4 12g of ammonium tungstate and 30ml of distilled water
α-alumina (200-300 mesh) after being dissolved in
After adding 100 g of the mixture, it was heated and evaporated to dryness, then transferred to an electric furnace and calcined at 500° C. for 10 hours under air circulation to prepare a catalyst.

Using 5 g of the catalyst prepared by the above procedure, a reaction was carried out under the same conditions and procedures as in Example 1, except that the oil bath temperature was changed to 150° C. and the reaction time was changed to 2 hours. The temperature inside the reactor at the start of the reaction was 130°C, and the concentration of methyl pyruvate at the end of the reaction was 2.7 mol/. As a result of analyzing the reaction mixture by gas chromatography,
The conversion rate of methyl lactate was 28%, and the selectivity to methyl pyruvate was 91%.

Example 5 40ml of n-propyl lactate instead of 40ml of methyl lactate
The reaction was carried out under the same conditions and operations as in Example 1, except that . The conversion rate of n-propyl lactate 3 hours after the start of the reaction was 30%, and the selectivity to n-propyl pyruvate was 92%.
Pyruvate n in the reaction mixture at the end of the reaction
-The concentration of propyl was 2.3 mol/.

Comparative Example 1 In the same four-necked flask as used in Example 1,
WO ₃ 2g, methyl lactate 15ml, methyl pyruvate 25
I prepared ml. The concentration of methyl pyruvate at this time was 6.7 mol/mol. While stirring the contents of the flask at room temperature at a rotation speed of 750 rpm, oxygen gas was introduced from the oxygen gas inlet at a flow rate of 10/hr.
The system was circulated for 15 minutes to replace the inside of the system. after that
A four-necked flask was immersed in an oil bath maintained at 160°C, and when the temperature inside the reactor reached 130°C, the contents were stirred at a rotational speed of 750 rpm and oxygen gas was introduced at a flow rate of 10/hr. The reaction was started during the introduction. Two hours after the start of the reaction, the reaction was stopped and the reaction mixture was analyzed by gas chromatography. As a result, the conversion rate of methyl lactate was 47%, and the selectivity to methyl pyruvate was 72%.

Claims (1)

[Claims] 1. Lactic acid ester is added in the liquid phase in the presence of tungsten oxide so that the concentration of pyruvate ester in the reaction mixture does not exceed about 5 mol/ml.
A method for producing pyruvic acid ester, characterized by oxygen oxidation at a temperature of 90 to 170°C.