JPS5862136A - Preparation of pyruvic acid ester - Google Patents

Abstract

PURPOSE:To prepare a pyruvic acid ester useful as an intermediate for various organic syntheses or fermentation raw material, etc., in high yield, by the method suitable for the industrial operation, by oxidizing a lactic acid ester with oxygen in a liquid phase in the presence of tungsten oxide under specific conditions. CONSTITUTION:A pyruvic acid ester is prepared, economically, by oxidizing a lactic acid ester such as methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate, etc. with oxygen in a liquid phase in the presence of a tungsten oxide, especially tungsten trioxide at 90-170 deg.C, preferably 100-150 deg.C keeping the concentration of the pyruvic acid ester in the reaction mixture to about <=5mol/ l, preferably <=4mol/l. Since the reaction is carried out in liquid phase, the process has a number of advantages such as low plant cost, excellent operation stability, applicability to an arbitrary production scale, extremely high selectivity of the reaction long catalyst life, etc.

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 it are extremely useful compounds as synthetic intermediates in various organic synthesis reactions, or as raw materials for fermentation and enzymatic reactions.

Conventionally, pyruvic acid was synthesized by reacting sodium cyanide with acetyl chloride to synthesize acetyl cyanide.

In order to hydrolyze it, it is produced 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, we use lactic acid ester as the raw material.

Interest has been focused on a method for producing pyruvate ester by oxidative dehydrogenation of this. Conventionally proposed methods include, for example, (1) 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 (
411 Publication No. 54-138514), (ii) A method of oxidizing lactic acid ester with oxygen in the gas phase in the presence of metal oxides of group Yb and group IIb of the periodic table (41 Ko 18Bg-3
662, 4I Publication No. 56-19854), etc. However, the method (1) above has the drawbacks that it requires an expensive precious metal catalyst, the reaction rate is slow, and the selectivity to pyruvate ester is not necessarily sufficient. The disadvantage of this method is 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 (11) have also been studied; for example, in JP-A-54-21982, ammonium metavanadate is attached together with oxalic acid and water to a carrier having a specific pKa value. It is stated that subsequent calcination yields a catalyst with excellent performance in terms of selectivity, yield and lifetime. However, JP-A-54-219
The production of pyruvate ester according to the description in Publication No. 82 has some drawbacks, such as the time-consuming preparation of the catalyst and the difficulty in controlling the production scale of pyruvate ester because it is a gas phase reaction. There is.

The present inventors conducted intensive studies to develop a process for producing pyruvate ester suitable for industrial implementation using lactic acid ester as a starting material. The concentration of pyruvate ester in the mixed solution is approximately 5 mol/! Please do not exceed 9
They discovered that pyruvate ester is produced in high yield when oxidized with oxygen at 0 to 170°C, leading to the completion of the present invention. This method has low equipment costs and stable operation because the reaction is carried out in the IK phase. The lactic acid ester used as a starting material in the method of the present invention has many advantages, such as excellent performance, adaptability to any production scale, extremely high reaction selectivity, and long catalyst activity life. There are no particular limitations on the lactate, 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 can be produced industrially by hydrolyzing acetaldehyde cyanohydrin with sulfuric acid and esterifying the resulting lactic acid amide/sulfate with methanol. In addition to being produced, this product converts vinyl acetate into a hydroform to form α-acetoxypropionaldehyde, which is then oxidized to form α-acetinocyglobionic acid. It can also be easily produced by reacting with

The tungsten oxide used as a catalyst in the method of the present invention may include several compounds depending on its oxidation number, but depending on the ease of availability and catalytic activity.

Tungsten dioxide (W
Os). Tungsten oxide is commercially produced and can be easily obtained.
By igniting ammonium tungstate or by washing and drying the precipitate obtained by adding nitric acid to the ammonium tungstate solution, according to the method described in Chijinshokan Co., Ltd. published on February 25, 2015. It can also be manufactured. The catalyst is silica and Al2.

It can also be used by being supported on a carrier such as activated carbon.

In consideration of reaction rate and reaction selectivity, the catalyst is generally used in a proportion of 0.5 to 10% by weight of the reaction mixture in terms of metal oxide. The concentration of □pyruvic acid ester in
This makes it possible to achieve high reaction selectivity.

It is undesirable that III[ of the pyruvate ester in the reaction mixture exceeds about 5 mol/I' because the pyruvate ester causes undesirable side reactions under the reaction conditions.

A method for adjusting the concentration of pyruvate ester in the reaction mixture is to control the average residence time of the reaction mixture by adjusting the feed rate f of lactic ester according to the reaction rate. The reaction is carried out while at least a portion of the reaction mixture is continuously or intermittently distilled out of the reaction system (reactive distillation method).

The reaction according to the method of the present invention, to which a general-purpose method is generally applicable, is carried out by bringing a mixed solution containing a catalyst and a lactic acid ester into contact with an oxygen-containing gas. In this case, as the reaction solvent, it is advantageous to use lactic acid ester as a raw material, pyruvic acid ester as a product, or a mixture thereof to serve as a solvent, but other ester solvents such as methyl acetate, ethyl acetate, Butyl acetate, methyl propionate, dimethyl succinate, etc. may 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 under stirring in a stirred reactant.

It can also be carried out using a gas stream in a bubble column reactor. 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 pressure from atmospheric pressure to 10 atm. Reaction temperature F190-170″C1 preferably Fi100-150
Selected from the range of °C.

If the reaction temperature is less than 90°C, the reaction rate will be slow, and if the reaction rate exceeds 170°C, the selectivity to pyruvate ester will be significantly lowered, which is not preferable.

Pyruvate ester can be obtained in high purity by conventional fractional distillation from the reaction mixture after removing the catalyst by sedimentation, filtration, centrifugation, etc. When the reaction is carried out using a reactive distillation method, a highly purified pyruvic acid ester can be obtained 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 A four-loaf flask with a temperature zood equipped with a temperature needle, a reflux condenser, a stirring device, an oxygen gas inlet, and an off-gas sampling port was charged with W.
Os "Purity 99.99 & Manufactured by Kishida Chemical Co., Ltd." 2F
, 401+73 methyl lactate were charged.

While stirring the contents of the flask at room temperature at a rotational speed of 75 orpm, oxygen gas was introduced at 1017 rpm from the oxygen gas inlet.
br for 15 minutes to replace the inside of the system. After that, it was kept at 130℃ and placed in a six-oil bath.
When the temperature inside the reactor reached 115°C, the reaction was started while stirring the contents at a rotational speed of 750 rpm and introducing oxygen gas at a flow rate of 1 OL/hr. . 3 hours after the start of the reaction 1 The reaction was stopped and the reaction mixture was analyzed by gas chromatography 0 As a result,
The conversion rate of methyl lactate was Fiss-, and the selectivity to methyl pyruvate was 93-. The Ikm of methyl pyruvate at the end of the reaction was 3.2 mol/I. 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 humid temperature for 30 minutes to precipitate the catalyst, and the supernatant liquid was separated by decantation. Methyl lactate (40-) was newly charged into the same four-bottom tube as used in Example 1, and then a reaction was 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. the result.

The conversion rates of methyl lactate in the 3rd, 6th, and 10th reactions were 3511.33L 32- and 5
No decrease in catalyst activity was observed due to repeated reaction and catalyst separation operations. In addition, the 3rd, 6th, and 1st O
The selectivity to methyl pyruvate in the second reaction was 931 g, 91 g, and 92%, respectively.

Example 3 The amount of methyl lactate used was 10 ml, and the reaction solvent was 30 ml of dimethyl succinate, and oil bath ii
The reaction was carried out under the same conditions and operations as in Example 1, except that t was changed to 160° C. and the reaction time was changed to 2 hours. The temperature inside the reactor at the start of the reaction tl is 135°C and 1
The concentration of methyl pyruvate at the end of the reaction was 1.2 mol/l. As a result of analyzing the reaction mixture by gas chromatography, the conversion rate of methyl lactate was 48%,
The selectivity to methyl pyruvate was F190%.

*S Example 4 After dissolving ammonium tungstate in 12 ft of distilled water, 10
0F was added thereto, then heated and evaporated to dryness, transferred to an electric furnace, and calcined at 500° C. for a true θ hour under air circulation to prepare a catalyst. 0 Of the catalysts prepared by the above procedure, 5f was used.

The reaction was carried out under the same conditions and operations as in Example 1, except that the oil bath section [1'' was changed to 50°C, 1 reaction time, and 2 hours.The temperature inside the reactor at the start of the reaction was 130°C!
The concentration of methyl pyruvate at the end of one reaction is 2.7
It was mol/j. Results of gas chromatography analysis of the reaction mixture.

The conversion rate of methyl lactate was 28%, and the selectivity to methyl pyruvate was 9191%.

Example 5 A reaction was carried out under the same conditions and operations as in Example 1, except that n-propyl lactate 404 was used instead of methyl lactate 40-. 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-. At the end of the reaction, the concentration of n-propyl acetate in the reaction mixture was 2.3 mol/l.
2f*Methyl lactate 15- and methyl pyruvate 25- were charged. The concentration of methyl pyruvate at this time is 6
．． It was 7 mol/l. The contents of the flask were heated to 75 ml at room temperature.
While stirring at a rotational speed of 0 rpm, oxygen gas was passed through the oxygen gas inlet at a flow rate of 101/hl for 15 minutes to replace gold in the system.

``Then, the four flasks were immersed in an oil bath maintained at 160°C, and when the temperature inside one reactor reached 130°C, the contents were stirred at a rotational speed of 750 rpm and oxygen gas was added to l' (11/hr, The reaction was started while introducing at a flow rate of 2 hours after the start of the reaction.One reaction was stopped and the reaction mixture was analyzed using a gas chromatograph.As a result, the conversion rate of pyruvic acid was 47%, and the conversion rate of pyruvic acid was 47%. The selectivity to methyl was 72%.O Patent applicant Kura Co., Ltd.Representative patent attorney Ken Honda

Claims (1)

[Claims] The preparation of the pyruvic ester in the reaction mixture in the liquid phase in the presence of tungsten oxide is approximately 5
1. A method for producing pyruvic acid ester, which comprises immersing it in oxygen at a temperature of 90 to 170° C. without exceeding mol/It.