JPS63132859A - Production of pyruvic acid ester - Google Patents

Abstract

PURPOSE:To obtain a pyruvic acid ester in high selectivity using an inexpensive and readily handleable catalyst, by oxidizing a lactic acid ester with oxygen in the liquid phase in the presence of the catalyst selected from titanium oxide, zirconium oxide and niobium oxide. CONSTITUTION:A lactic acid ester is oxidized with oxygen in the presence of a catalyst to produce a pyruvic acid ester useful as a raw material for amino acids, e.g. tryptophan, etc., and intermediate for various organic compounds. In the process, one or more compounds selected from titanium oxide, zirconium oxide and niobium oxide, preferably titanium oxide and zirconium oxide are used as the above-mentioned catalyst to carry out the afore-mentioned reaction in the liquid phase and industrially and advantageously afford the aimed compound in high selectivity. The amount of said catalyst used is about 5g based on 1mol lactic acid ester. The reaction temperature is 100-170 deg.C, preferably 120-150 deg.C and the reaction time if <=10hr, particularly preferably <=5hr.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for producing a pyruvate ester.

Pyruvate ester and pyruvic acid obtained by hydrolyzing it are useful substances that are attracting attention as raw materials for amino acids such as tryptophan and as intermediates for various organic compounds.

[Conventional technology]

The method for producing pyruvate ester is a method of liquid phase oxidation of lactic acid ester with potassium permanganate (Org, 5 synthesis) 1 unit,
59) is known, but as an industrial manufacturing method, (1)
Using vanadium, molybdenum and phosphorus oxides as a catalyst,
A method for gas-phase oxidative dehydrogenation of lactic acid ester using α-alumina as a carrier (Japanese Patent Publication No. 19854/1985), (2) ammonium metavanadate, Scheleric acid,
A method of carrying out gas phase oxidative dehydrogenation reaction of lactic acid ester using a catalyst prepared by adhering and calcining a mixture of water to a carrier having a pka value in the range of 3.3 to 9.3 (Japanese Patent Publication No. 57-2433
6), (3) A method of oxidizing lactic acid ester with oxygen in the presence of a precious metal catalyst such as platinum or palladium (Japanese Patent Laid-Open No. 5
4-138514) and (4) a method in which lactic acid ester is oxidized with oxygen in the liquid phase in the presence of tungsten oxide (Japanese Patent Laid-Open No. 58-62136).

[Problem that the invention seeks to solve]

However, the drawing methods (1) and (2) both involve gas phase reactions, and have the disadvantage that the scale of the equipment is too large for industrialization. The method (3) can be carried out in either a liquid phase or a gas phase, but it cannot be called an industrial method as it requires an expensive noble metal catalyst and harmful heavy metals.

In addition, method (4) is a liquid phase reaction, but the catalyst used is expensive, and it is difficult to develop a method for producing pyruvic acid ester that is easy to obtain and suitable for industrial implementation using a cheaper catalyst. It was wanted.

[Means for solving problems]

The present inventors conducted studies to develop a manufacturing method for pyruvate ester suitable for industrial implementation using lactic acid ester as a starting material. The present inventors have discovered that pyruvate ester is produced with high selectivity when oxidized with oxygen in the liquid phase in the presence of at least one of niobium oxide and niobium oxide, and has completed the present invention.

[Detailed description of the invention]

Examples of the lactic acid ester used as a starting material in the present invention include methyl lactate, ethyl lactate, n-propyl lactate, and h-pudel lactate.

The catalyst used in the method of the present invention is one or more selected from the group consisting of titanium oxide, zirconium oxide, and niobium oxide.

The titanium oxide used as a catalyst in the present invention is 2,
Although oxides and peroxides of 3.4-valent titanium are known, the commonly used 4-valent titanium dioxide (titania) is preferred in view of its ease of availability. Although three types of modification of titanium dioxide with different structures are known, there is no need to specifically limit the catalyst used in the present invention.

Zirconium oxide is also usually in the form of zirconium dioxide, which is preferred because of its ease of availability.

Starting from other compounds of titanium and zirconium,
Those that are converted into oxides during the reaction are naturally subject to the present invention. These are, for example, hydrates, hydroxides, nitrates, oxalates of titanium and zirconium oxides. Oxides of niobium, especially niobium oxide, can also be used in this method, but the selectivity to pyruvate ester is rather low;
Furthermore, since they are somewhat expensive, the catalysts made of titanium and zirconium are more preferable from the economic point of view.

The amount of catalyst may be about 5f per 1 motK of lactic acid ester, and even if it is larger than this, there is not much effect.

The reaction temperature is 100-170°C, preferably 120-15°C.
0℃, and if the temperature is not 100℃, the reaction rate will be slow and 1
When the temperature exceeds 70°C, the selectivity decreases significantly. The reaction pressure is generally preferably 1 to 10 atm.

The reaction time is not particularly limited, but as described later, since the reactivity of pyruvate ester is high, it is preferably as short as possible, and it is good to complete the reaction in 10 hours or less, more preferably 5 hours or less. .

As the oxygen-containing gas used for oxygen oxidation in the present invention, oxygen gas or a mixed gas (for example, air) of oxygen and nitrogen in any proportion can be generally used. In addition, the oxygen-containing gas can be supplied by stirring the reaction mixture and passing it through the gas phase, or by blowing it into the liquid.In the pressurized system, a pressure regulator or the like is used in an autoclave to adjust the oxygen partial pressure. One possible method is to keep it constant.

The pyruvate ester produced in the present invention has high reactivity and the reaction takes place at a high temperature of 100 to 170°C, so it is preferable that the concentration is as low as possible.

The concentration is preferably 4 mol/L or less, and in order to maintain high selectivity, it is necessary to keep the conversion rate low or to use a solvent. The solvent is ester-based,
In order to simplify purification, those having a higher boiling point than pyruvate ester are preferable, such as dimethyl succinate and diethyl succinate.

The product can be purified by separating the catalyst after the reaction by filtration, decantation, etc., and then performing an operation such as distillation under reduced pressure. Since the catalyst can be used repeatedly, the pyruvic acid ester product can be recovered by reducing the pressure after the reaction is completed.

[Experiment example]

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Example 1 Titanium dioxide “Wako Tsumugi Yakuhin (anatase type)” 2 was placed in a 100 m 74-hole flask equipped with a thermometer, reflux condenser, magnetic stirrer, oxygen gas inlet, and off-gas sampling port.
? , 42 f (0°403 mol) of methyl lactate were charged. Heat the oil bath to 130°C and add 1 liter of oxygen gas to the reaction solution.
The reaction was started by bubbling at a flow rate of 0 t/hrs and stirring with a magnetic stirrer. 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 38.2
%, the selectivity to methyl pyruvate was 93.9%.

Example 2 An experiment was carried out in the same manner as in Example 1, except that titanium dioxide 42 was charged and reacted in the same experimental apparatus as in Example 1. As a result, the conversion rate of methyl lactate was 37.5%, and the conversion rate of methyl pyruvate was 37.5%. The selectivity to was 93.5%.

Example 3 The reaction mixture obtained in Example 1 was cooled, left to stand, and then decanted to recover methyl pyruvate and methyl lactate. Methyl lactate 42f (0,403 mol) was newly charged, and the following examples were carried out. As a result of conducting the same experiment as in 1, the conversion rate of methyl lactate was 37.9%, and the selectivity to methyl pyruvate was 93.8%.

An experiment was carried out in the same manner as in Example 1 except that 2 tons of zirconium oxide was charged into the same experimental apparatus as in Example 1 and the reaction was carried out. As a result, the conversion rate of methyl lactate was 36.9%, and the conversion rate of methyl lactate was 36.9%. The selectivity to was 93.3%.

Example 5 An experiment was conducted in the same manner as in Example 1, except that 2 tons of niobium pentoxide was charged into the same experimental apparatus as in Example 1 and reacted.
The conversion rate of methyl lactate was 38.5%, and the selectivity to methyl pyruvate was 92.0%.

31! In the same experimental apparatus as in Example 1, 1.0% of titanium dioxide and 1.0% of zirconium oxide were placed. The experiment was carried out in the same manner as in Example 1 except that Of was charged and the reaction was carried out. As a result, the conversion rate of methyl lactate was 37.6%, and the selectivity to methyl pyruvate was 93.8%.
Met.

Comparative Example 1 2 tons of tungsten trioxide was added to the same experimental equipment as in Example 1.
An experiment was carried out in the same manner as in Example 1, except that the reaction was carried out by charging the reaction mixture. As a result, the conversion rate of methyl lactate was 21.7%, and the selectivity to methyl pyruvate was 82.0%.

Comparative Examples 2 to 8 In the same experimental apparatus as in Example 1, two of each catalyst listed in the table below were added.
The experiment was conducted in the same manner as in Example 1, except that f preparation reaction was performed.

(Margin below)

Claims (1)

[Claims] A method for producing a pyruvate ester, which comprises oxygen-oxidizing a lactic acid ester in a liquid phase in the presence of at least one of titanium oxide, zirconium oxide, and niobium oxide.