JPH07116094B2 - Method for producing glyoxylic acid - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing glyoxylic acid by oxidizing glyoxal. More specifically, it relates to an improvement in a method for producing glyoxylic acid by oxidizing glyoxal with hydrogen peroxide.

Conventional technology Glyoxylic acid has an aldehyde group and a carboxyl group in its molecule, is highly reactive, and is a very useful compound as an intermediate raw material for various chemical products such as pharmaceutical modifiers, cosmetics, fragrances, and agricultural chemicals. .

Various methods for producing glyoxylic acid by the oxidation reaction of glyoxal are known. For example, Japanese Examined Japanese Patent Publication 52-31851
JP-A-56-8018 describes a method of oxidizing glyoxal with nitric acid in the presence of a non-oxidizing acid, and JP-B-56-8018 discloses a method of oxidizing glyoxal with nitric acid while supplying oxygen to glyoxylic acid.

Further, JP-A-58-198437 discloses a method of oxidizing glyoxal with chlorine, and JP-B-56-36871 discloses a method of electrode oxidation of glyoxal in an electrolytic solution containing a halogen ion.

In addition, as a method for producing other glyoxylic acid that does not use glyoxal as a raw material, a method for recovering glyoxylic acid produced as a by-product during glyoxal production by nitric acid oxidation of acetaldehyde, a method for reducing oxalic acid to an electrode, and maleic acid are further used. A method is known in which an acid is ozone-oxidized and then reduced to give glyoxylic acid.

Problems to be Solved by the Invention As described above, there are various kinds of known methods for producing glyoxylic acid, but in the ozone oxidation of maleic acid and the electrode oxidation of oxalic acid, ozone generation equipment and electrodes are used. There is a drawback that the equipment cost of the reaction tank and the like becomes considerably expensive. Further, oxalic acid is expensive as a raw material for glyoxylic acid and is not economical.

Therefore, it is considered that a method using an oxidation reaction of glyoxal is preferable as a method for producing glyoxylic acid.

The nitric acid oxidation method which has been conventionally performed as one of the methods for producing glyoxylic acid by the oxidation reaction of glyoxal requires stepwise change of the reaction temperature and strict control, and it takes a long reaction time. The reaction operation itself is very complicated, such as the need to treat the nitrogen oxide produced as a by-product. Furthermore, in the nitric acid oxidation method, since excess nitric acid is used to complete the reaction, it is difficult to separate unreacted nitric acid, and there is a problem that the purification process becomes long. Further, the chlorine oxidation method has a problem in that it is necessary to separate twice the molar amount of hydrogen chloride, which is a by-product of stoichiometry with respect to the glyoxylic acid produced, and it takes more labor to separate ions. This problem also applies to the electrolytic oxidation method mentioned above, and there is a problem that the amount of ions to be separated is very large with respect to the glyoxylic acid to be recovered, and the separation cost is very high.

Means for Solving the Problems The inventors of the present invention have earnestly studied about a method for producing glyoxylic acid using glyoxal as a raw material and an oxidation method without the above problems, and as a result, hydrogen peroxide solution was used. The present inventors have completed the present invention by finding that by selectively adding divalent iron ions during oxidation, the selectivity of glyoxylic acid can be dramatically improved.

That is, the present invention, in the presence of divalent iron ions, in oxidizing glyoxal with hydrogen peroxide to produce glyoxylic acid, hydrogen peroxide solution and divalent iron ions are separately added to glyoxal. And a method for producing glyoxylic acid, which is characterized in that the glyoxylic acid is oxidized.

The glyoxal used as a raw material in the method of the present invention can be used as it is as an aqueous solution generally available for industrial use, and the concentration is not particularly limited,
It is normally distributed as 40% by weight and may be concentrated to 40% by weight or more, but it is generally convenient to carry out the reaction at 40% by weight or less. There is no particular lower limit to the concentration, but if it is less than 1% by weight, the volumetric efficiency of the reaction is poor, which is not desirable. Therefore, the practical concentration is preferably 5% by weight or more.

Hydrogen peroxide used as an oxidant is generally commercially available
An aqueous solution of 30 to 60% by weight can be used. It is not desirable to use it by concentrating it to a concentration exceeding 60% by weight, because there is a risk that hydrogen peroxide will be rapidly decomposed. In addition, it is not desirable to dilute it to less than 1% by weight, because the volumetric efficiency of the reaction becomes worse. Therefore, it is practically preferable to use 5 to 60% by weight.

This reaction can be carried out by any type of reaction method such as a batch system, a continuous system or a semi-batch system, but it is basically a reaction which generates a large amount of heat, and hydrogen peroxide solution which is an oxidant is converted into glyoxylic acid. Should be added.

Conversely, adding glyoxal to hydrogen peroxide solution
The desired product, glyoxylic acid, is sequentially oxidized by the excess hydrogen peroxide, and is mainly undesirable as a by-product such as oxalic acid and formic acid.

Examples of the divalent iron ion include ferrous chloride, ferrous bromide, ferrous iodide, ferrous sulfate and ferrous sulfate 5- or 7-hydrate, Mohr's salt, ferrous nitrate, etc. Inorganic compounds of divalent iron and organic carboxylates of divalent iron such as ferrous acetate, ferrous oxalate and ferrous lactate are used. Of these, the combination of ferrous sulfate and hydrogen peroxide is a well-known oxidizing agent generally called Fenton's reagent.

In the method of the present invention, an important point for obtaining glyoxylic acid with a high selectivity is to continuously or intermittently supplement the divalent iron ion in the course of the reaction.
That is, this reaction causes the oxidation reaction by adding hydrogen peroxide to glyoxal as described above, but in this case, divalent iron ions also become glyoxal continuously or intermittently with the addition of hydrogen peroxide solution. It is an important point to add and replenish. According to the method of the present invention, the glyoxylic acid selectivity can be remarkably improved as compared with the case where a predetermined total amount of divalent iron ions is put into glyoxal and then oxidized.

The amount of ferrous ion to be used cannot be necessarily limited depending on other reaction conditions, but it is required to be about 0.01 mol or more as a ferrous compound with respect to 1 mol of glyoxal as a reaction substrate. There is no particular upper limit, but it is about 5 times the molar amount. It is meaningless to use more ferrous iron than necessary since it takes time and labor to separate glyoxylic acid and iron ions after the reaction and further does not contribute to the improvement of the selectivity of goxylic acid. . On the other hand, if the amount is less than 0.01 mol, the selectivity of glyoxylic acid is lowered, which is not preferable.
Therefore, more preferably with respect to 1 mol of glyoxal
It is preferable to use it in an amount of about 0.05 mol to 0.5 mol,
In the adding process of hydrogen peroxide water, the above-mentioned amount of ferrous iron is supplemented continuously or intermittently.

As a method for continuously or intermittently adding ferrous ions, it is preferable to add hydrogen peroxide as an aqueous solution in parallel. Further, in starting the reaction, a part of the divalent iron ions to be used may be present in the aqueous glyoxal solution, and the remaining iron ions may be supplementarily added as the oxidation reaction proceeds.

The reaction temperature can be so-called normal temperature of 0 ° C to 30 ° C. Since the glyoxylic acid selectivity decreases at an elevated temperature exceeding 30 ° C, it is rather desirable to cool as much as possible and preferably carry out the oxidation reaction in the temperature range of about 0 ° C to 15 ° C.

Next, in order to obtain glyoxylic acid with a high selectivity in the main oxidation reaction, it is preferable to carry out the present reaction while avoiding contact with a gas phase containing molecular oxygen such as air. The presence of free dissolved oxygen in the reaction system, especially in the reaction solution, lowers the selectivity of glyoxylic acid and increases by-products of formic acid and oxalic acid. Therefore, in order to avoid the influence of dissolved oxygen, the dissolved oxygen in the glyoxal aqueous solution is removed in advance,
Further, in carrying out the reaction, it is desirable to avoid mixed contact between the gas phase containing molecular oxygen such as air and the reaction liquid phase.

Dissolved oxygen in the aqueous Glyoxal solution can be removed by a general method such as degassing under reduced pressure before use in the reaction, or by circulating an inert gas in the aqueous solution.

In order to carry out the reaction while avoiding mixed contact with molecular oxygen such as air, it is necessary to prevent at least partially, preferably substantially completely, mixing of these gas phases into the reaction system, Therefore, regardless of the type of reaction, the atmosphere in the reactor is filled with an inert gas, or the inert gas is circulated so that molecular oxygen and the reaction liquid phase do not come into direct contact with each other. desirable. Furthermore, it is desirable to react with free molecular oxygen and dissolved oxygen that may be generated in the reaction liquid phase while eliminating them.

Therefore, it is desirable that the hydrogen peroxide solution, which is an oxidizing agent, be subjected to an operation of removing free dissolved oxygen as in the case of the glyoxal aqueous solution. However,
Even if the free molecular oxygen dissolved in hydrogen peroxide water is expelled and the contact with the gas containing molecular oxygen such as air in the gas phase is blocked, a slight accident of hydrogen peroxide will occur. Since free oxygen is generated by decomposition, it is generally difficult to completely reduce the dissolved oxygen to zero even if the above-mentioned treatment can reduce the dissolved oxygen. However, it is necessary to remove dissolved oxygen in hydrogen peroxide as much as possible and use a material that does not cause accidental decomposition to transfer hydrogen peroxide solution. Further, it is preferable that the divalent iron ions added continuously or intermittently also at least partially remove the dissolved oxygen in the aqueous solution thereof.

As an inert atmosphere gas for carrying out this oxidation reaction while avoiding contact with molecular oxygen such as air, those generally called inert gases such as nitrogen, helium, and argon are typically used. To be As these inert gases, those of general quality which are industrially available can be used, and they can also be used for expelling dissolved oxygen in the glyoxal aqueous solution or the hydrogen peroxide solution. Generally, it is advantageous to use the cheapest nitrogen gas.

This oxidation reaction can be carried out in any form as long as it is carried out while avoiding substantial contact with molecular oxygen as described above. For example, in the case of performing the reaction in a batch system, it is easy to add an aqueous solution containing divalent iron ions similarly deoxygenated and hydrogen peroxide water to glyoxal deoxygenated in advance under an inert gas atmosphere. Glyoxylic acid can be obtained with high selectivity. However, the present invention is not limited to the above method.

In the oxidation reaction of glyoxal according to the method of the present invention, oxalic acid and a small amount of formic acid are produced as by-products, but since the reaction is carried out at a relatively low temperature, highly organic coloring components are not produced.

Therefore, after removing the ions derived from the ferrous compound with, for example, an ion exchange resin, oxalic acid is separated after crystallization, and formic acid is a high-quality product containing glyoxylic acid easily by azeotropic distillation separation with water. An aqueous solution of

Examples Hereinafter, the method of the present invention will be described in more detail with reference to Examples.
The analysis of the reaction product solution was performed by high performance liquid chromatography. As a mobile phase, 0.05 wt% phosphoric acid aqueous solution,
SHODEX X KC-811 was used as a separation column, an ultraviolet spectrophotometer detector and a differential refractometer detector were used as detectors, and the quantification was performed by the internal standard method.

Example-1 A 200 ml four-necked flask equipped with a stirrer, a thermometer, and a nitrogen bubbling tube was charged with 50 g of 10 wt% glyoxal aqueous solution (86 mmol as glyoxal), and the tip of the bubbling tube was immersed in the solution to introduce nitrogen. Deoxygenation of the aqueous Glyoxal solution was performed, and nitrogen substitution in the flask was sufficiently performed.

At the same time, for the two dropping funnels with side tubes equipped in the flask
2.5 g of 10 g of 30 wt% hydrogen peroxide solution (88 mmol as H ₂ O ₂ )
A solution of g of FeSO ₄ .7H ₂ O (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) in 15 ml of deionized water was added, and a bubbling tube was also immersed in this solution to carry out nitrogen bubbling in advance before starting the reaction.

Then, while maintaining nitrogen bubbling of each of the glyoxal aqueous solution, the hydrogen peroxide solution and the ferrous sulfate aqueous solution, the flask is cooled with ice water to 3 ° C to 8 ° C and stirred, and the hydrogen peroxide solution and the sulfuric acid solution are stirred. An aqueous solution of ferrous iron was added dropwise at the same time. The dropping time was 3 hours, and after the dropping was completed, stirring was continued for 30 minutes at 5 ° C., and then the temperature was returned to room temperature.

As a result of analyzing the reaction product solution, glyoxal conversion rate 85.2
%, Glyoxylic acid selectivity 80.5%, oxalic acid selection 18.7
%, Formic acid selectivity was 0.8%, and glyoxylic acid could be obtained with very high selectivity.

Comparative Example-1 In contrast to Example-1, a predetermined amount of the total amount was placed in an aqueous glyoxal solution without dropping divalent iron ions, and an oxidation reaction was performed with hydrogen peroxide solution.

In a 200 ml four-necked flask equipped with a stirrer, a thermometer, a nitrogen bubbling tube, and a dropping funnel with a side tube, 50 g of 10 wt% glyoxal aqueous solution (86 mmol as guoxal) and 2.5 g of
FeSO ₄ .7H ₂ O (Wako Pure Chemical Industries, Ltd. special grade reagent) was placed and the tip of the nitrogen bubbling tube was immersed in the liquid to introduce nitrogen. Nitrogen bubbling was carried out for about 30 minutes while rotating the stirrer to deoxygenate the glyoxal aqueous solution and to sufficiently replace the nitrogen inside the flask. On the other hand, the dropping funnel has 10g of 30w
A t% hydrogen peroxide solution (88 mmol as H ₂ O ₂ ) was added, and a nitrogen bubbling tube was also immersed therein to perform nitrogen bubbling in advance before starting the reaction.

Then, the reaction temperature was adjusted to 3 to 8 in the same manner as in Example-1.
Hydrogen peroxide solution was added dropwise over 3 hours while maintaining the temperature at ℃. After stirring was continued at 5 ° C. for another 30 minutes, the temperature was returned to room temperature.

As a result of analyzing the reaction product solution in the same manner as in Example-1, the glyoxal conversion rate was 78.4% and the glyoxylic acid selectivity was 75.
%, The oxalic acid selectivity was 20%, and the formic acid selectivity was 4%.

It was found that the glyoxylic acid yield in Example-1 was 10% higher than that of this Comparative Example.

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Claims (1)

[Claims] 1. When oxidizing glyoxal with hydrogen peroxide in the presence of divalent iron ions to produce glyoxylic acid, hydrogen peroxide solution and divalent iron ions are separately added to glyoxal. A method for producing glyoxylic acid, which comprises oxidizing by means of oxidation.