JPH0469131B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for oxidizing organic compounds, and can be used for producing oxygen-containing organic compounds such as aldehydes and carboxylic acids.

(Prior Art) Nitric acid oxidation method has been known for a long time as one of the oxidation methods in the field of organic chemistry.

For example, according to West German Patent No. 932369, a highly concentrated glyoxylic acid aqueous solution can be obtained by oxidizing glyoxal with 30 to 50% (the same percentage by weight) nitric acid. Nitric acid oxidation is also used to oxidize activated alkyl compounds and carbon-carbon double bond compounds. Examples of active alkyl compounds include alkyl carbonyl compounds (aldehydes and ketones) and aromatic side chain alkyl compounds. In these compounds, the carbon-hydrogen bond on the α carbon atom adjacent to the carbonyl group or aromatic nucleus is broken, producing aldehydes and carboxylic acids with carbon-oxygen bonds formed. Examples include the oxidation of acetaldehyde to glyoxal and the oxidation of pseudocumene to trimellitic acid. Also, an example of nitric acid oxidation of a carbon-carbon double bond compound is the oxidation of tetrahydrophthalic anhydride, which breaks a carbon-carbon bond and yields butanetetracarboxylic acid in which a carbon-oxygen bond is formed.

The nitric acid concentration used in these nitric acid oxidation reactions varies. For example, from the many examples shown in Yoshiro Ogata, Oxidation and Reduction of Organic Compounds (Nankodo), pp. 436-452, the lowest is 5 to 5.
15%, and as high as 90%. However, there seems to be no known example of oxidation occurring at a satisfactory rate at extremely low concentrations of nitric acid, such as 1% or less, and an excess of nitric acid is often used to make the reaction proceed smoothly.

Nitric acid is often used by a sequential addition method such as dropwise addition, but nitric acid is usually present in the reaction solution at a concentration of around 5% or more. For example, Japanese Patent Application Laid-Open No. 51-29441 describes 5 to 7%.

If a mixture containing a significant amount of nitric acid is obtained, purification treatment is required, but if it is difficult to apply distillation or crystallization methods, expensive special purification methods such as ion exchange resin treatment or electrodialysis may be necessary. The law had to be used. The purification process also resulted in the loss of some of the target product and residual nitric acid.

A method is known in which a compound selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, and aluminum nitrate is present to accelerate the reaction during nitric acid oxidation of an aqueous glyoxal solution (Japanese Patent Laid-Open Publication No. 103517/1983). These substances are usually used in an amount of 0.02 to 0.2 mol relative to glyoxal to reduce unreacted glyoxal and at the same time increase the yield of glyoxylic acid. However, the nitric acid concentration in the reaction solution was 80% after the dropwise addition.
Even after aging for 1 hour at °C, the concentration was about 3%, which was not particularly different from conventional nitric acid oxidation in that the concentration was around 5% or more during the nitric acid dropwise addition reaction.

The oxidizing agent composition made by mixing 1 volume of concentrated nitric acid and 3 volumes of concentrated hydrochloric acid has long been known as aqua regia, and contains nascent chlorine and nitrosyl chloride, such as HNO ₃ +3HClCl ₂ +NOCl+2H ₂ O. It has strong oxidation solubility. In addition, dilute aqua regia, which is diluted aqua regia twice with water, and inverse aqua regia, which has a reversed composition of 3 parts nitric acid and 1 part hydrochloric acid, are also known. Its use was limited to its use as an oxidizing solubilizer.

As described above, all of the known aqueous oxidizing agent compositions containing nitric acid and hydrochloric acid contain nitric acid at a fairly high concentration, and are not suitable for reactions that produce oxygen-containing organic compounds from active alkyl compounds or double bond compounds. It wasn't even used. Therefore, there is no known oxidation method that uses a nitrate acid mixture to directly obtain a reaction mixture with an extremely low concentration of residual nitric acid.

(Object of the invention) The present invention provides nitric acid oxidation of 1% or less, which is extremely low compared to the several % or more required in the known nitric acid oxidation method.
For example, at a nitric acid concentration of around 0.1% or less, an organic substrate is oxidized at a satisfactory reaction rate to obtain an oxygen-containing organic compound. This method has the advantage of eliminating the step of removing nitric acid from the reaction mixture and eliminating nitric acid loss.

(Structure of the Invention) The present inventor uses nitric acid as an oxidation source, but rather than reacting it directly with an organic substrate, it is sequentially added to nitric acid or a non-oxidizing strong acid aqueous solution so that the nitric acid concentration is 1% or less. By oxidizing the organic substrate in the form of an aqueous oxidant composition added and formed in the system, oxidation products are obtained at a satisfactory rate while keeping the nitric acid concentration in the system very low. I found out that it can be done.

(Sulfuric acid and non-oxidizing strong acids) Hydrochloric acid is a typical non-oxidizing strong acid, but strong acids such as hydrobromic acid and toluenesulfonic acid that are almost completely dissociated in aqueous solution (pKa<O ) and non-oxidizing acids such as perchloric acid can be used in the same manner. Also,
Sulfuric acid, such as dilute sulfuric acid, can be used as well. below,
Unless otherwise specified, non-oxidizing strong acids and sulfuric acid are included and simply referred to as "non-oxidizing strong acids."

Because there are differences in the type and concentration of acids, it cannot be said that they are exactly the same as aqua regia, but they are non-oxidizing strong acids,
It is thought that an oxidizing species stronger than nitric acid itself is produced by a chemical reaction in an oxidizing agent composition containing water and nitric acid as starting materials. From this point of view, the concentration of non-oxidizing strong acid is expressed in terms of the number of moles per 1 kg of the oxidizing agent composition. Although this concentration decreases as it is diluted by the water in the nitric acid that is successively added, it is preferable to maintain it at 1 mol/Kg or more at the beginning of the reaction and at 0.5 mol/Kg or more at the end of the reaction. This critical concentration can be determined experimentally by checking the nitric acid concentration in the reaction solution.

On the other hand, the concentration should not be made unnecessarily high; in the case of sulfuric acid, if the concentration is too high, it becomes oxidizing, and a mixed acid of concentrated sulfuric acid and nitric acid has other functions, such as being a nitrating agent. In the case of hydrochloric acid, the concentration usually supplied is 10 mol/Kg or less, which is also a practical upper limit. After all, the preferred initial concentration is 1 to 5 mol/
It is about kg. This value is more than 6 times the concentration of nitric acid that was dropped and currently exists in the system (1%: 0.16% or less).

Among non-oxidizing strong acids, hydrochloric acid is easily available as a large surplus as a by-product of organic chlorination reactions, and it is effective even at low concentrations.
This is the most preferable method because it improves the reaction selectivity and allows removal if desired by evaporation.

Not only weak acids such as acetic acid but also moderately strong acids such as phosphoric acid do not have the effect of the present invention of reducing the nitric acid concentration in the reaction solution.

(Sequential Addition of Nitric Acid) Considering the purpose of the present invention to proceed with the reaction at a low nitric acid concentration, a composition containing a high concentration of nitric acid such as aqua regia cannot be used as it is. In order to keep the nitric acid concentration as low as possible and effectively use the concentration of hydrochloric acid or sulfuric acid, nitric acid is dropped into an aqueous solution containing the substrate and hydrochloric acid or sulfuric acid. Of course, it may be added sequentially in a form other than dropwise addition.

As a result, the reaction begins with a very small amount of the oxidizing agent composition equivalent to the substrate, and the consumed oxidizing agent is regenerated from the nitric acid that is successively added and the non-oxidizing strong acid that is present in large amounts in the system. Since the non-oxidizing strong acid present in a relatively large amount immediately converts nitric acid into the oxidizing agent composition and quickly oxidizes the substrate, it is easy to maintain the nitric acid concentration in the system at 1% or less. Even if high concentration nitric acid, for example 40 to 50%, is dropped as in the prior art, the nitric acid concentration in the reaction solution is often 0.1% or less.

(Organic Substrate) The above oxidation method was first discovered regarding the reaction of oxidizing an oxygen-containing organic compound to a higher-order oxygen-containing organic compound. Examples of this type of reaction include reactions in which a carboxylic acid is obtained from a carbonyl compound and a carbonyl compound is obtained from an alcohol. It can be applied to the same types of substrates as those to which the conventional nitric acid oxidation method can be applied, such as from benzoin to bibenzoyl. It can also be used to oxidize active alkyl compounds. When alkylcarbonyl compounds such as aldehydes and ketones are oxidized, the alkyl group is oxidized next to the carbonyl (α-position). The production of glyoxal from acetaldehyde is an example. Similarly, the alkyl group of the aromatic side chain is oxidized at the active α-position, producing an aromatic aldehyde or an aromatic carboxylic acid. Methyl groups of xylenes, pseudocumene, duurene, bis(3,4-dimethylphenyl)ethane, etc. can be oxidized. The side chain alkyl group of an aromatic nucleus having a nitro group, such as p-nitrotoluene, is more difficult to oxidize than the above-mentioned ones.

Oxidation of compounds with carbon-carbon double bonds can also be carried out by the method of the invention. Butanetetracarboxylic acid is obtained from tetrahydrophthalic anhydride. Other examples of this type of substrate include cyclohexene and quinoline.

(Nitric acid) Nitric acid can be used in the same quality, concentration, and addition method as in the conventional nitric acid oxidation method.
For example, about 45% industrial nitric acid is dropped into the reaction solution and reacted. The oxidizing ability of nitric acid is transferred to the aqueous oxidizer composition obtained by the action with a non-oxidizing strong acid aqueous solution,
Organic substrates are rapidly oxidized. Nitric oxide corresponding to the consumed nitric acid exits into the gas phase of the reactor. Nitrogen oxide in the off-gas can be recovered as nitric acid using known methods such as air oxidation or passing through a water absorption tower.

(Reaction conditions) The reaction temperature can be appropriately selected depending on the substrate and target product. Generally, nitric acid is added dropwise from a temperature range of 0 to 100°C while keeping the temperature almost constant while checking the progress of the reaction, which is known for gas generation and heat generation. The following description is based on detailed experimental data from glyoxal to glyoxylic acid, but is generally applicable to other substrates as well. That is, at the end of the dropping, the nitric acid concentration in the reaction solution rises to 0.5%, but never exceeds 1%. The nitric acid concentration further decreases after the completion of the dropwise addition, usually reaching 0.005 to 0.03% after one hour, and a glyoxylic acid solution with a residual nitric acid concentration of 0.1% or less can be obtained without any particular purification. In the case of conventional nitric acid oxidation, even if about 0.1 mol of sulfuric acid or hydrochloric acid is added to accelerate the reaction, it is difficult to improve the rate of change of glyoxal by just adding nitric acid dropwise at around 40℃, and after the completion of dropping
Ripening was carried out by raising the temperature to about 80°C, but in the case of the present invention, there is no particular need to ripen by raising the temperature.

Known initiators such as sodium nitrite can also be used in the reaction. Further, alumina, ammonium vanadate, copper powder, etc. can be added and reacted.

(Operations and Effects of the Invention) When nitric acid is dropped into an aqueous solution containing a large amount of non-oxidizing strong acid, a strong oxidizing agent composition is formed, and the nitric acid concentration is so low that oxidation does not proceed in the conventional nitric acid oxidation method ( 1% or less), oxidation to oxygen-containing organic compounds progresses. As a result, an aqueous solution of the target product containing almost no residual nitric acid can be easily obtained. This has made it possible to omit the step of removing residual nitric acid, which was conventionally required, and to directly use it for organic synthesis reactions. Furthermore, if a target product that does not contain strong acids is required depending on the intended use, treatment such as evaporation of hydrochloric acid may be performed.

Since nitric acid as an oxidizing agent can be mostly recovered from nitrogen oxide in the off-gas, most of the nitric acid that cannot be recovered industrially and is lost is based on residual nitric acid in the reaction solution. Since the present invention drastically reduces this residual nitric acid, the effect of saving auxiliary raw materials is also large. Also,
Since the accumulation of nitric acid that often occurs in conventional nitric acid oxidation methods does not occur, the reaction does not run out of control, and large amounts of exhaust gas containing NOx are not emitted at once, making this method very effective from the standpoint of operation management and environmental conservation. It's advantageous.

(Example) Example 1 59.3 g of water, 30 g of sulfuric acid (concentration in aqueous solution 3.4 mol/Kg), 45.6 g of tetrahydrophthalic anhydride,
When the mixture was charged with 0.7 g of copper powder and 0.3 g of ammonium vanadate and heated, it became uniform at 70 to 80°C. 68% nitric acid was added dropwise and the reaction continued at 90-100°C. When water is added to the amount of 60 g dropped until the end of the reaction, the sulfuric acid concentration in the aqueous oxidizer composition at the end of the reaction is 2.8.
It was mol/Kg. The crystals (4.8 g) precipitated from the reaction mixture were butanetetracarboxylic acid. When the filtrate was methyl esterified and analyzed, butanetetracarboxylic acid was also found in the filtrate in the form of an ester.

Example 2 35.5% hydrochloric acid 149g, 10% sodium nitrite aqueous solution 8
g (HCl9.3mol/Kg) to 335g of acetaldehyde
288 g of 44% nitric acid was added dropwise at 40 to 42°C over 1.5 hours. The nitric acid concentration in the reaction solution was 0.25% or less, and about 55% of the acetaldehyde reacted. Using 149g of 5.15% hydrochloric acid instead of 35.5% hydrochloric acid,
Add 10% sodium nitrite aqueous solution (HCl 1.34 mol/
Kg), heated to 40°C with 355g of acetaldehyde, 5g of alumina was added, and 288g of 44% nitric acid was added dropwise (40°C, 1.5 hours) to react. Subtracting the acetaldehyde and paraaldehyde remaining in the reaction solution and trap, the conversion rate was about 31%, and 65.9 g of glyoxal was obtained in the reaction solution.
The reaction solution (696.1g) also contained formic acid (3.0%),
Other acids such as acetic acid (4.4%) and glyoxylic acid (11.1%) were analyzed.

Example 3 139 g of 18.2% sulfuric acid, 10 g of 3% sulfuric acid, and 10 g of 10% sodium nitrite (H ₂ SO ₄ , 1.6 mol/Kg) were mixed with 355 g of acetaldehyde and 10 g of alumina, and 288 g of 44% nitric acid was added at 40°C. dripped. Acetaldehyde (26.62%) in the reaction solution (717.2g)
and para-aldehyde (4.96%) remain, but 67.2 g of glyoxal (9.37%) remains as a reaction product.
was gotten. In addition, formic acid (2.27%), acetic acid (4.26%),
%) and acids such as glyoxylic acid (12.64%).

Reference example 1 Duurene in 300g of concentrated hydrochloric acid (HCl9.7mol/Kg)
40.3 g was added, and 167 g of 68% nitric acid was added dropwise. Progress of the oxidation reaction was observed at a reaction temperature of 70 to 95°C, as gas was generated and raw materials disappeared. Oxidation of active methyl groups was similarly observed when bis(3,4-dimethylphenyl)ethane was used as a raw material.

Reference Example 2 When 45% nitric acid was dropped at 40°C into a heterogeneous phase mixture of cyclohexene and hydrochloric acid (concentration 15.3%), an oxidation reaction proceeded and a product containing oxygen and chlorine was obtained.

Claims (1)

[Claims] 1. Nitric acid is successively added to an aqueous solution of sulfuric acid or a non-oxidizing strong acid with pKa < 0 so as to maintain the nitric acid concentration at 1% or less, and the aqueous oxidizing agent composition formed in the system removes organic substrates. (excluding glyoxal) to obtain an oxygen-containing organic compound. 2. The oxidation method according to claim 1, wherein the organic substrate is an active alkyl compound or a compound having a carbon-carbon double bond. 3. The oxidation method according to claim 1 or 2, in which hydrochloric acid is used as the sulfuric acid or the non-oxidizing strong acid.