JPS6115863A - Production of 2-chloro-4-nitrobenzoic acid - Google Patents

Abstract

PURPOSE:To obtain the titled compound useful as a raw material of pharmaceuticals, etc., economically, in high quality and yield, by oxidizing 2-chloro-4-nitrotoluene in acetic acid in the presence of a specific catalyst using a molecular oxygen-containing gas as the oxidizing agent. CONSTITUTION:2-Chloro-4-nitrotoluene is oxidized with a gas containing molecular oxygen (preferably air) in 1-5pts.wt. of acetic acid based on 1pt. of the starting compound, in the presence of a catalyst composed of a heavy metal compound (e.g. compound of Co, Mn, etc.) and a bromine compound (e.g. cobalt bromide). The obtained reaction liquid is concentrated, the acetic acid used as the solvent is distilled off, and water is added to the residual liquid to precipitate the objective 2-chloro-4-nitrobenzoic acid. A highly purified compound can be separated in high yield, by the recrystallization of the crude product precipitated by the above process, using an aromatic solvent such as benzene, toluene, chlorobenzene, etc.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing 2-chloro-4-nitrobenzoic acid by oxidizing 2-chloro-4-nitrotoluene with a molecular oxygen-containing gas. It is.

[Conventional technology]

2-Chloro-4-nitrobenzoic acid is a compound useful as a raw material for medicines, agricultural chemicals, pigments, etc.
It is desired to develop an economical process for producing -chloro-4-nitrobenzoic acid.

As a method for oxidizing 2-chloro-4-nitrotoluene to 2-chloro-4-nitrobenzoic acid, nitric acid oxidation (Japanese Patent Publication No. 30-7885, etc.) is known.

[Problem that the invention seeks to solve]

This method has disadvantages such as high chemical costs because nitric acid is used, the product is contaminated by by-product nitrogen compounds, and measures are required to purify waste gas and liquid containing nitrogen oxides. .

Therefore, the present inventors oxidized 2-chloro-4-nitrotoluene to 2-chloro-4-nitrobenzoic acid using a molecular oxygen-containing gas without the above-mentioned drawbacks as an oxidizing agent, and obtained a high-quality product. The present invention was achieved through extensive research into methods for efficient isolation.

[Means to solve the problem]

In other words, the present invention oxidizes 2-chloro-4-nitrotoluene in an acetic acid solvent with a molecular oxygen-containing gas in the presence of a catalyst consisting of a heavy metal compound and a bromine compound, and oxidizes the resulting reaction product liquid. After concentrating and distilling off the acetic acid, water was added to the residual liquid to precipitate 2-chloro-4-nitrobenzoic acid, and then the crude 2-chloro-4-nitrobenzoic acid obtained by separating it from the mother liquor was aromatized. 2, which is characterized by recrystallization in a group-based solvent.
- A method for producing chloro-4-nitrobenzoic acid.

The method of the present invention will be specifically explained below.

In the method of the present invention, 2-chloro-4-nitrotoluene is first brought into contact with a molecular oxygen-containing gas in an acetic acid solvent in the presence of a catalyst composed of a heavy metal compound and a bromine compound.

The appropriate amount of acetic acid used as a solvent is 1 to 5 times the weight of 2-chloro-4-nitro-1 to lueno, which is the substance to be oxidized. If the amount of acetic acid used is less than 1 times by weight, a sufficient reaction rate cannot be obtained, whereas if it exceeds 5 times by weight, the amount of acetic acid to be distilled off after the reaction will increase unnecessarily, and the decomposition loss of acetic acid will increase, causing damage to the reactor. This is disadvantageous because it also reduces productivity. Note that there is no particular problem even if water is present in the acetic acid in an amount of about 10% by weight or less.

As the oxidation catalyst, a catalyst system consisting of a heavy metal compound and a bromine compound is used.

In this case, a cobalt compound is most suitable as the heavy metal compound, but it is also preferable to use a heavy metal compound such as a mankat compound or a cerium compound together with a cobalt compound. Heavy metal compounds such as cobalt compounds can be used as long as they are soluble in acetic acid, but acetates, carbonates, hydroxides, and bromides are particularly preferred.

On the other hand, bromine compounds include inorganic bromine compounds such as bromine, hydrogen bromide, ammonium bromide, alkali metal bromides, cobalt bromide, manganese bromide, and tetrabromoethane.
Organic bromine compounds such as bromoacetic acid and benzyl bromide can be used, but cobalt bromide is particularly preferred.

The amount of cobalt compound used is in the range of 0.02 to 0.4% by weight as cobalt metal based on the solvent acetic acid,
Preferably it is in the range of 0.05 to 0.2% by weight. If the amount of cobalt catalyst used is less than 0.02% by weight, a sufficient reaction rate cannot be obtained, and if it exceeds 0.4% by weight, the labor and cost of separating the cobalt catalyst from the product will increase. This is disadvantageous because the decomposition of the reactants to carbon dioxide tends to increase.

When manganese compounds, cerium compounds, etc. are used together with cobalt compounds, the amount of manganese metal, cerium metal, etc.
It is preferably used in a range of 0% by weight, particularly in a range of 0.5 to 20% by weight.

The appropriate amount of the bromine compound to be used is 1 to 10 times the weight of cobalt metal, particularly 2 to 5 times the weight of cobalt metal.

If the amount of the bromine catalyst is less than 1 times by weight, sufficient catalytic activity cannot be obtained, and if it exceeds 10 times by weight, the contamination of the product by bromine and the burden of catalyst costs will become significant, which is not preferable.

The reaction temperature is in the range of 130 to 220 °C, especially 140 to 19
A range of 0°C is appropriate. At a reaction temperature lower than 130°C, the reaction rate becomes extremely slow, while at a reaction temperature higher than 220°C, the reaction product decomposes into carbon dioxide, chloro groups and nitro groups are eliminated, and colored impurities are produced as by-products. increases, which is not desirable.

Although pure oxygen or industrial exhaust gas can be used as the molecular oxygen-containing gas used as the oxidizing agent, air is usually most suitable for industrial purposes.

Reaction"4 (') Regarding the oxygen partial pressure, the total reaction pressure is 1
It is preferable to operate at a pressure in the range of -50 atm, especially in the range of 5-40 atm, and in such a way that the oxygen concentration of the exhaust gas from the reactor is in the range of 1-8% by volume. When the reaction pressure exceeds 50 atm, no particular advantage can be obtained despite the increased equipment costs and power costs for compressing the molecular oxygen-containing gas, and conversely, decomposition into carbon dioxide tends to increase. This is disadvantageous. Also, if the oxygen concentration in the exhaust gas exceeds 8% by volume,
There is a strong possibility that the reactor gas phase will form an explosive gas mixture, and from the viewpoint of safety measures, the oxygen concentration of the exhaust gas must be kept at 8% by volume or less.

The reactor used in the present invention is preferably of a forced mixing type rather than a simple bubble column type. That is, in order to achieve good gas-liquid mixing of the molecular oxygen-containing gas and the reaction liquid, to promote dissolution of molecular oxygen into the reaction liquid, and to ensure smooth contact between the reactants in the reactor, It is preferable to use a reactor equipped with a gas inlet consisting of a large number of pores in the lower part of the reactor, and in which forced stirring is performed using a rotating stirring blade or forced circulation is performed using a circulation pump outside the reactor.

The reaction method is a batch method in which the entire amount of the raw material mixture consisting of the substance to be oxidized, a solvent, and a catalyst is charged into a reactor in advance, and a molecular oxygen-containing gas is introduced without taking out the reaction product until the reaction is completed. A semi-continuous method in which the mixture or oxidizable material is continuously supplied to the reactor but the reaction product is not taken out until the reaction is completed, and a semi-continuous method in which the raw material mixture is continuously supplied to the reactor and the reaction product is continuously supplied. Any continuous method of taking out can be adopted.

Next, the target product, 2-chloro-4-nitrobenzoic acid, must be isolated from the reaction product solution obtained by carrying out the oxidation reaction under the conditions detailed above, but this product is easily soluble in acetic acid. Therefore, simply cooling the reaction solution makes it difficult for crystals to precipitate.

Crystals of the target product can be precipitated by distilling off acetic acid from the reaction product solution and concentrating and cooling the reaction product solution so that the weight of the residual acetic acid is less than the weight of the coexisting solids. A large amount of the target product remains dissolved, and both the yield and quality of the target product isolated by solid-liquid separation do not reach a satisfactory level.

Therefore, in the present invention, acetic acid is distilled off from the reaction product liquid until the weight of residual acetic acid becomes less than the weight of the coexisting solids, and preferably 2-chloro-4
- at least 1 part by weight of acetic acid per 1 part by weight of nitrobenzoic acid;
Distill the acetic acid until it becomes less than 1 part by weight, and add water, which is a poor solvent for 2-chloro-4-nitrobenzoic acid, to the residual liquid about 2 to 30 times the weight of the remaining acetic acid, preferably 3 to 10 times the weight. to precipitate 2-chloro-4-nitrobenzoic acid. In this case, the oxidation catalyst is easily soluble in water, and almost the entire amount remains dissolved in the liquid side.

However, the crude 2-chloro-4-nitrobenzoic acid obtained by separating it from the aqueous solution contains unreacted raw materials, intermediates, and colored byproducts that are poorly soluble in water, so the loss of the target product is minimized. Crude 2-chloro-4-nitrobenzoic acid must be purified with minimal steps and a high quality product free of these impurities must be isolated.

Therefore, in the present invention, in order to achieve such a purification purpose, the above-mentioned crude 2-chloro-4-nitrobenzoic acid is converted into benzene, toluene, xylene, ethylbenzene, cumene,
Aromatic hydrocarbons having about 6 to 10 carbon atoms, such as pseudocumene, butylbenzene, dichlorobenzene, etc.
Particularly preferably, recrystallization is performed using benzene, toluene, xylene, or chlorinated aromatic hydrocarbons such as chlorobenzene, dichlorobenzene, and chlorotoluene substituted with chlorine, preferably chlorobenzene.

That is, the aromatic solvent described above is crude 2-chloro-4
- Well dissolves unreacted raw materials, intermediates, colored by-products, etc. contained in nitrobenzoic acid, and 2-chloro-4-
The solubility of nitrobenzoic acid is large at high temperatures and small at low temperatures, so by recrystallizing crude 2-chloro-4-nitrobenzoic acid with the aromatic solvent described above, a high-purity product can be obtained in a high yield. It is possible to separate them. Note that by further washing the cake obtained by recrystallization with an aromatic solvent, the purity and color tone of the target product can be further improved.

In the present invention, the above two types of aromatic hydrocarbons are simply defined as aromatic solvents.

〔Effect of the invention〕

The method of the present invention detailed above makes it possible to economically produce 2-chloro-4-nitrobenzoic acid of good quality in high yield using a molecular oxygen-containing gas as an oxidizing agent. Ta.

The present invention will be specifically described below with reference to Examples.

〔Example〕

Example 1 130 parts of 2-chloro-4-nitrotoluene with a purity of 96.0% (all based on weight),
250 parts of 1.6% hydrated acetic acid, 2.8 parts of cobalt bromide anhydrous salt
7 parts (concentration of cobalt relative to acetic acid: 0.2% by weight) and 0.023 parts of manganese acetate tetrahydrate (concentration of manganese relative to cobalt: 1.0% by weight) were charged, and at a reaction pressure of 14 atm gauge and a reaction temperature of 140°C, Compressed air was blown from the bottom of the reactor at a flow rate such that the oxygen concentration in the exhaust gas was 8% or less, and the reaction was allowed to proceed for 4.5 hours.

405 parts of the reaction product liquid was heated to 150°C, concentrated, acetic acid was distilled off, and 191 parts of acetic acid distillate containing 8.0% water and 2-
Chlor-4-nitrotoluene 3.2%, 2-chloro-4
- 214 parts of a concentrate containing 60.6% of nitrobenzoic acid and 30.0% of acetic acid were obtained.

428 parts of water was added to 214 parts of the concentrate, cooled to 35°C, the resulting slurry was separated into solid and liquid, and wet cake 1 was prepared.
482 parts of liquid were obtained from 60 parts.

This wet cake was dried in a heated ML dryer at 75°C for 10 hours, and crude 2-chloro-4-nitrobenzoic acid (hereinafter referred to as 2
A total of 127 copies (abbreviated as C4NBA) were obtained.

2C4 obtained by alkali neutralization titration method of this crude 2C4NBA
The NBA-equivalent purity (hereinafter abbreviated as AY-value) was 92.4%. In addition, the color tone (hereinafter abbreviated as AT-value) of this crude 2C4NBA.2.0 parts of the sample was dissolved in 20 parts of a 1.0 N hydrium hydroxide aqueous solution, and the filtrate after filtering off insoluble matter was measured using a spectrophotometer. Thickness l (1 m, wavelength 460 mμ, expressed as transmittance measured using ion-exchanged water as a control solution) is 4.1
%Met.

Subsequently, 10 parts of dried rice 2C4NBA and 10 parts of p-xylene were charged into a glass container equipped with a reflux condenser, a stirrer, and a thermometer, heated to 120°C, and stirred for 30 minutes to dissolve the crude 2C4NBA.

Cool to 35°C while stirring, separate the slurry into solid and liquid, and remove 8.9 parts of p-xylene recrystallization wet cake.Liquid 9
．． Got 2 copies. This wet cake was dried in a 75° C. hot air dryer for 10 hours to obtain 8.5 parts of a dry cake. The AV-value of this dry cake is 98.796 and the AT-value is 28.
．． It was 696. In this case, the yield of 2C4NBA is 7
0.096 (vs. 2-chloro-4-nitrotoluene standard)
Met.

Example 2 The p-xylene recrystallized wet cake (before drying) obtained by solid-liquid separation in Example 1 was placed in the same glass device as in Example 1.
9 parts (including 0.3 parts of 2C4NBAI) and 8 parts of p-xylene
．． After stirring at 35° C. for 30 minutes, the slurry was separated into solid and liquid, and 10.5 parts of the wet cake was prepared.
I got 3 copies.

This wet cake was dried in a 75° C. hot air dryer for 10 hours to obtain 10 parts of a dry cake. AV of this dry cake
-value is 99.596, AT-value is 40.096'? '
A-) Ta. In the case of Kono, the yield of 2C4NBA is 966%
(vs. preparation 2C4 NBA standard).

Examples 3 to 9 Dry grains 2C4 obtained in Example 1 by almost the same method as Example 1
The results of recrystallization of NBA using various aromatic solvents are listed in the attached table.

Comparative Example 1 Dry rice 2 obtained in Example 1 was placed in the same glass device as Example 1.
Prepare 10 parts of C4NBA and 10 parts of p-xylene, 35
After stirring at ℃ for 30 minutes, the slurry was separated into solid and liquid to obtain 9.2 parts of liquid from which 10.1 parts of wet cake was obtained. This wet cake was dried in a 75° C. hot air dryer for 10 hours to obtain 8.1 parts of a dry cake. The AY-value of this dry cake is 97
．． 6%, and the AT-value was 15.8%. In this case, 2
The yield of C4NBA was 91.1%.

Comparative Example 2 Dried paddy 2C4NB obtained in Example 1 in substantially the same manner as Comparative Example 1
Wet cake 10 obtained by stirring 10 parts of A and 10 parts of cyclohexane at 35°C for 30 minutes and separating the slurry into solid and liquid.
．． Two parts were dried in a 75°C hot air dryer for 10 hours to obtain 9.3 parts of a dry cake. The AV-value of this dry cake is 97
．． 1%, and the AT-value was 83%. In this case, 2C
The yield of 4NBA was 97.7%.

Comparative Example 3 Dried paddy 2C4NB obtained in Example 1 in substantially the same manner as Example 1
Prepare 10 parts of A and 10 parts of Cyclohekisatsuno and heat to 155℃.
After stirring for 30 minutes (crude 2C4NBA was hardly dissolved), the slurry was cooled to 35°C, and 10.3 parts of the wet cake obtained by solid-liquid separation was dried in a hot air dryer at 75°C for 10 hours. , 92 parts of dry cake were obtained.

The AV-value of this dry cake is 97.2% and the AT-value is 1.
It was 0.2%. In this case, the yield of 2C4NBA is 9
At 67%.

Claims (2)

[Claims] (1) Oxidize 2-chloro-4-nitrotoluene in an acetic acid solvent with a molecular oxygen-containing gas in the presence of a catalyst consisting of a heavy metal compound and a bromine compound, and concentrate the resulting reaction product liquid to convert it into acetic acid. After distillation, water is added to the residual liquid to precipitate 2-chloro-4-nitrobenzoic acid.
-Production method of chloro-4-nitrobenzoic acid. (2) Oxidize 2-chloro-4-nitrotoluene with a molecular oxygen-containing gas in an acetic acid solvent in the presence of a catalyst consisting of a heavy metal compound and a bromine compound, and concentrate the resulting reaction product liquid to convert it into acetic acid. After distillation, water was added to the residual liquid to precipitate 2-chloro-4-nitrobenzoic acid, and then the crude 2-chloro-4-nitrobenzoic acid obtained by separating it from the mother liquor was recrystallized from an aromatic solvent. 2-chlor-4-
Method for producing nitrobenzoic acid.