JPH0114904B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing highly pure p-nitroaniline. More specifically, the present invention provides a method for producing p-nitroaniline with a low content of o-nitroaniline and high purity.

p-Nitroaniline is used as an intermediate in the production of medicines, agricultural chemicals, dyes, rubber drugs, polyamides, polyimides, and the like.

Generally, p-nitroaniline is produced by a method in which nitroacetanilide obtained by reacting acetanilide and nitric acid in the presence of concentrated sulfuric acid is further hydrolyzed. In this method, a small amount of o-nitroaniline is produced as a by-product and is mixed as an impurity into p-nitroaniline, which is the target product.
Among the above-mentioned uses of p-nitroaniline, depending on the purpose of use or special use, high purity, especially o
- High quality p-nitroaniline free of nitroaniline is required. Therefore, conventional methods involve purifying the nitration reaction mixture containing crude nitroacetanilide obtained in the nitration reaction by a recrystallization method, etc., and then hydrolyzing it, or partially hydrolyzing the nitration reaction mixture. A method in which the impurity o-nitroacetanilide is extracted into the aqueous phase as o-nitroaniline and then further hydrolyzed, or a method in which p-nitroaniline obtained by the above method is further purified by means such as a recrystallization method. Complicated methods such as These methods result in a large loss of p-nitroacetanilide or p-nitroaniline, and cannot be said to be excellent industrial methods for producing highly pure p-nitroaniline.

The present inventors investigated a method for improving the drawbacks of the conventional method for producing high-purity p-nitroaniline. As a result, the nitration reaction mixture obtained by the nitration reaction of acetanilide was diluted with water to produce p-nitroaniline. We have discovered that the above object can be achieved by precipitating and separating crude crystals of nitroacetanilide, immersing them in hot water, and then hydrolyzing them,
We have arrived at the present invention. The present invention is characterized in that highly pure p-nitroaniline can be obtained by treating the nitration reaction mixture in a simple manner.

That is, the present invention involves reacting acetanilide and nitric acid in the presence of concentrated sulfuric acid, separating crude crystals of p-nitroacetanilide from the resulting nitration reaction mixture containing o,p-nitroacetanilide, and By hydrolyzing p-
In the method for producing nitroaniline, (a) crude crystals of p-nitroacetanilide are precipitated by diluting the nitration reaction mixture with water, and then separated; (b) the p-nitroacetanilide is separated; After immersing the crude crystals of acetanilide in hot water at 40 to 70°C, the crystals of p-nitroacetanilide are separated; (c) the p-nitroacetanilide is hydrolyzed in the presence of a base; - A method for producing p-nitroaniline, characterized by separating nitroaniline.

In the method of the invention, a nitration reaction mixture is obtained by reacting acetanilide and nitric acid in the presence of concentrated sulfuric acid. The reaction between acetanilide and nitric acid is carried out by conventionally known methods. In this case, the nitric acid used is usually 60% by weight.
The concentration is preferably 94% by weight or more, and the molar ratio of nitric acid to acetanilide is usually in the range of 1 to 1.5. Also, concentrated sulfuric acid is usually
It is 90% by weight or more, preferably 97% by weight or more, and fuming sulfuric acid can also be used. The molar ratio of sulfuric acid to acetanilide is usually between 2 and
20, preferably in the range of 4 to 10. Also,
The molar ratio of sulfuric acid to nitric acid fed to the reactor usually ranges from 2 to 20, preferably from 3 to 10. In this nitration reaction, nitric acid and sulfuric acid can be used as a mixture of both, that is, a mixed acid, and in that case, the usage ratio is also as described above. The nitration reaction method includes a method in which the nitric acid is continuously or intermittently added to the mixture of the concentrated sulfuric acid and acetanilide and reacted with stirring, a method in which acetanilide and nitric acid are continuously or intermittently added to the concentrated sulfuric acid and the mixture is stirred. Examples include a method of reacting with acetanilide, and a method of continuously or intermittently adding acetanilide to the mixed acid. Among these methods, the second method reduces the selectivity to o-nitroacetanilide and increases the selectivity to p-nitroacetanilide in the nitration reaction mixture, and in this case is preferable because the molar ratio of concentrated sulfuric acid to acetanilide can be reduced to a range of 2 to 8. The temperature during this nitration reaction is usually -20 to 20℃, preferably -10℃.
to 10°C. The time required for the reaction is usually in the range of 0.5 to 5 hours, preferably 1 to 3 hours. Through this nitration reaction, p-
Nitroacetanilide, a small amount of by-product o-
A nitration reaction mixture containing nitroacetanilide, sulfuric acid and unreacted nitric acid is obtained.

In the method of the invention, crude crystals of o-nitroacetanilide are precipitated by diluting the nitration reaction mixture with water. The amount of water added during this dilution treatment is usually in the range of 1 to 10, preferably 3 to 5, as a weight ratio to the concentrated sulfuric acid in the nitration reaction mixture. By diluting the nitration reaction mixture by adding water, the temperature in the system increases due to the generation of heat of dilution, but by dilution, crude crystals of p-nitroacetanilide precipitate, and - A slurry of crude crystals of nitroacetanilide is formed. This slurry of crude crystals of p-nitroacetanilide is usually heated at 0 to 40°C.
Preferably the temperature is maintained in the range of 5 to 25°C. Next, the crude crystals of p-nitroacetanilide are separated. As the separation means, conventionally known means are employed, and specifically, other methods such as filtration, centrifugation, and hydrocyclones are employed.
The separated crude crystals of p-nitroaniline may be washed with cold water, if necessary, to remove the adhering sulfuric acid. In this way, crude crystals of p-nitroacetanilide are obtained.

In the method of the present invention, the crude crystals of p-nitroacetanilide are immersed in hot water. During this dipping treatment, the crude crystals of p-nitroacetanilide form a slurry. The temperature at that time needs to be in the range of 40 to 70°C, preferably in the range of 50 to 60°C. If the temperature during immersion treatment is higher than 70℃, p
- p- produced by hydrolysis of nitroacetanilide in water and a trace amount of sulfuric acid remaining
As more nitroaniline disappears due to dissolution in water, the yield of the desired p-nitroaniline decreases, and when the temperature drops below 40°C, the removal effect of o-nitroacetanilide decreases, resulting in high Purity of p-nitroaniline cannot be obtained. In addition, the ratio of hot water used during the immersion treatment is usually 2 to 20, preferably 3 by weight to the crude crystals of p-nitroacetanilide.
The range is from 1 to 10. p- treated with immersion treatment
Nitroacetanilide crystals are separated from the mother liquor. As the separating means, the above-mentioned separating means can be employed. This immersion treatment is usually carried out 1 to 5 times, depending on the amount of hot water used. By the immersion treatment, p-nitroacetanilide crystals are obtained.

In the method of the present invention, the p-nitroacetanilide crystals are hydrolyzed in the presence of a base. Sodium hydroxide or potassium hydroxide is preferably used as the base, and aqueous solutions of these bases are usually used. The proportion of the base to be used is usually in the range of 0.8 to 3, preferably in the range of 1 to 2, as a molar ratio to the crystals of p-nitroacetanilide. In addition, the amount of water added to the reaction system together with the base during the hydrolysis reaction is
- The weight ratio of nitroacetanilide to crystals is usually in the range of 2 to 10, preferably 3 to 8. The temperature during the hydrolysis reaction is usually in the range of 50 to 150°C, preferably 100 to 130°C. The time required for hydrolysis is usually in the range of 0.5 to 4 hours, preferably 1 to 3 hours. The reaction is usually carried out under stirring. After completion of the reaction, the mixture is usually heated at 0 to 50°C, preferably 10 to 30°C.
By maintaining the temperature within this range, crystals of p-nitroaniline, the product, are precipitated. This p-nitroaniline is separated from the mother liquor. As the separating means, the above-mentioned separating means can be employed. The separated p-nitroaniline may be further washed with cold water if necessary. In this way, highly pure p-nitroaniline is obtained.

According to the present invention, a nitration reaction mixture containing o,p-nitroacetanilide obtained by a nitration reaction of acetanilide is diluted with water, and p-
Crude crystals of nitroacetanilide are precipitated and separated, and then immersed in hot water and then hydrolyzed, making it possible to produce high-purity p-nitroaniline with a low content of o-nitroaniline in high yield through simple operations. can be manufactured.

Next, the method of the present invention will be specifically explained using examples.

Example 1 (1) Equipped with a stirrer, thermometer and dropping funnel
97% sulfuric acid 108 in a 200ml glass 4-necked flask
g (1.1 mol), and 6.75 g (0.05 mol) of acetanilide was gradually added thereto while stirring under ice cooling. After the acetanilide is completely dissolved, cool to an internal temperature of 0°C and stir at 94°C.
% nitric acid (0.053 moles) was added via addition funnel over a period of approximately 10 minutes. During this dripping, reduce the internal temperature to 10
It was kept below ℃. After repeating the operation of adding acetanilide and nitric acid three more times,
The reaction was completed by stirring for 30 minutes. In this nitration reaction, p-nitroacetanilide and o-nitroacetanilide were each converted to 91.0 mol%,
It was produced in a yield of 7.0 mol%.

The obtained nitration reaction mixture was gradually added to a container containing 400 g of ice and stirred to precipitate crystals of nitroacetanilide. During this dilution, the temperature of the slurry was kept below 25°C.
This was filtered under suction and further washed twice with 50 ml of cold water to obtain crude crystals of p-nitroacetanilide. The content of o-nitroacetanilide in the crude crystals of p-nitroacetanilide was 7.1% by weight.

(2) This crude crystal of p-nitroacetanilide
200 g of water was added, and the mixture was immersed and stirred at 50° C. for 30 minutes, followed by heating. This operation was repeated once more. The content of o-nitroacetanilide in the obtained p-nitroacetanilide was 0.2% by weight.

(3) Next, a mixture of this p-nitroacetanilide, 8 g (0.2 mol) of sodium hydroxide, and 100 g of water was heated under reflux for 1 hour with stirring. The reaction mixture was cooled to 25° C., and the precipitated p-nitroaniline was isolated by suction filtration, washed twice with 50 ml of cold water, and then dried. The content of o-nitroaniline is 0.05% by weight or less (below the detection limit)
24.7 g of p-nitroaniline was obtained.
The yield of p-nitroaniline was 89.4 mol% (based on acetanilide).

Example 2 Using the crude crystals of p-nitroacetanilide obtained in the nitration reaction of Example 1 (1), the immersion temperature was changed to
Treatment and hydrolysis were carried out under the same conditions as in Example 1 (2) except that the temperature was 60°C. At this time, p-nitroaniline with an o-nitroaniline content of 0.05% by weight or less (below the detection limit) was obtained in a yield of 88.5 mol%.

Example 3 Using the crude crystals of p-nitroacetanilide obtained in (1) of Example 1, the amount of water used for immersion was
The treatment and hydrolysis were carried out under the same conditions as in Example 1, except that the amount was 250 g. At this time, p-nitroaniline with an o-nitroaniline content of 0.05% by weight or less (below the detection limit) was obtained in a yield of 88.0 mol%.

Example 4 In the hydrolysis reaction of Example 1 (3), 11.2 g of potassium hydroxide was used instead of sodium hydroxide.
The operation was carried out under the same conditions as in Example 1 except that (0.2 mol) was used. At this time, p-nitroaniline with an o-nitroaniline content of 0.05% by weight or less (below the detection limit) was obtained in a yield of 89.0 mol%.

Comparative Example 1 Instead of immersing the crude crystals of p-nitroacetanilide obtained in the nitration reaction of Example 1 (1), the crude crystals of p-nitroacetanilide obtained in Example 1 (1) were washed with 400 g of 50°C warm water, and then
Hydrolysis was carried out in the same manner as in (3). p-Nitroaniline was obtained with a yield of 92.1 mol%. Its composition is p
-Nitroaniline and o-nitroaniline were 97.0% by weight and 3.0% by weight, respectively.

Comparative Example 2 In (2) of Example 1, the operation and reaction were carried out under the same conditions as in Example 1 except that the immersion temperature was 80°C. At this time, p-nitroaniline with an o-nitroaniline content of 0.05% by weight or less (below the detection limit) was obtained in a yield of 85.1 mol%.
The recovery rate of nitroaniline decreases.

Comparative Example 3 The treatment and reaction were carried out under the same conditions as in Example 1, except that the immersion temperature was 30°C. At this time, 4% by weight of o-nitroaniline
The p-nitroaniline contained therein was obtained in a yield of 89.7 mol%.

Claims (1)

[Scope of Claims] 1. A method of reacting acetanilide and nitric acid in the presence of concentrated sulfuric acid, separating crude crystals of p-nitroacetanilide from the resulting nitration reaction mixture containing o,p-nitroacetanilide, and In the method for producing p-nitroaniline by hydrolyzing p-nitroaniline, (a) the nitration reaction mixture is diluted with water to precipitate crude crystals of p-nitroacetanilide, and then this is separated. (b) immersing the crude crystals of p-nitroacetanilide in hot water at 40 to 70°C, and then separating the crystals of p-nitroacetanilide; (c) hydrating the p-nitroacetanilide in the presence of a base. A method for producing highly pure p-nitroaniline, which comprises decomposing the p-nitroaniline and separating the p-nitroaniline produced as a result. 2. The method according to claim 1, wherein the amount of water used for diluting the nitration reaction mixture is in the range of 3 to 5 as a weight ratio to concentrated sulfuric acid. 3. The method according to claim 1, wherein the proportion of hot water used during the immersion treatment is in the range of 3 to 10 in terms of weight ratio to the crude crystals of p-nitroacetanilide.