Method for removing 2-naphthylamine from 1-naphthylamine

Abstract

The invention discloses a method for removing an isomer 2-naphthylamine from 1-naphthylamine, which comprises the following steps: (1) adding a 1-naphthylamine crude product into a three-neck flask, and heating to 55 DEG C to enable the 1-naphthylamine crude product to be in a molten state; (2) adding specific carboxylic acid or acyl chloride, and continuously stirring at 55 DEG C for 1 hour; (3) filtering solid impurities while the solution is hot, and retaining filtrate; (4) heating the filtrate to 55 DEG C to ensure complete melting, adding specific carboxylic acid or acyl chloride into the filtrate again, and continuously stirring at 55 DEG C for 1 hour; (5) filtering solid impurities while the solution is hot to obtain a filtrate which is pure 1-naphthylamine, and the purity gt can be stably obtained by adopting the technical scheme provided by the invention; the content of the 2-naphthylamine isomer is 99.8%, and the content is 1t; the principle is that specific carboxylic acid or acyl chloride is selected to react with naphthylamine, due to the spatial structure effect of 1-naphthylamine, the steric hindrance of 1-naphthylamine is far larger than that of 2-naphthylamine, the competition of 1-naphthylamine and carboxylic acid or acyl chloride in the reaction is weaker than that of 2-naphthylamine, and reaction products and unreacted acid are solids and can be removed through simple filtration. On the basis, the amount of specific carboxylic acid or acyl chloride is controlled, so that 2-naphthylamine can be removed.

Description

Technical Field

[0001] The invention relates to a method for purifying 1-naphthylamine, and belongs to the field of organic matter purification technology. Background Art

[0002] 1-naphthylamine is a white needle-shaped compound, mainly used as the intermediate of direct dyes (such as direct light-fast blue B2RL, direct light-fast gray 3B), acid dyes, ice dye and disperse dyes etc., or the raw material of rubber antioxidant, pesticide.At present, the industrial preparation method of 1-naphthylamine mainly is to take naphthalene as raw material and carry out nitration reaction, makes 1-nitronaphthalene, then its catalytic hydrogenation is reduced to 1-naphthylamine, but this method can produce the isomer 2-naphthylamine of 1-naphthylamine when the nitration step, and 2-naphthylamine is a strong carcinogen, so its removal is particularly important. Currently, there are two main methods for purifying crude 1-naphthylamine in industry: (1) purification by distillation. However, since the boiling point difference between 1-naphthylamine and 2-naphthylamine is only 5°C, it is difficult to obtain pure 1-naphthylamine with a purity greater than 99% through this method, and distillation has the problem of extremely high energy consumption; (2) purification by melt crystallization using the melting point difference of the substance. This method can obtain pure 1-naphthylamine with a purity greater than 99.8%, but this method inevitably requires the use of special equipment, which requires a large investment in equipment and still inevitably has the problem of high energy consumption. Summary of the Invention

[0003] In order to solve the above problems of high purification difficulty, high energy consumption and large equipment investment, the present invention provides a method for purifying 1-naphthylamine through acylation reaction.

[0004] A method for removing 2-naphthylamine from 1-naphthylamine, characterized in that it comprises the following steps: (1) Add the crude 1-naphthylamine into a three-necked flask and heat it to 55°C to make it molten; (2) Add a specific carboxylic acid or acid chloride and continue stirring at 55°C for 1 hour; (3) Filter out solid impurities while hot and retain the filtrate; (4) The filtrate was heated to 55°C to ensure complete melting, and the specific carboxylic acid was added again, and stirred at 55°C for 1 hour; (5) Filter out solid impurities while hot, take samples of the filtrate, and perform HPLC analysis.

[0005] In the aforementioned step (2), the specific carboxylic acids are adamantanecarboxylic acid and camphorsulfonic acid, and the acyl chlorides are pivaloyl chloride and isobutyryl chloride.

[0006] In the above step (2), the equivalent ratio of carboxylic acid to crude 1-naphthylamine is (0.2-0.5):1.

[0007] The reaction time in step (2) is 1 h.

[0008] In the aforementioned step (4), the specific carboxylic acids are adamantanecarboxylic acid and camphorsulfonic acid, and the acyl chlorides are pivaloyl chloride and isobutyryl chloride.

[0009] In the above step (4), the equivalent ratio of carboxylic acid to crude 1-naphthylamine is (0.1-0.2):1.

[0010] The reaction time in step (4) is 1 h.

[0011] The technical effects of the present invention are: The present invention discloses a method for removing 2-naphthylamine from 1-naphthylamine. The method uses crude 1-naphthylamine as a raw material, undergoes a first purification step, and then filters out most impurities. It then undergoes a second purification step and again filters out impurities to obtain a pure product. The purification method disclosed in this application document can be used with a conventional reactor, requiring no special equipment and requiring low equipment investment. After two purification steps, a high-purity, fine product with a 1-naphthylamine purity of >99.8% and a 2-naphthylamine impurity content of <0.1% can be obtained. The method also shortens reaction and processing times, resulting in high yields. The required reaction temperature is only 55°C, resulting in low energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The figure is the HPLC detection spectrum of the crude product of 1-naphthylamine in the present invention.

[0013] Figure 2 This is the HPLC detection spectrum of the mother liquor after the first purification in the present invention.

[0014] Figure 3 It is the HPLC detection spectrum of the final product in the present invention. DETAILED DESCRIPTION

[0015] Example 1: A method for removing 2-naphthylamine from 1-naphthylamine, comprising the following steps: (1) Add 100 g of crude 1-naphthylamine into a 250 ml three-necked flask, place it in an oil bath, and heat it to 55°C to melt it; (2) Add adamantanecarboxylic acid at an equivalent ratio of 0.4:1 to the crude 1-naphthylamine, and continue stirring at 55°C for 1 hour; (3) Filter out solid impurities while hot and retain the filtrate; (4) The filtrate was heated to 55°C to ensure complete melting, and adamantanecarboxylic acid was added again at an equivalent ratio of 0.2:1 to the crude 1-naphthylamine, and the mixture was stirred at 55°C for 1 hour. (5) Filter out solid impurities while hot. The filtrate is pure product and tested by HPLC.

[0016] Depend on Figure 1It can be seen that before purification, the main impurity 2-naphthylamine content in the 1-naphthylamine crude product was 10.962% (retention time was 10.047 min), and the content of 1-naphthylamine was 89.038% (retention time was 12.875 min). After purification for the first time, the content of 2-naphthylamine impurity in the mother liquor was 1.333%, and the content of 1-naphthylamine was 98.415% (retention time was 12.875 min). Figure 2 As shown), the first purification yield was 70%; after the second purification, the content of 2-naphthylamine impurity in the mother liquor was 0.138%, and the content of 1-naphthylamine was 99.872% (as shown Figure 3 The second purification yield was 78%, and the total yield was 54.6%.

[0017] Example 2: A method for removing 2-naphthylamine from 1-naphthylamine, comprising the following steps: (1) Add 100 g of crude 1-naphthylamine into a 250 ml three-necked flask, place it in an oil bath, and heat it to 55°C to melt it; (2) adding camphorsulfonic acid at an equivalent ratio of 0.4:1 to the crude 1-naphthylamine, and stirring at 55°C for 1 hour; (3) Filter out solid impurities while hot and retain the filtrate; (4) The filtrate was heated to 55°C to ensure complete melting, and camphorsulfonic acid was added again at an equivalent ratio of 0.2:1 to the crude 1-naphthylamine product, and the mixture was stirred at 55°C for 1 hour. (5) Filter out the solid impurities while hot. The filtrate is pure. HPLC detection shows that the content of 1-naphthylamine is >99.8%.

[0018] Example 3: A method for removing 2-naphthylamine from 1-naphthylamine, comprising the following steps: (1) Add 100 g of crude 1-naphthylamine into a 250 ml three-necked flask, place it in an oil bath, and heat it to 55°C to melt it; (2) Add pivaloyl chloride in an equivalent ratio of 0.4:1 to the crude 1-naphthylamine, and continue stirring at 55°C for 1 hour; (3) Filter out solid impurities while hot and retain the filtrate; (4) The filtrate was heated to 55°C to ensure complete melting, and pivaloyl chloride was added again at an equivalent ratio of 0.2:1 to the crude 1-naphthylamine, and stirred at 55°C for 1 hour. (5) Filter out the solid impurities while hot. The filtrate is pure. HPLC detection shows that the content of 1-naphthylamine is >99.8%.

[0019] Example 4: A method for removing 2-naphthylamine from 1-naphthylamine, comprising the following steps: (1) Add 100 g of crude 1-naphthylamine into a 250 ml three-necked flask, place it in an oil bath, and heat it to 55°C to melt it; (2) Add isobutyryl chloride in an equivalent ratio of 0.4:1 to the crude 1-naphthylamine, and continue stirring at 55°C for 1 hour; (3) Filter out solid impurities while hot and retain the filtrate; (4) The filtrate was heated to 55°C to ensure complete melting, and isobutyryl chloride was added again at an equivalent ratio of 0.2:1 to the crude 1-naphthylamine, and the mixture was stirred at 55°C for 1 hour. (5) Filter out the solid impurities while hot. The filtrate is pure. HPLC detection shows that the content of 1-naphthylamine is >99.8%.

Claims

1. A method for removing 2-naphthylamine from 1-naphthylamine, characterized in that The following steps are involved: (1) Add the crude 1-naphthylamine into a three-necked flask and heat it to 55°C to make it molten; (2) Add a specific carboxylic acid or acid chloride and continue stirring at 55°C for 1 hour; (3) Filter out solid impurities while hot and retain the filtrate; (4) The filtrate was heated to 55°C to ensure complete melting, and the specific carboxylic acid was added again, and stirred at 55°C for 1 hour; (5) Filter out solid impurities while hot, take samples of the filtrate, and perform HPLC testing; 2. According to claim 1, the temperature in step (1) is 45-55°C.

3. According to claim 1, the carboxylic acid in step (2) is adamantanecarboxylic acid and camphorsulfonic acid, and the acyl chloride is pivaloyl chloride and isobutyryl chloride.

4. According to claim 1, the equivalent ratio of carboxylic acid to crude 1-naphthylamine in step (2) is (0.2-0.5):

1.

5. According to claim 1, the reaction time in step (2) is 1 hour.

6. The method according to claim 1, wherein the carboxylic acid in step (4) is adamantanecarboxylic acid and camphorsulfonic acid, and the acyl chloride is pivaloyl chloride and isobutyryl chloride.

7. According to claim 1, the equivalent ratio of carboxylic acid to crude 1-naphthylamine in step (4) is (0.1-0.2):

1.

8. According to claim 1, the reaction time in step (4) is 1 hour.

Images