A method for purifying p-nitroaniline and application thereof

Abstract

A method for purifying p-nitroaniline and application thereof, comprising the following steps: (1) dissolving: adding p-nitroaniline into an oxygen-containing polar solvent, and stirring until completely dissolved; (2) filtering: adding a filter aid into the above solution, and filtering, wherein the filter cake is tar impurities in the p-nitroaniline and the filter aid, and the filtrate is the purified p-nitroaniline solution; (3) post-treatment: adding water to the purified p-nitroaniline solution to perform rectification, wherein the solvent is collected at the top of the column, and is recycled and reused; the suspension of water and p-nitroaniline is collected at the bottom of the column, and is filtered, wherein the filter cake is the purified p-nitroaniline, and the filtrate is water, which is recycled and reused. The p-nitroaniline treated by the method has a bright yellow appearance, a small odor and no pungent smell, and can be directly used for catalytic hydrogenation reaction, especially the reaction of a noble metal catalyst, so that the catalyst can be continuously recycled, and the product quality meets the standards.

Description

Technical Field

[0001] This invention relates to a purification method for p-nitroaniline and its application, belonging to the field of chemical technology. Background Technology

[0002] p-Nitroaniline, abbreviated as PNA, is an important organic synthesis raw material, mainly used to manufacture azo dyes and p-phenylenediamine. In addition, p-nitroaniline is used to manufacture antioxidants with the p-phenylenediamine structure, such as antioxidants 33PD, 44PD, and 77PD.

[0003] The synthesis of antioxidants 33PD, 44PD, and 77PD employs a reductive alkylation process involving p-nitroaniline and ketones. This reductive alkylation is carried out via catalytic hydrogenation, typically using precious metals such as palladium or platinum as catalysts, with platinum showing superior performance. Due to the high cost and limited quantity of precious metal catalysts, the requirements for raw materials are extremely stringent. p-Nitroaniline is obtained by reacting p-nitrochlorobenzene with high-concentration ammonia at 180°C and 4.5 MPa for 10 hours. During this prolonged high-temperature, high-pressure reaction, a certain amount of tar is inevitably generated. This tar is fatal to precious metal catalysts, rapidly deactivating them and rendering them unusable. This results in low product quality, high catalyst costs, and severely impacts production. Commercially available p-nitroaniline, whether fresh, dried, or high-quality, even chemically pure or analytically pure, contains this tar. Therefore, for reactions using p-nitroaniline as a raw material for catalytic hydrogenation, especially those utilizing precious metal catalysts, the p-nitroaniline must be purified to remove the tar.

[0004] Chu Zheng reported in "Research on Preparation Process of High-Purity p-Nitroaniline" (Modern Chemical Industry, 2012, (3): 33-35) that the purity of p-nitroaniline can reach 99.9%. His analytical method uses gas chromatography area normalization to calculate the purity of p-nitroaniline, but there is no report on the treatment method of the tar contained in p-nitroaniline. Yuan Junxiu et al. reported a preparation method of high-purity p-nitroaniline in patent CN102001952A. The p-nitroaniline prepared by this method can reach a purity of up to 99.9%, but there is also no description of the treatment method of the tar contained in p-nitroaniline.

[0005] Hua Renqing reported a process for preparing odorless p-nitroaniline in patent CN1111236A. The process involves adding p-nitroaniline to methanol or ethanol, heating to reflux and maintaining the reflux for a certain period of time, then adding water to precipitate p-nitroaniline. The p-nitroaniline is then separated from the solvent and dried to obtain odorless p-nitroaniline. No method for treating the tar contained in p-nitroaniline was found.

[0006] Jiang Youan and Chen Sheng reported a production process for N,N'-di-sec-butyl-p-phenylenediamine in patent CN105061214B, which included a description of the treatment of p-nitroaniline tar: Butanone and p-nitroaniline are added to a mixing tank in a ratio of 1.3:1.2, heated to 120°C, and stirred for 20 minutes to dissolve the materials. Then, activated carbon with a particle size of 100 mesh is added and stirred for 5-10 minutes. The activated carbon is then filtered through a plate and frame filter. Under pressure, the activated carbon adheres to the filter plate and frame, adsorbing the tar in the raw material passing through the plate and frame. This method first requires heating methyl ethyl ketone (MEK) and p-nitroaniline to 120°C to dissolve the materials. However, MEK has a boiling point of 79.6°C at normal pressure. To reach 120°C, the mixing vessel must be sealed and pressure-resistant, increasing equipment investment. Secondly, since it is hot filtration, the filter and related pipelines must be heated in all directions to prevent temperature drops due to improper insulation, which could cause p-nitroaniline to precipitate. Once precipitated, it will clog the filter and related pipelines, making the filtration operation difficult. Its melting point of 147°C makes unblocking particularly difficult. Therefore, this method is not very practical in actual production and increases processing costs. Summary of the Invention

[0007] The purpose of this invention is to provide a purification method for p-nitroaniline, which involves selecting a suitable solvent to dissolve p-nitroaniline without dissolving the tar, thereby filtering out the tar and achieving the purpose of purifying p-nitroaniline.

[0008] The main technical solution of this invention: a purification method for p-nitroaniline, comprising the following steps:

[0009] (1) Dissolution: Add p-nitroaniline to an oxygen-containing polar solvent and stir until completely dissolved;

[0010] (2) Filtration: Add filter aid to the above solution and filter. The filter cake contains impurities such as tar in p-nitroaniline and filter aid. The filtrate is the purified p-nitroaniline solution.

[0011] (3) Post-processing: The purified p-nitroaniline solution was distilled with water. The solvent was collected from the top of the column and recycled. The bottom of the column was a suspension of water and p-nitroaniline. The suspension was filtered, and the filter cake was the purified p-nitroaniline. The filtrate was water and recycled.

[0012] In step (1), the oxygen-containing polar solvent can be an ester such as ethyl acetate or methyl acetate, or a ketone such as acetone, butanone, 2-pentanone, cyclohexanone, 4-methyl-2-pentanone, 5-methyl-2-hexanone, etc., with ketones being preferred as the solvent.

[0013] In step (1), the molar ratio of p-nitroaniline to solvent is 1:(4~20).

[0014] In step (2), the filter aid can be diatomaceous earth or activated carbon, and the mass ratio of p-nitroaniline to the filter aid is 1:0.01~0.05.

[0015] In step (2), after adding the filter aid, stir at room temperature for 30-60 minutes and then filter.

[0016] Steps (1) and (2) are performed at room temperature.

[0017] In step (3), the mass ratio of p-nitroaniline to deionized water is 1:(2~5).

[0018] The advantages of this invention are: (1) Compared with CN105061214B, the dissolution and filtration of p-nitroaniline are carried out at room temperature and normal pressure, avoiding high temperature and pressure operation, making the operation simple and requiring less equipment investment; (2) By adding a certain amount of water during distillation to recover the solvent, on the one hand, it washes the inorganic salts such as NH4Cl carried in p-nitroaniline, and on the other hand, it avoids the safety hazards caused by p-nitroaniline directly contacting the heating surface (inner wall of the reactor) as the solvent is continuously distilled out. Finally, the presence of water facilitates the discharge; (3) This invention does not produce wastewater, and the added water can be recycled for the next batch of operation. The p-nitroaniline treated by this invention has a bright yellow appearance, a mild odor, and is not pungent (before treatment, it is yellowish-brown and has a pungent odor). It can be directly used for catalytic hydrogenation reactions, especially reactions with precious metal catalysts, to achieve continuous use of catalysts and meet product quality standards, thus enabling smooth production. Therefore, this invention has better application prospects. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the method of an embodiment of the present invention. Detailed Implementation

[0020] The method of the present invention will be described in detail below with reference to the embodiments.

[0021] The following is a flowchart for reference. Figure 1 .

[0022] Example 1

[0023] At room temperature (30℃), 75g of p-nitroaniline (industrial grade, 93% purity) and 280g of acetone were added to a four-necked flask and stirred until dissolved. A large amount of black tar was found at the bottom of the flask. Then, 1g of diatomaceous earth was added, and stirring continued for 30 minutes. The mixture was then filtered through a triangular glass funnel lined with qualitative filter paper. After filtration, 200mL of distilled water was added to the filtrate, and the acetone was recovered by distillation. When the ambient temperature abruptly changed from 56.5℃ to 82℃ (at which point the liquid temperature was approximately 100℃), the temperature was lowered, and the residue was filtered. The mother liquor was reused for the next batch of acetone distillation. The filter cake contained 86g of p-nitroaniline, bright yellow crystals with no irritating odor.

[0024] Example 2

[0025] At room temperature (20℃), 75g of p-nitroaniline (industrial grade, 93% purity) and 300g of acetone were added to a four-necked flask and stirred until dissolved. A large amount of black tar was found at the bottom of the flask. Then, 1.5g of diatomaceous earth was added, and stirring continued for 30 minutes. The mixture was then filtered through a triangular glass funnel lined with qualitative filter paper. After filtration, 220mL of distilled water was added to the filtrate, and the acetone was recovered by distillation. When the ambient temperature abruptly changed from 56.5℃ to 82℃ (at which point the liquid temperature was approximately 100℃), the temperature was lowered, and the residue was filtered. The mother liquor was reused for the next batch of acetone distillation. The filter cake contained 82g of p-nitroaniline (industrial grade, 93% purity). It was a bright yellow crystal with no irritating odor.

[0026] Example 3

[0027] At room temperature (8℃), 75g of p-nitroaniline (industrial grade, 93% purity) and 350g of acetone were added to a four-necked flask and stirred until dissolved. A large amount of black tar was found at the bottom of the flask. Then, 1.5g of activated carbon was added, and stirring continued for 30 minutes. The mixture was then filtered through a triangular glass funnel lined with qualitative filter paper. After filtration, 250mL of distilled water was added to the filtrate, and the acetone was recovered by distillation. When the ambient temperature abruptly changed from 56.5℃ to 82℃ (at which point the liquid temperature was approximately 100℃), the temperature was lowered, and the residue was filtered. The mother liquor was reused for the next batch of acetone distillation. The filter cake contained 85g of p-nitroaniline (industrial grade, 93% purity). It was a bright yellow crystal with no irritating odor.

[0028] Example 4

[0029] At room temperature (28℃), 75g of p-nitroaniline (industrial grade, 93% purity) and 315g of butanone were added to a four-necked flask and stirred until dissolved. A large amount of black tar was found at the bottom of the flask. Then, 1g of diatomaceous earth was added, and stirring continued for 30 minutes. The mixture was then filtered through a triangular glass funnel lined with qualitative filter paper. After filtration, 200mL of distilled water was added to the filtrate, and the butanone was recovered by azeotropic distillation. When the air temperature abruptly changed from 73.5℃ (the azeotropic point of butanone and water) to 88℃ (at which point the liquid temperature was approximately 100℃), the temperature was lowered, and the residue was filtered. The mother liquor was reused for the next batch of azeotropic distillation of butanone. The filter cake was 85g of p-nitroaniline, a bright yellow crystal with no irritating odor.

[0030] Example 5

[0031] At room temperature (10℃), 75g of p-nitroaniline (industrial grade, 93% purity) and 360g of butanone were added to a four-necked flask and stirred until dissolved. A large amount of black tar was found at the bottom of the flask. Then, 1g of activated carbon was added, and stirring continued for 30 minutes. The mixture was then filtered through a triangular glass funnel lined with qualitative filter paper. After filtration, 200mL of distilled water was added to the filtrate, and the butanone was recovered by azeotropic distillation. When the air temperature suddenly changed from 73.5℃ (the azeotropic point of butanone and water) to 88℃ (at which point the liquid temperature was approximately 100℃), the temperature was lowered, and the residue was filtered. The mother liquor was reused for the next batch of azeotropic distillation of butanone. The filter cake was 82g of p-nitroaniline, a bright yellow crystal with no irritating odor.

[0032] Example 6

[0033] At room temperature (30℃), 75g of p-nitroaniline (industrial grade, 93% purity) and 720g of 5-methyl-2-hexanone (MIAK) were added to a four-necked flask and stirred until dissolved. A large amount of black tar was found at the bottom of the flask. Then, 2g of diatomaceous earth was added, and stirring continued for 30 minutes. The mixture was then filtered through a triangular glass funnel lined with qualitative filter paper. After filtration, 200mL of distilled water was added to the filtrate, and 5-methyl-2-hexanone was recovered by azeotropic distillation. When the air temperature abruptly changed from 94.5℃ (the azeotropic point of 5-methyl-2-hexanone and water) to 99℃ (at which point the liquid temperature was approximately 105℃), the temperature was lowered, and the residue was filtered. The mother liquor was reused for the next batch of azeotropic distillation of 5-methyl-2-hexanone. The filter cake contained 82g of p-nitroaniline, which was bright yellow crystals with no irritating odor.

[0034] Example 7

[0035] At room temperature (25℃), 75g of p-nitroaniline (industrial grade, 93% purity) and 8400g of ethyl acetate were added to a four-necked flask and stirred until dissolved. A large amount of black tar was found at the bottom of the flask. Then, 2g of activated carbon was added, and stirring continued for 30 minutes. The mixture was then filtered through a triangular glass funnel lined with qualitative filter paper. After filtration, 200mL of distilled water was added to the filtrate, and ethyl acetate was recovered by azeotropic distillation. When the air temperature abruptly changed from 70.5℃ (the azeotropic point of ethyl acetate and water) to 99℃ (at which point the liquid temperature was approximately 110℃), the temperature was lowered, and the residue was filtered. The mother liquor was reused for the next batch of azeotropic distillation of ethyl acetate. The filter cake contained 84g of p-nitroaniline, bright yellow crystals, with no irritating odor.

[0036] Example 8

[0037] The p-nitroaniline product treated by the method described in Example 1 was used to synthesize antioxidant 44PD (N,N'-di-sec-butyl-p-phenylenediamine) to investigate the catalyst application.

[0038] In a high-pressure reactor, p-nitroaniline (PNA), butanone (MEK), and 3% Pt / C catalyst were added sequentially at a ketone-amine ratio of 6:1 (mol ratio). After purging with N2 and H2, the pressure was increased to 3.2 MPa, stirring was started, and the temperature was raised. The reaction temperature was maintained at 85-105℃, and the reaction was carried out for about 2 hours under 3.2 MPa hydrogen pressure, followed by cooling to room temperature. The pressure was released, the product was discharged, and filtered. The filter cake was used as catalyst and reused in the next batch. The filtrate was first simply distilled under normal pressure. When the liquid temperature reached 110℃, a vacuum was slowly introduced. When the liquid temperature reached 140℃ and the air temperature dropped to 50℃ (absolute pressure 30-40 mmHg), no distillate was produced. The product was then cooled and discharged. The reactor liquid was the finished product. The distilled solvent was separated into layers. The upper layer was reused directly, and the lower layer was collected and concentrated for distillation and recovery.

[0039]

[0040] The catalyst was reused 15 times, achieving a 100% conversion rate of p-nitroaniline, an average product content of 98.07%, and an average yield of 97.12%. The catalyst activity did not decrease, and it can be reused to achieve the purpose of this invention.

[0041] Example 9

[0042] Compared with Example 8, p-nitroaniline was used directly to synthesize antioxidant 44PD without any treatment, and the reaction conditions were the same as in Example 8.

[0043]

[0044] As shown in the table above, the product quality drops sharply after the catalyst is reused without purification of p-nitroaniline. This indicates that p-nitroaniline contains impurities that poison the catalyst. Therefore, p-nitroaniline must be purified for the catalyst reuse to proceed smoothly.

[0045] Example 10

[0046] At 5m 3 700 kg of p-nitroaniline (industrial grade, 93% purity) and 3000 kg of acetone were added to a stirred stainless steel reactor. The mixture was stirred and dissolved at room temperature (25°C). Then, 10 kg of diatomaceous earth was added, and stirring continued for 30 minutes. The mixture was then filtered through a stainless steel sintered tube filter. After filtration, 2000 kg of deionized water was added to the filtrate, and acetone was recovered by distillation. When the air temperature suddenly changed from 56.5°C to 82°C (at which point the liquid temperature was approximately 100°C), the mixture was cooled. The reactor liquid was then filtered through a centrifuge. The mother liquor was reused for the next batch of acetone distillation. The filter cake was 850 kg of p-nitroaniline (industrial grade), bright yellow crystals, with no irritating odor.

[0047] The above-mentioned p-nitroaniline was applied to synthesize antioxidant 77PD (N,N'-bis(1,4-dimethylpentyl)p-phenylenediamine) to investigate the catalyst application.

[0048] At 1.5m 3 In a high-pressure reactor, p-nitroaniline (moiste), 5-methyl-2-hexanone, and 3% Pt / C catalyst were added sequentially. After purging with N2 and H2 respectively, the pressure was increased to 3.2 MPa, stirring was started, and the temperature was raised. The reaction temperature was maintained at 85~145℃, and the reaction was carried out for about 2~4 hours under 3.2 MPa hydrogen pressure, followed by cooling to room temperature. The pressure was released, the product was discharged, and filtered. The filter cake was used as catalyst and reused in the next batch. The filtrate was first simply distilled under normal pressure. When the liquid temperature reached 120℃, a vacuum was slowly introduced. When the liquid temperature reached 140℃ and the air temperature dropped to 50℃ (absolute pressure 30~40 mmHg), no distillate was produced. The product was then cooled and discharged. The reactor liquid was the finished product. The distilled solvent was separated into layers. The upper layer was reused directly, and the lower layer was collected and concentrated for distillation and recovery.

[0049]

[0050] It is evident that by using this invention to synthesize antioxidant 77PD in pilot production, the catalyst can be reused and the product quality meets the standards.

[0051] The scope of protection of this invention is not limited to the above embodiments. All modifications mentioned in the claims and those that can be deduced by those skilled in the art are within the scope of protection.

Claims

1. A method for purifying p-nitroaniline, characterized by the following steps: (1) Dissolution: Add p-nitroaniline to acetone and stir until completely dissolved to form a solution; (2) Filtration: Add filter aid to the above solution and filter. The filter cake is the impurities and filter aid in p-nitroaniline, and the filtrate is the purified p-nitroaniline solution; (3) Post-treatment: Add the above purified p-nitroaniline solution to deionized water for distillation. The solvent acetone is collected from the top of the column and recycled. The bottom of the column is a suspension of water and p-nitroaniline. Filter the suspension. The filter cake is the purified p-nitroaniline, and the filtrate is water, which is recycled. The (1) dissolution and (2) filtration steps are all carried out at room temperature. The treated p-nitroaniline is used to prepare antioxidants with the p-phenylenediamine structure of 33PD, 44PD, and 77PD.

2. The method of claim 1, wherein In the dissolution step (1), the molar ratio of p-nitroaniline to acetone is 1:(4~20).

3. The method of claim 1, wherein In the filtration step (2) described above, diatomaceous earth or activated carbon is selected as the filter aid.

4. The method according to claim 1, characterized in that... In the filtration step (2), the mass ratio of p-nitroaniline to filter aid is 1:0.01~0.

05.

5. The method of claim 1, wherein In the post-processing step (3), the mass ratio of p-nitroaniline to deionized water is 1:(2~5).

6. The method of claim 1, wherein In the filtration step (2) described above, after adding the filter aid, stir at room temperature for 30 to 60 minutes and then filter.

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