A method for preparing p-aminophenol

Abstract

The present invention belongs to the technical field of p-aminophenol preparation, and in particular to a preparation method for preparing p-aminophenol. The following steps are included, after sodium p-nitrophenol is neutralized by acid addition, p-nitrophenol is obtained after cooling and centrifugation, and an antioxidant is added to sodium p-nitrophenol before neutralization; p-nitrophenol is added to the first solvent, and then a catalyst is added, and a hydrogenation reaction is carried out under a hydrogen atmosphere, and the reaction is filtered after the reaction, and the obtained filtrate is placed in a crystallization kettle and the crystallization kettle atmosphere is replaced with a protective gas, and an antioxidant is added, and the temperature is reduced and crystallized, and centrifugation is performed to obtain a crude p-aminophenol; the crude p-aminophenol is added to an antioxidant solution, and after stirring at room temperature, centrifugation, and drying, refined p-aminophenol is obtained. The present invention controls the content of impurities 4,4'-diaminodiphenyl ether in p-aminophenol to less than 0.1%, and the content of impurities 4,4'-diaminodiphenyl ether in p-aminophenol produced in multiple batches is controlled to be stable, and the product qualification rate is high.

Description

Technical Field

[0001] This invention belongs to the field of p-aminophenol preparation technology, and specifically relates to a method for preparing p-aminophenol. Background Technology

[0002] p-Aminophenol, also known as p-hydroxyaniline, abbreviated as PAP, is a colorless or pale yellow flaky or needle-like crystal. It turns brown upon exposure to light or air. It is soluble in hot water and alcohol, slightly soluble in cool water, and almost insoluble in benzene and chloroform. PAP is a widely used organic chemical intermediate, primarily used in the rubber, pharmaceutical, dye, and photosensitive materials industries.

[0003] p-Aminophenol is synthesized from p-nitrochlorobenzene through hydrolysis and catalytic hydrogenation. When tested according to national standards, a very large unknown impurity is often found in the finished p-aminophenol product, affecting the purity of the product. Since p-aminophenol is the main raw material for the production of acetaminophen, its purity has a great impact on the yield and quality of acetaminophen.

[0004] Therefore, in order to obtain higher quality para-acetaminophen products and improve the pass rate of different batches of products in large-scale production, it is necessary to continuously study how to reduce the content of impurities in para-aminophenol during the preparation or purification process. Providing a preparation method for para-aminophenol with ultra-low impurity content is particularly important. Summary of the Invention

[0005] This invention provides a method for preparing p-aminophenol, the purpose of which is to solve the problem in the prior art that the presence of p-aminophenol impurities during the preparation of p-aminophenol affects the yield and quality of p-acetaminophenol.

[0006] In view of the above-mentioned technical defects, one of the objectives of this invention is to provide a method for preparing p-aminophenol.

[0007] In a first aspect, the present invention provides a method for preparing p-aminophenol, comprising the following steps:

[0008] Preparation of p-nitrophenol: After neutralizing sodium p-nitrophenol with acid, the mixture is cooled and centrifuged to obtain p-nitrophenol. Before neutralization, an antioxidant is added to sodium p-nitrophenol.

[0009] Preparation of crude p-aminophenol: p-nitrophenol is added to the first solvent, then a catalyst is added, and a hydrogenation reaction is carried out under a hydrogen atmosphere. After the reaction, the mixture is filtered, and the filtrate is placed in a crystallization vessel. The atmosphere of the crystallization vessel is replaced with a protective gas, and an antioxidant is added. The mixture is cooled and crystallized, and then centrifuged to obtain crude p-aminophenol.

[0010] Refined p-aminophenol crude product: Add p-aminophenol crude product to an antioxidant solution, stir at room temperature, centrifuge, and dry to obtain refined p-aminophenol.

[0011] In the above preparation method, as a preferred embodiment, the antioxidant includes one or more of sodium metabisulfite, metabisulfite, sodium sulfite, or sodium bisulfite.

[0012] In the above preparation method, as a preferred embodiment, in the preparation of p-nitrophenol, the molar ratio of sodium p-nitrophenolate to acid is 1:(1-1.3);

[0013] In the above preparation method, as a preferred embodiment, the acid is concentrated hydrochloric acid.

[0014] In the above preparation method, as a preferred embodiment, in the preparation of p-nitrophenol, the mass ratio of sodium p-nitrophenolate to antioxidant is 1:(0.005-0.01);

[0015] In this invention, the amount of antioxidant added is strictly controlled during the preparation of p-nitrophenol because if too much antioxidant is added, there will be too much residue in p-nitrophenol. During the catalytic hydrogenation process, sodium sulfite is oxidized to sodium sulfate, and the sulfate ion will poison the catalyst and affect the hydrogenation reaction.

[0016] In the above preparation method, as a preferred embodiment, in the preparation of p-nitrophenol, the neutralization temperature is 75-90℃ (e.g., 85℃) and the time is 20-60min (e.g., 40min, 50min);

[0017] And / or, the protective gas includes nitrogen and helium;

[0018] And / or, the neutralization reaction is terminated when the pH of the reaction system is 1-4 (e.g., 2, 3);

[0019] And / or, the cooling is to reduce the temperature to 20-30°C.

[0020] Antioxidants are added during neutralization to prevent the oxidation of p-nitrophenol. The amount of 4,4'-dinitrodiphenyl ether generated is controlled by controlling the amount of 4,4'-diaminodiphenyl ether generated.

[0021] In the preparation method of the present invention, in order to increase the removal effect of impurities, it is preferable to add an adsorbent such as activated carbon in each step of the preparation of p-nitrophenol to adsorb impurities.

[0022] In the above preparation method, as a preferred embodiment, in the preparation of crude p-aminophenol, the first solvent is selected from aqueous ethanol solution and / or aqueous methanol solution, wherein the volume fraction of ethanol in the aqueous ethanol solution is 50-80% (e.g., 60% or 70%), and the volume fraction of methanol in the aqueous methanol solution is 50-80% (e.g., 60% or 70%).

[0023] The mass ratio of p-nitrophenol to the first solvent is 1:(2-4);

[0024] The catalyst is selected from nickel catalysts or palladium on carbon catalysts;

[0025] The mass ratio of p-nitrophenol to catalyst is 1:(0.05-0.1);

[0026] The hydrogenation reaction is carried out at a temperature of 90-110℃ (e.g., 95℃, 105℃) for 2-3 hours (e.g., 2.5 hours).

[0027] The mass ratio of p-nitrophenol to antioxidant is 1:(0.005-0.01);

[0028] Cooling crystallization refers to crystallization when the temperature is lowered to 20-30℃.

[0029] In the above preparation method, as a preferred embodiment, in the purification of p-aminophenol, the mass ratio of crude p-aminophenol to antioxidant is 1:0.08-0.2;

[0030] In the above preparation method, as a preferred embodiment, the antioxidant solution is prepared by an antioxidant and a second solvent, and the mass ratio of crude p-aminophenol to the second solvent is 1:(2-3).

[0031] Preferably, the second solvent is water.

[0032] In the above preparation method, as a preferred embodiment, the stirring time in the purified p-aminophenol is 30-60 min (e.g., 40 min, 50 min).

[0033] Secondly, the present invention also provides a p-aminophenol obtained by the above preparation method, wherein the purity of the p-aminophenol is ≥99.70%.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. This invention can control the content of the impurity 4,4'-diaminodiphenyl ether in p-aminophenol to below 0.1%, and the content of the impurity 4,4'-diaminodiphenyl ether in p-aminophenol produced in multiple batches is stably controlled, resulting in a high product qualification rate.

[0036] 2. This invention controls the generation of impurities in three ways: first, an antioxidant is added during the neutralization of sodium nitrophenol to prevent the oxidation and reduction of p-nitrophenol to generate impurities; second, nitrogen is used to replace the crystallization vessel of p-aminophenol and an antioxidant is added; and third, p-aminophenol is fully coated with sodium metabisulfite solution during purification to prevent oxidation and the generation of impurities.

[0037] 3. The p-aminophenol prepared by this invention has a purity of ≥99.70%, which is high in purity, low in impurities, and has a high product qualification rate. Detailed Implementation

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below to enable those skilled in the art to practice and reproduce them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0039] The following examples provide a more detailed description of a method for preparing p-aminophenol with controlled p-aminophenol impurity content according to the present invention. These examples are provided only to illustrate the invention and are not intended to limit its scope. The examples provided below can serve as a basis for further improvements or applications by those skilled in the art and do not constitute a specific limitation on the invention in any way. The concentrated hydrochloric acid referred to in this application is conventional concentrated hydrochloric acid with a mass concentration of approximately 36.5%.

[0040] Example 1

[0041] Synthesis of p-nitrophenol: 2500 kg of sodium p-nitrophenolate and 13 kg of sodium metabisulfite were added to 1730 kg of concentrated hydrochloric acid and neutralized at 80 °C for 30 min until the pH was about 1. After neutralization, the temperature was lowered to 25 °C and centrifuged to obtain 2150 kg of p-nitrophenol.

[0042] Synthesis of p-aminophenol: The reactor was purged with hydrogen three times. 2150 kg of p-nitrophenol and 4300 kg of a 50% (v / v) aqueous ethanol solution were added to the reactor to completely dissolve the p-nitrophenol. Then, 108 kg of nickel catalyst was added. The temperature was raised to 100°C, and hydrogen was introduced for 3 hours until the hydrogen valve was closed, maintaining constant pressure inside the reactor. The catalyst was filtered, and the filtrate entered a crystallization reactor. The crystallization reactor was purged with nitrogen three times, and 11 kg of sodium metabisulfite was added. The temperature was lowered to 25°C, and the mixture was centrifuged to obtain 1680 kg of crude p-aminophenol.

[0043] Refining of p-aminophenol: Add 178 kg of sodium metabisulfite to 3560 kg of water and dissolve it completely to prepare a 4.8% sodium metabisulfite solution. Then add 1680 kg of crude p-aminophenol, stir for 30 min, centrifuge, and dry to obtain 1560 kg of finished p-aminophenol product.

[0044] Testing revealed that p-aminophenol had a purity of 99.78% and contained 0.03% of the impurity 4,4'-diaminodiphenyl ether. The yield of p-aminophenol was 92.1%.

[0045] Example 2

[0046] Synthesis of p-nitrophenol: 2500 kg of sodium p-nitrophenolate and 15 kg of sodium metabisulfite were added to 1730 kg of concentrated hydrochloric acid and neutralized at 90 °C for 20 min until the pH was about 4. After neutralization, the temperature was lowered to 25 °C and centrifuged to obtain 2190 kg of p-nitrophenol.

[0047] Synthesis of p-aminophenol: The reactor was purged with hydrogen three times. 2190 kg of p-nitrophenol and 4500 kg of an 80% (v / v) aqueous ethanol solution were added to the reactor to completely dissolve the p-nitrophenol. Then, 110 kg of nickel catalyst was added. The temperature was raised to 100°C, and hydrogen was introduced for 3 hours until the hydrogen valve was closed, maintaining constant pressure inside the reactor. The catalyst was filtered, and the filtrate entered a crystallization reactor. The crystallization reactor was purged with nitrogen three times, and 15 kg of sodium metabisulfite was added. The temperature was lowered to 25°C, and the mixture was centrifuged to obtain 1670 kg of crude p-aminophenol.

[0048] Purification of p-aminophenol: Add 300 kg of sodium metabisulfite to 3400 kg of water and dissolve it completely to prepare an 8.1% sodium metabisulfite solution. Then add 1670 kg of crude p-aminophenol, stir for 30 min, centrifuge, and dry to obtain 1550 kg of finished p-aminophenol product.

[0049] The purity of p-aminophenol was 99.82%, and the content of the impurity 4,4'-diaminodiphenyl ether was 0.02%. The yield of p-aminophenol was 91.5%.

[0050] Example 3

[0051] Synthesis of p-nitrophenol: 2500 kg of sodium p-nitrophenolate and 18 kg of sodium metabisulfite were added to 1730 kg of concentrated hydrochloric acid and neutralized at 85 °C for 30 min until the pH was about 3. After neutralization, the temperature was lowered to 25 °C and centrifuged to obtain 2140 kg of p-nitrophenol.

[0052] Synthesis of p-aminophenol: The reactor was purged with hydrogen three times. 2140 kg of p-nitrophenol and 4300 kg of a 60% (v / v) ethanol aqueous solution were added to the reactor to completely dissolve the p-nitrophenol. Then, 110 kg of nickel catalyst was added. The temperature was raised to 90°C, and hydrogen was introduced for 3 hours until the hydrogen valve was closed, maintaining constant pressure inside the reactor. The catalyst was filtered, and the filtrate entered a crystallization reactor. The crystallization reactor was purged with nitrogen three times, and 12 kg of sodium metabisulfite was added. The temperature was lowered to 25°C, and centrifuged to obtain 1650 kg of crude p-aminophenol.

[0053] Refining of p-aminophenol: 178 kg of sodium metabisulfite was added to 3560 kg of water and completely dissolved to prepare a 4.8% sodium metabisulfite solution. Then, 1650 kg of crude p-aminophenol was added, stirred for 30 min, centrifuged, and dried to obtain 1559 kg of finished p-aminophenol.

[0054] Testing revealed that p-aminophenol had a purity of 99.80% and contained 0.02% of the impurity 4,4'-diaminodiphenyl ether. The yield of p-aminophenol was 92.1%.

[0055] Comparative Example 1

[0056] Synthesis of p-nitrophenol: 2500 kg of sodium p-nitrophenol was added to 1730 kg of concentrated hydrochloric acid and neutralized at 85 °C for 30 min until the pH was about 3. After neutralization, the temperature was lowered to 25 °C and centrifuged to obtain 2150 kg of p-nitrophenol.

[0057] Synthesis of p-aminophenol: The reactor was purged with hydrogen three times. 2150 kg of p-nitrophenol and 4300 kg of a 60% (v / v) ethanol aqueous solution were added to the reactor to completely dissolve the p-nitrophenol. Then, 110 kg of nickel catalyst was added. The temperature was raised to 90°C, and hydrogen was introduced for 3 hours until the hydrogen valve was closed, maintaining constant pressure inside the reactor. The catalyst was filtered, and the filtrate was transferred to a crystallization reactor, cooled to 25°C, centrifuged, and dried to obtain 1650 kg of crude p-aminophenol.

[0058] Purification of p-aminophenol: Add 1650 kg of crude p-aminophenol to 3560 kg of water, stir for 30 min, centrifuge, and dry to obtain 1560 kg of finished p-aminophenol.

[0059] The purity of p-aminophenol was 97.25%, and the content of the impurity 4,4'-diaminodiphenyl ether was 2.58%. The yield of p-aminophenol was 92.1%.

[0060] Comparative Example 2

[0061] The only difference between this comparative example and Example 1 is the timing of adding the antioxidant during the synthesis of p-nitrophenol. All other process steps and dosages are the same. In this comparative example, the antioxidant is added after neutralization, stirred for 15 minutes, cooled to 25°C, and then centrifuged.

[0062] The p-aminophenol obtained in this comparative example had a purity of 99.69% and a 4,4'-diaminodiphenyl ether impurity content of 0.11%. The yield of p-aminophenol was 92.0%.

[0063] Comparative Example 3

[0064] The only difference between this comparative example and Example 1 is the amount of antioxidant added during the synthesis of p-nitrophenol; all other process steps and dosages are the same. In this comparative example, 38 kg of antioxidant was added during the synthesis of p-nitrophenol.

[0065] The p-aminophenol obtained in this comparative example had a purity of 89.65% and a 4,4'-diaminodiphenyl ether impurity content of 0.04%. The yield of p-aminophenol was 86.1%.

[0066] Comparative Example 4

[0067] Except for the timing of adding the antioxidant during the synthesis of p-aminophenol, which differs from Example 1, the other process steps and dosages in this comparative example are the same as in Example 1. In this comparative example, the antioxidant is added before the start of the reaction, followed by catalytic hydrogenation, cooling and centrifugation, purification of the crude product, and drying to obtain p-aminophenol.

[0068] The comparative example yielded p-aminophenol with a purity of 26.78% and an impurity content of 0.23% for 4,4'-diaminodiphenyl ether. The yield of p-aminophenol was 15.6%.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for preparing p-aminophenol, characterized in that, The following steps are involved: Preparation of p-nitrophenol: after adding acid to sodium p-nitrophenol for neutralization, cooling and centrifuging to obtain p-nitrophenol, before neutralization, adding an antioxidant to the sodium p-nitrophenol; Preparation of crude p-aminophenol: adding p-nitrophenol to a first solvent, then adding a catalyst, carrying out a hydrogenation reaction under a hydrogen atmosphere, filtering after the reaction, placing the obtained filtrate in a crystallization kettle, replacing the atmosphere of the crystallization kettle with a protective gas, adding an antioxidant, cooling and crystallizing, and centrifuging to obtain a crude p-aminophenol; Refining crude p-aminophenol: adding crude p-aminophenol to an antioxidant solution, stirring at room temperature, centrifuging, and drying to obtain refined p-aminophenol; The antioxidant includes one or more of sodium pyrosulfite, pyrosulfite, sodium sulfite or sodium bisulfite; In the preparation of p-nitrophenol, the mass ratio of sodium p-nitrophenolate to the antioxidant is 1:(0.005-0.01); In the preparation of crude p-aminophenol, the mass ratio of p-nitrophenol to antioxidant is 1:(0.005-0.01); In the refined p-aminophenol, the mass ratio of the crude p-aminophenol to the antioxidant is 1:(0.08-0.2).

2. The method for preparing p-aminophenol according to claim 1, characterized in that: In the preparation of p-nitrophenol, the molar ratio of sodium p-nitrophenolate to acid is 1:(1-1.3); And / or, the acid is concentrated hydrochloric acid.

3. The method for preparing p-aminophenol according to claim 1, characterized in that, In the preparation of p-nitrophenol, the neutralization temperature is 75-90°C and the time is 20-60min; And / or, the protective gas includes nitrogen and helium; And / or, the neutralization reaction is terminated when the pH of the reaction system is 1-4; And / or, the cooling is to 20-30°C.

4. The method for preparing p-aminophenol according to claim 1, characterized in that: In the preparation of crude p-aminophenol, the first solvent is selected from ethanol aqueous solution and / or methanol aqueous solution, the volume fraction of ethanol in the ethanol aqueous solution is 50-80%, and the volume fraction of methanol in the methanol aqueous solution is 50-80%; and / or, the mass ratio of the p-nitrophenol to the first solvent is 1:(2-4); And / or, the catalyst is selected from a nickel catalyst or a palladium-carbon catalyst; And / or, the mass ratio of p-nitrophenol to the catalyst is 1:(0.05-0.1); And / or, the hydrogenation reaction temperature is 90-110°C and the time is 2-3h; And / or, the cooling crystallization refers to crystallization by cooling to 20-30°C.

5. The method for preparing p-aminophenol according to claim 1, characterized in that: The antioxidant solution is prepared from an antioxidant and a second solvent, and the mass ratio of the crude p-aminophenol to the second solvent is 1:(2-3); The second solvent is water.

6. The method for preparing p-aminophenol according to claim 1, characterized in that: In the purification of p-aminophenol, the stirring time is 30-60 minutes.