Background and overview[1][2]
P-Aminophenol (PAP for short) is an important intermediate in the synthesis of medicines, pesticides and dyes. It is mainly used in the pharmaceutical industry for the synthesis of the antipyretic and analgesic drug acetaminophen (APAP for short).
Preparation[1]
At present, the synthesis process of para-aminophenol widely adopts the direct hydrogenation method of nitrobenzene. This process generally uses platinum or palladium supported on activated carbon or silica as a catalyst and is carried out in 10% to 20% sulfuric acid. During the reaction, nitrobenzene is first hydrogenated at the metal active site to form phenylhydroxylamine, and then phenylhydroxylamine is rearranged at the acidic site to form p-aminophenol. Since this process uses sulfuric acid as the reaction medium, it is highly corrosive. At the same time, the reaction liquid needs to be neutralized with ammonia water during the product separation process, resulting in a complicated post-treatment process and a large amount of waste liquid.
Invention patent CN101157622A discloses a new process for preparing para-aminophenol by catalytic hydrogenation of nitrobenzene in a metal salt solution, which solves the current problem of using sulfuric acid as the reaction medium, which is highly corrosive and harmful to equipment materials. The dilute ammonium sulfate solution with high requirements and a large amount of by-products needs to be comprehensively treated. The main problem with this process is that the reaction needs to be carried out in a higher concentration metal salt solution. If the metal salt concentration in the reaction solution is reduced, the yield of the product p-aminophenol will be significantly reduced. However, an excessively high metal salt concentration will increase the solubility of the product p-aminophenol in the reaction solution, causing a certain impact on the direct separation of the product p-aminophenol from the reaction solution. Therefore, the disclosed process proposes to first Hot toluene is added to the solution to extract the by-product aniline, and then ethanol is added to the reaction solution from which the aniline is separated to precipitate the metal salt. Finally, the ethanol and part of the water are evaporated from the reaction solution after the metal salt is separated, and the p-amino group is obtained by cooling, crystallization, and filtration. phenol. This process has many post-processing steps, high energy consumption, and large product loss.
CN201310075425.4 is based on the patent CN101157622A. By adding a reaction cocatalyst to the reaction solution, it effectively reduces the metal salt added to the reaction solution while ensuring a higher yield of the product p-aminophenol. concentration, the reaction can be carried out in a trace amount of metal salt solution. The reaction solution does not need to separate the metal salt after the reaction. After the aniline and part of the water are separated by evaporation, it can be directly cooled and crystallized to obtain the p-aminophenol product. The crystallization mother liquor can be directly recycled. , no waste liquid discharge. The technical solution is as follows:
A process for directly synthesizing p-aminophenol from nitrobenzene by hydrogenation. The process is to prepare p-aminophenol by catalytic hydrogenation of nitrobenzene in a trace metal salt solution, and includes the following steps:
In the first step, combine 0.04g zinc sulfate, 0.1g Pt/SiO2 catalyst with a Pt loading of 0.1%, 3g nitrobenzene, and 0.01g cetyltrimethyl bromide Ammonium chloride, 0.05g cocatalyst ethylenediaminetetraacetic acid and 50ml water were put into a high-pressure reaction kettle, in which the zinc ion concentration was 4.9mmol/L;
In the second step, in the above-mentioned high-pressure reaction kettle, replace the air with N2 for 8 to 12 minutes, then heat to 200°C and introduce H2 until the partial pressure of hydrogen is 1.0MPa. Reaction 8 hours to convert nitrobenzene into p-aminophenol;
The third step: after the reaction in the second step is completed, filter the reaction solution while it is hot to separate the solid phase catalyst and the reaction solution;
The fourth step is to distill the filtered reaction solution at 40-100°C and 0.05-0.1MPa pressure to evaporate the by-product aniline and part of the water;
The fifth step is to further concentrate the reaction solution evaporated in the fourth step to 15 ml, cool to 0°C, precipitate crystals, and filter. The obtained crystals are the product p-aminophenol. The yield of p-aminophenol was 71%. The crystallization mother liquor is returned to the reactor for recycling.
Apply[2-3]
CN201410394234.9 discloses a production method that uses p-aminophenol as a reducing agent to reduce silver ammonia complex, and sodium sulfite as a stabilizer and dispersant to prepare ultra-fine spherical silver powder. The silver ammonia complex aqueous solution is added to the reducing agent aqueous solution within 5-10 seconds at 10-30°C, and the molar ratio of the silver ammonia complex and p-aminophenol is controlled to 1:0.5-0.55, and the pH of the reaction solution is 10 -11, complete the reduction and precipitation process of silver grains within 3 minutes under stirring. Silver powder particles of the present inventionThe surface is smooth and spherical, the particle size is uniform, the average particle size is 1.0-3.0μm, the tap density is 4.0-5.0g/cm3, and the specific surface area is 0.4-1.0m2 sup>/g. The ultrafine spherical silver powder product of the present invention has high density and narrow particle size distribution, and can be used as a raw material for conductive silver paste for solar cells or electronic touch screens.
CN201210557199.9 discloses a process for the continuous hydrolysis of para-aminophenol to produce hydroquinone. Para-aminophenol hydrochloride is used as raw material, and after mixing with hydrochloric acid, it is preheated to 220~240°C and heated in a tower. The hydrolysis reaction takes 150-420 minutes in the reactor. After the reaction is completed, the hydrolysis reaction liquid overflows from the outlet of the tower reactor. The hydroquinone crude product is obtained after extraction, phase separation, and desolvation of the hydrolysis reaction liquid. The reaction system of the invention has the advantages of less waste water, continuous production, high production efficiency, high yield and simple process control.
Main reference materials
[1] CN201310075425.4 Process for directly synthesizing p-aminophenol from nitrobenzene by hydrogenation
[2] CN201410394234.9 Method for preparing ultra-fine spherical silver powder by reducing silver ammonia complex with p-aminophenol
[3] CN201210557199.9 A process for producing hydroquinone by continuous hydrolysis of p-aminophenol
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