Preparation Of P-Aminophenol By Catalytic Reduction Of Nitrobenzene In The CO₂/H₂O System

p-Aminophenol(PAP) is a useful and important chemical intermediate, and can be used in the pharmaceutical industry and in the dye industry, and widely in photographic chemicals and fine chemicals production.The preparation of p-aminophenol involves the rearrangement of N-phenylhydroxylamine in the presence of acid medium, H2SO4is widely used, and alkali needs to be added after the reaction, and a lot of wastewater is formed. In view of environmental concerns, it is important to open up an efficient method, which avoids using H2SO4.In this paper, carbonic acid in situ formed by combining CO2and H2O, replacing inorganic acid, is applied in the catalytic reduction of nitroarenes to the preparation of p-aminophenol. After reaction, carbonic acid can be self-neutralized by releasing CO2, and it follows the aim of green chemistry.This article screened the commonly used catalyst of nitrobenzene hydrogenation in CO2/H2O system, and filter out the best catalyst is Pd/C. The preparation of p-aminophenol by Pd/C catalysts selective hydrogenation of nitrobenzene in a CO2/H2O system was systematically researched. The effects of reaction time, the nNB:nPd, reaction temperature, pressure of CO2and H2, and additive DMSO on the reaction were investigated. The optimized experimental conditions were as follows:substrate to catalyst molar ratio5320:1. the volume of solvent water60mL, mDMSO=1mg, reaction temperature140℃, CO2initial pressure5.0MPa, H2initial pressure0.3MPa. reaction time8h, the conversion rate of nitrobenzene was99.3%, yield of p-aminophenol was53.3%.