Preparation Of P-aminophenol From Pt-catalyzed Hydrogenation Of Nitrobenzene In Pressurized CO₂/H₂O System

p-aminophenol (PAP) is of great importance as an intermediate for the synthesis of paracetamol. PAP's preparation by Pt-catalyzed hydrogenation of nitrobenzene (NB) has gained attention owing to its low cost of raw material and high product quality. Usually sulfuric acid was used for the rearrangement of the intermediate phenylhydroxylamine to PAP in this reaction, but a neutralization step was inevitably needed to separate PAP from the reaction mixture, during which a large volume of effluents was generated. In this thesis, aiming to develop a green preparation method of PAP, the self-neutralizable carbonic acid formed in pressurized CO2/H2O system was used as an alternative to sulfuric acid in this reaction, and the selectivity of PAP was 67%. Usually dimethylsulfoxide (DMSO) was used to modify the Pt catalyst for higher selectivity of PAP, but it was environmentally undesirable. Pt-Co catalyst was employed in the hydrogenation of NB in pressurized CO2/H2O system without any additives, and the selectivity of PAP could reach 67%, which was comparative with the selectivity when Pt/C and DMSO were used.Pt-Sn catalyst was firstly applied in the hydrogenation of NB in pressurized CO2/H2O system. By employing Pt-Sn/?-Al2O3 as catalyst, the selectivity of PAP could be 85%, which was comparative with that obtained by the conventional method using sulfuric acid and additives.The catalytic performance of Pt-Pb catalysts on the hydrogenation of NB in pressurized CO2/H2O system has been studied. Pt-Pb/SiO2 catalyst turned out to be effective for the selective formation of PAP, and the selectivity as high as 82%was obtained.Pt-M (M=Sn or Pb) catalysts with several different compsite supports and Pt-based multiple metal catalysts were also investigated for the selective conversion of NB to PAP, respectiviely. ZSM-5 or TiO2-C supported Pt-M catalysts was favorable for the selectivie formation of PAP. As for the Pt-Sn-Pb/SiO2 catalyst, PAP's selectivity of 82% was achieved under the optimized reaction conditons.