Hydrogenation of nitrobenzene to p-aminophenol using acidic ionic liquid as catalyst

A bifunctional catalytic system,Pt/SiO2 and a novel Brnsted acidic ionic liquid of quaternary ammonium type N,N,N-trimethyl-N-sulfobutyl hydrogen sulfate([HSO3-b-N(CH3)3]HSO4) was studied for the synthesis of p-aminophenol through the hydrogenation of nitrobenzene.The effect of ionic liquid concentration,amount of Pt/SiO2 and reaction conditions on the p-aminophenol yield and selectivity was investigated,and was compared with the result obtained over H2SO4 and Pt/SiO2 catalytic system.Under the reaction conditions of 85℃,4 h and 0.4 MPa,nitrobenzene conversion was 96.6% and p-aminophenol selectivity was 81.4% over Pt/SiO2 and [HSO3-b-N(CH3)3]HSO4,superior to the results over Pt/SiO2 and H2SO4.The possible reasons were the enhancement of nitrobenzene solubility influenced by ionic liquid,and the restriction of deep hydrogenation for phenylhydroxylamine.Pt/SiO2 catalyst could be recovered by filtration in vacuum,and p-aminophenol could be obtained from the filtrate by extraction,vacuum distillation and crystallization in sequence.Moreover,the ionic liquid and Pt/SiO2 catalytic system could be used for three times without obvious decrease of p-aminophenol yield.