Preparation of para-Aminophenol from Nitrobenzene through Bamberger Rearrangement Using a Mixture of Heterogeneous and Homogeneous Acid Catalysts

The direct preparation of para-aminophenol (PAP) from nitrobenzene (NB) through Bamberger rearrangement was studied in a biphasic medium using a mixture of NbOx/SiO2 and H2SO4 as an acid catalyst. After optimization of the reaction parameters, PAP was obtained with 85-88% selectivity that represents a 10% selectivity improvement compared to sulfuric acid alone. The optimized conditions were implemented in a scale-up reaction, and PAP was isolated in 84% yield (based on the recovered starting material) with 97% HPLC purity. Overall, this process requires less sulfuric acid than the traditional process, leading to a drastic reduction of the saline waste.