Au catalyzed synthesis of benzimidazoles from 2-nitroanilines and CO2/H2

Abstract

The gold-catalyzed synthesis of benzimidazoles from 2-nitroanilines and CO₂ in the presence of H₂ was reported, and a series of benzimidazoles were obtained under relatively mild conditions. Several supported Au catalysts including Au/TiO₂, Au/Al₂O₃, Au/ZnO, Au/polyurea and Au/hydrotalcite were examined for the synthesis of benzimidazole from the reaction of 2-nitroaniline with CO₂ and H₂, among which Au/TiO₂ displayed the best performance. The reaction mechanism was investigated, and it was found that the production of benzimidazole underwent the formation of o-phenylenediamine via the hydrogenation of 2-nitroaniline, followed by the cyclization of o-phenylenediamine with CO₂ and H₂. This work provides a CO₂-involved route for the synthesis of benzimidazoles, which may widen the applications of CO₂ in the chemical synthesis.