Regioselective nitration of phenols using Sr(NO3)2 or benzyltriphenylphosphonium nitrate in the presence of H2SO4-silica under solvent free conditions

Regioselective nitration of phenols using Sr(NO3)2 or benzyltriphenylphosphonium nitrate in the presence of H2SO4-silica had been realized under solvent free conditions. The reaction proceeds through the formation of nitronium ion, which attack the phenol ring preferential at ortho position in presence of Sr(NO3)2, forming mono nitrophenol. Para-orientation relative to hydroxyl group and mononitration of phenolic compounds was observed in the case of benzyltriphenylphosphonium nitrate. Some of the major advantages of this method are mild reaction conditions, high efficiency and regioselectivity of nitration and complementarity with other reported methods. In addition, benzyltriphenylphosphonium nitrate as nitrating reagent can be easily recycled.