HNO3@nano SiO2: An efficient catalytic system for the synthesis of multi-substituted imidazoles under solvent-free conditions

Concentrated nitric acid supported on nano silica (HNO3@nano SiO2) has been prepared via a simple procedure. The synthetic powder has been utilized as an effective catalytic system for the synthesis of various 2,4,5-trisubstituted imidazoles under solvent-free conditions at 100 °C in good to excellent yields. In addition, under the same reaction conditions, 1,2,4,5-tetrasubstitued imidazoles have also been performed successfully. The recovery and reusability of HNO3@nano SiO2 have been checked in 3 runs without activity loss. The significant features of this acidic nanocatalyst in the reported procedure, are high yield of products, short reaction times, green reaction media, and vast range of substrates usage. The proposed mechanism of the cyclo-condensation has also been represented.