Niobic Acid as a Recyclable Heterogeneous Catalyst for the Solvent-Free Synthesis of Substituted Benzimidazoles

We describe here a simple method for the synthesis of several substituted benzimidazoles using niobic acid Nb2O5.5H2O as heterogeneous catalyst and under solvent-free conditions. This new protocol is general and a range of aromatic and aliphatic aldehydes were condensed with o-phenylenediamine furnishing the corresponding 1,2-disubstituted benzimidazoles selectively in good yields. The catalyst was reused up four times giving the respective products in good yields but with a little decreasing in the selectivity.