A simple one pot nano titania mediated green synthesis of 2-alkylbenzimidazoles and indazole from aromatic azides under UV and solar light

TiO2-P25 and Ag/Pt doped TiO2 nanoparticles are efficient and highly chemo-selective photocatalysts for the reduction of aromatic azides to N-heterocyclics in O2-free alcoholic suspensions under solar and UV-A light. 2-Nitrophenyl azide with different alcohols on irradiation with TiO2 undergoes a combined redox reaction and condensation giving 2-alkylbenzimidazoles as the main product. In case of 2-nitrobenzyl azide, the reduced amine does not react with aldehyde but undergoes cyclization to form indazole. Doping of Ag/Pt enhanced the photoactivity of TiO2 significantly.