Solvent‐Free Oxidative Synthesis of 2‐Substituted Benzimidazoles by Immobilized Cobalt Oxide Nanoparticles on Alumina/Silica Support

Abstract

Abstract Highly active cobalt oxide nanoparticles supported on alumina/silica (Co 3 O 4 @Al 2 O 3 /SiO 2 ) were prepared by wet impregnation method and successfully employed for the solvent free (neat) oxidative coupling of benzyl alcohols/amines with o ‐phenylenediamines for the synthesis of 2‐substituted benzimidazoles. The catalyst prepared during this study was characterized by various techniques like XRD, XPS, HR‐TEM, SEM‐EDAX, BET surface area and ICP‐AES analysis. Porous alumina/silica (99:1) having high surface area served as a protective heterogeneous support on which the Co 3 O 4 nanoparticles (size 2–3.5 nm) acted as an active catalyst for air‐mediated oxidative coupling. The present methodology offers significant advantages for the preparation of bioactive benzimidazole scaffold and avoids the use of hazardous and toxic reagents/solvents, oxidizing agents and elevated reaction temperatures. Moreover, the catalyst can be recovered by centrifugation and its recyclability was demonstrated up to six successive runs without any appreciable loss in the catalytic activity