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

Abstract

Highly active cobalt oxide nanoparticles supported on alumina/silica (Co3O4@Al2O3/SiO2) 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 Co3O4 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

Selective photocatalytic oxidation of aromatic alcohols to aldehydes with air by magnetic WO3ZnO/Fe3O4. In situ photochemical synthesis of 2-substituted benzimidazoles

“…The imine intermediate is in equilibrium with the corresponding dihydrobenzimidazole (III), and subsequently, it can be catalytically dehydrogenated in the presence of air and by the mediation of the prepared nanocatalyst to form the desired nal benzimidazole product. 58…”

Recent Trends in the Synthesis of Benzimidazoles From o‐Phenylenediamine via Nanoparticles and Green Strategies Using Transition Metal Catalysts

“…using a neat reaction and cobalt oxide nanoparticles supported on alumina/silica (Co 3 O 4 @Al 2 O 3 /SiO 2 , 5 mol %) performed oxidative coupling of benzyl alcohols ( 36 ) or benzylamines ( 37 ) with o ‐phenylenediamines ( 4 ) using air, at 100–140°C. The synthesized 2‐substituted benzimidazoles ( 38 ) was obtained in an excellent yield of 82–98% in case of benzylamines (Scheme , Table , entry 1) .…”

Copper(II) Oxide Nanoparticles Impregnated on Melamine‐Modified UiO‐66‐NH2 Metal–Organic Framework for C–N Cross‐Coupling Reaction and Synthesis of 2‐Substituted Benzimidazoles

“…Magnetically recoverable ZnO supported catalyst on chitosan was reported by Tian and co‐workers for this synthesis . Numerous supported organic and metallic catalysts have been also introduced recently in the literature, for example, SiO 2 /Brønsted acidic ionic liquid gel , SiO 2 ‐dendrimer/Cu (II) , aluminum‐organic hybrid supramolecular material (Al‐ITQ‐HB) , Co 3 O 4 ‐Mo , Co 3 O 4 @Al 2 O 3 /SiO 2 , SiO 2 /Co@Fe 2 O 4 , Fe 3 O 4 ‐poly(melamine‐terephthaldehyde)/Cu , GO‐SO 3 H , activated carbon‐SO 3 H , Ir/N‐heterocyclic moieties , SiO 2 ‐Yb , P 2 O 7 ‐Sn , and Zeolite‐Y/Ni (II) . The reported methods had some drawbacks such as elevated temperature, longer reaction time, using organic solvent and high amount of catalyst, low yield, and use oxidant.…”