Biomass‐Derived N‐doped Carbon Materials with Silica‐Supported Ultrasmall ZnO Nanoparticles: Robust Catalysts for the Green Synthesis of Benzimidazoles

Abstract

Ultrasmall ZnO nanoparticles anchored on N-doped carbon materials with a silica support (ZnO/SiO -NC) were fabricated from chitosan and metal ions by using a one-pot self-assembly strategy and were successfully applied to the synthesis of 2-arylbenzimidazoles under mild conditions. These catalysts showed excellent stability and could be used six times without any loss of conversion and selectivity. The use of silica gel and the biomass chitosan as a source of hydrophilic N-doped carbon materials facilitated the uniform dispersion of the ZnO nanoparticles in methanol and therefore the contact of these nanoparticles with reactants, thus contributing to a high catalytic performance. TEM analysis showed that the ZnO nanoparticles were around 2.55 nm in diameter and uniformly distributed on the support surface. The binding behavior of ZnO and N-doped carbon materials affected the catalytic activity. Interestingly, temperature-programmed NH desorption indicated that the interactions between ZnO and N-doped carbon materials might induce the presence of more acidic sites in these catalysts, thus resulting in enhanced activity and hence promoting this transformation.

Selective Synthesis of Benzimidazoles from o-Phenylenediamine and Aldehydes Promoted by Supported Gold Nanoparticles

“…To date, the emphasis is given to developing new, efficient, and "green" methods for the conversion of o-phenylenediamine and aldehydes to benzimidazole derivatives. Several heterogeneous catalytic systems that involve inorganic salts [31][32][33][34], zeolites [35][36][37], heterogeneous ionic liquid gel [38], micelles [39], and metal oxides [40][41][42][43][44][45][46][47][48][49] have been reported (Scheme S1). This transformation can be also achieved via photocatalytic processes in the presence of photosensitized molecules or semiconductor materials (Scheme S2) [50][51][52][53][54][55][56].…”

Recent progress in the synthesis of azoles and related five‐membered ring heterocycles using silica‐supported heterogeneous catalysts

“…A novel catalyst, biomass-derived N-doped carbons with silica-supported ultrasmall ZnO nanoparticles was designed by Chen et al in 2017 for the synthesis of benzimidazoles. 2-Phenyl benzimidazole was synthesized using benzaldehyde, o-phenylenediamine, ZnO/SiO 2 -NC-600, H 2 O 2 , and refluxing in methanol for 1 h. The preparation of the novel catalyst, use of biomass chitosan as a precursor for N-doped carbon, high stability with numerous active sites for binding, and high dispersity of the catalyst are the salient features of this work (Scheme 3) [19].…”

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

“…using novel ZnO nanoparticles (2.55 nm in diameter) having N‐doped carbons, ZnO/SiO 2 ‐NC‐600, which were fabricated from renewable chitosan support, synthesized 2‐arylbenzimidazoles ( 25 ) in 80–94% yield in 1–4 h (Scheme , Table , entry 2). The reactants were stirred in methanol as a solvent, while H 2 O 2 was used as mild oxidant .…”