Synthesis Of 2-Benzimidazole Over Novel Zinc Oxide Nanocatalysts

Benzimidazoles are the important nitrogenous heterocyclic compounds,which are widely used in organic synthesis and bio-medicine due to their unique structure and properties.In the past years,a great deal of works on the synthesis of benzimidazoles have been carried out by the researchers,but the synthetic methods reported have still some problems such as high cost,low catalytic activity,and poor stability.Therefore,it is of important to design and develop a simple,inexpensive and efficient catalytic system,which has important research significance and application value.In the context,a series of zinc oxide composite nanocatalysts had been designed and prepared,whcih can be successfully applied to the synthesis of 2-benzimidazoles,and achieved good results.Firstly,ultrasmall ZnO nanoparticles anchored on N-doped carbons with silica support(ZnO/SiO2-NC)were fabricated from biomass-derived chitosan by using a simple self-assembly in suit strategy,and were successfully applied to the synthesis of 2-arylbenzimidazoles under mild conditions.These catalysts showed excellent catalytic activity,selectivity,stability and universality.It was found that nitrogen doped carbon can promote the high dispersity of ZnO nanoparticles and restrict ZnO nanoparticles size at approximately 2.55 nm.Meanwhile,nitrogen doped carbon and SiO2 composites can stabilize ZnO nanoparticles and inhibit their agglomeration inactivation,and the catalyst could be used six times without any loss of conversion and selectivity.Secondly,with low price and wide source of glucose as raw materials,uniformly dispersed carbon spheres were firstly prepared by a simple hydrothermal synthetic method,which could be used as sacrificing the template.Following the aboved step,a mesoporous aluminium oxide coated zinc oxide(mAl2O3@ZnO)nanocatalyst was successfully synthesized by the hard template method.The catalyst exhibited good activity and stability in the catalytic synthesis of 2-phenylbenzimidazole.These results indicated that the ZnO active site can be highly dispersed with the addition of the template,contributing to the excellent catalytic activity.Finally,a silica coated zeolite imidazole metal organic frameworks(ZIF-8)composite nanomaterial was firstly prepared by a simple sol-gel method,and then the hybrid nanocatalyst(mSiO2@NC-ZnO)was prepared in-situ by the pyrolysis of the previously prepared composite nanomaterial under the nitrogen atmosphere.The acid sites of mSiO2@NC-ZnO prepared by ZIF-8 precursor were more evenly distributed,which significantly improved the catalytic performance in the model reaction of 2-phenylbenzimidazole synthesis,and the conversion rate of raw materials and the selectivity of the products are above 90%.