sono-chemical synthesis of benzimidazoles, using bifunctional organocatalytic mixed ligands metal-organic frameworks of zrmofs

Mixed ligands metal-organic frameworks (ml-mofs) as a large category of hybrid bifunctional materials (metal as lewis acid and ligand functional group such as –nh2 as lewis base or organocatalysis) with porous and crystalline structures have received large attention because of their easy separation, reusability and processability [1]. zr-containing mof octahedrons (uio-66), possess high chemical stability, low economic cost [2] and excellent stability in aqueous solution that enables them to be a good candidate for catalytic heterocyclic organic molecules synthesis [3]. in this study, a uio-66 containing mixed ligands, terephthalic acid and aminoterephthalic acid (uio-66-nh2-h) has been synthesized and applied as a reusable catalyst to accelerate the benzimidazole synthesis. both syntheses were preceded under the ultrasound irradiation. this work also reports the efficiency of ultrasonic bath for raising the reaction conversion. the effect of various parameters such as temperature, sonication time, catalyst concentration and solvent on the reaction yield has been investigated. the as-prepared uio-66-nh2-h in combination with the presence of the ultrasonic irradiations achieves a remarkable improves in benzimidazole yields. the higher catalytic activity of uio-66-nh2-h could be originated from the highly porous structure containing zirconium oxide clusters leading to the large surface area and highly active sites in unit space. the high product yield, easy catalyst separation and its reusability are the exceptional features of this method. bet analysis confirmed the microporosity of the catalyst.