Ultrasound-assisted high-yield multicomponent synthesis of triazolo[1,2-a]indazole-triones using silica-coated ZnO nanoparticles as a heterogeneous catalyst?

Green Chemistry Pub Date: 2017-11-09 DOI: 10.1039/C7GC03279J

Abstract

We report here comprehensively detailed systematic investigations into a new method of an ultrasound-assisted synthesis of 4(a–m) triazolo[1,2-a]indazole-triones (TAITs) using the multicomponent condensation reaction among dimedone, 4-phenylurazole and various individual aryl aldehydes in the presence/absence of SiO2, ZnO and SiO2-coated ZnO (ZnO@SiO2) nanoparticles (NPs) or nanorods as heterogeneous catalysts in deionized water (DIW) at considerably low temperature (～60 °C). For this, the nanorods are synthesized in an efficient, facile and scalable wet chemical route in DIW at 27 °C. Oxygen-excessive ZnO nanorods of ～21 nm diameter with up to nearly 259 nm length become oxygen-deficient ZnO@SiO2 of about 48 nm diameter with rather complicated internal structures and a smooth-looking surface. Remarkably, attributed to oxygen deficiency, ZnO@SiO2 NPs exhibit excellent catalytic activities with good to high yields of TAIT products, brilliant recyclability up to six runs, over ?30 mV zeta potential (ζ) values, the smallest hydrodynamic diameter (HD) of 752 nm, best dispersion stability and largest specific surface area of 97.5 m2 g?1. Therefore, the greenest reaction medium for the syntheses of both these catalysts as well as TAITs was realized, making it an environmentally friendly doubly green reaction with a wide application potential due to its high efficiency, ease of handling and cost effectiveness.

Graphical abstract: Ultrasound-assisted high-yield multicomponent synthesis of triazolo[1,2-a]indazole-triones using silica-coated ZnO nanoparticles as a heterogeneous catalyst
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