Octahedral MnO2 molecular Sieve-Decorated Meso-ZSM-5 catalyst for Eco-Friendly synthesis of pyrazoles and carbamates

Abstract

Octahedral MnO2 molecular sieve (hereafter designated as OMS) was prepared in the presence of urea, and mesoporous ZSM-5 (designated as Meso-ZSM-5) was prepared using propyltriethoxysilane as additive under hydrothermal synthesis condition. OMS-decorated Meso-ZSM-5 was prepared by heating a grounded mixture of OMS and Meso-ZSM-5. Powder X-ray diffraction, N2-sorption, SEM, TEM, thermogravimetric analysis, FT-IR, diffuse reflectance UV−vis spectroscopy, and NH3 and CO2 temperature-programmed desorption techniques were used to characterize the material. The catalyst was demonstrated in a onepot, one-step synthesis of pyrazoles via cyclization followed by dehydrogenation as the key reaction steps. Synthesis of carbamates by the reaction of cyclic and acyclic carbonates/di-tert-butyl dicarbonate with amines was another important application of this catalyst. Catalyst exhibited efficient recyclability. No leaching of active species took place even after five recycles. A strong interface between OMS and Meso-ZSM-5 imparts strong acidity and distinguished activity in the synthesis of pyrazole heterocycles and organic carbamates.