Efficient synthesis of novel pyrazole-linked 1,2,4-triazolidine-3-thiones using bismuth on zirconium oxide as a recyclable catalyst in aqueous medium.

The Bi2O3 loading on ZrO2 as heterogeneous catalyst was established as an extremely efficient catalyst for the synthesis of a series of novel 5-(1-(2,4-dinitrophenyl)-3-substituted-phenyl-1H-pyrazol-4-yl)-1,2,4-triazolidine-3-thione derivatives (3a-o) with high yields (90-96%) by reaction of 1-(2,4-dinitrophenyl)-3-substituted-phenyl-1H-pyrazole-4-carbaldehydes and thiosemicarbazide using water as a greener solvent at 80 °C within 30-45 min. Materials with different percentages of Bi2O3 on ZrO2 were prepared by simple wet impregnation method. The synthesized material has been characterized by various techniques (XRD, TEM, SEM, BET). 2.5% Bi2O3/ZrO2 proved superior catalyst. The Bi2O3/ZrO2 catalyst is easily recoverable and reused up to sixth run with no loss of activity. Excellent yields, short reaction time, avoidance of hazardous solvents, and no need for chromatographic purifications are the proven advantages.