Step-economic, efficient, ZnS nanoparticle-catalyzed synthesis of spirooxindole derivatives in aqueous medium via Knoevenagel condensation followed by Michael addition

An environmentally friendly, one-pot, three-component ZnS nanoparticle-mediated synthesis of biologically important spirooxindole derivatives in water under ultrasonic irradiation is described herein. ZnS nanoparticles were synthesized by aqueous chemical method. The advantages of this method lies in its simplicity, cost effectiveness, environment friendliness, easier scaling up for large scale synthesis without using high pressure, temperature and toxic chemicals. Greenness of the process was well instituted as water was exploited both as reaction media as well as medium for synthesis of catalyst (ZnS nanoparticles). The particle size was determined by transmission electron microscopy (TEM) and XRD. Compared with other methods for synthesis of spirooxindole derivatives, satisfactory results were obtained with high yields, short reaction time, with simple experimental procedure. After reaction course, the ZnS NPs can be recycled and reused without any apparent loss of activity.