ZnCl(2) loaded TiO(2) nanomaterial: an efficient green catalyst to one-pot solvent-free synthesis of propargylamines

One-pot green synthesis of propargylamines using ZnCl(2) loaded TiO(2) nanomaterial under solvent-free conditions has been effectively accomplished. The aromatic aldehydes, amines, and phenylacetylene were reacted at 100 °C in the presence of the resultant catalyst to form propargylamines. The nanocrystalline TiO(2) was initially synthesized by a sol–gel method from titanium(iv) isopropoxide (TTIP) and further subjected to ZnCl(2) loading by a wet impregnation method. X-ray diffraction (XRD) patterns revealed the formation of crystalline anatase phase TiO(2). Field emission scanning electron microscopy (FESEM) showed the formation of agglomerated spheroid shaped particles having a size in the range of 25–45 nm. Transmission electron microscopy (TEM) validates cubical faceted and nanospheroid-like morphological features with clear faceted edges for the pure TiO(2) sample. Surface loading of ZnCl(2) on spheroid TiO(2) nanoparticles is evident in the case of the ZnCl(2) loaded TiO(2) sample. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ti(4+) and Zn(2+) species in the ZnCl(2) loaded TiO(2) catalyst. Energy-dispersive X-ray (EDS) spectroscopy also confirmed the existence of Ti, O, Zn and Cl elements in the nanostructured catalyst. 15% ZnCl(2) loaded TiO(2) afforded the highest 97% yield for 3-(1-morpholino-3-phenylprop-2-ynyl)phenol, 2-(1-morpholino-3-phenylprop-2-ynyl)phenol and 4-(1,3-diphenylprop-2-ynyl)morpholine under solvent-free and aerobic conditions. The proposed nanostructure-based heterogeneous catalytic reaction protocol is sustainable, environment-friendly and offers economic viability in terms of recyclability of the catalyst.