Preparation, characterization and catalytic activity of dendrimer-encapsulated phosphotungstic acid nanoparticles immobilized on nanosilica for the synthesis of 2H-indazolo[2,1-b]phthalazine-triones under solvent-free or sonochemical conditions

In this paper, we adopt a facile method to prepare a type of porous silica nanoparticles (n-SiO2) from tetraethyl orthosilicate as the source of silica. Then, dendritic polymer supported on nanosilica with surface amino groups was fabricated. Finally, H3PW12O40 nanoparticles (PWA(n)) were synthesized by the treatment of H3PW12O40 powder with n-Octane as solvent by a solvothermal method and then immobilized onto the dendrimer polymer functionalized nanosilica. The synthesized nanostructures were characterized by fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS), N-2 adsorption-desorption isotherm analysis, UV-Vis and elemental analysis. The morphology of the catalyst was characterized using transmission electron microscopes (TEM). The acidity of the catalyst was determined by FTIR pyridine adsorption spectroscopy. Then, this catalytic system was used as an efficient catalyst for the synthesis of 2H-indazolo[2,1-b]phthalazine-triones via multi-component and one-pot reactions of various aldehydes, phthalic anhydride, hydrazinium hydroxide, and dimedone under thermal solvent-free conditions or ultrasound irradiation at room temperature. Also, the catalyst can be easily recovered and reused for six consecutive reaction cycles without significant loss of activity.