Phosphotungstic acid-supported melamine-terephthalaldehyde covalent organic framework as a novel and reusable nanostructured catalyst in three-component synthesis of 2H-indazolo[2,1-b]phthalazine-trione derivatives

In this study, phosphotungstic acid (H3PW12O40)-supported melamine-terephthalaldehyde Covalent Organic Framework (COF-PTA) has been prepared as a novel solid acid catalyst for the synthesis of 2H-indazolo[2,1-b]phthalazine trions under solvent-free conditions. The catalyst was characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) surface area analysis. The advantages of using this ecofriendly protocol include: excellent yield in a shorter time period, inexpensive chemicals without any use of solvents, simple experimental and work-up procedure. The catalyst was readily separated and was recycled for several runs with no significant loss of catalytic property.