Montmorillonite K-10 clay as reusable heterogeneous catalyst for the microwave-mediated solventless synthesis of phthalazinetetraones

Different phthalazino[2,3-b]phthalazine-5,7,12,14-tetraones were synthesized in a simple and environmentally benign method from the reaction of some phthalic anhydrides with semicarbazide or thiosemicarbazide using montmorillonite K-10 clay as solid heterogeneous acidic catalyst and microwaves under solvent-free conditions in good yields and short reaction times. The present method has many obvious advantages compared with those reported in the literature, including high efficiency, higher yield, operational simplicity, environmental benignity, and the possibility of recycling the solid clay. The solid clay catalyst used in the first cycle of the reactions was successfully recovered and reused in the second cycle, showing a gradual decrease in activity.