Nano Bronsted solid acid containing double-charged diazoniabi-cyclo[2.2.2]octane chloride supported on nano rice husk silica: an efficient catalyst for the one-pot synthesis of phthalazine compounds

In the present work, amorphous silica nanoparticles were synthesized from low-cost rice husk ash (RH-SiO2). The nanoparticles were later modified by an acidic ionic liquid containing double-charged diazoniabi-cyclo[2.2.2]octane chloride using sol-gel method (RH@[SiPrDABCO@BuSO3H]HSO4). The structural properties of this Bronsted solid acid were systematically investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermal gravimetric analysis-derivative thermogravimetric analysis (TGA-DTG), and Brunauer-Emmett-Teller (BET) measurements. The catalytic activity of this nanocomposite was successfully tested through the one-pot synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-diones via three-component couplings of phthalhydrazide, aromatic aldehydes, and malononitrile. The heterogeneous catalyst could be recovered easily and reused without significant loss of its catalytic activity.