Synthesis of Pyranopyrazole Compounds Using Heterogeneous Base Catalyst Based on 1,3,5-Triazine-2,4,6-Triamine Modified Nano Rice Husk Silica

In the current study, amorphous silica nanoparticles were easily extracted from rice husk ash. The target composite was synthesized by the direct incorporation of chloropropyl groups through the condensation of nanosilica and 3-chloropropyl trimethoxysilane and then grafting of 1,3,5-triazine-2,4,6-triamine (Melamine) onto the propyl groups by the simple nucleophilic substitution reaction (RHA@Melamine). The resulting solid catalyst was characterized by infrared spectroscopy, scanning electron microscope and thermogravimetric analysis. The catalytic activity of this solid acid nanocomposite was probed through one-pot synthesis of 1,4-dihydropyrano[2,3-c] pyrazole via four-component couplings of aldehydes, hydrazine hydrate, ethyl acetoacetate and malononitrile under solvent-free conditions. In this reaction, RHA@Melamine shows good catalytic nature, easy to handle procedure, recycle exploitation and excellent isolated yields of products.