Synthesis and characterization of solid Brønsted acid derived from rice husks as an efficient catalyst for the preparation of some 2,4,5-trisubstituted imidazole derivatives

Solid Brønsted acid catalysts are crucial heterogeneous catalysts used as substitutes for liquid Brønsted acids in organic synthesis. In this research, solid Brønsted acid was synthesised in an easy and environmentally friendly method using rice husks as a raw material by converting them to dissolved sodium silicate and using sol–gel technique, silylating agents ((3-chloropropyl)triethoxysilane (CPTES)) reacted with sodium silicate to prepare RH-SiO₂PrCl. Through the nucleophilic reaction between RH-SiO₂PrCl and 1-Amin-2-naphthol-4-sulfonic acid, a solid acid catalyst (RH-SiO₂PrANSA) was prepared. The solid acid catalyst is characterized by many techniques, such as FTIR, EDX, CHNS, and BET. The results showed a secondary amine absorption band ( –N–H) at 3236 cm⁻¹. Also, the BET results for the catalyst indicated that its surface area was 61.74 m² g⁻¹ with an average pore diameter of 5.14 nm. The synthesized solid Bronsted acid was used as a catalyst to prepare 2,4,5-Trisubstituted imidazole derivatives by reacting six different subtenant aldehydes with benzil and ammonium acetate. All the products are characterized by FTIR, H NMR, and Mass spectroscopy, with around ~ 90% conversion yields.