Porous ionic copolymer-functionalized magnetic diatomite as a superior catalyst toward regioselective synthesis of pyridopyrimidines

Abstract

Although the modification of diatomite, a silica support derived from natural minerals, with various (carbohydrate) polymers has been reported, its functionalization with an imidazolium-based ionic polymer remains unexplored. Accordingly, a magnetic diatomite (Dt@CoFe₂O₄) was surface-reconstructed and functionalized with an ionic imidazole-epichlorohydrin copolymer ([IMEP][Cl]). The Dt@CoFe₂O₄/[IMEP][Cl] was obtained through a straightforward two-step sequence involving co-precipitation and chemical polymerization. The ionic copolymer enhances the charge density, surface area, and variety of functional groups on magnetic diatomite, while the inorganic component provides high chemical and thermal stability. As a result, the proposed Dt@CoFe₂O₄/[IMEP][Cl] composite exhibits key characteristics of an efficient nanocatalyst, including good thermal stability (60 % weight loss up to 800°C), a significant specific surface area (218.3 m²/g), and strong reusability over seven cycles. For the first time, the use of a diatomite-based composite as a heterogeneous nanocatalyst in a regioselective multicomponent reaction is presented. The Dt@CoFe₂O₄/[IMEP][Cl] catalytic activity was evaluated in the regioselective preparation of pyridopyrimidine ring systems under ultrasound agitation. Based on the observed data, the proposed composite facilitates the rapid construction (in 5 min) of various biologically active pyridopyrimidines with excellent yields (93–98 %) in an aqueous medium. As a pioneering effort, the combination of magnetic diatomite and ionic polymers has led to the creation of an effective architecture that offers a wide range of applications across different technological fields.