A Catalytic System Using Aminosilane-Modified Perlite-Geopolymer for the Synthesis of 4 H-Chromene Derivatives and DFT Electronic Characterization

Abstract

This work reflects both the synthesis and the characterization of a novel catalyst obtained by functionalizing geopolymers through the grafting of an amino group onto their surface. Expanded perlite (PE) was chosen as the primary raw material due to its high availability, low cost, and environmental compatibility. Its favorable structure and reactivity with alkaline agents make it an excellent candidate for geopolymer (GP) formation. Subsequently, 3-aminopropyltrimethoxysilane (APTMS) was grafted onto the GP surface to obtain a modified geopolymer catalyst (GPM). The modification enhanced the geopolymer's functionality, making it efficient, eco-friendly, safe, and reusable. Characterization by XRD, SEM, EDX, and TGA confirmed successful grafting and improved the thermal stability of the resulting GPM catalyst. The catalytic efficacy of this novel catalyst was explored for the first time in the synthesis of substituted 4H-chromene, using a direct, straightforward, and highly efficient one-step procedure within a multicomponent reaction. This reaction combines various aldehydes, malononitrile, and β-diketone in ethanol at ambient temperature. The catalyst enabled excellent yields ranging from 90 to 98% under mild and eco-friendly conditions. The resulting 4H-chromene derivatives were confirmed via melting point, FT-IR, ¹H NMR, and ¹³C NMR analyses. Moreover, the GPM catalyst demonstrated high recyclability, maintaining over 90% of its catalytic activity after five consecutive cycles. To complement the experimental findings, DFT calculations (B3LYP/6-31G(d,p)) were performed, providing insight into the electronic properties, including frontier molecular orbitals and molecular electrostatic potentials. These results highlighted the most reactive molecular regions, supporting the potential of the synthesized chromene derivatives in pharmaceutical applications and drug design. Overall, the study demonstrates the effectiveness, sustainability, and broader applicability of the newly developed heterogeneous GPM catalyst. These findings highlight the potential of geopolymer-based catalysts as sustainable alternatives in green chemistry and showcase their versatility for future applications in synthetic and medicinal chemistry.