Nanomagnetic ZrFe₂O₄-Decorated Porous Silica Sulfuric Acid as an Inorganic Solid Acid Catalyst for Synthesis of N-Heterocycles

The application of nanoparticles (NPs) in organic synthesis has gained significant attention, with magnetic nanoparticles (MNPs) distinguishing themselves from their nontoxicity, accessibility, and retrievability. Additionally, the tunability of selectivity and activity through surface modification increases the attractiveness of magnetic nanocatalysts. In this following investigation, a novel class of magnetic nanoparticles incorporating sulfonic acid groups (SO₃H) was developed as a carbon-free solid acid catalyst. The structural characteristics of zirconium ferrite nanoparticles silica sulfuric acid (ZrFe₂O₄@SSA), including crystallinity, morphology, the presence of functional groups, particle size, and elemental content over the surface were assessed by transform infrared spectroscopy transmission electron microscopy (TEM) scanning electron microscopy (SEM) image, X-ray atomic mapping spectrum, Fourier transform infrared (FT-IR) spectroscopy, energy-dispersive X-ray (EDX) analysis, diffusive gradients in thin films (DGT)/thermogravimetric Analysis (TGA), X-ray diffraction (XRD) pattern, brunauer, emmett, teller (BET)/barrett, joyner, halenda (BJH), and vibrating-sample magnetometry (VSM) analyses. XRD analysis confirmed the crystalline ZrFe₂O₄ structure in the ZrFe₂O₄@SSA composite, which exhibited a flower-like hierarchical morphology by TEM images. TGA, FT-IR, and EDX analyses indicated good stabilization and high solid acid stability. The catalytic activity of the nanocatalyst was assessed in the synthesis of 2,3-dihydroquinazolin-4(1<i>H</i>)-one and polyhydroquinoline <i>N</i>-heterocycles under environmentally benign conditions. The ZrFe₂O₄@SSA demonstrated remarkable reusability over five consecutive cycles without a notable decline in catalytic efficiency. The approach boasts several advantages, including low catalyst loading, high product yield, short reaction times, straightforward procedures, high atom economy, and facile catalyst handling.