Sonochemical synthesis of 1,4-dihydropyridines using a bio-derived magnetic nanocomposite based on the pectin modified with the di-sulfonic acids under mild conditions

In this study, we presented a bio-derived magnetic nanocomposite based on the pectin modified with 1-amino-8-naphthol-3,6-disulfonic acid in two steps. In the first step, 1-amino-8-naphthol-3,6-disulfonic acid (DSA) was grafted on the low-methoxy citrus pectin (Pec) and in the next step, simple immobilization of Fe3O4 nanoparticles resulted in the magnetized nanocomposites (Fe3O4-Pec-DSA). The structure of Fe3O4-Pec-DSA nanocomposites was confirmed by various physicochemical characterization methods. This nanocomposite was employed for the ultrasonic-assisted synthesis of biologically active 1,4-dihydropyridines in ethanol. Various parameters such as catalyst type, solvent, ultrasound power and frequency, temperature, time and catalyst loading were fully investigated to establish the optimal conditions. The remarkable activity of Fe3O4-Pec-DSA catalyst based on short reaction times (15-40 min) and high yields (84-95%) is ascribed to the synergistic effect derived from the catalyst structure due to the presence of -SO3H moiety and Fe3O4 nanoparticles and ultrasound waves. The magnetic character of the catalyst provided a clean and easy separation. The catalyst was stable at least 6 consecutive runs without remarkable structure alteration, verified by FT-IR, XRD, and EDX techniques. The stability and heterogonous nature of the catalyst were confirmed by a leaching test since no product was formed after removal of the catalyst magnetically. Moreover, the negligible leach of Fe3O4 nanoparticles in the acidic and basic mediums was supported by atomic absorption spectroscopy (AAS).

Automated summary

In this study, a bio-derived magnetic nanocomposite was prepared based on citrus pectin, modified with 1-amino-8-naphthol-3,6-disulfonic acid. The nanocomposite was used for ultrasonic-assisted synthesis of biologically active compounds, showing high efficiency and stability. Characterization methods confirmed the structure and stability of the nanocomposite, indicating its potential for further applications in organic synthesis.