p-Sulfonated calix[4]arene grafted on magnetic chitosan as efficient and recyclable multifunctional bio-nanocatalyst for various organic transformations

• Preparation of a novel chitosan-based magnetic nanocatalyst (SCA@MCS) • The synergistic effect of magnetic chitosan and sulfonated calix[4]arene on reaction yields • Efficient synthesis of dihydropyridine, dihydropyrimidine, dihydropyrrolone, and benzoate ester derivatives • The reusability of nanocatalyst with keeping its capability • The fast and facile separation of nanocatalyst from reaction vessel Biopolymers are abundant and sustainable materials that have various benefits, including reducing the development of secondary pollution because of their inherent environmental friendliness. For this reason, this study aims to prepare a chitosan-based magnetic nanocatalyst by grafting sulfonated calix[4]arene as a Brønsted acid moiety onto magnetic chitosan using isophorone diisocyanate as a linker. The prepared bio-based nanocatalyst, designated as SCA@MCS, was characterized using various analysis methods, including FT-IR, PXRD, TGA, SEM, EDS/MAPP, TEM, CHNS, VSM, and Zeta potential. The simultaneous presence of chitosan and p -sulfonated calix[4]arene endows SCA@MCS with both acidic and basic active sites, making it an effective multifunctional nanocatalyst. Consequently, the bio-based SCA@MCS was applied as a reusable heterogenous nanocatalyst for the efficient synthesis of various organic compounds, including dihydropyridine (89-98%), dihydropyrimidine (82-98%), dihydropyrrolone (89-95%), and benzoate ester derivatives (98-99%). The absence of toxic solvents, mild reaction conditions, simple work-up procedures, the use of a low amount of nanocatalyst, high reaction yields, and the reusability of the nanocatalyst are the key advantages of the introduced SCA@MCS magnetic nanocatalyst. These results demonstrate that the grafting of sulfonated calix[4]arene onto magnetic chitosan provides an efficient bio-based multifunctional nanocatalyst for the synthesis of various biologically active compounds and biodiesel production.