Facile synthesis of recyclable Mn-crosslinked chitosan schiff base composites as heterogeneous catalysts for selective oxidation of methyl phenyl sulfide with HO.

A novel manganese crosslinked chitosan composite (CS-Salen-Mn) was synthesized via Schiff base modification and coordination assembly. This composite showed excellent recyclability for heterogeneous catalytic oxidation. A Schiff base-modified chitosan (CS-Schiff) carrier was prepared via condensation of surface amines and salicylaldehyde, followed by coordination crosslinking with manganese acetate. Characterization via FT-IR, UV-Vis/DRS, TG, XPS, XRD, and SEM confirmed the successful integration of Mn coordination centers into the CS matrix while preserving the CS polysaccharide backbone. In the study of the HO oxidation reaction system of methyl phenyl sulfide, the catalytic system achieved 57.3 % substrate conversion rate and 100 % selectivity for the target product methyl phenyl sulfoxide under the following conditions: CS-Salen-Mn(1.1) (50 mg) as the catalyst, acetonitrile as the solvent, HO-to-substrate molar ratio of 2:1, reaction temperature of 0 °C, and reaction time of 24 h. Remarkably, the CS-based catalyst maintained >85 % of the initial activity after eight consecutive reuse cycles, which was attributed to the stable metal-ligand environment within the biopolymer framework. This work uses chitosan as a sustainable platform for designing robust heterophase catalysts, combining the process advantages of biopolymer carriers with the high catalytic activity of Salen-metal chemistry.