The design of reusable high-performance heterogeneous catalysts via the immobilization of chemical and biochemical species on magnetic nanoparticles increases the efficiency of catalytic systems by facilitating easy, fast, and clean separation processes. Laccase and 4-amino-2,2,6,6-tetramethylpiperidine-1oxyl were separately immobilized on amine functionalized iron (II, III) oxide nanoparticles with covalent bonding using glutaraldehyde as a coupling reagent. The prepared catalyst was used to synthesize 12 benzoxazole and benzimidazole derivatives. The one-pot, two-step enzymatic aerobic oxidation reaction included the condensation of in situ-produced salicylaldehyde derivatives with aromatic amines, followed by an enzymatic dehydrogenation process. Optimal reaction conditions consisted of a citrate buffer (10 mM, pH 4.5) at 40 8C for an incubation time of 10 h and a heterogeneous catalyst containing immobilized laccase (80 mg, 100 U) and immobilized 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) (40 mg, 2 mol%). The catalyst retained more than 85% of its initial activity after 10 runs. In addition to the potential for reuse without significant losses in performance, eco-friendly attributes of this catalytic system include its high catalytic activity and the ease with which it can be recovered from the reaction mixture using an external magnet.
Co‐immobilization of bio‐ and chemocatalysts produces sustainable, recyclable hybrid systems that open new horizons for green cascade approaches in organic synthesis. Here, the co‐immobilization of laccase and 2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPO) in mesoporous silica was used for the one‐pot aqueous synthesis of 30 coumarin‐3‐carboxylate derivatives under mild conditions through the condensation of in situ oxidized 2‐hydroxybenzyl alcohols and malonate derivatives. A maximum yield was obtained after incubating at pH 6.0 and 45 °C for 24 h. An efficient organic synthesis was catalyzed by the hybrid catalyst in 10 % organic solvent. More than 95 % of the initial activity of the enzyme was preserved after 10 cycles, and no significant catalyst deactivation occurred after 10 runs. This new system efficiently catalyzed the in situ aerobic oxidation of salicyl alcohols, followed by Knoevenagel condensation, which confirmed the possibility of producing efficient hybrid catalysts by co‐immobilization of catalytic species in mesoporous materials.
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