Abstract
In this study, the magnetization of kappa-carrageenan (Carr) and its modification by hyperbranched polyglycerol-sulfonic acid tags (PGly-SO3H) was found to be a good strategy to fabricate a bio-inspired solid acid as a heterogeneous nanocatalyst for the synthesis of 1-amidoalkyl-2-naphthols from aldehydes, 2-naphthol, and acetamide. The catalyst was produced by embedding Fe3O4 nanoparticles into carrageenan shell and modifying the as-produced Fe3O4@Carr with PGly tags. Then, the Fe3O4@Carr was modified by chlorosulfonic acid (Cl-SO3H) to obtain the Fe3O4@Carr-PGly-SO3H nanoparticles. The morphology and structure of Fe3O4@Carr-PGly-SO3H nanoparticles were studied by FT–IR, XRD, FE-SEM, EDX-mapping, TEM, VSM, and TGA. Aromatic aldehydes with electron-donor/ electron-acceptor substituents, heterocyclic aldehydes, and enolizable aldehyde gave the corresponding 1-amidoalkyl-2-naphthols with 85–96 % isolated yields within 15–35 min, under solvent-free conditions. The acidic content of Fe3O4@Carr-pPGly-SO3H nanoparticles was found to be 3.5 mmol H+/g, which determined by titration. As shown by TEM images, the Fe3O4 core facilitates the efficient magnetic separation. The use of a benign support material, ease of catalyst preparation and recovery, heterogeneous nature (on the basis of hot-filtration experiment), solvent-free conditions, and reusability of the nanoparticles (5 times) are some of the green aspects of the present study.
Published Version
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