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Two new calix[4]arene-based Lewis acid-type catalysts containing flexible and bulky groups (2 and 3) were successfully synthesized. Their structures were characterized using FTIR, 1H-NMR, COSY-NMR, 13C-NMR, APT-NMR, and elemental analysis techniques. Moreover, to provide easily recyclable, environmentally benign, cost effective and reusable catalysts, these calix[4]arene-based Lewis acid-type catalysts were grafted onto epoxyl-functionalized silica-coated Fe3O4 magnetic nanoparticles (EPPTMS-MN) to afford their corresponding calixarene-grafted magnetic nanoparticles (TMAC[4]But-MNP and P(Ph)3C[4]But-MNP). FTIR, TGA, TEM, VSM and elemental analysis techniques were performed to confirm their structures. In addition, the catalytic capabilities of four Lewis acid-type calixarene catalysts were evaluated in a three component Mannich reaction of benzaldehyde with aniline and acetophenone in aqueous media without co-solvents. The association of the effects of functional groups (flexible and bulky), molar equivalents, amount of water used, and reaction durations on their catalytic efficacies were also evaluated.

rsc advances

Synthesis of environmentally friendly, efficient and highly recyclable Lewis acid-type calix[4]arene catalysts containing flexible or bulky groups for the Mannich reaction