Propyl–SO3H functionalized SBA-15: Microwave-mediated green synthesis of biologically active multi-substituted imidazole scaffolds
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Propylsulfonic acid functionalized Santa Barbara Amorphous-15 (SBA-15–Pr–SO3H) catalyst has been synthesized using a surface modification of mesoporous SBA-15 via the one-pot co-condensation method. The synthesized SBA-15–Pr–SO3H has been characterized by peculiar characterization techniques such as small- and wide-angle XRD, SEM–EDX, TEM, TG–DTA, acidity, FT-IR, Py-FT-IR and BET surface area analysis. The catalytic activity of synthesized catalyst has been studied towards solvent-free MW irradiation for the green and rapid synthesis of multi-substituted imidazoles, [2,4,5-triphenyl-1(H)-imidazole (tri-imidazole) and 1-benzyl-2,4,5-triphenyl-1H-imidazole (tetra-imidazole)]. The SBA-15–Pr–SO3H catalyst was found to be an efficient and recyclable solid acid catalyst and this solvent-free MW protocol afforded products in good to excellent yields of both, tri and tetra imidazoles (> 95%) within shorter reaction time (3 min) at 600 W as compared to the SBA-15 and other existing protocols. The applicability of this protocol was further explored by conducting the experiments in the presence of varied solvents and substituted aldehydes to generate a library of both, tri- and tetra-imidazole scaffolds. The catalyst was found to be reusable up to several runs without loss of its catalytic activity. This report allows the rapid and scalable access to a variety of multi-substituted imidazoles using SBA-15–Pr–SO3H, as heterogeneous catalyst.
KeywordsGreen chemistry SBA-15–Pr–SO3H catalyst Tri and tetra imidazoles Solvent-free microwave irradiation technique MCRs
The authors are grateful to the director, SVNIT, Surat, for providing research and financial assistance. This research was supported by a research grant for assistant professor No: Dean (R&C)/1503/2013-14 from Sardar Vallabhbhai National Institute of Technology, Surat (SVNIT, Surat). The authors would also like to thank IISER-Mohali, India, for SAXS characterization facility.
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