Novel and Efficient Heterogeneous 4-Methylbenzenesulfonic Acid-Based Ionic Liquid Supported on Silica Gel for Greener Fischer Indole Synthesis.

In this work, a functionalizing active species 4-methylbenzenesulfonic acid-based IL on silica gel (IL-SOH-SiO) has been prepared, and characterized by FT-IR, XRD, TGA, SEM and EDX spectra. Then, IL-SOH-SiO was utilized as an efficient and heterogeneous catalyst for the synthesis of indoles via the one-pot Fischer reaction of phenyl hydrazines with ketones or aldehydes at room temperature. The heterogeneous catalyst could be recovered easily by filtration and reused many times without significant loss of its catalytic activity. Graphical Abstract: [ABSTRACT FROM AUTHOR]