Ordered organo-inorganic hybrid mesoporous solid acid catalysts (Zr–TMS–TFA) for Michael addition of indoles with α,β-unsaturated carbonyl compounds under environmentally benign solvent free conditions

Abstract

The trifluoromethanesulfonic (trflic) acid functionalized Zr–TMS materials were synthesized and characterized by powder XRD, N2-sorption, elemental analysis, FTIR spectroscopy, NH3–TPD, and 13C CP MAS NMR techniques. The samples with different loadings of triflic acid (TFA) over Zr–TMS (5–25wt.%) were synthesized. The acid density of TFA functionalised Zr–TMS (Zr–TMS–TFA) materials increased with loading of TFA from 5 through 25wt.%. The catalytic performance of Zr–TMS–TFA catalysts was evaluated in Michael addition of 3-methylindole to α,β-unsaturated ketones under liquid phase and solvent free reaction conditions. For example, the conversion of 3-methylindole increased with increasing loading of TFA from 38 through 87%. The selectivity of C2-adduct compared to that of N-adduct also increased with increasing loading of TFA. The higher conversion was observed in the case of electron-withdrawing group containing indoles with higher selectivity of C-adduct. The catalysts were found to be reusable.