Atom economical Michael addition of indole with methyl vinyl ketone over novel solid acid catalyst sulfated zirconia on silica tubes

• Sulfated zirconia on facetted silica tubes (SZ/ST) with chlorosulfonic acid treatment.
• Thorough characterization of virgin and used catalysts.
• 100% Atom economical reaction of indole with methyl vinyl ketone.
• Highly active, selective, robust catalyst for preparation of β-indolylketones.
• Kinetics and mechanism.

Porous structures of inorganic oxides with different morphology are being paid a great deal of attention because of their potential for providing ultra large specific surface areas, exceptionally fine inner pores, and catalytic surface properties. A facetted silica tube functionalized with sulfated zirconia was prepared and used to catalyze Michael addition reaction of indole with methyl vinyl ketone. The effect of mesoporous tubular structure in generation of mild acidic sites on silica is discussed. The reaction is 100% atom economical. The silica tubes were prepared by using tetraethylorthosilicate and (dl)-tartaric acid in basic medium. The support and catalyst were well characterized by XRD, FT-IR, ASAP, SEM and EDXS. The activity was also compared through benzylation of toluene in liquid phase with reference to sulfated zirconia. Several other catalysts were also evaluated. The effects of various parameters on the rate of reaction were investigated. Based on the experimental data, a suitable mechanism was developed and kinetic model deduced.

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