An efficient and ecofriendly WOx-ZrO2 solid acid catalyst for classical Mannich reaction

An ecofriendly WOx-ZrO2 solid acid catalyst has been employed for the synthesis of beta-amino ketones by a three-component Mannich reaction in the liquid phase under solvent-free conditions at ambient temperature. To make the WOx-ZrO2 catalyst, WOx from ammonium metatungstate was incorporated into the hydrous zirconia and calcined at 923 K. The incorporated promoter showed a strong influence on the surface and bulk properties of the zirconia. Surface and bulk properties of the catalyst were investigated by means of X-ray powder diffraction, temperature programmed desorption of ammonia, Raman spectroscopy, scanning electron microscopy, and BET surface area methods. Characterization studies reveal that the WOx-ZrO2 catalyst exhibits strong solid acidity. The catalytic activity results suggest that the methodology adopted offers significant improvements for the synthesis of beta-amino ketones with regard to yield of products, simplicity in the operation, and green aspects by avoiding toxic conventional catalysts and solvents.