12-Tungstophosphoric acid supported on nano sized MCM-41 as an efficient and reusable solid acid catalyst for the three-component imino Diels-Alder reaction

One pot three-component imino Diels-Alder reactions of various types of aldehydes, aniline and dihydropyrane were studied in the presence of nano sized MCM-41 supported 12-tungstophosphoric acid (TPA) as solid acid catalyst. MCM-41 as solid support was synthesized in nano size and the catalysts with different loading amounts of TPA (5-30 wt%) were prepared and characterized by XRD, FT-IR and SEM techniques. The results confirm a good dispersion of the heteropoly acid on the solid supports and based on the experimental results, the catalyst with 10 wt% heteropoly acid shows the best catalytic activity using 0.5 mol% heteropoly acid relative to the aldehyde. The recovery experiments show that the catalyst is reusable after calcination without significant loss in its activity.