Table 1. Entries 1–6 show the effect of various solvents on the yield of the reaction. Although acetonitrile and toluene afforded the product in high yields, we chose ethanol for its cheapness and environmental acceptability. Entry 3 describes the yields of five consecutive condensations leading to 4a. In these experiments the product was isolated by filtration and washing the solid residues with ethyl acetate, the remaining catalyst being reloaded with fresh reagents for further runs. No decrease in the yield was observed demonstrating that silica sulfuric acid can be reused as a catalyst in Biginelli condensations. Entry 7 shows the catalytic effect of silica sulfuric acid in the three-component condensation of benzaldehyde, urea and ethyl acetoacetate.