3.4. Catalyst Recycling Test

The catalyst recycling test was carried out repeating the model reaction between benzaldehyde, ethyl acetoacetate and urea for a given number of cycles, using the same recycled catalyst, until a substantial drop in the yield was observed. Between each cycle, the catalyst was filtered and left to dry in the oven overnight at 100 °C. The reaction was carried out at a temperature of 92 °C under solventless conditions. The reagents were present in a ratio of 5:5:6 mmol benzaldehyde:ethyl acetoacetate:urea. The reaction time of 4.5 h was maintained for all cycles.