The effect of the reaction temperature on the three component
condensation of urea with 4-nitrobenzaldehyde and ethyl
acetoacetate to synthesize the corresponding 3,4-dihydropyrimidin-
2(1H)-one in the presence of 5 mol% NH4H2PO4
was studied. The yield and reaction time were markedly influenced
by temperature. Increasing the reaction temperature
from 50 to 80 oC enhanced the conversion ~2.2 times and
reduced the required time about 1.4 times (Fig. 3). More increase
in reaction temperature slightly affected the yield. Increasing
the reaction temperature from 100 to 140 oC led to the
reduction of reaction time to reach 90% of conversion from 2 to
1.2 h. From technical considerations, a reaction temperature of
100 oC was selected for all the reactions.