A rapid and facile preparation of 5-arylidene barbituric or thiobarbituric acids through the Knoevenagel condensation reaction of aromatic aldehydes with barbituric or thiobarbituric acid was developed under microwave irradiation or grinding at room temperature in the presence of catalytic amount of room temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate [bmim]BF₄. The yields of the products were ranged from 78%～96% and 82%～98% under gringing at room temperature for 2 h and microwave irradiation at 160 w for 20 s respectively. The structures of all compounds were confirmed by ¹H NMR spectra.

Key words: 5-arylidenebarbituric acid, 5-arylidenethiobarbituric acid, synthesis, room temperature ionic liquid