In this work, the synthesis and characterization of 3-carboxypyridinium hydrogensulfate ([Hcpy]HSO 4 ) as a new Brønsted acidic ionic liquid are reported. This reusable, inexpensive, and green catalyst was employed for one-pot condensation of 1,3-dicarbonyl compounds, aromatic aldehydes and urea or thiourea for the synthesis of the corresponding 3,4-Dihydropyrimidin-2(1H)-ones. The reactions were carried out under solvent-free and ...