Efficient Knoevenagel condensation catalyzed by imidazole-based halogen-free deep eutectic solvent at room temperature

For the first time, we employed the halogen-free deep eutectic solvent(DES) into the Knoevenagel condensation between aromatic aldehydes and active methylene compounds at room temperature. The DESs [3 Im:PTSA] and [4 Im:PTSA] were prepared by imidazole(Im) and p-toluenesulfonic acid(PTSA), which were experimentally screened from a series of organic acids with imidazole. a, b-Unsaturated carbonyl compounds were obtained in good to excellent yields under solvent-free conditions with fast reaction rate. These two DESs can be reused for multiple times with no loss of catalytic activity.