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

Abstract

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 [3Im:PTSA] and [4Im:PTSA] were prepared by imidazole (Im) and p-toluenesulfonic acid (PTSA), which were experimentally screened from a series of organic acids with imidazole. α, β-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.

Keywords

• Halogen-free DES
• Knoevenagel condensation
• Room temperature
• Recyclable catalyst
• Solvent-free condition