Abstract: 1-(2-piperidyl-ethyl)-3-methylimidazolium 2-morpholinyl-4-ethane sulfonate ([Pemim]Mes) with two basic groups individually located in cation and anion exhibited synergistically catalytic behavior for Knoevenagel condensation. Under non-acidic conditions, [Pemim]Mes proved to be an active, stable, and universal catalyst for Knoevenagel condensation between aromatic aldehydes and active methylene compounds. The catalytic mechanism of Knoevenagel condensation synergistically catalyzed by the basic ion pair existing in [Pemim]Mes was tentatively proposed.

Key words: basic ionic liquid, synergistic effect, aromatic aldehyde, Knoevenagel condensation