Novel bi-SO₃H-functionalized ionic liquids based on piperazinium: Highly efficient and recyclable catalysts for the synthesis of β-acetamido ketones

A series of novel bi-SO₃H-functionalized ionic liquids were synthesized and acted as catalysts for the synthesis of β-acetamido ketones. Compared with traditional single-SO₃H-functionalized ionic liquids, less amount of catalysts, higher yields and shorter reaction time are the key features of this methodology. Hammett function values and the minimum-energy geometries of bi-SO₃H-functionalized ILs were calculated and the results revealed that the acidities and catalytic activities of ILs in synthesis of β-acetamido ketones were influenced by their structures. The IL [(PS)₂pi][OTf]₂ with the shortest HO bond distance had the strongest acidity and the highest catalytic activity.