Mannich reaction using acidic ionic liquids as catalysts and solvents

Abstract

Several Brønsted acidic ionic liquids were synthesized and successfully used as solvents and catalysts of three-component Mannich reactions of aldehdyes, amines, and ketones at 25 °C. The used Brønsted acidic ionic liquids include l-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]⁺[HSO₄]⁻), l-butyl-3-methylimidazolium dihydrogen phosphate ([Bmim]⁺[H₂PO₄]⁻), 1-methylimidazolium p-toluenesulfonic acid ([Hmim]⁺Tsa⁻) and 1-methylimidazolium trifluoroacetic acid ([Hmim]⁺Tfa⁻). Higher yields were obtained in the presence of [Hmim]⁺Tfa⁻ in comparison with other Brønsted acidic ionic liquids. The [Hmim]⁺Tfa⁻ was reused four times without considerable loss of activity.