Molecular Sieves in Ionic Liquids as an Efficient and Recyclable Medium for the Synthesis of Imines

Abstract

A great variety of imines were efficiently isolated in high yields from the reaction of aldehydes and amines in ionic liquids. The ionic liquids could be recovered and reused for at least five cycles without loss in the yields being a useful alternative to dichloromethane or diethyl ether, which are the commonly used solvents for this reaction.

Key words

ionic liquids - imines - green chemistry

References

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8

Part of this work has been presented at the X Brazilian Meeting on Organic Synthesis, August, 2003, São Pedro, SP, Brazil.

12

It was found in the reaction between piperonal and benzylamine that it is not really necessary to heat the ionic liquid under vacuum to recover its activity. It was still active even after 3 runs only by removing the solvent under vacuum.

13

Typical Experimental Procedure: A solution of aldehyde (1 mmol) and amine (1 mmol) in [bmim]BF₄ or [bmim]PF₆ (0.5-1.0 mL) containing 4 Å molecular sieves was stirred at r.t. until no starting material has left as confirmed by TLC. The reaction was then extracted with Et₂O (3 × 5 mL) by simple decantation. The combined organic phases were concentrated at reduced pressure to furnish the crude product. The recovered ionic liquid containing molecular sieves was dried at 60-70 °C under vacuum (0.1 mm Hg) for 0.5 h.

14

All the compounds gave satisfactory spectroscopic data.