Ionic Liquid–Catalyzed Internal Redox Esterification Reaction

Abstract

The internal redox esterification of α,β-unsaturated aldehydes and alcohols was carried out using different ionic liquids (ILs) as catalysts and reaction solvents. The basic ionic liquid, 1-butyl-3-methylimidazolium acetate ([bmim]OAc), exhibited the best activity for this reaction. The influences of the amount of ionic liquid catalyst and reaction time on yield of saturated ester have been investigated. The results showed that ionic liquid anions have a crucial effect on the redox esterification of α,β-unsaturated aldehydes and alcohols. The nucleophilic carbenes generated in situ from the ionic liquid cation were believed to be actual active species for this reactions.

GRAPHICAL ABSTRACT

Keywords:

• Basic ionic liquids
• carbene
• redox esterificartion
• α,β-unsaturated aldehydes

ACKNOWLEDGMENTS

The authors are grateful for support from the National Natural Science Foundation of China (No. 20773037, No. 21073058), the Research Fund for the Doctoral Program of Higher Education of China (No. 20100074110014), and the Commission of Science and Technology of Shanghai Municipality (No. 07J14023), China.

Notes

^a All reactions were carried out with cinnamaldehyde and ethanol in ionic liquids. Reaction conditions: cinnamaldehyde/ethanol = 1:3 (molar radio), ionic liquids 0.5 mmol, cinnamaldehyde 1.0 mmol, T = 70 °C.

^b High-molecular-weight side products were produced.

^a All reactions were carried out with cinnamaldehyde and ethanol in ionic liquid. Reaction conditions: cinnamaldehyde/ethanol = 1:3 (molar radio), ionic liquids 0.5 mmol, T = 70 °C, t = 2 h.

^a All reactions were carried out with α,β-unsaturated aldehyde with alcohol in [bmim]OAc. Reaction conditions: aldehyde/ethanol = 1:3 (molar radio), ionic liquids 0.5 mmol, α,β-unsaturated aldehyde 1 mmol, T = 70 °C.

^b The isomer of citral(carane 4,5-epoxide) was detected as a side product.

^a All reactions were carried out with cinnamaldehyde and ethanol in ionic liquids. Reaction conditions: cinnamaldehyde/ethanol = 1:3 (molar radio), ionic liquids 0.5 mmol, Cinnamaldehyde 1 mmol, T = 70 °C, t = 1 h.