Abstract
Five quaternary ammonium ionic liquid (IL) and two tetrabutylphosphonium ILs were prepared and characterized. An environmentally benign and convenient functionalized ionic liquid catalytic system was thus explored in the aldol condensation reactions of aromatic aldehydes with acetone. The aldol reactions proceeded more efficiently through microwave-assisted heating than through conventional thermal heating. The yield of products obtained under microwave heating for 30 min was approximately 90%, and the ILs can be recovered and reused at least five times without apparent loss of activity. In addition, this catalytic system can be successfully extended to the Henry reactions.
Highlights
Green chemistry, that possesses the spirit of sustainable development, has been booming since 1991 and continues to attract more and more interest [1]
We describe here the aldol condensation reactions between various aromatic aldehydes and acetone in the functionalized ionic liquid (IL)
Our first investigation focused on the model reaction of benzaldehyde and acetone in the amine-functionalized IL [N2222][EtNHC3SO3] (Scheme 1)
Summary
That possesses the spirit of sustainable development, has been booming since 1991 and continues to attract more and more interest [1]. A series of functionalized ILs incorporated with pyrrolidine and proline units have been synthesized and tested as organocatalysts for direct aldol reactions [46,47,48,49] These new TSILs were found to effectively catalyze the direct aldol reactions of cyclic ketone or acetone and various aromatic aldehydes. Our recent work has demonstrated that the cross-aldol condensation reactions of aromatic aldehydes with cyclopentanone proceeded efficiently in several amine-functionalized ILs [50]. Even so, limitations such as long reaction times, use of toxic organic compounds (TOCs) as additives, complicated post-treatment process and difficulty of separating condensation product from reaction system still need to be solved. [N2222][EtNHC3SO3], Alkyl=Ethyl [N2222][n-BuNHC3SO3], Alkyl=n-Butyl [N4444][MeNHC3SO3], Alkyl=Methyl [N1123][EtNHC3SO3], Alkyl=Ethyl [N1123][n-OctNHC3SO3], Alkyl=n-Octyl
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