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. © 2014 by the authors; licensee MDPI, Basel, Switzerland.
Figures
![Table 1. Aldol reactions of benzaldehyde and acetone (model reaction) in different catalytic systems containing 50 wt % [N2222][EtNHC3SO3] and 50 wt % solvent. Reaction conditions: 2.5 mmol benzaldehyde, 7.5 mmol acetone, 1.0 g [N2222][EtNHC3SO3], microwave temperature 80 °C, 0.5 h.](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/f1ece50a-625e-392c-a149-046126ea27cd/thumbnail-84a48a91-1520-466c-aa9a-1b4976db3780-1.png)
![Figure 2. Comparison of the yields of product 4a under the conditions of microwave heating and conventional heating. Reaction conditions: 2.5 mmol benzaldehyde, 7.5 mmol acetone, 3.4 mmol [N2222][EtNHC3SO3] (1.0 g) and 50 wt % of H2O (1.0 mL H2O), 80 °C.](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/f1ece50a-625e-392c-a149-046126ea27cd/thumbnail-b7fa0a33-e804-4b5d-a0f1-89929a37aa4c-2.png)
![Figure 3. Recycling of [N2222][EtNHC3SO3] aqueous solution in the model aldol reaction. Reaction conditions: 2.5 mmol benzaldehyde, 7.5 mmol acetone, 3.4 mmol (1.0 g) [N2222][EtNHC3SO3] and 50 wt % of H2O (1.0 mL), 80 °C, 0.5 h.](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/f1ece50a-625e-392c-a149-046126ea27cd/thumbnail-f61d31e5-f6c3-419e-8ad3-e7bc60d417c8-4.png)
![Table 3. Aldol reactions of various aromatic aldehydes with acetone in the [N2222][EtNHC3SO3] catalytic systems. Reaction conditions: 3.4 mmol ILs (1.0 g), 50 wt % of H2O (1.0 mL) of catalytic system, 2.5 mmol aromatic aldehydes, 7.5 mmol acetone, 80 °C, 0.5 h.](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/f1ece50a-625e-392c-a149-046126ea27cd/thumbnail-55c6f77d-317a-4294-8845-5876a03b1f1e-5.png)
![Table 4. Henry reactions of various aromatic aldehydes with acetone in the [P4444][Im] catalytic systems. Reaction conditions: 3.4 mmol ILs, 50 wt % of H2O (1.0 mL), 2.5 mmol aromatic aldehydes, 7.5 mmol acetone, 80 °C, 0.5 h.](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/f1ece50a-625e-392c-a149-046126ea27cd/thumbnail-6819c3d6-0af0-468b-ba34-fcdac312cfec-6.png)
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Wang, C., Liu, J., Leng, W., & Gao, Y. (2014). Rapid and efficient functionalized ionic liquid-catalyzed aldol condensation reactions associated with microwave irradiation. International Journal of Molecular Sciences, 15(1), 1284–1299. https://doi.org/10.3390/ijms15011284
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