Abstract Three hydroxyl functionalized zwitterionic liquids (ZILs) were found to be novel recyclable catalysts for the Knoevenagel condensation between aldehydes or ketones and active methylene compounds in aqueous medium. Both aldehydes and ketones gave satisfactory results. The products could simply be separated from the catalysts/water, and the catalysts could be recycled six times without noticeably decreasing the catalytic activity.
![3-[bis(2-hydroxyethyl)amino]propanesulphonic acid Structure](https://image.chemsrc.com/caspic/152/58431-91-7.png)