Novel DBU-based hydroxyl ionic liquid for efficient Knoevenagel reaction in water

ABSTRACT

Novel ionic liquid N-(2-hydroxy-ethyl)-DBU bromide ([HyEtDBU]Br), based on 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) and 2-bromoethanol, was introduced as catalyst for Knoevenagel condensation. Comparing with other non-hydroxyl ionic liquids, [HyEtDBU]Br showed a better catalytic activity, the hydroxyl group linked on the ionic liquid played an important role in facilitating the Knoevenagel condensation reaction. In the presence of [HyEtDBU]Br-H₂O-DABCO composite system, the corresponding Knoevenagel adducts were obtained in good to excellent yields within short times in all cases examined, the procedure is simple and the desired products could be easily separated and purified without any requirement of column chromatographic purification. The use of water as the reaction medium makes the process environmentally benign. The composite system [HyEtDBU]Br-H₂O can be recycled eight times without activity loss.

GRAPHICAL ABSTRACT

KEYWORDS:

• DBU
• hydroxyl ionic liquid
• Knoevenagel reaction
• hydrogen bond

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Sanhu Zhao received his M.Sc. degree in organic chemistry at the Shanxi University of Taiyuan in 2005. His PhD. work was in the field of green chemistry at the Shanxi University of Taiyuan, graduation in 2015. In 2012, he became a professor in chemistry at the Xinzhou Teachers University. His interest is focused on green chemistry, organic synthesis, teaching and learning innovations.

Dan Meng is a graduate student at Shanxi Normal University, supervised by professor Sanhu Zhao, who is currently studying green chemistry.

Lingling Wei is an undergraduate student at Xinzhou Teachers University, supervised by Professor Sanhu Zhao, who is currently studying organic reaction.

Yongsheng Qiao is a professor at Xinzhou Teachers University, His research interests are mainly in green chemistry.

Fugui Xi is a lecturer at Xinzhou Teachers University, His research interests are mainly in catalytic chemistry.

Additional information

Funding

We are grateful for financial support for this work from the Natural Science Foundation of Shanxi Provinc (No. 201601D102015), the Higher School Science & Technology Development Project of Shanxi Province Education Department (No. [2017]171) and the Key Research and Development Project of Xinzhou City ([2017]0302).