How to active ethanolamine for selective hydrogenation by imidazolium-based cation and conjugated π bond

Abstract

Ionic liquids (ILs) are unique substances with unique ionic sites. They are regarded as one of the most promising green solvents and catalysts in the 21st century. In this work, the synthesis of imidazolium-based ILs as metal-free catalysts by molecular design is reported for the first time. By using the ILs as precursors, hyper-crosslinked poly(ionic liquid) (HCPIL) was synthesized by Friedel–Crafts alkylation reaction. These metal-free catalysts can effectively activate ethanolamine for the hydrogenation of nitrobenzene, and they have definite active sites. As the synthesized HCPIL-Cl has a rich porous structure and IL structural units, it could maintain the catalytic activity of ILs and recover them via efficient facile filtration and washing. Density functional theory (DFT) calculation suggested that the imidazolium structure is essential to ethanolamine activation. The calculated results of DFT agree well with the experimental results. The hydrogenation of nitrobenzene has many intermediates whose selectivity can be regulated by different gas atmosphere or alkaline environments. This work provides a promising method for the design of metal-free catalysts.