Beijing Key Laboratory of Ionic Liquids Clean Process, CAS Key Laboratory of Green Process and Engineering State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, P. R. China.
School of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing, 100190, P. R. China.
ChemSusChem. 2020 Nov 20;13(22):5945-5953. doi: 10.1002/cssc.202001828. Epub 2020 Sep 30.
Oxidation of lignin to value-added aromatics through selective C-C bond cleavage via metal-free and mild strategies is promising but challenging. It was discovered that the cations of ionic liquids (ILs) could effectively catalyze this kind of strong bond cleavage by forming multiple weak hydrogen bonds, enabling the reaction conducted in air at temperature lower than 373 K without metal-containing catalysts. The cation [CPMim] (1-propylronitrile-3-methylimidazolium) afforded the highest efficiency in C-C bond cleavage, in which high yields (>90 %) of oxidative products were achieved. [CPMim] could form three ipsilateral hydrogen bonds with the oxygen atom of C=O and ether bonds at both sides of the C-C bond. The weak bonds joint effects could promote adjacent C-H bond cleave to form free radicals and thereby catalyze the fragmentation of the strong C-C. This work opens up an eco-friendly and energy-efficient route for direct valorization of lignin by enhancing IL properties via tuning the cation.
通过无金属和温和的策略选择性地裂解 C-C 键将木质素氧化为增值芳烃具有很大的前景，但也具有挑战性。人们发现，离子液体（ILs）的阳离子可以通过形成多个弱氢键有效地催化这种强键的裂解，从而使反应在低于 373 K 的温度下在空气中进行，而无需使用含金属的催化剂。阳离子 [CPMim]（1-丙腈-3-甲基咪唑鎓）在 C-C 键裂解中表现出最高的效率，其中氧化产物的收率高达 90%以上。[CPMim]可以与 C=O 的氧原子和 C-C 键两侧的醚键形成三个同侧氢键。弱键的联合作用可以促进相邻的 C-H 键断裂形成自由基，从而催化强 C-C 的断裂。这项工作通过调整阳离子来增强离子液体的性质，为直接利用木质素开辟了一条环保且节能的途径。
