Production of Methyl <i>p</i>-Hydroxycinnamate by Selective Tailoring of Herbaceous Lignin Using Metal-Based Deep Eutectic Solvents (DES) as Catalyst
Zhangmin Li, Jinxing Long, Qiang Zeng, Yuanhao Wu, Minglong Cao, Sijie Liu, Xuehui Li
Abstract
Catalytic conversion of lignin to versatile aromatic compounds is attracting increasing attention. However, it is highly desirable but challenging to produce a specific chemical with high yield through lignin depolymerization in a one-pot process because of the complex structure of the lignin molecule (mainly composed of H, G, and S units). In this study, a series of metal-based deep eutectic solvents (M-DESs) were prepared and used for the catalytic tailoring of lignin H units to produce value-added methyl p-hydroxycinnamate (MPC). In particular, M-DES ChCl[FeCl3]2 showed excellent catalytic performance for the selective production of MPC as the sole product with high yield and selectivity (105.8 mg g–1 and 74.1%, respectively). Extensive characterizations using 2D HSQC NMR, 13C NMR, and GPC demonstrated that MPC was obtained from the selective tailoring of p-coumaric acid (pCA) units via the cleavage of ester bonds in lignin. Furthermore, M-DES ChCl[FeCl3]2 also exhibited efficiency to other herbaceous lignins, and showed excellent recyclability. Therefore, this work provides an effective strategy for the valorization of lignin.