Zhang Chaofeng, Shen Xiaojun, Jin Yongcan, Cheng Jinlan, Cai Cheng, Wang Feng
Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Light Industry and Food Engineering, Nanjing Forestry University, Nanjing 210037, China.
State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
Chem Rev. 2023 Apr 26;123(8):4510-4601. doi: 10.1021/acs.chemrev.2c00664. Epub 2023 Apr 6.
Lignin, as a precious resource given to mankind by nature with abundant functional aromatic structures, has drawn much attention in the recent decade from academia to industry worldwide, aiming at harvesting aromatic compounds from this abundant and renewable natural polymer resource. How to efficiently depolymerize lignin to easy-to-handle aromatic monomers is the precondition of lignin utilization. Many strategies/methods have been developed to effectively degrade lignin into monomers, such as the traditional methods of pyrolysis, gasification, liquid-phase reforming, solvolysis, chemical oxidation, hydrogenation, reduction, acidolysis, alkaline hydrolysis, alcoholysis, as well as the newly developed redox-neutral process, biocatalysis, and combinatorial strategies. Therefore, there is a strong demand to systemically summarize these developed strategies and methods and reveal the internal transformation principles of the lignin. Focusing on the topic of lignin depolymerization to aromatic chemicals, this review reorganizes and categorizes the strategies/methods according to their mechanisms, orbiting the center of critical intermediates during the lignin linkage transformation, which includes the critical anionic intermediates, cationic intermediates, organometallic intermediates, organic molecular intermediates, aryl cation radical intermediates, and neutral radical intermediates. The corresponding introduction involves the generation and the transformation chemistry of the critical intermediates via the corresponding C-H/O-H/C-C/C-O chemical bond transformations, leading to the cleavage of the C-C/C-O linkage bonds. Accompanying the brief introduction of lignin chemistry and the final concluding remarks and perspectives on lignin depolymerization, this review aims to provide a current research process of lignin depolymerization, which may provide useful suggestions for this vigorous research field.
木质素作为大自然赋予人类的一种宝贵资源，具有丰富的功能性芳香结构，在近十年间受到了全球学术界和工业界的广泛关注，目标是从这种丰富且可再生的天然聚合物资源中获取芳香族化合物。如何将木质素高效解聚为易于处理的芳香族单体是木质素利用的前提条件。人们已经开发出许多策略/方法来有效地将木质素降解为单体，例如传统的热解、气化、液相重整、溶剂解、化学氧化、氢化、还原、酸解、碱水解、醇解方法，以及新开发的氧化还原中性过程、生物催化和组合策略。因此，迫切需要系统地总结这些已开发的策略和方法，并揭示木质素的内在转化原理。围绕木质素解聚为芳香族化学品这一主题，本综述根据其机理对策略/方法进行了重新组织和分类，围绕木质素键转化过程中的关键中间体展开，其中包括关键阴离子中间体、阳离子中间体、有机金属中间体、有机分子中间体、芳基阳离子自由基中间体和中性自由基中间体。相应的介绍涉及通过相应的C-H/O-H/C-C/C-O化学键转化生成关键中间体及其转化化学，从而导致C-C/C-O连接键的断裂。伴随着对木质素化学的简要介绍以及对木质素解聚的最终总结和展望，本综述旨在提供木质素解聚的当前研究进展，这可能为这个蓬勃发展的研究领域提供有用的建议。
