Dr. Ting Wang, Prof. Hong-Yuan Chen, Prof. Dr. Jing-Juan Xu, Prof. Dr. Jun Hu
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引用次数: 0
摘要
大量的水作为木质素连接的惰性环境,导致它们的自然半衰期延长了几个世纪。在这项研究中,我们提出了各种木质素模型在水微滴中自发和超快的C─O/C─C键裂解的惊人结果,产生了增值芳香化学物质。β - O - 4键是天然木质素中最丰富的单元间键,在Cβ - O键上被选择性地剪切,产生的酚的收率超过70%。机理研究表明,即使在没有额外碱的情况下,带负电荷的水微滴的空气-水界面上独特的碱性环境也会导致β - O - 4键的断裂。在β - O - 4和β - 1木质素键中,高度稳定的Cα─Cβ键也完成了具有挑战性的裂解,产生了有价值的苯甲酸产物。机理研究表明,分子氧氧化底物是Cα─Cβ键断裂的关键步骤。值得注意的是,所有中间体,包括易碎的过氧化物中间体,都是用质谱法鉴定的。结合自由基清除和18O标记的证据,明确了C─O/C─C键选择性裂解的机制,为木质素键的裂解开辟了一条新的绿色道路。
Catalyst-Free Cleavage of C─O/C─C Bonds in Lignin Linkages by Water Microdroplets
Bulk water serves as an inert environment for lignin linkages, resulting in their natural half-lives that extend over centuries. In this study, we present the striking results of the spontaneous and ultrafast C─O/C─C bond cleavage of various lignin models in water microdroplets, yielding value-added aromatic chemicals. The β-O-4 linkages, the most abundant interunit linkages in natural lignin, were selectively cleaved at Cβ─O bonds, producing phenols in yields exceeding 70%. Mechanistic studies elucidated that the cleavage of β-O-4 linkages is derived from the unique alkaline environment at the air–water interface of a negatively charged water microdroplet, even in the absence of extra alkalis. The challenging cleavage of the highly stable Cα─Cβ bonds in β-O-4 and β-1 lignin linkages was also accomplished, yielding valuable benzoic acid product. Mechanistic investigations revealed that the oxidation of the substrates by molecular oxygen is the key step for the Cα─Cβ bond cleavage. Notably, all intermediates, including the fragile peroxide intermediates, were identified using mass spectrometry. Accompanied by evidence from radical scavenging and 18O labeling, the mechanisms for the selective C─O/C─C bond cleavages have been unambiguously characterized, paving a new and green way for the cleavage of lignin linkages.
期刊介绍:
Angewandte Chemie, a journal of the German Chemical Society (GDCh), maintains a leading position among scholarly journals in general chemistry with an impressive Impact Factor of 16.6 (2022 Journal Citation Reports, Clarivate, 2023). Published weekly in a reader-friendly format, it features new articles almost every day. Established in 1887, Angewandte Chemie is a prominent chemistry journal, offering a dynamic blend of Review-type articles, Highlights, Communications, and Research Articles on a weekly basis, making it unique in the field.