Depolymerization of Lignin via a Microscopic Reverse Biosynthesis Pathway

The ionic liquids upon perchlorate to promote the C-C/C-O bonds cleavage in alkali lignin under photothermal synergism

Transforming lignin into aromatic monomers is critically attractive to develop green and sustainable energy supplies. However, the usage of the additional catalysts like metal or base/acid is commonly limited by the caused repolymerized and environmental issues. The key step is to mediate electron transfer in lignin to trigger lignin C-C/C-O bonds cleavage without the catalysts mentioned above. Here, we report that the ionic liquids [BMim][ClO4] was found to trigger lignin electron transfer to cleave the C-C/C-O bonds for aromatic monomers without any additional catalyst. The proton transfer from [BMim]+ to [ClO4]- could polarize the anion and decrease its structure stability, upon which the active hydroxyl radical generated and induced lignin C-C/C-O bonds fragmentation via free radical-mediated routes with the assistance of photothermal synergism. About 4.4 wt% yields of aromatic monomers, mainly composed of vanillin and acetosyringone, are afforded in [BMim][ClO4] under UV-light irradiation in the air at 80 °C. This work opens the way to produce value-added aromatic monomers from lignin using an eco-friendly, energy-efficient, and simple route that may contribute to the sustainable utilization of renewable natural resources.

Electrochemically Driven Deoxygenative Borylation of Alcohols and Carbonyl Compounds

We present a new, unified approach for the transformation of benzylic and allylic alcohols, aldehydes, and ketones into boronic esters under electroreductive conditions. Key to our strategy is the use of readily available pinacolborane, which serves both as an activator and an electrophile by first generating a redox-active trialkylborate species and then delivering the desired deoxygenatively borylated product. This strategy is applicable to a variety of substrates and can be employed for the late-stage functionalization of complex molecules.

Selective Cleavage of Lignin Model Compounds via a Reverse Biosynthesis Mechanism

Selective depolymerization of lignin remains a significant challenge in biomass conversion. The biosynthesis of lignin involves the polymerization of monolignol building blocks through oxidative radical coupling reactions. A strategy for lignin degradation leverages photoredox deoxygenative radical formation to trigger reverse biosynthesis, which cleaves model compounds of the β-O-4 and β-5-β-O-4 linkages to produce monolignols, precursors to flavoring compounds. This mild method preserves important oxygen functionality and serves as a platform for achieving selective lignin depolymerization.

Evidence for Ruthenium(II) Peralkene Complexes as Catalytic Species during the Isomerization of Terminal Alkenes in Solution

The isomerization (chain-walking) reaction of terminal to internal alkenes is catalyzed by part-per-million amounts of practically any Ru source when the reaction is carried out with a neat terminal alkene. Here, we provide evidence that the soluble starting Ru sources evolve to catalytically active peralkene Ru(II) species under reaction conditions. These species may also explain the isomerization products found during other Ru-catalyzed alkene processes, i.e., alkene metathesis reactions. A Finke-Watzky mechanism for catalyst formation is consistent with the evidence obtained.

Lignin to value-added products: Research updates and prospects

Due to the urgent need for renewable and clean energy, the efficient use of lignin is of wide interest. A comprehensive understanding of the mechanisms of lignin depolymerization and the generation of high-value products will contribute to the global control of the formation of efficient lignin utilization. This review explores the lignin value-adding process and discusses the link between lignin functional groups and value-added products. Mechanisms and characteristics of lignin depolymerization methods are presented, and challenges and prospects for future research are highlighted.