Understanding the hard journey of catalytic lignin amination valorization

Lignin, a pivotal component in biomass conversion, holds significant potential for the synthesis of nitrogen-containing compounds. However, studies on the amination of real lignin remain limited, primarily due to its complex structure compared to model compounds. This review explores the factors influencing lignin valorization, from its extraction to the synthesis of nitrogenous products. Organic solvent-extracted lignin, characterized by its intact molecular structure, abundance of functional groups, and absence of sulfur, facilitates easier degradation and amination due to enhanced catalyst targeting. Among various catalysts analyzed, ruthenium-based systems demonstrated superior performance, achieving high yields in clean, environmentally friendly solvents. The review delves into the distinct roles of catalysts in lignin amination reactions, providing insights into reaction mechanisms and catalyst performance. Additionally, the influence of solvents and their critical factors for effective amination are discussed, alongside minor contributors such as catalyst carriers, hydrogen and amine sources, and non-catalytic thermal reactions. The advantages and limitations of various conditions for lignin amination are critically compared, highlighting existing challenges. Finally, this review outlines future directions for advancing lignin amination systems, offering innovative perspectives for expanding the frontiers of lignin valorization.