Tuning lignin properties by mild ionic-liquid-mediated selective alcohol incorporation

The synthesis of ideal, well-defined, functionalized lignins is of great significance for realizing the full valorization potential of lignocellulosic biomass. Here, the application of acidified triethylammonium triflate is reported, allowing for the selective benzylic alkoxylation of different lignins at room temperature. Full benzylic alkoxylation of typically hard-to-process, high-molecular-weight lignin was achieved in this medium by simple mixing with different alcohols. Limited lignin degradation was observed, and lignin modification was also achieved within the lignocellulosic matrix. This allows the method to be used as a biomass pretreatment, which was shown to also enhance enzymatic saccharification. The reactivity, stability, and hydrophobicity of the lignin can be tuned based on the alcohol used. Effective recovery of the ionic liquid and recycling of the ionic liquid was achieved. Thus, a straightforward mild method is demonstrated to introduce new functionality in lignin, allowing it to be tuned towards novel applications.