Exploring allylation and claisen rearrangement as a novel chemical modification of lignin

The conversion of lignin into value-added products is traditionally hampered by its stochastic structure and its complex reactivity. In this work, for the first time, is reported the allylation reaction and the aromatic Claisen rearrangement of the allyl group on lignin as chemical modifications aimed at the development of new lignin-based materials and the improvement of its compatibility and ease of processing. In particular, the Claisen rearrangement of lignin was foreseen as a valuable approach to release phenolic groups in an already chemically modified lignin, giving additional reactive sites for further transformation. These reactions were carried out on a purely guaiacylic lignin (TMP), taken as reference material for its simplicity, and on a more structurally complex herbaceous lignin (P1000®). The Claisen rearrangement of the allylic chain was successfully achieved by treatment in dimethylformamide at reflux temperature for 15 hours. Finally, a screening of the antioxidant activity of reference, allylated, and Claisen rearranged lignins was carried out. Rearranged lignins exhibited satisfying antioxidant activities if compared to the reference ones.