Highly Unsaturated Lignin Through Clean and Efficient Ru-Catalyzed Glycerol Carbonate Allylation and Ring-Opening Reaction Strategies.

Innovative lignin functionalization strategies which graft a large amount of unsaturation onto lignin have been developed. Ruthenium catalysis using allyl alcohol or diallyl ether has been used to develop ready-to-graft allylic synthons based on glycerol carbonate and related derivatives. Allylated glycerol carbonate and glycidyl allyl ethers were thus used in effective ring-opening reactions with high atom economy to convert Kraft, Organosolv, and Soda lignins without prior purification. Glycidyl allyl ethers were grafted onto lignin with a substitution degree of hydroxyl groups up to 90%. Technical and modified lignins were characterized by nuclear magnetic resonance (NMR), infrared (IR), size-exclusion chromatography (SEC), and thermal properties were determined by differential scanning calorimetry (DSC). The grafting efficiency produces modified lignins with a high level of unsaturation, with thermal properties allowing material shaping, providing new opportunities for material applications.