A novel environmentally friendly approach to lignin-based cyclic carbonates
This work presents a new and highly attractive route towards a fully renewable lignin-based building block equipped with cyclic carbonate functionalities. No toxic or hazardous reactants are involved. In an operationally simple and efficient two-step procedure, lignins from different origin and processes were oxyalkylated with glycerol carbonate (GC) to insert adjacent hyroxyl groups. The oxyalkylated lignin was then reacted via trans-esterification with dimethyl carbonate (DMC) or ethylene carbonate (EC) producing cyclic carbonate functionalized lignin. The transesterification was studied as a function of time, type of catalyst, and catalyst amount using NMR spectroscopy. Reactions with K2CO3 as catalyst (0,4 eq) afforded lignin-based cyclic carbonate with almost complete conversion (96%) within 6 hours, as analyzed by 31P and 13C NMR spectroscopy. Thus, the cyclocarbonated lignin is a promising, sustainable synthon for further functionalization or direct polymerization to non-isocyanate polyurethanes (NIPUs) and has great potential in synthetic chemistry.