The DFRC method for lignin analysis. Part 3. NMR studies

Two key reactions in the DFRC method have been examined by NMR. Both acetyl bromide (AcBr) derivatization of lignin and Zn reductive elimination of the beta-bromo derivatives from lignin were highly selective and essentially quantitative. Treatment with AcBr in acetic acid efficiently converted beta-aryl ether substructures of lignins into beta-bromo ethers while gamma-hydroxy and phenol groups were acetylated; the following Zn step cleaved brominated beta-aryl ethers forming the expected cinnamyl acetates. In view of the high selectivity of AcBr reactions with lignin units and the solubilization of lignocellulosic materials, AcBr derivatization of lignins can be used for NMR characterization of whole lignins.