THE DFRC METHOD FOR LIGNIN ANALYSIS - PART 3 - NMR-STUDIES

Two key reactions in the DFRC method have been examined by NMR. Both a cetyl bromide (AcBr) derivatization of lignin and Zn reductive elimina tion of the beta-bromo derivatives from lignin were highly selective a nd essentially quantitative. Treatment with AcBr in acetic acid effici ently converted beta-aryl ether substructures of lignins into beta-bro mo ethers while gamma-hydroxy and phenol groups were acetylated; the f ollowing Zn step cleaved brominated beta-aryl ethers forming the expec ted cinnamyl acetates. In view of the high selectivity of AcBr reactio ns with lignin units and the solubilization of lignocellulosic materia ls, AcBr derivatization of lignins can be used for NMR characterizatio n of whole lignins.