Comprehensive study on the chemical structure of dioxane lignin from plantation Eucalyptus globulus wood

Results of a comprehensive study on the chemical structure of lignin from plantation Eucalyptus globulus Labill are presented. Lignin has been isolated by a modified mild acidolysis method and thoroughly characterized by functional group analysis, by a series of degradation techniques (nitrobenzene oxidation, permanganate oxidation, thioacidolysis, and Py-GC-MS), and H-1 and C-13 NMR spectroscopy. Plantation Eucalyptus globulus lignin was found to be of the S/G type with an extremely high proportion of syringyl (S) units (82-86%) and a minor proportion of p-hydrophenyl propane (H) units (roughly 2-3 mol %). Unknown C-6 substituted and 4-O-5 ', type syringyl substructures represent about 65% of lignin "condensed" structures. Eucalypt lignin showed high abundance of beta -O-4 (0.56/C-6) structures and units linked by alpha -O-4 bonds (0.23/C-6). The proportion of phenylcoumaran structures was relatively low (0.03/C-6). Different kinds of beta-beta substructures (pino-/syringaresinol and isotaxiresinol types) in a total amount of 0.13/C-6 were detected. ESI-MS analysis revealed a wide molecular weight distribution of lignin with the center of gravity of mass distribution around 2500 u.