CONDENSATION-REACTIONS OF LIGNIN DURING OXYGEN DELIGNIFICATION UNDER ACIDIC CONDITIONS

Spruce wood (Picea abies) has been subjected to delignification by oxy gen under acidic conditions using different solvent media. The residua l and removed lignins were submitted to permanganate oxidation and the products analyzed by GC and GC-MS. Results from the analysis of the r esidual lignins indicate that lignin ''condensation'' depends on the n ature of oxidation medium. It was found that the addition of acetone t o the aqueous liquor decreases both acid catalyzed and radical side re actions. Lignin ''condensation'' in water containing media is dominate d by radical reactions. Results from the analysis of the lignin remove d during oxygen delignification in an acetone/water medium indicate th at significant amounts of ''condensed'' structures are present, which are relatively stable towards oxidation. The presence of diphenylmetha ne, diarylether and biphenyl type structures in the removed lignin was confirmed by CP-MAS C-13 NMR spectroscopy.