Lignin analysis by permanganate oxidation. I. Native spruce lignin

Permanganate oxidation has long been used to estimate the concentrations of uncondensed and condensed structures in phenolic lignin fractions. Four monomers and two dimers are normally quantified for softwood lignins and the actual yield of each is corrected for incomplete oxidation. Based on the analysis of several model compounds and lignin samples the correction factors were refined to give a better correlation between the original phenolic hydroxyl (PhOH) content and the total yield of selected products. An alkaline CuO pretreatment was used to hydrolyze most of the interunitary ether bonds in the lignin of spruce woodmeal. The PhOH content increased from 12/100 C-9 units to 69/100 C-9 units. A composition of approximately 55 % uncondensed guaiacyls, 18% biphenyls and 14% beta-5 was estimated from KMnO4 oxidation of this sample.