ANALYSIS OF LIGNINS AS PROPIONATE DERIVATIVES BY NMR-SPECTROSCOPY

Lignin propionates were prepared by treating lignin samples with propi onic anhydride in pyridine solution and the derivatives obtained were examined by NMR spectroscopic methods. H-1 NMR spectroscopy of lignin propionates offers a possibility to determine the number of hydroxyl g roups based on the methyl proton signal (delta approximate to 1.2) as well as the methylene proton signal (delta approximate to 2.5) of the propionate groups. It was found to be advantageous to use propionate d erivatives for the analysis of hydroxyl groups in lignin products exhi biting signals (from >CH- and -CH2- groups) that interfere with the ac etate group signals. Analysis of ester groups by C-13 NMR spectroscopy gave practically the same results as those earlier reported for aceta te derivatives.