Abstract
Lignin derivatives (lignophenol derivatives) with different phenolic functionalities were synthesized from spruce (Picea jezoensis) and birch (Betula platyphylla) native lignins, through the phase-separative systems composed of phenol derivatives and 72% sulfuric acid. Their depolymerizations were carried out in alkaline media. Spruce lignocresol was depolymerized to Mw ca.900 by the NaOH treatment, whereas birch lignocresol to Mw ca.600, which were not affected by the NaOH concentration and the addition of external nucleophile (Na2S). The total amount of phenolic hydroxyl groups remained almost unchanged during the depolymerization. However, the amount of cresolic OH was decreased, whereas that of guaiacyl OH was increased. These facts indicated that the phenolic functionality was exchanged from cresolic nuclei to lignin nuclei by the attack of adjacent cresolic OH to β-carbons in Cβ-aryl ether units, accompanied by the depolymerization. There was a good correlation between the frequency of phenolic nuclei with Cβ-attackable OH and the depolymerization degree.
