The chemical structures of lignocresols derived from native lignins by the phase-separative treatment with cresol and sulfuric acid were characterized by spectral analyses and chemical degradations. The changes in the structure of lignin during the conversion process were discussed. Lignocresol had few conjugated systems, being pinkish white, its brightness comparable to milled wood lignin. Spruce lignocresol included 0.64mol/C9 of cresolic nuclei in the molecule (0.9mol/C9 in birch lignocresol), 77% of which were linked to lignin Cα-positions through carbon-carbon linkages, 16% possibly to Cy-positions, and the remaining 7% etherified to lignin side chains through its phenolic hydroxyl groups. The molecular weight (Mw) of lignocresol was ca. 3500 in spruce, lower in birch. Most of the β-and γ-positions in the side chains of Cg units remained intact, except the coniferyi alcohol and aldehyde units. These structural features were constant during the reaction time up to 60min. It is concluded that the fragmentation of lignin in the phase-separative reaction system was principally due to the cleavage of benzyl aryl ethers, and the skeleton of lignocresol represents those of lignin subblocks formed by the dehydrogenative polymerization of monolignols.

An original reaction system (the phase separative reaction system) has been designed for derivatizing native lignins to highly phenolic, functional polymers. This system is composed of a phenol derivative and concentrated acid, which are not miscible at room temperature. The key point of the lignin functionalization process, including the phase separative system, is that lignin and carbohydrates, which are totally different in structures and reactivities, are modified individually in the different phases: lignin is present in the organic phase and carbohydrates in the aqueous phase. Through the process, lignin was modified selectively at Calpha-positions of side chains, the most reactive sites, to give highly phenolic, light-colored, diphenylmethane-type materials which still retained original interunit linkages formed by the dehydrogenative polymerization during the biosynthesis. The carbohydrates were swollen, followed by partial hydrolysis and dissolution in the acid solution, resulting in the perfect decomposition of interpenetrating polymer network structures in the cell wall. Therefore, the functionalization of lignin and the separation of resulting lignin from carbohydrates were quickly achieved at room temperature, independent of wood species. This process would be a powerful tool for estimating structures and reactivities of lignins as well as the functionalization of lignins, because of the selective structural modifications.