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Milled wood lignin as well as wood meal from todo fir ( Abies sachalinensis  MAST) was treated with 70% aqueous 1,4-butanediol solution at 220°C without acid catalyst in order to elucidate the delignification mechanism during high-boiling solvent (HBS) pulping. HBS lignin was recovered from black liquor by precipitation, and was subjected to gel permeation chromatography and quantitative  13 C-NMR study. The average molecular weight of MWL decreased. The content of phenolic hydroxyl groups in MWL increased from 0.28 to 0.68/OMe. The decrease in the content of  β-O -4 substructures was evident, which may be attributed to the homolytic cleavage of phenolic  β -aryl ethers. The changes in the content of  β -5 and  β-β  substructures were rather small. The benzyl ether formation of  β-O -4 structures with 1,4-butanediol was also confirmed by  13 C-NMR. However, the signals corresponding to Hibbert's ketones were not observed, which suggests that acidolysis was not an important degradation pathway during HBS pulping.

Delignification Mechanism during High-Boiling Solvent Pulping Part 3. Structural Changes in Lignin Analyzed by 13C-NMR Spectroscopy