The oxidative degradation of lignin, a major component of lignocellulose, in alkaline media is important in both academic and applied research, serving as a fundamental approach for lignin analysis and chemical conversion. Although it is well known that the alkaline oxidation commonly yields benzaldehydes, benzoic acids, and acetophenones, the pathways underlying their formation remain insufficiently understood. This study focuses on the β‐ether, the most abundant interunit linkage in lignin, and investigates the formation pathways of vanillin, vanillic acid, and acetoguaiacone from guaiacyl lignin in 4.0 mol/L NaOH aq. at 120°C under O 2 . By examining the degradation behavior of a lignin model polymer LP composed exclusively of β‐ether, along with various dimeric models, we found that vanillin is mainly generated through a sequential reaction initiated from phenolic terminal units. Another vanillin formation pathway originating from nonphenolic internal units contributed to the overall oxidation process to some extent. Vanillic acid and acetoguaiacone were formed via pathways distinct from that of vanillin, with their formation largely attributed to reactions involving internal units. Further investigation of the degradation behavior of isolated lignin revealed that the contribution of the sequential vanillin formation pathway from phenolic terminals was lower than that observed for LP .
Ishikawa et al. (Sun,) studied this question.