Alkaline nitrobenzene oxidation of phenolic and non-phenolic dimeric, trimeric and oligomeric β-O-4 lignin model compounds

Phenolic and non-phenolic dimeric, trimeric and oligomcric β-O-4 lignin model compounds were prepared and subjected to alkaline nitrobenzene (ANB) oxidation. The contribution of the terminal phenolic hydroxy! groups to the vanillin yields against the degree of polymerization (DP) was discussed. The ratio of vanillin yields from the phenolic to the corresponding non-phenolic model compounds decreased with the increase of DP, from 2.5 (dimer) to 1.1 (oligomer). Consequently, the influence of the terminal structure (phenolic or non-phenolic) on vanillin yield was expected to be negligible in native lignin with high molecular mass, under the present ANB oxidation conditions. It was also suggested that the approximate contents of β-O-4 could be calculated from the vanillin yields of ANB oxidation.