Effect of Counter Cation on Alkaline Reaction of β-O-4-Type Substructure in Lignin

High-purity lignin fractions and nanospheres rich in phenolic hydroxyl and carboxyl groups isolated with alkaline deep eutectic solvent from wheat straw

“…VG was found to be completely converted in DES, resulting in almost stoichiometric production of guaiacol, and several products with ketone side chain were identified. These results were similar to the degradation of lignin models under alkaline cooking conditions, although it is difficult to determine the detailed mechanism due to the complexity of the reaction (Kato et al, 2019). This at least indicates that the cleavage of ether bonds is one of the main reaction routes causing the lignin depolymerization and facilitating lignin extraction from wheat straw (see supplementary material).…”

“…Although the further reactions of the epoxide side chain intermediates are quite complicated, the data of 2D-NMR showed that oxidized (Cα = O) guaiacyl units G' and syringyl units S' were the main structure of products, which are commonly found in alkaline lignin (Mancera et al, 2011). To conclude, based on the available evidence, the lignin degradation reaction mechanism in alkaline DES treatment is similar to that in NaOH pulping (Kato et al, 2019). This mechanism results in lignin with a high − OH and − COOH content, which can be a benefit in developing a wider range of lignin applications.…”

Degradation mechanism of a lignin model compound during alkaline aerobic oxidation: formation of the vanillin precursor from the β-O-4 middle unit of softwood lignin

“…Synthetic routes for the models in Scheme 2 and authentic compounds for the HPLC analysis are shown in Schemes S1–S4 in the ESI †. All the compounds were synthesized according to the route reported in the literature: 37,53,64,65 ref. 37 for VGL , ref.…”

“…One of the degradation pathways of 4 is the conversion the 4-methoxy group of 4 to OH to produce vanillin (2) 16 (pathway C in Scheme 3). S N 2 and S N Ar mechanisms have been suggested as two possible mechanisms of this reaction, 16,53,54 but its elucidation is out of the scope of this study. The formation of benzyl alcohol 1 and benzoic acid 3 is explained by disproportionation of aldehyde 4 by the Cannizzaro reaction (pathway B in Scheme 3).…”