Molecular oxygen lignin depolymerization: An insight within phenolic monomers stability.

It is well known that during oxidative depolymerization of lignin in aqueous alkaline medium using molecular oxygen as oxidant, the highly functionalized primary phenolic monomers are not stable products due to various and not fully identifying secondary reaction mechanisms. However, a better understanding of the mechanisms responsible for instability of the main part of the products of interest derived from lignin is of much interest. The evaluation of their individual reactivity and degradation under oxidative conditions should significantly help to find a better way to valorise the lignin polymer and to maximize the yields of target value-added products. Consequently, the main objective of the present work was to study the individual degradation of some selected lignin-based phenolic compounds such as vanillin, vanillic acid and acetovanillone, together with some other pure chemical compounds such as phenol and anisole to give an insight on the mechanisms responsible for the simultaneous formation and degradation of those products and the influence of the oxidation conditions. Various complementary strategies of stabilization are proposed, discussed and applied for the oxidative depolymerization reactions of a technical lignin extracted from Pinewood with a high content of B-O-4 interconnecting bonds to try to obtain enhanced yields of value-added products.