Catalytic Alkaline Oxidation of Lignin and its Model Compounds: a Pathway to Aromatic Biochemicals

Catalytic oxidation via the application of molecular oxygen and copper complexes is a useful pathway toward valuable low molecular mass compounds from in situ or waste stream lignins. In this study, two dimeric beta-ether model compounds, one beta-ether oligomer, and a milled wood lignin sample from Loblolly pine were catalytically oxidized. Yields and stability of the aromatic aldehyde and acid products were measured. Nuclear magnetic resonance spectroscopy and gel permeation chromatography were used to monitor structure/composition and molecular mass changes of the lignin before and after catalytic oxidation to study the degree of depolymerization and structure of the residual lignin. Oxidized units appear to be derived from beta-aryl ether, phenylcoumaran, and biphenyl ether components. To date, this method breaks down the lignin polymeric structure reasonably effectively, producing low molecular mass products; this work also highlights some of the issues that need to be overcome to optimize this approach.