Copper- and Vanadium-Catalyzed Oxidative Cleavage of Lignin using Dioxygen

Transition-metal-containing hydrotalcites (HTc) and V(acac)(3)/Cu(NO3)(2)3H(2)O (acac=acetylacetonate)mixtures were tested for their catalytic activity in the cleavage of the lignin model compound erythro-1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-l,3-propanediol (1) with molecular oxygen as oxidant. Both catalytic systems displayed high activity and good selectivity and afforded veratric acid as the main product. The catalyst behavior was studied by EPR spectroscopy, XRD, and Raman spectroscopy. After the catalysts were established for the model system, lignin depolymerization studies were performed with various organsolv and kraft lignin sources. The oxidative depolymerization and lignin bond cleavage were monitored by gel permeation chromatography (GPC), MALDI MS, and 2D-NMR (HSQC). Irrespective of the lignin pretreatment, both HTc-Cu-V and V(acac)(3)/Cu(NO3)(2)3H(2)O were able to cleave the -O-4 linkages and the resinol structures to form dimeric and trimeric products.