Oxidative Degradation of in Situ and Isolated Spruce Lignins by Water-Soluble Hydrogen Peroxide Resistant Pentafluorophenylporphyrin

The catalytic activity of a new oxidation-resistant Fe(III) meso -tetrakis(pentafluorophenyl)-β-tetrasulfonatoporphyrin [Fe(TF 5 PS 4 P)] on spruce milled wood lignin (MWL) and lignin in extractive free spruce wood (EFW) was investigated in the presence of H 2 O 2 . Size exclusion chromatography analysis shows that MWL was rapidly repolymerized by Fe(TF 5 PS 4 P)/H 2 O 2 before undergoing further degradation. IR and 1 H-NMR spectroscopy of oxidized lignins suggested that ring-opening reactions and demeth(ox)ylations occurred. Analysis by thioacidolysis of MWL revealed an 80−90% decrease in guaiacyl units involved in β- O -4 bonds after catalysis. The formation of some vanillin and vanillic acid structures in lignins was evidenced, confirming that Cα−Cβ cleavages are promoted by the metalloporphyrin. Lignin in EFW was also degraded by Fe(TF 5 PS 4 P)/H 2 O 2 in the same manner as MWL, but to a lesser extent. In conclusion, Fe(TF 5 PS 4 P)/H 2 O 2 mimics the action of fungal ligninolytic peroxidases but is also able to penetrate within the compact structure of wood and degrade lignin to a significant extent.