Aromatic Monomer Production from Lignin Through Catalytic Carbon-Carbon Bond Cleavage

The conversion of lignin, the heterogeneous aromatic polymer found in terrestrial plant cell walls, into renewable bio-derived chemicals is critical to enable a viable lignocellulose-based bioeconomy. While lignin finds some limited industrial uses today, cost-effective and robust processes for the depolymerization of lignin to aromatic monomers would substantially expand lignin applications to larger markets, such as sustainable polymers and commodity chemicals. Historically, catalytic lignin depolymerization has focused on aryl-ether bond cleavage. A large fraction of aromatics in lignin, however, is linked by various recalcitrant carbon-carbon (C-C) bonds, which present a challenging substrate for depolymerization to aromatic monomers at high yields. To increase monomer yields above those accessible through aryl-ether bond cleavage alone, here we report that autoxidation catalysis cleaves C-C bonds in various lignin substrates with high atom economy. The catalyzed autoxidations of phenol-protected reductive catalytic fractionation (RCF) oil oligomers and hydrodeoxygenation (HDO) oil are described. The stream oxygenated monomers produced from the various lignin substrates are bioavailable as demonstrated by their bioconversion to cis,cis-muconate by engineered strains of Pseudonomas putida.