Mechanistic Investigation of Rice Straw Lignin Subunit Bond Cleavages and Subsequent Formation of Monophenols

Lignin is a superb renewable feedstock for deriving petroleum-analogous biochemicals and value-added bioproducts. However, proper elucidation of its original biosynthetic structure and subsequent deconstruction is necessary to facilitate proper exploitation. Herein, its chemical substructure and linkages within an important global feedstock, rice straw, were interrogated by spectroscopy. Pyrolysis was chosen to cleave it and obtain guaiacyl (G), syringyl (S), and hydroxyphenyl (H) monophenols distributions at various temperatures. A unique relationship between product substructures and lignin depolymerization was revealed. The overall scope of the depolymerization mechanism into monophenols by cleavage of β-O-4 and β-5 in phenylcoumaran subunits were explored experimentally and through bond dissociation energy (BDE) theory.