Pulping Catalysts from Lignin (7). Nitrogen Dioxide Oxidation of a Lignin Model Dimer

Oxidation of a lignin model disyringyl dimer with nitrogen dioxide (NO2) in the presence of air and N-hydroxysuccinimide led to C1-Ca cleavage with the formation of approximately equal amounts of 2,6-dimethoxy-p-benzoquinone (DMBQ) and glyceraldehyde-2-syringyl ether type structures. The result indicates that only the phenolic end syringyl units of a lignin polymer will be converted to DMBQ upontreatment with the current NO2 reaction conditions. Internal (non-phenolic) lignin units, bonded by ..beta..-O-4 linkages, will resist oxidation.