PULPING CATALYSTS FROM LIGNIN .5. NITROGEN-DIOXIDE OXIDATION OF LIGNIN MODELS TO BENZOQUINONES

Several syringyl lignin models have been oxidized to 2,6-dimethoxy-p-b enzoquinone (DMBQ) in high yields with nitrogen dioxide (NO2) in metha nol solvent. The yields of DMBQ were high for syringyl alcohol, syring aldehyde, and disyringyl methane and moderate for several other phenol ic syringyl models. Benzoquinones were not formed from non phenolic su bstrates. The yields were slightly improved by the presence of N-hydro xysuccinimide. Guaiacyl lignin model compounds gave low benzoquinone y ields; the major products were C-5 nitro substituted compounds. A radi cal mechanism is proposed to explain the observed results.