Lignin is the second-most abundant renewable carbon source, comprising up to 25% of biomass. Biorefining processes for converting biomass into its individual components introduce drastic changes into lignin’s native structure, such as an increase in the amount of free phenolic groups. Therefore, developing catalysts that target lignin-like phenol oxidation would be a viable approach for determining the applicability of lignin as a chemical feedstock. Previous work from our group involved the development of a homogeneous asymmetric Co-Schiff base catalyst that incorporates a benzylpiperazine unit onto one of the salicylaldehyde moieties; this catalyst effectively oxidizes both S- and G-type phenolic lignin models to 2,6-dimethoxybenzoquinone (DMBQ) and methoxybenzoquinone (MBQ), respectively, demonstrating significantly higher reactivity than conventional Co-Schiff base catalysts. We then sought to expand the scope of the aforementioned study by designing both symmetric and asymmetric systems with differing nitrogenous base tethers (pyrrolidine, dimethylamine) to be examined for catalytic oxidative activity relative to our current lead catalyst. Results indicate that these catalysts are not as active toward phenolic oxidation to <i>para-</i>benzoquinones as our lead catalyst. Therefore, we refocused efforts toward the development of novel symmetric and asymmetric Co-Schiff base catalysts with differing arylpiperazine tethers. Preliminary results show that asymmetric catalysts comprising a diphenylmethyl or phenylethylene side chain display oxidative activity comparable to our lead catalyst for the conversion of S-type models to DMBQ. Evaluation of oxidative activity toward G-type models, as well as the syntheses of novel symmetric catalysts, is currently underway. All active catalysts will then be evaluated for the catalytic deconstruction of lignin. If successful, our library of arylpiperazine-tethered Co-Schiff base catalysts will be expanded, leading to new methodology for conversion of biorefinery lignin, which will streamline biorefinery operation and offer new catalytic routes to biobased chemicals and fuels from renewable carbon sources.<br/>

Development of novel nitrogenous base-tethered cobalt-Schiff base complexes for the selective catalytic cleavage of lignin

253rd National Meeting (2017)

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