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A STUDY OF LIGNIN DEPOLYMERIZATION BY SELECTIVE CLEAVAGE OF THE Cα-Cβ LINKAGES IN LIGNIN MODEL COMPOUNDS VIA BAEYER-VILLIGER OXIDATION Lignin is amorphous aromatic polymer derived from plants and is a potential source of fuels and bulk chemicals. Herein, we present a survey of reagents for selective stepwise oxidation of lignin model compounds. Specifically, we have targeted the oxidative cleavage of Cα-Cβ bonds as a means to depolymerize lignin and obtain useful aromatic compounds. In this work, we prepared several lignin model compounds that possess structures, characteristic reactivity, and linkages closely related to the parent lignin polymer. We observed that selective oxidation of benzylic hydroxyl groups using TEMPO/O2, followed by Baeyer-Villiger oxidation of the resulting ketones using H2O2, successfully cleaves the Cα-Cβ linkage in the model compounds. This process was also applied to depolymerization of Organosolv lignin. The deconstructed lignin was analyzed by a number of techniques, including ATR-IR, GPC, and 31P NMR of suitably derivatized samples. AN INVESTIGATION OF THE CHANNELING REACTION IN NITROGEN-DOPED MULTIWALLED CARBON NANOTUBES (N-MWCNTS) The reduction of nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) with Li/NH3 results in deep longitudinal cuts in the nanotubes structure. As the N-MWCNTs are anisotropic, we were able to investigate whether the unzipping process proceeds with equal efficiency from the tip end or from the root (catalyst) end of the N-MWCNT structure. To accomplish this we prepared polymer filled aligned arrays of N-MWCNTs, then exposed one or the other end. Through this approach we were able to shield the sidewalls and either end of the nanotubes from the Li/NH3 solution We have found that when the top end of the N-MWCNTs array was exposed to the reaction mixture, very few nanotubes suffered significant ‘unzipping’. However, when the root (substrate) side of the array is exposed to the reaction mixture, we observe the features characteristic of nanotubes with longitudinal cuts. Our finding provides some insight into the mechanism of the unzipping process, and provides evidence that the unzipping process has a directional preference-unzipping from the root end towards the tip end. And may provide a method for selective functionalization of the interior of tubes and create a new form of nanotube- based porous membrane.

The oxidation of lignin model compounds was studied in conventional solvents in parallel with oxidations in ionic liquid solvents. Catalyst systems were investigated in ionic liquid solvents to determine how reaction rates and the selectivity for benzylic carbon oxidation were affected. Oxidation rates were often lower in ionic liquids than in conventional solvents ‒ as indicated by lower conversion in a standard reaction time ‒ likely due, at least in part, to the higher viscosity of ionic liquids. Mechano chemical treatment of Indulin AT kraft lignin by ball milling with KOH and toluene produced significant carbonyl functionality, among other changes. The chemical reactivity of the lignin was increased, resulting in greater lignin degradation from porphyrin oxidation followed by Baeyer-Villiger oxidation. The mechanochemical treatment produced a level of lignin oxidation that was similar to that produced by porphyrin-catalyzed oxidation. Combining mechanochemical treatment with porphyrin oxidation produced a synergistic positive effect on the depolymerization of lignin, as demonstrated by a significantly higher yield of monomers. The methyl ester of vanillic acid was obtained as the main monomeric product (after methylation), along with a small amount of methyl 5-carbomethoxyvanillate.

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