Light-Driven Depolymerization of Native Lignin Enabled by Proton-Coupled Electron Transfer

Nguyen, Suong T.; Murray, Philip R. D.; Knowles, Robert R.

doi:10.1021/acscatal.9b04813

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Light-Driven Depolymerization of Native Lignin Enabled by Proton-Coupled Electron Transfer

Nguyen, Suong T.·Murray, Philip R. D.·Knowles, Robert R.

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Abstract

In this work, we report a catalytic, light-driven method for the redox-neutral depolymerization of native lignin biomass at ambient temperature. This transformation proceeds via a proton-coupled electron-transfer (PCET) activation of an alcohol O–H bond to generate a key alkoxy radical intermediate, which then facilitates the β-scission of a vicinal C–C bond. Of significance, this single-step depolymerization is driven solely by visible-light irradiation, requires no stoichiometric chemical reagents, and produces no stoichiometric waste. This method exhibits good efficiency and excellent selectivity for the activation and fragmentation of the β-O-4 linkage in the polymer backbone, even in the presence of numerous other PCET-active functional groups. The feasibility of this protocol in enabling the cleavage of the β-1 linkage in model lignin dimers was also demonstrated. These results provide further evidence that visible-light photocatalysis can serve as a viable method for the direct conversion of lignin biomass into valuable arene feedstocks.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY C−C bond cleavage alkoxy radicals lignin depolymerization photoredox catalysis proton-coupled electron transfer

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Nguyen, Suong T., Murray, Philip R. D., Knowles, Robert R.. 2019-12-13. Light-Driven Depolymerization of Native Lignin Enabled by Proton-Coupled Electron Transfer. https://doi.org/10.1021/acscatal.9b04813

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