Issue 20, 2020

Electrochemical oxidation mechanisms for selective products due to C–O and C–C cleavages of β-O-4 linkages in lignin model compounds

Abstract

Electrochemical oxidation is a promising and effective method for lignin depolymerization owing to its selective oxidation capacity and environmental friendliness. Herein, the electrooxidation of non-phenolic alkyl aryl ether monomers and β-O-4 dimers was experimentally (by cyclic voltammetry, in situ spectroelectrochemistry, and gas chromatography-mass spectroscopy) and theoretically (by DFT calculations) explored in detail. Compared to the reported literature (T. Shiraishi, T. Takano, H. Kamitakahara and F. Nakatsubo, Holzforschung, 2012, 66(3), 303–309), 1-(4-ethoxyphenyl)ethanol showed a distinguishable oxidation pathway, where the resulting carbonyl product surprisingly underwent a bond cleavage on alkyl–aryl ether to ultimately produce a quinoid like compound. In contrast, β-O-4 dimers, like 2-phenoxy-1-phenethanol and 2-phenoxyacetophenone also demonstrated electrochemical oxidation induced by Cβ–O and Cα–Cβ bond cleavages. For the oxidation products, the presence of the Cα-hydroxyl group in dimers was the key to selectively generate aldehyde-containing species under mild electrochemical conditions, otherwise it produces alcohol-containing products following a different mechanism compared to the Cα[double bond, length as m-dash]O containing dimers.

Graphical abstract: Electrochemical oxidation mechanisms for selective products due to C–O and C–C cleavages of β-O-4 linkages in lignin model compounds

Supplementary files

Article information

Article type
Paper
Submitted
26 Feb 2020
Accepted
28 Apr 2020
First published
28 Apr 2020

Phys. Chem. Chem. Phys., 2020,22, 11508-11518

Electrochemical oxidation mechanisms for selective products due to C–O and C–C cleavages of β-O-4 linkages in lignin model compounds

J. Chen, H. Yang, H. Fu, H. He, Q. Zeng and X. Li, Phys. Chem. Chem. Phys., 2020, 22, 11508 DOI: 10.1039/D0CP01091J

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