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

Authors：Chen, Jing; Yang, Hanling; Fu, Hongquan; He, Hongyan; Zeng, Qiang^*; Li, Xuehui^*

Source：Physical Chemistry Chemical Physics, 2020, 22(20): 11508-11518.

DOI：10.1039/d0cp01091j

• BOND-CLEAVAGE
• PHOTOCATALYTIC OXIDATION
• CATALYTIC-OXIDATION
• AEROBIC OXIDATION
• VISIBLE-LIGHT
• PB/PBO2 ANODE
• DEGRADATION
• DEPOLYMERIZATION
• HYDROGENOLYSIS
• COPPER

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 beta-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, beta-O-4 dimers, like 2-phenoxy-1-phenethanol and 2-phenoxyacetophenone also demonstrated electrochemical oxidation induced by C-beta-O and C-alpha-C-beta bond cleavages. For the oxidation products, the presence of the C-alpha-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 C-alpha = O containing dimers.

• Institution
  中国科学院