School of Chemistry and Chemical Engineering, State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou, Guangdong, 510640, China.
Phys Chem Chem Phys. 2020 May 28;22(20):11508-11518. doi: 10.1039/d0cp01091j. Epub 2020 May 12.
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 C-O and C-C bond cleavages. For the oxidation products, the presence of the C-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[double bond, length as m-dash]O containing dimers.
电化学氧化因其选择性氧化能力和环境友好性，是一种很有前途和有效的木质素解聚方法。在此，通过循环伏安法、原位光谱电化学和气相色谱-质谱联用实验（GC-MS），以及密度泛函理论（DFT）计算理论，详细探讨了非酚烷基芳基醚单体和β-O-4 二聚体的电氧化。与文献报道（T. Shiraishi, T. Takano, H. Kamitakahara and F. Nakatsubo, Holzforschung, 2012, 66(3), 303-309）相比，1-（4-乙氧基苯基）乙醇表现出一种可区分的氧化途径，其中生成的羰基产物在烷基-芳基醚上令人惊讶地发生键断裂，最终生成一种类醌化合物。相比之下，β-O-4 二聚体，如 2-苯氧基-1-苯乙醇和 2-苯氧基苯乙酮，也表现出由 C-O 和 C-C 键断裂引起的电化学氧化。对于氧化产物，二聚体中 C-羟基的存在是在温和的电化学条件下选择性生成含醛物种的关键，否则它会生成含醇产物，其机制与含 C[双键，长度 as m-dash]O 的二聚体不同。
