Department of Chemistry , University of Wisconsin-Madison , 1101 University Avenue , Madison , Wisconsin 53706 , United States.
Department of Energy Great Lakes Bioenergy Research Center, the Wisconsin Energy Institute , University of Wisconsin-Madison , Madison , Wisconsin 53726 , United States.
J Am Chem Soc. 2019 Sep 25;141(38):15266-15276. doi: 10.1021/jacs.9b07243. Epub 2019 Sep 16.
An electrochemical process has been developed for chemoselective oxidation of primary alcohols in lignin to the corresponding carboxylic acids. The electrochemical oxidation reactions proceed under mildly basic conditions and employ 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) and 4-acetamido-TEMPO (ACT) as catalytic mediators. Lignin model compounds and related alcohols are used to conduct structure-reactivity studies that provide insights into the origin of the reaction selectivity. The method is applied to the oxidation of lignin extracted from poplar wood chips via a mild acidolysis method, and the reaction affords a novel polyelectrolyte material. Gel permeation chromatography data for the oxidized lignin shows that this material has a molecular weight and molecular weight distribution very similar to that of the extracted lignin, but notable differences are also evident. Base titration reveals a significant increase in the acid content, and the oxidized lignin has much higher water solubility relative to the extracted lignin. Treatment of the oxidized lignin under acidic conditions results in depolymerization of the material into characterized aromatic monomers in nearly 30 wt% yield.
电化学过程已被开发用于木质素中伯醇的选择性氧化，生成相应的羧酸。电化学氧化反应在温和碱性条件下进行，并使用 2,2,6,6-四甲基-1-哌啶氮氧化物（TEMPO）和 4-乙酰氨基-TEMPO（ACT）作为催化介质。木质素模型化合物和相关醇类被用于进行结构反应性研究，为反应选择性的起源提供了深入了解。该方法应用于通过温和酸解方法从杨木木屑中提取的木质素的氧化，反应得到了一种新型的聚电解质材料。氧化木质素的凝胶渗透色谱数据表明，该材料的分子量和分子量分布与提取的木质素非常相似，但也明显存在差异。碱滴定表明酸含量显著增加，并且氧化木质素的水溶性相对于提取的木质素大大提高。在酸性条件下处理氧化木质素会导致材料解聚成近 30wt%产率的特征芳香族单体。
