Study on chemical conversion of highly condensed lignin into functional materials

硫酸木质素（SAL）是一种高度浓缩的木质素，本研究尝试将其化学转化为木质素磺酸盐作为功能材料。木质素磺酸盐是一种高分子量、反应性官能团少的木质素，是最常用的木质素化学品。因此，通过解聚增加溶解度和反应性对于将SAL转化为功能材料是必要的。首先对SAL进行酚化活化，得到酚化SAL（PSAL）。接下来，用甲醛处理PSAL以引入用于磺化的反应性羟甲基。羟甲基化产物的中性磺化得到定量产率的可溶性木质素磺酸盐。为了阐明上述反应中的反应机理和副反应，选择了一种具有β-芳醚结构的木质素模型化合物，得到了如下结果：（1）在反应过程中，木质素分子量分布和磺酸基含量与商业木质素磺酸盐的分子量分布和磺酸基含量基本一致;（1）缩合结构的选择性酚化;（2）在较高温度（120 ℃）下羟甲基化生成二芳基甲烷结构;（3）愈创木基环在羟甲基化中的反应活性高于对羟基苯基环;

Sulfuric acid lignin (SAL) was selected as highly condensed lignin and was attempted to chemically convert into lignosulfonate as a functional material. Lignosulfonates have high dispersibility and caking, and are most available lignochemicals.SAL is high molecular weight lignin with little reactive functional group. Therefore, the increase of the solubility by depolymerization and of the reactivity is necessary to convert SAL into functional materials. SAL was at first phenolized to activate, and phenolized SAL (PSAL) was obtained. Next PSAL was treated with formaldehyde to introduce a reactive hydroxymethyl group for sulfonation. Neutral sulfonation of the hydroxymethylated product gave soluble lignosulfonate in quantitative yield. A comparison of molecular wight distribution and sulfonic acid group content of the product with those of commercial lignosulfonates indicated the same extent of functionalyty.In order to elucidate reaction mechanisms and side reactions in the above reactions, a lignin model compound with beta-aryl ether structure was selected, and the following results was obtained ; (1) selective phenolation of condensed structure, (2) secondary formation of diarylmethane structure in hydroxymethylation at higher temperature (120ﾟC), (3) higher reactivity of guaiacyl nucleus than p-hydroxyphenyl nucleus in hydroxymethylation, and (4) hygh yields in sulfonation.