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首页> 外文期刊>ACS Sustainable Chemistry & Engineering >Reductive Degradation of Lignin and Model Compounds by Hydrosilanes
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Reductive Degradation of Lignin and Model Compounds by Hydrosilanes

机译：氢硅烷对木质素和模型化合物的还原降解

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The exploitation of lignin, the second most abundant naturally occurring polymer on earth, has been hampered by its network structure, which makes it difficult to process. Hydrosilanes have previously been shown to convert aryl ethers to hydrolyzable silyl ethers in the presence of B(C6F5)3. We demonstrate that the process is general and can be used to convert model lignin compounds to both aryl silyl ethers and alkanes. The relative reactivity of functional groups on model lignin compounds was found to be phenol > primary alcohol > methoxybenzene > alkyl silyl ethers. The process thus leads to cleavage of β-O-4, α-O-4, and methoxybenzene groups with concomitant silylation of phenolic and secondary alcohol groups. At longer time points provided su?cient silane was present, the full reduction of primary and secondary alcohols to alkyl groups was observed. Softwood lignin itself could only be partially solubilized (～30%) even using excess hydrosilane and high catalyst loadings; the products were not characterized in detail. The lack of further degradation was attributed to its highly branched network structure containing 5-5, β-5, 4-O-5, and other linkages derived from coniferyl alcohol monomers that are not susceptible to reductive silylation. By contrast, over 95% of hardwood lignin was efficiently reduced/degraded into organosoluble products by the monofunctional hydrosilane HMe2SiOSiMe3 over a few hours at 50 °C. The molecular weight of the silylated products was consistent with oligomeric structures comprised of 3-8 linked aryl groups. This process holds promise to increase the accessibility to value-added products using lignin as a starting material.
机译：木质素是地球上天然含量第二高的聚合物，其网络结构阻碍了其开采，这使其难以加工。先前已证明氢硅烷在B（C6F5）3的存在下将芳基醚转化为可水解的甲硅烷基醚。我们证明该过程是通用的，可用于将模型木质素化合物转化为芳基甲硅烷基醚和烷烃。发现官能团在模型木质素化合物上的相对反应性是苯酚>伯醇>甲氧基苯>烷基甲硅烷基醚。因此，该方法导致了β-O-4，α-O-4和甲氧基苯基的裂解，同时伴随着酚基和仲醇基的甲硅烷基化。如果存在足够的硅烷，则在较长的时间点上，可以观察到伯醇和仲醇完全还原为烷基。即使使用过量的氢硅烷和高催化剂用量，软木木质素本身也只能部分溶解（约30％）。产品没有详细描述。缺乏进一步的降解归因于其高度支化的网络结构，该结构包含5-5，β-5、4-O-5和其他衍生自松柏醇单体的键，这些键基不易发生还原甲硅烷基化反应。相比之下，单官能氢硅烷HMe2SiOSiMe3在50°C的几个小时内有效地将超过95％的硬木木质素还原/降解为有机可溶性产品。甲硅烷基化产物的分子量与由3-8个连接的芳基组成的低聚结构一致。这个过程有望增加使用木质素作为起始原料获得增值产品的机会。

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