23第三节木素的化学构造v培训讲学.ppt

单击此处编辑母版标题样式单击此处编辑母版副标题样式*1第三节 木素的化学构造Chapter 3 Chemical structure of ligninF木素的功能基F木素的结构单元F木素结构单元间的联接F光谱的基本概念及其在木素结构研究上的应用F木素模型构造图F木素-碳水化合物复合体（LCC）一、木素的功能基主要包括甲氧基（-OCH3）、羟基（-OH）和羰基（-CO）一）元素组成及甲氧基（methoxyl group）木素元素分析值/%示性式CHOOCH3云杉MWL64.776.3928.5816.13C9H8.83O2.37(OCH3)0.96山毛榉MWL60.586.2333.1921.46C9H8.49O2.86(OCH3)1.43云杉和山毛榉MWL的元素分析值与甲氧基含量 C/H比例比较高，显示芳香族特性2o甲氧基是木素最重要的特征基团，其含量为：n针叶木木素：1416n阔叶木木素：1922n草本类木素：1415阔叶木木素中甲氧基含量比针叶木高,why?木素中的甲氧基是联接在芳香环上的，而不是联接在脂肪族侧链上3How to analyze the Methoxyl Groups?nThe methoxyl content is a widely used for characterization of lignins. It gives a measure of their purity and of their plant origin. The method most widely used is based on the formation of methyl iodide when the sample is treated with hydriodic acid at reflux temperature.n5酚羟基（phenolic hydroxyl group）：存在于苯环上；脂肪族羟基（aliphatic hydroxyl group）：存在于木素结构单元侧链上。

1.酚羟基多数醚化，少数游离二）羟基（hydroxyl group）62.脂肪族羟基7使羟基甲基化的试剂硫酸二甲酯重氮甲烷几乎全部游离羟基甲基化游离的酸性酚羟基甲基化可以测得游离羟基的含量8-碳原子上的OH处于侧链上最活泼的部位，制浆化学反应中成为木素和制浆药液的反应点H9How to analyze the phenolic hydroxyl groups? vCommon instrumental methods for the estimation of phenolic groups in lignin are potentiometric and conductormeric titration, ionization difference UV spectroscopy, and NMR spectroscopyvChemical methods include determination of the increase in methoxyl content after reaction with diazomethane, selective deacetylation of acetylated lignin with aminolysis（氨基水解）, and determination of the amount of methanol formed after oxidation with sodium periodate10How to analyze the phenolic hydroxyl groups?（continued）vA more indirect method is based on permangnate oxidation after alkylation of the phenolic groupsvThe periodate method is based on the guaiacyl and syringyl structures with aqueous sodium periodate to o-quinone structures with the release of 1M methanol from each phenolic unit (Fig.4.27)11Fig. 4.2712How to analyze the phenolic hydroxyl groups (continued)? vThe aminolysis is based on the finding that phenolic acetates are cleaved with pyrrolidine(吡咯烷）much faster than aliphatic acetates. The pyrrolidine acetates formed in the reaction of an acetylated lignin is determined by GC (gas chromatography) (Fig.4.28)13Fig.4.2814How to analyze the aliphatic hydroxyl groups?The total amount of hydroxyl groups in a lignin preparation can be determined by acetylation with acetic anhydride and pyridine followed by hydrolysis of the acetate and titration of the liberated acetic acid with a standard sodium hydroxide solution.The aliphatic hydroxyl content is determined by subtraction of the phenolichydroxyl content from the total hydroxyl content of the lignin.15（三）羰基（carbonyl group） 存在于木素单元的侧链上，分为共轭羰基和非 共轭羰基。

1.共轭羰基 2.非共轭羰基16羰基的测定o全羰基可以通过硼氢化钠还原来测定o共轭羰基可以通过还原示差紫外吸收光谱法定量17How to analyze the carbonyl groups?oAn early method for the determination of the carbonyl content of lignin preparations is based on the use of hydroxyl amine.The carbonyl group reacts with hydroxyl amine hydrochloride forming an oxime and releasing 1M hydrochloric acid.The total carbonyl content of a lignin preparation can be determined by titration of the HCl acid.18oAlternatively, the carbonyl content may be determined by reduction with sodium or potassium borohydride（硼氢化钠）. After the reaction, excess of sodium or potassium borohydride is decomposed by addition of dilute sulfuric acid,and the volume of hydrogen thus liberated id measured volumetrically.The carboxyl content is consumed borohydride .19How to analyze the units containing double bonds?Two methods have been used with some success . One is based on the catalytic hydrogenation of the double bonds in cinnamaldehyde and cinnamyl alcohol structures and measurement of the UV difference spectrum. The other uses the difference in UV adsorption in neutral and alkaline solution to measure the amount of phenolic stilbene structures.20How to analyze those Carboxylic and Sulfonic Acid Groups? Both the residual lignin in kraft pulps and the soluble lignin in kraft black liquors contain carboxyl groups. Spectroscopic methods have been used for the determination of carboxylic acid groups in isolated lignin samples. 21 The residual lignin in sulfite pulps contains sulfonic acid groups that can be determined selectively in the presence of carboxyl groups.As for the soluble lignosulfonate samples isolated from sulfite spent liquors, perhaps the most reliable methods for their determination are those based on conductometric titration. 22针、阔叶材木质素主要官能团的比较23二、木素的结构单元o木素的基本结构单元为苯丙烷（phenyl propane unit），可用C9表示。

o如何证实木素是C9单元 ? o通过化学降解 的方法，如氢解、酸解、乙醇解、硫代醋酸解、硝基苯氧化、高锰酸钾氧化等证实木质素的C9单元 24（一）氧化分解法o高锰酸钾氧化-P8725o硝基苯氧化分解（nitrobenzene oxidation） -P88u分解产物中含有大量的香草醛，体现了木素的芳香性u产物中还含有紫丁香醛（酸）、5-甲酰基香草醛（酸）以及对羟基苯甲醛，证明了木素是由愈疮木基、紫丁香基和对羟基苯基三种结构单元构成u不同原料的木素其硝基苯氧化产物不同，每种氧化产物的含量也不一样26 针：香草醛少量对羟基苯甲醛 阔：香草醛 紫丁香醛少量苯甲醛 禾：香草醛 紫丁香醛对羟基苯甲醛可证明：针、阔、禾三中原料的木素结构是不同的 27（二）乙醇解（ethanolysis）o木素乙醇解的产物为一系列的希伯特酮的多种酮类化合物o针叶材主要产物有五种，都有愈疮木基，说明针叶材木素的单体是愈疮木基丙烷单元 o阔叶材木素乙醇解产物有十种，比针叶材增加五种紫丁香基型产物，说明阔叶材木素是由愈疮木基丙烷和紫丁香基丙烷单元构成 o草类木素乙醇解产物有十五种，除。