1 / 19

Chapter 5 Hemicellulose

Chapter 5 Hemicellulose. 5.1 Introduction. 1. Difination Except pectin and starch, those non-cellulose polysaccharides are called hemicellulose. Hemicellulose could be extracted by alkaline solution. Softwood: poly gluco mannose Hardwood: xylan Grass and straw: xylan. 5.1 Introduction.

donoma
Download Presentation

Chapter 5 Hemicellulose

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 5 Hemicellulose

  2. 5.1 Introduction 1. Difination Except pectin and starch, those non-cellulose polysaccharides are called hemicellulose. Hemicellulose could be extracted by alkaline solution. Softwood: poly gluco mannose Hardwood: xylan Grass and straw: xylan

  3. 5.1 Introduction • 2. Units • (1) Hexose: D-glucose, D-mannose, D-galactose • (2) Pentose: D-xylose, L-arabinose • (3) Uronic acid: D-glucronic acid • (4) Deoxy-hexose: L-rhamnose, L-fucose

  4. 5.1 Introduction Haworth structures

  5. 5.2 Isolation and purification 1.Pretreatment （1）Benzene-alcohol（or acetone）extraction: remove terpenoids, fats, waxes, and tannins. （2）Water extraction（ or 70% ethanol）： remove monosaccharides and water soluble oligosaccharides （3）Ammonium oxalate extraction: remove pectin （4）Holocellulose preparation: remove lignin

  6. 5.2 Isolation and purification 2.Preparation （1）Alkaline extraction: 17.5% NaOH , 24% KOH （2）Precipitation: ethanol （3）Chelate dissolution: Na2B4O7 polyglucomannose （4）Chelate precipitation: Ba(OH)2polyglucomannose （5）Retaining acetyl groups: DMSO

  7. 5.3 Chemical Structure • 1. Study methods • Acid hydrolysis • Periodate oxidation: ethylene glycol structure • Smith degradation • Methanolysis

  8. 5.3 Chemical Structure • Periodate oxidation

  9. 5.3 Chemical Structure Smith degradation

  10. 5.3 Chemical Structure

  11. →4βDXp1→4βDXp1→4(βDXp)n1→4βDXp1→4βXp1→4βDXp→4βDXp1→4βDXp1→4(βDXp)n1→4βDXp1→4βXp1→4βDXp 2 3 ∣ ∣ 1 1 4-O-Me-αGlupA L-Araf Poly arabinose-4-O-methyl glucronic acid xylose βDXp: β-D-xylose, pyran-type 4-O-Me-α-GlupA: 4-O-methyl-α-glucronic acid, pyran-type L-Araf: L-arabinose, furan-type 5.3 Hemicelluloses & structures

  12. →[4βDXp1]7-8→4βDXp1→4βDXp1→4βDXp1→ 3or2 2 ↑ ↑ 1 1 Acetyl (MeO)4-αD-GlupA →4βDMp1→4βDGp1→4βDMp1→4βDMp1→4βDGp1→ 5.3 Hemicelluloses & structures

  13. 5.4 physical structure With branches: less ordered Mostly amorphous regions Rare crystalline regions Comparation: cellulose and hemicellulose Homopolysaccharide, straight chains, no branches, composed of β-D-glucopyranose units, crystalline and amorphous regions, swelling and dissolution, degradation and derivatives

  14. 5.4 Chemical Structure Pentose ≻ Hexose β ≻ α Furan-type ≻ Pyran-type Non acidic saccharides ≻ Acidic saccharides （Arabinose ≻galactose ≻xylose ≻mannose ≻glucose）

  15. 5.5 Chemical Properties Alkaline degradation: peeling reaction

  16. 5.5 Chemical Properties

  17. 5.6 Industrial utilization • 1. Hexose • Ethanol • 2. Petose • Furfural • Xylose and xylitol

  18. 半纤维素复习题 一、答下列各题 １.依据纤维素与半纤维素在化学结构和超分子结构的区别，比较二者在化学反应能力上的不同？ ２.在针叶木、阔叶木和禾本科三类植物原料的半纤维素分离时，哪类原料不可以直接用碱提取？哪类原料可以直接用碱提取？为什么？ 二、写或简述下列各题 1 简写针、阔叶材木材主要半纤维素的化学结构简式（各两种简式） 2.半纤维素高聚糖在100oC NaOH溶液中发生哪些化学反应？ 写出一例反应式。 3. 论述木材聚戊糖测定原理和方法，有何注意事项。

  19. 补充 • 1.半纤维素的含义 • 2.半纤维素在植物界的分布 • 3.针、阔叶木的半纤维素组成的区别 • 4.从植物体中分离半纤维素的基本方法 • 5.Smith降解 • 6.阔叶木主要半纤维素的化学结构与纤维素比较有何区别? • 7.半纤维素在酸、碱蒸煮中行为是什么?

More Related