Wood Chemistry Wood Chemistry Wood Carbohydrates

l Major Components Wood Chemistry » Hexoses – D-Glucose, D-Galactose, D-Mannose PSE 406/Chem E 470 » Pentoses – D-Xylose, L-Arabinose Lecture 3 » Uronic Acids Wood Sugars – D-glucuronic Acid, D Galacturonic Acid l Minor Components » 2 Deoxy Sugars – L-Rhamnose, L-Fucose

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Wood Chemistry Wood Sugars: L Arabinose Wood Chemistry Wood Sugars: D Xylose

l Pentose (5 carbons) CHO l Pentose CHO l Of the big 5 wood sugars, l Xylose is the major constituent of H OH arabinose is the only one xylans (a class of hemicelluloses). H OH found in the L form. » 3-8% of softwoods HO H HO H l Arabinose is a minor wood » 15-25% of hardwoods sugar (0.5-1.5% of wood). HO H H OH

CH OH 2 CH2OH

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1 1 Wood Chemistry Wood Sugars: D Mannose Wood Chemistry Wood Sugars: D Glucose

CHO l Hexose (6 carbons) CHO l Hexose (6 carbons) l Glucose is the by far the most H OH l Mannose is the major HO H constituent of Mannans (a abundant wood monosaccharide (cellulose). A small amount can HO H class of hemicelluloses). HO H also be found in the » 7-13% of softwoods hemicelluloses (glucomannans) H OH » 1-4% of hardwoods H OH H OH H OH

CH2OH CH2OH

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Wood Chemistry Wood Sugars: D Galactose Wood Chemistry Wood Sugars

CHO CHO l Hexose (6 carbons) CHO H OH H OH l Galactose is a minor wood D Xylose L Arabinose HO H HO H monosaccharide found in H OH HO H H OH certain hemicelluloses CH2OH HO H CHO CH2OH CHO CHO » 1-6% of softwoods HO H H OH H OH » 1-1.5% of hardwoods HO H HO H HO H HO H

HO H H OH H OH H OH H OH H OH H OH

CH2OH CH2OH CH2OH CH2OH D Mannose D Glucose D Galactose

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2 2 Wood Chemistry Sugar Numbering System Wood Chemistry Uronic Acids

CHO 1 CHO l Aldoses are numbered l Uronic acids are with the structure drawn HO H 2 polyhydroxy carboxylic H OH vertically starting from the aldehydes. The acid group top (the aldehyde group) HO H 3 is at the # 6 carbon. HO H as the #1 carbon. H OH 4 l Only glucuronic and H OH l Numbering is important galacturonic acids exist in H OH 5 H OH as we learn about ring wood. formation and CH2OH 6 l They are minor components COOH substitution. of hemicelluloses. D Glucuronic Acid

PSE 406 - Lecture 3 9 PSE 406 - Lecture 3 10

Wood Chemistry Uronic Acids II Wood Chemistry Deoxy Sugars

CHO l In hemicelluloses, CHO l Deoxy sugars are very CHO glucuronic acid often HO H H OH minor constituents of H OH has a methyl ether at cell wall polymers. the # 4 carbon. H OH H OH HO H l Notice that the #6 l This is important HO H HO H H OCH 3 carbon is a CH3 group because this ether HO H HO H linkage is easily broken instead of an alcohol. H OH CH3 (during CH3 pulping/bleaching) COOH L Rhamnose L Fucose resulting in the release of methanol. 4- O- Methyl Glucuronic Acid

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3 3 Wood Chemistry Ketoses Wood Chemistry Aldonic acids

l Ketoses are polyhydroxy CH 2OH l Aldonic acids are poyhdroxy COOH ketones. Fructose is the best carboxylic acids. The acids O H OH known example. group is on the #1 carbon. HO H l They are found in extremely l Aldonic acids do not occur HO H

limited amounts in wood but are H OH naturally in wood. H OH found in larger amounts in l They are produced through H OH some plants. the acid sulfite treatment of H OH

CH 2OH l Ketoses can be formed through sugars. CH 2OH alkaline rearrangements of » Xylonic, arabonic, gluconic, aldoses. Fructose galactonic, and mannonic acids. D Gluconic Acid

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The Unloved Pentoses Wood Chemistry Alditols Wood Chemistry (not found in wood polymers (D or L))

l Do not occur naturally CH 2OH CHO CHO in wood. HO H CH 2OH l Can be made by H OH HO H H OH microorganisms. HO H H OH HO H l Made through the H OH HO H reduction of sugars. H OH H OH H OH H OH

l Commercial CH 2OH CH2OH CH OH sweeteners. CH 2OH 2 D Mannitol D Xylitol D Ribose D Lyxose

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4 4 The Unloved Hexoses Wood Chemistry (not found in wood polymers (d or L)) Wood Chemistry Physical Properties of Sugars

Melting H2O Solubility CH3OH Sol. CHO CHO CHO CHO CHO Point (°C) (g/100ml) (g/100ml) H OH HO H H OH HO H HO H

H OH H OH H OH H OH HO H Glucose 146 91/100 ~1/100

H OH H OH HO H HO H HO H Mannose 133 250/100 ~1/100 H OH H OH H OH H OH H OH

CH OH CH OH CH OH 2 CH2OH 2 CH2OH 2 Xylose 143-145 125/100 ? D Talose D Allose D Altr ose D G ulose D I dose Fructose Dec. 103 freely 7/100

Xylitol 93-94.5 64/100 6/100

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