Uronic acids acetates

HemiceUulose is a mixture of amorphous branched-chain polysaccharides consisting of a few hundred sugar residues. They are easily hydrolyzed to monomeric sugars and uronic and acetic acids. Many different hemiceUuloses have been isolated from wood. 

From the presence of uronic acid, sulfate half-ester, pymvyl cycUc acetal, or succinate half-ester groups. 

Pectins is a general term for a group of natural polymers based on polymerized galacturonic acid partly esterified with methanol. In addition these polymers must be considered as copolymers due to existence of neutral sugar branched zones. [1]. Some uronic acid units may also be esterified on 0-2 or 0-3 position with acetic acid. The pectins occur in the cell wall of higher plants and control at least partly the mechanical properties, the ion exchange properties and the swelling of the cell walls. 

Neutral sugars were quantified by trifluoroacetic acid hydrolysis (3) and gas chormatography of alditol acetates (4). Uronic acids were determined by Blumenkrantz method... 

Uronic acids and pectic material have partly or mainly been dissolved and removed from commercial boards on pressurized refining. On heating wood they will contribute considerably to CO2 release (33). Organic acids such as formic and acetic acid are also split off from side chains of wood polymers. 

The mechanism of pyrolysis reactions of biomass was extensively discussed in an earlier study (Demirbas, 2000). Water is formed by dehydration. In the pyrolysis reactions, methanol arises from the breakdown of methyl esters and/or ethers from decomposition of pectin-like plant materials. Methanol also arises from methoxyl groups of uronic acid (Demirbas and Giillii, 1998). Acetic acid is formed in the thermal decomposition of all three main components of wood. When the yield of acetic... 

In aqueous alkaline solution or in acetic acid, potassium permanganate is a nonspecific oxidant that has been used in the preparation of uronic acids and derivatives. Thus, good yields of D-galacturonic acid (35) may be obtained by oxidation of 1,2 3,4-di-(3-isopropylidene-a-D-galactopyra-nose.154 D-Glucuronic acid (34) can be prepared from starch by oxidation... 

The dinitrophenylhydrazones of the fission products of sugars are detectable with sodium hydroxide.160 Also, a wide variety of sugars and their acetates, and uronic acid lactones may be detected with sodium hydroxide followed by heating,161 Sensitivity is poor, however. After paper electrophoresis, chondroitinsulfate may be distinguished from proteins by means of Toluidine Blue.162... 

The hemicelluloses are polymolecular, random-coil, often branched hetero-glycans interspersed with cellulose microfibrils and starch granules in vivo. Glucose, xylose, and arabinose are the prominent sugars, although lesser quantities of galactan, mannan, etc., and minor concentrations of acetic, ferulic and uronic acids, etc., are in evidence. Heterogeneity extends to dimensions and conformation. 

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