Polysaccharide Oxidation

Polysaccharides.—Very few oxidations of polysaccharides have been carried out with lead tetraacetate, a situation in marked contrast to the voluminous literature on polysaccharide oxidations with periodate.22 The main reason for this discrepancy has undoubtedly been the fact that polysaccharides are insoluble in the solvents generally used for lead tetraacetate oxidation. 

Each of these polysaccharide oxidations has involved a very small or a... 

Sanderson and Wilson [16] described a coupling procedure for polysaccharide matrices based on periodate oxidation. The general course of the reaction follows that of polysaccharide oxidation by periodate as described by Guthrie [17]. In the matrix activation step, the polysac-... 

In polysaccharides oxidized with periodic acid, one molar proportion of each individual, oxidized monosaccharide reacts with only one mole of... 

The formazan reaction has also proved suitable for demonstration of the presence of aldehyde groups in polysaccharides oxidized by other means, even where these groups are limited in number or are the products of some side reaction. 

Vibrio anguilarum polysaccharide Oxidized heplose-6-NH-o Cellulose-O-o Cellulose-O-j Cellulose-Os Cellulose-O—. 

L. Hough, Periodate oxidation of neutral polysaccharides Oxidation to formaldehyde. Methods Carbohydr. Chem., 5 (1965) 370-377. 

The polyketals can be readily derivatized. For example, aldehyde groups of an intermediate product of a polysaccharide oxidation can be converted into alcohol groups, amines, thioacetals, carboxylic acids, amides, esters, or thioesters. 

Direct oxidation of hydroxyl groups provides interesting routes for the introduction of carbonyl and carboxyl groups into polysaccharides. Oxidation of secondary hydroj rl groups has been achieved by various oxidation reagents, e.g., periodate and hypochlorite, which results In oxidative scission of 1,2-diols and the formation of dialdehyde and dicarboxyUc... 

Oxidation of polysaccharides is a far more attractive route to polycarboxylates, potentially cleaner and less cosdy than esterification. Selectivity at the 2,3-secondary hydroxyls and the 6-primary is possible. Total biodegradation with acceptable property balance has not yet been achieved. For the most part, oxidations have been with hypochlorite—periodate under alkaline conditions. In the 1990s, catalytic oxidation has appeared as a possibiUty, and chemical oxidations have also been developed that are specific for the 6-hydroxyl oxidation. 

Catalytic oxidation ia the presence of metals is claimed as both nonspecific and specific for the 6-hydoxyl depending on the metals used and the conditions employed for the oxidation. Nonspecific oxidation is achieved with silver or copper and oxygen (243), and noble metals with bismuth and oxygen (244). Specific oxidation is claimed with platinum at pH 6—10 ia water ia the presence of oxygen (245). Related patents to water-soluble carboxylated derivatives of starch are Hoechst s on the oxidation of ethoxylated starch and another on the oxidation of sucrose to a tricarboxyhc acid. AH the oxidations are specific to primary hydroxyls and are with a platinum catalyst at pH near neutraUty ia the presence of oxygen (246,247). Polysaccharides as raw materials ia the detergent iadustry have been reviewed (248). 

PolysuWde Process. One modification to the kraft process being appHed commercially is the polysulfide process (38). Under alkaline conditions and relatively low temperature (100—120°C), polysulfides oxidize the active end group of the polysaccharide polymer to an alkaH-stable aldonic acid. This reaction, known for many years (39), was not produced on a commercial scale until the development of an efficient method for in situ generation of the polysulfide in kraft white Hquor. 

Nonionic Polyethylene oxide Polyethylene glycol Polysaccharides Pullulans Dextrans Cellulosics Polyvinyl alcohol Polyacrylamide 0.1 M NaNOj... 

For food and pharmaceutical applications, the microbial count must be reduced to less than 10,000 viable cells per g exopolysaccharide. Treatment with propylene oxide gas has been used for reducing the number of viable cells in xanthan powders. The patented process involves propylene oxide treatment for 3 h in a tumbling reactor. There is an initial evacuation step before propylene oxide exposure. After treatment, evacuation and tumbling are alternated and if necessary the reactor is flushed with sterile nitrogen gas to reduce the residual propylene oxide level below the Food and Drug Administration permitted maximum (300 mg kg 1). The treated polysaccharide is then packaged aseptically. 

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