Oxidized starches carboxylic groups

Figure 30.3 C NMR spectrum of oxidized starch. (Signals at 171.6 and 180.5 ppm are attributed to carboxyl and aldehyde groups, respectively).

The oxidation of starch in aqueous suspension with H202 in the presence of iron phthalocyanine gives both carboxylic and carbonyl groups (Table 3.1). The best yields were obtained with a molar ratio 12900/1 (0.0078 mol%), but the oxidation was still quite efficient with 0.0039 mol% of catalyst [25800 per anhydroglucose unit (AGU)/catalyst ratio]. The oxidized starch had almost the same final Fe-content as the initial potato starch. Still, the efficiency of this method in view of scaling up was limited by comparatively low activity and product isolation problems. 

Significant volumes of low oxidized starch are used at the size press. These starches are made by treatment in alkaline suspension with sodium hypochlorite so that from 1 to 2% active chlorine acts on the starch. The reaction is simple to perform. However, the reaction products are complex. Chain scission occurs at the same time that carboxyl and carbonyl groups are formed in the starch. It is most desirable to prepare the highest ratio of carboxyl to carbonyl as possible and this reaction is a function of the pH in the slurry. 

Oxidized Starches. Alkaline hypochlorite treatment introduces carboxyl and carbonyl groups, effects some depolymerization, and produces whiter (bleached) products that produce softer, clearer gels. Ammonium persulfate is used in some paper mills with continuous thermal cookers to prepare in situ bigb solids, low viscosity dispersions. Most of the hypochlorite-oxidized starch and all the ammonium persulfate-oxidized starch is used in the paper industry. The low solution viscosity and good binding and adhesive properties of these products make them especially effective in high solids, pigmented... 

The oxidation of starch leads to the formation of carbonyl and carboxyl groups in the polymer chain. Depolymerisation also occurs and starch turns yellowish. 

Oxidized starch 1404 E1404 active oxygen <0.45 Ammonium persulfate <0.075% and sulfur dioxide <0.05% Sodium chlorite <0.5% Potassium permanganate <0.2% Chlorine (as sodium hypochlorite) <5.5% Sulfur dioxide <50 mg/ka No chlorite Manganese <50 mg/kg Carboxyl groups <1.1%... 

The TEMPO - sodium hypochlorite - sodium bromide system has been applied to starch ether derivatives, particularly hydroxyethyl starch, which has a primary hydroxyl group on the hydroxyethyl ether group that can also be oxidized to a carboxyl group and carboxymethyl starch. The apparent goal was improved sequestering agents via higher carboxyl content and the proper multidentate conformations... 

Specifically, D-glucose < maltose < maltotriose < amylose < starch < amylo-pectin < cellulose (Greenwood, 1967). Trends indicated are that thermochemical stability increases with the DP, branching, and 1,4-fi bonding. Chemical bonds other than 1,4-a and 1,4-(3 introduce heat and acid instability. Either of these two bonds is less easily depolymerized when the sixth pyranose carbon is oxidized to the carboxyl group rather than esterified for this reason, low-methoxyl pectin is more stable than high-methoxyl pectin. 

The reaction appears to be well suited for selective conversion of biomass carbohydrates into their corresponding oxidized derivatives. This system serves to oxidize several polymeric carbohydrates including starches and pullulan.445 49 More recent work has described the TEMPO-catalyzed introduction of carboxyl groups in native cellulose and its different morphological forms,45(M52 cellulose derivatives,453 and the surface of cellulose nanocrystals.454 The related biopolymer, chitin, also is oxidized under these conditions.455... 

Moderate Oxidation (Oxidized Starch) The maximum specified treatment introduces about 1 carboxyl group per 28 anhydroglucose units. The starch is whitened, and its molecular weight and viscosity are reduced. 

The consumption of cyanide is accurately determined by argentometric titration. The method was found to apply both to oxidized starch [439] as well as to cellulose [418], The method is accurate and recently the coefficient of variance and standard deviation for an oxidized cellulose containing 5.60 mmol per 100 g of ketone groups, were found to be 0.0046 and 0.0068, respectively. The corresponding values for the carboxyl groups by the methylene blue method of the same samples were 0.001 and 0.031 [440]. 

Alkaline h) ochlorite is the most common method of oxidizing starch granules. The reaction is the oxidation of the secondary alcohols to ketones and the primary alcohol to a carboxyl group [146,147,148]. Alkaline hypochlorite oxidation is sometimes used to produce thin-boiling starches instead of acid hydrolysis. 

Primary alcohol groups can be exclusively oxidized to aldehyde groups with pyridinium dichromate [149,150] and to carboxyl groups with the 2,2,6,6-tetramethyl-1-piperidine oxoammonium ion (TEMPO) [151]. The aldehydes can then be reduced to primary alcohols by reaction with NaB H4 [150,152], giving radiolabeled H-starch and the carboxyl group can be inverted by the action of Azotobacter vinlandii poly- 8-D-marmuronic acid C-5-epimerase to give L-iduronic acid [153]. 

Oxidation of starch, which is commonly done with sodium hypochlorite and generates carboxyl groups at the aldehyde end groups and at some OH groups from C-6... 

The water-soluble starch used contains 27 % amylose and 73 % amylopectin, and the oxidized starch can be isolated as a gel. The characteristic signal for the carboxylic Cg group was monitored at <5 = 176.5. Signals due to the corresponding aldehyde groups were not seen (Structure 4). 

Stronger oxidation leads to oxidation of the C-6 atoms to carboxyl groups, as well as of the hydroxyl groups on the C-1, C-2, and C-3 atoms. " Only oxidations useM in dextrinization are considered here. Oxidized starches yield darker dextrins. More-advanced discussion ofthe problems of starch oxidation is given in the Radley monograph. ... 

Like the simple formazans, the formazans of oxidized polysaccharides form complexes with heavy metal salts with ease. On warming the formazans of oxidized cellulose, starch, dextrin, dextran, or inulin with copper, cobalt, nickel, or uranium salt solutions, their characteristically-colored metal complexes are obtained. The presence of carboxyl groups in the polysaccharide formazans frequently facilitates complex formation. ... 

Oxidation of starch with chlorous acid produces an oxystarch (with carboxyl groups in uronic acid units, aldehyde groups formed from the primary hydroxyl groups, and ketone groups from the secondary hydroxyl groups) which is more sensitive to alkali than is chromic acid oxystarch. ... 

Carboxylic groups in oxidized starches have been analyzed with silver nitrophenolate or copper(II) acetate.489 A colorimetric method based on the affinity of Methylene Blue for the carboxylic group in oxidized starch is also known.490 Determination of the carboxylic and carbonyl groups can be performed... 

Polysulfates of oxidized starches, being heparin-like compounds, show blood anticoagulant activity. Their activity increases with the number of sulfate residues, and the 6-carboxyl groups decreased the toxicity of the compound.533-536,619 Complexes of these anticoagulants with pepsin had no proteolytic activity.620,621 Methyl... 

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