Oxidation of starch

Interest in detergent products derived from renewable resources and with better biodegradability has driven evaluation of oxidized sugars and starches as builders or co-builders in detergents.113 Builders and co-builders complex calcium and magnesium ions in hard water to prevent sealing or deposits due to precipitation of insoluble carbonate salts. In current powder detergents, the builders are usually zeolites used in combination with polycarboxylate polymers derived from synthetic acrylic-maleic acid copolymers.114 

Dinitrogen tetraoxide (N2O4) selectively oxidizes some of the primary hydroxyl groups. One solvent-based process involves selective oxidation of starch with N204 in the presence of oxygen119 to give a product with 75% uronic acid units. Co-builders for use with zeolites have been produced by oxidation and hydrolysis of starch with a gas phase of N02/N204 in a fluidized bed.120 

DAS + 2 NaC102 — Dicarboxyl starch + 2 NaOCl H202 NaCl + H20 + 02 

Dicarboxyl starch can also be made by oxidation with sodium hypochlorite or hypobromite (see reference 116). Reaction with hypochlorite is accelerated by use of catalytic amounts of sodium bromide.123,124 

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 

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We have developed an efficient and practical method for clean oxidation of starch (21-23) resulting in the oxidation of primary alcohol function in Ce position and the cleavage of vicinal diols in C2 and C3 position (Figure 30.2). We used small amounts of cheap iron tetrasulfophthalocyanine catalyst, pure water as reaction medium and H2O2 as clean oxidant to achieve a one-pot conversion of starch resulting in the introduction of aldehyde and carboxyl functions in polymer chains. The iron content... 

Table 3.1 Oxidation of starch in aqueous suspension with H2O2 in the presence of iron phthalocyanine.a> Effect of substrate/catalyst ratio.

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. 

Describe the reaction engineering of a kitchen toaster. The reactions are thermal drying (which alone makes stale bread) and thermal decomposition and oxidation of starch, which requires temperatures of -300°C. [Recall that the bread appears white until it is nearly done, and then it browns quickly and blackens if left in too long. Recall also that good toast has a brown layer < 1 mm thick while the interior is still white and soft. The control of temperature profiles and heat transfer aspects are essential in producing good toast.]... 

Two methods by which D-glucofuranurono-6,3-lactone (63) has been synthesized are shown in Scheme 9. The oxidation of starch to oxidized starch (64) has been described by a number of workers. Heyns and Graife338 were able to obtain 50-55% yields of 64 by oxidation with nitric acid plus nitrogen tetraoxide. From 64, D-glucofuran-... 

Oxidation of Starch.97- 98- 114 Oxidation in Aqueous -Suspension. Ten grams of cornstarch or potato starch, previously dried at 100° for about twenty hours, is suspended in 290 cc. of 0.533 M aqueous periodic acid solution. After being shaken thoroughly, the mixture is kept at 20-25° for twenty-four hours. About one mole of periodic acid per C H oOs unit of starch reacts to yield oxidized starch (LYI). The product is filtered, washed free from iodic acid and excess periodic acid with cold water, and dried at 40-50°. The yield is quantitative. Over 99% of the substance dissolves in forty parts of water at 100° during two hours [a]o = +9°. 

Starch pastes irradiated with 130,000 V, 15 mA X-rays lost their viscosity, and there was concurrent decrease of iodine-binding ability and pH. Other properties measured after such treatment point to dextrinization and oxidation of starch.78-79 Other results of such irradiation is the cleavage of phosphoric acid esters from glucose units of potato starch. This effect is observed at 50,000 V and 8 mA as well as at 150,000 V and 12 mA. The effect of X-ray irradiation is similar in this respect to irradiation with 7-rays, whereas neither sonication with ultrasound nor exposure to UV light evoke such effects.5 Starch irradiated by X-rays, contains free radicals, and thus the presence of free radicals in starch provides evidence of previous irradiation. 

Fig. 39 compares results of the anodic oxidation of starch in acidic and alkaline solution, the former showing the lower reactivity. D-Glucuronic acid is also available by oxidation in an electrolyzer in which chlorine is electrochemically generated from a solution of sodium chloride.326... 

The oxidation of starch to starch dialdehyde is the most frequently studied process, with periodate being the most commonly used oxidant. An electrolytic method provides for continuous regeneration of the oxidant.327-328 The anode is usually made of lead328 or lead(IV) oxide.329-330 Cathodes are made of steel. A 99 1 Pb- Ag alloy anode and a steel cathode were used for preparation of starch... 

Fig. 39.—Comparison of the rate of anodic oxidation of starch in 40% phosphoric acid (O) and in 1 M sodium hydroxide ( ) solutions at 80°C (from Ref. 325).

A novel method for oxidation of starch to starch dialdehyde has been presented. The oxidant (periodate) could be continuously recovered by electro-oxidation and the product was isolated on ion exchangers. The procedure permits full conversion (degree of oxidation = 1) of starch to starch dialdehyde .333,334... 

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

Besemer, A.C., The Bromide-Catalyzed Hydrochlorite Oxidation of Starch and Inulin Calcium Complexation of Oxidized Fructans. Ph.D. thesis, Delft University of Technology, Delft, The Netherlands, 1993. 

Nelson and Cretcher " applied the method of Hudson and Isbell to the oxidation of D-mannose and the crystalline lactone was prepared. A good yield was obtained in contrast to that reported in the earlier work of Fischer and Hirschberger in which no control of pH was attempted. The method was also applied to the oxidation of starch by Felton, Farley and Hixon and by Kihara. " ... 

Starch was oxidized by Jackson and Hudson,who used periodic acid at room temperature. Considerable study has recently been made of the oxidation of starch on a commercial basis, using electrolytically regenerated periodic acid. The reaction is carried out under what are normally drastic conditions for a periodate oxidation, namely pH 1.2-1.4 and 100°F, apparently without occurrence of any over-oxidation. Oxystarch is known commercially as dialdehyde starch. ... 

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... 

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. ... 

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