Bromine, starch oxidized

Com and rice starches have been oxidized and subsequently cyanoethylated (97). As molecular size decreases due to degradation during oxidation, the degree of cyanoethylation increases. The derivatized starch shows pseudoplastic flow in water dispersion at higher levels of cyanoethylation the flow is thixotropic. Com and rice starches have been oxidized and subsequently carboxymethylated (98). Such derivatives are superior in the production of textile sizes. Potato starch has been oxidized with neutral aqueous bromine and fully chemically (99) and physically (100) characterized. Amylose is more sensitive to bromine oxidation than amylopectin and oxidation causes a decrease in both gelatinization temperature range and gelatinization enthalpy. 

Substances containing active chlorine or bromine oxidize iodide ions — if necessary under the influence of UV light - to iodine, which reacts with starch to yield the well-known intense blue starch-iodine inclusion complex. 

Iodine in aqueous solution may be measured quantitatively by acidifying the solution, diluting it, and titrating against a standard solution of sodium thiosulfate, sodium arsenite or phenyl arsine oxide using starch indicator. The blue color of the starch decolorizes at the end point. The indicator must be added towards the end of titration when the color of the solution turns pale yellow. Prior to titration, iodine in the dilute acidic solution is oxidized to iodate by adding bromine water or potassium permanganate solution. Excess potassium iodide is then added. The liberated iodine is then titrated as above. 

A sample (approximately 0.2 g.) is weighed accurately and dissolved in 25 ml. of water then 25 ml. of 0.1 N hydrochloric acid and 0.2 g. of potassium bromide are added. The solution is titrated with 0.017 M potassium bromate until a permanent yellow color is produced. Potassium iodide (0.1 g.) is added, and the solution is backtitrated to a starch end point with 0.1 N sodium thiosulfate. The blue color returns in about a minute since the high acidity promotes air oxidation of excess iodide. The accuracy is only slightly less if the appearance of a faint yellow bromine color is taken as the end point. One mole of potassium bromate is equivalent to 3 of sodium /8-styrenesul-fonate. 

The action of chlorine in alkaline media is much slower than that of bromine. Lewin29 reported that the rate of oxidation of D-glucose at pH 9.8 by hypobromite is 1360 times higher than that by hypochlorite at the same pH. For cellulose, the ratio is much smaller (33 to 1). The complexity of the latter system is, however, revealed by the variability of this ratio over the pH range of 8-13 at pH 6-7, the action of hypochlorite is actually slightly faster than that of hypobromite. Maltodextrins and starch have been oxidized with alkaline sodium hypochlorite. The resulting oxidized polysaccharide formed stable complexes with calcium cations.30... 

In the presence of a small excess of iodide, Pd gives Pdt which is sparingly soluble in acidic media. When shaken with benzene or DIPE, PdE passes into the organic phase it has been the basis for a sensitive indirect determination method. The suspension of Pdh in the organic solvent is stripped by dilute ammonia. The aqueous solution is acidified, then the iodide is oxidized by bromine to IO3. This iodate reacts with added T to liberate iodine, which is determined as its coloured complex with starch (see Section 25.2.1). One Pd atom in PdE is equivalent to twelve atoms of iodine. 

In a hydrochloric acid medium (optimum concentration -0.5 M HCl), thallium(I) is oxidized with bromine to thallium(III). Thallium(III) oxidizes iodide to iodine, which gives a blue complex with starch. The molar absorptivity of the starch-iodine complex is 3.9-10 (a = 0.19) at 590 nm. 

The oxidation of thallium(I) with bromine occurs quantitatively in the cold. The excess of bromine is conveniently removed by reaction with phenol. The formation of a suspension of bromophenol (which interferes in the absorbance measurement) can be avoided, if the exeess of bromine is small. The aqueous glycerol solution of starch is stable and gives a good reproducibility of results. The excess of stareh does not affect the colour. The amount of the added KI should always be the same. Atmospheric oxygen slowly liberates iodine from the iodide, but the resulting increase in absorbance amounts to scarcely 7% in one hour. 

Chlorine is more potent an oxidant than is bromine but less so than fluorine (Clifford, 1961a). Thus, chlorine is able to oxidize both bromide and iodide ions to Br2 and I2, respectively, whereas fluorine oxidizes chloride, bromide, and iodide to their corresponding halogens. The oxidizing ability of chlorine is the basis for the starch-iodide test for chlorine. Here, a mixture of potassium iodide, soluble starch, and zinc chloride produces a blue-violet color in the presence of chlorine. Unfortunately, and like many spot tests, this is a nonspecific test and gives a positive result with many oxidants, for example, bromine. 

The use of bromine in alkaline media resulted in the formation of uronic acids.416,417 Oxidation to some non-uronic acid products, (carbonyl compounds) accompanied the major oxidation pathway.418-420 The 2,2,6,6-tetramethyl-l-piperidinyloxy-mediated oxidation by hypobromite was highly selective for the 6-OH groups of the glucose residues.421 Potassium bromate (HB1-O3) was also used.338 The kinetics of oxidation with bromine at pH 6-8 has been studied 422 It was observed that oxidation decreases the heat and temperature of gelation as the oxidation proceeds. Simultaneously, the molecular weight of starch and the viscosity of its aqueous solutions decreased. Subsequent reduction of the oxidation products increased the viscosity. Microscopic observations revealed that the starch granularity vanished at a low level of oxidation.423... 

Materials Lead, oxides of lead, concentrated hydrochloric acid, starch iodide paper, bromine water, charcoal. 

Antimony lll) 12 Starch Precipitate Mg + with 8-quinolinol, add excess KBrOs/KBr to brominate precipitate, determine excess KBrOs by oxidation of r I2... 

Greater utilization of periodate as an oxidant has been suggested in the development of an electrolytic method (228) starch is oxidized in 2 % sulfuric acid containing iodic acid. This method is similar in concept to the electrolytic bromine method of Isbell and Frush 179),... 

Yellow or brown vapors. Bromine derived from bromides in the presence of oxidizing agents nitrogen oxides derived from nitrates or nitrites chromyl chloride, provided both bichromate and water-containing chlorides are present. (Bromine vapors turn starch paper yellow in contrast to nitrogen oxides that have no visible action on this paper.)... 

Determination of Extent of Hydrolysis. Modified Dow Color Test, This method is based on the measurement of acrylamide groups remaining intact after thermal aging. The amide functional groups are brominated to A-bromo amide in a buffered solution at pH=3.5. The excess bromine is reduced by sodium formate, and the A-bromo amide is then used to oxidize iodide to iodine, which forms a blue complex with starch. The absorbance Of this blue complex and a calibration curve can be used to determine the extent of hydrolysis for a given aged solution. 

Another method suitable for the determination of small amounts of iodine in organic materials involves the amplification technique. The iodide ions obtained after decomposition of the sample are oxidized to iodate by the addition of bromine in an acetate buffer. Excess bromine is removed with formic acid. Then the iodate is determined by liberation of iodine on addition of iodide in sulfuric acid solution, followed by titration of the liberated iodine with standardized sodium thiosulfate solution with starch as the indicator. The sequence of reactions can be depicted as follows ... 

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