Iodine starch complex

Treatment with chlorine gas converts amines to chloramines, whose active chlorine oxidizes iodide to iodine. This then forms the well-known, deep blue iodine-starch complex [13]. 

Iodine-starch inclusion compounds la 46 Iodine-starch complex lb 195 Iodine substitution under the influence of light la 47... 

Condition/ Absorbance of the liberated iodine-starch complex for different durations... 

Since the time of Schardinger, one of the most important reasons for studying the cyclodextrins was for the information they might yield on the structure of starch and of the well known blue iodine-starch complex. In fact, the similarity between the iodine-starch reaction and the iodine-alpha cyclodextrin reaction was first noted by Schardinger in 1911, in his final paper on the cyclodextrins. 

I2 + starch — iodine — starch complex (blackish-blue)... 

Iodates, III, 138, 157, 178 Iodic acid, as oxidant, III, 178 Iodine, adsorption by starch, I, 256 colors of products formed from starch by amylases, V, 261 as oxidant, III, 151, 169 solubility of, III, 136 Iodine starch complex, dichroism of flow of, I, 266... 

Soluble starch, available from chemical supply houses, is readily dispersed in water. The iodine-starch complex has limited water solubility, and it is therefore important not to add the starch indicator until near the end point when the iodine concentration is low. Because starch is subject to attack by microorganisms, the solution usually is prepared as needed. Among the products of hydrolysis is dextrose, which can cause large errors because of its reducing action. Various substances have been recommended as preservatives, including mercury(II) iodide and thymol. With formamide a clear solution containing 5% starch is obtained that is stable indefinitely. 

Figure 1.8 Chromatogram of iodide in seawater by size exclusion chromatography with UV detection. Iodide in seawater could be determined indirectly after it was converted to iodine-starch complex. Conditions column, Shim-pack DIOL-150 mobile phase, methanol-0.01 mol 1 aqueous phosphoric acid...

There s a chemistry battle between starch and vitamin C. The starch wants to turn blue as it s reduced, but the vitamin C keeps it from being reduced and turning blue. Eventually, an iodine starch complex forms and gives the solution a blue color. In this experiment, you change the amount of time it takes for the liquids to change color. 

In the final step of the analysis, the iodine is titrated with thiosulphate. The iodine is reduced to iodide, and the thiosulphate in turn is oxidized to the tetrathionate ion. The concentration of the thiosulphate solution used for the titration must be known precisely. The endpoint of the redox titration is commonly indicated by a starch indicator or by photometric or amperometric endpoint detection. The starch indicator forms an enclosure compound with iodine. The large electron cloud of the iodine interacts with the hydroxo dipoles in the starch helix resulting in an intensely blue colour of the iodine starch complex. Nevertheless, the iodine molecules can leave the starch hehx easily and thus can be reduced by thiosulphate. The endpoint of the titration is clearly marked by the change from blue to colourless. 

In the iodine clock reaction, a colorless solution suddenly changes to a blue-black iodine—starch complex in a predetermined amount of time (dependent upon the temperature and the concentrations of the reactants). The iodine is produced by the reaction of iodic acid and hydrogen iodide as represented in the following unbalanced equation. Identify the oxidiang and reducing agents in this reaction and balance the equation. 

The solution is immediately titrated with standard 0.1 N sodium thiosulfate solution from a 25-mL buret (with efficient swirling, but not shaking) to near disappearance of the yellow color. At this point, a few drops of a 1% soluble starch solution may be added to form the intensely blue iodine-starch complex for easier detection of the endpoint. The titration should take no more than about 1 min to minimize air oxidation of the iodide to additional iodine. The titration reaction is... 

Fig. 9. ORD (--------) and absorption spectra (—) of starch (a), KI3 (b) and iodine-starch-complex...

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