Halogens, starch oxidized

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. 

Catalysis, enzyme-substrate and intermediate compound theory in homo-and heterogeneous, V, 51 Catalysts, for acetonation, III, 51 for acetylation of starch, I, 284, 286 Bourguel s, II, 109, 110, 113 for esterification of cellulose, I, 312 in oxidation of carbohydrates by halogens, III, 177... 

The solutions required are iodic acid, 50 grms. in 250 c.c. deci-normal sodium thiosulphate 20 per cent, potassium iodide and starch paste. Into the flask of a Fresenius or Mohr s iodometric apparatus, 0-5-0-6 gramme of antimonious oxide is weighed, 20-25 c.c. of iodic acid are added, and 10 c.c. of potassium iodide solution are placed in the condensing apparatus. The contents of the flask are boiled until colourless, and the collected iodine determined with thiosulphate. From antimony compounds the sulphide is precipitated by sulphuretted hydrogen, then dissolved in HCl, and the oxide obtained by the action of sodium carbonate. The halogen acids, sulphurous acid, and sulphuretted hydrogen must be dissolved in... 

Complex side-reactions, including overoxidation, are likely to occur in the oxidations, and information on the mechanism of periodate oxidation and the periodate-oxidation products of starch, cellulose, xylan, and other polysaccharides have been discussed. Thus, the limit of periodate oxidation is not always that expected, and the formation of interresidue hemiacetal structures during the oxidation can cause an early halt. - It is not until these structures have been reduced that oxidation can proceed once more. Other oxidants, such as dichromate-sulfuric acid, dichromate-oxalic acid, and sodium hypochlorite (which cause more extensive reactions), have been investigated with respect to cellulose and periodate-oxidized cellulose. Further oxidation of 2,3-dialdehydocel-lulose with halogen peroxy acids gives 2,3-dicarboxycellulose. ... 

The halogens and their oxyacids probably are the most important oxidants used in the carbohydrate field. They are widely used as bleaching agents, but the mechanism of this action remains to be clarified. As reagents for preparatory purposes (particularly for aldonic acids and lactones) and for analytical procedures, they are very important. Periodic acid, discussed in a later section, has an important application for the elucidation of structures of carbohydrates. A number of valuable commercial products are made by treatment of polysaccharides with halogens, particularly chlorine or hypochlorous acid, but the nature of these actions, such as the modification of starch, has not been clarified. 

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