Alkaline Hypoiodite as an Analytical Reagent

As this lengthy reaction time proved objectionable from the analytical viewpoint, certain modifications were applied. Willstatter and SchudeP shortened the time to twenty minutes by adding a definite excess of iodine (100%) and of alkali (150%) the latter was added slowly to a mixture of the sugar and iodine. In this way the formation of iodate was lessened and over-oxidation minimized. 

Procedure of Willstdtter and Scfcudet To 10 cc. of a solution containing 100 mg. of aldose is added 20 cc. of 0.1 N iodine-potassium iodide solution (11,11 cc. is required for a hexose) and then 30 co. of 0,1 N sodium hydroxide solution is added gradually. The mixture is allowed to stand for ten to twenty minutes. It is then acidified with dilute hydrochloric or sulfuric acid and titrated with 0.1 N thiosulfate solution. Each cc. of 0.1 N iodine consumed is equivalent to 9.005 mg. of an aldo-hexose, 7.004 mg. of an aldopentose and 17.11 mg. of a reducing C12 disaccharide. 

GoebeP made a study of the effect of the rate of addition of alkali upon the formation of iodate from hypoiodite (reaction 15). He found 

Kline and Acree studied the hypoiodite oxidation extensively. The alkali and iodine were both added in small portions throughout the reaction. In this manner the concentration of sugar relative to the sodium hypoiodite was kept at a level favorable to the sugar oxidation (reaction 14). At the end of the reaction, the formation of iodate increased rapidly (reaction 15), taking precedence over the oxidation of ketoses and non-reducing sugars. 

The earlier work on this oxidation by Slater and Acree was in error because of their failure to distinguish between the iodine equivalence of thiosulfate in acid and in alkaline solution. In acid solution (reaction 15o) the equivalence is 1 1, with sodium tetrathionate as a product. In alkaline solution 1 mole of thiosulfate is equivalent to 8 atoms of iodine (reaction 156), with sodium sulfate as a product. 

---