Starch derivatives hydrogenation/reduction

Reductive decomposition of the formazans of oxidized polysaccharides, by means of hydrogen sulfide, as with the simple sugar formazans, yields sulfur-containing, nitrogenous polysaccharide derivatives which contain thionic acid phenylhydrazide groups. For example, when a pyridine-ethanol solution of oxy-starch formazan or oxy-dextrin formazan is saturated with hydrogen sulfide, the vividly red solution turns colorless and a yellow precipitate, which gives the Wuyts reaction characteristic of the thionic acid phenylhydrazides, separates. 

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