Preparation of Aldothionic Acid Phenylhydrazides

Reductive decomposition of sugar formazans with hydrogen sulfide leads to sugar derivatives containing nitrogen and sulfur.  

A 1% solution of D-galactose diphenylformazan in alcohol is red when treated with hydrogen sulfide, it is rapidly decolorized and, after a few days, gives D-thiogalactonic acid phenylhydrazide, which crystallizes in colorless needles. Phenylhydrazine, a byproduct of the decomposition reaction, may be isolated from the mother liquor. 

A freshly prepared solution of D-thiogalactonic acid phenylhydrazide gives no reaction either with sodium nitroprusside or with lead acetate, but, when allowed to stand for a considerable time, both reactions are positive, presumably in consequence of decomposition. Boiled for an hour in aqueous solution, D-thiogalactonic acid phenylhydrazide is transformed into D-galactonic phenylhydrazide. 

Aldothionic acids and their derivatives were unknown until 1953. De- 

The ascending portion of the mutarotation curve asymptotes at a value 

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