Structure of Sugar Phenylhydrazones

When Emil Fischer, some 70 years ago, prepared sugar phenylhydrazones, he represented them as open-chain compounds. The conception of ring structure arose later to account for mutarotational effects in solution. The question is still a moot one, although many workers have attempted to clarify the point. 

Frferejacque found that definitive evidence could not be obtained from a study of hydrolysis rates and rotational values of the hydrolyzate. Later, Stempel, on the basis of similar experiments, came to the same conclusion. 

The formazan reaction permits an interpretation of the mutarotation curves of the sugar phenylhydrazones. i  

Earlier workers - had concluded from the nature of the curves that there are at least three modifications participating in the mutarotation, yet it remained undetermined until the present whether they were all cyclic, or whether the aldehydo form was represented among them, and if so in what proportion. 

This point can now be clarified. At certain critical points during mutarotation, the phenylhydrazone solutions are coupled to form formazan, and the yields at the different rotational values indicate the proportion of phenylhydrazone present in the aldehydo form. These data are presented in the lower curves in Figs. 7 to 10. 

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