Phenylhydrazones mutarotation

Attempts have been made to solve the problem by examining the rate of hydrolysis of the two D-glucose phenylhydrazones, and Frere-jacque/ who used oxalic acid and picric acid to remove the phenyl-hydrazine from the sphere of the reaction as an insoluble salt, claimed to show that both of the D-glucose a - and 9 -phenylhydrazones are derived from a-D-glucose on account of the downward trend of the mutarotation observed on making the solutions alkaline. This result is therefore not in conflict Avith the conclusions of Behrend. From similar studies StempeP concluded that "no information of value concerning... 

Another controversial aspect of the bishydrazone structure concerns the hydrazone residues. The bishydrazone was proposed to have the structure 46, which mutarotates in solution to 47 (47). More recently, on the basis of a comparative study of the spectroscopic properties of the bis(phenylhydrazone) with some related compounds, the bishydrazone was assigned the structure 2,3-dideoxy-3-phenylazo-2-phenylhydrazino-L-threo-hex-2-enone-l,4-lactone (48) (48). However, this latter structure was inconsistent with its NMR spectra (49). 

D-Glucose phenylhydrazone [3713-25-5] M 358.4, m three forms. Crystallise the hydrazone from 70% aqueous EtOH or EtOH/Et20. Three forms have been described a form m 159°, 160° which mutarotates from [a] -87° to -50° (H2O) [Fischer Bcr 20 821 1887, Behrends Justus Liebigs Ann Chem 353 106 1907], p form m 140-141°, 142° which mutarotates from [a] -2° to -50° (H2O) [Behrends LohrLiebigs Ann Chem 362 78 790S], and Skraup s form m 115-116° which mutarotates from [a] -70° to -47° (H2O) [Skraup Monatsh Chem 10 406 1889, Butler Crechter J Am Chem Soc 51 3161 1921]. These mutarotate to the formazan. [Beilstein 1 IV 4322, Mester Major 7 A/n Chem Soc 77 4297 7955, Stanek et al. The Monosaccharides, Academic Press 1963, pp 539-541,543.]... 

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. 

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

Fig. 7.—Upper Curve Mutarotation of n-Mannose Phenylhydrazone [c 0.9, pyridine-ethanol (9 1 by vol.)] Lower Curve n-Mannose Diphenylformazan Formation.

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. 

Fig. 8.—Upper Curve Mutarotation of L-Rhamnose Phenylhydrazone [c 1.27, pyridine-ethanol (l lbyvol.)] LowerCurve L-RhamnoseDiphenylformazan Formation.

Fig. 9.—Upper Curve Mutarotation of o-Galaotose Phenylhydrazone (c 5.4 pyridine) Lower Curve n-Galactose Diphenylformazan Formation.

The formazan reaction, carried out at certain critical rotational values, also permits the interpretation of the structural changes observable during mutarotation of n-galacturonic acid phenylhydrazone (see Fig. 11). 

Fig. 11.— Lower Curve Mutarotation of n-Galacturonic Acid Phenylhydrazone (pyridine-ethanol, 1 1 by vol.) Upper Curve n-Galacturonic Acid Af.AT -Diphenyl-formazan Formation.

The hydrazones of sugars are capable of existing in various cyclic forms, whose presence is apparent from their nuclear magnetic resonance (NMR) spectra and from the complex mutarotation curves they exhibit110,111117118 (which seldom follow first-order kinetics). The principal structures encountered in saccharide hydrazones are the acyclic, Schiff base-type true hydrazones and the cyclic hydrazino forms, namely glycopyranosyl- and gly-cofuranosylhydrazines. For example, three isomeric forms of D-glucose phenylhydrazone have been isolated.119 The Schiff base derivatives can be... 

D-Glucose phenylhydrazone [3713-25-5] M 358.4, m three forms. Crystallise the hydrazone from 70% aqueous EtOH or Et0H/Et20. Three forms have been described a form m 159°, 160° which mutarotates from [a]g> -87° to -50° (H2O) [Fischer 20 821 1887, Justus Liebigs Ann Chem 353 106 1907],... 

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