Mutarotation, of osazones

The osazones are yellow, crystalline compounds that melt with decomposition. They exhibit mutarotation this had previously been attributed to a variety of causes, ranging from cyclization to partial hydrolysis.The present view, however, is that mutarotation of osazones is due to chelation. This explanation was devised because it was found that mutarotation occurs only with osazones capable of forming chelated rings the disubstituted osazones, such as n-araWno-hexulose 2-methyl-2-phenylosazone, do not mutarotate. Furthermore, mutarotation takes place only in such basic solvents as pyridine, which might cause a partial breakdown of the chelated ring. 

In general, we find that the nonreducing disaccharides give none of the carbonyl reactions observed for glucose, such as mutarotation and osazone formation, except when the conditions are sufficiently acidic to hydrolyze the acetal linkage. 

These sugar osotriazoles show sharp melting points and rotations (with no mutarotation) and give promise of aiding the precise characterization of osazones. 

Mutarotation of a sugar osazone was first observed by Levene and co-workers, but they did not attempt to give an explanation of the... 

It was found that the mutarotation of the sugar phenylosazones indicates a reaction of the first order, as shown in Fig. 14. With the solvent carefully evaporated in vacuo, the osazone is recovered unchanged. Repeated mutarotation takes practically the same course. As regards the ultraviolet spectra of the phenylosazones during mutarotation, a slight shift of the characteristic maximum at about 395 ma toward shorter wavelengths and a gradual disappearance of the minimum around 345 m/x are distinctly noticeable (see Fig. 15) the same holds true in respect to the recovered material. 

The observations of Weygand and coworkers on the mutarotation of 5,6-di-O-methyl-n-orobfno-hexose p-bromophenylosazone, and those of Jones and coworkers i on the mutarotation of n- Zj/cero-tetrulose phenyl-osazone and its derivatives, leave no room for a concept which holds that mutarotation might be caused by cyclization starting at C2. 

Osazones, phenyl-, of sugars, 139 mutarotation of, 144 structure of, 129 Osones, deoxy-, 73, 74, 76 Oxidation,... 

Chapman and co-workers followed the nuclear magnetic resonance spectra of osazones in methyl sulfoxide during the process of mutarotation, and observed that the spectra become constant when the optical rotation reaches the equilibrium values. They found that, during the course of mutarotation, new NH resonances appear in the region of the unchelated... 

These findings are consistent with the fact that, during mutarotation, a shift of the ultraviolet absorption maximum to a shorter wave-length takes place, and that the starting isomer is recovered from the equilibrium mixture. Another interesting phenomenon in the optical properties of osazones is their thermomutarotation the optical rotations of these compounds are greatly influenced by temperature. 

Fischer represented the hydrazones and osazones as open chain structures one sees at once, however, other structural possibilities since mutarotation occurs in solution in many cases. Unless this is due to decomposition, some form of tautomeric equilibrium must be postulated, and Haworth pointed out that cyclic structures must be considered Behrend and Lohr recognized the possibility of the existence of syn and anti forms, and it has also been suggested that there may be an equilibrium between hydrazone and azo structures in the osazones. 

Maltose a-D-glucose + a-D-glucose a(1 -+4) Germinating cereal and malt Forms osazone with phenylhydrazme. Fermentable by enzyme maltase present in yeast. Hydrolysed to two molecules of D-glucose. Undergoes mutarotation. 

Reaction of the n-glucose phenylosazone remaining, in samples taken from the mutarotating solution after increasing periods of time, with diazo solution, yields less and less osazone formazan (see Fig. 16). This is obviously attributable to the same structrual change as that which is optically... 

The chemistry of carba sugars is quite similar to that of cyclitols both groups lack the latent carbonyl groups of their saccharide counterparts, and therefore fail to exhibit many of the characteristic properties of monosaccharides. Thus carba sugars and cyclitols do not form hydrazones or osazones, nor do they mutarotate, or reduce heavy-metal salts in base, in contrast to their oxidation products, the inososes. 

The (2,4-dinitrophenyl)osazone of 3-deoxy-D-fifl /cero-pentosulose was isolated by Kato from the decomposition of iV-butyl-D-xylosylamine or A -butyl-D-arabinosylamine. Later, " the free pentosulose was isolated in 2% yield as a colorless solid. It shows properties similar to those of the 3-deoxyhexosuloses, no strong absorption in the range 210-400 m t, and a weak mutarotation C ]d —13.4 -+ —17.2° (in water). It readily forms a (2,4-dinitrophenyl)osazone which yields a diacetate. The osazone was... 

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