Osazones sugar

The sugar osazones usually are crystalline and are useful for characterization and identification of sugars. Fischer employed them in his work that established the configuration of the sugars. The kind of information that can be obtained is illustrated by the following example ... 

Although, as mentioned previously, other possibilities of isomerism exist, most attention has been devoted to attempts to decide whether sugar osazones are cyclic or acyclic. The results of methylation experiments indicate that under these conditions the osazones react as cyclic structures, but there is less certainty about the structure of acetylated osazones. 

Roberts, who pointed out the difference in the chemical behavior of ascorbic acid and sugar osazones, preferred a 3-phenylhydrazino-4-phenylazo-5//-furan-2-one structure, which he supported by its remarkably high UV absorption [79JCS(P1)6O3]. However, this type of structure was ruled out by the C-NMR spectra. 

Coupled with diazo compounds in pyridine-alcohol solution, the sugar osazones fail to yield formazans. This may be due to one or both of the following reasons. 

In order to find the reason for the failure of formazan reaction, a model experiment was set up using 2-quinolinecarboxaldehyde phenylhydrazone whose structure, if the nitrogen of the quinoline be considered, is like that of a phenylosazone, with the six-membered chelate ring in it as proposed by Fieser and Fieser for sugar osazones. 

Analogous to the formazans obtained by loosening the chelate ring in the above manner, the sugar osazones of supposedly chelate structure were found to undergo reaction in alkaline alcohol and to give n-glucose phenylosazone formazan in dark-violet needles. Mild acetylation produces the black tetraacetate of this compound. 

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

In the year 1884, Emil Fi8cheri prepared the first sugar osazones and suggested their use for identification purposes. He later used the fact that D-glucose and n-mannose give the same osazone in his determination of the structure of these two monosaccharides, and he accomplished, through osazone formation, the conversion of aldoses into ketoses. Since then, osazone formation has been used in a multitude of syntheses in the carbo-... 

Finally, to facilitate the identification of sugar osazones, crystallographic studies have been made. ... 

Subheading 5.3.2. makes reference to the use of derivatives such as sugar osazones in fractional crystallisation. 

Fischer110 was the first to report that sugar osazones (172) are hydrolyzed by the action of hydrochloric acid. This hydrolysis is an example of... 

Because of the chelated structure of sugar osazones, the osazone formazan 181, obtained by coupling diazotized [14C]aniline to a saccharide phenylosazone (180) loses 42%) of the label (as aniline) upon conversion to an osolriazole (182), whereas the formazan of an unchelated osazone, such as pyruvaldehyde osazone loses exactly half of the radioactivity as aniline during osolriazole formation (Scheme 40).168... 

In view of their sharply defined physical constants, sugar osotriazoles have been used for the identification of sugars and their osazones. It has now become customary to confirm the identity of sugar osazones by comparing their phenylosotriazoles. ... 

The sugar osazones are particularly prone to acid-catalyzed dehydration, and form monoanhydro derivatives when their alcoholic solutions are boiled with a trace of acid 69), (See also Chapter VIII.) With the hexose phenylosazones, there is produced a mixture of the epimeric 3,6-anhydro-hexose phenylosazones resulting from dehydration with and without... 

Sugar Osazones, By treatment of sugars with an excess of phenylhydrazine at 100°C., two phenylhydrazine residues are introduced into the molecule, and sugar osazones, difficultly soluble in water, are formed 216), Optimal conditions for the preparation of glucosazone have been determined 217), The reaction proceeds most rapidly in the presence of acetate buffers at a pH of about 4 to 6 in more acid solution (particularly in the absence of air), and with the free base, only the hydrazone is formed 208, 218), The presence of sodium bisulfite in the reaction mixture inhibits the formation of colored by-products 219),... 

Since the sugar osazones mutarotate in alcoholic pyridine solution (231) the classical formula for these substances may be questioned, and there is much evidence that they exist in cyclic as well as acyclic forms. The mutaro-tation has been ascribed to a partial hydrolysis of the osazones, and appreciable quantities of the sugar and hydrazine exist in the equilibrium solution (232). This explanation is also supported by the ease with which the hydrazine radicals of the osazones are exchanged with hydrazine molecules in the solvent (233). When the second hydrazine is different from that used in making the osazone, mixed osazones are formed (232, 234) ... 

A comparison of the absorption curves of the sugar osazones with those of simple substances 232) indicates that the sugar osazones are acyclic, but methylation studies 236) show the presence of a ring structure as illustrated in the following series of reactions ... 

In a study of the deacetylation of acetylated sugar osazones it has been shown that under alkaline conditions and depending upon the substrate, either an external nucleophile fe.a.. Na, MeO , NH3) can be incorporated at C-3 or a 3,6-anhydride can be formed. The 3-methoxy-epimers (49) were thus formed from the L-ervthro-pentose osazone triacetate presumably by formation and 1,4-addition to a phenylazo-ene intermediate." The 2-acetoxy group of aldose diphenylformazan peracetates is also readily displaced. 2-Deoxy-D-arabino-hexose diphenylformazan (50) was thus formed when penta-Q-acetyl-D-glucose or -D-mannose H H diphenylformazan was treated with sodium borohydride." ... 

However, when the sugar phenylhydrazones are boiled with excess of phenylhydrazine an important reaction occurs. The alcohol group adjacent to the hydrazone radicle is oxidised to a ketone or an aldehyde group, which in turn reacts with phenylhydrazine to produce a double hydrazone, or osazone. Sugar osazones are sparingly soluble in water, have characteristic crystalline shapes and melting points, and provide a valuable means for sugar identification, alone or in mixtures. 

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