Osazones of sugars

A high degree of specificity is claimed for this method. Any osazones of sugars that may be formed decompose in the concentrated sulphuric acid and for this reason a delay of 30 min after development of colour before measurement is recommended. Furthermore, thiourea or stannous chloride is added to avoid interference from non-ascorbic acid chromogens. Nevertheless, care should be exercised in its use in the determination of ascorbic acid References p. 94... 

The photographs of the osazones were kindly supplied by Thomas Kerfoot and Co. Lid., of Vala of Bardsley, Ashton.under-Lyue, the weU-known manufacturers of sugars. 

Another reaction that is characteristic of a-hydroxy aldehydes or ketones, which has been found of value for the characterisation of sugars, is the formation of osazones with phenylhydrazine. This reagent reacts with either an aldose... 

D-Galactosido-D-glucosone and D-glucosido-D-galactosone were prepared by Fischer and Armstrong203 by the action of benzaldehyde on the osazones of synthetic disaccharides. Both osones were hydrolyzed by emulsin. There is some doubt as to the precise structure of the parent sugars.206... 

See p. 298 for information about the production of the osazones of the simple sugars. The osazones of d-glucose, d-fructose, and d-mannose are identical. 

Many oxidizing agents have been used, especially copper sulfate and other cupric salts. Potassium dichromate in acetic acid and manganese dioxide are good oxidants for benzil bis(phenylhydrazone). Nitrous acid has been used for the osazones of acetylated sugars and for phenylglyoxal bis(phenylhydrazone). ... 

Figure 2. Electron spin resonance spectra of sugar phenylhydrazones and osazones (2.5 mM to 3.5 mM, in Me2SO-l% K-tert-BuO)...

Phenylhydrazinc, as hydrochloride solution plus sodium acetate, reacts with polyhydroxy aldehydes or ketones yielding osazones or diphenyl-hydrazones, yellow solids, of definite melting point and utilized in identification of sugars, e.g.. phenyl-d-glucosazone. CH OH (CHOH), C (NNHC6H5)CH (NNHCftH,) plus aniline C6H5NH plus NH,... 

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 ... 

Since the discovery of the reaction of phenylhydrazine with sugars to form osazones by Fischer,35 many investigations have utilized this reaction in the identification and separation of sugars, but the precise structures of osazones and their mode of formation are still in doubt.34 There is no doubt, however, that the initial reaction involves the formation of a hydrazone, which then reacts further to yield eventually a f)u-l,2-hydrazone or osazone. 

The melting points (more accurately termed the decomposition points) of sugars and some of their derivatives, e.g. osazones, are not so definite as those of other classes of organic compounds they vary with the rate of heating and the differences between individual members are not always large. There are, however, a number of reactions and derivatives which will assist in the characterisation of the simple sugars. 

Glucose and fructose (and also mannose) form the same osazone. The osazones are usually yellow, well-defined crystalline compounds and are sparingly soluble in cold water. The characteristic crystalline forms of the osazones of the commonly occurring sugars, when examined under the microscope, may be employed for their identification (Fig. 9.1) the melting or decomposition... 

The action of lead tetraacetate on osazones of Cw-labeled sugars in warm aqueous acetic acid has been employed46 for determining specific activity of the oxidizable carbon atoms present, that is, C4, C5, and C6 of D-glucose phenylosotriazole. In the potassium acetate-catalyzed oxidation, D-glucos-azone (o-arabino-hexose phenylosazone) yielded two moles of formic acid... 

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