Osazone, crystalline

Both maltose and lactose, being reducing sugars, give osazones which differ from one another and from glucosazone in crystalline form. Sucrose (G-r-r-F), having no potential aldehyde or ketone grouping, does not form an osazone. 

If it is desired to observe the crystalline form of the osazone, draw up in a glass tube a few drops of the cold filtrate containing the fine crystals, and transfer to a microscope slide. Cover the drops with a slip and examine under the microscope unless the filtrate has been cooled very slowly and thus given moderately-sized crystals, the high power of the microscope will probably be required. Note the fine yellow needles aggregated in the form of sheaves. Compare with Fig. 63(A). 

Osazone formation. Forms a yellow osazone, m.p. 208° soluble in hot water. See p. 137 for preparation. If examined under the microscope very characteristic clusters of hedge-hog crystals will be seen (Fig. 63(c), p. 139). The difference in the crystalline appearance of lactosazonc and maltosazone should be very carefully noted, as this difference forms the chief and most reliable method of differentiating between these two sugars. 

The approximate times of osazone formation in minutes are given in Table 111,139. The product from mannose is the simple hydrazone and is practically white. Arabinose osazone separates first as an oil, whilst that from galactose is highly crystalline. Lactose and maltose give no precipitate from hot solution. 

Simple sugars undergo reaction with phenylhydrazine, PhNHNH2, to yield crystalline derivatives called osazones. The reaction is a bit complex, however, as shown by the fact that glucose and fructose yield the same osazone. 

LaForge and Hudson194 prepared an osone from the phenylosazone obtained from sedoheptulose (D-aZ(ro-heptulose). The osone reduced Fehling solution strongly, formed the original osazone with phenylhydrazine, and gave a crystalline derivative with o-phenylenediamine. 

Historically, techniques such as the formation of osazones and the demonstration of fermentation have contributed significantly to the separation and identification of carbohydrates. Observation of the characteristic crystalline structure and melting point of the osazone derivative, prepared by reaction of the monosaccharide with phenylhydrazine, was used in identification. This method is not completely specific, however, because the reaction involves both carbon atoms 1 and 2 with the result that the three hexoses, glucose, fructose and mannose (Figure 9.19), will yield identical osazones owing to their common enediol form. 

The fourth student in this group, Stanford Moore, began his doctoral thesis research with Link in 1935. His work involved the development of a new, and still useful, procedure for oxidizing aldoses to the aldonic acids by potassium hypoiodite in methanol solution the resulting aldonic acids were then converted into nicely crystalline benzimidazole derivatives that proved more suitable for the characterization of carbohydrates than the classical osazones. This method, developed by Moore and Link (1940), was extended to the characterization of hexuronic acids, as their bis(benzimidazole)s, after oxidation to the glycaric acid (R. Lohmar, Dimler, Moore, and Link, 1942), of lactic acid (Moore, Dimler, and Link, 1941 Dimler and Link, 1942), and of ribose, fucose, and digitoxose (Dimler and Link, 1943). During these... 

Melting Points of Monosaccharide Osazone Derivatives Many carbohydrates react with phenylhydrazine (C6H5NHNH2) to form bright yellow crystalline derivatives known as osazones ... 

The reaction of glucose with an excess of phenylhydrazine (phenyl-diazane) is particularly noteworthy because two phenylhydrazine molecules are incorporated into one of glucose. Subsequent to the expected phenyl-hydrazone formation, and in a manner that is not entirely clear, the —CHOH— group adjacent to the original aldehyde function is oxidized to a carbonyl group, which then consumes more phenylhydrazine to form a crystalline derivative called an osazone, or specifically glucose phenylosazone ... 

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 ... 

Watters, Hockett and Hudson1 have prepared a non-crystalline monomethylmannose which forms an osazone with the same properties as those of 6-methyl-n-glucosazone. The synthesis was achieved by methylation of methyl 2,3,4-triacetyl-a-D-mannopyranoside, followed by hydrolysis. Schmidt and Heiss,13 studying the epimerization of 6-methyl-D-gluconic acid, have claimed to have isolated the phenyl-hydrazide of 6-methyl-n-mannonic acid. 

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... 

On interruption of the reaction at the minimum point, only a low yield of the final product, 5-(methoxymethyl)-2-furaldehyde, could be isolated as the semicarbazone, but a crystalline phenylosazone (m.p. 120.5-121.5°, [< ]d —9° in chloroform) was obtained. It was not isolable at the end of the reaction. No osazone was obtainable from the hydroxy-glycal without prior, acid treatment. Analyses of the osazone indicated that it was a mono-O-methyl derivative of the parent CgHgCh. This is the same formula that was found by Bergmann and Zervas (see above ) for the parent of the phenylosazone obtained by direct treatment of 2,3,4,6-tetra-0-acetyl-(2-hydroxy-D-glucal) with phenylhydrazine. Whereas Bergmann and Zervas were unable to acetylate the compound further, Wolfrom, Wallace and Metcalf introduced an O-acetyl group into their mono-O-... 

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