Sugars phenyl osazones

Although advantageous for the identification of the sugars, the phenyl osazones are not applicable to the isolation of sugars. The phenylhydrazine groups are removed by treatment with benzaldehyde, concentrated hydrochloric acid, or particularly well by pyruvic acid (230), but the resulting product, a sugar osone, is a mixed ketose-aldose. 

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,... 

He shows that n-fructose methylphenylosazone in contact with phenyl-hydrazine at room temperature yields n-fructose methylphenylphenyl-osazone and with p-nitrophenylhydrazine, n-fructose methylphenyl-p-nitrophenylosazone. It is possible to interpret this result in another way, namely that since the competing base removes one methylphenyl-hydrazine residue but not both, one is less firmly bound than the other, and might be admitted as evidence that the two methylphenylhydrazine residues are bound by different types of linkage to the sugar, as in fact the cyclic formulation demands. 

Osones.—We are not yet done with the interesting reactions of these compounds for the osazones when warmed with concentrated hydrochloric acid, take up water and split off the two phenyl hydrazine residues and yield a compound containing both the aldehyde and the ketone groups of the original aldose and ketose sugars. The resulting compound is known as an osone. 

Since they contain no active methine groups, - the fcetose phenyl-hydrazones do not yield formazans this lack of reaction is therefore suitable for distinguishing ketoses from aldoses. It is more specific than the osazone test, frequently used in the identification of sugars, for it yields a different formazan from each aldose, whereas the osazone test does not differentiate between epimers. 

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

For many years the precise structures of some of the products obtained from reaction of sugars with phenylhydrazine have been the subject of much discussion. Reaction of D-mannose phenyl-hydrazone with acetic anhydride in pyridine yields D-ara6fwo-3,4,5,6-tetraacetoxyl-l-phenylazo-1-hexene. The n.m.r. spectrum of this compound clearly establishes its structure. Acyclic structures have similarly been assigned to various phenylhydrazones and osazones. The work of Wolfrom and his co-workers perhaps best illustrates the kind of approach that has been adopted. The n.m.r. spectrum of o-lyxohexose phenylosazone was measured in dimethyl sulphoxide. The three possible structures of the osazone (44, 45, 46) were considered in terms of the spectrum. 

The phenylosotriazoles of a considerable number of reducing sugars have been prepared (see Table II, p. 117). Apart from these phenyl derivatives, several other substituted arylosotriazoles have been prepared, usually from the corresponding osazones (see Table III, p. 120). 

The methylene group at C2 will not be oxidized to a carbonyl (or a hydroxyl) and the sugar will form a phenyl-hydrazone but not an osazone. Osazone formation is specific to a-hydroxy carbonyl compounds. 

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