Phenylosazone formation

See page 311, Chapter 30, for Tollens test and page 444, Chapter 51, for phenylosazone formation. 

Reaction with reducing sugars. For evidence on the mechanism of phenylosazone formation, see Chapman el aU ... 

Since phenylosazone formation also does not affect the stereochemistry about C3 and Ci of the pentose, the above structure also represents D-ribose whose structure differs only at the C-2 chiral center. Such compounds, differing in stereochemistry only about one carbon, are termed epimers. D-ribose is reduced to an optically inactive alditol, ribitol, and therefore we can determine the structure of D-ribose and its epimer, D-arabinose. 

Formation of a Glycoside 988 Hydrolysis of a Glycoside 989 Phenylosazone Formation 1000... 

The formation of D-glucose phenylosazone from chitosamine showed its relationship to D-glucose and D-mannose and Irvine and Hynd7 succeeded in preparing both D-mannose and D-glucose from chitosamine. 

Intermediate formation of a triose (identified as phenylosazone) was also proved by the authors and the following sequence of reactions is suggested ... 

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 ... 

Several mechanisms34 have been proposed for this reaction. That of Weygand,36 in which an Amadori rearrangement is proposed, has considerable merit.37 Illustrations of unusual osazone formation are described by Bonner and Drisko.38 When phenyl /S-D-xylopyranosyl sulfone (XXII) or /J-D-glucopyranosyl sulfone (XXIV) is oxidized by periodic acid, a dialdehyde oxidation product (XXIII or XXV), which is susceptible toward further oxidation, is obtained. The reaction of XXIII or XXV with phenylhydrazine yields glyoxal phenylosazone and benzenesulfinic acid. Surprisingly, both XXII and XXIII react with phenylhydrazine to form D-xylosazone and D-glucosazone, respectively. 

Very little conclusive evidence for the position of the methyl group in 2-methyl-D-mannose is available. Pacsu and Trister4 showed that the sugar reacted with phenylhydrazine in the cold to give a phenylhydrazone but not a phenylosazone. More drastic conditions were required to form the phenylosazone, during which reaction the methyl group was lost with the formation of D-glucosazone. 

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