Glucose phenylhydrazine

Dissolve I g. of glucose (or fructose) in 5 ml. of water in a boiling-tube. In another tube dissolve 2 ml. of glacial acetic acid in 5 ml. of water, add 2 ml. of phenylhydrazine, and shake until... 

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. 

Reducing sugars can be detected by reaction with phenylhydrazine to yield a hydrazone product, except the result of the reaction is not what one might imagine giving the structure of aldoses and ketoses. Glucose, for example, can react with phenylhydrazine to yield the anticipated... 

It has recently been reported21 that a mixed osazone of 3,4-di-O-methyl-D-glucose can be converted, by treatment with p-nitrobenzaldehyde, into an osone which reacts with phenylhydrazine to give 3,4-di-O-methyl-D-glucose phenylosazone. Von Lebedev29 claimed to have obtained D-glu-cosone 6-phosphate, isolated as an amorphous lead salt, by the action of hydrochloric acid on the phenylosazone prepared from D-fructose 6-phosphate. 

Experiment.—Heat a solution of 2 g. of phenylhydrazine in dilute acetic acid (1-5 c.c. of acid, 15 c.c. of water) with 1 g. of d-glucose dissolved in 5 c.c. of water on the water bath at 80°. After about twenty minutes the osazone begins to separate in fine small yellow needles. After the lapse of an hour collect the crystals at the pump, wash with water, and dry in the air. Melting point 205°. 

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. 

Da das Phenylhydrazon der Glucose ein Zwischenprodukt bei der Osazonbildung darsteUt und von den drei zur Reaktion benotigten Molekeln Phenylhydrazin eines in Anilin und Ammoniak umgewandelt wird 86,87) deutete E. Fischer 88) den Reaktionsverlauf so, daB die a-standige Alkoholgruppierung durch das Phenylhydrazin dehydriert... 

Problem 22.16 Acetylation of glucose produces two isomeric pentaacetates that do not react with either phenylhydrazine or Tollens solution. Explain. 

L-Mannitol does not occur naturally but is obtained by the reduction of L-mannose or L-mannonic acid lactone (80). It can be synthesized from the relatively abundant L-arabinose through the L-mannose and L-glucose cyanohydrins, conversion to the phenylhydrazines which are separated, liberation of L-mannose, and reduction with sodium borohydride (81). Another synthesis is from L-inositol (obtained from its monomethyl ether, quebrachitol) through the diacetonate, periodate oxidation to the blocked dialdehyde, reduction, and removal of the acetone blocking groups (82). 

Pentoses and hexoaes could be distinguished readily with phenylhydra-zine. The compound hitherto called isodulcitol was identified as a sugar by means of phenylhydrazine, and was designated as rhamnose from that time on. Glucose and fructose (which H. Kiliani had discerned to be an aldohexose and a ketohexose, respectively) and mannose were found to give one and the same phenylosazone the three sugars, therefore, have the same configuration at carbon atoms 3, 4, and 5. 

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 ... 

A hexose, C6H1206, which we shall call X-ose, on reduction with sodium amalgam gives pure D-sorbitol, and upon treatment with phenylhydrazine gives an osazone different from that of D-glucose. Write a projection formula for X-ose and equations for its reactions. 

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