Monosaccharides reactions with phenylhydrazine

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 reaction of phenylhydrazine with oxysucrose was found to be similar to that described for oxidized monosaccharide derivatives above, as only two molecules of the base reacted with the four potential aldehyde groups the product was assigned structure (89). Mester found that this derivative forms an amorphous bis(diphenylformazan) with benzenediazonium chloride, and so he assigned structure (90) to it. Acetylation of the formazan gave an amorphous product, identical with the formazan prepared from... 

Condensation of o-phenylenediamine with methylglyoxal, aldohexoses and aryl or alkyl acyloins gave the corresponding quinoxalines 76. Indoloquinoxalines were obtained from isatin. Carbethoxymethylation of isatin and then reaction with o-phenylenedimine gave the respective indoloquinoxalines 77, whereas hydrazide was condensed with aromatic aldehydes and monosaccharides. L-Ascorbic acid or D-isoascorbic acid were oxidized with iodine and then reacted with o-phenylenediamine and phenylhydrazine to give quinoxalinones 78, which were cyclized to pyrazolyl-quinazolinones . ... 

Manninotriose (0.8 g.) was heated with 1.44 g. of phenylhydrazine hydrochloride, 0.22 g. of o-phenylenediamine, and 0.5 g. of glacial acetic acid in 20 ml. of water at 100° in a stoppered tube. After 3 hours, the reaction mixture was cooled and neutralized with 40 ml. of 0.5 N sodium hydroxide. The trisaccharide flavazole was isolated by fractional extraction of the solution with ether (to remove organic bases and colored impurities), ethyl methyl ketone (to remove traces of monosaccharide and disaccharide flavazoles, as well as other colored impurities), and butanol (which extracted the trisaccharide flavazole). Each step in the fractionation process was followed by... 

We recall that hydrazine and 2,4-dinitrophenylhydrazine react with carbonyl compounds to give hydrazones. However, monosaccharides do not give simple phenylhydrazone derivatives. After the initial formation of a phenylhydrazone, further reaction occurs to give the osazone, which has two molecules of phenylhydrazine incorporated into it. 

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