Osazones structure

It has been assumed in the preceding section that the phenylosazones of turanose, maltose, and D-glucosyl-D-arabinose have structures like that of D-glucose pjienylosazone. This normal osazone structure is now proved40 by the following data for the turanose and maltose osazones, and there can be little doubt that it also holds for the osazone of d-glucosyl-D-arabinose. Turanose phenylosazone has been converted by... 

The formazan reaction offers a means for clarifying the structure of the mixed A and mixed B osazones. The former was described by Voto6ek and Vondra6ek as acyclic n-glucose l-(iV -phenyl)-2-(Ar -methyl-A -phenyl)osazone, and the latter as acyclic n-glucose l-(A -methyl-i r -phenyl)-2-(V -phenyl)osazone. The Percivals assigned the same n-fruc-topyranose l-(Ar -phenyl)-2-(V -methyl-Ar -phenyl)osazone structure to the compounds, but differentiated them as probable syn and avli forms. 

However, since mixed osazone A undergoes no formazan reaction, even in alkaline solution, it would appear that the n-glucose l-(iV -methyl-iV -phenyl)-2-(iV -phenyl)osazone structure, - hitherto thought to be incapable of coupling, should be assigned to this substance (instead of to the mixed osazone B). This view is fully confirmed by recent work of Henseke and Hautschel. ... 

The principal reactions of this class of compounds are summarized in Scheme 172. In most of these reactions the reactive nucleophilic center is the terminal NHj group, although the other exocyclic nitrogen may also be involved, as shown by acetylation, which yields 284 and 285. However, the structure of compound 281 is not the one proposed in a recent report (1582) that attributes the attack to the other exocyclic nitrogen. The formation of osazones (287) from sugars, 2-hydrazinothiazoles, and hydrazine has been reported (525, 531). 

D-Galactosido-D-glucosone and D-glucosido-D-galactosone were prepared by Fischer and Armstrong203 by the action of benzaldehyde on the osazones of synthetic disaccharides. Both osones were hydrolyzed by emulsin. There is some doubt as to the precise structure of the parent sugars.206... 

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 trihydroxypropyl derivative 63 was prepared from dehydro-L-ascorbic acid phenylosazone (62) by opening the lactone ring with warm alkali and acidifying the mixture after a few minutes, whereupon the pyrazolinone 63 separated immediately.63 The structure of this compound was established by degradation,63 and confirmed by a study of its n.m.r. spectrum.64 The p-tolyl-, p-(bromophenyl)-, and p-(iodophenyl)-osazones of dehydro-L-ascorbic acid were also converted into the corresponding l-aryl-4-phenylazo-3-(trihydroxy-propyl)-5-pyrazolinone, and their acetylation and benzoylation products were prepared.64... 

Another type of substituted pyrazole is obtained by refluxing osazones with acetic anhydride during the acetylation, two molecules of water per molecule are removed. The structure of the resulting 5-(D-g/ycero-diacetoxyethyl)-3-formyl-l-phenylpyrazole 2-acetyl-2-phenylhydrazone (71) was determined by deacetylation followed by oxidation with (a) periodate to a pyrazolaldehyde (72), and (b) permanganate to the known l-phenyl-pyrazole-3,5-dicarboxylic acid (73), as well as by a study of its n.m.r. spectrum, which confirmed the pres-... 

Problsm 22.26 The pentoses o-xylose and o-lyxose give the same osazone. Xylose and lyxose are oxidized to an optically inactive and optically active dicarboxylic acid, respectively. Give their shorthand structural formulas. <... 

Problem 22.34 (a) Write shorthand structures for the three o-2-ketohexoses other than o-fructose. (b) Which one does not give a meso alditol on reduction (c) Which one gives the same osazone as does D-galactose (Problem 22.22)7 <... 

Problem 22.57 (a) Write shorthand open structures for a ketohexose (I) and an aldohexose (II) which form the same osazone as D-(-)-altrose (III), the C epimer of o-mannose, and for the aric acid (IV) formed by HNOj oxidation of the o-aldohexoses (III) and o-talose (V). (b) Write shorthand and conformational structures for -D-altropyranose (VI). ... 

Peat, Stanley, The Chemistry of An-hydro Sugars, 2, 37-77 Peat, Stanley. See also, Bourne, E. J. Percival, E. G. V., The Structure and Reactivity of the Hydrazone and Osazone Derivatives of the Sugars, 3, 23-44... 

Since the discovery of the reaction of phenylhydrazine with sugars to form osazones by Fischer,35 many investigations have utilized this reaction in the identification and separation of sugars, but the precise structures of osazones and their mode of formation are still in doubt.34 There is no doubt, however, that the initial reaction involves the formation of a hydrazone, which then reacts further to yield eventually a f)u-l,2-hydrazone or osazone. 

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