Osazone, formation formula

Problem 22.38 Use shorthand formulas to show how osazone formation establishes the glucose unit of lactose to have the hemiacetal linkage (Problem 22.37). ... 

Kinetics One of the many applications of studies of reaction kinetics (see Sec. 1.7.3 for experimental details) is in the determination of structural formulas and especially stereoformulas. A familiar example is osazone formation Glucose, matmose, and fructose give the same osazone, but at quite different rates so that they can easily be distinguished by a kinetic study. As another example, suppose a complex cyclohexanone is reduced with lithium aluminum hydride to give a mixture of two cyclo-hexanols. If one of these alcohols is acetylated much more rapidly than the other, it is very likely that the former has the equatorial hydroxyl group and the latter the axial hydroxyl group. Often qualitative observations of relative rates will serve as in this case. 

Formazan formation, the presence of two 0-acetyl groups in the acetylation product of the osazone formazan obtained, and the comparative study of the ultraviolet spectra, are all in harmony with formula XXII proposed by Hardegger and Schreier i and afford evidence of its correctness. 

The structure of the osazone derived from dehydroascorbic acid remains in dispute. Recently (Vol. 13, p. 95) it was described as the phenylhydrazine-phenylazo-structure (34), but it is now claimed that the bis(hydrazone) formula (35) fits the n.m.r. and u.v. data more satisfactorily. The structure of the bi-cyclic oxidation product of (35) has been shown to be a 3,6-anhydride (36) by n.m.r. and m.s. A n.m.r. study of the formation of dehydroascorbic acid hydrazones revealed that the two 2-phenylhydrazides (37) were formed initially and subsequently underwent dehydration to give the two rotationally isomeric 2-phenyIhydrazones. Reaction of 6-bromo-6-deoxy-isoascorbic acid (D-ery thro) with phenyl hydrazine afforded the cyclized bis(hydrazone) (38). Treatment of D-threo-ascorbic acid bis(phenylhydrazone) with caustic soda afforded the cyclized product (39). The corresponding D-erythro- and L-threo-isomers were also prepared and the side-chains have been modified in various ways. 

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