Osazone, formation

Compelling evidence that pathway A was operating came from work in which N was introduced into the 2-position of / -nitrophenylhydrazine , This was then used to make the p-nitrophenylhydrazones of glucose, benzoin and 2-hydroxycyclohexanone. These were reacted with excess unlabelled p-nitrophenylhydrazone and the ammonia liberated was shown to possess, in the early stages of the reaction, the same isotopic composition as N2 of the parent p-nitrophenylhydrazine. In the 2-hydroxycyclohexanone case, the imine intermediate was isolated (as its A-acetylenamine) and shown to proceed to osazone after hydrolysis. 

As expected from both mechanisms A and B, [l- H]mannose and -glucose form osazones in which the label is almost completely retained,whereas 

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Phenylhydrazine is, however, frequently supplied in the form of its hydro chloride or sulphate, since these salts on exposure to light darken less rapidly than the free base. If these salts are used, however, osazone formation is unsatisfactory, partly because the mineral acid formed by hydrolysis of... 

Phenylhydrazine on exposure to light slowly darkens and eventually becomes deep red in colour salts of the base share this property but to a lesser degree, the sulphate and acetate (of the common salts) being most stable to light. Phenylhydrazine is largely used in organic chemistry to characterise aldehydes and ketones as their phenyl-hydrazones (pp. 342, 345), and carbohydrates as their osazones (pp. 136-140). It is readily reduced thus in the process of osazone formation some of the phenylhydrazine is reduced to aniline and ammonia. On the... 

Osazone formation. The preparation of glucosazone has already been given (p. 137). It may be carried out on a small scale by either of the following methods, according as (a) the phenyl hydrazine base, or (Z>) one of its salts, is used. 

Osazone formation. Fructose forms an osazone identical with that obtained from glucose. It is, however, usually formed more quickly... 

Osazone formation. Forms an osazone, m.p. 206 (see however footnote, p. 140) this osazone, unlike glucosazone, is soluble in hot water. See p. 139 for preparation. Examine the crystals under the microscope and note the sheaves of plates, not needles (Fig. 63(B),... 

Osazone formation. Forms a yellow osazone, m.p. 208° soluble in hot water. See p. 137 for preparation. If examined under the microscope very characteristic clusters of hedge-hog crystals will be seen (Fig. 63(c), p. 139). The difference in the crystalline appearance of lactosazonc and maltosazone should be very carefully noted, as this difference forms the chief and most reliable method of differentiating between these two sugars. 

The approximate times of osazone formation in minutes are given in Table 111,139. The product from mannose is the simple hydrazone and is practically white. Arabinose osazone separates first as an oil, whilst that from galactose is highly crystalline. Lactose and maltose give no precipitate from hot solution. 

Glycosides don t form osazones (see the later Osazone formation section for more on these). 

The carbonyl group (and adjacent alcohol) oxidizes with excess phenyl hydrazine (PhNHNH2) to form an osazone (see Figure 16-15). Osazone formation is very important in determining the relationship between various monosaccharides. For example, both D-glucose and D-mannose produce the same osazone, so they re epimers. Epimers differ by only one chiral center, which osazone formation destroys. 

Since mannose and glucose are C epimers, they are identical at the C, C. C, and C" portions of the molecule, which are unaltered during osazone formation. The chiral C , which differs in each hexose, loses chirality in the osazone and becomes identical for both mannose and glucose. 2-Ketohexoses give osazones in which the C CH,OH is oxidized. Since C, C, C and C of fructose and glucose are identical (Problem 22.8), fructose also gives the same osazone. Identical portions are in the boxes below. 

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). ... 

Fischer confirmed the disaccharide formulation for twranose by osazone formation (1894). Turanose is formed from the trisaccharide melezitose, which is fermentable with yeast. 

B Reactions with Amines and Hydrazines Osazone Formation... 

In general, we find that the nonreducing disaccharides give none of the carbonyl reactions observed for glucose, such as mutarotation and osazone formation, except when the conditions are sufficiently acidic to hydrolyze the acetal linkage. 

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. 

These recent investigations may lead to further clarification of the mechanism of osazone formation, one of the classical sugar reactions. 

Chelation, in osazone formation, III, 43 Chemical constitution, physiological activity and, of ascorbic acid analogs,... 

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