Osazone test

Reaction (reduction) with phenylhydrazine (osazone test) The open chain form of the sugar reacts with phenylhydrazine to produce a pheny-losazone. Three moles of phenylhydrazine are used, but only two moles taken up at C-1 and C-2. 

Heat amygdalin with dilute sulphuric acid under reflux for a short time. Remove benzaldehyde and hydrocyanic acid by steam distillation. Test for benzaldehyde (phenylhydrazone test) and hydrocyanic acid (Prussian blue test) in distillate, and for glucose (osazone test) in residue. 

Since they contain no active methine groups, - the fcetose phenyl-hydrazones do not yield formazans this lack of reaction is therefore suitable for distinguishing ketoses from aldoses. It is more specific than the osazone test, frequently used in the identification of sugars, for it yields a different formazan from each aldose, whereas the osazone test does not differentiate between epimers. 

Incubate at 40°, 10 ml. of sucrose solution with 1 ml. of sugar-free invertase extract, prepared from yeast. After ten to fifteen minutes test samples of the mixture for reducing sugar, or demonstrate the presence of glucose and fructose by the osazone test, which, however, does not differentiate between these two sugars. 

Glucose is by far the commonest reducing sugar found in urine it may be identified by the osazone test (p. 115), and by yeast fermentation (p. 113), and verified by the observation of an accompanying hyperglycsemia. 

The osazone method is still of use as a confirmatory test. The urine... 

Problem 22.13 Why do aldoses give positive Fehling and osazone reactions but negative Schiff and bisulfite tests M... 

Put 1-mL portions of phenylhydrazine reagent into each of four cleaned, numbered test tubes. Add 3.3-mL portions of 0.1 M solutions of glucose, fructose, lactose, and maltose and heat the tubes in the beaker of hot water for 20 min. Shake the tubes occasionally to relieve supersaturation and note the times at which osazones separate. If after 20 min no product has separated, cool and scratch the test tube to induce crystallization. 

The typical aldehyde reactions of D-(-H)-glucose—osazone formation, and perhaps reduction of Tollens and Fehling s reagents—are presumably due to a small amount of open-chain compound, which is replenished as fast as it is consumed. The concentration of this open-chain structure is, however, too low (less than 0.5%) for certain easily reversible aldehyde reactions like bisulfite addition and the Schiff test. 

Hexosamines, Dische test for, 49 Hexose, o-arabino-, (p-bromophenyl)-osazone, 5,6-dimethyl ether, 148 (A -methyl-JV -phenyl)osazone, 138, 141... 

The choice between Weygand s Schemes A and B proved difficult, with authors at one time favoring one Scheme and then the other. An early attempt to test the validity of the respective Schemes was made by Ruggli and Zeller, using diphenylacetoin (p-bromophenyl)hydrazone and di-phenylacetoin (p-nitrophenyl)hydrazone, which they treated with phenylhydrazine they obtained the bis(phenylhydrazone) in both cases. This result was taken by them to exclude Scheme B, which, under similar conditions, should yield a mixed osazone, but this conclusion is now invalidated by our knowledge of transhydrazonation, that is, the exchange of hydrazone residues, as in (20) (21), a possibility, which has caused... 

---