Alloxan-5-oxime

Alloxan 5-oxime EINECS 201-741-4 5-Hydroxyimino-barbituric acid 5-lsonitrosobarbituric acid NSC 56338 2,4,5,6(1H,3H)-Pyrimidinetetrone, 5-oxime Violuric acid. Crystals mp = 240-241 (dec) insoluble in H2O, soluble in EtOM. 

The action of nitrous acid on isobarbituric acid yields isovioluric acid (alloxan-6-oxime), which is rearranged to violuric acid (alloxan-5-oxime) by means of add, but otherwise behaves much like alloxan. 

Alloxan forms an oxime (1007) which is the same compound, violuric acid, as that formed by nitrosation of barbituric acid likewise, a hydrazone and semicarbazone. Reduction of alloxan gives first alloxantin, usually formulated as (1008), and then dialuric acid (1004 R = OH) the steps are reversible on oxidation. Vigorous oxidation with nitric acid and alkaline hydrolysis both give imidazole derivatives (parabanic acid and alloxanic acid, respectively) and thence aliphatic products. Alloxan and o-phenylenediamine give the benzopteridine, alloxazine (1009) (61MI21300). 

We have found that the action of nitrous acid on isobarbituric add (IV) leads to the formation of an isomer of violuric acid which we term iso-violuric acid (VI). Since the phenolic character of isobarbituric add has been established by its behavior toward acetic anhydride, hydroxylamine, hypobromous acid, diazomethane and potassium ferricyanide, it was anticipated that 5-hydroxy-6-nitrosouracil (V) would be obtained. The behavior of the product, however, indicated it to be the tautomeric form (VI) (alloxan-6-oxime). 

Since isovioluric acid represents an unusual oxime of alloxan, it is not surprising to find that dilute hydrochloric add rearranges it to violuric acid. The simplest mechanism which suggests itself for this reaction involves two steps (1) the hydrolysis of isovioliuic add to alloxan and hydroxylamine, and (2) the recondensation of these to form violuric add. 

Alloxan-6-oxime-5-phenylhydrazone VIII).— The preparation of this product was similar to that of the dioxime given above. An 80% 5deld of brilliant yellow platelets, m. 268° (dec.) was obtained. 

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