UREIDES 



Alloxantin is readily reduced or oxidised. 



Alloxan is prepared : 3 gm. of finely powdered alloxantin are mixed with 

 3 gm. of concentrated nitric acid and 7 gm. fuming nitric acid (sp. gr. i -5). 

 Slow oxidation occurs on standing and large crystals of alloxan are formed. 

 The oxidation is complete in about 2 days and is shown by the complete 

 solubility of the crystals in water. The crystals are placed on a porous plate 

 to drain off the nitric acid and dried in the air. They are recrystallised from 

 water. 



Properties. 



Alloxan is a white crystalline substance which separates from water in 

 long shining rhombic prisms containing 4 molecules of water of crystallisation ; 

 on exposure to air, the crystals effloresce and lose 3 molecules of water ; the 

 last molecule of water is driven off by heating to 150. 



It is easily soluble in water ; the solution has an acid reaction and dis- 

 agreeable taste and it slowly turns the skin a purple red. A deep indigo 

 blue colour is formed when ferrous sulphate is added to its solution. 



If a few drops of its solution in water be evaporated to dryness and the 

 reddish residue be treated with ammonia, it turns purple. 



Reactions. 



(1) Alloxantin is formed by the action of reducing agents upon alloxan 

 in the cold : 



NH-CO , CO NH 



I I /\ I I 

 CO C C CO 



II II 



NH CO CO NH 



Alloxantin. 



(2) Dialuric acid is formed by the action of reducing agents on alloxan 

 on warming. 



(3) Parabanic acid and carbon dioxide are formed by the oxidation of 

 alloxan with boiling dilute nitric acid. 



(4) Barbituric acid is obtained from alloxantin by the action of con- 

 centrated sulphuric acid. 



(5) Dilituric acid is formed by the action of fuming nitric acid upon 

 alloxantin, or by the oxidation of violuric acid. 



(6) Violuric acid is formed by the action of potassium nitrite upon 

 alloxantin, or by the action of hydroxylamine upon alloxan. 



(7) Uramil is formed by the reduction of dilituric acid and violuric 

 acid. 



These ureides are white crystalline substances which are easily soluble 

 in water; uramil is only slightly soluble and becomes red on exposure to 

 the air. 



