CHEMICAL BASIS OF THE ANIMAL BODY. 171 



2. Allantoin series. 



By oxidation with potassium permanganate uric acid is decomposed 

 into allantoin and carbonic anhydride. 



NH CO NH CO NH, 



I I 



CO 



CO 



CO 



CO C NH x 



NH C NH X + H 2 O + O = NH CH NH + C0 2 . 



When allantoin is boiled with nitric acid it is hyd rated and 



decomposes into a molecule of urea and one of allanturic acid. 



NH CO NH 2 NH CO 



I 



CO 



CO 



CO 



CH 



Allanturic acid is itself a substituted urea, viz. glyoxyl-urea, and 

 may be converted into parabanic and hydantoic acids. 



NH CO NH CO NH 2 CO. OH 



CO 



I 

 CO 



CO 



I 



NH CH (OH) = NH CO + NH CH 2 . 



Of these two acids the parabanic may as before be converted into 

 oxalic acid and urea, and hydantoic acid is a derivative, by simple 

 hydration, of hydantoin, which is itself a substituted urea, viz. 

 glycolyl-urea, containing a residue of glycolic acid, [CH 2 (OH) . COOH]. 



NH CO NH 2 CO. OH 



CO CO 



NH CH 2 (Hydantoin) + H 2 O - NH CH 2 . (Hydantoic acid.) 



The above reactions and decompositions show clearly how close is 

 the chemical relationship of urea and uric acid, and the connection is 

 still more evident when it can be shown that many of the products 

 described above as obtained during the decomposition of uric acid, viz. 

 the ureides, can be prepared from urea directly. Thus parabanic acid 

 (oxalyl-urea) is readily formed by the action of phosphorus oxychloride 

 on a mixture of urea and oxalic acid : 



NH CO 



^NH 2 CO. OH CO 



^NH 2 + CO.OH NH CO + 2H 2 0. 



