170 



URIC ACID. 



The latter by prolonged boiling with water is converted into 

 urea and oxalic acid. 



NH CO 



CO 



NH 2 



NH 



8 v 

 )CO 



CO. OH 

 + CO. OH 



2. Allantoin series. 



By oxidation with potassium permanganate uric acid is decom- 

 posed into allantoin and carbonic anhydride. 



NH CO NH CO NH, 



CO C NH 



I I! )co 



NH C NH X 



CO 



CO 



-f H 2 -f = NH CH NH + C0 2 . 



When allantoin is boiled with nitric acid it is hydrated and 

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



NH CO NH 2 NH CO 



CO CO CO 



k /NH 9 



H CH NH-f-H 2 = CO 



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 



I I I 



2 CO CO CO 



I I I 



NH CH(OH) = NH CO + NH 



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 = 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 connec- 

 tion 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. 



