THE UREIDS. 83 



sodium amalgam uric acid is first transformed into xanthin, and sub- 

 sequently into hypoxanthin. The close relationship which exists 

 between the nucleinic bases and uric acid is thus further shown 

 (see page 80). 



Analogous to the synthetic formation of uric acid from urea and 

 glycocoll, we find that on decomposition with hydriodic acid the 

 substance yields carbon dioxide, ammonia, and glycocoll, viz., the 

 same products which are obtained from the nucleinic bases. 



From the reactions which have thus far been described the nature 

 of uric acid as a ureid is not apparent. If the hydrolytic decom- 

 position of the substance is effected less energetically, this becomes 

 manifest at once. On prolonged boiling with water it is decom- 

 posed into urea and dialuric acid, which latter further yields urea 

 and tartronic acid. In this manner the character of uric acid as a 

 diureid of the first order is demonstrated. The reactions which 

 take place are represented by the equations : 



(1) C 5 H 4 N40 3 + 2H 2 O = C 4 H 4 N 2 4 + CO(NH 2 ^ 2 



Uric acid. Dialuric acid. Urea. 



(2) C 4 H 4 NA + 2H 2 = C 3 H 4 4 + CO(NH 2 ) 2 



Dialuric acid. Tartronic acid. Urea. 



On treating with an oxidizing agent, in the presence of water, uric 

 acid is similarly decomposed into urea and the mono-ureid alloxan, 

 which can be further decomposed into urea and mesoxalic acid : 



(1) C 3 H 4 N 4 3 + H 2 O + O = C 4 H 2 N 2 O 4 + CO(NH 2 ) 2 

 Uric acid. Alloxan. 



(2) C 4 H 2 N 2 O 4 .+ H. 2 O = C 3 H 2 ? -f CO(NH 2 ) 2 



Alloxan. Mesoxalic 



acid. 



Its relation to the di-ureids of the second order is shown by oxidiz- 

 ing the substance with peroxide of manganese in neutral solution at 

 a moderate temperature. In this manner allantoin is formed, from 

 which, on further oxidation, urea and oxalic acid result : 



(1) C 5 H 4 N 4 3 + H 2 + O = C 4 H.N 4 8 + CO, 



Allantoin. 



(2) C 4 H 6 N 4 3 + 2H 2 + O = C 2 H 4 O 2 + 2CO(NH 2 ) 2 



Oxalic 

 acid. 



Of special interest, further, is the formation of murexid, or 

 ammonium purpurnte, which results when uric acid, even in minimal 

 amounts, is evaporated together with nitric acid, and the reddish 

 residue is brought in contact with ammonia. A beautiful purplish- 

 red color then develops, which is characteristic of uric acid and its 

 salts (murexid test). The reactions which take place may be rep- 

 resented by the equations : 



(1) C 5 H 4 N 4 3 +2H 2 = C 4 H 4 N 2 4 + CO(NH 2 ) 2 



Dialuric acid. 



(2) C 4 H 4 N 2 O 4 -f NH 4 OH = C 4 H 3 (NH 4 )N 2 O 4 + H 2 O 



Ammonium 



dial unite. 



(3) 2C 4 H 3 (NH 4 )NA + = C 8 H 4 ( NH 4 )N 6 O. + 3H 2 O 

 Ammonium dialurate. Murexid. 



