170 



URIC ACID. 



contains the residues of two molecules of urea. This corresponds to 

 the fact that nearly all the possible decompositions of uric acid yield 

 either a molecule of urea along with the more specific product of the 

 decomposition, frequently itself a derivative of urea, or else some 

 substance which can by further change be decomposed into urea and 

 some other product which is as before frequently a derivative of urea. 

 The close chemical relationship of urea and uric acid is thus clearly 

 shown, and may be further emphasized by the following reactions, 

 which illustrate and amplify at the same time the general statement 

 which has just been made. 



The decomposition of uric acid takes place in two stages, yielding- 

 two series of products, of which one is headed by alloxan and the other 

 by allantoin ; from these two substances respectively the other members 

 of each series are derived by subsequent decomposition. 



1. Alloxan series. 



By careful oxidation with nitric acid uric acid is decomposed into 

 a molecule of alloxan and one of urea. 



NH CO NH CO 



C NH CO CO NH 2 



il ;co ^co. 



H C NH^ + H 2 O + O = NH CO + NH 2 ^ 

 Alloxan is itself a substituted urea or ureide (antea, p. -164), viz. 

 mesoxalyl-urea, and by oxidation can be further converted into 

 parabanic acid (oxalyl-urea) and carbonic anhydride. 

 NH CO NH CO 



CO CO CO 



NH CO + =NH CO + CO 2 . 



By heating with alkalis parabanic acid is hydrated and yields 

 oxaluric acid. 



NH CO NH CO 



CO 



CO 



J, 



N'H- 



CO. OH. 



The latter by prolonged boiling with water is converted into urea 

 and oxalic acid. 



NH CO 



CO 



I 

 NH 



NH 2 CO . OH 



CO 



+CO.OH 



