CHEMICAL PROPERTIES 371 



or as a removal of an atom from the monohydrate. Dialurate is oxidized 

 to alloxan by Og and many other oxidants, so that it is diabetogenic by 

 virtue of its conversion to alloxan. 



It is somewhat surprising that the quinonoid structure for alloxan, which 

 one would expect to be of some importance, is not reduced to isodialuric 



OH OH 



I I +2 H ^ *• I |l 



O^ N OH HO N OH 



Alloxan Isodialuric acid 



(quininoid 

 structure) 



acid, the aromatic resonance stabilizing the tetrahydroxy structure. This 

 is an important point with regard to the reaction with thiols and the 

 formation of alloxantin. It is questionable if the characterization of these 

 substances is as precise or reliable as is usually assumed, and perhaps more 

 attention should be paid to the quinonoid character of alloxan. 



Eeduction of alloxan is often accompanied by the formation and precipi- 

 tation of the relatively insoluble alloxantin, which is usually formulated 



O o 



HN' Y r NH 



O^^N A O^N^O 

 H H 



Alloxantin 



as shown, arising by conjugation of alloxan and dialuric acid, but again one 

 can speculate that alloxantin is a molecular compound such as is formed 

 from quinones and hydroquinones (i. e., a quinhydrone), possibly by hydro- 

 gen bonding. This might be expected to occur with alloxan and isodialuric 

 acid. The rates of formation and splitting of alloxantin appear to be very 

 fast. The equilibrium constant, K = (alloxan) (dialuric acid)/(alloxantin), 



