294 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Hypoxanthine. 



Hypoxanthine, like xanthine, occurs widely distributed in the 

 tissues of animals and plants. 



Its constitution has been proved by synthesis by Emil Fischer. 

 Preparation. 



It is prepared most easily by the action of nitrous acid upon adenine. 

 Its isolation from tissues necessitates a complicated process of separation from 

 other purine bases (p. 584). 



Properties. 



Hypoxanthine forms colourless microscopic crystals, soluble with difficulty 

 in water; i part is soluble in 1400 parts of water at 19 and in 70 parts of 

 boiling water. It is practically insoluble in alcohol. 



It is soluble in dilute acids and a^alies and in ammonia and forms salts 

 with acids, bases and other salts, which crystallise readily.' 



The hydrochloride C 5 H 4 N 4 O . HCl + H 2 O and other salts with acids 

 decompose on recrystallisation from water. 



The nitrate C 5 H 4 N 4 O . HNO 3 + H 2 O is insoluble in nitric acid. Platino- 

 chlorides, picrates and other salts are known. 



Reactions. 



Hypoxanthine differs from xanthine in not giving reactions with nitric 

 acid and chlorine water, but the reaction with diazobenzene sulphonic acid is 

 positive if an excess of alkali be avoided. 



It is precipitated from solution by ammoniacal silver nitrate and by copper 

 sulphate and sodium bisulphite. 



Guanine. 



Guanine is also found widely distributed in the tissues of animals 

 and plants and is a constituent of nucleic acid It is the chief con- 

 stituent of the excrement of spiders and is found in Peru guano in 

 small quantities. It is deposited in the muscles and joints of pigs in 

 certain cases of illness and it occurs in fish scales and other epidermal 

 structures of fishes. 



Fischer has proved its constitution by synthesis. 



Preparation. 



From Guano. 



The material is extracted with boiling dilute lime water and then with 

 sodium carbonate solution as long as the extracts are coloured. On acidify- 

 ing the extracts with acetic acid, uric acid and guanine separate out. This 

 mixture is boiled with dilute hydrochloric acid and made alkaline with am- 

 monia ; the guanine is precipitated. 



