296 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Adenine. 



Adenine was first obtained by Kossel from the pancreas, but has 

 since been obtained from other organs and from plants. Its constitu- 

 tion was proved by synthesis (Emil Fischer). 



Preparation. 



Adenine may be prepared from extracts of tea, or from nucleic acid, or 

 from tissue extracts (p. 584). 



From Nucleic Acid. 



The ammoniacal filtrate free from guanine is acidified with 20 per 

 cent, sulphuric acid, heated to boiling and treated with 10 per cent, copper 

 sulphate solution as long as a white precipitate is formed and until yellow 

 cuprous oxide begins to be formed. (Usually sodium bisulphite solution is 

 added with the copper sulphate solution, but this is not necessary when the 

 solution contains pentose.) The mixture is boiled for several minutes and 

 filtered. The precipitate is washed with boiling water, suspended in hot 

 water and decomposed with hydrogen sulphide. The filtrate from the 

 copper sulphide is evaporated to dryness and the residue of adenine is 

 crystallised from hot 5 per cent, sulphuric acid and decolorised with char- 

 coal, if necessary. Pure adenine sulphate is obtained. 



Properties. 



Adenine forms long colourless needles with 3 molecules of water of crystal- 

 lisation, or whetstone-like crystals ; the former become opaque on exposure 

 to air and if heated in insufficient water become opaque at 53. It sublimes 

 at 220 and at 250 partially decomposes. It melts if heated rapidly in a 

 capillary tube at 360-365, becoming brown before reaching the melting-point, 

 at which temperature it decomposes. 



It is soluble with difficulty in cold water, i part in 1086 parts, but it is 

 more easily soluble in hot water. The solution has a neutral reaction. It 

 dissolves in alkalies, mineral acids and acetic acid and is precipitated on 

 neutralising the solutions. It is more easily soluble in ammonia than guanine, 

 but less so than hypoxanthine. 



It forms salts with acids and other salts ; the double salt with gold chloride 

 helps to distinguish it from the other nuclein bases. The picrate is very in- 

 soluble and serves for isolating it from solution and separating it from hypo- 

 xanthine. 



Reactions. 



Adenine gives no reaction on evaporation with nitric acid or with chlorine 

 water. The reaction with diazobenzenesulphonic acid is positive if excess of 

 alkali be avoided. 



Adenine behaves in a characteristic manner on heating with zinc and 

 hydrochloric acid on the water-bath. The solution turns purple-red ; if 

 filtered, made strongly alkaline with caustic soda and allowed to stand or 

 shaken with air, it turns ruby-red and then brownish-red. Guanine does not 

 give this reaction, but hypoxanthine gives the colours, though fainter. 



