ADENIK 353 



is soon oxidized by the oxygen of the atmosphere into a brownish, 

 amorphous substance, apparently identical with azulmic acid. 



Ferric chlorid imparts to an aqueous solution of adenin an intense 

 red color which is not affected by heating. Copper sulphate pro- 

 duces an amorphous grayish-blue precipitate, which is easily soluble 

 in dilute acids and ammonia. The light-blue solution in fixed alka- 

 lis on warming gives a precipitate of copper oxid. 



Drechsel's reaction. In 1892 Drechsel showed that certain xan- 

 thin bases are precipitated by an ammoniacal solution of cuprous 

 chlorid ; or from fixed alkaline solution by Fehling's solution in the 

 presence of a reducing substance. In addition to uric acid, which 

 has been known to give this reaction, xanthin, guanin, hypoxanthin, 

 creatin, and creatinin, the latter on boiling, reacted. Balke applied 

 the test to fixed alkaline solutions, using Fehling's solution, and as 

 reducing substances hydroxylamin hydrochlorid, or dextrose. He 

 found that adenin, hypoxanthin, xanthin, heteroxanthin, paraxanthin, 

 carnin, protamin, and uric acid gave precipitates, whereas theobro- 

 min and caffein did not. Kriiger employed copper sulphate and 

 sodium bisulphite, the advantage being that the precipitation can 

 take place in neutral, acid, or alkaline solutions. The results differ 

 somewhat with the kind of reducing agent employed. Thus copper 

 sulphate and sodium bisulphite precipitate uric acid, adenin, methyl 

 adenin, hypoxanthin, guanin, also dimethyl hypoxanthin from cold 

 concentrated solution ; theobromin, caffein, creatin, creatinin are 

 not precipitated. With copper sulphate and sodium hyposulphite, 

 adenin, methyl adenin, and guanin are readily precipitated ; hypo- 

 xanthin only on heating (separation from adenin), whereas the other 

 six compounds are not precipitated. The precipitates are soluble in 

 excess of sodium hyposulphite. 



Adenin and hypoxanthin can, therefore, be completely precipi- 

 tated, especially by the aid of heat, from their solution by copper 

 sulphate and sodium bisulphite. Hence this reagent could be used 

 as a substitute for ammoniacal silver solution in the method of sepa- 

 ration and even of estimation by determining either the amount of 

 copper, or of nitrogen by Kjeldahl's method. The adenin precipi- 

 tate is colorless and gelatinous ; changes on exposure to a light or 

 brownish green, and on drying it becomes dark green. It is easily 

 soluble in mineral acids, especially nitric; slowly soluble in hot 

 acetic acid. It is not decomposed with sodium hydrate; readily de- 

 composed with alkali sulphids, and is readily soluble in ammonia. 

 It is soluble in about 200,000 parts of hot water. 



On treatment with nitrous acid it is converted into hypoxanthin 

 according to the equation : 



C5H5N5 + HNO, = CbH^N^O + N, + H,0. 



Kossel obtained 72 per cent, of the theoretical yield. Since then 

 23 



