PARAXANTHIN. 401 



succeeded in transforming theobromin into this base. Later with 

 Clemm he synthesized it direct from 1.7-dimethyl uric acid, which 

 with phosphorus oxychlorid yields chlorparaxanthin. 



The supposition of Fischer that paraxanthin in the urine was de- 

 rived from caffein in the same way that heteroxanthin results from 

 theobromin, i. e., by the splitting off of the methyl group in position 

 3 has been recently confirmed. When caffein is fed to a dog in small 

 doses it is excreted as 3 -methyl xanthin. If, however, large doses 

 of caffein are administered some of the base passes through un- 

 changed. In addition the urine contains all three dimethyl xanthins 

 (paraxanthin, theophyllin and theobromin) and also 3-methyl xan- 

 thin (Kriiger^). In view of this fact and inasmuch as paraxanthin 

 has not been met with as a direct cleavage product of nuclein nor 

 found in the urine of dogs or of leukemic patients it is evident that 

 this base when present in the urine owes its origin to the caffein con- 

 tained in coffee or tea. 



Paraxanthin is obtained in colorless, glassy, generally six-sided 

 plates which are arranged in tufts or rosettes. From very concen- 

 trated aqueous solutions it crystallizes in long, colorless, interwoven 

 needles which on drying exhibit the silky luster of tyrosin. The 

 crystals belong to the monoclinic system, and may crystallize with, 

 as well as without, water (Salomon^). 



If water is present, on careful heating (110°) the crystals lose 

 their brilliancy and become whitish and opaque, and at 120°— 130° 

 the water is completely driven off. The conditions under which 

 crystals containing water are formed are not known, probably by 

 slow crystallization, whereas rapid crystallization from hot concen- 

 trated solution yields the anhydrous needles. At about 170°— 180° 

 sublimation takes place. The melting-point is at about 284° (Kossel), 

 295°- 296° (Fischer). Theophyllin melts at 264°, while theobromin 

 sublimes without melting, and caffein melts at 232°- 233°. It can 

 be heated to 250° without melting or suffering any decomposition, 

 but when heated more strongly it gives off white vapors which 

 possess a distinct iso-nitril odor ; at the same time it carbonizes and 

 takes fire. When evaporated with concentrated nitric acid, as in the 

 ordinary xanthin test, it gives only a slight yellow residue. On the 

 other hand when evaporated with chlorin water or with an acid and 

 a chlorate the dry residue on exposure to an ammoniacal atmosphere 

 under a bell-jar, gives a beautiful rose-red color (so-called Weidel's 

 test). 



It is difficultly soluble in cold water (though more easily than 

 xanthin); somewhat more readily soluble in hot water (24 parts, 

 Fischer) ; insoluble in ether and alcohol. It is soluble in ammonium 



^Beriehte, 32, 2818. 



'Virchov/ a Archives, 125,554; Berichte, 16,195; 18, 3406; Zeits. physiol. Chem., 

 11, 415 ; 13, 187. 

 26 



