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XANTHINE. 189
advantage in their precipitation (Kruger) 1
. This behavior of the
purine bases serves just as well as the behavior with the silver solution
for their precipitation and preparation.
HN—CO
I I
Xanthine, C5H4 N402 ,
= OC C—NHV (2, 6-dioxypurine) is f0Und
I II
>CH
HN—C — W
in several cellular organs. It occurs in small quantities as a physio-
logical constituent of urine, and it occasionally has been found as a urinary
sediment, or calculus. It was first observed in such a stone by Marcet.
Xanthine is found in larger amounts in a few varieties of guano (Jarvis
guano)
.
Xanthine can be prepared, according to E. Fischer, by boiling uric
acid with 25 per cent hydrochloric acid or, according to Sundvik 2
by
heating uric acid with anhydrous oxalic acid in glycerin to about 200° C.
Xanthine is amorphous, or forms granular masses of crystals, or may
also, according to Horbaczewski,3
separate as masses of shining, thin,
large rhombic plates with 1 mol. water of crystallization. It is very
slightly soluble in water, in 14,151-14,600 parts at 16° C, and in 1300-
1500 parts at 100° C. (Almen 4
). It is insoluble in alcohol or ether, but
is readily dissolved by alkalies and with difficulty by dilute acids. With
hydrochloric acid it gives a crystalline, difficultly soluble combination.
With very little caustic soda it gives a readily crystallizable compound,
which is easily dissolved by an excess of alkali. Xanthine dissolved in
ammonia gives with silver nitrate an insoluble, gelatinous precipitate
of silver xanthine. This precipitate is dissolved by hot nitric acid, and
by this means an easily soluble crystalline double compound is formed.
Xanthine in aqueous solution is precipitated on boiling with copper
acetate. At ordinary temperatures xanthine is precipitated by mercuric
chloride and by ammoniacal basic lead acetate. It is not precipitated
by basic lead acetate alone.
When evaporated to dryness in a porcelain dish with nitric acid,
xanthine gives a yellow residue, which turns, on the addition of caustic
soda, first red, and after heating, purple-red. If we place some chlorinated
lime with some caustic soda in a porcelain dish and add the xanthine
1
Balke, Zur Kenntnis der Xanthinkorper, Inaug.-Diss. Leipzig, 1893 ; Kruger
Zeitschr. f. physiol. Chem., 18.
2
E. Fischer, Ber. d. d. chem. Gesellsch, 43; Sundvik, Zeitschr. f. physiol.Chem.
76. In regard to the synthesis of xanthine and other purines see E. Fischer, footnote
3, p. 186.
5
Zeitschr. f. physiol. Chem., 23.
4
Journ. f. prakt. Chem., 96.
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