1911 Encyclopædia Britannica/Caffeine

CAFFEINE, or Theine (1.3.7 trimethyl 2.6 dioxypurin), C₈H₁₀N₄O₂·H₂O, a substance found in the leaves and beans of the coffee tree, in tea, in Paraguay tea, and in small quantities in cocoa and in the kola nut. It may be extracted from tea or coffee by boiling with water, the dissolved tannin precipitated by basic lead acetate, the solution filtered, excess of lead precipitated by sulphuretted hydrogen and the filtered liquid then evaporated to crystallization; or, tea is boiled with water, and the whole then evaporated to a syrup, which is mixed with slaked lime, evaporated to dryness on the water-bath and extracted with chloroform (P. Cazeneuve, Bull. de la soc. chim. de Paris, 1876–1877, 27, p. 199). Synthetically it may be prepared by the methylation of silver theobromine and silver theophyllin or by boiling heteroxanthine with methyl iodide and potash. E. Fischer and L. Ach (Berichte, 1895, 28, p. 3135) have synthesized it from dimethyl alloxan, whilst W. Traube (Berichte, 1900, 33, p. 3435) has obtained it from 1.3 diamethyl 4.5 diamino 2.6 dioxypyrimidine. On the constitution of caffeine see Purin and also E. Fischer (Annalen, 1882, 215, p. 253).

Caffeine crystallizes in long silky needles, which are slightly soluble in cold water. It becomes anhydrous at 100°C. and melts at 234° to 235°C. It has a faint bitter taste and gives salts with mineral acids. On oxidation with nitric acid caffeine gives cholesterophane (dimethyl parabanic acid), but if chlorine water be used as the oxidant, then it yields monomethyl urea and dimethyl alloxan (E. Fischer).