XI] PLANT BASES 181 



It occurs in the leaves and beans of the Coffee plant (Coffea arabica), 

 in leaves of the Tea plant {Thea sinensis), in leaves of Ilex paragueiisis 

 ("Paraguay Tea"), in the fruit of Paullinia Cupana and in Kola nuts 

 (Cola acuminata). 



Expt. 164. Preparation of caffeine from tea i. Digest 100 gms. of tea with 500 c.c. 

 of boiling water for a quarter of an hour. Then filter through thin cloth or fine 

 muslin using a hot-water filter in order to keep the liquid hot. Wash the residue 

 with a further 250 c.c. of boiling water. Add to the filtrate a solution of basic lead 

 acetate until no more precipitate is formed. This removes proteins and tannins. 

 Filter hot and to the boiling filtrate add dilute sulphuric acid until the lead is pre- 

 cipitated as sulphate. Filter from the lead sulphate, and concentrate the solution, 

 with the addition of animal charcoal, to 250-300 c.c. Filter and extract the filtrate 

 three times with small quantities (50 c.c.) of chloroform. Distil off the chloroform 

 on a water-bath, and dissolve the residue in a small quantity of hot water. On 

 allowing the solution to evaporate very slowly, long silky needles of caifeine separate, 

 which may have a slightly yellow tint, in which case they should be drained, re- 

 dissolved in water, and boiled with the addition of animal charcoal. The yield 

 should be about 1*5 gm. 



Evaporate a little of the caffeine on a water-bath with bromine water. A reddish- 

 brown residue is left which becomes purple when treated with ammonia. 



Theobromine is 3, 7-dimethylxanthine: 



HN— c=0 



I I 

 0=C C— N • CH^ 



\ 

 CH 



CHg-N— C— N 



It occurs in the fruit of the Cocoa plant ( Theohroma Cacao), in leaves 

 of the Tea plant {Thea sinensis) and in the Kola nut {Cola acuminata). 



The chief pyrimidine bases found in the plant are uracil (2, 6-dioxy- 

 pyrimidine) and cytosine (6-amino-2-oxy-pyrimidine). They are con- 

 stituents of the molecule of nucleic acid (see p. 141). 



It seems appropriate at this point to mention the fact that urea is 

 said to have been detected in small quantity in the Spinach {Spinacia 

 oleracea), Cabbage (Brassica oleracea), Carrot (Daucus Carota), Potato 

 (Solanum tuberosum), Chicory {Cichorium Intybus) and other plants. 

 A point of considerable interest is the occurrence in the seeds of the Soja 

 Bean {Glycine hispida) and other Leguminosae of an enzyme, urease, 

 which decomposes urea into ammonia and carbon dioxide: 



/NH2 

 o=c(^ + HoO = 2NH3 4- CO.,. 



1 From Cohen, Practical Organic Cliemistry. 



