X] THE PLANT BASES 165 



The chief purine bases which occur in plants are xanthine, caffeine, 

 theobromine, guanine, hypoxanthine and adenine. 



Xanthine may be regarded as 2, 6-dioxypurine: 

 HN— c=0 



I I 



O^C C— NH 



\ 

 CH 



HN— C— N 

 It is widely distributed in plants and has been found in leaves of the 

 Tea plant {Thea sinensis), in the sap of the Beetroot {Beta) and in various 

 seedlings. 



Caffeine or theine is 1, 3, 7-trimethylxanthine: 



CHa'N— c=0 



I i 

 0=C C— N • CH. 



\ 

 CH 



CHg-N— C— N 



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 paraguensis 

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

 (Cola acuminata). 



Expt. 158. Preparation of caffeine from tea^. Digest 100 gms. of tea with 500c.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 cafteiue 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. 



1 From Coaen, Practical Organic Chemistry. 



