THE CHEMISTRY OF COFFEE 167 



two oxygen atoms attached to the carbon atoms, numbers 2 and 6 

 respectively, and hence the term 2 : 6 dioxypurine. 



Theobromine or 3 : 7 dimethyl-xanthine. 

 NH CO 



CO 



c- 



N(CH3) 

 )CH 



NCCHs) C N 



Formula demonstrates that theobromine is derived from xanthine by 

 the replacement of two hydrogen atoms, at numbers 3 and 7 respec- 

 tively, by methyl groups (CH3). 



Caffeine or 1:3:7 trimethyl-xanthine or 1:3:7 trimethyl 2 : 6 

 dioxypurine. 



N(CH3) CO 



NCCHa) 

 ^^CH 



-N 



r 



CO 



NCCHs)— 



Formula indicates that caffeine is derived from xanthine by the re- 

 placement of three hydrogen atoms, at numbers i, 3, and 7 respec- 

 tively, by methyl groups (CH3). 



For further evidence to help substantiate this formula for caffeine, 

 it will be noted that caffeine contains three nitrogen-methyl groups 

 (i.e. 3 methyl-amino groups). Hence the caffeine formula may be 

 written C5HN02(NCH3)3. The relation of caffeine to uric acid 

 is shown by the nature of its oxidation products Thus, as uric acid, 

 when treated with potassium chlorate and hydrochloric acid, decom- 

 poses into alloxan and urea ; so caffeine, when similarly treated, 

 changes into dimethylalloxan and monomethylurea. 



