NITROGEN COMPOUNDS 71 



Formic acid Carbamic acid 



1. CH 2 2 + NH 2 = CH 3 N0 2 +H. 

 (H-CO-OH) (NH 2 .CO-OH) 



Carbonic acid Carbamic acid 



or CH 2 3 +NH 2 = CH 3 N0 2 +OH. 

 (OH-CO-OH) (NH 2 .CO-OH) 



Carbamic acid Urea 



2. CH 3 N0 2 +NH 2 = CH 4 N 2 + OH. 

 (NH 2 .CO-OH) (NH 2 .CO.NH 2 ) 



Other substances may be formed from urea by still 

 further substitution. Thus, if the oxygen of urea is 

 replaced by an imido-group, NH, it will form guani- 

 dine, CH 5 N 3 . 



The xanthin compounds are closely related to 

 urea. Many if not all of them actually arise from 

 the decomposition of nucleo-proteids, which are 

 combinations of nucleic acid with true proteids. 

 The nucleic acids are not all of the same composi- 

 tion, although they generally contain four atoms of 

 phosphorus. They also yield different products, 

 but these always include one or more of the purin- 

 bases, which are derived from purin, C 5 H 4 N 4 , and 

 the most important of which are the following : 



Hypoxanthin or oxy-purin, C 5 H 4 N 4 0. 

 Xanthin or di-oxypurin, C 5 H 4 N 4 2 . 

 Uric acid or tri-oxypurin, C 5 H 4 N 4 3 . 

 Adenine or amino-purin, C 5 H 5 N 5 . 

 Guanine or amino-oxypurin, C 5 H 5 N 5 0. 

 Theobromine or dimethylxanthin, C 7 H 8 N 4 2 . 

 Caffeine or tri-methylxanthin, C 8 H 10 N 4 O 2 . 

 Carnine, C 7 H 8 N 4 5 . 



