AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 83 



the latter of which we have just been considering and which 

 we have termed the hydroxy-acids, so also we have mixed com- 

 pounds containing amino and carboxyl groups which, similarly, 

 we know as amino-acids. 



CH3- COOH, CH2CI- COOH, CHo(OH) - COOH, CHoCNHo) - COOH 



Acetic acid Chlor-acetic acid Hydroxy-acetic acid Amino-acetic acid 



These amino-acids are acids in which a hydrogen of the radi- 

 cal is replaced by the amino group. This substitution may 

 take place in any one of the carbon groups composing the 

 hydrocarbon radical of the acid. The hydroxy-acids are both 

 alcohol and acid compounds and the amino-acids similarly 

 possess the properties of both acids and amines. As acids they 

 form salts, both metallic salts and esters, also acid chlorides 

 and acid amides. As amines they form amine or ammonium 

 salts with acids. They also react like ammonia with acid 

 chlorides, yielding acid amides in which the amino- acid less one 

 of the amine hydrogens replaces the hydroxyl group of another 

 acid. They may be prepared directly from the halogen acids 

 by the action of ammonia. 



Taking one of the simpler compounds, e.g. amino-acetic 

 acid, as an illustration, these relations may be clearly shown. 



CH3-COOH -> CH2CI-COOH+NH3 -> CH2(NH)2-COOH+HCl 

 Acetic acid Chlor-acetic acid Amino-acetic acid 



CHsCNHs) - COOR 



Ester 



CHsCNHa) - COONH4 



Ammonium salt (metal salt like 

 ammonium acetate) 



CHsCNH.) - COOH^- CHsCNHs) - CONH2 



Amino-acetic acid \^\^ Acid amide 



CH2NH2.HCI - COOH 



Hydrochloride (Amine salt like 

 methyl amine hydrochloride) 



CH2 - COOH 



NH-OC-R 



Acyl-amino-acid 



