CH. IV.] AMINO-ACIDS. 69 



GROUP III. Basic ampholytes. 



Lysine (a, e, di-amino caproic acid) 



CH 2 (NH 2 ).CH 2 .CH 2 .CH 2 .CH(NH 2 ).COOH. 



Arginine ((S-guanidine-a-amino valeric acid) 



MTLT ^^ 



NH ^> C - NH - CH 2-CH 2 .CH 2 .CH(NH 2 ).COOH. 



Histidine (^-imidazole-alanine) 

 CH 

 / \ 

 NH N 



2 .CH(NH 2 ).COOH. 



General reactions of the amino-acids. 



i . They form two classes of salts : 



(a) With acids, owing to the presence of the 



- NH 2 group (see Ex. 80). 



(b) With bases, owing to the presence of the 



- COOH group (see Ex. 79). 



2. When dissolved in alcohol and saturated with dry 

 hydrochloric acid they form esters, which are bases (see 

 Ex. 78). 



R.CH.NH 2 R.CH.NH 2 



+ C 2 H 5 .OH = + H 2 0. 



COOH COOC 2 H 5 



This reaction is of considerable importance, as Fischer's 

 method of separation of the amino-acids is based on the 

 fractional distillation of the esters. 



3. They combine with aldehydes to form methylene 

 compounds, which are acids (see Ex. 260). 



