INDOLE AND ITS DERIVATIVES 



349 



Reactions. 



Tryptophan, even when mixed with other amino acids, is readily 

 recognised in solution by the following reactions : 



(1) Bromine water reaction. About 5 c.c. of the solution are 

 acidified with acetic acid and bromine water is added drop by drop ; 

 a reddish-violet colour appears. This gradually deepens, but disap- 

 pears if too much bromine water be added, giving a yellow solution. 

 When the maximum reddish-violet colour is obtained, the solution is 

 shaken with 2 or 3 c.c. of amyl alcohol ; the amyl alcohol dissolves 

 the pigment and separates coloured reddish-violet. 



(2) Glyoxylic acid reaction. A small quantity of glyoxylic acid 

 solution is added to about 5 c.c. of the solution and concentrated 

 sulphuric acid is run under its surface ; at the point of junction a 

 reddish-violet ring appears and on gently mixing the two liquids the 

 colour spreads throughout the mixture. 



(3) On mixing a tryptophan solution with an alcoholic solution of benzal- 

 dehyde and running underneath it concentrated sulphuric acid containing 

 ferric sulphate, a blue colour is formed at the junction. 



(4) Using formaldehyde instead of benzaldehyde, the colour at the junc- 

 tion of the liquids is blue-violet. 



(5) With p-dimethylaminobenzaldehyde and concentrated hydrochloric 

 acid a red colour is formed (see under indole). 



(6) A pine shaving wetted with hydrochloric acid, washed with water, 

 dipped into a concentrated solution of tryptophan and dried, becomes purple 

 in colour. 



The Biological Relationship of the Indole Derivatives. 



Indole and scatole have long been known to be putrefactive pro- 

 ducts of protein, the other compounds were found later. The discovery 

 of tryptophan and the determination of its constitution has shown 

 that all these compounds are derived from it ; in many cases the direct 

 conversion of tryptophan in putrefaction has been carried out. The 

 stages in the decomposition of tryptophan are similar to those which 

 tyrosine undergoes, namely : 



CH 2 -CH(NH 2 1COOH 



C'CH 3 -CH-COOH 



NH 

 Indole propionic acid. 



Indole acetic acid. 



H 



Indole. 



