INDOLE AND ITS DERIVATIVES 347 



Reactions. 



(1) On adding a few drops of pure nitric acid and drop by drop a 2 per 

 cent, solution of potassium nitrite to a solution of indole-acetic acid, a cherry- 

 red colour is formed, followed by a turbidity and separation of a red pigment. 



(2) A purple-red colour and precipitate is formed when an equal volume 

 of concentrated hydrochloric acid and a few drops of a 1-2 per cent, solu- 

 tion of bleaching powder are added to its solution. 



(3) A violet colour is formed (before and after boiling) if an equal volume 

 of concentrated hydrochloric acid and a few drops of ferric chloride solution 

 be added to a solution of indole-acetic acid. 



(4) A red colour is formed with p-dimethylaminobenzaldehyde (see 

 under indole). 



The Urorosein Reaction of Urine. 



This reaction consists in the formation of a red pigment when 

 concentrated hydrochloric acid and a drop or two of sodium nitrite 

 solution is added to urine. Stale urines give this reaction on the 

 addition of hydrochloric acid only, as nitrites are formed by bacterial 

 decomposition of other constituents in the urine. The colour disap- 

 pears on adding alkali but reappears on acidifying. 



Urorosein is insoluble in ether and chloroform, but dissolves in 

 alcohol and amyl alcohol with a red colour. The amyl alcoholic 

 solution shows an absorption band in the green, between D and E, but 

 nearer D. Urorosein is most probably nitrosoindole-acetic acid. 



Indole-^-Propionic Acid. 



Indole propionic acid has also been shown 



/\ ~ to De a putrefactive decomposition product of 



,H 2 -CH 2 -C proteins. 



k Jk JcH It crystallises in prisms or irregular plates, 



^ Xf-Q.. is slightly soluble in water, but easily soluble 



in alcohol and ether. 



Reactions. 



(1) Indole-/?-propionic acid forms a nitroso compound with potassium 

 nitrite. In concentrated solution on the addition of concentrated potassium 

 nitrite and acetic acid, a yellow crystalline mass may be obtained. 



(2) An aqueous solution gives a white turbidity with ferric chloride which 

 becomes red on heating. 



Indole-ethylamine. 



Indole- ethylamine is another substance 



C'CH 2 < CH 2 *NH 2 which is formed in the putrefaction of proteins 

 and of tryptophan. It is one of the amines 

 which have a marked physiological action, but 

 is not so marked in its action as p-hydroxy- 

 phenyl-ethylamine or iminazolyl-ethylamine. 



