INDOLE AND ITS DERIVATIVES. 



Indigo, tryptophan, scatole, Indole are natural substances which 

 contain the heterocyclic indole ring the complex nucleus made up of 

 a benzene ring and a pyrrole ring : 



NH 



The compounds containing this ring have the properties of benzene 

 and of pyrrole. 



Indole. 



Indole was first obtained by the reduction of indigo by distillation 

 with zinc dust and also in the same way from other products obtained 

 from indigo. It was identified as one of the products of the putre- 

 faction of protein, together with scatole, and it is present in animal 

 excrement. It is a constituent of coal tar and is isolated from the 

 fraction of basic character which distils between 240 and 260. Its 

 constitution has been shown to be : 



CH 



Hi 



JH NH 



Preparation. 



Indole is most easily prepared by the putrefaction of meat or other pro- 

 teins, i kilo, of meat is minced and mixed with about 4000 c.c. water ; 2 gm. 

 of potassium phosphate, 5 gm. of magnesium sulphate and about 30 gm. of 

 crystallised sodium carbonate and a piece of putrid meat are added. The 

 vessel is closed and connected with another flask containing lead acetate and 

 the two vessels are placed in a warm place at about 35. Bubbles of gas are 

 evolved containing hydrogen sulphide, mercaptan, etc.; these are absorbed 

 by the lead acetate. 



The mixture is kept for about 5 or 6 days, acidified with acetic acid and 

 distilled. The distillate, which contains indole and scatole and phenols, is 

 made alkaline with soda and again distilled. Such a solution gives the 

 reactions of indole. The distillate is acidified with hydrochloric acid and 

 treated with picric acid. The precipitate is distilled with ammonia and this 

 distillate is extracted with ether. The ethereal solution on evaporation gives 

 a mixture of indole and scatole. The mixture is dissolved in absolute 

 alcohol and treated with 8-10 volumes of water. The scatole is precipi- 

 tated. The two compounds thus separated are purified by crystallisation 

 from aqueous alcohol or ligroin. 



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