350 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Indole is oxidised and converted into indoxyl which is combined 

 with sulphuric acid (or glucose) to form indican. Indican on hydrolysis 

 yields indoxyl, which is oxidised in the air or by oxidising agents to 

 indigo blue. 



frt 



vU 



NH 



O SO 3 K 

 H 



TH 



Indican. 



OH 



QUINOLINE AND ISOQUINOLINE. 



These compounds have the empirical formula C 9 H 7 N and are pre- 

 sent in coal tar and bone oil. Their constitution is expressed by the 

 formulae : 



N 

 Quinoline. Isoquinoline. 



The presence of the pyridine ring in these compounds is shown by 

 their oxidation. Quinoline gives quinolinic acid : isoquinoline gives 

 A 7-pyridine dicarboxylic acid or cinchomeronic acid and phthalic 

 acid. The formulae of both compounds have been proved by synthesis. 



Preparation. 



Quinoline is usually prepared by synthesis. Isoquinoline is pre- 

 pared from the fraction of coal tar or bone oil which distils between 

 236 and 243. The bases are converted into sulphates and fraction- 

 ally crystallised from alcohol. The sulphate is decomposed by potash 

 and the base distilled. 



Properties. 



Quinoline is a colourless oily liquid which boils at 239 and has a 

 specific gravity of I -095 at 20 It has a peculiar and pleasant smell 

 and is only slightly soluble in water. Isoquinoline is a colourless 

 solid which melts at 23, boils at 241 and closely resembles quinoline. 



Both compounds are tertiary amines and form salts with acids. 

 They are stable ring compounds resembling naphthalene and pyridine. 



