PYRIDINE AND ITS DERIVATIVES 309 



Homologues of Pyridine. 



The following homologues of pyridine, mixed with pyridine, are contained 

 in the basic fraction of coal tar and bone oil and are separated by fractional 

 distillation as stated under pyridine. 



I. The monomethyl pyridines or picolines : 



CH, 

 /\ 



N N N 



a-methylpyridine /8-methylpyridine y-methylpyridint 



or or or 



o-picoline. -picoline. 7-picoline. 



II. The Dimethyl pyridines or lutidines. 



III. The trimethyl pyridines or collidines. 

 They closely resemble pyridine in properties. 



Pyridine Carboxylic Acids. 



The side chain of the methyl pyridines on oxidation is converted into 

 carboxyl and the pyridine carboxylic acids are obtained : 



COOH 



I 

 COOH 



N N 



Picolinic acid. Nicotinic acid. Isonicotinic acid. 



These compounds are white crystalline solids soluble in water. They 

 possess basic properties and acidic properties forming salts with acids and 

 bases. 



Nicotinic Acid is formed by the oxidation of nicotine (p. 353). This 

 substance therefore contains a substituting group in the /?-position of the ring. 



Picolinic Acid gives a red coloration with ferrous sulphate. This 

 reaction is given by all acids derived from pyridine containing a carboxyl group 

 in the a-position. 



Quinolinic Acid is formed by the oxidation of quinoline with per- 

 manganate. Quinolinic acid is a dibasic acid having the constitution : 



Ac, 



:OOH 

 JCOOH 



N 



It is a crystalline solid, soluble with difficulty in water. It gives an 

 orange coloration with ferrous sulphate which shows that one carboxyl 

 group is in the a-position. It is converted into nicotinic acid when it is 

 heated to 190. These reactions show the position of the carboxyl groups. 



