266 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



It is now prepared almost entirely from phenol : Sodium phenate 

 is heated in carbon dioxide ; sodium phenyl carbonate is formed : 



C 6 H 5 ONa + CO 2 = C 6 H 5 . O . COONa. 

 On heating, this is changed into sodium salicylate : 



>ONa 

 2C 6 H 5 . O . COONa = C fi H 5 OH + C C H 4 <^ 



X COONa; 



half the phenol used is recovered. 



If the sodium phenyl carbonate be heated under pressure at 120- 

 140, it yields the acid salt of salicylic acid : 



OH 

 C 6 H 6 . O . COONa = C 6 H/ 



\COONa. 



Salicylic acid forms colourless needles which melt at 155. It is 

 not easily soluble in cold water, but dissolves readily in hot water, alco- 

 hol, ether and other organic solvents. It is an antiseptic, like phenol, 

 and is used for preserving food-stuffs and also largely in medicine, 

 more frequently in the form of its derivatives, aspirin and salol. 



Salicylic acid behaves as an acid and as a phenol ; it dissolves in 

 caustic alkali forming a salt with the carboxyl and phenolic groups ; 

 in alkali carbonates forming a salt only with the carboxyl group. 



Reactions. 



(1) On heating it melts and sublimes, but on further heating it loses 

 carbon dioxide and yields phenol. 



The formation of phenol takes place more readily on heating with 

 soda lime. 



(2) As it is a phenol it gives the reactions : 



(a) With ferric chloride a violet colour. This is discharged by 

 mineral acids, but not by acetic acid. It may thus be distinguished from 

 phenol: 



Note. Only the hydroxy acid containing the OH group in the 

 ortho position gives a violet colour with ferric chloride. 

 The m- and p-compounds do not give colours with ferric 

 chloride. 



(b) With bromine water a yellowish-white precipitate of dibromo- 

 and tribromosalicylic acids. 



(c) With nitric acid a yellow colour intensified on making the 

 solution alkaline with ammonia. 



(d} With Millon's reagent a red colour on heating. 



