246 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Aminobenzene or Aniline. C 6 H 5 . NH 2 . 



Nitrobenzene is converted into aniline by the action of reducing 

 agents in acid solution : 



|N0 2 f]NH 2 



+ 3 H 2 = + 2H 2 0. 



\x V 



Preparation. 



To 3 or 4 drops of nitrobenzene about 4 gm. of granulated 

 tin and 3-4 c.c. of concentrated hydrochloric acid are added. The 

 mixture is warmed to start the reaction and it is kept warm until the 

 reaction ceases and until the smell of nitrobenzene is no longer per- 

 ceptible. An excess of caustic soda is added and the alkaline solution 

 is extracted with ether. The ether is allowed to evaporate in a basin 

 and the residue is tested for aniline by treating it with bleaching 

 powder solution ; a purple colour appears which becomes dirty red. 



On a larger scale 20 gm. of nitrobenzene and 40 gm. of granulated tin are 

 placed in a litre flask and warmed on a water-bath for a few minutes. The 

 flask is removed from the bath and fitted with an air condenser. 80 c.c. 

 of concentrated hydrochloric acid are added in portions of 5 c.c. during the 

 course of half an hour. If the mixture react violently, it is cooled in water. 

 The reaction is completed by heating the flask on a boiling water-bath for 

 about one hour. If the smell of nitrobenzene be still observed more hydro- 

 chloric acid may be added and the heating continued until it vanishes. 



The double salt (C 6 H 5 . NH 2 . HC1) 2 . SnCl 4 separates out if the product 

 be allowed to cool; it is diluted with a 100 c.c. of water and immediately 

 decomposed by carefully adding 65 gm. of caustic soda dissolved in a 100 c.c. 

 of water. Heat is developed on neutralising and stannic hydrate is precipi- 

 tated ; this dissolves in excess of caustic soda and there results a dirty liquid 

 containing aniline floating on the surface. The aniline is separated by distilla- 

 tion in steam (p. 1 2). The distillate is collected so long as drops of aniline pass 

 over. The aniline is extracted by shaking it with ether and the ethereal solution 

 is dried with solid caustic soda. The ether is distilled off from a water-bath 

 and the residue is' distilled over a flame. Aniline passes over at 182-184' 

 as a pale yellow liquid. 



Properties. 



Aniline is a pale yellow oily liquid which boils at 182 and has a 

 peculiar odour. It gradually turns brown on exposure to light and 

 air. 



Aniline is soluble with difficulty in water, but easily in alcohol and 

 ether. 



The solubility of aniline in water can be readily seen by placing 

 3 or 4 drops in a test tube full of water and shaking vigorously. The 

 oily drops will be no longer visible. 



Aniline is a weak base and forms salts with acids from which it is 

 liberated by alkalies, thus : 



