COMPLEX AROMATIC COMPOUNDS 331 



It yields nitro compounds, ammo compounds and other derivatives. 

 These derivatives form the group of rosaniline dyes (p. 335). 



When oxidised with chromic acid it is converted into triphenylcarbinol 

 (C 6 H 5 ) 3 . C . OH. 



Diphenyl. 



Diphenyl is the first instance of aromatic com- 

 pounds in which the benzene rings are directly 

 joined together by a single bond. It is prepared 

 by treating an ethereal solution of bromobenzene 

 with sodium : 



C 6 H 5 Br + Na 2 + C 6 H 6 Br = aNaBr + C 6 H 5 C 6 H 5 , 

 or it is formed when benzene vapour is passed through a red-hot tube. 



It is a colourless solid melting at 71 and boiling at 254; it closely re- 

 sembles benzene in its reactions. On oxidation it yields benzoic acid. 



Azoxybenzene. 



When nitrobenzene is reduced with alkaline reducing 

 agents, such as sodium and alcohol, it yields azoxybenzene. 

 Azoxybenzene is a yellow crystalline solid melting at 36. 

 It is insoluble in water, but soluble in alcohol, ether and 

 organic solvents. 



Azobenzene. 



Azobenzene is formed when azoxybenzene is carefully 

 N N ^ ^j distilled with three parts of iron filings. 



It is a brilliant red crystalline solid which melts at 68 

 and distils at 293. It is not soluble in water, but dis- 

 solves in organic solvents. 



Hydrazobenzene. 



OWhen azobenzene is reduced with alkaline reagents, 

 ammonium sulphide, or zinc and caustic soda, it is 

 converted into hydrazobenzene. 

 Hydrazobenzene forms colourless crystals which 

 melt at 131. It is reduced by zinc dust and acetic acid to aniline. 



Benzidine. 



Benzidine, or diamino - diphenyl, is 

 formed when hydrazobenzene is treated 

 with concentrated hydrochloric acid ; intra- 

 molecular rearrangement takes place. 



It may be obtained by treating azobenzene with tin and concentrated 

 hydrochloric acid. 



Benzidine forms colourless crystals which melt at 128. 

 It is a base like aniline, forming salts with acids. The sulphate is very 

 insoluble and is used for estimating sulphates. 



It is diazotised by nitrous acid and, like aniline, is used largely in the 

 preparation of dyes. 



Naphthalene. 



Naphthalene, the hydrocarbon which is present in 

 coal tar in the largest quantity, is present in the second 

 fraction, boiling from 170-230, when the tar is 

 fractionally distilled. 



