AROMATIC COMPOUNDS 



/N0 2 

 Dinitrobenzenes, C 6 H/ 



X N0 2 . 



m-Dinitrobenzene is obtained by nitrating benzene with sulphuric acid 

 and nitric acid and heating. It is a yellow crystalline solid melting at 90. 



o- and p- Dinitrobenzenes are formed in, small quantities at the same 

 time. They are colourless solids melting at 118 and 173 respectively. 



NH 2 

 Diaminobenzenes, or Phenylenediamines, C 6 H 4 <' 



X NH 2 . 



Like aniline they are obtained by reducing the dinitrobenzenes. 

 They also resemble aniline. m-Phenylenediamine melts at 63. It gives a 

 deep yellow colour with nitrites and is used for detecting nitrites in small. 

 quantities. 



S0 3 H 

 Benzene Disulphonic Acids, C 6 H 4 ^ 



X S0 8 H. 



The m-compound is formed by heating benzene with two molecular 

 proportions of sulphuric acid. 



Dihydroxy- Benzenes, 



OH. 



The three isomeric dihydroxy benzenes are natural compounds 

 and are termed : 



Catechol, Hydroquinone, 



or or 



pyrocatechin Resorcinol quinol 



OH OH OH 



'OH 

 Ortho. Meta. 



Catechol occurs in catechu, a resin obtained from Acacia catechu, 

 and was first obtained from this source. It is prepared by fusing 

 o-phenolsulphonic acid with potash, or by reducing guaiacol with 



hydriodic acid : 



/OCH 8 /OH 



C 6 H / + HI = CH 3 I + C 6 H 4 ( 



\OH \OH. 



It is a colourless crystalline solid melting at 104. 



Resorcinol is obtained by fusing benzene-m-disul phonic acid and 

 the other disulphonic acids with potash at higher temperatures. 



It forms colourless crystals which melt at 110 and are easily 

 soluble in water, alcohol, ether. It is used largely for making eosin 

 and other dyes. 



Quinol is formed by the hydrolysis of the glucoside, arbutin, by 

 boiling with water. It is usually prepared by reducing quinone 

 with sulphurous acid. It is a colourless crystalline solid melting at 

 169 and very easily soluble in water. 



