274 TOLUENE. 



froups with the greatest ease. When chlorine or 

 romine is allowed to act on toluene that is kept 

 well cooled or to which is added iodine, substitution 

 takes place only in the benzene residue; at boiling 

 temperature, and in the absence of iodine, on the con- 

 trary, the hydrogen of the methyl is replaced. Of the 

 substitution-products of the first class there are, fur- 

 ther, certain isomeric modifications possible, the differ- 

 ence of which depends upon the different relative posi- 

 tions of the substituting atoms with reference to each 

 other, and with reference to the methyl-group already 

 present in the molecule (See p. 252). The entrance of 

 one atom of chlorine into toluene can accordingly give 

 rise to the formation of four different compounds, 

 C 6 H 5 .CH 2 C1; and three modifications of C 6 H 4 C1.CH 3 . 

 The direct action of chlorine, bromine, or nitric acid 

 causes chiefly the formation of compounds belonging 

 to the para-series (1:4); but, together with these, small 

 quantities of ortho- or meta-compounds are also formed. 

 Both the latter are obtained in a pure condition by 

 treating the substitution-products of the amido-deriva- 

 tives (toluidins) with nitrous acid, thus converting 

 them into diazo-compounds, and then decomposing the 

 sulphates of the diazo-compounds by boiling with abso- 

 lute alcohol (See diazobenzenesulphate, p. 266). The 

 conduct of the monosubtitution-products by oxidation 

 with potassium bichromate and dilute sulphuric acid 

 is very characteristic. The compounds, in which the 

 substitution has taken place in the methyl, are by this 

 means, like toluene itself, converted into benzoic acid : of 

 the other compounds, those belonging to the meta- and 

 para-series are oxidized directly to meta- and para- 

 substitution-products of benzoic acid (by simple oxi- 

 dation of the group, CH 3 to CO. OH) ; the ortho-com- 

 pounds on the contrary are completely burnt up with- 

 out yielding an aromatic acid. 



Ortho-, Meta-, andParachlortoluene, C 6 H 4 C1.CH 3 , 

 are very stable liquids, boiling at 156-158. Benzyl 

 chloride C 6 H 3 ,CH 2 C1, a liquid boiling at 176. 



