AROMATIC COMPOUNDS 



Toluene. C 6 H 5 . CH 3 . 



Toluene, or methyl benzene, or phenylmethane, is present in coal 

 tar and is contained with benzene in the first fraction on fractionally 

 distilling the tar. It is separated from benzene by fractional distillation. 



Toluene is also obtained from balsam of tolu, or from toluic acid 

 by distillation with soda lime a reaction analogous to the preparation 

 of methane from sodium acetate : 



,CH 3 



C 6 H 4 ( = C 6 H 5 .CH 3 + C0 2 . 



\COOH 



Toluene can be prepared from benzene by either of the following 

 two reactions : 



(1) Fittig's Reaction. A mixture of bromobenzene and methyl 

 bromide is heated with sodium ; 



C 6 H fl Br + Na., + CH 3 Br = C 6 H 6 . CH 3 + 2 NaBr. 



(2) Friedel and Craft's Reaction. Benzene is heated with 

 methyl iodide in the presence of aluminium chloride : 



C 6 H 6 + CH 3 I = C 6 H 5 . CH 3 + HI. 



In this reaction a compound of benzene and aluminium chloride 

 is probably first formed and this compound reacts with the alkyl 

 halide : 



C 6 H 6 + AL,C1 6 = C 6 H 5 . A1 2 C1 5 + HC1 

 C 6 H 5 A1 2 C1 8 + CH 3 C1 = A1 2 C1 6 + C 6 H S . CH 3 . 



Dry benzene is treated under a reflux condenser with a third of its weight 

 of aluminium chloride and the alkyl chloride is slowly added. The benzene 

 may be mixed with a neutral solvent such as ether or petroleum ether. The 

 mixture is heated on a water-bath until halogen acid is no longer evolved. 

 The mixture is allowed to cool and water added to dissolve the aluminium 

 chloride ; the layer of benzene and ether is separated, dried with calcium 

 chloride, the ether distilled off and the residue distilled. 



Properties. 



Toluene, an oily colourless liquid with characteristic smell, boils 

 at 110 and has a sp. gr. of -882 at o. It burns with a smoky 

 luminous flame, is insoluble in water, but soluble in organic solvents. 

 It is known commercially as toluole. Toluene closely resembles ben- 

 zene in its properties in forming nitro- and other derivatives, but it 

 differs from benzene in being also an aliphatic compound. Toluene 

 is the first instance of an aromatic compound containing a side chain. 

 It is this side chain which gives toluene the properties of an aliphatic 

 compound (See benzyl chloride, alcohol, benzaldehyde, etc.) 



On oxidation with dilute nitric acid and other oxidising agents, 

 the nucleus remains intact but the side chain is oxidised to a carboxyl 

 group : 



C a H 8 . CH 8 + 30 = C a H B . COOH + H a O. 



