252 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Ethylbenzene, C 6 H 5 . C 2 H 5 , and other Homologues of Benzene. 



Ethylbenzene is also contained in coal tar and can be prepared 

 from benzene by the reactions given under toluene, It is a liquid 

 like toluene, but boils at 1 34 and is isomeric with the xylenes (p. 260). 



The other homologues, propyl, butyl, etc., benzene can be prepared 

 in the same way. 



These homologues of benzene contain both a benzene nucleus and 

 an aliphatic radicle or side chain. They behave as aromatic compounds 

 by forming nitro and sulphonic acid derivatives. They behave as 

 aliphatic compounds in forming halogen derivatives in which the 

 halogen atom can be replaced by OH and other groups. On oxida- 

 tion the side chain undergoes shortening until ulimately benzoic acid 

 is formed : 



C 6 H B . CH 2 . CH 2 . CH 8 -> C 6 H 5 . CH 2 . CH 2 . COOH -> C 6 H 5 . CH 2 . COOH -> 



C 6 H 6 .COOH. 



Styrene or Phenylethylene, C 6 H 5 . CH = CH 2 , is an aromatic hydro- 

 carbon containing an unsaturated group in the side chain. It is obtained by 

 heating cinnamic acid. 



Benzyl Chloride, CH 5 . CH 2 C1. 



Benzyl chloride is the chief representative of an aromatic compound 

 in which a halogen atom is present in the side chain. Like aliphatic 

 compounds it can be obtained by the action of phosphorus pentachloride 

 upon the corresponding alcohol benzyl alcohol C 6 H 5 . CH 2 OH. The 

 radicle C C H 5 . CH 2 is termed benzyl in order to distinguish it from 

 the radicle C 6 H 5 which is termed phenyl. 



Preparation. 



Benzyl chloride is prepared by passing a stream of dry chlorine 

 into toluene, heated under a reflux condenser, until the increase in 

 weight corresponding to the equation has been reached. The product 

 is then separated and purified by distillation. The reaction takes 

 place most readily if the flask be exposed to sunlight. The following 

 reaction takes place : 



C a H 5 . CH 3 + Cl a = C fl H 6 . CH 2 C1 + HC1. 



The procedure is quite different to that used in the preparation ot 

 bromobenzene and chlorotoluene (p. 241). 



Properties. 



Benzyl chloride is a colourless liquid which boils at 176. It has 

 an unpleasant smell, is insoluble in water, but soluble in alcohol, ether 

 and benzene. 



It is nitrated, sulphonated, etc., by nitric or sulphuric acid, but 

 in its other reactions it resembles ethyl chloride. It is mainly used 

 for the preparation of benzaldehyde. 



