332 PRACTICAL ORGANIC AND BtO-CHEMtSTRY 



The second fraction on cooling deposits crystals of naphthalene. These 

 are separated from phenols, etc., by pressure. The impure mass is shaken 

 with caustic soda to remove the remainder of the phenols, washed and 

 warmed with sulphuric acid, which sulphonates the impurities, dissolving them. 

 The naphthalene is obtained by distillation or sublimation. 



Naphthalene is a colourless solid crystallising in shining plates which 

 melt at 79 and boil at 218. It has a characteristic smell and is extremely 

 volatile. All the naphthalene formed by the distillation of coal is not condensed 

 and a portion reaches the gas mains and gas pipes ; in cold weather the 

 naphthalene crystallises out and may cause blocking of the pipes. It does 

 not dissolve in water, but it dissolves easily in hot alcohol, ether and other 

 organic solvents. It combines with picric acid, like other complex hydro- 

 carbons, to form a yellow crystalline solid which melts at 149. 



When naphthalene is oxidised by dilute nitric acid or chromic acid, it 

 yields o-phthalic acid. On nitration it yields a-nitronaphthalene; oramino- 

 naphthalene is formed by the reduction of the nitro compound. Nitro- 

 naphthalene on oxidation gives nitrophthalic acid: aminonaphthalene gives 

 phthalic acid. The formation of phthalic acid shows the presence of one 

 benzene ring with substituting groups in the o-position. The same is shown 

 by the oxidation of nitronaphthalene, but the oxidation of aminonaphthalene 

 shows that a different benzene ring is oxidised to that which is oxidised in 

 the case of nitronaphthalene. Naphthalene would thus contain two benzene 

 rings joined together in the ortho-position as represented by the formula. 

 This constitution is proved by synthesis and emphasised by the similarity in 

 behaviour of naphthalene to benzene. 



Derivatives of Naphthalene. 



Naphthalene resembles benzene in forming nitro, sulphonic acid, amino- 

 derivatives. Two monosubstitution derivatives can be formed, the d and the 

 ft forms. In some cases both are formed, in other cases only one is formed 

 The accompanying formulae show how these derivatives are prepared from 

 naphthalene : 



OH 



fl-naplithol 



naphthalene 

 sulphonic acid 



NH.C1 



KOH 



at 1GO C 



HN0 3 



'-naphthylamine 



a naphthaquinone 



naphthalene 



in 

 acetic acid 



diazotise 



N0 2 



a -nitronaphthalene 



r 



, 3 H 



a -naphthalene 

 sulphonic acid 



OH 



tf-naphthol 



NH 2 



a -naphthylamine 



