AROMATIC COMPOUNDS 241 



(2) Middle oil, or carbolic oil, which distils from 150-210 and 

 contains naphthalene and carbolic acid. It forms 8-10 per cent 



(3) Heavy oil, or creosote oil, which distils from 210-270 and 

 forms 8-ro per cent. 



(4) Anthracene oil, which distils from 270-400 and contains 

 anthracene. It is coloured green and forms 16-20 per cent. 



Pitch remains in the still. 



The terms light oil, middle oil, heavy oil denote the specific gravity 

 of the distillate with regard to water. A sample is run into water 

 during the distillation ; if it floats it is light oil, if it sinks it is 

 heavy oil. The middle oil passes over as soon as light oil no longer 

 distils over. 



Benzene and its homologues are prepared from the light oil. The 

 fraction is shaken with strong sulphuric acid which removes basic sub- 

 stances, such as aniline, pyridine, and also unsaturated hydrocarbons. 

 It is next shaken with sodium hydroxide which removes acid sub- 

 stances, carbolic acid and the sulphuric acid. It is washed by 

 shaking with water and fractionally distilled. Pure benzene is isolated 

 from the first fraction by careful fractional distillation. 



Propertied 



Benzene is an oily colourless liquid with peculiar smell and boils 

 at 80. It solidifies on cooling and the crystals melt at 5-4. Its 

 specific gravity is -874 at 20. It is inflammable and burns with 

 a smoky and luminous flame. It is insoluble in water, but mixes with 

 alcohol and ether. Benzene is a good solvent for resins, fats, etc., and 

 is frequently used for extraction. It dissolves iodine, phosphorus, 

 sulphur, etc. 



Benzene is called benzole commercially, the terminal e being added 

 to show that it does not possess a hydroxyl (OH) group ; the suffix 

 0/, as previously mentioned, is used to designate alcohols. 



Chlorobenzene, C 6 H 5 C1. Bromobenzene, C 6 H 5 Br, lodobenzene, 

 QH 5 I. 



Like the aliphatic hydrocarbons benzene is acted upon by the 

 halogens, chlorine and bromine, and converted into substitution deriva- 

 tives. This reaction proceeds most easily in the presence of a halogen 

 carrier, such as iodine (iodine chloride is formed which chlorinates more 

 vigorously) : 



r\ 



+ Br 9 = HBr + 



