Sources of aromatic compound:
Benzene and other aromatic compound are obtained from coal tar and petroleum
It can also be prepared in laboratory using some simple aliphatic compounds
Preparation of benzene
Coal tar is a viscous liquid obtained by the pyrolysis of coal. During fractional distillation, coal tar is heated and distills away its volatile compounds namely benzene, toluene, xylene in the temperature range of 350 to 443 K. These vapours are collected at the upper part of the fractionating column (Table 13.5.)
Acetylene on passing through a red –hot tube trimerises to give benzene. We have already studied this concept in polymerization of alkynes.
When sodium benzoate in heated with sodalime, benzene vapours distil over.
When phenol vapours are passed over zinc dust, then it is reduced to benzene.
When a solution of bromo benzene and iodo methane in dry ether is treated with metallic sodium, toluene is formed.
When benzene is treated with methyl chloride in the presence of anhydrous aluminium chloride, toluene is formed.