Preparation of benzene

The simplest arene is benzene (C6H6). Benzene is a typical arene and it gives all the typical reactions of arenes. Benzene was first isolated by Faraday (1825) from the cylinders of the compressed illuminating gas obtained from natural sources. In 1845, Hoffmann isolated benzene from coal-tar. Coal-tar is the chief source of benzene.

Preparation of Benzene

Benzene and its homologues may be prepared by the following methods.

By the decarboxylation of sodium benzoate

This method is used in the laboratory to obtain benzene. Sodium benzoate is heated with soda-lime and when it gets decarboxylated (removal of carbon dioxide) benzene is obtained.

decarboxylation of sodium benzoate

sodium benzoate sodalime Benzene

By heating phenol with zinc

When phenol vapours are passed over heated zinc dust, benzene is formed.

formation of benzene from phenol

phenol benzene

By the polymerization of ethyne (acetylene)

When ethyne (acetylene) is passed through a red hot copper tube, it polymerises to benzene.

polymerization of ethyne

By the reduction of benzene diazonium chloride

Benzene is formed on the reduction of benzene diazonium chloride with sodium stannite or hypophosphorus acid.

C6H5NCl- + H3PO2 + H2Oformation of benzene from benzenediazoniumchlorideC6H6 + N2 + H3PO3 + HClbenzenediazoniumchloride

By the hydrolysis of sulphonic acid

Benzene sulphonic acid on hydrolysis with superheated steam gives benzene.

C6H5.SO3H + H2Oformation of benzene from benzene sulphonic acid C6H6 + H2SO4

benzene sulphonic acid benzene

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