Jul 212013
 


Benzene is a cyclic compound which consists of six carbon atoms where there is presence of alternate double bonds and single bonds. It is an aromatic hydrocarbon which consists of six carbon atoms where there is presence of alternate double bonds and single bonds. The general structure of Benzene is given below:

Structure of Benzene

The structure of benzene was first proposed by a scientist called August Kekulé in the 1865 A.D. The resonating hybrid structure of Benzene is given below:

resonance hybrid structure
The carbon-carbon bond length in the case of benzene is intermediate between carbon-carbon double bond and carbon-carbon single bond. The bond length of carbon-carbon double bond is 1.34Å, and that of carbon-carbon single bond is 1.54Å. In the case of benzene, the carbon-carbon bond length is 1.39Å.

General Methods of Preparation of Benzene

1. By decarboxylation reaction: When sodium benzoate is heated with soda lime (mixture of NaOH and CaO in the ration of 3:1), benzene is produced by the removal of CO2 in the form of sodium carbonate.decarboxylation2. From phenol: When phenol is heated with zinc dust, benzene is produced.

phenol3. From chlorobenzene: When cholorobenzene is reduced in the presence of different reducing agents such as LiAlH4, NaBH4, Ni/H2, Pt/H2, Na/C2H5OH, Ni-Al/NaOH etc., benzene is produced.chlorobenzene

When chlorobenzene is heated with magnesium in the presence of dry ether, phenyl magnesium chloride (Grignard’s reagent) is produced, which on hydrolysis in the presence of acid gives benzene.

chlorobenzene 2

4. From ethyne (acetylene): When ethyne is passed through red hot copper tube, three molecules of ethyne undergo polymerization to form benzene.ethyne