Question

How will you convert benzene to biphenyl?

Answer 1

Hint: To answer this question you must recall the Wurtz Fittig reaction. This reaction is used to prepare substituted aromatic compounds. The reaction takes place between alkyl or aryl halides and sodium in the presence of dry ether as a catalyst and solvent.

Complete step by step answer:
- Wurtz Fittig reaction is the reaction of aryl halides with other aryl or alkyl halides for the formation of substituted aromatic compounds. Aryl halides are also known as haloarenes. A hydrogen atom bonded to an aromatic ring is replaced by a halide ion which results in the formation of an aryl halide. Using this method, we can attach any desired hydrocarbon on the benzene ring.
- To convert benzene to biphenyl, we use the Wurtz Fittig reaction. First we convert the benzene ring to chlorobenzene using chlorine gas in the presence of anhydrous aluminium chloride through a chlorination reaction. Now we convert the chlorobenzene to biphenyl in presence of sodium in dry ether.
${C_6}{H_6} + C{l_2}\xrightarrow[{}]{{AlC{l_3}}}Ph - Cl + HCl$
$2Ph - Cl + 2Na\xrightarrow[{}]{{{\text{dry ether}}}}Ph - Ph + 2NaCl$

Note:
The Wurtz Fittig reaction involves a two- step mechanism for the conversion of aryl halides to an organic hydrocarbon. In the first step, the halogen atom present on the aromatic ring leaves with a sodium ion forming sodium halide. This step proceeds by the free radical mechanism and the cleavage of the carbon halogen bond is homolytic. The intermediate form is an aromatic ring with a free unpaired electron or a free radical.
Now, another sodium atom performs a similar reaction with the other alkyl or aryl halide derivative forming a compound with halogen and a free radical. Now the two hydrocarbon free radicals join their free electrons with each other forming a covalent bond.