What is Wurtz reaction ? Explain with examples. What are its limitations?

Explanation

Wurtz reaction: This reaction is used in the preparation of alkanes. Reaction of alkyl halides (generally bromide or iodide) with metallic sodium in dry ether, gives a symmetrical alkane containing twice the number of carbon atoms present in the alkyl group. For example,
`underset("Ethyl iodide")(CH_(3)CH_(2)I) + 2Na + CH_(3)CH_(2)I overset("dry ether")rarr underset("Butane")(CH_(3)CH_(2)CH_(2)CH_(3)) + 2NaI`
When reacting halides are different, then a mixture of three alkanes are obtained. For example, if the mixture of halides containing ethyl iodide and methyl iodide treated with sodium in dry ether, then a mixture of propane, butane and ethane is obtained.
`underset("Ethyl iodide")(CH_(3)CH_(2)I) + 2Na + underset("Methyl iodide")(CH_(3)I) overset("dry ether")rarr underset("Propane")(CH_(3)CH_(2)CH_(3)) + 2NaI`
`underset("Ethyl iodide")(CH_(3)CH_(2)I) + 2Na + CH_(3)CH_(2)I overset("dry ether")rarr underset("Butane")(CH_(3)CH_(2)CH_(2)CH_(3)) + 2NaI underset("Methyl iodide")(CH_(3)I + 2Na) + CH_(3)I overset("dry ether")rarr underset("Ethane")(CH_(3)CH_(3)) + 2NaI`
Limitations of Wurtz reaction
By wurtz reaction, it is easy to prepare alkanes containing even number carbon atoms (ethane, butane, etc) as it includes same alkyl halide reaction with Na/dry ether.
But during the preparation of alkanes containing odd number of carbon atoms (propane, pentane, etc). it includes different alkyl halide reaction with Na/dry ether, which gives mixture of three different alkanes.
So, it is difficult to separate the alkanes from the mixture, thus this method is not suitable for the preparation of alkanes with odd number of carbon atoms.