Question

How will you convert ethane into butane?

Answer 1

Wurtz reaction:

• This is the reaction in which the form of a coupling reaction where two lower alkyl halides are reacted in the presence of a dry ether medium and sodium metal to form a higher alkane.

$\underset{\mathrm{Alkyl}\mathrm{halide}}{2\mathrm{R}-\mathrm{X}}+\underset{\mathrm{Sodium}}{2\mathrm{Na}}\to \underset{\mathrm{alkane}}{\mathrm{R}-\mathrm{R}}+\underset{\mathrm{sodium}\mathrm{bromide}}{2\mathrm{NaX}}$

Step 1: Photochemical halogenation

• Ethane is reacted with Bromine in the presence of light which is known as photochemical halogenation.

$\underset{\mathrm{Ethane}}{{\mathrm{CH}}_3-{\mathrm{CH}}_3}+\underset{\mathrm{Bromine}}{{\mathrm{Br}}_2}\stackrel{\mathrm{h\nu }}{\to }\underset{\mathrm{Bromoethane}}{{\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{Br}}$(in presence of light)

Step 2: Reaction with metallic sodium

• The ethylene bromide thus formed is treated with metallic sodium and dry ether to produce butane.
• A transfer of one electron from a sodium atom makes a free radical of alkyl.
• Then once again sodium atom releases one more electron to the free radical and provides a carbonium ion.
• A halide ion is displaced by an alkyl anion from another molecule of alkyl halide.
• This reaction can be considered an ${\mathrm{S}}_{\mathrm{N}}2$ reaction.

$\underset{\mathrm{Bromoethane}}{2{\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{Br}}\stackrel{\mathrm{Na}/\mathrm{Ether}}{\to }\underset{\mathrm{Butane}}{{\mathrm{CH}}_3{\mathrm{CH}}_2-{\mathrm{CH}}_2{\mathrm{CH}}_3}$ (in presence of Na/ether)