Question

Write the steps to convert methane to ethane.

Answer 1

Hint: For these conversions, usually Wurtz synthesis is used. The Wurtz reaction, is a coupling reaction in organic chemistry, organometallic chemistry and recently inorganic main-group polymers, whereby two alkyl halides are reacted with sodium metal in dry ether solution to form a higher alkane. It is also used for the preparation of higher alkanes containing even numbers of carbon atoms.

Complete answer:
Wurtz reaction:
1.Methane is first treated with chlorine gas in the presence of sunlight or ultraviolet. Here, methane gets converted into chloromethane.
2.Chloromethane is treated with sodium metal and dry ether to form the product ethane.
This process is known as Wurtz synthesis. In place of chlorine, bromine can also be used. The chemical reaction of this change is as follows:
$$C{H}_4+C{l}_2\stackrel{sunlight}{\to }C{H}_{3}Cl+HCl$$
$$2C{H}_{3}Cl+Na\stackrel{\begin{array}{l}dry\\ ether\end{array}}{\to }{C}_2{H}_6$$ (Wurtz synthesis)
Second method:
1.Methane is converted to ethyne by the process of pyrolysis. In this, methane is heated to a temperature of around $${1500}^{\circ }C$$.
2.Ethyne is then converted to ethene by catalytic hydrogenation. The catalyst used here is usually nickel.
The chemical reaction of this change is as follows:
$$2C{H}_4\underset{{1500}^{\circ }C}{\overset{\mathrm{\Delta }}{\to }}{C}_2{H}_2+3H_2$$ (Pyrolysis)
$$C_2{H}_2+H_2\stackrel{Ni}{\to }{C}_2{H}_4$$ (Catalytic hydrogenation)
$$C_2{H}_4+H_2\underset{\mathrm{\Delta }{200}^{\circ }C}{\overset{Ni}{\to }}{C}_2{H}_6$$

Note:
The Wurtz reaction is seldom used because of side reactions. It has limited use to the synthesis of symmetric alkanes. If two dissimilar alkyl halides are taken as reactants, then the product is a mixture of alkanes that is often difficult to separate by fractional distillation as the differences between the boiling points of the products are typically very low. This type of reaction fails in case of tertiary halides.