Q.Describe two methods of preparation of ethane. Give any three reactions of ethane.

Ethane can be made by the Wurtz reaction on methyl iodide or by hydrogenating ethylene; it undergoes combustion, halogenation and pyrolysis (three representative alkane reactions).

Preparation of ethane — two methods

1. Wurtz reaction: An alkyl halide is treated with sodium metal in dry ether:

2CH3-I + 2Na --(dry ether)--> CH3-CH3 + 2NaI

Methyl iodide couples to give ethane.

2. Catalytic hydrogenation of ethylene (alkene): Ethylene gas is passed with hydrogen over a finely divided nickel (or Pt/Pd) catalyst (Sabatier-Senderens reaction):

CH2=CH2 + H2 --(Ni, heat)--> CH3-CH3

Three reactions of ethane

1. Combustion: Ethane burns completely in excess oxygen/air to give carbon dioxide and water, releasing heat (it is used as a fuel):

2C2H6 + 7O2 --(burn)--> 4CO2 + 6H2O

2. Halogenation (substitution): In the presence of sunlight or heat, ethane undergoes free-radical substitution with chlorine, replacing H atoms progressively:

C2H6 + Cl2 --(sunlight)--> C2H5Cl + HCl (and can continue to give more highly chlorinated products)

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