Preparation of Alkanes

Alkanes are saturated hydrocarbons. These organic compounds are made up of carbon and hydrogen atoms. They possess a single bond between carbon-carbon and carbon-hydrogen atoms. Their general formula is CnH2n+2. Methane, ethane, propane, butane, pentane etc. are examples of alkanes. Suffix ‘ane’ is added at the end of the name of each alkane. Alkanes can be prepared by various methods.


Methods of Preparation of Alkanes 

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  • From Unsaturated Hydrocarbons (Sabatier and Senderens Method)

Unsaturated hydrocarbons such as alkenes and alkynes on catalytic hydrogenation give alkanes. Generally, in these reactions Nickel and Platinum are used as catalysts. General equation is given below –

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For example, ethene can be converted into ethane by hydrogenation in presence of nickel (catalyst) at 200 - 300.

  • From Haloalkanes 

Alkanes can be prepared by reduction of haloalkanes. One of these preparation methods of alkanes was given by Wurtz which is called Wurtz Reaction. 

  • Wurtz Reaction  

When alkyl halide reacts with metallic sodium in presence of dry ether, it forms alkane with double the number of carbon atoms present in the alkyl halide of reactants. This reaction is called Wurtz Reaction. 

Wurtz Reaction can be written as follows – 

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  • By Reduction 

Alkanes can be prepared by reduction of alkyl halide. In these reactions LiAlH4, H2/Pd or nascent hydrogen etc. are used as reducing agents. General equation is given below taking nascent hydrogen as reducing agent –

R-X + 2[H] 🡪 R-H + HX

  • By Reduction of Aldehydes and Ketones 

Alkanes can be prepared by reducing aldehydes and ketones by amalgamated zinc and con. hydrochloric acid. Reactions are given below –

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  • By Grignard’s Reagent 

Alkanes can be prepared by hydrolysis of Grignard’s reagent in presence of dry ether. General equation is given below –

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  • By Salts of Carboxylic Acid or Decarboxylation 

Alkanes can be prepared from salts of carboxylic acids. One of these methods include Kolbe’s electrolytic method. 

  • Kolbe’s Reaction – On electrolysis aqueous concentrated solution of salts of carboxylic acid give alkanes. 

RCOONa 🡪 RCOO- + Na+

RCOO- gains electrons and forms unstable RCOO which gives R-R (alkane) and carbon dioxide gas. 

  • By Heating Sodium Salts of Carboxylic Acids – Alkanes can be prepared by heating sodium salts of carboxylic acids with soda lime (mixture of NaOH and CaO). In this reaction carbon dioxide is removed, thus the alkane obtained by this reaction has one carbon less than reactant salt. This reaction is called decarboxylation. Methane gas is prepared by this method in laboratories.  Reaction is given below –

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  • By Metal Carbides 

Alkanes can be prepared by reaction of metal carbide with pure water. In the reaction metal carbide such as aluminium carbide (Al4C3), beryllium carbide (Be2C) etc. can be used. Reactions are given below –

Be2C + H2O 🡪 CH4 + Be(OH)2

Al4C3 + 12H2O 🡪 4Al(OH)3 + 3CH4

So, this is all about Preparation of Alkanes. We hope you enjoyed learning about it. For more details and other topics, please log on to Vedantu website and download Vedantu learning app.