Octane Wurtz reaction

When an alkyl halide is treated with sodium, the main product is the paraffin hydrocarbon. The final result may be represented by the equation  

This preparation illustrates the preparation of a liquid hydrocarbon from a Grignard reagent. The Grignard reagent from n-hexyl bromide may be decomposed either with dilute sulphuric acid or with solid ammonium chloride the latter gives a somewhat better 3neld. 

Aliphatic hydrocarbons can be prepared by the reduction of the readily accessible ketones with amalgamated zinc and concentrated hydrochloric acid (Clemmensen method of reduction). This procedure is particularly valuable for the prep aration of hydrocarbons wdth an odd number of carbon atoms where the Wurtz reaction cannot be applied with the higher hydrocarbons some secondary alcohol is produced, which must be removed by repeated distillation from sodium. 

Amylene is a general name for the ethylenic hydrocarbons of the molecular formula CjHio. Two of these hydrocarbons are the main products of the dehydration of the appropriate amyl alcohols  

Tertiary alcohols are more readily dehydrated than secondary alcohols, whilst primary alcohols are dehydrated with comparative difficulty. Thus the reaction proceeds easily with 33 per cent, sulphuric acid (1 acid 2 water, by volume) for crt.-amyl alcohol, but 50 per cent, (by volume) is required for aec.-amyl alcohol. Higher concentrations of acid tend to lead to increasing polymerisation of the olefine and are therefore usually avoided. 

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The symmetrical Wurtz coupling has been found to give particularly good yields in the case of the higher alkane homologues. Selected illustrative examples (hexane, octane, decane and dodecane) are to be found in Expt 5.7. A related reaction is to be found in the synthesis of hexa- 1,5-diene (Expt 5.7, cognate preparation), which illustrates the symmetrical coupling of two molecules of allyl iodide by the action of sodium metal. 

Write equations for the reactions by which (a) the two butanes may be made by the Wurtz syntheses, (6) a hexane can be made from butane, and (c) an octane can be made from ethane. 

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