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Grade 12th passOrganic Chemistry

How will you synthesize alkanes by wurtz reaction and from grignard's reagent?discuss rhe mechanism of chlorination

Profile image of Titosh nayak
7 Years agoGrade 12th pass
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1 Answer

Profile image of Arun
7 Years ago
 

In wourtz reaction  a solution of alkyl halide in ether on heating with sodium gives alkane.

R-X + 2Na + X-R \overset{Dry Ether}{\rightarrow} R-R + 2NaX

An alkyl halide on Wurtz reaction leads to the formation of symmetrical alkane having an even number of carbon atoms. Two different alkyl halides, on Wurtz reaction give all possible alkanes.

CH3X + Na + C2H5X → CH3CH2CH3 + CH3CH3 + CH3CH2CH2CH3

The different involved are steps are:

CH3X + 2Na + C2H5X → CH3CH2CH3 + 2NaX

CH3X + 2Na + C2H5X →CH3CH3 + 2NaX

C2H5X + 2Na + C2H5X → C2H5C2H5 + 2NaX

The separation of mixture into individual members is not easy because their boiling points are near to each other and thus Wurtz reaction is not suitable for the synthesis of alkanes containing odd number of carbon atoms.


When  Zn is used in Wurtz reaction  in place of Na, the reaction is named as Frankland method.

Limitations of Wurtz reaction :

a.Methane can not be obtained by this method

b.The reaction fails in case of tertiary halides

Mechanism of Wurtz reaction : 

The mechanism of Wurtz reaction is although not clear however two mechanisms are proposed for this reaction.

The first proposed mechanism of Wurtz reaction involved  formation of an  Intermediate organometallic compound:

 RX + 2Na →   [RNa]  + NaX

                     Intermediate

RX + [RNa] → R-R + NaX

Another proposed mechanizm of Wurtz reaction involved  formation of Intermediate  free radicals:
 RX + Na → R. + Nax

                 Free radicals

 R. + R. → R-R