Why, Wurtz reaction is limited to the synthesis of symmetric alkanes ?

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Sapna Kumari

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Because the product will be a mixture of alkanes which is difficult to separate.For unsymmetrical alkane use COREY HOUSE Reaction
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Wurtz reaction can also be used for the reaction of 2 different alkyl halides. But there will be 3 different products formed due to 3 different possible reactions that occur. For example consider iodomethane (CH3-I) and iodoethane (CH3-CH2-I) and you want to prepare propane by Wurtz reaction then these...
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Wurtz reaction can also be used for the reaction of 2 different alkyl halides. But there will be 3 different products formed due to 3 different possible reactions that occur. For example consider iodomethane (CH3-I) and iodoethane (CH3-CH2-I) and you want to prepare propane by Wurtz reaction then these reactions will take place: CH3-I + 2Na + I-CH2-CH3 -----> CH3-CH2-CH3 + 2NaI CH3-I + 2Na + I-CH3 -----> CH3-CH3 + 2NaI CH3-CH2-I + 2Na + I-CH2-CH3 ------> CH3-CH2-CH2-CH3 + 2NaI The products formed ( propane, ethane and butane ) have very less difference in their boiling points. Therefore it will be difficult to separate the products with fractional distillation. It is because of this reason that only symmetrical alkanes are generally synthesized using wurtz reaction. read less
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Mechanism of the simple Wurtz reaction. R---X + 2Na -----> (R)-(Na)+ this (R)- joins the 'R' from another R----X molecule and the (Na) joins the X part giving R----R + NaX. Thus you are able to create only symmetric alkanes. If you use two different alkyl halides then a mixture with small percentage...
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Mechanism of the simple Wurtz reaction. R---X + 2Na -----> (R)-(Na)+ this (R)- joins the 'R' from another R----X molecule and the (Na) joins the X part giving R----R + NaX. Thus you are able to create only symmetric alkanes. If you use two different alkyl halides then a mixture with small percentage of unsymmetric alkanes are produced but because of their very similar boiling points and their physical properties they cannot be separated and thus Wurtz reaction is not good for producing unsymmetric alkanes. read less
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Chemistry for CBSE,STAE ,ISC AND IIT-JEE,MH-CET,PMT and all other level +12 competitive level exam.

If we use the unsymmetrical alkyle halide their is probability to formation of byproducts which is very difficult to separate from reaction mix,as the boiling point of these product is very similar.
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Chemistry Tutor

if two different alkyl halogens are reacting with Na, then the formation of two or more alkanes may form, since its due to formation of two different radicals and it is also noted that the formed products (Alkanes) are very closed billing points, hence its difficult to separate from the mixture.
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B.Sc, M.Sc, Ph.D, MBA (Finance and Marketing)

In wurtz reaction if take a single haloalkane as reactant it gives symmetric alkanes but if two or more different haloalkanes r taken it results in mixture of alkanes (symmetric and asymmetric) and they r difficult to separate even through fractional distillation. Becoz they form azeotropic mixture...
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Engineer

The Wurtz reaction is limited to synthesis of symmetrical alkanes with even number of carbon atoms only. The number of carbons in the alkane is double that of alkyl halide (n ---> 2n type reaction) If dissimilar alky halides are used, a mixture of alkanes is formed. It is usually difficult to separate...
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The Wurtz reaction is limited to synthesis of symmetrical alkanes with even number of carbon atoms only. The number of carbons in the alkane is double that of alkyl halide (n ---> 2n type reaction) If dissimilar alky halides are used, a mixture of alkanes is formed. It is usually difficult to separate the mixture and hence wurtz reaction not a suitable method to synthesize unsymmetrical alkanes. read less
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In Wurtz reaction, two alkyl halide molecules are coupled in presence of sodium metal in anhydrous ether or Tetrahydrofuran to form a new carbon carbon bond and thus by giving a symmetrical alkane. Dry Ether R-X + 2Na + X-R -----------------> R-R + 2NaX Where X = halogen * The Wurtz reaction must...
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In Wurtz reaction, two alkyl halide molecules are coupled in presence of sodium metal in anhydrous ether or Tetrahydrofuran to form a new carbon carbon bond and thus by giving a symmetrical alkane. Dry Ether R-X + 2Na + X-R -----------------> R-R + 2NaX Where X=halogen * The Wurtz reaction must be performed under anhydrous conditions because the alkyl free radical formed (see the mechanism) during the reaction is strongly basic and can abstract proton from water. * In case of alkyl and aryl fluorides as well as aryl chlorides, tetrahydrofuran is used as solvent instead of ether. * The Wurtz reaction is limited to synthesis of symmetrical alkanes with even number of carbon atoms only. The number of carbons in the alkane is double that of alkyl halide (n ---> 2n type reaction) * If dissimilar alky halides are used, a mixture of alkanes is formed. It is usually difficult to separate the mixture and hence wurtz reaction not a suitable method to synthesize unsymmetrical alkanes. E.g. The Wurtz reaction between R-X and R'-X yields not only R-R' but also R-R and R'-R'. This mixture cannot be separated easily. * Methane cannot be prepared by this method. * A modification of this reaction involving alkyl and aryl halides is called Wurtz-Fittig reaction. If only aryl halides are subjected to coupling, the reaction is called as Fittig reaction. read less
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Msc

this is known as one of the drawbacks of Wurtz reaction.The reasons are- 1. If assymetrical alkanes are used with odd numer of carbon atoms they react with each other as well as among themselves producing a mixture of three alkanes.Example- CH3-I + 2Na + I-CH2-CH3 -----> CH3-CH2-CH3 + 2NaI CH3-I...
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this is known as one of the drawbacks of Wurtz reaction.The reasons are- 1. If assymetrical alkanes are used with odd numer of carbon atoms they react with each other as well as among themselves producing a mixture of three alkanes.Example- CH3-I + 2Na + I-CH2-CH3 -----> CH3-CH2-CH3 + 2NaI CH3-I + 2Na + I-CH3 -----> CH3-CH3 + 2NaI CH3-CH2-I + 2Na + I-CH2-CH3 ------> CH3-CH2-CH2-CH3 + 2NaI 2. Moreover these alkanes cannot be separated (as they have high boiling points) by fractional distillation. Hope this will help you. read less
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difficult to separate as the difference in the boiling points of the products is very low in these cases, making distillation unusable. Also, since the reaction involves free radical species, a side reaction occurs to produce an alkene
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