Wurtz reaction

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Wurtz reaction
Named after Charles-Adolphe Wurtz
Reaction type Coupling reaction
Identifiers
Organic Chemistry Portal wurtz-reaction
RSC ontology ID RXNO:0000074

The Wurtz reaction, named after Charles-Adolphe Wurtz, is a coupling reaction in organic chemistry, organometallic chemistry and recently inorganic main group polymers, whereby two alkyl halides are reacted with sodium to form a new alkane:

2R–X + 2Na → R–R + 2Na+X

Other metals have also been used to effect the Wurtz coupling, among them silver, zinc, iron, activated[further explanation needed] copper, indium and a mixture of manganese and copper chloride.[1] The related reaction dealing with aryl halides is called the Wurtz-Fittig reaction.This can be explained by the formation of free radical intermediate and its subsequent disproportionation to give alkene.

Mechanism[edit]

The reaction consists of a halogen-metal exchange involving the radical species R• (in a similar fashion to the formation of a Grignard reagent and then the carbon–carbon bond formation in a nucleophilic substitution reaction.)

One electron from the metal is transferred to the halogen to produce a metal halide and an alkyl radical.

R–X + M → R• + M+X

The alkyl radical then accepts an electron from another metal atom to form an alkyl anion and the metal becomes cationic. This intermediate has been isolated in several cases.

R• + M → RM+

The nucleophilic carbon of the alkyl anion then displaces the halide in an SN2 reaction, forming a new carbon-carbon covalent bond.

RM+ + R–X → R–R + M+X

Examples and reaction conditions[edit]

Due to several limitations this reaction is seldom used. For example, it is intolerant of a range of functional groups. Wurtz coupling is, however, useful in closing small, especially three-membered, rings. Bicyclobutane was prepared this way from 1-bromo-3-chlorocyclobutane in 95% yield. The reaction is conducted in refluxing dioxane, at which temperature, the sodium is liquid.[2]

Wurtz-reaction Bicyclobutane synthesis.svg

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Limitations[edit]

The Wurtz reaction is limited to the synthesis of symmetric alkanes. If two dissimilar alkyl halides are taken as reactants, then the product is a mixture of alkanes that is often difficult to separate as the difference in the boiling points of the products is very low in these cases, making distillation unusable.[citation needed] Also, since the reaction involves free radical species, a side reaction occurs to produce an alkene. This side-reaction becomes more significant when the alkyl halides are bulky at the halogen-attached carbon.Methane can not be obtained by this method.The reaction fails in case of tertiary halides.

See also[edit]

References[edit]

  1. ^ March Advanced Organic Chemistry 5th edition p. 535
  2. ^ Gary M. Lampman and James C. Aumiller "Bicyclo[1.1.0]butane" Organic Syntheses, 1971, volume 51, pp 55-9. doi:10.15227/orgsyn.051.0055