Wurtz coupling
| 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 metal in dry ethereal solution to form a higher alkane:
Other metals have also been used to effect the Wurtz coupling, among them silver, zinc, iron, activatedcopper, indium and a mixture of manganese and copper chloride. 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. The Wurtz reaction occurs through a free radical mechanism.
The reaction consists of a halogen-metal exchange involving the radical species R• (in a similar fashion to the formation of a Grignard reagent) with carbon–carbon bond formation occurring in a nucleophilic substitution reaction.
One electron from the metal is transferred to the halogen to produce a metal halide and an alkyl radical.
The alkyl radical then accepts an electron from another metal atom to form an alkyl anion. This intermediate has been isolated in several cases.
The nucleophilic carbon of the alkyl anion then displaces the halide in an SN2 reaction, forming a new carbon-carbon covalent bond.
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. This reaction has poor yield which is a consequence of multiple product formation. In the case of (1,3), (1,4), (1,5), (1,6) dihalides, it leads to formation of cyclic products. In vicinal dihalides, it forms alkenes whereas in geminal dihalides, it forms alkynes.
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