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In
organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...
, the Wurtz reaction, named after
Charles Adolphe Wurtz Charles Adolphe Wurtz (; 26 November 181710 May 1884) was an Alsatian French chemist. He is best remembered for his decades-long advocacy for the atomic theory and for ideas about the structures of chemical compounds, against the skeptical opinio ...
, is a
coupling reaction A coupling reaction in organic chemistry is a general term for a variety of reactions where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M (R = ...
whereby two
alkyl halide The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely ...
s are treated with sodium metal to form a higher alkane. : 2 R−X + 2 Na → R−R + 2 NaX The reaction is of little value except for intramolecular versions. A related reaction, which combines alkyl halides with aryl halides is called the Wurtz–Fittig reaction.


Mechanism

The reaction proceeds by an initial
metal–halogen exchange In organometallic chemistry, metal–halogen exchange is a fundamental reaction that converts a organic halide into an organometallic product. The reaction commonly involves the use of electropositive metals (Li, Na, Mg) and organochlorides, bromid ...
, which involves this idealized stoichiometry: : R−X + 2 M → RM + MX This step involves the intermediacy of
radical Radical may refer to: Politics and ideology Politics *Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...
species R·. This step resembles the formation of a
Grignard reagent A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide ...
. These RM intermediates have been isolated in several cases. The organometallic intermediate next reacts with the alkyl halide forming a new carbon–carbon covalent bond. : RM + RX → R−R + MX The process resembles an SN2 reaction, but the process is probably complex, which may explain the inefficiency of the reaction.


Examples and reaction conditions

The reaction is intolerant of a range of
functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...
s which would be attacked by sodium. For similar reasons, the reaction is conducted in unreactive solvents such as ethers. In efforts to improve the reaction, other metals have also been evaluated to effect the Wurtz-like couplings among them
silver Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...
,
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
,
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
,
activated "Activated" is a song by English singer Cher Lloyd. It was released on 22 July 2016 through Vixen Records. The song was made available to stream exclusively on ''Rolling Stone'' a day before to release (on 21 July 2016). Background In an interv ...
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
,
indium Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts p ...
and a mixture of
manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
and copper chloride. Wurtz coupling is useful in closing small, especially three-membered, rings.
Bicyclobutane Bicyclobutane is an organic compound with the formula C4H6. It is a bicyclic molecule consisting of two ''cis''-fused cyclopropane rings, and is a colorless and easily condensed gas. Bicyclobutane is noted for being one of the most strained co ...
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. :


Extensions to main group compounds

Although the Wurtz reaction is only of limited value in
organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...
, analogous couplings are useful for coupling main group halides.
Hexamethyldisilane Hexamethyldisilane ( TMS2) is the organosilicon compound with the formula Si2(CH3)6, abbreviated Si2Me6. It is a colourless liquid, soluble in organic solvents. Synthesis and reactions Hexamethyldisilane can be produced by Wurtz-like coupling o ...
arises efficiently by treatment of
trimethylsilyl chloride Trimethylsilyl chloride, also known as chlorotrimethylsilane is an organosilicon compound ( silyl halide), with the formula (CH3)3SiCl, often abbreviated Me3SiCl or TMSCl. It is a colourless volatile liquid that is stable in the absence of water. ...
with sodium: :
Tetraphenyldiphosphine Tetraphenyldiphosphine is the organophosphorus compound with the formula Ph2sub>2, where Ph = phenyl In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the sym ...
is prepared analogously: : Similar couplings have been applied to many main group halides. When applied to main group dihalides, rings and polymers result.
Polysilane Polysilanes are organosilicon compounds with the formula (R2Si)n. They are relatives of traditional organic polymers but their backbones are composed of silicon atoms. They exhibit distinctive optical and electrical properties. They are mainly use ...
s are produced in this way :


Limitations

The Wurtz reaction is seldom used because of side reactions.March Advanced Organic Chemistry 7th edition p. 512 It has limited use 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 by fractional distillation as the differences between the boiling points of the products are typically very low. Methane can not be obtained by this method. This type of reaction fails in case of tertiary halides. Also, since the reaction involves free radical species, a
side reaction A side reaction is a chemical reaction that occurs at the same time as the actual main reaction, but to a lesser extent. It leads to the formation of by-product, so that the yield of main product is reduced: : + B ->[] P1 : + C ->[] P2 P1 is th ...
occurs to produce an alkene. This side reaction becomes more significant when the alkyl halides are bulky at the halogen-attached carbon atom.


See also

* Wurtz–Fittig reaction *
Ullmann reaction The Ullmann reaction or Ullmann coupling is a coupling reaction between aryl halides. Traditionally this reaction is effected by copper, but palladium and nickel are also effective catalysts. The reaction is named after Fritz Ullmann. Mechanism ...


Further reading

* *
Organic-chemistry.org
*''Organic Chemistry'', by Morrison and Boyd *''Organic Chemistry'', by Graham Solomons and Craig Fryhle, Wiley Publications


References

{{reflist, colwidth=30em Condensation reactions Carbon-carbon bond forming reactions Name reactions