Wurtz reaction
Wurtz reaction | |
---|---|
Named after | Charles Adolphe Wurtz |
Reaction type | Coupling reaction |
Identifiers | |
Organic Chemistry Portal | wurtz-reaction |
In
- 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
Mechanism
The reaction proceeds by an initial metal–halogen exchange, which is described with the following idealized stoichiometry:
- R−X + 2 M → RM + MX
This step may involve the intermediacy of
- RM + RX → R−R + MX
The process resembles an SN2 reaction, but the mechanism is probably complex.
Examples and reaction conditions
The reaction is intolerant of a many functional groups 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 yields, other metals have also been tested to effect the Wurtz-like couplings: silver, zinc, iron, activated copper, indium, as well as mixture of manganese and copper chloride.
Wurtz coupling is useful in closing small, especially three-membered, rings. In the cases of 1,3-, 1,4-, 1,5-, and 1,6- dihalides, Wurtz-reaction conditions lead to formation of cyclic products, although yields are variable. Under Wurtz conditions, vicinal dihalides yield alkenes, whereas geminal dihalides convert to alkynes. 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]
Extensions to main group compounds
Although the Wurtz reaction is only of limited value in organic synthesis, analogous couplings are useful for coupling main group halides. Hexamethyldisilane arises efficiently by treatment of trimethylsilyl chloride with sodium:
- 2 Me3SiCl + 2 Na → Me3Si−SiMe3 + 2 NaCl
Tetraphenyldiphosphine is prepared analogously:
- 2 Ph2PCl + 2 Na → Ph2P−PPh2 + 2 NaCl
Similar couplings have been applied to many main group halides. When applied to main group dihalides, rings and polymers result. Polysilanes and polystananes are produced in this way[3]
- n Me2SiCl2 + 2n Na → (Me2Si)n + 2n NaCl
See also
Further reading
- Adolphe Wurtz (1855). "Sur une nouvelle classe de radicaux organiques". Annales de chimie et de physique. 44: 275–312.
- Adolphe Wurtz (1855). "Ueber eine neue Klasse organischer Radicale". .
- Organic-chemistry.org
- Organic Chemistry, by Morrison and Boyd
- Organic Chemistry, by Graham Solomons and Craig Fryhle, Wiley Publications