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ANIMATED VIDEO PRESENTATION ON FITTIG REACTION
* In Fittig reaction, two aryl halides are coupled in presence of sodium metal in dry ether or tetrahydrofuran to furnish biaryls compounds. It's named after the German chemist Wilhelm Rudolph Fittig who discovered it in 1860.
| Dry Ether | ||
| Ar-X + 2Na + X-Ar | -----------------> | Ar-Ar + 2NaX |
Where Ar = aryl group, X = halogen
* The Fittig reaction plays a crucial role in the creation of carbon-carbon bonds and connecting aromatic rings directly.
* The yields will be improved by using ultrasound, especially in two-phase reactions.
* A modification of reaction which involves, an alkyl halide and an aryl halide is called Wurtz-Fittig reaction.
* Refer Wurtz reaction for a similar reaction between alkyl halides.
MECHANISM OF FITTIG REACTION
The mechanism of the Fittig reaction proceeds through the following steps:
* Formation of Aryl free radical
Initially, a single electron is transferred from sodium metal to the aryl halide, causing heterolytic cleavage of the Ar-X bond. This results in the formation of an aryl free radical and a halide ion.
| Ar-X | + | Na | ---------> | Ar. | + | NaX |
| Aryl free radical |
* Formation of carobonium ion
In the next step, one more electron is transferred from second sodium atom to the free radical to give an aryl carbonium ion.
| Ar. | + | Na | ---------> | Ar-Na+ | ||
| Aryl sodium |
* Nucleophilic Substitution
The aryl carbanion generated in the previous step replaces the halide group in another aryl halide through nucleophilic substitution, resulting in the formation of a biaryl compound. This step follows second-order kinetics.
| Ar- Na+ | + | Ar-X | ---------> | Ar-Ar | + | Na+X- | |
| Symmetrical biaryl |
FITTIG REACTION EXAMPLES
1) A well-known demonstration of the Fittig reaction is the formation of biphenyl when bromobenzene reacts with sodium metal in dry ether as shown below:
