Fittig & Wurtz-Fittig Reactions: Aryl Coupling
The Fittig Reaction and Wurtz-Fittig Reaction are organometallic coupling reactions used to synthesize polyaromatic compounds and alkylarenes, respectively. They are extensions of the classic Wurtz reaction, utilizing Sodium metal in Dry Ether.
1. Fittig Reaction
The Fittig reaction involves the coupling of two Aryl Halide molecules in the presence of Sodium metal and dry ether to form Diaryl (Biphenyl) compounds.
Example: Synthesis of Diphenyl
When Chlorobenzene reacts with Sodium in dry ether, Diphenyl (Biphenyl) is formed.
2. Wurtz-Fittig Reaction
This is a crossover reaction involving the coupling of one molecule of Alkyl Halide ($R-X$) and one molecule of Aryl Halide ($Ar-X$) with Sodium to form an Alkylarene.
Example: Synthesis of Toluene
Reaction between Bromobenzene and Methyl Bromide.
3. Mechanism
Similar to the Wurtz reaction, two mechanisms are proposed: Organometallic and Free Radical.
- Organometallic Pathway: Formation of an organosodium intermediate ($C_6H_5^-Na^+$) which then acts as a nucleophile attacking the alkyl halide ($S_N2$).
- Radical Pathway: Sodium transfers electrons to halides forming free radicals ($C_6H_5^\bullet$ and $R^\bullet$) which then combine.
4. Comparison Table
| Reaction | Reactants | Main Product |
|---|---|---|
| Wurtz Reaction | 2 Alkyl Halides ($2R-X$) | Alkane ($R-R$) |
| Fittig Reaction | 2 Aryl Halides ($2Ar-X$) | Diaryl / Biphenyl ($Ar-Ar$) |
| Wurtz-Fittig | Aryl Halide + Alkyl Halide | Alkylarene ($Ar-R$) |
5. Limitations (Wurtz-Fittig)
Side Products
Since Wurtz-Fittig involves two different halides, side reactions occur due to self-coupling.
Example: Mixing $Ph-X$ and $R-X$ yields a mixture of:
1. $Ph-R$ (Major desired product)
2. $Ph-Ph$ (Biphenyl - Fittig side product)
3. $R-R$ (Alkane - Wurtz side product)
Reaction Mastery Quiz
Test your concepts on Aryl coupling. 10 MCQs with explanations.
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