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Fittig Reaction

Fittig Reaction is a form of ‘Coupling Reaction’ in which two aryl(aromatic) groups combine in the presence of Sodium in dry ether or THF(Tetrahydrofuran) to form a biaryl species.

Example: Halobenzene reacts in the presence of sodium metal in dry ether to form biphenyl. Here, X = Cl, Br, I.

Halobenzene reacts in the presence of sodium metal in dry ether to form biphenyl.
Halobenzene reacts in the presence of sodium metal in dry ether to form biphenyl.

Although very similar but this reaction should not be confused with Wurtz-Fittig Reaction and Wurtz Reaction. In Wurtz-Fittig Mechanism, an aryl group combines with an alkyl group. Wurtz Reaction happens when two alkyl groups combine in the presence of Sodium metal in dry ether. While, in this reaction, two aryl groups combine with each other.

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History

Wilhelm Rudolph Fittig
Wilhelm Rudolph Fittig (Source)

Wurtz Reaction was first reported by Charles Adolphe Wurtz in 1855.

Wilhelm Rudolph Fittig extended the work by Wurtz to include Aryl halides in the reaction. This gave rise to the Fittig Reaction and Wurtz-Fittig Reaction.

Fittig Reaction Mechanism

 There are mainly two experimentally proven reaction pathways of the Fittig Reaction:

  1. Free Radical Mechanism
  2. The Organo-Alkali Mechanism

The Free Radical Mechanism

The free radical mechanism involves the formation of free phenyl radicals, which are highly reactive.

Step 1: Formation of Phenyl Free Radical

In the presence of Sodium in dry ether, homolysis of the C-X bond of the Aryl Halide happens. This leads to the formation of a phenyl-free radical and NaX salt.

Step-1 of Free Radical Mechanism - Fittig Reaction
Step-1 of Free Radical Mechanism

Step 2: Coupling of the Benzene Rings

The phenyl radicals formed in the previous step are highly reactive. Two phenyl radicals combine to form biphenyl(phenylbenzene or diphenyl).

Step-2 of Free Radical Mechanism - Fittig Reaction
Step-2 of Free Radical Mechanism

 The Organo-Alkali Mechanism

Another proven pathway to undergo this reaction is through the formation of an “Organo-Alkali” intermediate. Organic compounds form bonds with Alkali metals to form Organo-Alkali compounds.

Step 1: Formation of the Organo-Alkali Intermediate

Homolysis of the C-X bond in the Aryl Halide leads to the formation of phenyl radical, which combines with the sodium atom to form the Aryl-Sodium.

Step-1 of Free Organo-Alkali Mechanism
Step-1 of Free Organo-Alkali Mechanism

Step 2: Nucleophilic Attack of the Organo-Alkali to the Aryl Halide

Organo-Alkali is highly reactive in nature. The Aryl-Sodium here acts as a strong nucleophile and attacks the Aryl Halide present in the reaction mixture. This leads to the heterolysis of C-Na and C-X bonds. Na+ and X combine to form a salt. Phenyl-benzene is formed as the product of this nucleophilic addition.

Step-2 of Free Organo-Alkali Mechanism
Step-2 of Free Organo-Alkali Mechanism

Applications of Fittig Reaction

This coupling reaction is not used in industry because of the reason that side-reactions like elimination and rearrangement are highly likely. Even then, this reaction is used in labs for the coupling of various aromatic rings in complex organic compounds.

Wurtz-Fittig reaction, a modification of this reaction, is used in labs to prepare Organo-Silicon compounds. It is also used for the Alkylation of Aryl Halides.

FAQs

What is the Fittig Reaction?

This reaction is a form of ‘Coupling Reaction’ in which Aryl Halide reacts in the presence of Sodium metal in dry ether or Tetrahydrofuran to produce a bi-aryl compound and Sodium salt of the halide.
For example, Chlorobenzene reacts in the presence of Sodium metal in dry ether or Tetrahydrofuran to produce biphenyl and NaCl.
\(2C_6H_5Cl \ + \ 2Na \, \small{\text{(in dry ether)}} \rightarrow (C_6H_5)_2 \ + \ 2NaCl\)

What is the difference between the Wurtz reaction, Fittig Reaction, and Wurtz-Reaction?

Wurtz Reaction involves a reaction between Alkyl halides and Alkyl Halides.
Fittig Reaction involves a reaction between Aryl Halides and Aryl Halides.
Wurtz-Fittig Reaction involves a reaction between Aryl Halides and Alkyl Halides.

More Organic Reactions

Perkin ReactionSandmeyer Reaction
Finkelstein ReactionGattermann Reaction
Reimer Tiemann ReactionStephen Reaction
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