Consider the following reaction:

Name of the reaction is :

Fittig reaction

The correct answer is option 4. 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, \(X = Cl, Br, I\).

Mechanism:

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

(i) Free Radical Mechanism

(ii) The Organo-Alkali Mechanism

(i) 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 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).

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 \(C-Cl\) bond in the Aryl Halide leads to the formation of phenyl radical, which combines with the sodium atom to form the Aryl-Sodium.

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 \(C-Cl\) bonds. \(Na^+\) and \(Cl^–\) combine to form a salt. Phenyl-benzene is formed as the product of this nucleophilic addition.