Q.70. - Organic Chemistry

Question

Question: The Birch reduction is a dissolving metal reaction that converts substituted benzenes to cyclohexa-1,4-dienes using Li and liquid ammonia in the presence of an alcohol. Draw a stepwise mechanism for the following Birch reduction.

Step-by-Step Solution

Answer

Answer

 

The stepwise mechanism for the following Birch reduction is as given below:

Step 1: Birch reduction

In Birch reduction, aromatic rings undergo a 1,4-reduction to provide unconjugated cyclohexadiene.

 

Sodium or lithium metal in the liquid ammonia are used as reducing agent in Birch reduction. It is performed in the presence of alcohol.

Step 2: Stepwise mechanism for the Birch reduction

The following reaction shows the Birch reduction:  

• The reagents used in the Birch reduction are metals donating their electron to the organic compound.

 

• In the first step, the electron adds to the double bond leading to the formation of the radical anion. 

A radical anion contains both a lone pair of electrons and a negative charge. 

• In the second step, the addition of one more electron in the structure leads to the formation of the radical anion. Moreover, the solvent serves the purpose of protonating the anion, leading to the formation of the product.

Step 1

Step 2