Mechanism

1. Birch Reduction
Mr. Yashvant V. Khandare

2. M liq. NH3 M [H3N-------e-------NH3]
M = Na /Li (Solvated Electron)
The Birch reduction is an organic reaction where
aromatic compounds undergo partial reduction to 1,4-
unconjugated cyclohexadiene compounds in presence
of alkali metals in liquid ammonia i.e. solvated
electrons.
H H
(Aromatic)
H H
(Non-aromatic)
M / Liq. NH3
M = Na / Li
The reduction is conducted by Sodium or Lithium
metal in liquid ammonia at -33oC
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3. Radical
In chemistry, a radical is an atom, molecule, or ion that
has an unpaired valence electron.
• It may be generated in a number of ways, but typical
methods involve redox reactions.
• Ionizing radiation, heat, electrical discharges, and
electrolysis are known to produce radicals.
A radical is the hydroxyl radical, a
molecule that has one unpaired
electron on the oxygen atom.

4. The examples are triplet oxygen and triplet carbene which
have two unpaired electrons.

5. Examples of Birch Reduction

6. The alkali metal donate an electron to the aromatic comp,
forming the alkali metal cation and radicle anion.
The radicle anion is basic and abstract the proton from
protic solvent to give ion.
This pick up another electron to give ion. Its is quenched
again by the proton to give dihydro comp.

7. Mechanism
It consist of three steps
Step-1 :- Sodium oxidises to Na+ and radical anion I.
Step-2:- Radical anion accepts a proton from the
alcohol to give radical II which is reduced to carbanion
III by another sodium atom.
Step-3:- Carbanion III then accept a proton from
alcohol to give product 1,4-Cyclohexadiene.

8. Mechanism

9. e
M / liq.NH3
H
H
H H
e
H
H H
H
H H
H
HOR
ROH
H
(Radical Anion)
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MECHANISM