Clemmensen reduction- Heterocyclic and Organic chemistry- As per PCI syllabus

1. CLEMMENSEN REDUCTION
Dr Akhil Nagar
RCP-IPER

2. CLEMMENSEN REDUCTION
• Ketones and aldehydes on reduction with zinc amalgam and
HCl gives the corresponding hydrocarbons, i.e carbonyl
group is converted to methylene group. This is known as
Clemmensen Reduction.
Zn/Hg/HCl
RCOR’ -------------- RCH2R’

3. • The Clemmensen Reduction allows the deoxygenation of
aldehydes or ketones, to produce the corresponding
hydrocarbon.
• The substrate must be stable to strong acid. The
Clemmensen Reduction is complementary to the Wolff-
Kishner Reduction, which is run under strongly basic
conditions. Acid-labile molecules should be reduced by the
Wolff-Kishner protocol.

5. Mechanism of the Clemmensen Reduction
The reduction takes place at the surface of the zinc catalyst. In this
reaction, alcohols are not postulated as intermediates, because subjection
of the corresponding alcohols to these same reaction conditions does not
lead to alkanes. The following proposal employs the intermediacy of zinc
carbenoids to rationalize the mechanism of the Clemmensen Reduction.

6. Application

7. • Amalgam – is the alloy of mercury. The zinc amalgam is the
alloy of mercury with zinc.
• The zinc metal or dust used are not so effective as the
activation will dissolve the zinc and H2 gas is been released.
• To prevent this the zinc reacted with the mercury to form
amalgam-A Trap of metal ion. The zinc particles are
smoothly dissolves and evenly distributed in mercury alloy.
• The HCl was then added in solution which don’t allow the
H2 gas to get released from system. The active molecules
(Nascent Hydrogen) of H are then used to treat the solution.