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Clemmensen Reduction

Clemmensen reduction   Named Reactions in Organic Synthesis

Reaction category:
Reduction Reactions

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In 1913 the Danish chemist Erik Christian Clemmensen reported that simple ketones and aldehydes reacted with amalgamated zinc (Zn/Hg) in the presence of 40% aqueous hydrochloric acid and in a hydrophobic solvent such as toluene to give the corresponding alkanes after several hours under reflux conditions. Ever since, this method of converting carbonyl groups to the corresponding methylene group has been known as the Clemmensen reduction.

The Clemmensen reduction's original harsh conditions are not conducive to acid sensitive substrates so several modifications have been made to increase its synthetic utility by expanding the functional group tolerance. Yamamura and his colleagues developed a milder procedure using organic solvents such as tetrahydrofuran saturated with hydrogen halides such as hydrogen chloride or bromide in the presence of activated zinc dust at ice-bath temperatures. Some carbonyl compounds exhibit poor solubility in the usual solvents, and thus a second solvent such as acetic acid, ethanol or dioxane is added to increase solubility and facilitate the reaction.

Many heterocyclic 1,3-dicarbonyl compounds possessing alkyl substituents at the electronegative “2” position exhibit interesting biological properties. Synthesis of many of these molecules was expedited by Thomas Kappe and co-workers using a version of the Clemmensen reduction.


Mechanism of the Clemmensen reduction

Clemmensen reduction reaction mechanism

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Other reaction categories:
Radical reactions NEW!
Electrophilic aromatic substitution
Nucleophilic substitution reactions
Heterocycle formation
Transition metal-catalyzed couplings
Reactions involving carbonyl compounds
Rearrangement reactions
Electrophilic addition reactions

Some relevant Alfa Aesar products for the Clemmensen reduction:

Zinc powder, -100 mesh, 97+%
Zinc powder, -140+325 mesh, 99.9% (metals basis)
Zinc granules, ACS, -20 mesh, 99.8% min
Zinc powder, -100 mesh, 99.9% (metals basis)
Zinc mossy, 2.5cm (0.98in) & down, 99% (metals basis) Mercury(II) chloride, 98+%
Mercury(II) chloride, ACS, 99.5% min
Mercury(II) chloride, Puratronic®, 99.999% (metals basis)
Hydrochloric acid, 99.999% (metals basis), 36.5% min
Hydrochloric acid, 99.999999% (metals basis), 33% min

We have many aldehydes and ketones within the Alfa Aesar portfolio.




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