Question

What is the difference between Clemmensen reduction and Wolff Kishner reduction?

Answer 1

Hint: Reduction reactions are those in which loss of oxygen or addition of hydrogen takes place. In both Clemmensen reduction and Wolff Kishner reduction, the reduction of aldehyde and ketone functional groups into alkanes takes place. However, both reactions are different only in the use of reagents.

Complete answer:
Both Clemmensen reduction and Wolff Kishner reduction lead to the reduction of aldehyde and ketone functional groups into alkane. However, both are differ in the use of reaction conditions. In Clemmensen reduction, Zinc-amalgam in presence of aqueous $HCl$ under heating is used for the reduction. This is illustrated in the following diagram:
 $RCO{R}^{\prime }\stackrel{Zn-Hg,dilHCl}{\to }RC{H}_2{R}^{\prime }$
However, in the Wolff Kishner reduction, hydrazine in the presence of strong bases such as $KOH$ under heating has been used for the reduction purpose. This is illustrated in the following diagram.
 $RCO{R}^{\prime }\stackrel{N{H}_{2}N{H}_2,KOH}{\to }RC{H}_2{R}^{\prime }$
From the above two reactions, we conclude that Clemmesen provides the strong acidic conditions for performing the reduction while Wolff Kishner provides the strong basic conditions for performing the reduction. Therefore, in acidic sensitive (or labile) substrates, Clemmensen reduction can be preferred to use. In contrast, in base sensitive (or labile) substrates, Wolff Kishner reduction will be preferred.

Note:
It is important to note that both Clemmensen reduction and Wolff Kishner reduction lead to the reduction of aldehyde and ketone functional groups into alkane. However, both are differ in the use of reaction conditions. Zinc-amalgam in the presence of aqueous $HCl$ is used in Clemmensen reduction while hydrazine under strong base is used in Wolff Kishner reduction.