Difference Between Clemmensen and Wolff Kishner Reduction

The key difference between Clemmensen and Wolff Kishner reduction is that the Clemmensen reduction involves the conversion of ketone or aldehydes into alkanes whereas the Wolff Kishner reduction involves the conversion of carbonyl groups into methylene groups.

Both these processes do these conversions via reducing the functional groups. Therefore, these processes require specific reaction conditions and catalysts for the successful progression of the reaction. Since the reactants for each process are organic molecules, we use these processes in organic synthesis reactions.

CONTENTS

1. Overview and Key Difference
2. What is Clemmensen Reduction
3. What is Wolff Kishner Reduction
4. Side by Side Comparison – Clemmensen vs Wolff Kishner Reduction in Tabular Form
5. Summary

What is Clemmensen Reduction?

Clemmensen reduction is an organic chemical reaction in which we convert a ketone or aldehydes into an alkane. We need to use a catalyst for this reaction; it is amalgamated zinc (mercury alloyed with zinc ) with hydrochloric acid. Therefore, the mercury alloyed with zinc does not participate in the reaction. It only provides a clean, active surface for the reaction. The name of the processes derived after the Danish scientist Erik Christian Clemmensen.

This process is highly effective in the reduction of aryl-alkyl ketones. Moreover, the zinc metal reduction is much more effective with aliphatic or cyclic ketones. More importantly, the substrate of this reaction has to be unreactive towards the strongly acidic conditions of the reaction.

What is Wolff Kishner Reduction?

Wolff Kishner reduction is an organic chemical reaction that we use to convert a carbonyl functional group into a methylene group. This reaction got its name after the two scientists Nikolai Kirschner and Ludwig Wolff. The major applications of this reaction are in the synthesis of scopadulcic acid B, aspidospermine and dysidiolide.

Unlike Clemmensen reduction, this reaction requires strongly basic conditions. Therefore, in the reaction process, the first step is to generation hydrazone via condensation of hydrazine with the ketone or aldehyde substrate. Then as the second step, we should deprotonate the hydrazone using alkoxide base. Afterwards, comes the step in which a diimide anion forms. Then this anion collapses releasing N₂ gas, and it leads to the formation of an alkylation. Eventually, we can protonate this alkylation to get the desired product.

What is the Difference Between Clemmensen and Wolff Kishner Reduction?

Clemmensen and Wolff Kishner reduction is very important in the organic synthesis of different chemical compounds. However, the key difference between Clemmensen and Wolff Kishner reduction is that the Clemmensen reduction involves the conversion of ketone or aldehydes into alkanes whereas the Wolff Kishner reduction involves the conversion of carbonyl groups into methylene groups. Moreover, we use a catalyst in the Clemmensen reduction reaction; it is amalgamated zinc. But we do not use a catalyst for Wolff Kishner reduction reaction. Another difference between Clemmensen and Wolff Kishner reduction is that Clemmensen reduction uses strongly acidic conditions, hence not suitable for acid-sensitive substrates. Whereas, Wolff Kishner reduction uses strongly basic conditions; thus, not suitable for base sensitive substrates.

The below infographic tabulates the difference between Clemmensen and Wolff Kishner reduction in more detail.

Summary – Clemmensen vs Wolff Kishner Reduction

There are many different organic chemical reactions that we use in organic chemistry for the synthesis of important compounds. Hence, Clemmensen and Wolff Kishner reduction are such two reactions. The key difference between Clemmensen and Wolff Kishner reduction is that the Clemmensen reduction involves the conversion of ketone or aldehydes into alkanes whereas the Wolff Kishner reduction involves the conversion of carbonyl groups into methylene groups.

Reference:

1. Libretexts. “Clemmensen Reduction.” Chemistry LibreTexts, Libretexts, 6 Aug. 2017. Available here 
2. “Wolff–Kishner Reduction.” Wikipedia, Wikimedia Foundation, 26 July 2018. Available here  

Image Courtesy:

1.”Clemmensen Reduction Scheme” (Public Domain) via Commons Wikimedia
2.”Wolff-Kishner-reaction scheme-new”By C kleinlein – Own work, (CC BY-SA 3.0) via Commons Wikimedia