Master Organic Chemistry Reaction Guide

Wolff Kishner Reaction – conversion of ketones/aldehydes to alkanes

Description: The Wolff-Kishner is a reaction for converting carbonyls (such as ketones and aldehydes) into alkanes.
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30 thoughts on “Wolff Kishner Reaction – conversion of ketones/aldehydes to alkanes

  1. Yes, but for a Wolff-Kishner reaction that does not imply the use of a strong base (i.e. hydroxide), would water be able to deprotonate that amine in step one to give the N-N double bond? I ask because in the synthesis of the drug Amiodarone, they do not specify basic conditions. Rather, they allude that they use hydrazine hydrate only.

    1. Water isn’t basic enough to deprotonate. The pKa of the hydrazone hydrogens is about 22, whereas that of H3O(+) is -2. The equilibrium would be 24 orders of magnitude in opposition to the desired reaction.
      I found a publicly available reference to the synthesis here: : http://bit.ly/J2TCRA
      Although they don’t specifiy basic conditions in the reaction scheme, it’s not uncommon to leave out details such as base, solvent and heat. The Wolff Kishner is generally a very unfavorable reaction as it is – it requires heating at 180 degrees C or more – so I am nearly 100% certain that they merely omitted writing base in the scheme here.

    1. Ethylene glycol serves as a solvent here. It has a very high boiling point (~200 degrees C); the fact that the reaction needs to be heated so much is why this solven tis used.

      1. Good question. One reason I’ve read is the greater strength of the C-O (pi) bond as opposed to the C-C (pi) bond. I’m not sure this is the whole picture but it is at least a component.

    1. I suppose you could use potassium carbonate but it will not deprotonate ethylene glycol irreversibly; at 200 degrees C, however, the reaction should still proceed well.

  2. In the Wolff kishner we first convert ketone or aldehyde to hydrazone. Hydrazone formation is done in acid medium. Now if we have a carbonyl compound with an Acetal and Ketone, will the acetal be also reduced in Wolff kishner due to equilibrium being established in during hydrazone formation (acid medium form ketone and ketone formed along with original one will react to form two Hydrazone sites, which can be reduced in proceeding step with strong base. Couldn’t find any answer to this.

    Thanks in advance!

    1. Probably because the acid and base need to be able to reach each other, which is generally not possible unless they are 5 or 6 atoms apart. So I would use an external base / external acid to perform the proton transfer.
      In fairness that is probably a better way to do it, but it takes forever to write out. My approach is a bit of a short cut.

  3. Sir, what will be the product if we imply wolf kishner reaction on carboxylic acids with ketone group like
    CH3-CO-COOH.
    Does it will just reduce ketone group only or will react will acid group also?
    Please reply!

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