【Organic Chemistry】Wolff-Kishner Reduction

It's uneasy to decide which topic is suitable for the first entry of this blog, but as a chemistry student I think Organic Chemistry is the best.

Have you ever heard of Wolff-Kishner Reduction? This is probably the most famous reaction to reduce carbonyl funnctionalities to methylene groups.

The simplest scheme of this reaction is given as follows. Sorry for the poor quality :(

As this figure shows, a carbonyl functionality is firstly converted to an imine (aka Schiff Base), followed by the formation of a methylene group.

The mechanism of the first step in this scheme can be explained as a typical reaction between a carbonyl functionality and a hydrazine. A moderate acidic condition will be necessary in my opinion because this step begins with the protonation of the carbonyl functionality. On the other hand, adding too much acid also protonates hydrazine and the reaction does not proceed.

After that, the hydrazine moiety is further converted to a methylene group.Unlike the first step, base (e.g. KOH) will be required to complete this reaction. It deprotonates the hydrazine moiety, producing a carbanion.

It reacts with water and will be neutralized for the moment, but another deprotonation by the base produces a carbanion again. The hydrazine moiety is eliminated after this step.Finally, the carbanion reacts with water again, producing a methylene group.

This reaction is named after Ludwig Wolff, a German Chemist, and Nikolai Kischner, a Russian Chemist. (idk why "c" in "Kischner" was eliminated in the name of this reaction...)

Clemmensen reduction is another option to achieve the objective (conversion of a carbonyl functionality to a methylene group). I'm gonna review it in the near future.

Thank you for your attention!