Wolff–Kishner reduction

Wolff -Kishner reaction or Wolff -Kishner reduction is a chemical reaction, by whose means it is possible to reduce the aldehydes and ketones to alkanes. The reaction is named after its discoverer, the German chemist Ludwig Wolff and the Russian chemist Nikolai Kischner.

Mechanism

In the reaction, the carbonyl compound is first reacted with hydrazine to give the hydrazone. Then, without isolation of the hydrazone by strong bases (in this hydroxide ion ) eliminates nitrogen, and it remains the alkane. Wolff -Kishner reaction is complementary to the Clemmensen reduction which acts under acidic conditions for the reduction of ketones and aldehydes. The Wolff- Kishner reaction is due to the harsh reaction conditions (high temperature, addition of solid Koh's ) Only suitable for base-stable compounds.

Variant of Huang Minion

The variant according to Huang Minion, a Chinese chemist who performs using a high boiling solvent to better yields. The use of solid KOH in diethylene glycol nowadays therefore the use of potassium hydroxide replaced completely.

The variant was discovered, flew as in a response, the plug of a piston from the glass flask and evaporated the water contained. The content had not decomposed as expected, it was even more product emerged as expected. Further investigations have shown, this is based on the fact that the reaction is > 100 ° C takes place preferably at temperatures of.

Variant according to Cram

A modern variant of Donald J. Cram dimethylsulfoxide used as the solvent and potassium tert-butoxide as the base. As potassium tert- butoxide is more basic than potassium hydroxide, the reaction can already be carried out at room temperature.

Similar reactions

One of the Wolff -Kishner reaction related reaction used, as shown below, toluenesulfonylhydrazine; The resulting hydrazone is then reduced with sodium borohydride to the alkane. The advantage of both strongly acidic and strongly basic reaction conditions in the avoidance, so that reductions in the α -position to the chiral centers are possible. However, as no diaryl ketones may be reduced.

The Clemmensen reduction can be considered in which an aldehyde or ketone can be reduced by amalgamated zinc to form the corresponding methyl or methylene compounds in hydrochloric acid medium to be complementary to the Wolff-Kishner reaction.