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Question
Explain Wolf-Kishner reduction reaction.
Solution
The carbonyl group of aldehydes and ketones is reduced to the methylene group \[\ce{[- CH2 -]}\] on treatment with hydrazine followed by heating with sodium or potassium hydroxide in a high-boiling solvent like ethylene glycol, known as the Wolf-Kishner reduction.
| \[\begin{array}{cc} \ce{O}\phantom{...................................}\\ ||\phantom{.....................}\backslash\phantom{.............}\\ \ce{C + \underset{(Hydrazine)}{NH2 - NH2} ->[-H2O] \underset{(Hydrazone)}{C = N - NH2}}\\ /\phantom{..}\backslash\phantom{....................}/\phantom{..............}\\ \end{array}\] |
| \[\begin{array}{cc} \backslash\phantom{.............................}\backslash\phantom{..............}\\ \ce{\underset{(Hydrazone)}{C = N - NH2} ->[KOH, \Delta][Ethylene glycol] \underset{(Methyl group)}{CH2} + N2}\\ /\phantom{.............................}/\phantom{..............}\\ \end{array}\] |
Here the oxygen of the carbonyl group is replaced by two hydrogen atoms.
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