Which of the reactions is used in the conversion of a ketone into hydrocarbon ?
Show Hint
Use Clemmensen reduction \( (\text{Zn-Hg / HCl}) \) for substrates that are sensitive to bases.
Both reactions remove the oxygen and add two hydrogens to the carbonyl carbon.
- Reimer-Tiemann reaction
- Wolff-Kishner reduction
- Aldol condensation
- Stephen reaction
The Correct Option is B
Solution and Explanation
• The complete reduction of a carbonyl group \( (\gt \text{C=O}) \) to a methylene group \( (\gt \text{CH}_2) \) is termed deoxygenation.
• This transformation effectively converts aldehydes and ketones into their parent hydrocarbons.
• Two primary named reactions achieve this: Wolff-Kishner reduction (basic conditions) and Clemmensen reduction (acidic conditions).
Step 1: Formation of the hydrazone intermediate
In the Wolff-Kishner reduction, the ketone \( (\text{R}_2\text{C=O}) \) is reacted with hydrazine \( (\text{NH}_2\text{NH}_2) \).
The initial product is a hydrazone \( (\text{R}_2\text{C=N-NH}_2) \).
\[ \text{R}_2\text{C=O} + \text{NH}_2\text{NH}_2 \rightarrow \text{R}_2\text{C=N-NH}_2 + \text{H}_2\text{O} \]
Step 2: Base-catalyzed decomposition and nitrogen evolution
The hydrazone is then heated with a strong base like KOH or \( \text{NaOCH}_2\text{CH}_3 \) in a high-boiling solvent like ethylene glycol.
The base deprotonates the nitrogen, leading to the loss of Nitrogen gas \( (\text{N}_2) \) and the formation of an alkane.
\[ \text{R}_2\text{C=N-NH}_2 \xrightarrow{\text{KOH, glycol, } \Delta} \text{R}_2\text{CH}_2 + \text{N}_2 \]
Step 3: Final conclusion
This specific pathway using basic conditions and hydrazine is the Wolff-Kishner reduction.
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