Concept:
To convert a ketone into a hydrocarbon, the carbonyl group (\( C=O \)) must be completely removed and replaced by hydrogen atoms. This type of transformation is called reduction of carbonyl compounds to alkanes. Two major reactions do this:
Clemmensen reduction (acidic medium)
Wolff-Kishner reduction (basic medium)
Among the given options, only one performs complete reduction of a ketone to a hydrocarbon.
Step 1: Understanding each option. (A) Reimer-Tiemann reaction:
Used for formylation of phenols to give salicylaldehyde.
It does not reduce ketones.
(B) Wolff-Kishner reduction:
This reaction converts aldehydes or ketones into hydrocarbons using hydrazine (\( NH_2NH_2 \)) and strong base at high temperature:
\[
R{-}CO{-}R' \xrightarrow[\text{KOH, heat}]{NH_2NH_2} R{-}CH_2{-}R'
\]
Thus, the carbonyl group is completely removed.
(C) Aldol condensation:
Forms \( \beta \)-hydroxy aldehydes/ketones or \( \alpha,\beta \)-unsaturated compounds.
It is a C–C bond forming reaction, not a reduction.
(D) Stephen reaction:
Used to convert nitriles into aldehydes.
It is unrelated to ketone reduction.
Step 2: Final selection.
Only the Wolff-Kishner reduction converts a ketone into a hydrocarbon.
\[
\therefore \text{Correct answer = (B) Wolff-Kishner reduction}
\]
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