Correct Option: (B) Wolff-Kishner reduction
Step 1 (Governing Reaction Principle): [1/3 Mark]
The conversion of a carbonyl group ($C=O$) of aldehydes and ketones into a methylene group ($CH_2$) is known as reduction of the carbonyl group. The Wolff-Kishner reduction specifically utilizes hydrazine ($NH_2NH_2$) followed by heating with a strong base like potassium hydroxide ($KOH$) in a high-boiling solvent such as ethylene glycol.
Step 2 (Step-by-Step Reaction Mechanism): [1/3 Mark]
The reaction proceeds via the formation of a hydrazone intermediate, which subsequently undergoes base-catalyzed elimination of nitrogen gas ($N_2$) to yield the hydrocarbon:
$$R_2C=O + NH_2NH_2 \xrightarrow{-H_2O} R_2C=NNH_2 \xrightarrow{KOH / \Delta} R_2CH_2 + N_2 \uparrow$$- Step A: Formation of hydrazone ($R_2C=NNH_2$).
- Step B: Base-catalyzed deprotonation and loss of $N_2$ gas to form the alkane ($R_2CH_2$).
Step 3 (Final Concluded Answer): [1/3 Mark]
Among the given choices, (B) Wolff-Kishner reduction is the specific chemical process used to reduce ketones directly to hydrocarbons. Other options like Reimer-Tiemann (formylation of phenols), Aldol condensation (C-C bond formation), and Stephen reaction (nitriles to aldehydes) do not perform this conversion.
💡 EL10 Concept Insight: Think of the Wolff-Kishner reduction like a "chemical eraser" that strips away the oxygen atom from a ketone and replaces it with two hydrogen atoms, effectively turning the ketone into a simple alkane.