Step 1: Understanding the Question:
A disproportionation reaction is a redox reaction where the same element or compound is simultaneously oxidized and reduced.
Step 2: Key Formula or Approach:
Analyze the mechanisms of the named reactions:
1. Clemmensen and Wolff-Kishner are purely reduction reactions (Carbonyl \(\rightarrow\) Alkane).
2. Cannizzaro occurs for aldehydes without \(\alpha\)-hydrogens in concentrated alkali.
Step 3: Detailed Explanation:
In the Cannizzaro reaction, two molecules of an aldehyde (like formaldehyde or benzaldehyde) react.
One molecule acts as a hydride donor and is oxidized to a carboxylic acid salt.
The second molecule accepts the hydride and is reduced to a primary alcohol.
Example:
\[ 2HCHO + NaOH \rightarrow HCOONa + CH_3OH \]
Here, formaldehyde is oxidized to sodium formate and reduced to methanol.
Since the same reactant undergoes both oxidation and reduction, it is a disproportionation reaction.
Step 4: Final Answer:
The Cannizzaro reaction is the disproportionation reaction.