Question

Which reagent converts an aldehyde into a carboxylic acid?

• A. $\text{LiAlH}_4$
• B. $\text{H}_2/\text{Ni}$
• C. $\text{KMnO}_4$
• D. $\text{NaBH}_4$

Hint:

Always classify chemical reagents as oxidizing or reducing agents when dealing with organic conversions.
Aldehydes have a hydrogen atom attached to the carbonyl carbon, which makes them very easy to oxidize.
Even a mild oxidizing agent like Tollens' or Fehling's reagent, or a strong one like \(\text{KMnO}_4\), can complete this conversion.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify the correct chemical reagent that can oxidize an aldehyde functional group to a carboxylic acid group.

Step 2: Key Formula or Approach:
Converting an aldehyde to a carboxylic acid is an oxidation reaction that requires an oxidizing agent.
\[ \text{R–CHO} \xrightarrow{\text{Oxidizing Agent [O]}} \text{R–COOH} \]

Step 3: Detailed Explanation:

• Role of Potassium Permanganate: \(\text{KMnO}_4\) (Potassium permanganate) is a strong oxidizing agent. It readily supplies oxygen to convert aldehydes into their corresponding carboxylic acids.
  
• Role of Lithium Aluminium Hydride: \(\text{LiAlH}_4\) is a powerful reducing agent. Instead of oxidizing, it reduces aldehydes to primary alcohols (\(\text{R–CH}_2\text{OH}\)).
  
• Role of Sodium Borohydride: \(\text{NaBH}_4\) is a mild reducing agent that is also used to reduce aldehydes and ketones to alcohols.
  
• Role of Hydrogen with Nickel: \(\text{H}_2/\text{Ni}\) is a catalytic hydrogenation system. This is a reducing agent that converts aldehydes to primary alcohols.
  
• Conclusion on Reagents: Since three of the given options are reducing agents, only \(\text{KMnO}_4\) can perform the oxidation.
  

Step 4: Final Answer:
The reagent that converts an aldehyde into a carboxylic acid is \(\text{KMnO}_4\), which corresponds to option (C).