Question

In which of the following sets, reactant and reagent are correctly matched to get corresponding carboxylic acid? \[ \begin{array}{ll} \textbf{I.} & \mathrm{CH_3CH_2CH_2OH} \;\xrightarrow{\mathrm{CrO_3,\ H_2SO_4}}\; ? \\[2mm] \textbf{II.} & \mathrm{CH_3CH_2CH_2Br} \;\xrightarrow{\mathrm{CO,\ H_3O^+}}\; ? \\[2mm] \textbf{III.} & \mathrm{CH_3CHO} \;\xrightarrow{\mathrm{KMnO_4/OH^-,\ H_3O^+}}\; ? \end{array} \] The correct answer is

• A. I only
• B. I, II only
• C. I, III only
• D. II only \bigskip

Hint:

Primary alcohols and aldehydes can be oxidised to carboxylic acids using strong oxidising agents such as: \[ \mathrm{KMnO_4,\ K_2Cr_2O_7,\ CrO_3/H_2SO_4} \]

Answer 1

The Correct Option is C

This question checks which reactant to reagent combinations genuinely give a carboxylic acid. Go through each statement one at a time.

1. Statement I: $\mathrm{CH_3CH_2CH_2OH}$ is a primary alcohol. A strong oxidising agent like Jones reagent ($\mathrm{CrO_3/H_2SO_4}$) oxidises a primary alcohol all the way to a carboxylic acid, so $\mathrm{CH_3CH_2CH_2OH}$ gives $\mathrm{CH_3CH_2COOH}$. Statement I is correct.
2. Statement II: $\mathrm{CH_3CH_2CH_2Br}$ is an alkyl bromide. Treating an alkyl halide directly with carbon monoxide and then water does not give a carboxylic acid in one step. That kind of conversion needs a metal catalyst, such as a palladium-catalysed carbonylation, or it must go through a Grignard reagent reacting with carbon dioxide. Plain $\mathrm{CO}$ and $\mathrm{H_3O^+}$ cannot do this job. Statement II is incorrect.
3. Statement III: $\mathrm{CH_3CHO}$ is an aldehyde. Aldehydes are readily oxidised further, and alkaline potassium permanganate ($\mathrm{KMnO_4/OH^-}$) followed by acidification ($\mathrm{H_3O^+}$) oxidises the aldehyde to the matching carboxylic acid, $\mathrm{CH_3COOH}$. Statement III is correct.

Only statements I and III describe a genuine reactant to carboxylic acid conversion, so option (C), "I, III only," is the correct choice.

Let's summarize:

• Primary alcohols are oxidised to carboxylic acids by strong oxidising agents such as Jones reagent.
• A plain alkyl halide does not turn into a carboxylic acid just by treatment with $\mathrm{CO}$ and water, that step needs a catalyst or a different route.
• Aldehydes are oxidised to carboxylic acids by reagents like alkaline $\mathrm{KMnO_4}$.

So the correct answer is (C): I, III only.