Chemistry Carboxylic Acids MDCAT 2019
PMDC Verified Question 66 of 94
Carboxylic acids can be reduced into corresponding alcohols. Which of the following reagent can be used for this purpose?
A
\( \text{K}_2\text{Cr}_2\text{O}_7 \)
B
\( \text{LiAlH}_4 \)
C
\( \text{H}_2\text{SO}_4 \)
D
\( \text{KMnO}_4 \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( \text{LiAlH}_4 \)
Concept:

Carboxylic acids are highly oxidized and strongly resist mild reduction. Only very powerful hydride donors can reduce them to primary alcohols.

Formula:

$$ \text{R-COOH} \xrightarrow{\text{1) LiAlH}_4, \text{ether}} \xrightarrow{\text{2) H}_3\text{O}^+} \text{R-CH}_2\text{OH} $$

Solution:

  • Lithium aluminum hydride (\( \text{LiAlH}_4 \)) is a potent source of hydride (\( \text{H}^- \)) ions.


  • It successfully attacks the stubborn carboxylate intermediate, forcing the reduction completely down to a primary alcohol.


Why other options are incorrect:

\( \text{K}_2\text{Cr}_2\text{O}_7 \) and \( \text{KMnO}_4 \) are strong oxidizing agents, not reducers. \( \text{H}_2\text{SO}_4 \) is merely an acid/dehydrating agent.

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