JEE Chemistry 2023 Question with Solution

Given: Assertion A says $\ce{CH3COOH}$ can be easily reduced using Zn-Hg/HCl to $\ce{CH3CH2OH}$. Reason R says Zn-Hg/HCl reduces a carbonyl group to a $\ce{-CH2-}$ group.

Find: Which option correctly evaluates Assertion $A$ and Reason $R$.

Zn-Hg/HCl is the Clemmensen reduction reagent. It is used to reduce the carbonyl group of aldehydes and ketones to a methylene group.

Therefore, Reason $R$ is true.

Assertion $A$ is false because a carboxylic acid such as $\ce{CH3COOH}$ is not easily reduced by Zn-Hg/HCl to $\ce{CH3CH2OH}$. The strongly acidic medium makes Clemmensen reduction unsuitable for this conversion. The acid sensitive alcohol group reacts with HCl, hence this method is not suitable for the above conversion.

Therefore, the correct option is A.

Given: The reagent is Zn-Hg/HCl.

Find: Whether it can convert $\ce{CH3COOH}$ into $\ce{CH3CH2OH}$.

Clemmensen reduction works for aldehydes and ketones, where the carbonyl carbon is reduced all the way to a methylene carbon. It does not serve as a general reducing agent for converting carboxylic acids into primary alcohols.

Also, the medium contains concentrated HCl, so acid-sensitive functionalities do not survive appropriately under these conditions. Hence the proposed conversion in Assertion $A$ is not valid, even though the general statement in Reason $R$ about reduction of carbonyl groups to $\ce{-CH2-}$ is correct.

Thus, Assertion A is false but Reason R is true.