Question

In the following equation $ C{H_3} - CH = CH - CHO\xrightarrow{A}C{H_3} - C{H_2} = C{H_2} - C{H_3} $
The best suitable reagent ‘A’ is
(A) $ {{\text{C}}_{\text{3}}}{{\text{H}}_{\text{8}}}{{\text{S}}_{\text{2}}}{\text{/}}{{\text{H}}_{\text{2}}}{\text{/Ni}} $
(B) $ {{\text{N}}_{\text{2}}}{{\text{H}}_{\text{4}}}{\text{/KOH}} $
(C) $ {\text{Zn - Hg/ConcHCl}} $
(D) $ {\text{H/P}}\left( {{\text{red}}} \right) $

Answer 1

Hint: We need to convert aldehyde. We need to identify the reagent here. This question requires the concepts of organic chemistry. The reaction occurring here is also known as Clemmensen reduction.

Complete step by step answer:
We already know that,
Aldehydes and ketones undergo nucleophilic addition reactions due to the polarity in the carbonyl bond that makes them vulnerable to a nucleophile.
Here $ C{H_3} - CH = CH - CHO $ undergoes reduction to a hydrocarbon in presence of reagents like zinc, mercury amalgam in concentrated HCl.
This reaction is named as Clemmenson reduction. Since the reaction occurs at room temperature therefore, it is best suitable for this question.
So, we need to select the correct option.
The correct option is C.

Note:
Clemmensen reduction is a chemical reaction described as a reduction of ketones (or aldehydes) to alkanes using zinc amalgam and concentrated hydrochloric acid. The original Clemmensen reduction conditions are particularly effective at reducing aryl-alkyl ketones, such as those formed in a Friedel-Crafts acylation. The reaction of aldehydes and ketones with zinc amalgam (Zn/Hg alloy) in concentrated hydrochloric acid, which reduces the aldehyde or ketone to a hydrocarbon, is called Clemmensen reduction. It has been reported that alcohol is not the intermediate of the Clemmensen reduction and carbonium is involved in this reduction
Thus, Clemmensen reduction reaction is carried by using Zinc amalgam (Zn/Hg) and Hydrochloric acid (HCl) which is often referred to as Clemmensen's reducing agent.
Also, Aldehydes are typically more reactive than ketones due to the following factors. The carbonyl carbon in aldehydes generally has more partial positive charge than in ketones due to the electron-donating nature of alkyl groups. Aldehydes only have one e- donor group while ketones have two.