Question

Stephen’s reduction is used to prepare aldehydes from :
(A) Alcohol
(B) Alkyl Cyanide
(C) Alkanone
(D) Acid chloride

Answer 1

Stephen’s reduction involves HCl, $SnC{{l}_{2}}$ and water as reagents. The compound from which aldehyde is obtained in Stephen’s reduction reaction has an sp hybridized carbon in its structure.

Complete step by step answer:
- We are given that Stephen’s reaction is a reduction reaction and produces aldehydes. Now, alcohols are already reduced form of aldehydes. So, alcohols upon reduction cannot give aldehydes. So, we can say that option (A) cannot be the correct answer.
- Now, to choose from option (B), (C), and (D), we need to know the reaction.
- Stephen’s reaction is a reduction reaction which converts alkyl or aromatic nitriles into corresponding aldehydes when they are allowed to react with HCl, Tin chloride $(SnC{{l}_{2}})$and water. So, it is a redox type reaction and can be written as below.

 $$R-C\equiv N\xrightarrow[{{H}_{2}}O]{\begin{smallmatrix}   

i)HCl \\
ii)SnC{{l}_{2}}
\end{smallmatrix}}R-CHO$$

- Here, first the cyanide reacts with HCl to make a salt and it reacts with $SnC{{l}_{2}}$ to get reduced by a single electron transfer mechanism. Then, the reduced form of cyanide undergoes hydrolysis reaction and finally forms a corresponding aldehyde molecule.
- This reaction is more feasible with aromatic nitriles than alkyl nitriles but in some cases of aromatic nitriles, the product yield obtained is lower.
So, the correct answer is “Option B”.

Note: Remember that reducing agent is a redox reagent that reduces other compounds and oxidizes itself. Here, in this reaction, $SnC{{l}_{2}}$ is used as a reducing agent as Sn is in +2 oxidation state in this compound and can be oxidized to +4 state.