Question

Catalyst ${\text{SnC}}{{\text{l}}_{\text{2}}}{\text{/HCl}}$ is used in:
A.Stephen’s reduction
B.Cannizzaro’s reduction
C.Clemmensen reduction
D.Rosenmund’s reduction

Answer 1

To solve this question, it is required to have knowledge about some naming reactions and the catalysts used in them. ${\text{SnC}}{{\text{l}}_{\text{2}}}{\text{/HCl}}$ react to give ${\text{SnC}}{{\text{l}}_{\text{4}}}$ and nascent hydrogen which is used for reduction. Nascent hydrogen can react with cyanides to form imine, which can be reduced by hydrolysis into aldehydes.

Complete step by step answer:
We know that acids along with metal halides are mostly used in reduction processes. They can reduce nitriles to carbonyls, carbonyls to alcohol and even carbonyls to alkenes.
In option A, we know that Stephen’s reduction is used to convert nitrile into aldehydes. The reaction occurs through two steps. The first step involves the reaction of nitrile group with nascent hydrogen to form imine. The second step involves the hydrolysis of that imine to form an aldehyde. The nascent hydrogen in the first step is generated by the reaction of ${\text{SnC}}{{\text{l}}_{\text{2}}}$ with ${\text{HCl}}$ to give ${\text{SnC}}{{\text{l}}_{\text{4}}}$ and nascent hydrogen. Thus, the catalyst ${\text{SnC}}{{\text{l}}_{\text{2}}}{\text{/HCl}}$ is used in Stephen’s reduction. The reaction occurs as:
${\text{R - C}} \equiv {\text{N + }}2\left[ {\text{H}} \right]{\text{ + HCl}} \to {\text{R - CH = NH}}{\text{.HCl}}\xrightarrow{{{{\text{H}}_{\text{2}}}{\text{O}}}}{\text{R - CHO + N}}{{\text{H}}_4}{\text{Cl}}$
In option B, we know that Cannizzaro’s reaction involves the reaction of aldehydes without alpha-hydrogen to form a primary alcohol and carboxylic acid. It occurs in the presence of a strong base like ${\text{NaOH}}$.
In option C, Clemmensen’s reduction involves the conversion of a carbonyl compound to an alkene. It occurs in the presence of zinc amalgam and concentrated hydrochloric acid.
In option D, Rosenmund’s reduction is the hydrogenation process where acyl chloride is selectively reduced to an aldehyde. The reaction occurs in the presence of palladium with barium sulphate and hydrogen gas.
$\therefore$ The correct answer is option A, i.e. Stephen’s reduction.

Note: Stephen’s reduction is useful to convert nitriles/cyanides into aldehydes with an extra carbon atom. The aldehydes can be further oxidised to give carboxylic acid or reduced to give primary alcohol.