Question

Explain Stephen’s reaction and Rosenmund’s reduction.

Answer 1

(i) Stephen’s reaction:

Cyanides are reduced to aldehydes by treating their ethereal solution with stannous chloride and hydrogen chloride gas at room temperature. Imine hydrochloride is initially formed which upon boiling with water gives aldehyde. This reduction is called Stephen’s reaction.

(ii) Rosenmund’s reduction:

Aliphatic as well as’ aromatic aldehydes can be prepared by the reduction of acid chlorides with H₂ in the presence of palladium (Pd) deposited over barium sulphate along with a small amount of sulphur or quinoline. This mixture is called Lindlar’s catalyst, Both sulphur and quinoline poison palladium and check its ability to reduce aldehyde into alcohol. This reaction is called Rosenmund’s reduction.

Answer 2

PREPARATION OF ALDEHYDES AND KETONES BY ROSENMUND REDUCTION - FORMULA

Hydrogenation of acid chloride with Palladium over Barium Sulphate catalyst gives aldehyde. This reaction is called Rosenmund reduction.

PREPARATION OF ALDEHYDES AND KETONES BY STEPHEN REACTION - DEFINITION

Nitriles on reduction with Stannous chloride (SnCl2​) in the presence of Hydrochloric acid (HCl) give corresponding imines, which on hydrolysis give corresponding aldehydes. This reaction is called Stephen reaction.