Question

Describe Rosenmund reduction.

Hint:

BaSO$_4$ acts as a catalyst poison here. Without it, the highly active Pd catalyst would reduce the aldehyde further into a primary alcohol.

Answer 1

1. Definition: Rosenmund reduction is a chemical reaction used to convert acid chlorides (acyl chlorides) into aldehydes.
2. Reagents: Hydrogen gas (H$_2$) is passed through the solution in the presence of a catalyst, which is Palladium (Pd) deposited on Barium Sulphate (BaSO$_4$). The catalyst is often poisoned with sulfur or quinoline to prevent further reduction to alcohols.
3. Reaction:
R-COCl + H$_2$ $\xrightarrow{\text{Pd/BaSO}_4}$ R-CHO + HCl
4. Example: Benzoyl chloride is reduced to Benzaldehyde.
C$_6$H$_5$COCl + H$_2$ $\xrightarrow{\text{Pd/BaSO}_4}$ C$_6$H$_5$CHO + HCl