Rosenmund reduction
An acyl chloride is hydrogenated over palladium on barium sulphate to give an aldehyde.
Benzoyl chlorideC₆H₅COClAcyl chloride - Step 1
H₂, Pd/BaSO₄
BenzaldehydeC₆H₅CHOAldehyde
How it works
- The acyl chloride is hydrogenated on the catalyst surface.
- Barium sulphate poisons the palladium so the aldehyde is not reduced further.
- The aldehyde and HCl form.
What it makes
Aldehydes (not methanal) from acyl chlorides.
Where it fails
The catalyst must be poisoned or the product goes on to the alcohol. Methanal cannot be made as HCOCl is unstable.
Class 12, Chapter 8 Aldehydes, Ketones and Carboxylic Acids
Rosenmund reduction: quick answers
What is the role of BaSO4?
It partly deactivates the palladium so reduction stops at the aldehyde.
Can methanal be made by this method?
No, formyl chloride is unstable.
What does the acid chloride lose?
It loses Cl and gains H, so RCOCl becomes RCHO.