Question

I've studied that in non extreme conditions, aldehydes and Ketones may be reduced into their respective alcohols with Pt/H₂, and that lindlar catalyst on acid halides converts it into aldehydes through Rosenmund reduction, although can unpoisoned Pt/H₂ convert acid halide into an Alcohol?

Answer 1

Unpoisoned Pt/H₂ is capable of reducing acid halides, but it typically reduces them all the way to the corresponding primary alcohols, not stopping at the aldehyde stage like the controlled Rosenmund reduction reaction does.

Step-by-step explanation:

While catalytic hydrogenation utilizing Pt/H₂ is effective for the reduction of aldehydes and ketones into their respective alcohols, acid halides require different conditions for their reduction. Unpoisoned Pt/H₂ is indeed capable of reducing acid halides, but it does so with such vigor that the reaction does not stop at the aldehyde stage and typically proceeds to produce the corresponding primary alcohol.

In contrast, the Rosenmund reduction, which typically utilizes a poisoned catalyst such as palladium on barium sulfate (Pd/BaSO₄) with quinoline or sulfur, specifically reduces acid halides to aldehydes without further reduction to alcohols.

For example, when acyl chlorides are treated with catalysts like Pd/BaSO₄ in the presence of hydrogen gas, the formation of the aldehyde is favored. However, with unpoisoned hydrogenation catalysts like Pt/H₂, the tendency is to fully reduce the compound to the alcohol, because the catalyst is not modified to moderate the activity and selectively stop at the formation of an aldehyde.