Question

Identify the product formed when benzoyl chloride is reduced by hydrogen using palladium catalyst poisoned with barium sulphate?

• A. Chlorobenzene
• B. Benzyl alcohol
• C. Benzene
• D. Benzaldehyde

Hint:

Whenever you see an acid chloride (R-COCl) reacting with $\text{H}_2$ alongside $\text{Pd/BaSO}_4$ (or sulfur/quinoline), instantly think of the Rosenmund Reduction!
The product of a Rosenmund reaction is always an aldehyde (R-CHO). Simply swap out the $-\text{Cl}$ atom for a $-\text{H}$ atom.

Answer 1

The Correct Option is D

Step 1: Read the conditions.
Benzoyl chloride is treated with hydrogen gas over palladium that sits on barium sulphate. We must name the product.
Step 2: Recognise the named reaction.
$\text{H}_2$ with $\text{Pd/BaSO}_4$ acting on an acid chloride is the Rosenmund reduction. It is a special way to make aldehydes.
Step 3: Understand the poison.
The $\text{BaSO}_4$ weakens the palladium on purpose. This makes the catalyst gentle so the reaction stops at the aldehyde and does not go further.
Step 4: Apply it to benzoyl chloride.
Benzoyl chloride is $\text{C}_6\text{H}_5\text{COCl}$. The hydrogen replaces the chlorine at the carbonyl carbon: \[ \text{C}_6\text{H}_5\text{COCl} + \text{H}_2 \xrightarrow{\text{Pd/BaSO}_4} \text{C}_6\text{H}_5\text{CHO} + \text{HCl} \]
Step 5: Name the product.
$\text{C}_6\text{H}_5\text{CHO}$ is benzaldehyde.
Step 6: Note why not benzyl alcohol.
Without the poison, plain palladium would push on and give benzyl alcohol. The poison is what keeps the product as an aldehyde. \[ \boxed{\text{Benzaldehyde}} \]