CH₃COCl  X; then X is?

Rosenmund reaction: The Rosenmund reaction is a hydrogenation process where molecular hydrogen reacts with the acetyl chloride in the presence of catalyst – palladium on barium sulfate. 

• The barium sulfate reduces the activity of the palladium due to its low surface area, thereby preventing over-reduction.
• This reaction is used in the preparation of aldehyde from acyl chloride.

Additional Information

• Acetyl chloride is produced in the laboratory by the reaction of acetic acid with chlorodehydrating agents such as PCl₃, PCl₅, SO₂Cl₂, phosgene, or SOCl₂. 

CH3COOH + PCl_{5 ------------>} CH3COCl