Consider the following Rosenmund reaction,
`RCOCl + H_(2) overset(Pd//BaSO_(4))rarrRCHO + HCl`
Here, `BaSO_(4)`

Options

A. Promotes catalytic activity of Pd
B. Removes the HCl formed in the reaction
C. Deactivates Pd
D. Activates Pd

Answer

To solve the question regarding the Rosenmund reaction, we need to analyze the role of BaSO4 in the reaction between acyl chloride (RCOCl) and hydrogen (H2) in the presence of palladium (Pd).

### Step-by-Step Solution:

1. **Understanding the Reaction**:
The Rosenmund reaction involves the reduction of acyl chlorides to aldehydes using hydrogen gas in the presence of a catalyst. The general reaction can be represented as:
\[ RCOCl + H_2 \xrightarrow{Pd/BaSO_4} RCHO + HCl \]

2. **Identifying the Role of BaSO4**:
In this reaction, BaSO4 (Barium sulfate) is used as a support for the palladium catalyst. However, it also plays a crucial role in modifying the activity of the palladium.

3. **Deactivation of Palladium**:
One of the key functions of BaSO4 in this reaction is to deactivate the palladium catalyst. This is important because if palladium were fully active, it could lead to over-reduction of the acyl chloride, resulting in the formation of alcohols instead of aldehydes.

4. **Conclusion**:
Therefore, BaSO4 serves to limit the activity of palladium, ensuring that the reaction selectively produces the desired aldehyde (RCHO) rather than further reducing it to an alcohol.

5. **Selecting the Correct Option**:
Based on the analysis, we conclude that BaSO4 deactivates the palladium catalyst. If the options provided in the question include this information, we would select the option that states that BaSO4 deactivates palladium.

### Final Answer:
BaSO4 deactivates the palladium catalyst in the Rosenmund reaction.

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