Question

X and Y in the below reaction are ______ and ______ respectively

C\(_6\)H\(_5\)–CO\(_2\)H + X \(\xrightarrow{\text{Heat}}\) C\(_6\)H\(_5\)–COCl \(\xrightarrow{\text{H}_2/\text{Pd/BaSO}_4\text{, Quinoline}}\) Y

• A. SOCl\(_2\) and C\(_6\)H\(_5\)CHO
• B. (COCl)\(_2\) and C\(_6\)H\(_5\)CH\(_3\)
• C. SOCl\(_2\) and C\(_6\)H\(_5\)CH\(_3\)
• D. (COCl)\(_2\) and C\(_6\)H\(_5\)CH\(_2\)OH
• E. SOCl\(_2\) and C\(_6\)H\(_5\)CH\(_2\)Cl

Hint:

Thionyl chloride (\(\text{SOCl}_2\)) is preferred for making acid chlorides because the by-products (\(\text{SO}_2\) and \(\text{HCl}\)) are gases, making the purification of the product very simple.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The reaction sequence involves two distinct chemical transformations. The first is the conversion of a carboxylic acid into an acyl chloride using a chlorinating agent. The second is the Rosenmund Reduction, a specific catalytic hydrogenation that reduces an acyl chloride to an aldehyde.

Step 2: Key Formula or Approach:
1. Preparation of Acyl Chloride: \(\text{R-COOH} + \text{SOCl}_2 \rightarrow \text{R-COCl} + \text{SO}_2 + \text{HCl}\).
2. Rosenmund Reduction: \(\text{R-COCl} \xrightarrow{\text{H}_2, \text{Pd-BaSO}_4} \text{R-CHO}\).

Step 3: Detailed Explanation:
1. Benzoic acid (\(\text{C}_6\text{H}_5\text{COOH}\)) reacts with thionyl chloride (\(\text{SOCl}_2\)) to produce Benzoyl chloride (\(\text{C}_6\text{H}_5\text{COCl}\)). Thus, \(X\) is \(\text{SOCl}_2\).
2. Benzoyl chloride then undergoes Rosenmund Reduction. The \(\text{Pd/BaSO}_4\) catalyst is "poisoned" with sulfur or quinoline to stop the reduction at the aldehyde stage.
3. This process converts \(\text{C}_6\text{H}_5\text{COCl}\) into Benzaldehyde (\(\text{C}_6\text{H}_5\text{CHO}\)). Thus, \(Y\) is \(\text{C}_6\text{H}_5\text{CHO}\).

Step 4: Final Answer
The values for X and Y are \(\text{SOCl}_2\) and \(\text{C}_6\text{H}_5\text{CHO}\) respectively.