Question:
Identify the reagent 'R' used in the following reaction
\(\text{C}_6\text{H}_5\text{COCl}\overset{\text{R}\,}{\rightarrow }\text{C}_6\text{H}_5\text{CHO}+\text{HCl}\)
Identify the reagent 'R' used in the following reaction
\(\text{C}_6\text{H}_5\text{COCl}\overset{\text{R}\,}{\rightarrow }\text{C}_6\text{H}_5\text{CHO}+\text{HCl}\)
\(\text{C}_6\text{H}_5\text{COCl}\overset{\text{R}\,}{\rightarrow }\text{C}_6\text{H}_5\text{CHO}+\text{HCl}\)
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Rosenmund reduction uses H2 over poisoned palladium.
Updated On: Oct 1, 2026
- \(\text{CO},\text{HCl}\)
- \(\text{H}_2,\text{Pd}-\text{BaSO}_4\)
- \(\text{DIBAl}-\text{H}\)
- \(\text{H}_2\text{O}\)
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Converting an acid chloride to an aldehyde needs a gentle reduction that stops at the aldehyde stage. In Rosenmund reduction the catalyst is palladium on barium sulphate, which is partly poisoned so it does not reduce the aldehyde further.
Step 2: Key Formula or Approach:
\(\text{RCOCl} + \text{H}_2 \xrightarrow{\text{Pd-BaSO}_4} \text{RCHO} + \text{HCl}\).
Step 3: Detailed Explanation:
Applying this: \(\text{C}_6\text{H}_5\text{COCl} + \text{H}_2 \xrightarrow{\text{Pd-BaSO}_4} \text{C}_6\text{H}_5\text{CHO} + \text{HCl}\), which matches the given equation, including the HCl by-product.
CO with HCl is the Gattermann-Koch reagent, used to put a CHO group on benzene. Water would hydrolyse the acid chloride to benzoic acid.
Final Answer:
The reagent is \(\text{H}_2\) with \(\text{Pd-BaSO}_4\), option (B). \[ \boxed{\text{H}_2,\ \text{Pd-BaSO}_4} \]
Converting an acid chloride to an aldehyde needs a gentle reduction that stops at the aldehyde stage. In Rosenmund reduction the catalyst is palladium on barium sulphate, which is partly poisoned so it does not reduce the aldehyde further.
Step 2: Key Formula or Approach:
\(\text{RCOCl} + \text{H}_2 \xrightarrow{\text{Pd-BaSO}_4} \text{RCHO} + \text{HCl}\).
Step 3: Detailed Explanation:
Applying this: \(\text{C}_6\text{H}_5\text{COCl} + \text{H}_2 \xrightarrow{\text{Pd-BaSO}_4} \text{C}_6\text{H}_5\text{CHO} + \text{HCl}\), which matches the given equation, including the HCl by-product.
CO with HCl is the Gattermann-Koch reagent, used to put a CHO group on benzene. Water would hydrolyse the acid chloride to benzoic acid.
Final Answer:
The reagent is \(\text{H}_2\) with \(\text{Pd-BaSO}_4\), option (B). \[ \boxed{\text{H}_2,\ \text{Pd-BaSO}_4} \]
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