Question

Identify the reagent used in the following reaction.
Benzoic acid $\xrightarrow{\text{Reagent}$ Benzoyl chloride + Phosphorus oxychloride + Hydrogen chloride}

• A. PCl$_3$
• B. HCl
• C. PCl$_5$
• D. SOCl$_2$

Hint:

$\text{PCl}_5$ always gives $\text{POCl}_3$ as a byproduct when reacting with oxygen-containing organic compounds.

Answer 1

The Correct Option is C

Step 1: Analysis of Products
The products are Benzoyl chloride ($C_6H_5COCl$), $\text{POCl}_3$ (Phosphorus oxychloride), and $\text{HCl}$.
Step 2: Reagent Match
- Reaction with $\text{PCl}_5$: $R\text{COOH} + \text{PCl}_5 \to R\text{COCl} + \text{POCl}_3 + \text{HCl}$. - Reaction with $\text{PCl}_3$: $3R\text{COOH} + \text{PCl}_3 \to 3R\text{COCl} + \text{H}_3\text{PO}_3$. - Reaction with $\text{SOCl}_2$: $R\text{COOH} + \text{SOCl}_2 \to R\text{COCl} + \text{SO}_2 + \text{HCl}$.
Step 3: Conclusion
Only $\text{PCl}_5$ yields $\text{POCl}_3$ as a byproduct.
Final Answer: (C)