Question

Identify the reagent used in following reaction.
\(\text{Benzoic acid}\rightarrow _{\Delta \,}^{\text{Reagent}\,}\text{Benzoyl chloride}+\text{phosphorous oxychloride}+\text{Hydrogen chloride}\)

• A. \(\text{PCl}_3\)
• B. \(\text{HCl}\)
• C. \(\text{PCl}_5\)
• D. \(\text{SOCl}_2\)

Hint:

The by-products POCl3 and HCl point to PCl5.

Answer 1

The Correct Option is C

Step 1: Look at the products
Phosphorus oxychloride contains phosphorus with oxygen, so the reagent must contain phosphorus and plenty of chlorine.

Step 2: Balance
One OH of the acid takes Cl from $\text{PCl}_5$, giving $\text{POCl}_3$ and HCl together.

Step 3: Compare
PCl3 would leave $\text{H}_3\text{PO}_3$ and SOCl2 would leave $\text{SO}_2$.

Step 4: Answer
Option (C).

Final Answer:
The reagent is PCl5. This is option (C). \[ \boxed{\text{(C) }\text{PCl}_5} \]