Question

Reaction of thionyl chloride with white phosphorus forms a compound [A], which on hydrolysis gives [B], a dibasic acid $[ A ]$ and $[ B ]$ are respectively

• A. $P _4 O _6$ and $H _3 PO _3$
• B. $PCl _5$ and $H _3 PO _4$
• C. $PCl _3$ and $H _3 PO _3$
• D. $POCl _3$ and $H _3 PO _4$

Answer 1

The Correct Option is C

The question involves the reaction of thionyl chloride (\( \text{SOCl}_2 \)) with white phosphorus (\( \text{P}_4 \)) to form a compound [A], which upon hydrolysis gives a dibasic acid [B]. We need to identify compounds [A] and [B].

1. When thionyl chloride (\( \text{SOCl}_2 \)) reacts with white phosphorus (\( \text{P}_4 \)), phosphorus trichloride (\( \text{PCl}_3 \)) is formed. The balanced chemical equation for this reaction is:

\(\text{P}_4 + 8\text{SOCl}_2 \rightarrow 4\text{PCl}_3 + 4\text{SO}_2 + 2\text{Cl}_2\)

1. Here, [A] is \( \text{PCl}_3 \).
2. Next, consider the hydrolysis of phosphorus trichloride (\( \text{PCl}_3 \)). In an aqueous environment, \( \text{PCl}_3 \) reacts with water to form phosphorous acid (\( \text{H}_3\text{PO}_3 \)), which is a dibasic acid:

\(\text{PCl}_3 + 3\text{H}_2\text{O} \rightarrow \text{H}_3\text{PO}_3 + 3\text{HCl}\)

1. Thus, [B] is \( \text{H}_3\text{PO}_3 \).
2. The correct compounds identified are:
   • [A]: \( \text{PCl}_3 \)
   • [B]: \( \text{H}_3\text{PO}_3 \)
3. Now, let's justify why other options are incorrect:
   • \( \text{P}_4\text{O}_6 \) and \( \text{H}_3\text{PO}_3 \): This does not involve thionyl chloride or correctly follow the reaction pattern.
   • \( \text{PCl}_5 \) and \( \text{H}_3\text{PO}_4 \): \( \text{P}_4 \) does not directly react this way with thionyl chloride, nor does it produce a trihalide or tetrahalide.
   • \( \text{POCl}_3 \) and \( \text{H}_3\text{PO}_4 \): The hydrolysis product \( \text{H}_3\text{PO}_4 \) is a tribasic acid, not a dibasic acid.

Conclusively, based on the reactions and hydrolysis, the correct compounds [A] and [B] are \( \text{PCl}_3 \) and \( \text{H}_3\text{PO}_3 \), respectively.