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

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:

Accepted Answer

Given: White phosphorus reacts with thionyl chloride to form compound [A]. On hydrolysis, [A] gives [B], which is a dibasic acid.

Find: The identities of [A] and [B].

From the given reaction sequence in the solution:

P_4 + 8SOCl_2 \rightarrow 4PCl_3 + 4SO_2 + 2S_2Cl_2

So, [A] = $PCl_3$ .

Now hydrolysis of $PCl_3$ gives:

PCl_3 + 3H_2O \rightarrow H_3PO_3 + 3HCl

Thus, [B] = $H_3PO_3$ .

Phosphorous acid, $H_3PO_3$ , is a dibasic acid. Therefore, [A] and [B] are $PCl_3$ and $H_3PO_3$ respectively.

The solution states "Correct Option is C", but its worked steps conclude $PCl_3$ and $H_3PO_3$ , which matches option B in the listed options. Hence, the defensible correct option is B.

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