Question

Oxoacids of phosphorus are formed in the following reactions. The acid formed in which of the following reactions does contain P - P bond?

• A. White $P_4 +$ alkali $\rightarrow$
• B. $P_4O_6 + H_2O \rightarrow$
• C. $PCl_3 + H_3PO_3 \rightarrow$
• D. Red $P_4 +$ alkali $\rightarrow$

Hint:

{P-P bond:} Hypophosphoric acid ($H_4P_2O_6$). {P-O-P bond:} Pyrophosphoric ($H_4P_2O_7$), Pyrophosphorous ($H_4P_2O_5$), Metaphosphoric ($HPO_3)_n$.

Answer 1

The Correct Option is D

Step 1: Analyze Reactions and Products:

• (A) White $P_4 +$ alkali: Produces Phosphine ($PH_3$) and Hypophosphite ($NaH_2PO_2$). Hypophosphorous acid ($H_3PO_2$) has one $P=O$, two $P-H$, one $P-OH$. No P-P bond.
• (B) $P_4O_6 + H_2O$: Produces Orthophosphorous acid ($H_3PO_3$). Has one $P=O$, one $P-H$, two $P-OH$. No P-P bond.
• (C) $PCl_3 + H_3PO_3$: Produces Pyrophosphorous acid ($H_4P_2O_5$). Structure has $P-O-P$ linkage. No direct P-P bond.
• (D) Red $P_4 +$ alkali: Oxidation of Red Phosphorus with alkali produces salts of Hypophosphoric acid ($H_4P_2O_6$). The structure of Hypophosphoric acid contains a direct P-P bond ($HO-P(O)(OH)-P(O)(OH)-OH$).

Step 2: Conclusion:
Hypophosphoric acid ($H_4P_2O_6$), formed from Red P and alkali, contains a P-P bond.