Phosphorus trioxide

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Phosphorus trioxide is the chemical compound with the formula P4O6. This colorless solid is structurally related to adamantane. It is the anhydride of the unstable tautomer of phosphorous acid, P(OH)3. It is a white waxy substance and has a garlic odour.

P4O6 is a ligand for transition metals, comparable to phosphite.


It is obtained by the combustion of phosphorus in a limited supply of air.

P4 + 3 O2 → 2 P2O3

Chemical Properties

It reacts with cold water to form phosphorous acid ( H3PO3 ).

P2O3 + 3 H2O → 2 H3PO3

It reacts with hot water vigorously to form flammable phosphine gas ( PH3 ).

2 P2O3 + 6 H2O → PH3↑ + 3 H3PO4