Phosphorus trioxide reacts with water to form phosphorous acid, reflecting the fact that it is the anhydride of that acid.

P₄O₆ + 6 H₂O  →   4 H₃PO₃
It reacts with hydrogen chloride to form H₃PO₃ and phosphorus trichloride.

P₄O₆ + 6 HCl → 2 H₃PO₃ + 2 PCl₃
With chlorine or bromine it forms the corresponding phosphoryl halide, and it reacts with iodine in a sealed tube to form diphosphorus tetraiodide.

P₄O₆ reacts with ozone at 195 K to give the unstable compound P₄O₁₈.
P₄O₁₈ decomposes above 238 K in solution with the release of O₂ gas.
 Decomposition of dry P₄O₁₈ is explosive.

In a disproportionation reaction, P₄O₆ is converted into the mixed P(III)P(V) species P₄O₈ when heated in a sealed tube at 710 K, with the side product being red phosphorus.
Phosphorus trioxide reacts with water to form phosphorous acid, reflecting the fact that it is the anhydride of that acid.
P₄O₆ + 6 H₂O  →   4 H₃PO₃
It reacts with hydrogen chloride to form H₃PO₃ and phosphorus trichloride.
P₄O₆ + 6 HCl → 2 H₃PO₃ + 2 PCl₃
With chlorine or bromine it forms the corresponding phosphoryl halide, and it reacts with iodine in a sealed tube to form diphosphorus tetraiodide.
P₄O₆ reacts with ozone at 195 K to give the unstable compound P₄O₁₈.
P₄O₁₈ decomposes above 238 K in solution with the release of O₂ gas.  Decomposition of dry P₄O₁₈ is explosive.
In a disproportionation reaction, P₄O₆ is converted into the mixed P(III)P(V) species P₄O₈ when heated in a sealed tube at 710 K, with the side product being red phosphorus.
Phosphorus trioxide