Pentoxide

Pentoxide is a traditional name used for certain oxides that contain five oxygen atoms in formula units, or that are commonly described as five-oxygen oxides of a pentavalent element. The term is most often encountered with two well-known compounds: dinitrogen pentoxide, N2O5, and phosphorus pentoxide, P4O10 (often written as P2O5 in its empirical form). These compounds illustrate how pentoxide names are applied to oxides of elements in the +5 oxidation state.

Dinitrogen pentoxide (N2O5) is a colorless solid at low temperatures that decomposes upon heating to nitrogen dioxide (NO2) and oxygen. It is a strong nitrating and oxidizing agent; in concentrated acid media it can generate the nitronium ion (NO2+), making it useful for nitration reactions in organic synthesis. N2O5 is sensitive to heat and shock and is handled under controlled conditions due to its oxidizing power and toxicity.

Phosphorus pentoxide (P4O10) is a white, highly hygroscopic solid that is widely described as the anhydride of phosphoric acid. It hydrolyzes immediately in water to form phosphoric acid: P4O10 + 6 H2O → 4 H3PO4. Because of its powerful drying activity, P4O10 is commonly used as a desiccant for gases and solvents and as a dehydrating agent in chemical synthesis. The molecular form is P4O10, while the commonly cited empirical formula is P2O5.

Safety and handling: both pentoxides are strong oxidizers and corrosive. They should be stored away from moisture and organic materials and handled with appropriate protective equipment and procedures.