Diphosphorous pentoxide is an alternative name for the compound phosphorous pentoxide, P2O5, which is a crystalline, white solid that acts as a desiccant. Other common names for phosphorous pentoxide include phosphoric anhydride and phosphorous (V) oxide.
Phosphorous pentoxide's dehydrating properties are powerful enough to cause severe chemical burns upon contact with the skin, eyes, digestive tract or lungs. It generates heat when reacting with water; this heat is sufficient to ignite flammable materials. Phosphoric pentoxide itself is not flammable.
As of 2014, it is not legally classified as a hazardous material by the federal government, but state regulations in Massachusetts, New Jersey and Pennsylvania place it on "right to know" lists. Workers in these states have a right to know when they are working with phosphorous pentoxide, they must be trained in its safe use and a Materials Safety Data Sheet must be provided.
Phosphorous pentoxide's primary use is in laboratories as a chemical dehydrating agent. Historically, it has been used to increase the potency of phosphoric acid, but safer and more efficient procedures replace it in modern phosphoric acid preparation. Phosphorous pentoxide is produced by burning elemental phosphorous in the presence of oxygen; burning white phosphorous in open air is sufficient to produce the compound.