Phosphorus pentoxide (P4O10) is a white, crystalline solid that is highly hygroscopic, meaning it readily absorbs water vapor from the air. It is a powerful desiccant and dehydrating agent, making it useful in various industrial applications. Phosphorus pentoxide is commonly used in laboratories for drying gases and solvents, as well as in the production of chemicals.

One of its important applications is in the conversion of primary and secondary alcohols to the corresponding chlorides. It also plays a role in the preparation of anhydrides from carboxylic acids. In addition, phosphorus pentoxide is used in the synthesis of various phosphorus compounds and as a dehydrating agent in the pharmaceutical industry.