Hyperoxides

Hyperoxides are compounds that contain the hyperoxide (superoxide) anion O2−. They are part of the broader family of oxygen-rich anions encountered in inorganic chemistry, which also includes peroxides (O2^2−). In many contexts, hyperoxide specifically denotes salts in which the superoxide ion is the predominant oxide unit, typically paired with alkali or alkaline earth metal cations.

The hyperoxide ion is a diatomic O2 molecule bearing one extra electron, giving it a single unpaired electron. This makes hyperoxides paramagnetic and typically strong oxidants. In solid salts, the O2− units are arranged with metal cations in an ionic lattice. The O–O bond in the superoxide ion is shorter than a typical peroxide bond, reflecting its bond order between a single and a double bond.

Common examples of hyperoxides include potassium superoxide (KO2), rubidium superoxide (RbO2), and cesium superoxide (CsO2). These compounds are typically moisture sensitive and readily hydrolyze in water, releasing reactive oxygen species. They are more reactive toward water and acids than many peroxides.

Reactions and applications: Hyperoxides react with water to release oxygen and hydrogen peroxide, for example in a representative hydrolysis: 2 KO2 + 2 H2O → 2 KOH + H2O2 + O2. They serve as chemical oxygen sources in closed environments such as submarines and spacecraft, where they can provide oxygen while absorbing carbon dioxide. They are powerful oxidants and require careful handling to avoid unwanted reactivity with organic materials.

Safety and handling: Hyperoxides are moisture-sensitive and can pose fire or explosion hazards upon contact with organic substances or reducing agents. They should be stored and used under strictly controlled conditions.