airoxidation

Air oxidation, sometimes referred to as airoxidation, is the chemical process by which a substance reacts with oxygen from the atmosphere, resulting in oxidation of the material. It is a common pathway for the deterioration of organic compounds and a route used in some industrial oxidation processes where molecular oxygen serves as the oxidant.

Most air oxidation involves autoxidation, a radical chain process that begins with initiation (thermal, photochemical, or catalytic formation of radicals), followed by propagation where oxygen reacts with substrate-derived radicals to form peroxy radicals and hydroperoxides, and ultimately decompose to oxidized products. The rate depends on temperature, substrate structure (especially allylic or benzylic C–H bonds), presence of metals or catalysts, light exposure, and oxygen partial pressure. In many substrates, peroxides and carbonyl-containing compounds form; in polymers, chain scission and cross-linking can occur, accelerating degradation.

Industrially, air oxidation is used for specific oxidation steps and surface treatments where oxygen acts as the oxidant. Uncontrolled air oxidation is a major cause of material degradation, including polymer aging, lipid rancidity, and metal corrosion (for example, rust on iron). Oxygen diffusion into solids and the kinetics of radical reactions often determine the overall rate.

Mitigation strategies include storing susceptible materials under inert atmospheres, adding antioxidants or stabilizers, using UV protection, and applying coatings to limit oxygen access. Removing catalytic metals or inhibiting radical formation are also common approaches to slow or prevent undesired air oxidation.