selfoxidation

Selfoxidation, often called autoxidation, is the chemical oxidation of a substance by molecular oxygen from the air without a deliberately added oxidant. It commonly occurs as a free-radical chain reaction that starts with initiation steps creating reactive radicals, followed by propagation steps in which peroxy radicals oxidize substrate molecules and form hydroperoxides, and eventually termination when radicals combine. The reaction can proceed at moderate temperatures and in the presence of trace catalysts such as metal ions or light. Products include hydroperoxides, aldehydes, ketones, and acids, and the process tends to increase with unsaturation in the substrate.

Autoxidation is especially important in fats and oils, polymers, fuels, and some metals. In lipids, polyunsaturated fats are prone to peroxidation, leading to rancid flavors and odors. In polymers, autoxidation causes chain scission, discoloration, and embrittlement, reducing material performance. In metals, oxidation can proceed from, for example, Fe2+ to Fe3+ by dissolved oxygen, forming surface oxides or rust under humid conditions. Rate is influenced by temperature, light exposure, metal inhibitors, and the presence of moisture.

Control measures include adding antioxidants (such as tocopherols or synthetic phenolics), metal chelators, and radical inhibitors; reducing exposure to heat, light, and air; using inert atmospheres or sealed packaging; and stabilizing formulations with stabilizers in polymers. Monitoring methods include peroxide value measurements, TBARS assays, or chromatography to quantify carbonyl compounds and aldehydes.