autoxidation
Technical term in chemistry for spontaneous oxidation by atmospheric oxygen at room temperature, without an external ignition source.
Unsaturated fatty acids are prone to autoxidation.
酸化 is general oxidation, while 自動酸化 specifically refers to spontaneous oxidation without an external ignition source.
Compound of 自動 (automatic) and 酸化 (oxidation), likely a calque from English 'autoxidation' or German 'Autoxidation'.