The exceptions are called entropic explosives and include organic peroxides such as acetone peroxide. The alkali metal peroxides and superoxides are powerful oxidising agents. Upon reacting with oxygen, alkali metals form oxides, peroxides, superoxides and suboxides. Infrared spectroscopy shows formation of carbonyl groups, epoxides, and peroxides. AIBN or organic peroxides are used as initiators. The alkali metal peroxides are ionic compounds that are unstable in water. I oxidants are moderately sensitive to peroxides and ethanol. Synthesis by oxidation of acetic anhydride by peroxides, is conceptually similar. Such species include free radicals and peroxides. It also converts metal oxides into the corresponding peroxides. Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Both peroxides and superoxides may react explosively with metallic potassium. Such compounds are a subset of organic peroxides, which have the formula ROOR. THF is normally more likely to form such peroxides than diethyl ether. In addition, the glutathione "S"-transferases show high activity with lipid peroxides.