Superoxide, potassium, with

Potassium Superoxide. Potassium, mbidium, and cesium form superoxides, MO2, upon oxidation by oxygen or air. Sodium yields the peroxide, Na202 lithium yields the oxide, Li20, when oxidized under comparable conditions. Potassium superoxide [12030-88-5] KO2 liberates oxygen in contact with moisture and carbon dioxide (qv). This important property enables KO2 to serve as an oxygen source in self-contained breathing equipment. 

The principal product of the reaction of the alkali metals with oxygen varies systematically down the group (Fig. 14.15). Ionic compounds formed from cations and anions of similar radius are commonly found to he more stable than those formed from ions with markedly different radii. Such is the case here. Lithium forms mainly the oxide, Li20. Sodium, which has a larger cation, forms predominantly the very pale yellow sodium peroxide, Na202. Potassium, with an even bigger cation, forms mainly the superoxide, K02, which contains the superoxide ion, O,. ... 

The earlier references, which state that this powerful oxidant is stable when pure, but explosive when formed as a layer on metallic potassium [1,2], are not wholly correct [3], because the superoxide is manufactured uneventfully by spraying the molten metal into air to effect oxidation [4], Previous incidents appear to have involved the explosive oxidation of unsuspected traces of mineral oil or solvents [3]. However, mixtures of the superoxide with liquid or solid potassium-sodimn alloys will ignite spontaneously after an induction period of 18 min, but combustion while violent is not explosive [3], The additional presence of water (which reduces the induction period) or hydrocarbon contaminant did produce explosion hazards under various circumstances [5], Contact of liquid potassium with the superoxide gives no obvious reaction below 117°C and a controlled reaction between 117 and 177°C, but an explosive reaction occurs above 177°C. Heating at 100°C/min from IT caused explosion at 208°C [6],... 

Cesium reacts with water in ways similar to potassium and rubidium metals. In addition to hydrogen, it forms what is known as superoxides, which are identified with the general formula CsO When these superoxides react with carbon dioxide, they release oxygen gas, which makes this reaction useful for self-contained breathing devices used by firemen and others exposed to toxic environments. 

Oxidation of Potassium Peroxide. Determination of Potassium Superoxide. Potassium peroxide was prepared by the addition of a tert-butyl alcohol solution of 90% hydrogen peroxide to potassium tert-butoxide in DMSO or tert-butyl alcohol. Oxygen absorption was followed in the standard manner (20). Analysis of solid precipitates for potassium superoxide followed exactly the method of Seyb and Kleinberg (23). Potassium superoxide formed in the oxidation of benzhydrol was determined in a 15-ml. aliquot of the oxidation solution. To this aliquot 10 ml. of diethyl phthlate was added to prevent freezing of the solution. The mixture was cooled to 0°C., and 10 ml. of acetic acid-diethyl phthlate (4 to 1) added over a period of 30 minutes with stirring. The volume of the evolved oxygen was measured. 

The most reliable technique for the analysis of superoxides is that developed by Seyb and Kleinberg. In this method the superoxide sample is treated with a mixture of glacial acetic acid and diethyl or dibutyl phthalate. The superoxide reacts with the acetic add to yield oxygen, hydrogen peroxide, and potassium acetate. The amount of superoxide in the sample is related to the amount of oxygen evolved which is measured with a gas buret. The stoichiometry of the analytical reaction is ... 

The reaction of potassium with atmospheric oxygen leads to a surface layer of potassium superoxide. When this oxidizing layer is embedded in the metal, an explosion may result. Therefore, the oxidized surface layer must be scraped off before the metal is cut. Presumably a similar problem exists with rubidium and cesium. 

When potassium superoxide reacts with water, oxygen gas is evolved ... 

Reaction with hydrazo compounds. Potassium superoxide reacts with various hydrazo and related compounds in a variety of ways as shown in the examples. Oxidation of arylhydrazines also results in biaryls derived from the solvent and thus involves free aryl radicals. 

Oj have been studied in toluene solution of the potassium 18-crown-6 salt. With spin traps adducts are observed mainly derived from 0 , derived from reaction (45). Reactions of superoxide, Oj, with ascorbic acid involve deprotonation... 

Preparation of Most of the pure potassium metal produced is converted to a superoxide (KO,), a yellow potassium solid, directly by combustion in dry air or burning the potassium amalgam with oxygen, superoxide Potassium superoxide is extensively used as a source of oxygen in respiratory equipment, since it generates oxygen and also absorbs carbon dioxide forming the carbonate. 

When potassium, rubidium, and cesium react with molecular oxygen, the superojddes, MOj, are produced. A rather clear relationship seems to exist between the size of the alkali-metal cation and the stability of the superojddes. In the salts of the smaller cations, such as those of lithium and sodium, too much contact between the large superojdde ions evidently destabilizes the lattices. The larger cations provide a better match of ionic sizes. Not surprisingly, therefore, the most stable superoxide occurs with cesium. 

Potassium superoxide is produced commercially by spraying molten potassium iato an air stream, which may be enriched with oxygen. Excess air is used to dissipate the heat of reaction and to maintain the temperature at ca 300°C. It can also be prepared ia a highly pure state by oxidizing potassium metal that is dissolved ia Hquid ammonia at —50° C. 

Primary and secondary alkyl haUdes and sulfonates react with potassium superoxide to form dialkyl peroxides (101,102) (eq. 28). Dia2oalkanes, eg, dia2omethane, have been used to alkylate hydroperoxides (66) (eq. 29). 

Phenols with bulky ortho- and para-substituents, eg, phenoHc antioxidants, do not undergo this reaction however, they scavenge radicals generated by thermolysis of diacyl peroxides and other peroxides. Diacyl peroxides react with potassium superoxide, KO2, forming singlet oxygen (207). 

Oxygen masks for producing 02 in emergency situations contain potassium superoxide, K02. It reacts with C02 and H20 in exhaled air to produce oxygen ... 

Potassium superoxide is used in self-contained breathing devices for firefighters and miners. It reacts with the moisture in exhaled air to generate oxygen ... 

A self-contained breathing apparatus contains 248 g of potassium superoxide. A firefighter exhales 116 L of air at 37°C and 748 mm 1%. The volume percent of water in exhaled air is 6.2. What mass of potassium superoxide is left after the water in the exhaled air reacts with it ... 

---