|
A superoxide, also known by the obsolete name hyperoxide,〔IUPAC: (''Red Book.'' ) p. 73 and 320.〕 is a compound that contains the superoxide anion with the chemical formula . The systematic name of the anion is dioxide(1−). Superoxide anion is particularly important as the product of the one-electron reduction of dioxygen O2, which occurs widely in nature.〔Sawyer, D. T. ''Superoxide Chemistry'', McGraw-Hill, 〕 Whereas molecular oxygen (dioxygen) is a diradical containing two unpaired electrons, the addition of a second electron fills one of its two degenerate molecular orbitals, leaving a charged ionic species with single unpaired electron and a net negative charge of −1. Both dioxygen and superoxide ion are free radicals that exhibit paramagnetism. ==Properties== Superoxides are compounds in which the oxidation number of oxygen is −½. The O–O bond distance in is 1.33 Å, vs. 1.21 Å in O2 and 1.49 Å in . The salts CsO2, RbO2, KO2, and NaO2 are prepared by the direct reaction of O2 with the respective alkali metal.〔Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.〕 The overall trend corresponds to a reduction in the bond order from 2 (O2), to 1.5 (O2−), to 1 (O22−). The alkali salts of are orange-yellow in color and quite stable, provided they are kept dry. Upon dissolution of these salts in water, however, the dissolved undergoes disproportionation (dismutation) extremely rapidly (in a pH dependent manner): :4 + 2 H2O → 3O2 + 4 OH− This reaction (with moisture and carbon dioxide in exhaled air) is the basis of the use of potassium superoxide as an oxygen source in chemical oxygen generators, such as those used on the space shuttle and on submarines. Superoxides are also used in firefighters' oxygen tanks in order to provide a readily available source of oxygen. In this process acts as a Brønsted base, initially forming the radical HO2·. But the pKa of its conjugate acid, hydrogen superoxide (HO2·, also known as "hydroperoxyl" or "perhydroxy radical"), is 4.88 so that at neutral pH 7 all but 0.3% of superoxide is in the anionic form, . Potassium superoxide can be dissolved in dimethyl sulfoxide (facilitated by crown ethers) and is stable as long as protons are not available. Superoxide can also be generated in a-protic solvents by cyclic voltammetry. Salts also decompose in the solid state, but this process requires heating: :2 NaO2 → Na2O2 + O2 The derivatives of dioxygen, O2, have characteristic O–O distances that correlate with the bond order of the O–O bond. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「superoxide」の詳細全文を読む スポンサード リンク
|