Zur kinetik des sauerstoffaustauschs der oxyanionen des mangans mit dem wasser—I: Die Kinetik des Sauerstoffauschs zwischen Permanganat und Wasser

Abstract

Kinetics of oxygen exchange between permanganate and water were investigated using KMn 18O 4, the falling drop densimetric, and the mass spectrometric method of isotope analysis. In neutral solutions oxygen exchange between MnO 4 − and H 2O is very slow ( k = 3·7· 10 −7 l mol −1 sec −1). It is faster by three orders of magnitude in alkaline solutions and by a factor 10 5 in acid solutions. The kinetic law observed is R = ( k + k s [H +] + k L [OH −])[MnO 4 −][H 2O] It suggests that in neutral solutions the oxygen in MnO 4 − is replaced by solvent oxygen by means of nucleophilic substitution. Intermediate anhydride formation (Mn 2O 7) is supported by the kinetics observed in acid solutions. In alkaline solutions, the kinetics of exchange, the salt effect, the catalysis by heavy metal cations and OH − ions, and the disappearence of the latter in the presence of Ba 2 ions suggests that some MnO 4 2− is always formed, this quickly exchanges its oxygen with water and its electron with MnO 4 − thus effecting a fast exchange of oxygen between MnO 4 − and the solvent.