Insight into the degradation of a manganese(III)-citrate complex in aqueous solutions

Abstract

AbstractKinetics of the electron transfer process between citrates and manganese(III) ions has been studied in acidic aqueous solutions. Acidification of the reaction mixture increased the reaction rate. The reaction is dependent on pH because there are two main protolytic forms of the Mn(III)-citrate complex in the studied pH range (4.5–6.5). Reduction potentials of Mn(III)/Mn(II) system in acidic and basic solutions as well as protolytic equilibria play a crucial role in understanding the pH profile of the studied system. The rate constants for Mn(III)citH and Mn(III)citH2+ species degradation processes are presented (citH3− and citH22− are trivalent and divalent anions of citric acid, citH4, respectively). Protolytic constant (expressed as pK′a) for Mn(III)citH protonation is estimated and discussed.