Kinetics and mechanism of oxidation of chromium(III)-L-glutamic acid complex by periodate

Abstract

The kinetics of oxidation of the chromium(III)-L-glutamic acid complex, [CrIII(L)₂(H₂O)₂]⁺ , by periodate in aqueous solutions has been found to obey the following-equation:<br> <br> <i>d</i>[Cr^VI]/<i>dt</i>=<i>k</i>₂<i>K</i>₅[Cr^III]_T[IV^II]_T /{1+([H⁺]/<i>K</i>₁)+<i>K</i>₅[I^VII]_T}<br> <br> where <i>k</i>₂<i> </i>is the rate constant for the electron transfer process, <i>K</i>₁the equilibrium constant for dissociation of [Cr^III(L)₂ (H₂O)₂⁺] to of [Cr^III(L)₂ (H₂O)(OH)] + H⁺, and <i>K</i>₅<i> </i>the pre-equilibrium formation constant. Values of <i>k</i>₂<i> </i>= 2.93×10^-3 s^-1,<i>K</i>₁<i> </i>= 6.26 ×10^-4 mol dm^-3 and <i>K</i>₅<i> </i>= 88.41 dm³ mol^-1 have been obtained at 30°C and <i>I= </i>0.2 mol dm^-3 . Thermodynamic activation parameters have been calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO₄^- to chromium(III).