Kinetics and mechanism of oxidation of the chromium(III)-DL-valine complex/periodate reaction. Evidence for iron(II) catalysis

Oxidation of the chromium(III)-DL-valine complex [Cr-III(L)(2)(H2O)(2)](+) by periodate has been investigated in aqueous medium. The kinetics of the reaction in aqueous medium in the presence of iron(II) as catalyst obeyed the rate law: d[Cr-VI]/dt=[Cr-III(L)(2)(H2O)(2)(+)]{[Fe-II](k(7) + K(1)k(8)/[H+]) + [I-VII](k(9)k(11)/(k(-9) + k(11)) + K(1)k(10)k(12)/(k(-10) + k(12))[H+])} Catalysis by iron(II) is believed to be due to the oxidation of iron(II) to iron(III), which acts as the oxidizing agent. The thermodynamic activation parameters were calculated and we propose that electron transfer proceeds through an inner-sphere mechanism via coordination of IO4- to chromium(III).