The kinetics and mechanism of reaction between ethylenediaminetetraacetomanganate(III) and cyanide ion

Summary The title reaction has been followed spectrophotometrically at 325 nm (_max of Mn(CN)₆]^3–) under pseudo-first order conditions with cyanide in a large excess at pH=10.0, I=0.1M (NaClO₄) and 25°C. The reaction follows first-order kinetics in MnEDTA(OH)]^2– and exhibits variable-order dependence in CN^–] one at high cyanide concentration, and two at low cyanide concentration. The product of above reaction has been identified as Mn(CN)₆]^3–.The kinetics of the reverse reaction,i.e., the reaction of Mn(CN)₆]^3- with EDTA^4– have also been followed spectrophotometrically. This reactions is first-order with respect to both Mn(CN) ₆ ^3– ] and EDTA^4–] and exhibits an inverse first-order dependence on CN^–]. A six-step mechanism has been proposed in which the penultimate step is rate-determining. The activation parameters have been obtained and support the postulated mechanism.