Mechanism of octahedral substitutions. Part IX. Grunwald–Winstein treatment of spontaneous aquation of trans-chloronitro- and trans-dichlorobisethylenediaminecobalt(III) ions in mixed aqueous solvents

Abstract

The first-order rate constants of spontaneous aquation of trans-chloronitro- and trans-dichlorobis(ethylenedi-amine)cobalt(III) ions were measured in a range of binary mixed solvents, including methanol–, ethanol–, dioxin–, and acetone–water solutions extended to 10%(v/v) water content. Both complexes equated completely in water-rich mixtures and incompletely in solutions containing higher percentages of organic component.

The logarithms of rate constants correlated linearly with Grunwald–Winstein solvent Y values, with slopes of m= 0·32 for the dichloro- and m= 0·09 for the chloronitro-complex. The lower susceptibility of the chloronitro-complex to solvent ionizing power indicates that the remaining bonding to the leaving chloride in the transition state is larger in the chloronitro- than in the dichloro-complex. Mechanistic implications are discussed.