Mechanism of nucleophilic substitution in chromium(III) complexes. II. Formation of Acetatopentamminechromium(III)-ion from aquopentamminechromium(III)-ion in acetic acid — sodium acetate buffer media

The rate of formation of the acetatopentamminechromium(III)ion from the aquopentammine complex in HOAc? NaOAc buffer media has been investigated spectrophotometrically. The results suggest that the reaction occurs by two concurrent paths one of which is independent of acetate ion while the other is first order with respect to acetate ion concentration. The values of the rate constants for both the steps and the corresponding activation parameters, ΔH^≠ and ΔS^≠, have been evaluated. The results are consistent with an S_N1 mechanism for the acetate independent path and an S_N1 IP mechanism for the acetate dependent path. Evidence for ion-pair formation is given.