Abstract: | The rate for the substitution reaction of Co(edta)? with ethylenediamine was greatly enhanced by the presence of an excess of Co(II) ion in solution. The rate constant is (13±2) M?-sec?1 at μi=0.10M LiClO4, pH=11.1, en]=0.10M and T=25°C. The mechanism for the reaction is discussed on the basis of the Marcus theory for outer-sphere processes corrected for electrostatic effects. This catalytic effect was not observed when the Co(II) was present in small amount due to the stability of the Co(edta)?2 complex toward substitution. The rate constant for direct substitution of Co(edta)? under the same conditions has also been measured and the value is (3.66±0.40)×10?4sec?. |