Salt effects in an outer-sphere reaction between cations

Abstract

The rate of the reaction ^*Ru(bpy)²⁺₃+ Co(sep)³⁺→ products has been measured in the presence of different salts at various concentrations. In the presence of the chlorides of sodium, barium and lanthanum the rate does not depend upon the ionic strength, but upon the chloride concentration. This is the Olson–Simonson effect, which has been observed in almost all reactions between anions, but has seldom been investigated in reactions between cations. Anions of high charge do not give large salt effects, in contrast to cations of high charge in reactions between anions. Univalent anions show marked specific effects, and the rate constants increase in the order F^– < Cl^– < Br^– < ClO^–₄. An inverse correlation is found with the salting-out of benzene by the sodium salts of these anions.