Salt effects in nucleophilic substitution reactions

The effect of electrolytes on the Raton of SN1 reactions was attributed by the Hughes-Ingold electrostatic theory to their effect on the stability of the transition state, their effect on the initial state being considered as negligibly small. More recently Grumwald put forward a theory in which the effect of electrolytes on the initial as well as the transition state was considered to be important. Experimental support for the latter theory was rather weak as it consisted solely of results obtained using different organic compounds for the solubility and rate determinations (the solubility data showing the effect of electrolytes on the initial state). It was therefore thought desirable to study the effect of electrolytes on the solubility and on the rate of hydrolysis of the same organic compound (p-nitrobenzhydrylchloride). The results show that the effect of electrolytes on the solubility of the initial state is certainly not negligibly small, and that the requirements of Grumwald’s quantitative treatment are obeyed for many of the electrolytes studied. However factors not taken into account by this treatment appear to be of importance for some of the electrolytes employed (e.g. NaC10(_4), HC10(_4)). These factors may arise from short-range interactions between the electrolyte and the substrate.