How to design a kinetic-catalytic method of analysis based on ligand substitution reactions

Abstract

From a mechanistic consideration on the formation constant of a metal complex, the catalytic effect of a third ligandA on ligand substitution reaction is found to be given by log(k ^A _f )=αE(A)+βH(A)+γE(A), wherek _f andk ^A _f refer to the rate constants for a non-catalyzed reaction path and catalyzed reaction path, respectively, andE andH are the electron donor constant and basicity constant of the specified ligand, respectively,α,β, andγ are constants characteristic of a metal ion and their values have been estimated from the mechanistic consideration on the reactivity of a metal ion and its complex. With this equation and the parametersα,β,γ,E, andH, the acceleration effect of halide ions on the ligand substitution reaction of mercury(II)-4-(2-pyridylazo)resorcinol complex with l,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid was quantitatively demonstrated. With the same parameters some possibilities to design a new kinetic-catalytic method of analysis based on ligand substitution reactions were proposed.