The formation of cobalt(II) dithizonate in a liquid/liquid system: A kinetic comparison between an interfacial and a homogeneous reaction pathway

Abstract The kinetics of the chemical extraction of cobalt ions has been investigated at swarms of monodisperse droplets of carbon tetrachloride loaded with dithizone. In the range of low ion concentrations it was concluded unequivocally from the resulting independence of the flux from the exposed area that the homogeneous pathway of the reaction is rate controlling. For the range of higher ion concentrations a linear dependence of the flux on the area was always observed, and for this region, by applying the principle of exclusion, it was proven that the complexation at the interface is the rate determining step. By converting the rate constant of the heterogeneous reaction onto the scale of homogeneous reactions an interesting comparison of both rate constants could be achieved. The results obtained show that the reaction at the interface is more than two orders of magnitude more rapid than the homogeneous reaction in the aqueous phase. Qualitatively, this could be attributed to the influence of the dielectric constant in the interfacial transition layer on ionic reactions.