Mechanisms of sodium and potassium ions transfer facilitated by dibenzo-15-crown-5 across the water /1,2-dichloroethane interface using micropipettes

The transfer of sodium and potassium ions facilitated by dibenzo-15-crown-5 (DB15C5) has been studied at the micro-water/1,2-dichloroethane (water/DCE) interface supported at the tip of a micropipette. Cyclic voltammetric measurements were performed in two limiting conditions: the bulk concentration of Na⁺ or K⁺ in the aqueous phase is much higher than that of DB15C5 in the organic phase (DB15C5 diffusion controlled process) and the reverse condition (metal ion diffusion controlled process). The mechanisms of the facilitated Na⁺ transfer by DB15C5 are both transfer by interfacial complexation (TIC) with 1:1 stoichiometry under these two conditions, and the corresponding association constants were determined at log β1 = 8.97 ±0.05 or log β₁ = 8.63 ±0.03. However, the transfers of K⁺ facilitated by DB15C5 show different behavior. In the former case it is a TIC process and its stoichiometry is 1:2, whereas in the latter case two peaks during the forward scan were observed, the first of which was confirmed as the formation of K⁺(DB15C5)₂ at the interface by a TIC mechanism, while the second one may be another TIC process with 1:1 stoichiometry in the more positive potential. The relevant association constants calculated for the complexed ion, K⁺(DB15C5)₂, in the organic phase in two cases, logβ₂, are 13.64 ±0.03 and 11.34 ±0.24, respectively.