Chloride Transfer across the Liquid–Liquid Interface Facilitated by a Mono-Thiourea as a Hydrogen-Bonding Ionophore

Applicability of a thiourea-based hydrogen-bonding ionophore 2, N,N′-bis(p-nitrophenyl)thiourea, for amperometric anion sensors is presented. Chloride transfer across the nitrobenzene (NB)–water interface facilitated by this ionophore is studied by using ion transfer polarography. When 2 is present in the organic phase, a well-defined wave can be observed, indicating that the chloride transfer across the NB–water interface is facilitated by 2 via formation of hydrogen bonds. The analysis of ion transfer polarograms shows that the chloride transfer is assisted by 1 : 1 complexation between 2 and chloride, and that the transfer process is reversible and controlled by diffusion of 2 from the bulk NB phase to the interface. Despite its simple binding mode based on two point interactions, mono-thiourea 2 has a strong ability to facilitate chloride transfer, which is comparable to that obtained for a highly preorganized bis-thiourea ionophore 1, 2,7-di-t-butyl-4,5-bis(N′-butylthioureylene)-9,9-dimethylxanthene, in which four hydrogen bonds are involved in the chloride binding.