Alkylphosphoric acid armed crown ethers having a specific cation binding ability

The syntheses, transport via a bulk liquid membrane, and cation binding properties of alkylphosphoric acid armed crown ethers are reported, The new armed crown ethers and monoaza crown ether containing 13-19-membered crown rings are synthesized by two methods: (a) the reaction of a hydroxymethyl-substituted crown ether with dichloroalkylphosphate followed by hydrolysis; (b) the one-pot reaction of a hydroxymethyl crown ether with an alkylphosphate in the presence of dicyclohexylcarbodiimide-pyridine. The transport experiments reveal that (i) the alkylphosphoric acid armed crown ethers exhibit specific transport abilities for alkali metal cations which fit the cavity size of their crown rings, (ii) the structure of the bridgehead carbon which bears the pendant arm (trimethylene unit and dimethylene unit) significantly influences the cation selectivity, and (iii) for the zwitterion-type phosphoric acid armed monoaza crown ether the cation selectivities can be controlled by altering the aqueous phase in the liquid membrane transport system. Computer and CPK modelling suggested that the phosphoric acid site is a cooperative coordination site, Spectroscopic data (C-13 nuclear magnetic resonance and IR) supported the proposed interaction of the cavity complexed crown ether with the side arm.