ALKYLPHOSPHORIC ACID ARMED CROWN-ETHERS HAVING A SPECIFIC CATION-BINDING ABILITY

The syntheses, transport via a bulk liquid membrane, and cation bindin g properties of alkylphosphoric acid armed crown ethers are reported, The new armed crown ethers and monoaza crown ether containing 13-19-me mbered crown rings are synthesized by two methods: (a) the reaction of a hydroxymethyl-substituted crown ether with dichloroalkylphosphate f ollowed by hydrolysis; (b) the one-pot reaction of a hydroxymethyl cro wn ether with an alkylphosphate in the presence of dicyclohexylcarbodi imide-pyridine. The transport experiments reveal that (i) the alkylpho sphoric acid armed crown ethers exhibit specific transport abilities f or 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 a cid armed monoaza crown ether the cation selectivities can be controll ed by altering the aqueous phase in the liquid membrane transport syst em. 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 c avity complexed crown ether with the side arm.