Cation Binding Properties of Benzo-type Crown Ethers. 3. Effect of Large Ring Size upon Complexation Phenomena of Crown-9 and Crowm-10 Derivatives

The cation-binding by two large ring-sized benzo-27-crown-9 and benzo-30-crown-10 has been evaluated by a solvent extraction of monovalent metal picrates (Na^+, K^+, Rb^+, Cs^+, Ag^+, and Tl^+) between water and dichlolomethane. The effect of ring size and benzo group upon the cation binding ability is discussed. The results are compared with benzo-type crown-6-8 (benzo-18-crown-6, benzo-21-crown-7 and benzo-24-crown-8) and simple unsubstituted crown-6-8 ethers (18-crown-6, 21-crown-7 and 24-crown-8) The cation-binding ability and complex formation are discussed in view of the size of the crown ether ring and the basicity of oxygen atoms.