Effect of Crown Ether Lipophilicity on the Facilitated Transport of Guanidinium Thiocyanate through an Immobilized Liquid Membrane

Article abstract of DOI:10.1021/ja00198a050

The flux of guanidinium thiocyanate through a supported liquid membrane has been measured for substituted benzo crown ethers and dibenzo crown ethers.This flux depends on the water solubility of the carrier.The more lipophilic crown ethers (7-14 and 16) show a higher flux and form more stable supported liquid membranes.The effect of the lipophilic substituents on the partition coefficient of the benzo crown ethers has been calculated and verified by partition experiments.The observed fluxes have been interpreted by a developed general model for the transport of salts through supported liquid membranes containing crown ethers.This thermodynamic model takes into account the interface equilibria, viz. the partition of crown ether and salt, as well as complexation equilibria in the membrane and aqueous phase.The model has been applied for the calculation of the complexation constants in the membrane phase.The lipophilic benzo crown ethers with 27 ring atoms show lower complexation constants than the corresponding benzo crown ether with 30 ring atoms.The complexation constants of the dibenzo crown ethers and guanidinium thiocyanate are smaller than those of the corresponding complexes of the substituted benzo crown ethers.During the diffusion process of the complex through the membrane phase complexation and decomplexation take place continuously as was concluded from the small value of the inverse Damkoehler number.