Synthesis of new proton-ionizable multidentate ligands

Abstract

As part of the continuing investigation of novel proton-ionizable ligands for efficient and selective extraction of metal ions, a variety of novel host molecules, including proton-ionizable acyclic polyether ligands, monocyclic lariat ethers ligands and polycyclic calix[4]arene-crown ligands, were designed and synthesized in this dissertation research. Calix[4]arene functionalized-silica gel was also prepared for metal ion absorption study.

Three series of structurally related proton di-ionizable acyclic polyethers with rigid termini were prepared for use in metal ion extraction and ion flotation studies. The rigidity and orientation of aromatic terminal groups were changed systematically. The acidity tunable N-(X)sulfonyl oxyacetamide groups [OCH2C(O)NHSO2X], in which the X group was varied from methyl to phenyl to 4-nitrophenyl to trifluomethyl were used as the proton-ionizable groups.

Proton-ionizable dibenzo-14-crown-4 and -16-crown-5 lariat ethers with different lipophilic geminal alkyl groups and different proton-ionizable groups were synthesized. The geminal lipophilic groups that were applied to both lariat ether platforms were butyl, heptyl and decyl groups. The hydrocarbon chains introduced into the ligands were designed to improve their solubility in hydrocarbon solvents and thereby increase the extraction efficiency by reducing loss into contacting aqueous phases.The proton-ionizable group was varied from carboxylic acid group to N-(trifluoromethyl)sulfonyl carboxamide to a sodium 3-propanesulfonate group.

Proton di-ionizable p-tert-butylcalix[4]arene-1,2-crown-3 ligands in cone and 1,2-alternate conformations and p-tert-butylcalix[4]arene-1,2-thiacrown-3 compounds in the cone conformation were designed and prepared. The result of solvent extraction experiments indicates that these compounds are effective extractants of mercury(II) cation. Their selectivities for alkaline earth metal cations were greatly influenced by the acidity of the proton-ionizable groups and the conformations of the ligands.

Immobilization of conformationally mobile proton-ionizable calix[4]arene units onto silica gel through covalent linkages with different lengths was achieved. The calix[4]arenes synthesized contained only one linker on upper rim to obtain better flexibility after attachment to silica gel. Evaluation of the metal ion absorption properties of the resulting silica gel can rationalize the importance of conformational mobility in this system.