METAL EXTRACTION BY ALKYL SUBSTITUTED DIPHOSPHONIC ACIDS .2. P,P'-DI(2-ETHYLHEXYL) ETHANEDIPHOSPHONIC ACID AGGREGATION AND IR STUDY

The complexation and aggregation behavior of P,P'-di(2-ethylhexyl) eth anediphosphonic acid, H2DEH[EDP], a novel solvent extraction reagent f or metal ions, was investigated. The aggregation of H2DEH[EDP] was stu died in toluene at 25 degrees C by vapor pressure osmometry. H2DEH[EDP ] was found to be hexameric in the concentration range 0.2-0.005 (m) u nder bar. Metal ions introduced into the organic phase were shown to h ave little effect on the aggregation of the extractant. The infrared s pectra of metal containing solutions of the extractant and that of the ligand itself suggest that H2DEH[EDP] exists in toluene as a cyclic h examer similar to an inverted micelle with a large hydrophilic cavity. Ca(Il), Ba(II), Eu(III), Fe(III), Th(IV) and U(VI) salts of H2DEH[EDP ] were also investigated. The infrared spectra of these compounds reve al that the asymmetric, nu(asym)(POO-), and symmetric, nu(sym)(POO-), phosphorus-oxygen stretching modes of the ligand are sensitive to the metal ion present. The shift of both nu(asym)(POO- and nu(sym)(POO-) t o lower frequencies relative to their values in the sodium salt indica tes symmetrical coordination of the phosphonate groups through chelate and/or bridging interactions. The difference (Delta nu) between the t wo frequencies, i.e. [nu(asym)(POO-)-nu(sym)(POO-)], becomes smaller a s the ionic potential of the metal ion increases.