Metal extraction by silyl-substituted diphosphonic acids. II. Effect of alkylene bridge length on aggregation and metal ion extraction behavior

Abstract

In an ongoing effort to determine the relationship between structure and function in diphosphonic acids, the aggregation and solvent extraction chemistry of four novel silicon-substituted diphosphonic acids, P,P 0 -di[3-(trimethylsilyl)-1-propyl] propylene-(H 2 DTMSP[PrDP]), butylene-(H 2 DTMSP[BuDP]), pentylene-(H 2 DTMSP[PDP]), and hexylene diphosphonic acid (H 2 DTMSP[HDP]), were investigated. Vapor pressure osmometry indicates that H 2 DTMSP[PrDP] and H 2 DTMSP[PDP] are dimeric in toluene at 258C, while H 2 DTMSP[BuDP] and H 2 DTMSP[HDP] are primarily trimeric and hexameric, respectively. The solvent extraction of selected alkaline earth cations (Ca, Sr, and Ba) and representative tri-, tetra-, and hexavalent actinides 2289[Am(III), Th(IV), and U(VI)], from nitric acid solutions into oxylene solutions of the ligands has been studied and compared to results reported previously for some analogous di(2-ethylhexyl)-substituted diphosphonic acids. Differences observed in the magnitude of distribution ratios, based on the number of bridging methylene groups, have been explained considering factors such as ligand aggregation, chelate ring size, PyO basicity (qualitatively determined by 31 P nuclear magnetic resonance and infrared spectroscopy), and the relative acidities of the ligands.

Extraction of Alkaline Earth and Actinide Cations by Mixtures of Di(2-Ethylhexyl) Alkylenediphosphonic Acids and Neutral Synergists

“…For H 2 DEH[BuDP], little interaction with TBP is observed until a neutral ester-to-acid ratio of at least 4 : 1 is reached, suggesting that H 2 DEH[BuDP] forms more strongly hydrogen-bonded aggregates than H 2 DEH[EDP], a conclusion consistent with the higher basicity expected for the phosphoryl group of H 2 DEH[BuDP] [28]. Bands possibly due to free (i.e., not hydrogen-bonded) phosphoryl groups of H 2 DEH[EDP] and to hydrogen-bonded neutral ester appearing at higher neutral ester to H 2 DEH[EDP] concentration ratios.…”

Carbon Dioxide Solubility Enhancement through Silicone Functionalization: “CO2-philic” Oligo(dimethylsiloxane)-substituted Diphosphonates∗

“…We have long had an interest in metal ion complexants bearing a phosphoryl (P ¼ O) group, especially chelating ligands containing two such groups (18)(19)(20)(21)(22)(23)(24)(25). Based on their extensive use as chelating agents, these diphosphonates are a logical choice for use as extractants in CO 2 .…”