W. J. Mcdowell

Crown Ethers as Solvent Extraction Reagents: Where do We Stand?

Abstract It is perhaps prophetic that among the first applications of crown ethers was their use as solvent extraction reagents. In 1962 the compound 2, 3, 11, 12-dibenzo-1, 4, 7, 10, 13, 16-hexaoxacycloocta-2, 11-diene, now mercifully called dibenzo-18-crown-6. was identified and was found to form alkali-metal-salt adducts that were soluble in organic solvents. These serendipitously discovered extraction properties of crown ethers were later used to compare the complex-formation properties of metal ions with crown ethers, and it was observed that salts of organophilic anions were more readily transferred to aprotic solvents. Plcrate salts were extensively used in this role. However, those seeking analytical or process applications of the unusual complexing abilities of macrocycles needed the aqueous anion to be one of the more common mineral acid anions such as chloride, nitrate, or sulfate. This problem was circumvented in the late 1970′s when it was discovered that crown ethers mixed with an organophil...

Investigations of ion-size-selective synergism in solvent extraction

Abstract Organophilic crown ethers and other similar macrocyclic compounds produce a synergistic enhancement of the extraction of several metal ions by organic-phase—soluble carboxylic, phosphoric, and sulfonic acids. Ions examined include the alkali metals, the alkaline earths, and some first-row transition elements. In many cases, the synergistic effects are clearly related to the correspondence of the ion size to the macrocycle cavity diameter. In other cases this is less true, and occasionally, complete lack of syner-gism or even antagonism is observed. These phenomena have been investigated by systematic studies of the systems involved, by equilibrium studies of selected extraction systems, and by vapor-pressure osmometric studies of the iritermolecular bonding between the organic-phase macrocycles and acids. Lack of synergism (when it is expected from size correspondence) does not appear to be due to bonding interactions between the macrocycle and the extractant acid, Other considerations suggest th...

Studies of the Size-Selective Extraction of Alkali Metal Ions by the Synergistic Extraction System, Crown Ether-DI(2-Ethylhexyl) Phosphoric Acid-Benzene

Abstract In order to take practical advantage of the size-selective cation-coordinating ability of the cyclic polyethers (crown ethers), experiments seeking a means of avoiding the problem of solubilizing a mineral-acid anion in a nonpolar organic diluent were performed. Mixtures of several known extractants and crown ethers were tried. Results presented indicate that organic soluble cation exchangers mixed in solution with crown ethers produce a synergistic extractant mixture that largely exhibits the size-selective properties expected of the crown ether. Data are presented for the extraction of macro concentrations of alkali metals by di(2-ethylhexyl) phosphoric acid—dicyclohexyl-18-crown-6 mixtures at a single pH, and at nonloading condition(σ metal cone < 0.04 M) as a function of pH, 2 to 6. In both cases potassium is synergized most strongly presumably because of its best fit to the crown ether cavity. Other data indicate, however, that the size-fit principle is not as consistent for all alkali metal...

Bifunctional Phosphinic Acid Resins for the Complexation of Lanthanides and Actinides

Abstract Phosphinic acid ion exchange/redox resins are synthesized by the reaction between polystyrene beads and phosphorus trichloride followed by base hydrolysis. The reaction requires a temperature of 73°C for full functionalization to occur. The effect of lower functionalization temperatures on resin acid capacity was determined and the concomitant effect on ion exchange investigated. The acid capacity was found to vary from 1.68 mequiv/g to 4.79 mequiv/g in the functionalization temperature range studied (15°C to 73°C). The percent resin sites loaded with zinc ions is independent of the actual capacity. The extracting ability of the phosphinic acid resin for europium, thorium, uranium, americium, and plutontutn was examined as a function of acid concentration from acid nitrate solutions both at varying and constant ionic strength. The phosphinic resins show better extraction for these ions than the sulfonic resins, especially from high acid solution (4M HNO3) due to the superior coordination ability ...

LIQUID-LIQUID EQUILIBRIUM ANALYSIS IN PERSPECTIVE.PART 1. SLOPE ANALYSIS OF THE EXTRACTION OF URANYL NITRATE FROM NITRIC ACID BY DI-2-ETHYLHEXYLSULFOXIDE

ABSTRACT Slope analysis is critically examined as a stand-alone method for analyzing the representative extraction system uranyl nitrate, nitric acid, sodium nitrate, water, di-2-ethylhexylsulfoxide (DEHSO). n-dodecane at 25 °C. The use of detailed computer calculations of free extractant concentrations and activity coefficients has permitted assessment of commonly employed assumptions of slope analysis in the data treatment. On the basis of slope analysis alone, the extraction of nitric acid in the absence of U(VI) can be partly described by the formation of the 1:1 adduct (DEHSO)(HNO3), but complications due to nonideality effects and the formation of at least two other species hinder further reliable analysis. Under the limiting conditions of low DEHSO molarity, low aqueous nitric acid molarity, and low U(VI) loading, a slope-analysis treatment of U(V1) extraction data shows unambiguously that the predominant extracted species of U(VI) is UO2(N03)2(DEHSO)2(H20)w (w not determined). However, it is diffi...

The Synerqistic Solvent Extraction of Manganese by Macrocyclic Crown Ethers in Combination with Didodecylnaphthalene Sulfonic Acid: Effect of Macrocycle Substituents

Abstract Crown ethers in combination with organophilic cation exchangers synergize the extraction of certain metai ions from aqueous solutions, and their selectivity has been thought largely dependent on the correspondence between the crown others cavity diameter and the metal ion diameter. This work focuses on two crown ethers, tert. -butylbenzo -15-crown-5 (tBB15C5). and tert, -butylcyclohexano 15-crown-5 (tBC15C5) each of which has a cavity diameter of 1.7 to 2.2 × 10−10 m. and their extraction of Mn2+ (ionic diameter 1.4 to 2.2 × 10−10 m) from aqueous nitrate solutions. The organophilic cation exchanger used was didodecylnaphthalene sulfonic acid (HDDNS). The data show no observable complexes of the manganese salt of HDDNS

Selective Extraction of Cu2+ and Ag+ Ions from Sulfuric Acid by Synergistic Combinations of Tetradentate Thia Macrocycles with Dioodecylnaphthalene Sulfonic Acid

Abstract The aqueous-insoluble thia macrocycles tetrathia-14-crown-4 (TT14C4) and tetrathia-16-crown-4 (TT16C4) strongly and selectively synergize the extraction of Cu2+ and Ag+ ions from aqueous sulfuric acid solutions by the organophilic cation exchanger didodecylnaphthalene sulfonlc acid (HDDNS) in toluene diluent. Over a range of sulfuric acid concentrations, the selectivity is given by the order Ag2 > Cu2+ > Mn2+, Fe2+, Fe3+, Co2+, Ni2+, and Zn2+, where synergism occurs only for Ag+ and Cu2+. Selectivity factors greater than 300 have been achieved for Cu2+ over ubiquitous Fe3+. The synergistic extraction of Cu2+ and Ag+ was explored as a function of sulfuric acid concentration, relative concentration of macrocycle vs. HDDNS, and loading.

Approaches Toward Synthesizing Novel Extractant Systems: Polymeric Bifunctional Extractants with Synergistic Possibilities

Abstract The synthesis of a monoarylphosphinic acid-diarylphosphine oxide extractant system supported on macroporous polystyrene beads is reported. The bifunctional resin was used in separate zinc and copper(I1) ion extraction studies. Results wth both metals show an excellent extent of extraction under low loading conditions and solution pH of 1–2; at equivalent meta1:resin concentrations, the resin absorbs 50% of the metalin solution. Comparison with lower absorption values reported in the literature for similar systems suggests the possibility of a synergisticextraction due to cooperation between the acid and oxide moieties.

Novel Bifunctional Resins in Metal Ion Separations: Ion Exchange/Coordination Resins and Ion Exchange/Precipitation Resins

Abstract Dual mechanism bifunctional polymers (DMBPs) as metal ion extractants are described within the context of two new examples. The carboxylic acid/pseudocrown resin is a new example of the DMBP class of resins described as ion exchange/ coordination resins. The polyethylene glycol ligand within the resin functions as a coordinating site for metal ions which are brought into the resin via ion exchange with the acid ligand. Initial studies with alkali metal ions are presented. The third general class of DMBPs is also presented. In this case, precipitation is the reaction occurring along with ion exchange thus yielding the ion exchange/precipitation resins. Barium recovery from aqueous solution via barium sulfate precipitation is described.

Dual mechanism bifunctional polymers: Phosphinic acid ion-exchange/redox resins and the kinetics of metal-ion complexation

Abstract The detailed study of bifunctional phosphinic acid resins has recently been introduced. It has been shown that they operate through the dual mechanism of ion exchange and metal-ion reduction. A key component in the synthesis is the Friedel-Crafts catalyst used for the reaction between PCl3 and polystyrene. We now find that the order of catalyst activity is AlCl3 > FeCl3 > ZnCl2 > SnCl4. Ferric chloride catalysis also operates by an additional redox mechanism which yields a phosphonic acid resin. The extent of loading onto phosphinic and sulfonic acid resins by zinc ions at equilibrium was studied as a function of the anion present both with and without the presence of an excess of sodium ions. Both sets of resins exchange at a comparable rate upon the introduction of macroporosity into the polystyrene support. The influence of the redox process as an additional variable in the phosphinic resin kinetics was studied with silver and mercury(II) nitrate solutions. All of the primary acid sites are oxidized after a 9-hour contact time with Ag(I) ions and a 2-hour contact time with Hg(II) ions. The mercury loading curves and the different behavior of silver, which shows more ion exchange than redox at short times while leaving a residual ion concentration on the resin irrespective of whether all of the primary acid sites have been oxidized or not, can be explained by the termolecular nature of the Ag(I) redox reaction in contrast to the bimolecular nature of the Hg(II) reaction. Studies with other ions show that the minimum metal-ion reduction potential below which no redox occurs with the phosphinic resins is probably between 0.0 and 0.3 V.