Synergism of crown ethers in the thenoyl trifluoroacetone extraction of americium(III) in benzene medium

The synergism of the crown ethers (CE) dicyclohexano-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6) and 18-crown-6 (18C6) has been investigated in the thenoyl trifluoroacetone (HTTA) extraction of americium(III) in benzene medium from an aqueous phase of ionic strength 0.5 and pH 3.50 at room temperature (23°C). The extracted synergistic species have the general formula Am(TTA)₃ · CE except for DC18C6 in which case the species Am(TTA)₃·2CE was also observed at high CE concentrations. The order of synergism was found to be DC18C6>DB18C6>18C6, which is the order of the basicity of CE as indicated by their ability to extract hydrogen ions from nitric acid solutions.     

Extraction of several lanthanide and actinide radionuclides with crown ethers

The solvent extraction of several lanthanide radionuclides (¹⁴⁴Ce,¹⁴⁷Nd,¹⁵⁴Eu,¹⁷⁰Tm and¹⁶⁹Yb from aqueous picric acid solutions with (4-methylbenzo-15-crown-5) in chloroform has been investigated. The extracted species are found to be 1∶2∶3 (metal/crown/ picrate) complexes from slope analysis. The extraction equilibrium constants (K_ex) have been determined at 25 °C. The order of K_ex values for trivalent lanthanides is Nd³⁺> >Eu³⁺>Ce³⁺>Tm³⁺>Yb³⁺. This suggests that the ionic size of Nd³⁺ (r=0.995 Å) may be nearer to the cavity size of (4-methylbenzo-15-crown-5) than the other lanthanides. The extraction of thorium(IV) and uranium(IV, VI) by some crown ethers from nitric, hydrochloric and picric acid solutins have been studied. In nitric acid media, thorium(IV) forms a 1∶2 complex with DC18C6 or DC24C8, resembling plutonium(IV) and neptunium(IV) (identification of these reagents is given in Table 1 and Fig. 1). In hydrochloric acid media, the extraction of uranium(IV, VI) leads to a large loading and may be suitable for practical application. The far infrared spectra of the extracted complex in 1,2-dichloroethane have been examined for the UO₂Cl₂?DCI8C6, UO₂Cl₂?DC24C8, Th(NO₃)₄?DC18C6 and Th (NO₃)₄?DC24C8 systems. The spectra show the existence of direct bonding between the extracted metal ion and the oxygen donor in the ring of these crown ethers.     

Molecular design of macrocyclic extractants for extraction and separation of alkali and alkaline-earth metals

The distribution coefficients of the alkaline and alkali-earth metal nitrates are determined for the processes of extraction from nitric acid solutions with crown ethers, which differ in sizes of their cycles (from 18 to 22 atoms) and in side phenyl and cyclohexyl substituents, but have unchanged number of the O atoms in a cycle. The phenyl and cyclohexyl derivatives of 18-crown-6 are found to be more efficient extractants of alkali metals as compared with unsubstituted crown ethers. However, the selectivity of separation of a pair Cs-Na remains low. The 18-crown-6 derivatives with one and two cyclohexyl fragments selectively extract Sr, which can be used to separate it from the remaining alkali and alkaline-earth metals. An increase in the size of a macrocycle from 18 to 20 and 22 atoms leads to a reduction in the extraction efficiency for all alkali and alkaline-earth metals, insignificantly improves separation of a pair Cs-Na, but noticeably deteriorates Sr-Na separation.     

Extraction of tetrafluoroborate with crown ethers and its application to silicate rock analysis

Summary The extraction behaviour of tetrafluoroborate with crown ethers was studied. A high distribution ratio of tetrafluoroborate is obtained by extraction with dicyclohexano-18-crown-6 (DC18C6) in an organic solvent of high dielectric constant from potassium fluoride solution. The molar ratios of crown ether to KBF₄ in the extracted species are probably 1:1 for DC18C6, dibenzo-18-crown-6 and 18-crown-6, and 2:1 for benzo-15-crown-5 and 15-crown-5. The flow-injection extraction-spectrophotometric determination of tetrafluoroborate with Brilliant Green was worked out. Many rock reference samples were analyzed for boron (1–150 ppm).     

Ion-pair extraction of tetravalent plutonium from hydrochloric acid medium using crown ethers

Ion-pair extraction behaviour of plutonium (IV) from varying concentrations of HCl solution was studied employing crown ethers (benzo-l5-crown-5 (B15C5), 18-crown-6, (18C6), dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6, (DC18C6), dibenzo-24-crown-8 (DB24C8) and dicyclohexano-24-crown-8 (DCH24C8)) in nitrobenzene as the extractant. Ammonium metavanidate was used as the holding oxidant in the aqueous phase and the conditions necessary for the quantitative extraction of the tetravalent ion were found. The co-extraction of species of the type [HL⁺].[HPu(Cl) ₆ ^– ] and [HL⁺]2·[Pu(Cl) ₆ ^2– ] as ion-pairs (where L represents the crown ether) is suggested.     

Synergistic behaviour of crown ethers in the thenoyltrifluoroacetone extraction of technetium

The synergism of the crown ethers /CE/ dibenzene-18-crown-6 /DB18C6/ and 18-crown-6 /18C6/ has been investigated in the thenoyltrifluoroacetone /HTTA/ extraction of technetium from aqueous phase containing NaBH₄ into benzene at room temperature. The extracted synergistic species have the general formula TcO/OH/.TTA.CE. The order of synergism was found to be 18C6>DB18C6.     

The extraction behavior of some dicarbollylcobaltate crown extraction systems

The extraction of cesium, strontium and barium by a nitrobenzene solution of dicarbollylcobaltate in the presence of various crown ethers has been investigated and the influence of the substituent of crown to the extraction possibility has been observed. It has been found, that the addition of DB15C5, DB18C6 and DB21C7 (but not DB24C8 and DCH24C8) increases the distribution ratio of Cs by one order of magnitude. The fivemembered crowns are usually more efficient extractants for strontium than DCH18C6, which is widely used for strontium separation. The distribution ratio of strontium D_Sr decreases in the order 15-crown-5>benzo-15-crown-5>2-hydroxymethyl-15-crown-5>cyclohexyl-15-crown-5 >dibenzo-15-crown-5> nitrobenzo-15-crown-5. The selectivity α(Sr/Ca) decreases in the order 15C5>B15C5>DB15C5>2HM15C5>CH15C5. A selectivity factor α(Sr/Ca)≥1000 can be reached in the presence of 15C5 and B15C5. Six-membered and four-membered crowns extract strontium worse than most of the five-membered crowns. The selectivity factors α(Sr/Ca)≈100 have been reached for six-membered crowns and α(Sr/Ca)<1 has been found for 12C4. The extraction of barium by a nitrobenzene solution of dicarbollylcobaltate in the presence of 15C5 is even more efficient as the extraction of strontium. In that system D_Sr>10⁴ and D_Ba>10⁴ have been found for the extraction of Sr and Ba by a 0.01M nitrobenzene solution of dicarbollylcobaltate (c_B=0.01 mol/l) from 0.1M HNO₃. Maximal values of separation factor α(Ba/Sr) have been found in the system containing DB21C7.     

Extraction of uranium from hydrochloric acid solutions by alkylated crown ethers

The extraction recovery of uranium from 1–10 mol/L hydrochloric acid solutions into solutions of alkylated crown ethers di-tert-butyldibenzo-18-crown-6 (DTBDB18C6) and di-tert-butyldicyclohexyl-18-crown-6 (DTBDCH18C6) in organic solvents (nitrobenzene, 1,2-dichloroethane, chloroform, 1-octanol) was studied. It was found that with increasing HCl concentration, the value of the distribution coefficients of uranium (D) between the organic and aqueous phases increased to a maximum value at 9 mol/L HCl for DTBDB18C6 and 6–7 mol/L HCl for DTBDCH18C6. The properties of the solvent also greatly affect the values of D, reaching a maximum in the application of nitrobenzene, dichloroethane, or their mixture. Under these conditions, D for a 0.01 mol/L solution of DTBDCH18C6 in nitrobenzene is 830, which is the highest of known values. It was determined by the slope method and the complete saturation method that the extracted complexes of the studied alkylated crown ethers with uranyl ions have the 2 : 1 composition. Thus, new supramolecular extractants of uranium from hydrochloric acid solutions have been studied, having an extremely high extraction capacity, which can be used in the analytical and preparative chemistry of uranium.     

Effect of the 18-crown-6 and benzo-18-crown-6 on the solvent extraction and separation of lanthanide(III) ions with 8-hydroxyquinoline

The synergistic solvent extraction of 13 lanthanides with mixtures of 8-hydroxyquinoline (HQ) and the crown ethers (S) 18-crown-6 (18C6) or benzo-18-crown-6 (B18C6) in 1,2-dichloroethane has been studied. The composition of the extracted species has been determined as LnQ₃ · S. The values of the equilibrium constant and separation factor have been calculated. Here, the effect of the synergistic agent (18C6 or B18C6) on the extraction process is discussed.     

Extraction of rare-earth elements by crown ethers from acid solutions into 1,1,7-trihydrododecafluoroheptanol

Extraction of rare-earth elements from acid solutions in the 1,1,7-trihydrododecafluoroheptanol-water system was studied using crown ethers: dicyclohexano-18-crown-6 (DCH18C6; isomer A) and di-tert-butyldicyclohexano-18-crown-6 (DTBDCH18C6). All other conditions being equal, the extractability of rareearth elements by DTBDCH18C6 is far higher than for DCH18C6 itself. Trifluoroacetic and trichloroacetic acids increase metal distribution ratios. The distribution ratios for the cerium rare earths considerably exceed those for the yttrium rare earths. The stoichiometry of the rare-earth complexes of crown ethers was determined. The component ratio in the extracted complexes, M: crown ether, is 1: 1 in all cases. Rare-earth separation factors are due to different stability constants of extracted complexes.     

Separation of rhenium by extraction with crown ethers and flow-injection extraction—spectrophotometric determination with Brilliant Green

The extraction behavior of perrhenate with crown ethers was studied and methods for the separation and determination of rhenium were developed. The distribution ratio of perrhenate with dicyclohexano-18-crown-6 (DC18C6) increases with increases in the dielectric constant of organic solvents and in the potassium ion concentration of aqueous solution. The molar ratios of crown ether to KReO₄ in the extracted species are probably 1:1 for DC18C6, dibenzo-18-crown-6 and 18-crown-6 and 2:1 for benzo-15-crown-5 and 15-crown-5. Microgram amounts of rhenium were satisfactorily separated from large amounts of molbdenum(VI) by extraction with DC18C6 in 1,2-dichloroethane from 2 M potassium hydroxide solution containing tartrate and by back-extraction with sodium phosphate buffer solution after the addition of a twofold volume of hexane to the organic phase. Rhenium was determined by the flow-injection extraction-photometric method with Brilliant Green. Rhenium was satisfactory determined in molybdenite and other ore samples.     

The synergistic extraction of thorium(IV) and uranium(VI) with mixtures of 3-phenyl-4-benzoyl-5-isoxazolone and crown ethers

The extraction of thorium(IV) and uranium(VI) from nitric acid solutions has been studied using mixtures of 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) and dicyclohexano-18-crown-6, benzo-18-crown-6, dibenzo-18-crown-6 or benzo-15-crown-5. The results demonstrate that these metal ions are extracted into chloroform as Th(PBI)(4) and UO(2)(PBI)(2) with HPBI alone and as Th(PBI)(4) . CE and UO(2)(PBI)(2) . CE in the presence of crown ethers (CE). The equilibrium constants of the above species have been deduced by non-linear regression analysis. The addition of a CE to the metal chelate system enhances the extraction efficiency and also improves the selectivities between thorium and uranium. IR spectral data of the extracted complexes were used to further clarify the nature of the complexes. The binding to the CEs by Th(PBI)(4) and UO(2)(PBI)(2) follows the CE basicity sequence but with DC18C6 and DB18C6, steric effects become more important.     

Copper(II) thiocyanide complexes extractable with [dibenzo-18-crown-6-K] + in chloroform

Summary Cu^II can be extracted from aqueous KSCN solutions using 2,3,11,12-dibenzo-1,7,10,13,16-hexaoxacyclooctadiene (di-benzo-18-crown-6) in CHCl₃. Raman and i.r. spectroscopies establish that the species present in the organic phase after extraction corresponds to [Cu₂OH(SCN)₅]-[dibenzo-18-crown-6-K ⁺]₂, where the Cu^II thiocyanide complex and the K⁺ crown complex are ionically associated.     

Nature of the strong basicity of superbases,unsolvated hydroxide ions?

The basicity of so-called superbases is ascribed to the presence of free, i.e., naked, hydroxide ions. Infrared spectroscopic studies of various KOH (and KOCH₃) crown ether dicyclohexyl-18-crown-6 and dibenzo-18-crown-6) and Sr(OH)₂ cryptand(222) solutions in polar (methanol, chloroform) and non-polar solvents (toluene, n-heptane) revealed that unsolvated OH⁻ ions are not present in such strong basic solutions. Formation of potassium crown ether complexes shown by the i.r. bands at 1095–1102 and 990–995 cm⁻¹ (dicyclohexyl-18-crown-6) is always accompanied (and only possible if) by that of methoxide ions (i.r. band at 1050–1060 cm⁻¹). The presence of solvated OH⁻ ions cannot be excluded.     

Effect of crown ethers on the solvent extraction and separation of lanthanide(III) ions with 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one

Synergistic solvent extraction of 14 lanthanides with mixtures of 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (HP) and the crown ethers (S), 18-crown-6, benzo-18-crown-6 or dibenzo-18-crown-6 from an aqueous chloride medium with the constant ionic strength of 0.1 mol dm⁻³ was investigated using benzene as a diluent. The composition of the species extracted was determined as LnP3 · S. The addition of a crown ether to the chelating extractant produced rather significant synergistic effects. On basis of experimental data, values of equilibrium constants, synergistic coefficients, and separation factors were calculated.     

Extraction of some lanthanides by nitrobenzene solutions of dicarbolide in the presence of 18-crown-6

The extraction of¹⁴⁴Ce and^152,154Eu microamounts by nitrobenzene solutions of bis-1,2-dicarbollylcobaltate in the presence of 18-crown-6 from aqueous solutions of nitric acid has been investigated. The protonisation constants of 18-crown-6 in water and in nitrobenzene were determined and the corresponding equilibrium constants for cerium and europium extraction were evaluated.     

Synergistic extraction of americium(III) with 2-thenoyltrifluoroacetone and crown ethers

Extracton, of Am³⁺ in benzene with 2-thenoyltrifluoroacetone (HTTA) and crown ethers (CEs) such as 15-crown-5, 18-crown-6, dicyclohexano-18-crown-6, dibenzo-18-crown-6, dicyclohexano-24-crown-8, and dibenzo-24-crown-8 was investigated. Synergistic effect by CE was observed regardless of the kind of CE examined. The extracted species was found to be Am(TTA)₃(CE), and adduct formation constants between Am(TTA)₃ and CE in the organic phase were determined. The sequence of constant could not be explained only by basicity of CE and the steric effect of CE should be taken into account to elucidate the adduct complex formation.     

Separation of components of the solution modeling PUREX raffinate via extraction by crown ethers to 1,1,7-trihydrododecafluoroheptanol

We study the extraction of strontium, cesium, and some other elements by dicyclohexano-18-crown-6 (DCH18C6) and its di-tert-butyl derivative (DTBDCH18C6) in the system 1,1,7-trihydrododecafluoroheptanol-water from the solution modeling PUREX raffinate. We show that strontium under these conditions is extracted in a single contact with distribution ratios of 100–200 and separates from sodium, whose distribution ratio is less than 0.01. Strontium extraction in a single contact reaches 99.5%. The stoichiometry and stability constants are determined for nitric acid complexes of the crown ethers studied with coextraction of nitric acid (1: 1). The mutual solubilities of the components in the system 1,1,7-trihydrododecafluoroheptanol-water are calculated using chromatography/mass spectrometry: water in alcohol is 0.5 wt %, and alcohol in water is 0.16 wt %.     

Extraction of rare-earth elements by alkylated dibenzo-18-crown-6 and dicyclohexano-18-crown-6 from acid solutions

The extraction of rare-earth elements (REE) by alkylated crown ethers (dibenzo-and dicyclohexano-18-crown 6; DB18C6 and DCH18C6) from acid solutions in the chloroform-water system is studied. The extraction of the REE with DCH18C6 and its alkylated derivatives in the presence of trichloroacetic acid (TCA) is far more efficient than the extraction with DB18C6 and its alkylated derivatives or when nitric or acetic acid is used instead of TCA. The distribution coefficients for the cerium metals are far higher than for the yttrium metals. The metal: crown ether ratio in the extracted complex in all cases is 1:1.     

Extraction of cesium-137 from nitric acid medium in the presence of macrocyclic polyethers

Extraction behavior of¹³⁷Cs was studied from nitric acid medium using dibenzo 18 crown 6 (DB18C6), 4,4'(5')di-acetylbenzo 18 crown 6 (DAB18C6), 4, 4'(5')di-hexanoylbenzo 18 crown 6 (DHB18C6), 4,4'(5')di-nonanoylbenzo 18 crown 6 (DNB18C6) and 4,4'(5')di-t-butylbenzo 18 crown 6 (DTBB18C6) in nitrobenzene medium. The stoichiometry of the species extracted with dibenzo 18 crown 6 (L) conformed to ML⁺. NO₃ ⁻ TheD _Cs values were found not to be affected by the presence of aluminium nitrate in the aqueous phase. The separation behavior of fission products obtained from an irradiated natural uranium target was also studied. Presence of 0.004M phosphotungstic acid found to enhance theD _Cs values at lower acidities.