M. L. P. Reddy

Para‐Substituted 1‐Phenyl‐3‐methyl‐4‐aroyl‐5‐pyrazolones as Chelating Agents for the Synergistic Extraction of Thorium(IV) and Uranium(VI) in the Presence of Various Crown Ethers

Abstract Para‐substituted 1‐phenyl‐3‐methyl‐4‐aroyl‐5‐pyrazolones, namely, 1‐phenyl‐3‐methyl‐4‐(4‐fluorobenzoyl)‐5‐pyrazolone (HPMFBP) and 1‐phenyl‐3‐methyl‐4‐(4‐toluoyl)‐5‐pyrazolone (HPMTP) were synthesized and utilized for the extraction of thorium(IV) and uranium(VI) from nitric acid solutions. For comparison, studies have also been carried out with 1‐phenyl‐3‐methyl‐4‐benzoyl‐5‐pyrazolone (HPMBP). The results demonstrate that thorium(IV) and uranium(VI) are extracted into chloroform according to: where HX refers to 1‐phenyl‐3‐methyl‐4‐aroyl‐5‐pyrazolone and K ex,0 denotes the equilibrium constant. The equilibrium constants of the extracted complexes have been calculated by nonlinear regression analysis taking into account the aqueous‐phase complexation of the metal ion with inorganic ligands and all plausible complexes extracted into the organic phase. The equilibrium constants of thorium(IV) and uranium(VI) with various 4‐aroyl‐5‐pyrazolones follow the order HPMFBP > HPMBP > HPMTP, which is in accordance with their pK a values. The synergistic solvent extraction of thorium(IV) and uranium(VI) was also investigated with mixtures of HPMFBP and 18‐crown‐6 (18C6), dicyclohexano‐18‐crown‐6 (DC18C6), dibenzo‐18‐crown‐6 (DB18C6), and benzo‐15‐crown‐5 (B15C5). The complexation strength of Th(PMFBP)4 chelate with crown ethers follows the order B15C5 > 18C6 > DC18C6 > DB18C6. The high extraction efficiency of thorium(IV) with B15C5 can be explained on the basis of “size‐fitting effect.” On the other hand, the complexation strength of UO2(PMFBP)2 chelate with various crown ethers follows the order 18C6 > DC18C6 > B15C5 > DB18C6, which can be explained on the basis of the crown ether basicity sequence and steric effects. Solid complexes of these metal ions with HPMFBP and crown ethers have been isolated and characterized by elemental analyses, IR and 1H NMR spectroscopic techniques to further clarify the nature of the extracted complexes.

Crown ethers as synergists in the extraction of trivalent lanthanoids with 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone

Summary This paper highlights the results of investigations carried out on the extraction of lanthanoids such as Nd(III), Eu(III) and Tm(III) from nitrate solutions into chloroform with 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone (HFBPI) in the presence and absence of various crown ethers (CE); 18-crown-6 (18C6), dicyclohexano-18-crown-6 (DC18C6), benzo-18-crown-6 (B18C6) and dibenzo-18-crown-6 (DB18C6). The results demonstrated that these trivalent metal ions were extracted into chloroform as Ln(FBPI)3 with HFBPI alone and as Ln(FBPI)3·CE in the presence of a CE. The equilibrium constants of the above extracted complexes deduced by a non-linear regression analysis were found to increase monotonically with a decrease in ionic radii of these metal ions. The addition of a CE to the metal chelate system significantly improves the extraction efficiency of these metal ions. The complexation strength of trivalent lanthanoids with various CEs follows the order: DC18C6 > 18C6 > B18C6 > DB18C6. Solid complexes of Eu(III) with HFBPI alone and with mixtures of HFBPI and various crown ethers have been isolated and characterised by IR and 1H NMR spectral data to further clarify the nature of the extracted complexes.

Solvent extraction of uranium(VI) and thorium(IV)from nitrate media by Cyanex 923

The extraction behaviour of uranium(VI) and thorium(IV) from nitrate solutions has been investigated using Cyanex 923 (TRPO) in xylene as an extractant. The extraction data have been analyzed by both graphical and theoretical methods by taking into account complexation of the metal ion in the aqueous phase with inorganic ligands and all plausible complexes extracted into the organic phase. The results demonstrate that these metal ions are extracted into xylene as Th(NO3)4 · 2 TRPO and UO2(NO3)2 · 2 TRPO. The equilibrium constants of the extracted complexes have been deduced by non-linear regression analysis. Infrared spectral data of the extracted complexes have been used to further clarify the nature of the complexes. The selectivities between these metal ions were evaluated and compared with commercially important extractants like tri-n-butylphosphate (TBP).

Synergistic Solvent Extraction of Trivalent Lanthanoids with Mixtures of 1‐Phenyl‐3‐methyl‐4‐pivaloyl‐5‐pyrazolone and Crown Ethers

Abstract This paper embodies the results of the investigations carried out on the extraction behavior of lanthanoids such as Nd(III), Eu(III), and Tm(III) from perchlorate solutions into chloroform with 1‐phenyl‐3‐methyl‐4‐pivaloyl‐5‐pyrazolone (HPMPP) in the presence and absence of various crown ethers (CE), 18‐crown‐6 (18C6), dicyclohexano‐18‐crown‐6 (DC18C6), and dibenzo‐18‐crown‐6 (DB18C6). The results demonstrate that these trivalent metal ions are extracted into chloroform as Ln(PMPP)3, with HPMPP alone, and in the presence of CE as Ln(PMPP)3·CE. The equilibrium constants of the extracted complexes have been determined by nonlinear regression analysis and are found to increase monotonically with decreasing ionic radii of these metal ions. The addition of a CE to the metal chelate system not only enhances the extraction efficiency but also improves the selectivities among these trivalent lanthanoids, especially in the presence of DB18C6.

ENHANCED EXTRACTION AND SEPARATION OF TRIVALENT LANTHANOIDS WITH 4,4,4-TRIFLUORO-1-PHENYL-1,3-BUTANEDIONE AND CROWN ETHER

Synergistic extraction of the trivalent lanthanoids Nd, Eu and Tm with mixtures of 4,4,4-trifluoro-l-phenyl-l,3-butanedione (Hbtfa) and 18-crown-6, dicyclohexano-18-crown-6 or dibenzo18-crown-6 (CE) in 1,2-dichloroethane from Perchlorate solutions was investigated. Characteristic ion-pair extraction of the Nd(III) or Eu(III) was observed with 1,2-dichloroethane containing Hbtfa and crown ether, in which the cationic complex, Ln(btfa)2 · CE, was formed and extracted. On the other hand, the heavier lanthanoid, Tm(III), was extracted as Tm(btfa)3 · CE. The addition of a crown ether to the metal chelate system not only enhances the extraction efficiency of these trivalent metal ions but also improves the selectivities significantly among the lighter and middle lanthanoids. Hence, such a system would be of practical value in the mutual or group separation of trivalent lanthanoids.

Mixed-Ligand Chelate Extraction of Trivalent Lanthanides and Actinides with 3-Phenyl-4-Benzoyl-5-Isoxazolone and Neutral Oxo-donors

Mixed-ligand chelate extraction of trivalent lanthanides such as La, Eu and Lu and a trivalent actinide, Am, into xylene with mixtures of 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) and bis-2-ethylhexyl sulphoxide (B2EHSO) or tributylphosphate (TBP) from Perchlorate solutions has been investigated. The results demonstrate that these trivalent metal ions are extracted as M(PBI)3 with HPBI alone, in the presence of B2EHSO as M(PBI)3 · 2 B2EHSO or in the presence of TBP as M(PBI)3 • 2 TBP. The equilibrium constants of the above species are found to increase monotonically with decreasing ionic radii of these metal ions. Although addition of an adduct-forming reagent to the chelate system can bring a decrease in the separation factor between Eu-Lu, it is notable that the addition of neutral oxo-donor improves the separation of the Eu-Am and La-Eu pairs. The thermodynamic parameters for the extraction of Eu(III) with HPBI alone as well as with mixtures of one of the neutral oxo-donors in xylene have also been calculated at 298 °K using the temperature coefficient method.

Enhanced extraction and separation of trivalent lanthanoids with 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone and dicyclohexano-18-crown-6

Abstract The synergistic extraction of trivalent lanthanoids Nd, Eu and Tm with mixtures of 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone (HFBPI) and dicyclohexano-18-crown-6 (DC18C6) in 1,2-dichloroethane from nitrate solutions has been investigated. The results demonstrated that these trivalent lanthanoids were extracted into 1,2-dichloroethane as Ln(FBPI)3 with HFBPI alone and as Ln(FBPI)3· DC18C6 in the presence of crown ether. The equilibrium constants of the above extracted complexes have been deduced by non-linear regression analysis. The equilibrium constants of the synergistic species were found to increase monotonically with decrease in ionic radii of these metal ions. The addition of a crown ether to the metal chelate system not only enhanced the extraction efficiency significantly but also improved the selectivites among these trivalent lanthanoids. Solid complexes of these metal ions with HFBPI and with mixtures of HFBPI and crown ether have also been isolated and characterised by IR and 1H NMR spectroscopic techniques.

Enhanced extraction of thorium(IV) and uranium(VI) with 1-phenyl-3-methyl-4-pivaloyl-5-pyrazolone in the presence of various neutral organophosphorus extractants

Summary This paper describes the results of the investigations carried out on the extraction of thorium(IV) and uranium(VI) from dilute nitric acid solutions into chloroform with 1-phenyl-3-methyl-4-pivaloyl-5-pyrazolone (HPMPP) in the presence and absence of various neutral organophosphorus extractants, tributylphosphate (TBP), octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and trioctylphosphine oxide (TOPO). The results demonstrated that these metal ions were extracted into chloroform as Th(PMPP)4 and UO2(PMPP)2 with HPMPP alone and as Th(PMPP)4·S and UO2(PMPP)2·S in the presence of neutral organophosphorus extractants (S). High selectivity (S.F.=2.8×105) has been observed between thorium(IV) and uranium(VI) when extracted with HPMPP alone. The equilibrium constants of the extracted complexes have been deduced by non-linear regression analysis. The equilibrium constants of the synergistically extracted complexes have been correlated with the donor ability of the phosphoryl oxygen of the neutral organophosphorus extractants in terms of their 31P NMR chemical shifts and basicity values (KH = nitric acid uptake constant). The addition of a neutral organophosphorus extractant to the metal chelate system significantly enhances the extraction efficiency of these metal ions. Thorium(IV) and uranium(VI) complexes of HPMPP and mixtures of HPMPP and neutral organophosphorus extractants were synthesized and characterized by IR spectral data to further clarify the nature of the extracted complexes.

Crown Ethers as Synergists in the Extraction of Trivalent Lanthanides by 1 -Phenyl-3-methyl-4-trifluoroacetyl-pyrazolone-5

Synergistic extraction of trivalent lanthanides such as Nd, Eu and Tm with mixtures of l-phenyl-3-methyl-4-trifluoroacetylpyrazolone-5 (HPMTFP) and 18-crown-6 or dibenzo-18-crown-6 or 15-crown-5 or monobenzo-15-crown-5 (CE) in chloroform has been investigated. Lanthanides are found to be extracted as Ln(PMTFP)3 with HPMTFP alone and in the presence of crown ether (CE) as Ln(PMTFP)3 · CE. The equilibrium constants of the above species are found to increase monotonically with decreasing ionic radii of these metal ions. The addition of a crown ether to the metal chelate system not only enhances the extraction efficiency but also improves the selectivities among these trivalent lanthanides. Introduction Macrocyclic polyethers are known to form stable complexes of different stoichiometry with trivalent lanthanides [1]. The stability of crown complexes in solvent extraction depends on the following factors: crown cavity to cation diameter ratio, the counter anion, ligand flexibility and the type of donor atoms in the macrocyclic host [2], Samy et al. [3] reported good selectivities for the extraction of lanthanides with 18crown-6 using trichloroacetate as counter anion. Most recently, remarkable increases of an extractability and selectivity were achieved by Kitatsuji and coworkers [4] in the synergistic ion-pair extraction of lanthanides with 18-crown-6 or dicyclohexano-18-crown-6 in the presence of thenoyltrifluoroacetone (ΗΤΤΑ). Significant enhancement in the extraction of trivalent lanthanides with ΗΤΤΑ in the presence of 15-crown-5 was reported by Aly et al. [5]. Compared with studies on the synergistic solvent extraction of trivalent lanthanides involving ΗΤΤΑ and crown ethers, the systematic study of the synergistic extraction systems involving crown ethers as synergists in the presence of 4acyl pyrazolone is sparse [6, 7], Among 4-acyl pyrazolones, l-phenyl-3-methyl-4trifluoroacetyl-pyrazolone-5 (HPMTFP) exhibits an * Author for correspondence. extremely strong acidity (pKa = 2.56) caused by the strong electron withdrawing nature of the trifluoromethyl group. Recently, Reddy and coworkers [8] have studied the extraction of trivalent lanthanides with HPMTFP in the presence of bis(2-ethylhexyl)Ν,Ν-diethylcarbamoyl-methyl phosphonate as a synergist and reported better extraction efficiencies and selectivities among these trivalent lanthanides. This gives added impetus to further investigate new synergistic solvent extraction systems involving macrocyclic ligands as synergistic agents and 4-acylpyrazolone as a chelating agent for the extraction of trivalent lanthanides. In this paper, we report the synergistic solvent extraction of trivalent lanthanides with mixtures of HPMTFP and various crown ethers in chloroform with a view to elucidate the nature of the species extracted into the organic phase and also to investigate the selectivity of these mixed-ligand systems. Experimental HPMTFP (m.p. 144° C) was synthesized in our laboratory by the procedure described by Jensen [9]. Crown ethers were obtained from Aldrish Chemical Company Inc. and recrystallized from n-hexane. Radioisotopes Nd, 152 Eu and Tm were supplied by Board of Radiation and Isotope Technology (BRIT), India. All other chemicals were of reagent grade. Stock solutions of lanthanides were prepared from their oxides (Rare Earth Products, Cheshire, U.K., 99.99%) by dissolving in concentrated hydrochloric acid and diluting with distilled water. Initial metal ion concentration was maintained at 1 X 10~ mol/dm. Equal volumes of aqueous phase (0.01 mol/dm chloroacetate buffer of pH = 2.7 + 0.1 mol/dm NaC104) spiked with respective tracers of trivalent lanthanide were equilibrated with an equal volume of organic phase for 60 min in a centrifugal tube by mechanical shaker at 303 ± 1° K. Preliminary experiments showed that the extraction equilibrium was attained within 40 min. The solutions were allowed to settle, centrifuged, separated and assayed radiometrically using a Nal(Tl) gamma scintillation counter. The distribution ratio of Ln(III) was 12 Punam Thakur, Κ. C. Dash, Μ. L. P. Reddy, R. Luxmi Varma, T. R. Ramamohan and A. D. Damodaran calculated as the radioactivity ratio. All the computer programmes were written in Fortran 77 and executed on a 32-bit mini-computer (HCL HORIZON III). Results and discussion Extract ion of tr ivalent lanthanides with H P M T F P alone The lanthanide ion in the aqueous phase takes a variety of complex forms in the presence of chloroacetate ions, however under the present experimental conditions, it will form only the first two complexes defined by Ln3+ + /CI · Ac ß„ Ln Ln(Cl · Ac)P (1) where Ln3+ = Nd, Eu and Tm, CI · Ac = the chloroacetate ion and / = 1 ,2 . Then the total Ln(III) concentration in the aqueous phase (Ln,) is given by Ln, = [Ln3+] {1 + /?, [CI • Ac] + ß2 [CI · Ac]2} . (2) The values of stablity constants (log /?1Nd = 1.31; log ß2m = 3.08; log A,eu = 1-38; log βΧΈΜ = 2.04; log#,Xm = 1.10; log /?2,Tm = 1.91) were obtained from the literature [10]. Chloroacetate ion concentration was calculated with the knowledge of dissociation equilibrium of chloroacetic acid I HA H+ + A ; pKa = 2.95 and material balances. The extraction equilibria of Nd(III), Eu(III) and Tm(III) with HPMTFP alone may be expressed as LnL+ + 3HPMTFP„ ;Ln(PMTFP)3org + (3) Kp, [Ln(HPMTFP)3] [Ln3+] [HPMTFP]3 The distribution coefficient, D, is given by KPMTFP [HPMTFP]3 D • (4) [H+]3 (1 + β, [CI · Ac] + ß2[Cl • Ac]2) It should be noted that in the range of concentrations employed here, no significant dimerization of the HPMTFP occurs in the chloroform. The distribution of HPMTFP from the polar chloroform to the aqueous phase has been neglected in the present work. The extraction of trivalent lanthanides Nd, Eu and Tm from 0.01 mol/dm3 chloroacetate buffer solution with HPMTFP alone in chloroform as a function of extractant concentration (0.008 —0.07 mol/dm3 HPMTFP) and pH (2.2 to 2.7), respectively were studied. The relevant log-log plots gave straight lines with slopes of 3 ±0.02, indicating the extraction of the simple metal chelates, Ln(PMTFP)3. The extraction constants for the above species were determined by nonlinear regression analysis and are shown in Table 1. It can be clearly seen from Table 1 that the equilibrium constant (/sTPmtfp) of these trivalent metal ions increases with decreasing ionic radii of the Ln3+ ion. Comparing the equilibrium constants of various /?-diketones for the extraction of Eu(III) (ΚττΑ = 2.19ΧΙΟ 8 [11]; KPMTFP = 1.70ΧΙΟ 5 [12]; KPMTFP = 1.63ΧΙΟ3 [present values]) with their pKa values (thenoyltrifluoroacetone, ΗΤΤΑ = 6.25; 1-phenyl3-methyl-4-acetyl-pyrazolone-5, HPMAP = 3.78; HPMTFP = 2.56), it can be concluded that the log equilibrium constant value increases linearly as pKa decreases (Fig. 1). Extraction of trivalent lanthanides with a mixture of HPMTFP and crown ether The extraction equilibria of Nd(III), Eu(III) and Tm(III) with HPMTFP in the presence of a crown ether (CE) can be written as Ln^ + 3HPMTFPOTg + nCEorg = • nCEOIg + 3H^ Ln(PMTFP)3 (5) where η = the number of crown ether molecules attached to the chelate system and is equal to 0 or 1. Then D can be written as D Ksyn,„ [PMTFP]3 [CE] —ο [H+]3 (1 + β, [CI · Ac] + β2 [CI · Ac]2) (6) where [CE]org = [CE] i n i t iy + — J . The values of partition coefficient (KD) of various crown ethers were obtained from the literature (log KDASC6 = 0.8, log KD.DB18C6 = 3.9; log KDA5C5 = 0.9 and log KD,m5C5 = 2.5) [13]. It should be noted that there is negligible interaction between HMPTFP and crown ether in Table 1. Two phase equilibrium constants of trivalent Nd, Eu and Tm-HPMTFP-crown ether-chloroform systems Complex Log equilibrium constant Nd(III) Eu(III) Tm(III) Ln(PMTFP)3 -4 .18 + 0.005 -2 .79 ±0.001 2 . 2 4 ±0.001 Ln(PMTFP)3 18C6 0.31 ±0.002 1.77 ±0.001 2.24 ±0.001 Ln(PMTFP)3 DB18C6 -0 .65 ±0.001 0.68 ±0.002 1.24 ±0.005 Ln(PMTFP)3 • 15C5 -0 .24 ±0.004 1.29 ±0.005 1.64 ±0.001 Ln(PMTFP)3 B15C5 -0 .33 + 0.001 1.19 ±0.003 1.54 ±0.005 Crown Ethers as Synergists in the Extraction of Trivalent Lanthanides by l-Phenyl-3-methyl-4-trifluoroacetyl-pyrazolone-5 13

Effect of Polymethylene Chain Length of 4‐Acylbis(1‐phenyl‐3‐methyl‐5‐pyrazolones) on the Extraction of Vanadium(V): Synergistic Effect with Neutral Organophosphorus Extractants

Abstract Various 4‐acylbis(1‐phenyl‐3‐methyl‐5‐pyrazolones), namely, 4‐adipoylbis(1‐phenyl‐3‐methyl‐5‐pyrazolone) (H2AdBP), 4‐sebacoylbis(1‐phenyl‐3‐methyl‐5‐pyrazolone) (H2SbBP) and 4‐dodecandioylbis(1‐phenyl‐3‐methyl‐5‐pyrazolone) (H2DdBP) were synthesized and examined with regard to the solvent extraction behavior of vanadium(V) and other multivalent metal ions that are present in the waste chloride liquors of titanium mineral‐processing industry. The results demonstrate that vanadium(V) is selectively extracted into chloroform with 4‐acylbis(1‐phenyl‐3‐methyl‐5‐pyrazolones) as VO2(HX), where H2X refers to the 4‐acylbis(1‐phenyl‐3‐methyl‐5‐pyrazolone) and K ex,V(V) denotes the equilibrium constant. On the other hand, magnesium(II), aluminum(III), titanium(IV), chromium(III), manganese(II), iron(II), and iron(III), were not found to be extracted into the organic phase. The K ex,V(V) values of various 4‐acylbispyrazolone derivatives follow the order H2SbBP>H2DdBP>H2AdBP. Solid complexes of vanadium(V) with various 4‐acylbis(1‐phenyl‐3‐methyl‐5‐pyrazolones) have been isolated and characterized by elemental analyses and IR spectral data to further clarify the nature of the extracted complexes. The synergistic effect on the addition of various neutral organophosphorus extractants to the metal‐chelate system has been investigated, revealing significant enhancement in the extraction efficiency of vanadium(V). The equilibrium constants of the synergistically extracted complexes have been correlated with the donor ability of the phosphoryl oxygen of the neutral organophosphorus extractants in terms of their 31P NMR chemical shifts and their basicity values (K H =nitric acid uptake constant). The potential of these reagents as extractants for the separation and recovery of vanadium(V) from the waste chloride liquors of the titanium mineral processing industry has also been assessed.