Ion-exchanger ultraviolet spectrophotometry for uranium(VI)

A sensitive method based on solid-phase spectrophotometry has been developed for the microdetermination of uranium(VI) in water samples. Uranium is sorbed on the anion-exchanger QAE-Sephadex from thiocyanate solution and the absorbance of the exchanger is measured at 300 nm. This method is about 30 times more sensitive than solution spectrophotometry. Absorption spectra of various metals in the anion-exchanger phase are presented and their interferences discussed. A procedure for the cation-exchange separation of uranium from accompanying elements before spectral measurement of uranium is proposed.     

Preparation of soluble ternary heteroazo dye complexes for the spectrophotometric determination of trace uranium(VI)

The complexing ability of typical pyridylazo, quinolylazo and thiazolylazo dyes with uranium(VI) in aqueous ethanol media are investigated in the presence and absence of aromatic carboxylic acid. Uranium(VI) forms solubilized ternary complexes with PAN, PAR, TAM, 5-Br-PADAP, 3,5-diBr-PADAP and QADAP in 48% ethanol solution containing sufficient amounts of sulfosalicylic acid and triethanolamine buffer (pH 7.8). Aromatic carboxylic acids contribute to expel the coordinated water molecules from the uranium (VI) moiety and their chelating effects have been explained by ternary complex formation. An increase in molar absorptivity and no shift in the wavelength of maximum absorbance are observed for all uranium(VI) complexes investigated. The 11 stoichiometry of uranuim(VI) and heteroazo dye in the binary complex does not change through ternary complex formation. The molar absorptivity of the uranium(VI)-3,5-diBr-PADAP-sulfosalicylic acid ternary complex at 595 nm is 8.4×10⁴l mol^–1 cm^–1 and Beer's law is valid up to 2.5gmg ml^–1 of uranium(VI). The interferences due to coexisting metal ions can be effectively masked by addition of CyDTA or Ca-CyDTA.     

Thermal behaviour of uranium(VI) complexes

The solid-state syntheses of complexes of uranyl acetate dihydrate andN-phenylthiourea have been attempted by heating various stoichiometric mixtures of the reactants directly in a DSC and in a TA apparatus. Both the DSC and the TG results indicate that only the 1∶1 adduct is formed, independently of the molar ratios of the reactants. It appears that the reaction is complete only with a large excess ofN-phenylthiourea, in agreement with IR data.     

Spectrophotometric determination of uranium(VI) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol in a flow-injection system

The direct determination of uranium(VI) by a flow-injection procedure is based on spectrophotometric measurement with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol in the present of fluoride. The interfering effects of many commonly occuring elements were studied. The calibration curve was linear over the range 0.5–20 mg 1^?1 uranium(VI). The relative standard deviation obtained on a leach liquor containing 10 mg 1^?1 uranium(VI) was 1.9%. The procedure is rapid and convenient, and up to 40 samples can be analysed per hour.     

Polarographic study of uranium(VI)-succinate complexes

The polarographic behavior of uranium(VI)-succinate complexes was studied in 0.5M NaClO₄ medium at 30°C at a dropping mercury electrode. It was found that only the doubly charged succinate ion formed the complexes stable enough to be detected. The experimental evidence for this is discussed. The stability constant of uranium(V) (succinate)₂ complex was evaluated.     

Extraction of uranium(VI) with octyldodecylsulfoxide (ODoSO)

Complexes of Hf with polyaminopolycarboxylic acids viz. diethylene-triamine-penta-acetic acid (DTPA) and its dimethoxy derivative DMDTPA have been studied using paper chromatography at different acidities. Kinetic stabilities of the complexes have also been looked at. Behaviors of these two ligands in complexing with Hf(IV) have been found to be similar. The extent of complexation reduces slowly with acidity and increase with time and reaches a maximum around 70-80% after about 24 hours.     

Thermal decomposition of pentacoordinate uranium(VI) complexes

The thermal decomposition of some mixed uranyl complexes with Schiff bases and DMSO, EtOH or (Ph)₃PO as neutral ligand, were investigated and the corresponding activation energy, E*_a, and enthalpy of dissociation, ΔH_d, values were calculated.

The results obtained indicate that for the same neutral ligand, the thermal stability of the uranyl complexes is influenced by the Schiff base used; for the same Schiff base, the presence of (Ph)₃PO results in a greater thermal stability of the mixed complexes than when the other two neutral ligands are present.     

Silver(I) complexes of bis[2-(diphenylphosphino)phenyl] ether

The reaction of AgOTf in dichloromethane with bis(2-(diphenylphosphino)phenyl) ether (DPEphos) in an equimolar ratio afforded a dinuclear complex [Ag₂(κ²-P,P′-DPEphos)₂(μ-OTf)₂] (1), whereas the similar reaction in a 1:2 molar ratio resulted in the formation of a bis-chelating complex [Ag(κ²-P,P′-DPEphos)₂][OTf] (2). The silver(I) complex 1 was obtained as a dimer, in which two silver atoms are bridged by two triflate groups to form three adjacent eight-membered spirocyclic rings. The mixed-ligand complex [Ag(κ²-P,P′-DPEphos)(2,2′-bpy)][OTf] (3) was obtained in the reaction of 1 in dichloromethane with 2,2′-bipyridine. The crystal structures of complexes 1–3 were determined by single crystal X-ray analyses.     

Extraction of uranium(VI) by bis(hexylsulfinyl)methane

The extraction of uranium(VI) with bis(hexylsulfinyl)methane (BHxSM) from nitric acid aqueous solution has been investigated. It was found that the extraction increased with increasing nitric acid concentration up 8.5 mol/l and then decreased. Extraction distribution ratio also increased with the bis(hexylsulfinyl)methane concentration. The extraction species appear to be UO₂(NO₃)₂ ^.2BHxSM. The influences of temperature, salting-out concentration and oxalate concentration on the extraction equilibrium were also investigated, and the enthalpy of the extraction reaction was obtained. The result shows that the reaction of uranium(VI) extraction with BHxSM is an exothermic one.     

Extraction of uranium(VI) with bis(octylsulfinyl)methane

The liquid-liquid extraction of uranium(VI) from aqueous nitric acid with bis(octylsulfinyl)methane (BOSM) has been studied over a wide range of conditions. The extracted species appear to be UO₂(NO₃)₂·2BOSM. It was found that the extraction increased with increasing nitric acid concentration up to 8.5 mol/l and then descreased. Extraction also increased with increasing extractant concentration. The influence of temperature and salting-out agent concentration on the extraction equilibrium has also been investigated, and the enthalpy of the extraction reaction was estimated.     

Synthesis and structure of lipophilic dioxo-molybdenum (VI) bis(hydroxamato) complexes

New methods for the synthesis of complexes of molybdenyl with hydrophobic alkyl-substituted hydroxamic acids have been developed. A number of novel coordination compounds of the general formula MoO₂L₂ (where HL is decano-, N-methyl-decano-, N-methyl-hexano-, N-methyl-1-adamantano- and N-tert-butyl-hexanohydroxamic acids) have been synthesized. All compounds obtained have been characterized by IR, ¹H NMR spectroscopy and X-ray crystallography. The effect of the electron donating and steric properties of ligand substituents on the structure of complexes is discussed.     

Improved spectrophotometric determination of uranium(VI) with 4-(2-pyridylazo)resorcinol in the presence of benzyldimethylstearyltrimethylammonium chloride

An improved spectrophotometric determination of uranium(VI) is proposed using 4-(2-pyridylazo)resorcinol(PAR) in the presence of benzyldimethylstearyltrimethylammonium chloride(BSTAC) as a cationic surfactant. The calibration graph is linear in the range of 0.3–60 g/10 ml uranium(VI), measuring the absorbance at 550 nm. The reproducibility for 19.0 g/10 ml uranium(VI) is 0.57%. The third-derivative method using the third-derivative distance (d³A/d³) among ₁ 530 nm, ₃ 594 nm and ₂ 565 nm was also investigated.     

Improved spectrophotometric determination of uranium(VI) with 4-(2-pyridylazo)resorcinol in the presence of benzyldimethylstearyltrimethylammonium chloride

An improved spectrophotometric determination of uranium(VI) is proposed using 4-(2-pyridylazo)resorcinol(PAR) in the presence of benzyldimethylstearyltrimethylammonium chloride(BSTAC) as a cationic surfactant. The calibration graph is linear in the range of 0.3-60 microg/10 ml uranium(VI), measuring the absorbance at 550 nm. The reproducibility for 19.0 microg/10 ml uranium(VI) is 0.57%. The third-derivative method using the third-derivative distance (d(3)A/dlambda(3)) among lambda(1) 530 nm, lambda(3) 594 nm and lambda(2) 565 nm was also investigated.     

Extraction and spectrophotometric determination of uranium(VI) withN-phenylcinnamohydroxamic acid

Uranium(VI) reacts withN-phenylcinnamohydroxamic acid to form an orange-yellow complex in the pH range 5.5–8.5. The orange-yellow complex, having the composition of 12 (metal:ligand), is quantitatively extractable into ethyl acetate. The spectrum of the complex exhibits a maximum absorption at 400 nm with a molar absorptivity of 6500 M^–1·cm^–1. The coloured system obeys Beer's law in the concentration range 2–40g·ml^–1 of uranium(VI). The photometric sensitivity of the colour reaction is 0.037 g·cm^–2 of uranium(VI). Most of the common ions do not interfere and the method has been found to be simple, precise, and free from the rigid control of experimental conditions. The method has been applied to the determination of uranium in synthetic matrices and potable water.     

Spectrophotometric determination of uranium(VI) with 2-(3,5-dibromo-2-pyridylazo)-5-diethylaminophenol in the presence of anionic surfactant

A highly sensitive method for spectrophotometric determination of uranium has been devised. The method is based on formation of a red-violet 1:2 (metal:ligand) complex from the reaction of uranium(VI) with 2-(3,5-dibromo-2-pyridylazo)-5-diethylaminophenol (3,5-diBr-PADAP) in the presence of an anionic surfactant, sodium lauryl sulphate. Its molar absorptivity is found to be 9.1 x 10(4)l.mole(-1).cm(-1). The absorbance is constant in the range pH 8.4-9.9 Beer's law is obeyed for 0-1.4 mug/ml concentrations of uranium. In the presence of DCTA the method is selective for uranium, and can be used for the determination of trace amounts of uranium in water samples.     

Polarography of uranium(VI) and lead(II) complexes with l-glutamine

The complexes of uranium(VI) and lead(II) with 1-glutamine were investigated polarographically. For uranium(VI), the complexes UO(2)G(+2), UO(2)G(2)(+2) and UO(2)(OH)Ga(2)(+) were identified at pH < 2.5, pH 2.5-4.1 and pH 4.1-5.2 respectively. With lead(II), complexes PbG(+2), Pb(OH)G(+) and Pb(OH)G(2)(+) were formed at pH 2.0-5.0, pH 5.0-7.0, and pH 7.0-8.5, respectively. The concentration dissociation constant of Pb(OH)G(2)(+) was found to be pK(c) = 10.16 +/- 0.04 at ionic strength 0.6.     

Spectrophotometric determination of uranium with 1-(2-pyridylazo)-2-naphthol

1-(2-Pyridylazo)-2-naphthol (PAN) rcacts with uranium to form a deep red precipitate in ammoniacal solutions, this can be extracted with chloroform if sodium chloride or sulfate is added and it has a maximum absorption at 560 mμ The color is stable and follows Beer's law. Trace amounts of uranium may be determined in the presence of many metals without prior separation if strong complexing agents, such) as EDTA or cyanide, are added     

Synthesis and reactivity of bis(imido) uranium(VI) cyclopentadienyl complexes

The bis(imido) uranium(VI)-C(5)H(5) and -C(5)Me(5) complexes (C(5)H(5))(2)U(N(t)Bu)(2), (C(5)Me(5))(2)U(N(t)Bu)(2), (C(5)H(5))U(N(t)Bu)(2)(I)(dmpe), and (C(5)H(5))(2)U(N(t)Bu)(2)(dmpe) can be synthesized from reactions between U(N(t)Bu)(2)(I)(2)(L)(x) (L=THF, x=2; L=dmpe, x=1) and Na(C(5)R(5)) (R=H, Me); these complexes represent the first structurally characterized C(5)H(5)-compounds of uranium(VI) and they further highlight the differences between UO(2)(2+) and the bis(imido) fragment.     

Extraction of uranium(IV) and uranium(VI) by primary and tertiary-amines from sulphate solutions

In developing a method for possible low level isotopic enrichment, which uses to advantage the equilibrium isotope effect observed during U(1V)-U(VI) electron exchange reaction in sulphate solutions, details of a solvent extraction process involving high concentration of a mixture of U(IV) and U(VI) and at low acid concentrations, are described. The extraction behaviour of uranium under these conditions is discussed. During the extraction with amines, U(IV) tended to get oxidised in sulphate solutions.