Photochemical reduction of uranyl ion with triethylamine

Uranyl ion is photochemically reduced to uranium(IV) in the presence of triethylamine and triethylamine is oxidized to secondary amine and acetaldehyde. On the basis of product analysis, temperature independent quantum yields for uranium(IV) formation and abnormal Stern-Volmer plots rule out the simple collisional photochemical annihilation of excited uranyl ion with triethylamine. Static annihilation has a significant contribution in addition to dynamic annihilation.     

Photochemical reduction of uranyl ion with ditertiary phosphines in dry acetone

Time-resolved transient absorption spectra have been observed using monochromatic light (=347.1 nm) from a 25 ns pulsed ruby laser. Collision between optically excited uranyl ion and ditertiary phosphines lead to photochemical reduction of uranyl ion to uranium(V) in non-aqueous medium. Stern-Volmer constants measured from lifetime measurement and quantum yields for uranium(V) formation reveal that electron transfer phenomenon competes with photophysical deactivation because of the presence of phenyl groups. Since ditertiary phosphines have two electron donating phosphorus atoms, are better reductant than monodentate phosphines in non aqueous medium.     

Photochemical reduction of uranyl ion in nitric acid medium using a XeCl excimer laser

This paper describes the results of photoreduction of uranyl (UO₂ ²⁺) ion to U⁴⁺ in 0.2M HNO₃ and ethanol using a 308 nm XeCl excimer laser. The effects of different concentrations of ethanol and the addition of sulfamic acid on the quantum yield for U⁴⁺ formation are discussed.     

Photochemical reduction of n-tosylsulfilimines with thiolate anion

The reaction between N-tosyldiarylsulfilimines and p-toluenethiolate anion did not take place in the dark even upon heating up to 62° but proceeded smoothly upon irradiation with visible light in DMF at room temperature, affording S-N bond cleavage products.     

Separation of uranyl ion using polyaniline

Polyaniline (Pani) was synthesized by the chemical oxidation of aniline. The use of persulphate instead of dichromate was desired in order to avoid the incorporation of chromium in the polymer matrix. The presence of chromium in the matrix, when dichromate was used as an oxidant, was confirmed by various techniques. The batch mode experiments showed that Pani could be used for separation of different metal ions. These ions were converted into their anionic complexes using suitable complexing agents. It was found that EDTA was used as a suitable reagent for the separation of Cu²⁺ from Zn²⁺ whereas the uranyl ion uptake could be increased to about 95 % when carbonate was used instead of EDTA as complexing agent. A possible application of the above exchange system to preconcentration of uranyl ion from seawater has also been examined.     

Studies on the co-precipitation of uranyl ion with zirconium hypodiphosphate

Summary Studies on the co-precipitation or/and the uptake of uranyl ion by zirconium hypodiphosphate have been carried out in hydrochloric acid medium of different normalities. The degree of co-precipitation or/and uptake was found to depend on the acidity, the amount of carrier used and the temperature at which precipitation of carrier took place.

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Zusammenfassung Untersuchungen über die Mitfällung oder/und das Mitreißen von Uranylionen mit Zirkoniumhypodiphosphat wurden in salzsauren Lösungen verschiedener Normalität vorgenommen. Es wurde eine Abhängigkeit festgestellt von der Acidität, der Menge des verwendeten Trägers und der Fällungstemperatur.

     

Photochemical synthesis of heteroatom-containing polycyclic aromatic compounds

Anthra[2,1-b]furan, anthra[2,1-b]benzo[d]furan, anthra[2,1-b]thiophene, anthra[1,2-b]thiophene, anthra[2,1-b]benzo[d]thiophene, anthra[2,1-b]pyrrole and naphtho[2,3-c]carbazole derivatives were synthesized in fairly good yields by a one-pot photocycloaddition reaction of 2,3-disubstituted 1,4-naphthoquinone with 1,1-diarylethylene. This is the first reported synthesis of these aromatic compounds.     

Thermodynamics of mixtures formed by polycyclic aromatic hydrocarbons with long chain alkanes

Thermodynamic properties of polycyclic aromatic hydrocarbons (PAH) and long chain alkanes determine the phase behaviour of heavy petroleum fractions. Studying thermodynamic excess functions of these systems is difficult and consequently experimental data available in the literature are scarce. Enthalpies of mixing of 13 PAH-alkane systems at temperature above the melting point of both components are reported in this paper. Morever, 13 solid-liquid equilibria of the same family of systems are presented. Experimental results were correlated using S.S.F. model (Rogalski and Malanowski, 1977). Several regularities observed in the liquid-solid phase diagrams of the systems studied are discussed     

Complexation of poly(acrylic acid)s with uranyl ion

The complexation of uranyl ion (UO₂²⁺) in aqueous solution with polymers containing carboxylic acid groups was studied potentiometrically. Overall formation constants of the uranyl complexes with poly(methacrylic acid) and crosslinked poly(acrylic acid) were much larger than those with the corresponding low molecular carboxylic acids. Decrease in the viscosity of the polymer solution on adding uranyl ion indicated that poly(acrylic acid) forms intra-polymer chelates with uranyl ion. The crosslinked poly(acrylic acid) adsorbed uranyl ions at higher efficiency than transition metal ions.     

Reduction of the photoexcited uranyl ion by water

Photooxidation of water by the uranyl ion was studied. Solutions of uranyl in 0.01–4.0M H₂SO₄, HClO₄, or 0.1–1.0M Na₂SO₄ and NaClO₄ containing “lacunary” heteropolytungstate (HPT) K₁₀P₂W₁₇O₆₁ or K₈SiW₁₁O₃₉ were irradiated with a nitrogen laser, a mercury or xenon lamp, or visible light. Spectrophotometric analysis showed that the irradiation results in the accumulation of U^IV. Simultaneously the formation of H₂O₂ proceeds. The quantum yield Φ of the reaction increases as the concentration of the acid or salt increases. For aerated solutions of 1M H₂SO₄ or 1M HClO₄, irradiation by light with λ=337.1 Φ is close to (1.5–2)·10⁻³. The irradiation of solutions with pH −4 for many days leads to an almost quantitative transformation of UO₂ ²⁺ into U^IV. When the irradiation was carried out in the absence of HPA, U^IV was not detected, although hydrogen peroxide was observed in the solution. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 2, pp. 282–287, February, 2000.     

Photochemical reduction of thallium(III) with hydrogen peroxide

A convenient method for determination of thallium(III) is based on photochemical reduction with hydrogen peroxide in the presence of bromide as catalyst, followed by oxidation of thallium(I) with potassium bromate.     

Synergistic extraction of uranyl ion with acylpyrazolones and dicyclohexano-18-crown-6

Synergistic extraction of uranyl ion with acylpyrazolones such as 1-phenyl-3-methyl-4-trifluoroacetylpyrazolone-5 (HPMTFP, pKa=2.7), 1-phenyl-3-methyl-4-acetylpyrazolone (HPMAP, pKa=3.8) or 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (HPMBP, pKa=4.2) in combination with dicyclohexano-18-crown-6 (DC-18-C6) has been studied at various fixed temperatures. The results indicate that the equilibrium constants of the organic phase addition reaction, log Ks, at 30°C are almost constant, viz., 2.72, 2.69 and 2.84, respectively, for the above three systems. The similarity and low log Ks values with DC-18-C6 as compared with TBP systems with these pyrazolones appears to arise due to the limitation to the approach of the large crown ether molecule in bonding with the uranyl chelate. This is in contrast to the fact that the relative basicities of the two donors (equilibrium constant for nitric acid uptake) are comparable. Thermodynamic data for chelate extraction with HPMTFP evaluated by the temperature coefficient method indicates that a hydrated chelate is extracted into the organic phase. Also, the organic phase addition reaction with DC-18-C6 is stabilized by exothermic enthalpy change, the entropy change counteracting in all the three cases.     

Selective oxo functionalization of the uranyl ion with 3d metal cations

The linear uranyl dication [UO2]2+ can be bound in one of two coordination sites in the ditopic Pacman-shaped pyrrolic macrocyle H4L. Incorporation of Mn2+, Fe2+, or Co2+ cations in the second donor compartment affords the first uranyl complexes with a transition-metal-functionalized oxo group.     

Photochemical water reduction by molybdenum tetrachloride

The photolysis of MoCl₄(MeCN)₂ in MeCN in the presence of small amounts of H₂O proceeds according to the equation Mo^IVCl₄·H₂OMo^VIOCl₄ + H₂. It is suggested that a ligand field excited state of MoCl₄(H₂O) _n , which is initially populated by light absorption, is deactivated to a reactive metal-to-ligand (Mo^IVH₂O) charge transfer state.     

Macrocyclic hexaketone as a specific host of uranyl ion

A novel synthetic method was described for a new macrocyclic hexaketone, 1,3,9,11,17,19-hexaoxocyclotetracosane, which extracted 98 % of uranyl ion into benzene phase from a dilute (10 ppm) aqueous solution of pH 8.     

On the coordination symmetry of the hydrated uranyl ion

The literature indicates a four-fold or six-fold coordination symmetry for UO²⁺₂ in aqueous solution. However, the uranyl ion in crystalline UO₂(ClO₄)₂·7H₂O has been found by X-ray diffraction to be coordinated by five water molecules. From the MCD of aqueous UO₂(ClO₄)₂·nH₂O we have found evidence for five-fold coordination. A tentative assignment for the excited states in the visible spectrum is also proposed.