Kinetic isotope effect in pentavalent plutonium disproportionation in heterogeneous systems

A kientic isotope effect in Pu(V) disproportionation in nitric acid solutions have been observed in a heterogeneous system with phenyloctylphosphonic acid deposited on hydrophobized silicagel. The isotope separation coefficient for²⁴²Pu/²³⁹Pu isotopes was found to be 1.022 at 25°C. The rate constant of Pu(V) disproportionation in this heterogeneous system was determined to be 5.0±0.6 1²mol^–2s^–1 at 25°C, [HNO₃]= 0.87–1.5 mol l^–1 and 11 phase ratio (10% extractant on the support).     

Kinetics and kinetic isotope effect in pentavalent plutonium disproportionation activated by power ultrasound

A kinetic isotope effect in Pu(V) disproportionation has been observed in nitric acid solution under the effect of power ultrasound with intensity 0.9W·cm^–2 and frequency 22 kHz. The isotope separation coefficient for²⁴²Pu/²³⁹Pu isotopes was found to be 1.0081 at 20°C. Without sonication the k.i.e. was not observed. The rate constant of Pu(V) disproportionation was found to be accelerated under sonication. The rate constant determined was (5.7±0.6)·10^–3 1²·mol^–2·s^–1 atl=0.9 W·cm^–2,v=22 kHz, [HNO₃]=0.5 mol·l^–1 andT=20°C. It is supposed that the acceleration of Pu(V) disproportionation and the kinetic isotope effect are due to the activation of plutonoyl groups in the interface between the cavitation bubble and the bulk solvent.     

Phosphates de protactinium pentavalent

Protactinium orthophosphate PaO(H₂PO₄)₃·2H₂O (phase I) crystallises from 10⁻¹ M Pa(V) solutions in 14 M H₃PO₄. Phase I is stable up to 250°C. On further heating the following transformations occur:

. The existence of a “homologous serie” of phosphorus and protactinium oxides can be invoked to explain the structural analogies between the phosphates (VI) and (VII).Interplanar distances and intensities, lattice parameters, and the experimental and calculated densities are given for some phosphates.     

Mica surfaces stabilize pentavalent uranium

High-resolution X-ray photoelectron spectroscopy was used to demonstrate that reduction of aqueous U6+ at ferrous mica surfaces at 25 degrees C preserves U5+ as the dominant sorbed species over a broad range of solution compositions. Polymerization of sorbed U5+ with sorbed U6+ and U4+ is identified as a possible mechanism for how mineral surfaces circumvent the rapid disproportionation of aqueous U5+. The general nature of this mechanism suggests that U5+ could play an important, but previously unidentified, role in the low-temperature chemistry of uranium in reducing, heterogeneous aqueous systems.     

Self-assembled macrocycles with pentavalent silicon linkages

Organic substrates containing two catechol (ortho-dihydroxybenzene) components at opposite ends self-assemble with a silicon substrate containing three nucleofugic groups (methoxy or ethoxy) under basic conditions to produce macrocycles ranging from monomers to pentamers. Silicon in all the macrocycles is pentacoordinate, negatively charged, and possessed of one organic monodentate ligand attached via carbon and two catechol bidentate ligands attached via oxygen. The organic materials with the two catechol structures thus serve as struts between the corners provided by the pentacoordinate silicon atoms.     

o-Carboranyl-containing esters of pentavalent phosphorus acids

Conclusions Some new carboranyl esters of pentavalent phosphorus acids were synthesized from the appropriate propargyl esters and decaborane.See [1] for preliminary communication.Translated from Izvestiya Akademii NaukSSSR, Seriya Khimicheskaya, No. 11, pp. 2640–2644, November, 1983.     

Triple points and plutonium equilibrium

Summary Equilibrium prevails at all points in plutonium predominance region diagrams. Triple points combine equilibrium with equal fractions of three Pu oxidation states. A rearrangement equation can be used to describe plutonium at a triple point. Two-reaction-product disproportionation equations are not satisfactory for that purpose.     

Determination of uranium and plutonium in plutonium based fuels by sequential amperometric titration

A method is described for the sequential determination of uranium and plutonium in plutonium bearing fuel materials. Uranium and plutonium are reduced to U(IV) and Pu(III) with titanous chloride and then titrated with dichromate to two end points which are detected amperometrically using two polarized platinum electrodes. Uranium-plutonium solutions of known concentrations containing plutonium in the proportions of 4, 30, 50, and 70% were analyzed with precisions better than 0.3%, maintaining the amounts of plutonium per aliquot in the range of 2–10 mg. No significant bias could be detected. Several samples of (U, Pu)O₂ and (U, Pu)C were analyzed by this procedure. The effects of iron, fluoride, oxalic acid and mellitic acid on the method were also studied.     

Dosage du plutonium dans les alliages plutonium aluminium par fluorescence-x

An X-ray fluorescence method is described for the determination of plutonium in Pu-Al alloys. In order to obtain satisfactory reproducibility, the alloy is first dissolved in a nitric acid-mercury (II) nitrate mixture. The Lα emission of plutonium is measured, to eliminate matrix effects, an internal standard with a wavelength near that of the Pu emission is used. Equipment and sample preparation are described. Extension of the method to other determinations is discussed.     

Airborne plutonium monitoring

Methods of monitoring low plutonium concentration in the inner and outer atmosphere are analyzed and compared. It is shown that monitors based on the gross alpha counting of air filters are not sensitive enough to measure reliably plutonium activities below 1 MPC. A spectrometric discontinuously operating monitor using a gridded ionization chamber and a membrane filter having 70 cm² active area is described. Plutonium activities of the order of 0.01 MPC /1 mBq.m^–3/ can be measured by the spectrometer at 1 h sampling and 1 h counting time.     

Synthesis and reactivity of chiral pentavalent bismuth derivatives

Eight new pentavalent organobismuth derivatives were synthesized by the reactions of triphenylbismuth or phenyl-2,2"-biphenylenebismuth with chiral (1R)-(–)-camphor-10-sulfonic, (–)-menthyloxyacetic, or (R)-3-phenylbutyric acids. Enantioselective C-arylation of enolizable substrates with organobismuth reagents was carried out for the first time. Unlike iodine, sulfur, and selenium derivatives, which contain a five-membered heterocycle including the 2,2"-biphenylene fragment, phenyl-2,2"-biphenylene organobismuth analogs enter into C-arylation reactions accompanied by the selective transfer exclusively of the phenyl group to the organic substrate.     

Selenium-containing esters of pentavalent phosphorus acids

New carboranyl selenophosphates and selenophosphonates have been prepared. A series of S--carboranylselenoethyl esters of pentavalent phosphorus acids has been prepared. These compounds hold interest as potentially physiologically active compounds.Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1653–1655, July, 1990.     

Synthesis and properties of pentavalent antimony and bismuth fluorides

Properties of Sb^v and Bi^v fluorides and M^IIF₂-M^vF₅ (M^v ? Sb, Bi; M^II ? Mg, Ca, Sr, Ba), HalF₃-BiF₅ (Hal ? Cl, Br) systems have been studied. Only M_II(M^vF₆)₂ and HalF₂[BiF₆] are shown to be formed in these systems. M_II(M^vF₆)₂ and HalF₂[BiF₆] contain M^vF₆-octahedra in their crystal lattices. SbF₅ is found to be a stronger Lewis acid than BiF₅ and to be capable to substitute the latter in its fluoro complexes. BiF₅, in contrast to SbF₅, does not form polyfluoro anions (e.g.MF₁₁-etc.). The thermal stability of Sb_v and Bi_v fluorides and their transformations at high temperature were studied.     

Easy access to stable pentavalent uranyl complexes

Reaction of UO2I2(THF)3 with 1 molar equivalent of KC5R5 (R = H, Me) in pyridine led to the uranyl(V) compound {[UO2(Py)5][KI2(Py)2]}(infinity), which is an infinite 1D polymer in its crystalline form; the UO2X(THF)n (X = I, OSO2CF3) complexes were obtained by reduction of their U(VI) parents with TlC5H5 or KC5R5 in THF.     

Surprising coordination for plutonium in the first plutonium(III) borate

The first plutonium(III) borate, Pu(2)[B(12)O(18)(OH)(4)Br(2)(H(2)O)(3)]·0.5H(2)O, has been prepared by reacting plutonium(III) with molten boric acid under strictly anaerobic conditions. This compound contains a three-dimensional polyborate network with triangular holes that house the plutonium(III) sites. The plutonium sites in this compound are 9- and 10-coordinate and display atypical geometries.