Structural Periodicity in the Coordination Chemistry of Aqueous Pu(IV) Sulfates

Extended X-ray absorption fine structure measurements have been conducted on solutions of Pu(IV) with varying concentrations of sulfate anion in aqueous solution. Data support the periodic progression to primarily bidentate sulfate coordination about An(IV) centers when moving heavier in the actinides. This observation is attributed to the increase in Lewis acidity of the tetravalent actinides across the series, a consequence of the filling of the 5f orbitals and the actinide contraction. Though the changes in the chemical formation energies of the An(IV) complexes between Th and Pu are small, it is these small energetic differences that are critical to understanding how to effect more efficient and effective chemical separations among isovalent metal ions.     

Radiation-Induced Oxidation Reactions of 2-Selenouracil in Aqueous Solutions: Comparison with Sulfur Analog of Uracil

One-electron oxidation of 2-selenouracil (2-SeU) by hydroxyl (^●OH) and azide (^●N₃) radicals leads to various primary reactive intermediates. Their optical absorption spectra and kinetic characteristics were studied by pulse radiolysis with UV-vis spectrophotometric and conductivity detection and by the density functional theory (DFT) method. The transient absorption spectra recorded in the reactions of ^●OH with 2-SeU are dominated by an absorption band with an λ_max = 440 nm, the intensity of which depends on the concentration of 2-SeU and pH. Based on the combination of conductometric and DFT studies, the transient absorption band observed both at low and high concentrations of 2-SeU was assigned to the dimeric 2c-3e Se-Se-bonded radical in neutral form (2^●). The dimeric radical (2^●) is formed in the reaction of a selenyl-type radical (6^●) with 2-SeU, and both radicals are in equilibrium with K_eq = 1.3 × 10⁴ M⁻¹ at pH 4 (below the pK_a of 2-SeU). Similar equilibrium with K_eq = 4.4 × 10³ M⁻¹ was determined for pH 10 (above the pK_a of 2-SeU), which admittedly involves the same radical (6^●) but with a dimeric 2c-3e Se-Se bonded radical in anionic form (2^●−). In turn, at the lowest concentration of 2-SeU (0.05 mM) and pH 10, the transient absorption spectrum is dominated by an absorption band with an λ_max = 390 nm, which was assigned to the ^●OH adduct to the double bond at C5 carbon atom (3^●) based on DFT calculations. Similar spectral and kinetic features were also observed during the ^●N₃-induced oxidation of 2-SeU. In principle, our results mostly revealed similarities in one-electron oxidation pathways of 2-SeU and 2-thiouracil (2-TU). The major difference concerns the stability of dimeric radicals with a 2c-3e chalcogen-chalcogen bond in favor of 2-SeU.     

Formation of Si(IV) and Ge(IV) Fluoride Complexes in Dilute Aqueous Solutions

An analogy in the behavior of silicon (IV) and germanium (IV) fluoride complexes in dilute aqueous solutions was established on the basis of analysis of published data on their formation equilibria. The analogy manifests itself in the similarity of existing equilibria and effects of pH on them.     

Aminoguanidinium closo-Borates and Their Reactions with Copper(II) Salts in Aqueous Solutions

Aminoguanidinium hexa-, deca-, and dodecaborates of (AguH)₂B _n H _n · xH₂O (Agu = (CN₄H₆), n= 6, 10, 12; x= 1, 2) composition were synthesized and studied by elemental analysis, magnetic susceptibility, and IR spectroscopy methods. Their reactions with copper(II) salts in aqueous solutions were investigated. A cation–anion interaction was shown to occur in aminoguanidinium closo-borates and to increase in the series B₁₂< B₁₀< B₆. Depending on the closo-anion (B _n H^2– _n ), the reactions of aminoguanidinium closo-borates with copper(II) salts in aqueous solutions yield either complex compounds (n= 10, 12) or metallic copper (n= 6).     

Interaction of Sulfur Dioxide with Aqueous Solutions of Amides

The interactions in the systems H₂O-Am-SO₂ (Am is formamide, dimethylformamide, acetamide, urea, tetramethylurea, tert-butylurea) at 278 and 293 K were studied pH-metrically. The results suggest formation of intermolecular and ion-molecule associates. The composition and stability of the compounds formed strongly depend on the structure and concentration of the solution components and on temperature.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 5, 2005, pp. 771–777.Original Russian Text Copyright © 2005 by Khoma, Gavrilenko, Nikitin.     

Selenium(IV) Oxide Catalyzed Oxidation of Aldehydes to Carboxylic Acids with Hydrogen Peroxide

A convenient method for oxidative transformation of aromatic, hetero-aromatic and aliphatic aldehydes into carboxylic acids is presented. It is based on the oxidation of aldehydes in THF using 30% hydrogen peroxide in the presence of 5 molar % of selenium(IV) oxide. The scope and limitation of the method are discussed.     

On Reaction of Sulfur Dioxide with Aqueous Solutions of Carbamide

A mechanism of SO₂ chemisorption by aqueous solutions of carbamide was suggested. The effective rate constants of accumulation of hydrogen ions in the reaction of sulfur dioxide with aqueous solutions of carbamide in the range 278-313 K were determined.     

Nickel(II) Oxide Solubility and Phase Stability in High Temperature Aqueous Solutions

A platinum-lined, flowing autoclave facility was used to investigate the solubility behavior of nickel(II) oxide (NiO) in deoxygenated ammonium and sodium hydroxide solutions, between 21 and 315°C. Solubilities were found to vary between 0.4 and 400 nmol-kg^–1. The measured nickel ion solubilities were interpreted via a Ni(II) ion hydroxo- and ammino-complexing model, and thermodynamic functions for these equilibria were obtained from a least-squares analysis of the data. Two solid phase transformations were observed: at temperatures below 149°C, the activity of Ni(II) ions in aqueous solution was controlled by a hydrous Ni(II) oxide (theophrastite) solid phase rather than by anhydrous NiO (bunsenite); above 247°C, Ni(II) activities were controlled by cubic rather than by rhombohedral bunsenite.     

Stationary Kinetics of Light Olefin Oxidation by Hydrogen Peroxide in Aqueous Alkali Solutions in the Presence of Fe(III) Oxide

The steady-state kinetics of ethylene and propylene oxidation by hydrogen peroxide in the presence of Fe(III) oxide in aqueous solutions with the permanent adding of H₂O₂ to the reaction medium was studied. The use of an original method for the study of the steady-state reaction kinetics with gas chromatographic detection of substrate consumption from the gas phase made it possible to estimate the apparent rate constants of ethylene oxidation, the ratio of the rate constants of propylene and ethylene oxidation, the reaction orders with respect to the substrate and oxidant concentration, the dependence of the apparent rate constant of ethylene oxidation on the catalyst weight and on the pH of solution, and the apparent activation energy of the process under condition of substrate distribution between the gas and liquid phases. It was found that the kinetic isotope effect in ethylene oxidation is almost absent when completely deuterated ethylene is used.     

Electrochemical Determination of Hydrogen Peroxide and Glucose by Titanium(IV) Oxide Nanotube Arrays

Titanium(IV) oxide nanotube arrays (TiO₂) prepared by electrochemical oxidation were used as a sensor for the catalytic reduction of hydrogen peroxide. The effects of pH, applied voltage, interferences, and linear dynamic range were characterized. The electrode showed rapid response and a linear dynamic range from 5.0 micromolar to 12.0 millimolar in phosphate buffer at pH 6.5 at a working voltage of ?0.8 volt. The maximum sensitivity was 474 milliamperes per molar per square centimeter with good reproducibility and reusability. The electrode was also employed for the electrochemical determination of glucose without a mediator by the immobilization of glucose oxidase on the electroactive surface. The resulting biosensor exhibited good activity and rapid response toward glucose and allowed the determination of glucose from 20 micromolar to 1 millimolar and 1–10 millimolar.     

Thermal Reactions of Sulfur and Hydrogen Sulfide and Its Derivatives with Organic Compounds

The review summarizes the results of the authors' studies on thermal reactions of sulfur, hydrogen sulfide, and their derivatives with organic compounds, performed since 1944 till 2000.     

Detoxication of Aqueous Cyanide Solutions with Oxygen in the Presence of S(IV) and Cu(II) Compounds

Oxidation of cyanide anions with atmospheric oxygen in aqueous solutions in the presence of Na₂SO₃ and NaHSO₃ mixture and CuSO₄ as a catalyst was studied. The reaction mechanism was proposed.     

Reactions of silylated Schiff bases with organotitanium(IV) and organotin(IV) chlorides

The interactions of silylated dibasic quadridentate Schiff bases derived fromo-hydroxyacetophenone and ethylenediamine and orthophenylenediamine with (π-C₅H₅)TiCl₃, (π-C₅H₅)(MeO)TiCl₂, (MeO)₂TiCl₂, Me₂SnCl₂ and MeSnCl₃ yield a new series of organotitanium(IV) and tin(IV) compounds. The reactivity of (π- C₅H₅)Ti(L₁)Cl and MeSn(L₁)Cl, towards MeSH, Me₂NSiMe₃, SiMe₃N₃ and Me₃SiC = CPh are also described. The structures for the compounds isolated are proposed on the basis of elemental analyses, molecular weights, IR and¹H nmr spectroscopic studies.     

Uranium(IV) Sulfates: Investigating Structural Periodicity in the Tetravalent Actinides

Chemical trends within the periodic table are frequently used as guides for predicting reactivity, structure, and electronic properties of the elements. While these trends have been rigorously investigated for the transition metals, the understanding of trends within the actinide series is elementary in comparison. Herein, we report the synthesis and characterization of five new U(IV) sulfate compounds and discuss their relationship to previously reported An(IV) sulfate species, an analysis that allows for the elucidation of solid state trends across the actinides. One such trend suggests the increase in Lewis acidity that occurs when traversing the actinides from thorium to plutonium promotes bidentate binding of the sulfate ligand as long as complexation can outcompete the resulting increase in steric pressure. This hypothesis correlates well with the experimental results previously reported for the solution phase speciation in An(IV) sulfate systems.     

Reactions of a Dioxidomolybdenum(VI) Complex with Thionation Reagents—Formation of Mo(IV) Species with Sulfur Donors

Molecular molybdenum complexes with sulfur donor ligands are generally studied as soluble model compounds for molybdenum enzymes essential for life. The dioxidomolybdenum(VI) complex with tetradentate aminobisphenolate ligand undergoes a reaction with thionation reagent P₂S₅ or its organic derivative, Lawesson’s reagent, to yield stable Mo(IV) aminobisphenolate complexes, where pristine oxido ligands have been replaced by bidentate sulfur donors tetrasulfide, S₄²⁻ or (4-methoxyphenyl)phosphonotrithioate residue derived from Lawesson’s reagent. This is in contrast to the behaviour of analogous dioxidotungsten(VI) complex, which, under similar conditions, yields W(VI) S₂ systems. The overall cis,trans,cis geometry of the parent dioxidomolybdenum(VI) aminobisphenolate is retained, namely, the neutral nitrogen donors are in cis positions, phenolate oxygens are trans to each other and sulfur donors are cis. Although formally Mo(IV), thus d² system, the studied complexes have diamagnetic singlet electron configurations as a result of the axially compressed octahedral structures.     

Thermochemistry of Aniline Solution in Isomeric Butyl Alcohols and Their Aqueous Solutions

The enthalpies of solution (_s H ⁰) of aniline in isomeric butyl alcohols and their aqueous solutions at 25°C were determined. The dissolution of aniline becomes more endothermic with increasing content of alcohol in aqueous solution. The enthalpy coefficients of pair interaction alcohol-aniline in aqueous solution were calculated. This interaction is enhanced in the order tert-butanol-sec-butanol-iso-butanol-n-butanol. The correlations of these characteristics with physicochemical properties of solvents were revealed.     

Study of Ligand Substitution Reactions at Pentacyanoferrates(II) in Aqueous Salt and Micellar Solutions

The ligand substitution reactions Fe(CN)(5)(4-(t)bupy)(3-) + 4-CNpy and Fe(CN)(5)(4-(t)bupy)(3-) + pzCO(2)(-) (4-(t)Bupy = 4-tert-butylpyridine; 4-CNpy = 4-cyanopyridine; pzCO(2)(-) = pyrazinecarboxylate) were studied in several aqueous salt and micellar solutions. Kinetic data in aqueous solutions showed that the two processes follow a dissociative mechanism, D, and the dependence of the first-order rate constants on [salt] on electrolyte aqueous solutions allow the estimation of the activation volumes corresponding to both reactions. Under true first-order conditions no kinetic micellar effects were found in anionic (SDS) and nonionic (Triton X-100) aqueous micellar solutions. In cationic micellar solutions (CTAB, CTAC, and TTAB) small kinetic micellar effects were found. These were related to the different ionic concentrations and the different polarity and structure of the Stern layer surrounding the cationic micellar aggregates, where the reactions take place, with respect to pure water. Copyright 2000 Academic Press.