The role of oxidizing radicals in neptunium speciation in γ-irradiated nitric acid

The irradiation of aqueous nitric acid solutions generates transient, reactive species that are known to oxidize neptunium. However, nitrous acid is also a long-lived product of nitric acid irradiation, which reduces neptunium. When we irradiated nitric acid solutions of neptunium and measured its speciation by UV/Vis spectroscopy, we found that at short irradiation times, oxidation of Np(V) to Np(VI) occurred due to reactions with radicals such as ^?OH, ^?NO₃ and ^?NO₂. However, at higher absorbed doses and after a sufficient amount of nitrous acid was produced, reduction of Np(VI) to Np(V) began to occur, eventually reaching an equilibrium distribution of these species depending on nitric acid concentration. Neptunium(IV) was not produced.     

The complex reaction kinetics of neptunium including redox and extraction process in 30% TBP—nitric acid system

In order to understand the complex and dynamic neptunium process chemistry in the TBP-HNO₃ system, the kinetics involved reversible redox reaction and extraction mass transfer was investigated. The results indicates that the mass transfer rate of Np(VI) is much faster than the redox reaction in aqueous solution. The concentrations of nitric acid and nitrous acid not only can change the Np(V) oxidation reaction and Np(VI) reduction reaction rate, but also can ultimately determine the distribution of neptunium extraction equilibrium. The variety of temperature can only influence the extraction equilibrium time, but cannot alter the equilibrium state of neptunium.     

Conformational changes of DNA γ-irradiated in the presence of aliphatic alcohols in solution

The conformational changes of DNA in aqueous solutions containing ethanol and iso- and n-propanol having concentrations of 0–23 wt.% and ionic strength μ = 0.003 NaCl and exposed to γ radiation at doses from 0 Gy to 30 Gy were studied by low-gradient viscosimetry and circular dichroism. The dependence of the specific volume (V _sp) of DNA on the radiation dose changed at different contents of alcohol. There is a critical concentration (C _cr) at which the structure of the mixed solvent is rearranged. The V _sp of DNA decreased as the radiation dose increased at C _alc = 12 wt.% < C _cr and increased at C _alc = 23 wt.% > C _cr. In both cases, the largest V _sp of DNA was observed in water ethanol solutions. The secondary structure of the macromolecule in the systems corresponds to the form. It was shown that the observed conformational changes in irradiated DNA at C _alc < C _cr and C _alc > C _cr could not be explained only by the ability of alcohols to intercept the radicals formed in radiolysis of water.     

Thermochemical study of the reactions of acid–base interaction in an aqueous solution of α-aminobutyric acid

The heat effects of the interaction between a solution of α-aminobutyric acid and solutions of HNO₃ and KОН are measured by means of calorimetry in different ranges of рН at 298.15 K and values of ionic strength of 0.25, 0.5, and 0.75 (KNO₃). The heat effects of the stepwise dissociation of the amino acid are determined. Standard thermodynamic characteristics (Δ_r H ⁰, Δ_r G ⁰, and Δ_r S ⁰) of the reactions of acid–base interaction in aqueous solutions of α-aminobutyric acid are calculated. The connection between the thermodynamic characteristics of the dissociation of the amino acid and the structure of this compound is considered.     

Standard enthalpies of formation of γ-aminobutyric acid and the products of its dissociation in aqueous solution

Heat effects of the dissolution of crystalline γ-aminobutyric acid in water and potassium hydroxide solutions are determined by direct colorimetry at 298.15 K. Standard enthalpies of formation of γ-aminobutyric acid and the products of its dissociation in aqueous solution are calculated.     

A facile electrochemical synthesis of caffeic acid derivatives in the presence of acetylacetone or methyl acetoacetate in aqueous medium

The anodic oxidation of caffeic acid in the presence of acetylacetone or methyl acetoacetate in aqueous solution has been studied by cyclic voltammetry and controlled-potential electrolysis techniques. The result showed that caffeic acid was oxidized to the corresponding o-benzoquinone, which underwent further Michael-addition with acetylacetone or methyl acetoacetate to produce caffeic acid derivative 3,4-dihydroxy-6-(1-acetylacetone)-yl cinnamic acid 4a or 3,4-dihydroxy-6-(1-acetyl-methylacetate)-yl cinnamic acid 4b.     

The catalytic condensation of ω-phenyl-substituted alcohols in the presence of an iron oxide

The results of gas-phase conversion of ω-phenyl-substituted alcohols (benzyl alcohol, 2-phenylethanol, 3-phenyl-1-propanol) and their equimolar mixtures with primary normal alcohol (1-octanol) are presented. Reactions were carried out at atmospheric pressure in the presence of an iron catalyst in the temperature range of 568–673 K and load of 2.0 h⁻¹. 2-Phenylethanol and 3-phenyl-1-propanol undergo dehydrogenation to aldehydes and condensation to esters. At higher temperatures symmetrical ketones containing ω-phenyl group as substituent are formed. Mixtures of these alcohols with 1-octanol give among others asymmetrical aromatic-aliphatic ketones.     

Thermodynamic quantities for the ionization of nitric acid in aqueous solution from 250 to 319°C

The aqueous reaction, HNO₃(aq)=H⁺+NO ₃ ^– was studied as a function of ionic strength I at 250, 275, 300 and 319°C using a flow calorimeter and the equilibrium constant K and enthalpy change (H) at I=0 were determined. Using these experimental values, equations describing logK, H, the entropy change S and the heat capacity change C _p of reaction at I=0 and temperatures from 250 to 319°C were derived. The increasing importance of ion association as temperature rises was discussed. The use of an equation containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was applied to the logK values reported here and to those determined by others. The resulting plot of logK for the isocoulombic reaction vs. 1/T was fairly linear which supports the postulate that the principle is a useful technique for the extrapolation of logK values from low to high temperatures.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.     

Efficiency of energy transfer from γ-irradiated ammonium halides in aqueous iodide and nitrate solutions

It is well known that ammonium halide (NH₄X) crystals, on -exposure, store energy in the form of primary and secondary radiolytic products. Such crystals on dissolution in aqueous iodide and nitrate solutions result in oxidation of iodide and reduction of nitrate, respectively. The yields of iodine and nitrite are determined by chemical methods under varying conditions of the amount, dose and particle size of the irradiated ammonium halide salts. The maximum values of the efficiency of energy transfer for oxidation and reduction processes for ammonium halide salts correspond to 40% and 10%, respectively. At low doses, an empirical relation proposed between the percent efficiency of energy transfer and the absorbed dose is valid. The concentrations of inherent oxidizing and reducing species initially present are 7.0×10¹⁸ and 1.0×10¹⁸ per mol of ammonium halide, respectively.     

Extraction of 211At from nitric acid solutions into various organic solvents for use as an α-source for radiation chemistry studies

Journal of Radioanalytical and Nuclear Chemistry - The partitioning of 211At from an irradiated bismuth target using solvent extraction into several organic solvents is presented. Although astatine...     

The deposition of nanostructured β-PbO2 coatings from aqueous methanesulfonic acid for the electrochemical oxidation of organic pollutants

Highly crystalline, nanostructured, three-dimensional β-PbO₂ coatings were successfully obtained by galvanostatic deposition from baths containing aqueous lead(II) and methanesulfonic acid (CH₃SO₃H). This constitutes a much more environmentally friendly methodology compared to plating of β-PbO₂ in HNO₃. The deposits exhibited high quality and good adherence. The crystallite size was in the range 20–30 nm and AFM imaging revealed very uniform, rough deposits (i.e., 255–275 nm rms). The oxidative destruction of Methyl Orange azo dye was studied by electrochemical advanced oxidation processes (EAOPs). An electro-Fenton process with a high surface area carbon-felt cathode performed better than the single anodic oxidation. Rapid and complete decolorisation was achieved following pseudo first-order kinetics. The stability of the β-PbO₂ electrodes during the electrolyses was also demonstrated.     

Features of autoxidation of ferrocenylcarboxylic acid and its methyl ester in organic solvents in the presence of Brønsted acids

We have studied the autoxidation of ferrocenecarboxylic acid and its methyl ester in organic solvents in the presence of perchloric and trifluoroacetic acids. Based on the results of kinetic studies and data on the composition of the reaction products, we suggested the possible reaction mechanisms, including those of molecular and radical-chain macrostages of the process. The features of the solvent influence on the rate of oxidation of metallocomplexes and the reasons for its extreme dependence with increasing concentration of perchloric acid are discussed.     

Kinetics of thermal decomposition of γ-irradiated and unirradiated complexes of mandelhydroxamic acid

The thermal decomposition of -irradiated and unirradiated complexes of mandel-hydroxamic acid (HMA), Co(HMA)₂.1/2H₂O, Mn(HMA)₂.2H₂O, Ba(HMA)₂.2H₂O and Cd(HMA)₂.2H₂O have been studied thermogravimetrically (under isothermal conditions). The thermal dehydration of each complex occurred in one step, while the decomposition of dehydrated complexes occurred in two steps. The kinetic parameters for dehydration were computed by different models. The thermal dehydration is regulated by random nucleation A₃ for Co-, Mn-, and Cd-complexes and by phase-boundary (R₃) for Ba-complex. The effect of -irradiation on the kinetic parameters of thermal decomposition is discussed. Radiation did not modify the mechanism of the reaction but accelarated the dehydration steps in the case of Mn- and Co-complexes.     

Spin trapping of the short-lived free radicals formed in γ-irradiated alcohols

Short-lived free radicals formed in γ-irradiated methanol, ethanol and 2-propanol have been detected by E.S.R. combined with spin trapping method using 2,4,6-tri-t-buthylnitrosobenzene (BNB) as a spin trap. The observed spectra could be identified clearly by the help of deuterated alcohols. The hydrogen spin adduct, which had not been clearly identified in earlier works, was observed together with alkoxy radicals and other radicals. It was revealed that a part of the hydrogen adduct could come from proton transfer to the anion radical of BNB, which was produced by electron capture during irradiation. From the change of ¹CH₂OH/CH₃O¹ ratio with that of added spin trap concentration one may conclude that the methoxy radical and hydrogen atom are primary radicals in radiolysis of liquid phase methanol. This conclusion is also supported by both the change of the ratio with irradiation temperature and the isotope effect on the spin adduct yields.     

Catalyzed selective direct α- and γ-alkylation of aldehydes with cyclic benzyl ethers by using T(+)BF4- in the presence of an inexpensive organic acid or anhydride

The cross dehydrogenative coupling (CDC) of cyclic benzyl ethers with aliphatic and α,β-unsaturated aldehydes has been developed. The mild reaction conditions, in which an N-oxoammonium salt derived from TEMPO (2,2,6,6-tetramethyl-1-piperidinoxyl) is employed as the oxidant in combination with a Cu catalyst, allow the use of relatively redox-unstable aldehydes under oxidative CDC conditions. The addition of a catalytic amount of trifluoroacetic acid (TFA) or Ac(2)O facilitates the reaction and increases the efficiency and selectivity. In contrast to the expected α-alkylation obtained with aliphatic aldehydes, α,β-unsaturated aldehydes led preferentially to the more challenging γ-alkylated products. The utility of the developed methodology was demonstrated by the synthesis of isochromane-derived bioactive compounds, such as the dopamine antagonist sonepiprazole.     

Ion-chromatographic separation of metal cations in the presence of α-hydroxyisobutyric acid

Separations of metal cations on a column packed with the strongly acidic cation exchanger Separon SGX CX were investigated in the presence of alpha-hydroxyisobutyric acid (HIBA) in the mobile phase. A retention model based on the general theory of side equilibria was elaborated and relations describing dependences of capacity factors of analytes on the compositon of the mobile phase were derived. Effects of HIBA concentration and pH of the mobile phase on the analyte retention were studied in detail. Stability constants of divalent metal cations (Cd(2+), Co(2+), Mn(2+), Ni(2+) and Zn(2+)) with HIBA were calculated from the experimental dependences of the reciprocal values of capacity factors on the ligand concentration.     

Pulse radiolysis studies of vitaminK1 in an aqueous–organic mixed solvent

Pulse radiolysis studies of VK₁ were carried out in a nitrogen-saturated aqueous–isopropanol–acetone mixed solvent. We studied the spectroscopic characteristics of semiquinone radicals of VK₁ and determined the kinetic parameters of formation and decay of the species. It was found that the decay process of semiquinone radicals of VK₁ was according to a first-order reaction, this was different from the case in ethanol solution, possible reasons were also analyzed.     

β-Aminoselenenation of alkenes with arylselenenamides in the presence of sulfamic acid

Russian Chemical Bulletin -     

The features of nitric acid ‘mercerization’ of cellulose

Transformation of native cellulose species into cellulose-II polymorph through the additive Knecht compound formed under the action of 68.5% nitric acid has been studied. Probable causes of peculiar temperature effects in the course of phase transformations taking place in cellulose of various origin, crystallite dispersity, or morphologic structure are discussed. The processes of hydrolytic destruction and esterification of starting materials during their mercerization by this non-traditional agent at 20 °C and 0 °C are quantitatively characterized. In the case of mercerization of wood microcrystalline cellulose at 20 °C a decrystallizing effect due to side reactions of partial nitration is noted.