Kinetics of the Catalytic Oxidation Reactions of Thiol Compounds in Aqueous Solutions in the Presence of Copper Ions

The kinetics of the catalytic oxidation reactions of thiol compounds with molecular oxygen in aqueous solutions in the presence of copper ions was studied in relation to the structures of oxidized thiols and the pH of the solution. A modified procedure used for the determination of [O₂] allowed us to obtain the kinetic characteristics of more than 30 thiols over a wide pH range. We found that weakly chelating thiols exhibited a first order of reaction with respect to [Cu⁺] and [O₂] under conditions when the [(Cu⁺)(RS^–)₂] complex occurred. In the oxidation of strongly chelating thiols in an alkaline medium, the order of reaction with respect to [Cu⁺] was equal to 2, and the rate of reaction was independent of [O₂]. We found that the introduction of small amounts of strongly chelating thiols into Cu⁺ solutions containing difficult-to-oxidize mercaptans resulted in a dramatic acceleration of mercaptan oxidation. We hypothesized that O₂ was effectively bound to the [(Cu⁺)(RS^–)₂] complexes in an alkaline medium in the case of strongly chelating thiols, and this was not the case with the complexes of weakly chelating thiols.     

Origin of the Rate Acceleration in the C−C Reductive Elimination from Pt(IV)-complex in a [Ga4L6]12− Supramolecular Metallocage

The reductive elimination on [(Me₃P)₂Pt(MeOH)(CH₃)₃]⁺, 2P , complex performed in MeOH solution and inside a [Ga₄L₆]¹²⁻ metallocage are computationally analysed by mean of QM and MD simulations and compared with the mechanism of gold parent systems previously reported [Et₃PAu(MeOH)(CH₃)₂]⁺, 2Au . The comparative analysis between the encapsulated Au(III) and Pt(IV)-counterparts shows that there are no additional solvent MeOH molecules inside the cavity of the metallocage for both systems. The Gibbs energy barriers for the 2P reductive elimination calculated at DFT level are in good agreement with the experimental values for both environments. The effect of microsolvation and encapsulation on the rate acceleration are evaluated and shows that the latter is far more relevant, conversely to 2Au . Energy decomposition analysis indicates that the encapsulation is the main responsible for most of the energy barrier reduction. Microsolvation and encapsulation effects are not equally contributing for both metal systems and consequently, the reasons of the rate acceleration are not the same for both metallic systems despite the similarity between them.     

Gold Dissolution Electrocatalysis in Thiourea Electrolytes in the Presence of Chemisorbed Sulfide Ions

Adding a microscopic quantity of sodium sulfide (～10^?5 M) into acid solutions of thiourea leads to a dramatic acceleration of anodic dissolution of gold. The acceleration effect is greater at larger thiourea concentrations (c) and longer times of the electrode contact with solution (Δt) before the beginning of measurements. The effect diminishes after a polarization curve passes through a maximum at E ? 0.5 V. Regularities of the gold dissolution in a solution containing 0.1 M thiourea and 0.5 M H₂SO₄ at given values of c and Δt are studied with use made of the technique of renewing the electrode surface by cutting off a thin surface layer of metal. The discovered regularities are given an explanation which is based on the assumption that the dissolution process is catalyzed by sulfide ions adsorbed on the electrode surface.     

Thermal decomposition of 1,3,3-trinitroazetidine in the gas phase, solution, and melt

1,3,3-Trinitroazetidine (TNAZ) was synthesized using the alternative approach based on the transformation of 3-oximino-1-(p-toluenesulfonyl)azetidine in the reaction with nitric acid through intermediate pseudonitrol. The thermal decomposition of TNAZ in the gas phase, melt and m-dinitrobenzene solution in a wide concentration range (5–80%) was studied by manometry, volumetry, thermogravimetry, IR spectroscopy, and mass spectrometry. In the gas phase in the temperature range from 170 to 220°C the thermal decomposition proceeds according to the first-order kinetic law with the activation energy 40.5 kcal mol^?1 and pre-exponential factor 10^15.0 s^?1. The major gaseous reaction products are N₂, NO, NO₂, CO₂, H₂O, and nitroacetaldehyde, and trace amounts of CO and HCN are formed. The rate-determining step of the process is the homolytic cleavage of the N-NO₂ bond in the TNAZ molecule. In melt at 170–210 °C the thermal decomposition proceeds with the pronounced self-acceleration and the maximum reaction rates are observed at conversions 53.9–67.4%. The solid decomposition products accelerate the reaction. It is most likely that the autocatalysis of TNAZ decomposition in the liquid phase is due to the autocatalytic decomposition of 1-nitroso-3,3-dinitroazetidine, which is formed by the thermal decomposition of TNAZ. In m-dinitrobenzene TNAZ also decomposes with self-acceleration. The higher the concentration in the solution, the more pronounced the self-acceleration. Additives of picric acid moderately accelerate the thermal decomposition of TNAZ, whereas hexamethylenetetraamine additives exert a strong acceleration.     

Fractal analysis of pit morphology of Inconel alloy 600 in sulphate,nitrate and bicarbonate ion-containing sodium chloride solution at temperatures of 25–100 °C

Pit morphology of Inconel alloy 600 in sulphate (SO₄ ^2-), nitrate (NO₃ ^-) and bicarbonate (HCO₃ ^-) ion-containing 0.5 M sodium chloride (NaCl) solution was analysed in terms of fractal geometry as functions of solution temperature and anion concentration using the potentiostatic current transient technique, scanning electron microscopy, image analysis and ac-impedance spectroscopy. Potentiostatic current transients revealed that the pitting corrosion is facilitated by the increase in solution temperature, irrespective of anion additives, and that it is hindered by the increase in NO₃ ^- and HCO₃ ^- ion concentration, regardless of solution temperature. Above 60 °C, it was also found that the addition of SO₄ ^2- ions impedes pit initiation, but enhances pit growth. The value of fractal dimension D _f of the pits increased with increasing solution temperature and with decreasing NO₃ ^- and HCO₃ ^- ion concentration. Moreover, the value of D _f increased above 60 °C with increasing SO₄ ^2- ion concentration. This is caused by the increase in the ratio of pit perimeter to pit area, implying the formation of pits with micro-branched shape due to the acceleration of the local attack in the pits. From the decrease of the depression parameter with increasing solution temperature, it is inferred that the roughness of the pits increased with increasing solution temperature. In addition, the depression parameter was found to increase with increasing NO₃ ^- and HCO₃ ^- ion concentration. But, above 60 °C, in the case of SO₄ ^2- ion addition, the depression parameter decreased with increasing SO₄ ^2- ion concentration. From the experimental findings, the three-dimensional pit morphology is discussed in terms of the values of D _f of the pits and the depression parameter, with respect to anion concentration and solution temperature.     

Chemiluminescence during decomposition of 1,4-dimethylnaphthalene endoperoxide on the silica gel and alumina surface

Decomposition of 1,4-dimethylnaphthalene endoperoxide supported on the silica gel and alumina surface is accompanied by chemiluminescence (CL) in the IR and visible spectral regions. The CL emitter in the IR region is singlet oxygen. The ¹O₂ dimol contributes mainly to the emission at λ_max = 630 and 700 nm. It was shown by the IR-CL method that endoperoxide decomposition on the sorbent surface follows the first-order kinetics. The activation parameters of the process were determined. On the Al₂O₃ and silica gel surfaces a substantial acceleration of the decomposition of 1,4-dimethylnaphthalene endoperoxide is observed compared to the solution. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 199–204, February, 2007.     

Role of oxidizers in the active dissolution and passivation of metals

It was established that addition of hydrogen peroxide to a solution of sulphuric acid leads to acceleration of the active dissolution of chromium and to the shift of its passivation potential in negative direction. Similar data were obtained for Fe-28% Cr alloy in H₂SO₄ solution containing H₂O₂ and for iron in sulphuric acid with K₂Cr₂O₇ additions. The conclusion was made that depending on the potential the molecules of oxygen-containing oxidizers can undergo different transmissions on the surface of the metal, including transformations connected with the direct participation of the oxidizer in the anodic dissolution of the metal or in the building of inhibiting or passivating layers on the metallic surface.     

Homologation of methyl acetate to ethyl acetate with ruthenium catalysts: Part II. effect and role of lewis and protonic acids as promoters

Upon the addition of Lewis and protonic acids, promoters to ruthenium carbonyl iodide catalysts ([Ru(CO)₃I₃]⁻), important effects are observed on the activity and selectivity of the hydrogenation, carbonylation and homologation reactions of methyl acetate.The improvement in selectivity to the valuable products acetic acid and ethyl acetate, and the decrease of the formation of hydrocarbons are related to the acceleration by Lewis acids of the alkyl migration-carbonyl insertion step of the process.The effect on the kinetics is related to the formation and maintenance in the catalytic solution of the hydrido species, HRu(CO)₃I₃, and to the availability of I⁻ involved in the activation of the substrates.     

Photostimulated electron tunnel transfer in solid matrices

Tunnel recombination of photoseparated charges in frozen vitreous alcoholic solutions of zinc porphyrin (ZnP) and CCl₄ has been investigated. Considerable acceleration of the recombination in such systems when exposed to light in the ZnP⁺ or the CCl₄^? absorption band region is observed. Possible mechanisms which increase the charge recombination efficiency are considered in detail. The acceleration of the tunnel recombination of ZnP⁺ and CCl₄^? under irradiation in the porphyrin absorption band is shown to be due to energy transfer from an excited acceptor to a transferred electron. It is shown that data on the kinetics of photostimulated tunnel reactions can be used to determine the binding energy of a tunnelling electron.     

DDTC-Na-based colorimetric chemosensor for the sensing of cyanide in water

Sodium diethyldithiocarbamate (DDTC-Na) was demonstrated to be a new colorimetric cyanide chemosensor by utilizing an indirect trick. First, some copper ions were added to the colorless aqueous solution of DDTC-Na. Then, the resultant brown solution was studied upon the addition of different anions, including Cl⁻, I⁻, IO₃⁻, SO₄²⁻, NO₂⁻, Br⁻, H₂PO₄⁻, F⁻, SCN⁻, HSO₄⁻, ClO₄⁻ and CN⁻. It was observed by naked eyes that the brown solution changed to colorless immediately after the addition of the trace cyanide, but there were no changes towards other anions, making DDTC-Na a good selective cyanide chemosensor in pure water. Supported by the National Natural Science Foundation of China (Grant Nos. 20674059 & 20402011)     

The role of migration mass transfer in the electrodeposition of nickel from sulfate-chloride and chloride solutions containing succinic acid

The electrodeposition of nickel from 0.5 M sulfate-succinate-chloride (I) and 0.3 and 0.5 M chloride-cuccinate (II) solutions at a temperature of 50°C is studied. It is found that, depending on the pH₀ of solution and the concentration of succinic acid and nickel, the maximum cathodic current density for producing high-quality nickel deposits is to 35 A/dm² in electrolytes I and to 60 A/dm² in electrolytes II. This corresponds to the metal deposition rates to 23 and 48 A/dm², respectively. It is shown experimentally that high buffer properties of solutions (succinate buffer) are one of the reasons for high permissible current densities of nickel electrodeposition. The computer-calculated data showed that the intensification of nickel electrodeposition is caused also by the acceleration of mass transfer due to the presence of a considerable fraction of nickel in the form of positively charged complexes and a high concentration of components stabilizing pH_S in the near-cathode layer.     

The effect of the electrolyte concentration in the solution on the voltammetric response of insertion electrodes

A solid-state redox reaction involving an insertion of ions is analyzed with respect to the influence of the concentration of inserting ions in the solution phase. The voltammetric response is independent of the mass transfer in the solution provided that z = (D _ss/D _aq)^1/2 ρ/[C⁺]* is smaller than 0.1 (D _ss: diffusion coefficient of the cation C⁺ in the crystal; D _aq: diffusion coefficient of the cation C⁺ in the solution; ρ: density of the solid compound; [C⁺]*: concentration of cations in the bulk of the solution). In real cases this condition will be satisfied at solution concentrations above 1 mol/l. Received: 15 December 1997 / Accepted: 5 March 1998     

Study of intermediates formed in the oxidation of thiols

The oxidation of aminoethanethiol (1) was investigated in acid solutions on a glass carbon anode. It was shown that at relatively low anode potentials thiyl radicals RS^· are released into the solution, but this does not lead to binding of the oxygen in the solution. Raising the anode potential leads to binding of oxygen, which is probably due to the formation of the intermediate RS⁺. The oxidation of 1 was studied in Ce(SO₄)₂+H₂SO₄ solution. It was shown that under certain conditions the intermediate is RS⁺, which subsequently converts to a product that could not be identified as any previously described product of the oxidation of thiols. Proposals are made regarding its structure and conversion pathways.B. P. Konstantinov Institute of Nuclear Physics, Russian Academy of Sciences, 188350 Leningrad. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 278–288, February, 1992.     

Use of acetate as a leaving group in palladium-catalyzed nucleophilic substitution of benzylic esters

The palladium complex prepared in situ from [Pd(η³-C₃H₅)(cod)]BF₄ and bidentate phosphine DPPF was a good catalyst for the nucleophilic substitution of benzyl acetate. Significant acceleration of the palladium-catalyzed substitution was observed when an alcohol was employed as a reaction solvent. The palladium catalyst was effective for the benzylation of various stabilized carbanions, amines, and benzenesulfinate with benzylic acetates.     

Enhanced Viscosity of Poly(acrylamide) Solution in the Presence of Chromium Citrate Triggered by Release of CO2

Partially hydrolyzed polyacrylamide (HPAM) has been widely used for water shut-off and profile control to enhance oil recovery. Herein, we reported a novel technique by which the crosslinking between HPAM and Cr³⁺ in aqueous solutions at 60 ℃ can be delayed effectively. Citric acid was selected as an organic complexing agent of Cr³⁺ so that the crosslinking between HPAM and Cr³⁺ can be prevented completely. Due to the decomposition of the bicarbonate (HCO₃^-) embedded in solution, CO₂ released from solution and the pH value of solution increased gradually. The degree of ionization of HPAM and its ability to complex with Cr³⁺ increased accordingly. When the complexation of Cr³⁺ with HPAM is stronger than that with citric acid, the viscosity of the HPAM solution increased significantly. Under the closed condition, together with the existence of potassium dihydrogen phosphate (KH₂PO₄), the release of CO₂ was very slow and the condition was highly controlled so that the ionization of HPAM was prevented initially. Furthermore, the hydrogen bonding interactions between HPAM and melamine embedded in solution previously also postponed the ionization of HPAM. As a result, the crosslinking between HPAM and Cr³⁺ can be delayed for almost one month, completely meeting the requirements for deep water shut-off and profile control to enhance oil recovery.     

Separation of fission produced 106Ru and 137Cs from aged uranium targets by sequential distillation and precipitation in nitrate media

Summary Ruthenium-106 and ¹³⁷Cs have been separated from thermal-neutron irradiated UO₃ targets aged for ~2.5 years by distillation and surface interactions in nitrate media of controlled chemical composition. After digestion of the aged targets with their aluminum wrapper in 2M NaOH solution, nitric acid was added to complete dissolution of the formed residue. The prepared fission product solution was separated from ¹²⁹I and 91.8% ¹⁰⁶Ru by sequential distillation from 20% and 40% HNO₃ solutions containing H₂O₂ and KMnO₄, as oxidants, and by boiling for 4 and 2.5 hours, respectively. The recovery yield of ¹⁰⁶Ru collected in 0.1M NaOH solution was ~68.2% with a radionuclidic purity of 399.99%. Thereafter, the fission product solution was brought to pH 9.5 by addition of NaOH solution to precipitate Al(OH)₃, MnO₂, and Na₂U₂O₇ which selectively retained the remaining fission products leaving, mainly, ¹³⁷Cs in the supernatant solution. The recovery yield of ¹³⁷Cs was ≥97.3% with ~99.75% radionuclidic purity. The gamma-ray emitter contaminants which could be detected and identified in the recovered ¹³⁷Cs solution, were ~0.25% ¹³⁴Cs and ~1.4 ^. 10^-3% ^152,155Eu.     

Photodissociation of protonated β-diketones in the gas phase

The gas phase photodissociation spectra of four protonated β-diketones were obtained and compared with the absorption spectra of the corresponding ions in solution. Protonated 2,4-pentanedione was observed to undergo the photodissociation process [C₅H₉O₂]⁺ +hν → [CH₃CO]⁺ +C₃H₆O with a λmax at 276±10 nm compared with a solution absorption maximum at 286 nm. Protonated 2,4-hexanedione was observed to undergo the photodissociation processes [C₆H₁₁O₂]⁺ +hν → [CH₃CO]⁺ +C₄H₈O and [C₆H₁₁O₂]⁺ +hν → [C₂H₅CO]⁺ +C₃H₆O with a λmax at 279±10 nm compared with a solution absorption maximum at 288 nm. Protonated 3-methyl-2,4-pentanedione was observed to undergo the photodissociation process [C₆H₁₁O₂]⁺ +hν → [CH₃CO]⁺ +C₄H₈O with a λmax at 295±10 nm compared with a solution absorption maximum at 305 nm. Protonated 1,1,1-trifluoro-2,4-pentanedione was observed to undergo the photodissociation process [C₅H₆F₃O₂]⁺ +hν → CF₃H+[C₄H₅O₂]⁺ with a λmax at 273±10 nm compared with a solution absorption maximum at 288 nm. The [CH₃CO]⁺ and [C₂H₅CO]⁺ produced photochemically with the first three ions react to regenerate the protonated β-diketone leading to a photostationary state. Photodissociation of the protonated alkyl β-diketones is believed to occur from the protonated keto form, whereas photodissociation of protonated 1,1,1-trifluoro-2,4-pentanedione is believed to occur from the protonated enol form. Mechanisms for the observed photodissociation processes are proposed and comparisons with results from related techniques are presented.     

Silver cementation with magnesium in cyanide solutions

Contact precipitation of silver with a magnesium powder from 0.0025–0.01 M solutions of the system [Ag(CN)₂]^?-CN^? in the hydrodynamic mode was studied. The dependence of the silver cementation rate in the initial stage on the concentration of the [Ag(CN)₂]^? complex and on the surface area of the cementing agent was examined, and the relationship of the temperature factor with the depolarization of silver reduction on microcathodes and acceleration of magnesium dissolution on microanodes was analyzed.     

Effects of the thermal history and concentration on the aggregation of Erwinia gum in an aqueous solution

The aggregation of Erwinia (E) gum in a 0.2 M NaCl aqueous solution was investigated by multi‐angle laser light scattering and gel permeation chromatography (GPC) combined with light scattering. The GPC chromatograms of five fractions contained two peaks; the fractions had the same elution volume but different peak areas, suggesting that aggregates and single chains coexisted in the solution at 25 °C. The apparent weight‐average molecular weights (M_w) of the aggregates and single chains for each fraction were all about 2.1 × 10⁶ and 7.8 × 10⁴, respectively. This indicates that the aggregates were composed of about 27 molecules of E gum in the concentration range used (1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ g/mL). The weight fraction of the aggregates (w_ag) increased with increasing concentration, but the aggregates still existed even in an extremely dilute solution. The fractionation process and polymer concentration hardly affected the apparent aggregation number but significantly changed w_ag. The E‐gum M_w decreased sharply with an increase in temperature. When the E‐gum solution was kept at 100 °C, w_ag decreased sharply for 20 h and leveled off after 100 h. Once the aggregates were decomposed at a higher temperature, no aggregation was observed in the solution at 25 °C, indicating that the aggregation was irreversible. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1352–1358, 2000     

266 nm光照下水溶液中氯苯与H2O2的反应机理研究

利用瞬态吸收光谱技术研究了不同条件下C₆H₅Cl与H₂O₂水溶液的激光闪光光解情况, 初步考察了其瞬态物种的生长和衰减等行为. 研究表明, •OH自由基和C₆H₅Cl反应生成C₆H₅Cl-OH adduct, 其反应速率常数在近中性、酸性条件下约为(5.89±0.65)×10⁹和(7.07±0.61)×10⁹ L•mol^－1•s^－1; 其衰减则符合双分子二级反应, 速率常数2k/εl＝1.1×10⁶ s^－1, 而在碱性时则为(4.34±0.51)×10⁹ L•mol^－1•s^－1, 衰减呈准一级反应, 速率常数为2.11×10⁵ s^－1. 在有氧条件下, O₂与C₆H₅Cl-OH adduct反应生成C₆H₅Cl-OHO₂ adduct, 其反应速率常数为6.8×10⁸ L•mol^－1•s^－1.