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1.
The quantitative study of the equilibrium Pu4++Cl⇋Pu3++1/2 Cl2 in LiCl−KCl (70–30% mol) at 455, 500, 550 and 600°C by visible and near I.R. absorption spectrophotometry allows the calculation of the reaction's equilibrium constant, the mean thermodynamic data ΔH=27±14 kJ·mol−1 and ΔS=37±17 J·mol−1·K−1 and the standard potential of the couple .   相似文献   

2.
Oxidation of 3-(4-methoxyphenoxy)-1,2-propanediol (MPPD) by bis(hydrogenperiodato) argentate(III) complex anion, [Ag(HIO6)2]5− has been studied in aqueous alkaline medium by use of conventional spectrophotometry. The major oxidation product of MPPD has been identified as 3-(4-methoxyphenoxy)-2-ketone-1-propanol by mass spectrometry. The reaction shows overall second-order kinetics, being first-order in both [Ag(III)] and [MPPD]. The effects of [OH] and periodate concentration on the observed second-order rate constants k′ have been analyzed, and accordingly an empirical expression has been deduced:
where [IO4 ]tot denotes the total concentration of periodate and k a = (0.19 ± 0.04) M−1 s−1, k b = (10.5 ± 0.3) M−2 s−1, and K 1 = (5.0 ± 0.8) × 10−4 M at 25.0 °C and ionic strength of 0.30 M. Activation parameters associated with k a and k b have been calculated. A mechanism is proposed, involving two pre-equilibria, leading to formation of a periodato–Ag(III)–MPPD complex. In the subsequent rate-determining steps, this complex undergoes inner-sphere electron-transfer from the coordinated MPPD molecule to the metal center by two paths: one path is independent of OH, while the other is facilitated by a hydroxide ion.  相似文献   

3.
The acid catalysed dissociation of the copper(II) and nickel(II) complexes of 5,7-dioxo-1,4,8,11-tetra-azacyclo-tetradecane (dioxocyclam = LH2) has been studied using nitric acid solutions over a range of temperatures at I = 1.0 mol dm si-3. The kinetic data for the copper complex can be fitted to the rate expression k obs = k K 2[H+]/(1 + K 2 [H+] with K = 24.7s−1 and K 2 = 65dm3mol−1 at 25° C. The analogous constants for the nickel(II) complex are K = 3.3s−1 and K 2 = 45dm3mol−1. The acid dissociation can be rationalized in terms of the kinetic scheme
  相似文献   

4.
The potential energy surface crossings for 1,2-dithiete have been investigated using the complete active space self-consistent field(CASSCF) method and simple group theory.Using the full Pauli-Breit spin-orbit coupling(SOC) operator(■) SO) which consists of the one-electron(■) SO1) and two-electron(■) SO2) terms,we estimate the strengths of the SOC(198.37 cm-1 when symmetry is imposed,and 211.35 cm-1 with no symmetry constraints),which plays an essential role in the spin transitions between different spin s...  相似文献   

5.
Results of solubility experiments involving crystalline nickel oxide (bunsenite) in aqueous solutions are reported as functions of temperature (0 to 350 °C) and pH at pressures slightly exceeding (with one exception) saturation vapor pressure. These experiments were carried out in either flow-through reactors or a hydrogen-electrode concentration cell for mildly acidic to near neutral pH solutions. The results were treated successfully with a thermodynamic model incorporating only the unhydrolyzed aqueous nickel species (viz., Ni2+) and the neutrally charged hydrolyzed species (viz., Ni(OH)20)\mathrm{Ni(OH)}_{2}^{0}). The thermodynamic quantities obtained at 25 °C and infinite dilution are, with 2σ uncertainties: log10Ks0o = (12.40 ±0.29),\varDeltarGmo = -(70. 8 ±1.7)\log_{10}K_{\mathrm{s0}}^{\mathrm{o}} = (12.40 \pm 0.29),\varDelta_{\mathrm{r}}G_{m}^{\mathrm{o}} = -(70. 8 \pm 1.7) kJ⋅mol−1; \varDeltarHmo = -(105.6 ±1.3)\varDelta_{\mathrm{r}}H_{m}^{\mathrm{o}} = -(105.6 \pm 1.3) kJ⋅mol−1; \varDeltarSmo = -(116.6 ±3.2)\varDelta_{\mathrm{r}}S_{m}^{\mathrm{o}} =-(116.6 \pm 3.2) J⋅K−1⋅mol−1; \varDeltarCp,mo = (0 ±13)\varDelta_{\mathrm{r}}C_{p,m}^{\mathrm{o}} = (0 \pm 13) J⋅K−1⋅mol−1; and log10Ks2o = -(8.76 ±0.15)\log_{10}K_{\mathrm{s2}}^{\mathrm{o}} = -(8.76 \pm 0.15); \varDeltarGmo = (50.0 ±1.7)\varDelta_{\mathrm{r}}G_{m}^{\mathrm{o}} = (50.0 \pm 1.7) kJ⋅mol−1; \varDeltarHmo = (17.7 ±1.7)\varDelta_{\mathrm{r}}H_{m}^{\mathrm{o}} = (17.7 \pm 1.7) kJ⋅mol−1; \varDeltarSmo = -(108±7)\varDelta_{\mathrm{r}}S_{m}^{\mathrm{o}} = -(108\pm 7) J⋅K−1⋅mol−1; \varDeltarCp,mo = -(108 ±3)\varDelta_{\mathrm{r}}C_{p,m}^{\mathrm{o}} = -(108 \pm 3) J⋅K−1⋅mol−1. These results are internally consistent, but the latter set differs from those gleaned from previous studies recorded in the literature. The corresponding thermodynamic quantities for the formation of Ni2+ and Ni(OH)20\mathrm{Ni(OH)}_{2}^{0} are also estimated. Moreover, the Ni(OH)3 -\mathrm{Ni(OH)}_{3}^{ -} anion was never observed, even in relatively strong basic solutions (mOH - = 0.1m_{\mathrm{OH}^{ -}} = 0.1 mol⋅kg−1), contrary to the conclusions drawn from all but one previous study.  相似文献   

6.
Kinetics of aqua ligand substitution from cis-[Ru(bpy)2(H2O)2]2+ by three vicinal dioximes, namely dimethylglyoxime (L1H), 1,2-cyclohexane dionedioxime (L2H) and α-furil dioxime (L3H) have been studied spectrophotometrically in the 45–60 °C temperature range. The rate constants increase with increasing dioxime concentration and approach a limiting condition. We propose the following rate law for the reaction in the 3.5–5.5 pH range: where k 2 is the interchange rate constant from outer sphere to inner sphere complex and K E is the outer sphere association equilibrium constant. Activation parameters were calculated from the Eyring plots for all three systems: ΔH  = 59.2 ± 8.8, 63.1 ± 6.8 and 69.7 ± 8.5 kJ mol−1, ΔS  = −122 ± 27, −117 ± 21 and −99 ± 26 J K−1 mol−1 for L1H, L2H and L3H, respectively. An associative interchange mechanism is proposed for the substitution process. Thermodynamic parameters calculated from the temperature dependence of the outer sphere association equilibrium constants give negative ΔG 0 values for all the systems studied at all the temperatures (ΔH 0 = 30.05 ± 2.5, 18.9 ± 1.1 and 11.8 ± 0.2 kJ mol−1; ΔS 0 = 123 ± 8, 94 ± 3 and 74 ± 1 J K−1 mol−1 for L1H, L2H and L3H, respectively), which also support our proposition.  相似文献   

7.
The kinetics of the reaction between [ReN(H2O)-(CN)4]2− with different κ2 N,O-donor ligands (quin and 2,3-dipic, respectively) have been studied in the pH 4–12 range in aqueous solution. Two consecutive reaction steps with the formation of the [ReN(η1-quin)(CN)4]3− and [ReN(μ2-quin) (CN)3]2− complexes, respectively, were spectrophotometrically observed and kinetically investigated. The same reaction mechanism is proposed for these two ligands. The first fast reaction (for quin) is attributed to the aqua substitution of [ReN(H2O)(CN)4]2− with forward and reverse rate constants of 1.96(5) × 10−1 M−1 s−1 and 5.6(3) × 10−2 s−1, while a rate of 2.64(3) M−1 s−1 was observed for the reaction between the conjugate base [ReN(OH)(CN)4]3− and quin at 40.2 °C. Due to small absorbance changes, it was difficult to obtain any good quality data for the fast reactions for 2,3-dipic. The second, slower reaction is attributed to cyano substitution with rate constants (k 3 K 1) of 4.17(4) × 10−3 for quin and 4.68(7) × 10−3 M−1 s−1 for 2,3-dipic, at 80.02 °C, respectively. The acid dissociation constant for the aqua complex was spectrophotometrically determined as 11.58(3) and 11.54(2) and kinetically as 11.51(8) and 11.41(1), at 80.4 °C, respectively. Negative values of −83.5(2) and −144.1(2) J K−1 mol−1 as well as the of 71.4(3) and 47.3(3) kJ mol−1, for the slow quin and 2,3-dipic reactions, respectively, point to an ordered transition state where bond formation is responsible for the major driving force of the reaction. The and for the fast forward reaction of quin is indicative of expected associative activation in the transition state. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

8.
The kinetics of hexacyanoferrate(III) reduction by hydrogen peroxide in strongly alkaline media leading to hexacyanoferrate(II) ion have been studied spectrophotometrically within the wavelength range 300–500 nm. The reaction obeys a simple pseudo-first-order rate expression under the applied conditions, namely, a large excess of the reductant and OH anion concentrations, and a low oxidant concentration. The linear dependences of the pseudo-first-order rate constant on OH and H2O2 concentrations are consistent with the rate law of the form: where and are the second- and the pseudo-third-order rate constants for the electron transfer from HO2 and O2 2− to [Fe(CN)6]3−, respectively. The apparent activation parameters determined at 0.4 M NaOH are as follows: ΔH # = (18.0 ± 1.0) kJ mol−1 and ΔS # = (−155 ± 3.5) J K−1 mol−1. The possible mechanism of the reaction is discussed.  相似文献   

9.
The reductive release of iron from ferritin by UV light or ionizing radiation has been investigated in separate experiments. When ferritin is exposed to light, the mineral core is the main photoreceptor for the Fe(III) reduction. In radiolytic studies, we determined that, in the absence of oxygen, the hydrated electron (eaq) is the reducing agent triggering redox reactions associated with iron mobilization from ferritin. In an aerobic system, the superoxide radical anion (O2•−) is also involved in the iron release process. We found that, in photochemical and radiolytical studies, Fe(II) mobilization from ferritin required an iron chelator. Without a chelator, ferritin is an electron-storage molecule for a long period, on the order of at least several hours. The reductant or chelator entry into the ferritin core is not necessary for iron release. The ferrozine is a convenient chelating agent to monitor Fe(II) mobilization, due to a high extinction coefficient of \textFe ( \textferrozine )34 - {\text{Fe}}\,\left( {\text{ferrozine}} \right)_{3}^{4 - } and a high rate constant of complexation process (2.65 × 104 dm3 mol−1 s−1).  相似文献   

10.
The evaporation of benzene, cyclohexane, n-heptane, toluene, 2-xylene, 3-xylene and 4-xylene was studied in H2, He, N2 or CO2 as purge gases for control of the introduced methods of evaluation and the sensitivity limits of TG measurements. Ii as a function of (1−α) and the following equation proved very suitable for a quantitative comparison of 28 independent and different TG measurements and for a very sensitive characterization of the thermal processes, even within an energy level difference of 3 kJ mol−1, in spite of the known great inconsistency in the formal kinetic parameters:
The purge gases definitely influence the evaporation. The influence on the average vapour pressure is an exponential function of the product of the molecular mass and the boiling temperature. With regard to the number of factors in the TG measurement, and the great sensitivity of Ii and the above function, it can be supposed that these equations exhibit some multivariate regression character, besides their natural parameter content. The evaluation methods introduced help to extend the application of TG. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

11.
For getting an insight into the mechanism of atmospheric autoxidation of sulfur(IV), the kinetics of this autoxidation reaction catalyzed by CoO, Co2O3 and Ni2O3 in buffered alkaline medium has been studied, and found to be defined by Eqs. I and II for catalysis by cobalt oxides and Ni2O3, respectively.
(I)
(II)
The values of empirical rate parameters were: A{0.22(CoO), 0.8 L mol−1s−1 (Co2O3)}, K 1{2.5 × 102 (Ni2O3)}, K 2{2.5 × 102(CoO), 0.6 × 102 (Co2O3)} and k 1{5.0 × 10−2(Ni2O3), 1.0 × 10−6(CoO), 1.7 × 10−5 s−1(Co2O3)} at pH 8.20 (CoO and Co2O3) and pH 7.05 (Ni2O3) and 30 °C. This is perhaps the first study in which the detailed kinetics in the presence of ethanol, a well known free radical scavenger for oxysulfur radicals, has been carried out, and the rate laws for catalysis by cobalt oxides and Ni2O3 in the presence of ethanol were Eqs. III and IV, respectively.
(III)
(IV)
For comparison, the effect of ethanol on these catalytic reactions was studied in acidic medium also. In addition, alkaline medium, the values of the inhibition factor C were 1.9 × 104 and 4.0 × 10L mol−1 s for CoO and Co2O3, respectively; for Ni2O3, C was only 3.0 × 102 only. On the other hand, in acidic medium, the values of this factor were all low: 20 (CoO), 0.7 (Co2O3) and 1.4 (Ni2O3). Based on these results, a radical mechanism for CoO and Co2O3 catalysis in alkaline medium, and a nonradical mechanism for Ni2O3 in both alkaline and acidic media and for cobalt oxides in acidic media are proposed.  相似文献   

12.
Inthefieldofpolymerphysics,thecrystallinestateofpolymershaslongbeenofinterest.TheexistenceofpolymersinglecrystalwasfirstdiscoveredbyJaccodine[1]in1955.Thethicknessofmostsolutiongrowthcrystalsisfoundtobeoftheorderof~10nm.Thisobservationissomewhatsurprising.S…  相似文献   

13.
Non-perovskite SrFeCo0.5O x (SFC2) was found to have high electronic and ionic conductivities as well as structural stability. At 800°C in air, total and ionic conductivities of 17 and 7 S·cm−1 were measured, respectively; the ionic transference number was calculated to be ≈0.4. This material is unique because of its high electronic conductivity and comparable electronic and ionic transference numbers. X-ray diffraction analysis showed that air-sintered SFC2 consists of three phase components, ≈75 wt% , ≈20 wt% perovskite , and ≈5 wt% rock salt CoO. Argon-annealed SFC2 contains brownmillerite Sr2(Fe1−x Co x )2O5 and rock salt CoO. Dense SFC2 membranes were able to withstand large pO2 gradients and retain mechanical strength. A 2.9-mm-thick disk membrane was tested in a gas-tight electrochemical cell at 900°C; an oxygen permeation flux rate ≈2.5 cm3(STP)·cm−2·min−1 was measured. A dense thin-wall tubular membrane of 0.75-mm thickness was tested in a methane conversion reactor for over 1,000 h. At 950°C, the oxygen permeation flux rate was ≈10 cm3(STP)·cm−2·min−1 when the SFC2 thin-wall membrane was exposed with one side to air and the other side to 80% methane balanced with inert gas. Results from these two independent experiments agreed well. The SFC2 material is a good candidate as dense ceramic membranes for oxygen separation from air or for use in methane conversion reactors.  相似文献   

14.
A method for estimating the critical temperatures (T b) of thermal explosion for energetic materials is derived from Semenov’s thermal explosion theory and the non-isothermal kinetic equation dα/dt=A 0 T B f(α)e−E/RT using reasonable hypotheses. The final formula of calculating the value of T b is $ \left( {\frac{B} {{T_b }} + \frac{E} {{RT_b^2 }}} \right) $ \left( {\frac{B} {{T_b }} + \frac{E} {{RT_b^2 }}} \right) (T bT e0=1. The data needed for the method, E and T e0, can be obtained from analyses of the non-isothermal DSC curves. When B=0.5 the critical temperature (T b) of thermal explosion of azido-acetic-acid-2-(2-azido-acetoxy)-ethylester (EGBAA) is determined as 475.65 K.  相似文献   

15.
The theory of the polarographic catalytic currents (mechanism CE) has been developed for the system: Ni2+-L-Xp− where L: pyridine (Py), nicotinamide (NA), N,N-diethylnicotinamide (DEN), nicotine (NC) and Xp−: NO 3, AcO, HPO2− 4 . The theory is based on the kinetic parallel heterogeneous catalytic reactions:
(1a)
(1b)
with the use of Langmuir’s adsorbed isotherm. The kinetic equations obtained for average and instantaneous currents allowed to determine the Langmuir’s parameters (NA<DEN<NC), kinetic parameters and the contribution of reactions 1a and b to the summary catalytic currents. The k h value rises with the increase of the NiX2−p stability constant. The correlation k hk h was explained by the additional effect of the field electrode through Xp−. These effects base the reaction 1b instead of accepted early alternative reaction of the ligand exchange. In spite of the fact that k hk h, the contribution of the reaction 1a in the summary catalytic current attained more than 60% (Py, DEN) due to the influence of the ψ0 potential. Dedicated to Professor Zbigniew Galus on the occasion of his 70th birthday and in recognition of his many contributions to electrochemistry  相似文献   

16.
A ternary binuclear complex of dysprosium chloride hexahydrate with m-nitrobenzoic acid and 1,10-phenanthroline, [Dy(m-NBA)3phen]2·4H2O (m-NBA: m-nitrobenzoate; phen: 1,10-phenanthroline) was synthesized. The dissolution enthalpies of [2phen·H2O(s)], [6m-HNBA(s)], [2DyCl3·6H2O(s)], and [Dy(m-NBA)3phen]2·4H2O(s) in the calorimetric solvent (VDMSO:VMeOH = 3:2) were determined by the solution–reaction isoperibol calorimeter at 298.15 K to be \Updelta\texts H\textmq \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2phen·H2O(s), 298.15 K] = 21.7367 ± 0.3150 kJ·mol−1, \Updelta\texts H\textmq \Updelta_{\text{s}} H_{\text{m}}^{\theta } [6m-HNBA(s), 298.15 K] = 15.3635 ± 0.2235 kJ·mol−1, \Updelta\texts H\textmq \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2DyCl3·6H2O(s), 298.15 K] = −203.5331 ± 0.2200 kJ·mol−1, and \Updelta\texts H\textmq \Updelta_{\text{s}} H_{\text{m}}^{\theta } [[Dy(m-NBA)3phen]2·4H2O(s), 298.15 K] = 53.5965 ± 0.2367 kJ·mol−1, respectively. The enthalpy change of the reaction was determined to be \Updelta\textr H\textmq = 3 6 9. 4 9 ±0. 5 6   \textkJ·\textmol - 1 . \Updelta_{\text{r}} H_{\text{m}}^{\theta } = 3 6 9. 4 9 \pm 0. 5 6 \;{\text{kJ}}\cdot {\text{mol}}^{ - 1} . According to the above results and the relevant data in the literature, through Hess’ law, the standard molar enthalpy of formation of [Dy(m-NBA)3phen]2·4H2O(s) was estimated to be \Updelta\textf H\textmq \Updelta_{\text{f}} H_{\text{m}}^{\theta } [[Dy(m-NBA)3phen]2·4H2O(s), 298.15 K] = −5525 ± 6 kJ·mol−1.  相似文献   

17.
2-Pivaloylamino-6-acetonyl-isoxanthopterin (1, ) has been reacted with under suitable conditions for synthesizing the new compound ] (2). It has been characterized by elemental analysis, electrospray ionization mass spectrometry, magnetic susceptibility measurement, different spectroscopic techniques, and cyclic voltammetry. Molecular mechanics (MM2) method provided with its optimized geometry (having lowest steric energy), consistent with the above data; the optimized bond lengths and bond angles data tally with the literature X-ray structural data. Reactivity of (2) towards phenylalanine in the presence of in methanol has been followed both kinetically and stoichiometrically; a reasonable amount of tyrosine could be recovered from the reaction medium. The negative value (−274.0 J mol−1 indicates an associative pathway for this process. (2) is also able to react with bromobenzene as indicated by time-dependent absorption spectra as well as product identification. Efficacy of the pterin ligand residue of (2) in rendering the latter reactive towards the above-mentioned organic compounds, has been discussed on the basis of experimental evidence.  相似文献   

18.
Two novel multidentate ligands: 2,9-bis- -1,10-phenanthroline(L1) and 2,9-bis- -1,10-phenanthroline(L2) were synthesized and characterized by elemental analysis and 1H-n.m.r. spectroscopy. Protonation of the ligands and the stability of complexes of the ligands with rare earth metal ions were investigated. The mononuclear metal complexes [GdIII and SmIII] of the ligands were studied as catalysts for the transphosphorylation of the RNA-model substrate 2-hydroxypropyl-p-nitrophenylphosphate(HPNP). Kinetic studies show the second-order rate constants of HPNP hydrolysis catalyzed by complexes LnL and LnLH−1, respectively. We found that both LnL and LnLH−1 have catalytic activity, but GdL1H−1 was the most efficient catalyst of them, which indicated that the structure of the ligands has obviously influence on the activity of corresponding complexes. A new mechanism was proposed for HPNP hydrolysis reaction catalyzed by LnL and LnLH−1.  相似文献   

19.
The mixed-valence 24-vanadophosphate (1) has been synthesized and characterized in the solid state by IR, magnetism, EPR, XPS, and elemental analysis. Single-crystal X-ray analysis was carried out on (Na-1), which crystallizes in the triclinic system, space group , with a = 17.168(3) ?, b = 18.1971(14) ?, c = 20.1422(13) ?, α = 114.753(3)°, β = 99.390(4)°, γ = 95.124(4)°, and Z = 2. Polyanion 1 has an unusual, open structure composed of 2 RuIIIO6 octahedra, 2 VIVO6 octahedra, 14 VVO5 square-pyramids, 8 VVO4 tetrahedra, and 2 PO4 tetrahedra which are all directly linked via edges and corners. The outer surface of 1 is decorated with six RuII(dmso)3 groups. XPS studies on Na-1 confirm the presence of 2 RuIII and 6 RuII as well as 22 VV and 2 VIV centers. Magnetic susceptibility data on Na-1 show that the VIV–RuIII pairs are coupled antiferromagnetically, with J 1 = −13 K and J 2 ∼ −3 K. We did not detect any peak in our EPR measurements on Na-1, thus supporting the conclusion that Na-1 is diamagnetic in its ground state. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. In Memoriam Prof. F. A. Cotton  相似文献   

20.
The electrochemical properties of boron-doped diamond (BDD) polycrystalline films grown on tungsten wire substrates using ethanol as a precursor are described. The results obtained show that the use of ethanol improves the electrochemistry properties of “as-grown” BDD, as it minimizes the graphitic phase upon the surface of BDD, during the growth process. The BDD electrodes were characterized by Raman spectroscopy, scanning electronic microscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The boron-doping levels of the films were estimated to be ∼1020 B/cm3. The electrochemical behavior was evaluated using the and redox couples and dopamine. Apparent heterogeneous electro-transfer rate constants were determined for these redox systems using the CV and EIS techniques. values in the range of 0.01–0.1 cm s−1 were observed for the and redox couples, while in the special case of dopamine, a lower value of 10−5 cm s−1 was found. The obtained results showed that the use of CH3CH2OH (ethanol) as a carbon source constitutes a promising alternative for manufacturing BDD electrodes for electroanalytical applications.  相似文献   

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