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1.
Abdel-Khalek Ahmed A. Mohamed Adel A. Ewais Hassan A. 《Transition Metal Chemistry》1999,24(2):233-238
The kinetics of oxidation of the chromium(III)-DL- aspartic acid complex, [CrIIIHL]+ by periodate have been investigated in aqueous medium. In the presence of FeII as a catalyst, the following rate law is obeyed:
Catalysis is believed to be due to the oxidation of iron(II) to iron(III), which acts as the oxidizing agent. Thermodynamic activation parameters were calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO
4
-
to CrIII. 相似文献
2.
The oxidation of a ternary complex of chromium(III), [CrIII(DPA)(Mal)(H2O)2]?, involving dipicolinic acid (DPA) as primary ligand and malonic acid (Mal) as co-ligand, was investigated in aqueous acidic medium. The periodate oxidation kinetics of [CrIII(DPA)(Mal)(H2O)2]? to give Cr(VI) under pseudo-first-order conditions were studied at various pH, ionic strength and temperature values. The kinetic equation was found to be as follows: \( {\text{Rate}} = {{\left[ {{\text{IO}}_{4}^{ - } } \right]\left[ {{\text{Cr}}^{\text{III}} } \right]_{\text{T}} \left( {{{k_{5} K_{5} + k_{6} K_{4} K_{6} } \mathord{\left/ {\vphantom {{k_{5} K_{5} + k_{6} K_{4} K_{6} } {\left[ {{\text{H}}^{ + } } \right]}}} \right. \kern-0pt} {\left[ {{\text{H}}^{ + } } \right]}}} \right)} \mathord{\left/ {\vphantom {{\left[ {{\text{IO}}_{4}^{ - } } \right]\left[ {{\text{Cr}}^{\text{III}} } \right]_{\text{T}} \left( {{{k_{5} K_{5} + k_{6} K_{4} K_{6} } \mathord{\left/ {\vphantom {{k_{5} K_{5} + k_{6} K_{4} K_{6} } {\left[ {{\text{H}}^{ + } } \right]}}} \right. \kern-0pt} {\left[ {{\text{H}}^{ + } } \right]}}} \right)} {\left\{ {\left( {\left[ {{\text{H}}^{ + } } \right] + K_{4} } \right) + \left( {K_{5} \left[ {{\text{H}}^{ + } } \right] + K_{6} K_{4} } \right)\left[ {{\text{IO}}_{4}^{ - } } \right]} \right\}}}} \right. \kern-0pt} {\left\{ {\left( {\left[ {{\text{H}}^{ + } } \right] + K_{4} } \right) + \left( {K_{5} \left[ {{\text{H}}^{ + } } \right] + K_{6} K_{4} } \right)\left[ {{\text{IO}}_{4}^{ - } } \right]} \right\}}} \) where k 6 (3.65 × 10?3 s?1) represents the electron transfer reaction rate constant and K 4 (4.60 × 10?4 mol dm?3) represents the dissociation constant for the reaction \( \left[ {{\text{Cr}}^{\text{III}} \left( {\text{DPA}} \right)\left( {\text{Mal}} \right)\left( {{\text{H}}_{2} {\text{O}}} \right)_{2} } \right]^{ - } \rightleftharpoons \left[ {{\text{Cr}}^{\text{III}} \left( {\text{DPA}} \right)\left( {\text{Mal}} \right)\left( {{\text{H}}_{2} {\text{O}}} \right)\left( {\text{OH}} \right)} \right]^{2 - } + {\text{H}}^{ + } \) and K 5 (1.87 mol?1 dm3) and K 6 (22.83 mol?1 dm3) represent the pre-equilibrium formation constants at 30 °C and I = 0.2 mol dm?3. Hexadecyltrimethylammonium bromide (CTAB) was found to enhance the reaction rate, whereas sodium dodecyl sulfate (SDS) had no effect. The thermodynamic activation parameters were estimated, and the oxidation is proposed to proceed via an inner-sphere mechanism involving the coordination of IO4 ? to Cr(III). 相似文献
3.
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
4.
K. S. Gupta R. K. Mehta A. K. Sharma P. K. Mudgal S. P. Bansal 《Transition Metal Chemistry》2008,33(7):809-817
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.
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.
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 × 103 L 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
(I) |
(II) |
(III) |
(IV) |
5.
The kinetics and mechanism of the reduction of enneamolybdonickelate(IV) by arsenite in aqueous acid solution was studied by spectrophotometry. The reaction rate increases with increasing concentrations of H+ and with temperature. The associated rate law is:
. The rate constants and activation parameters of the rate-determining step were evaluated. A mechanism related to this reaction was proposed. 相似文献
6.
The oxidation of H2NOH is first-order both in [NH3OH+] and [AuCl4
–]. The rate is increased by the increase in [Cl–] and decreased with increase in [H+]. The stoichiometry ratio, [NH3OH+]/[AuCl4
–], is 1. The mechanism consists of the following reactions.
The rate law deduced from the reactions (i)–(iv) is given by Equation (v) considering that [H+] K
a.
The reaction (iii) is a combination of the following reactions:
The activation parameters for the reactions (ii) and (iii) are consistent with an outer-sphere electron transfer mechanism. 相似文献
7.
The stoichiometries, kinetics and mechanism of the reduction of tetraoxoiodate(VII) ion, IO4
− to the corresponding trioxoiodate(V) ion, IO3
− by n-(2-hydroxylethyl)ethylenediaminetriacetatocobaltate(II) ion, [CoHEDTAOH2]− have been studied in aqueous media at 28 °C, I = 0.50 mol dm−3 (NaClO4) and [H+] = 7.0 × 10−3 mol dm−3. The reaction is first order in [Oxidant] and [Reductant], and the rate is inversely dependent on H+ concentration in the range 5.00 × 10−3 ≤ H+≤ 20.00 × 10−3 mol dm−3 studied. A plot of acid rate constant versus [H+]−1 was linear with intercept. The rate law for the reaction is:
- \frac[ \textCoHEDTAOH2 - ]\textdt = ( a + b[ \textH + ] - 1 )[ \textCoHEDTAOH2 - ][ \textIO4 - ] - {\frac{{\left[ {{\text{CoHEDTAOH}}_{2}^{ - } } \right]}}{{{\text{d}}t}}} = \left( {a + b\left[ {{\text{H}}^{ + } } \right]^{ - 1} } \right)\left[ {{\text{CoHEDTAOH}}_{2}^{ - } } \right]\left[ {{\text{IO}}_{4}^{ - } } \right] 相似文献
8.
The oxidation of aquaethylenediaminetetraacetatocobaltate(II) [Co(EDTA)(H2O)]−2 by N-bromosuccinimide (NBS) in aqueous solution has been studied spectrophotometrically over the pH 6.10–7.02 range at 25 °C.
The reaction is first-order with respect to complex and the oxidant, and it obeys the following rate law:
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