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1.
The kinetics of oxidation of Fe2+ by [Co(C3H2O4)3]3? in acidic solutions at 605 nm showed a simple first-order dependence in each reactant concentration. The second-order rate constant dependence on [H+] is in accordance with eqn (i) k2 = k′2 + k3[H+] (i) where k′2 and k3 have values of 73.4 ± 14.0 M ?1 s?1 and 353 ± 41 M?2 s?1, respectively, at 1.0 M ionic strength (NaClO4) and 25°C. At 310 nm the formation and decomposition of an intermediate, believed to be [FeC3H2O4]+, was observed. The increase in the rate of oxidation with increasing [H+] was interpreted in terms of a “one-ended” dissociation mechanism which facilitates chelation of Fe2+ by the carbonyl oxygens of malonate in the transition state. 相似文献
2.
Summary The copper(III)-imine-oxime complexes [CuIII(Enio)]+ and [CuIII(Pre)]+ {EnioH2 =N,N-ethylene bis(isonitrosoacetylacetoneimine) and PreH2 = N,N-propylene bis (isonitrosoacetylacetoneimine)} react very rapidly with iodide. The rate law under fixed conditions for the reaction is given by the equation: –d[CuIII]/dt = (2k2[I–] + 2k3[I–]2)[CuIII] The [CuIII(Enio)]+ reaction was pH-independent whereas the [Cu (Pre)]+ reaction rate increased with increasing pH. Both the k2 and the k3 pathways are believed to involve one-electron transfer. An inner-sphere mechanism may operate in the pathway, first-order in [I–]. 相似文献
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Biphasic Oxidation of cis‐Diaquabis(1,10‐phenanthroline)chromium(III) by N‐Bromosuccinimide and the Formation of Chromium(IV) and Chromium(V)
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The oxidation of cis‐diaquabis(1,10‐phenanthroline)chromium(III) [cis‐CrIII(phen)2(H2O)2]3+ by ‐bromosuccinimide (NBS) to yield cis‐dioxobis(1,10‐phenanthroline)chromium(V) has been studied spectrophotometrically in the pH 1.57–3.56 and 5.68–6.68 ranges at 25.0°C. The reaction displayed biphasic kinetics at pH < 4.0 and a simple first order at the pH > 5.0. In the low pH range, the reaction proceeds by two successive steps; the first faster step corresponds to the oxidation of Cr(III) to Cr(IV), and the second slower one corresponds to the oxidation of Cr(IV) to Cr(V), the final product of the reaction. The formation of both Cr(IV) and Cr(V) has been detected by electron spin resonance (ESR). The ESR clearly showed the formation and decay of Cr(IV) as well as the formation of Cr(V). Each oxidation process exhibited a first‐order dependence on the initial [Cr(III)]. The pseudo–first‐order rate constants k34 and k45, for the faster and slower steps, respectively, were obtained by a computer program using Origin7.0. Both rate constants showed first‐order dependence on [NBS] and increased with increasing pH. 相似文献
5.
The kinetics of oxidation of [CrIIIcdta(H2O)]? and [CrIIIdtpa(H2O)]2? (where cdta = trans‐1,2‐diaminocyclohexane‐N,N,N′,N′‐tetraacetate and dtpa = diethylenetriaminepentaacetate) by periodate ion has been studied in aqueous solutions. The oxidation of these complexes was carried out in the pH range 5.52–7.44 for the [CrIIIcdta(H2O)]? complex and the pH range 5.56–8.56 for the [CrIIIdtpa(H2O)]2? complex. The reaction exhibited an uncommon second‐order dependence on [CrIIIL(H2O)]n (L = cdta or dtpa and n=?1 or ?2, respectively) and a first‐order dependence on [IO?4]. At fixed reaction conditions, the reaction rate is described by Eq. (i). The third‐order rate constant, k3, varied with [H+] according to Eq. (ii). (i) (ii) A mechanism in which simultaneous one‐electron transfer from two [CrIIIL(OH)]n?1 ions to I(VII) is proposed. The two [CrIIIL(OH)]n?1 ions are bridged to I(VII) via the hydroxo group. Periodate ion is known to undergo rapid substitution or expansion of its coordination number from four to six. The activation parameters ΔH* and ΔS* were calculated using the Eyring equation. The relatively high negative values of ΔS* are consistent with an associative process preceding electron transfer. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 729–735, 2012 相似文献
6.
The kinetics of oxidation of cis-[CrIII(ox)2(H2O)2]– (ox = C2O4
2–) by IO4
– showed a first-order dependence on the initial CrIII complex concentration in the presence of a vast excess of [IO4
–]. The dependence of the pseudo-first-order rate constant on [IO4
–] is complex and is consistent with the formation of a precursor complex. It is proposed that this complex is formed through the coordination of the two carbonyl oxygens of the ox ligand with the IO4
– ion, forming a cyclic intermediate. The kinetics are consistent with the hydroxo form of the CrIII complex being the reactive species, whereas the aqua species forms an unreactive complex. 相似文献
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Copper(III) complexes stabilized by tetradentate imine–oxime ligands were characterized by elemental analysis, cyclic voltammetry, u.v.–visible, and e.s.r. spectra. Electrode potentials of copper(III/II) couples having five-, six-, five-membered chelate rings are pH-dependent. Copper(III/II) couples with five-, five-, five-membered chelate rings were independent of pH. The magnitude of E
1/2
0 is affected by both the size and electron-donor ability of substituent groups. 相似文献
9.
Summary The kinetics of oxidation of [CoII(phen)3]2+ (phen = 1,10-phenanthroline) by copper(III) imine-oxime complexes are first-order in each reactant. All reactions proceed via two parallel pathways; one pH independent, the other pH dependent. The second-order rate constant varies with [H+] as k2 = k
inf2
supo
+ k
inf2
supH
[H+]. The rapidity of the electron transfer step, coupled with the relative inertness of [CoII(phen)3]2+ over the pH range studied and the absence of a bridging atom on the phen ligand, supports an outer-sphere mechanism for this process. Reasonably good agreement between the experimental rate constants and those calculated using the Marcus equation has been obtained. 相似文献
10.
Two tridentate imine–oxime–amine ligands have been synthesized and their corresponding copper(II) complexes have been isolated. These copper(II) complexes are readily oxidized both chemically and electrochemically to give relatively stable copper(III) complexes. In the pH range 1.5–3.0 the electron transfer process is electrochemically reversible with ΔEp = 60 mV and ipa/ipc ∼ 1. Plots of E1/2 versus pH are linear with a slope = −60 indicating the involvement of one proton in the electron transfer process. Aqueous solutions of copper(III) complexes have high molar absorption at λmax with ε > 104 M−1 cm−1. Solid samples of the complexes are diamagnetic consistent with a d8 square planar geometry. It seems that only imine–oxime nitrogens are coordinated to copper(II) with the NH2 group being free as indicated by i.r. spectra. Substitution of a –CH3 group on the carbon atom adjacent to the oxime group by the more electron donating group –CH(CH3)2 lowers electrode potential by more than 90 mV. This is consistent with an earlier observation that electron-donating substituents on the carbon atom adjacent to the oxime group lower the potential of CuIII/CuII couples and stabilize the higher oxidation state. 相似文献