共查询到20条相似文献,搜索用时 31 毫秒
1.
P. Vani K. Krishna Kishore R. Rambabu L. S. A. Dikshitulu 《Journal of Chemical Sciences》2001,113(4):351-359
Kinetics and mechanism of oxidation of L-methionine by iron(III)-1,10-phenanthroline complex have been studied in perchloric
acid medium. The reaction is first order each in iron(III) and methionine. Increase in [phenanthroline] increases the rate
while increase in [HClO4] decreases it. While the reactive species of the substrate is the zwitterionic form, that of the oxidant is [Fe(phen)2(H2O)2]3+. The proposed mechanism leads to the rate law
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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.
The kinetics of oxidation of cis-[CrIII(gly)2(H2O)2]+ (gly = glycinate) by $ {\text{IO}}_{ 4}^{ - } $ has been studied in aqueous solutions. The reaction is first order in the chromium(III) complex concentration. The pseudo-first-order rate constant, k obs, showed a small change with increasing $ \left[ {{\text{IO}}_{ 4}^{ - } } \right] $ . The pseudo-first-order rate constant, k obs, increased with increasing pH, indicating that the hydroxo form of the chromium(III) complex is the reactive species. The reaction has been found to obey the following rate law: $ {\text{Rate}} = 2k^{\text{et}} K_{ 3} K_{ 4} \left[ {{\text{Cr}}\left( {\text{III}} \right)} \right]_{t} \left[ {{\text{IO}}_{ 4}^{ - } } \right]/\left\{ {\left[ {{\text{H}}^{ + } } \right] + K_{ 3} + K_{ 3} K_{ 4} \left[ {{\text{IO}}_{ 4}^{ - } } \right]} \right\} $ . Values of the intramolecular electron transfer constant, k et, the first deprotonation constant of cis-[CrIII(gly)2(H2O)2]+, K 3 and the equilibrium formation constant between cis-[CrIII(gly)2(H2O)(OH)] and $ {\text{IO}}_{ 4}^{ - } $ , K 4, have been determined. An inner-sphere mechanism has been proposed for the oxidation process. The thermodynamic activation parameters of the processes involved are reported. 相似文献
4.
The kinetics of oxidation of [FeII(phen)2(H2O)2]2+ (phen = 1,10-phenanthroline) by periodate were investigated in aqueous acidic medium at different [H+] over a temperature range of 20–40 °C. The reaction was studied under pseudo-first-order conditions by taking [IO 4 ? ] > tenfold over [FeII(phen)2(H2O) 2 2+ ]. The reaction rate increases with increasing [H+], and the kinetics of oxidation obeyed the following rate law:The surfactant sodium dodecyl sulfate was found to enhance the rate, whereas cetyltrimethylammonium bromide had little effect. Activation parameters associated with k 2 and k 3 were calculated. An electron transfer from Fe(II) to I(VII) is identified as the rate-determining step. The I(VI) species thus generated reacts in a fast step with another Fe(II) complex.
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$$ {\text{Rate}} = \left[ {{\text{Fe}}^{\text{II}} ({\text{phen}})_2({\text{H}}_{2} {\text{O}})_{2}^{2 + } } \right]\left[ {{\text{IO}}_{4}^{ - } } \right]\left\{ {k_{4} K_{2} + k_{5} K_{1} K_{3} [{\text{H}}^{ + } ]} \right\} $$
5.
Garimella Visweswara Rao Rajesh Bellam Nageswra Rao Anipindi 《Transition Metal Chemistry》2012,37(2):189-196
The substitution of bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II),
\textFe(TPTZ) 2 2 + {\text{Fe(TPTZ)}}_{ 2}^{{ 2 { + }}} by 2,2′,6,2″-terpyridine (terpy) occurs on a time scale of about 6 m. The kinetics of this reaction was followed by stopped-flow
spectrophotometry in the pH range of 3.6–5.6 in acetate buffer. The data indicate that the reaction occurs in two consecutive
steps: kinetic data for both steps were acquired simultaneously and analyzed independently. The first step is assigned to
the reaction between
\textFe(TPTZ) 2 2 + {\text{Fe(TPTZ)}}_{ 2}^{{ 2 { + }}} and terpy to give Fe(TPTZ)(terpy)2+, followed by its reaction with another terpy molecule to give the final product,
\textFe(terpy) 2 2 + {\text{Fe(terpy)}}_{ 2}^{{ 2 { + }}} . The rate of the reaction increases with increases in [terpy] and pH. The kinetic and activation parameters determined for
both steps suggest that they involve both associative and dissociative paths. The ternary complex Fe(TPTZ)(terpy)2+ has been prepared, and the kinetics of its reaction with terpy suggest that this reaction is identical with the second step
of the
\textFe(TPTZ) 2 2 + {\text{Fe(TPTZ)}}_{ 2}^{{ 2 { + }}} -terpy system, supporting the proposed mechanism. 相似文献
6.
The kinetics of electron transfer from mannitol to hexacyanoferrate(III), catalyzed by osmium(VIII), has been studied in alkaline medium. The substrate order is complex, whereas it is one with respect to the catalyst. The rate is independent of the concentration of oxidant. Also, the rate increases with increasing concentration of hydroxide ion in a complex manner. A kinetic rate law corresponding to the proposed mechanism has been suggested as follows:
where [Mtol] is for mannitol. The kinetic parameters have been evaluated and the value of K1 is in agreement with the value determined spectrophotometrically. 相似文献
7.
Ahmed A. Abdel-Khalek Said M. Sayyah Fadia F. Abdel-Hameed 《Transition Metal Chemistry》1994,19(1):108-110
A novel chromium(III) complex of tetraoxalylurea was prepared. In aqueous solutions, [CrIII(H2L)(H2O)]+ (H2L = diprotonated tetraoxalylurea) is oxidized by IO
4
–
according to the rate law
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8.
The kinetics of anation of chromium(III) species, [Cr(H2O)6]3+ and [Cr(H2O)5OH]2+, by DL-methionine have been studied spectrophotometrically. Effects of varying [methionine]T, [H+], and temperature were investigated. The results are in accord with a mechanism involving a fast 11 outer-sphere association between chromium(III) species and amino acid zwitterion, followed by transformation of the outer-into inner-sphere complex by slow interchange. The rate law consistent with the mechanism is as follows:
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