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  • 1990-1994  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of the reduction of dodecatungstocobaltate(III) by α-hydroxyacids in aqueous acid solution. Evidence for alkali metal ion catalysis (1991)
    Springer
    Transition metal chemistry 16 (1991), S. 160-164 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The kinetics of the redox reaction of dodecatungstocobaltate(III) [abbreviated as CoIIIW] with three α-hydroxy-carboxylic acids:e.g., mandelic, glycolic and lactic acid, were investigated in the 0–5.4 pH range where the complex remains stable and does not decompose. All reactions are first-order both in oxidant and reductant over the experimental pH range. A specific metal ion effect has been observed. Oxidations of the molecular form of the three acids and the anionic form of mandelic acid are catalysed by alkali metal ions and follow a general rate law: $$ - d[Co^{III} W]/dt = 2(k_s + k_c [M^ + ])[R][Co^{III} W]$$ where ks and kc account for the spontaneous and catalysed paths respectively, M+ is either an alkali metal ion (Li+, Na+ or K+) and [R], the reductant concentration. The oxidation of lactate and glycolate ions occurs only in the presence of alkali cations. The cation catalytic order: K+〉Na+〉Li+ observed in this study is in accord with the polarizability of the cations. An outer-sphere alkali cation-bridged mechanism is suggested for the electron transfer step.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01032824
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of the reaction oftrans-cyclohexane-1,2-diamine-N N N' N'-tetra-acetatomanganate(III) with substituted thioureas in aqueous medium (1991)
    Springer
    Transition metal chemistry 16 (1991), S. 355-357 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The kinetics of reduction of [MnIII(cydta)]− (where H4cydta=trans-cyclohexane-1,2-diamine-N N N' N'-tetraacetic acid) by some thiourea reductants have been studied in aqueous solution by stopped-flow techniques in the pH ranges 2.5–4.5 and 9.2–10.2. An initial increase in absorbance followed by a steady decrease indicated the formation of a precursor complex prior to the electron transfer step. The reactions are first order in both oxidant and reductant. The observed increase in rate in going from low to high pH is attributed to the difference in reactivities of the aqua and hydroxo species of the MnIII complex; the higher reactivity of the latter is consistent with the formation of a ligand-bridged activated species prior to electron transfer. The reactivity order for the thiourea derivatives follows the order of their reported substituent effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01024082
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of the oxidation of some cyclic and acyclic ketones by dodecatungstocobaltate(III) - A comparative study (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 22 (1990), S. 81-94 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of oxidation of cyclohexanone(chxn), 2-butanone(but), and 1,3-dihydroxy-2-propanone (dhp) have been investigated in aqueous acidic media. A first-order dependence in complex is obtained at high acid and low oxidant concentration for these ketones. However, a zero-order rate prevails at high oxidant and low acid concentration, and this rate has been shown to be the acid catalyzed enolization rate of the ketone. A general rate expression has been derived to explain these behaviors and plausible mechanism has been offered by assuming the enol as the reactive species.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550220107
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetics of electron transfer reactions of manganese (III) complexes of trans-cyclohexane-1,2-diamine,-NNN′N′-tetraacetic acid and 2,2′-bipyridyl with ascorbic acid in aqueous acid media (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 23 (1991), S. 105-112 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the reactions of manganese(III) complexes of trans-cyclohexane-1,2-diamine-NNN′N′-tetraacetic acid (H4cydta) and 2,2′-bipyridyl (bpy) have been investigated in the acid ranges [H+] = 1.00 ×10-5 - 3.16 × 10-3 M and [H+] = 0.10 - 1.00 M, respectively, at different temperatures and at a constant ionic strength. Both the molecular and mono-anionic forms of ascorbic acid have been found to be reactive in the experimental acid ranges. The monoanionic species has been found to be more reactive than the molecular form. Attempts have been made to correlate the kinetic results in terms of the Marcus relationship for outer-sphere electron transfer reaction. Differences between the calculated rates (k0.8) and experimental rates (k) by approximately four and seven orders of magnitude (k0.8≪ k) suggest an innersphere pathway for the reaction of Mn(cydta)(H2O)-. Inner-sphere reaction is also believed to be operative for the other reaction. The activation parameters have been evaluated and compared with other reported systems.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550230202
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    Paper (German National Licenses)
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