共查询到20条相似文献,搜索用时 15 毫秒
1.
Sarmistha Das Samirgopal Bhattacharya Rupendra Nath Banerjee Debabrata Banerjea 《Transition Metal Chemistry》1982,7(5):249-252
Summary The title complex aquates in acid media, first to [Co(mal)-(H2O)2(en)]+ (1) (Step 1) and subsequently to [Co(H2O)4(en)]3+
(2) (Step 2). Complex species (1) has been separated and characterised in solution. While Step 1 involves only a second-order acid catalysed path, Step 2 involves both a first-order acid independent path and a second-order acid catalysed path. The rate constants and activation parameters evaluated for these reaction paths have been compared with those for similar carboxylato-cobalt(III) complexes. This, together with an observed isokinetic relation, indicates that the rate-determining step involves opening of the unprotonated (in the spontaneous acid independent path) or the protonated (for the acid catalysed path) chelate ring of the malonate ligand and insignificant solvation of the central metal ion. 相似文献
2.
Abdullah S. Babaqi Mohamed T. Mohamed Salah S. Massoud Mohamed F. Amira 《Transition Metal Chemistry》1988,13(3):201-204
Summary The aquation of chloropentamminecobalt(III) ion has been studied in ethylene glycol-water mixtures up to 80% by weight at five temperatures from 35 to 55°C. Specific solvent effects on the reaction rate and mechanism have been investigated and discussed. The validity of our previously proposed equations, correlating the specific reaction rate with the dielectric constant of the medium has been examined. The thermodynamic parameters of activation have been calculated and presented as evidence for the solvation effects and in support of the proposed reaction mechanism. 相似文献
3.
The rates of formation of penta-ammineglycinecobalt(III) ion from aquopenta-amminecobalt(III) ion and glycine in acidic media have been studied spectrophotometrically at different glycine concentration and different pH in the range of 50–70°C. The ΔH≠ and ΔSz≠ values are 27.6 kcal mole?1 and +5.2 e. u. respectively, and increase in ionic strength causes only a slight acceleration of the rate. The results are consistent with a mechanism involving outer-sphere association between the aquopenta-amminecobalt(III) complex and glycine, followed by its transformation into the product by an essentially dissociative process in which rupture of the Co(III)? OH2 bond is primarily important in the transition state (SN1IP mechanism). 相似文献
4.
Gehan M. El-Subruiti Salah S. Massoud Aziza K. Chehata 《Transition Metal Chemistry》1996,21(5):437-441
Summary The trans-[Co(meen)2Cl2]Cl complex was prepared and characterized by elemental analysis, and u.v.-vis. and i.r. spectroscopies. The kinetics of the
primary aquation of trans-[Co(meen)2Cl2]+ in H2O and H2O-MeOH have been investigated over a wide range of solvent compositions and temperatures (45–60 °C). Plots of rate constants
(log k) versus the reciprocal of the dielectric constant of the medium (D
infs
sup−1
) and Grunwald-Winstein values of the solvent (Y) were non-linear. The variation of enthalpies (ΔH
*) and entropies (ΔS
*) of activation with solvent composition have been determined. Plots of ΔH
* or ΔS
*
versus the mole fraction of the solvent exhibit a maximum at x
2 ca. 0.1 and a minimum of x
2 ca. 0.3; a linear plot of ΔH
*
versus ΔS
* is obtained. Furthermore, the cycle relating the free energy of activation in H2O to that in H2O-MeOH shows that changes in the solvent structure in H2O-MeOH mixtures generally stabilize the five-coordinate cation in the transition state, more than the cation in the initial
state as the mole fraction of MeOH increases. The results are discussed and compared with other related systems. 相似文献
5.
6.
7.
The kinetics of the aquation of (H2O)5Cr(O2CCCl3)2+ have been examined at 35–55°C and 1.00M ionic strength with [H+] = 0.01?1.00M. The reaction follows the rate equation -d ln [Crtotal]/dt = (a[H+]?1 + b + c[H+])/(1 + d[H+]), where [Crtotal] is the stoichiometric concentration of the complex. At 45°C a = (1.41 ± 0.03) × 10?7M/s, b = (1.66 ± 0.02) × 10?5 s?1, c = (7.0 ± 0.8) × 10?5M?1·S?1 and d = 2.3 ± 0.3M?1. Two mechanisms consistent with this rate law are discussed, with evidence being presented in favor of an ester hydrolysis mechanism involving steady-state intermediates. Equilibrium and activation parameters were determined. 相似文献
8.
《Journal of Inorganic and Nuclear Chemistry》1976,28(7):1313-1315
The kinetics of dissociation of oxalatobis(phenanthroline)cobalt(III) ion into cis-diaquobis(phenanthroline)cobalt(III) ion in aqueous HClKCl media have been studied. The rate is first-order with respect to acid concentration (1–2 M) with a specific rate constant, kH = 6.2 × 10−4M−1min−1 at 75°C (μ, 2 M); ΔH≠ and ΔS≠ values are 22.1 kcal mole−1 and −18.7 e.u., respectively. The magnitude of the ΔS≠ value appears consistent with a dissociation mechanism involving reaction of the conjugate acid form of the complex (SN 1CA mechanism). 相似文献
9.
The chromium(III)-quinolinato complexes, [Cr(quinH)3]0, [Cr(quinH)2(H2O)2]+ and [Cr(quinH)(H2O)4]2+ (where quinH = N,O-bonded quinolinic acid anion), were obtained and characterized in solution. The tris-quinolinato complex
undergoes acid-catalyzed aquation to give the diaqua-product, whereas subsequent ligand liberation processes are exceptionally
slow. Kinetics of the aquation were studied spectrophotometrically over the 0.1–1.0 M HClO4 range, at I = 1.0 M. The first aquation stage, the chelate-ring opening at the Cr-N bond, is much faster than the second one. The following rate
laws were established: k
obs = k
1 + k
−1/Q
1[H+] and k
obs = k
2
Q
2[H+]/(1 + Q
2[H+]), where k
1 and k
2 are the rate constants for the chelate-ring opening and the ligand liberation, respectively, k
−1 is the rate constant of the chelate-ring closure, Q
1 and Q
2 are the protonation constants of the pyridine nitrogen and 3-carboxylate group in the one-end bonded intermediate, respectively.
Kinetic parameters have been determined and the mechanism has been discussed. 相似文献
10.
Summary The aquation ofcis-[(en)2Co(CO2H)2]+ tocis-[(en)2Co(OH2)(CO2H)]2+ is catalysed by Cu2+ and the rate equation, –d[complex]t/dt=(kCu[Cu2+]+kH [H+]) [complex)T is valid at [Cu2+]T=0.01–0.1, I=0.5 and [HClO4]=0.005 mol dm–3. The rate measurements are reported at 30, 35, 40 and 45°C and the rate and activation parameters for the Cu2+ and H+-catalysed paths are: kH(35°C)=(2.44±0.09)×10–2 dm3 mol–1 s–1, H=83±13 kJ mol–1, S=–8±42 JK–1 mol–1, k
Cu
(35°C)=(3.30±0.09)×10–3 dm3 mol–1 s–1, H=73.2±6.1 kJ mol–1, S=–55±20 JK–1 mol–1. The formate-bridged innersphere binuclear complex,cis-[(en)2Co{(O2CH)2Cu}]3+ may be involved as the catalytically active intermediate in the copper(II)-catalysed path, just as the corresponding H+-bridged species presumed to be present in the acidcatalysed path. 相似文献
11.
Kinetics of aquation ofcis- andtrans-[Co(en)2NO2Cl]+ were investigated in aqueous mixtures of MeOH, EtOH,i-PrOH andt-BuOH at 298.1 K. The values of transfer functions corresponding to the transfer of reactant and activated complex from H2O to the solvent mixtures were calculated from kinetic measurements and from solubilities of the complex salt. The results
of the analysis of solvent effect are discussed in terms of D and Id mechanisms.
TMC 2676 相似文献
12.
Subrata Mukhopadhyay Shibnath Kundu Rupendranath Banerjee 《Journal of Chemical Sciences》1995,107(4):403-410
In acidic aqueous media the complex [AgIIILL−)3+[L = ethylenebis (bi-guanide)] reacts quantitatively with oxalic acid and bioxalate ion to produce CO2, Ag+ and L. Kinetic evidence indicates preequilibrium adduct formation, but the reactions appear to be outer-sphere with these
adducts (I1 and I2) acting as kinetic dead ends.No Ag+ catalysis could be detected. 相似文献
13.
Summary The aquation of pentaammine (substituted salicylato) cobalt(III) complexes [(NH3)5CoO2CC6H3(X)OH]2+,X = 5-SO3, 5-Br, 5-NO2, and 3-NO2 in the presence of ferric ion was studied spectrophotometrically in the 65°–80° range. Ferric ion catalyses the aquation of the substratesvia formation of a reactive binuclear species.Reprints of this article are not available. 相似文献
14.
15.
The kinetics of oxidation of pectin polysaccharide as a natural polymer by permanganate ion in aqueous perchloric acid at a constant ionic strength of 2.0 mol dm−3 has been investigated spectrophotometrically. The reaction time curves showed two distinct stages, the initial stage was relatively slow, followed by an increase in the rate of oxidation at longer times. The results of the initial rates reveal first-order kinetics in permanganate ion and fractional-order with respect to pectin concentration. Kinetic evidence for the formation of an intermediate complex between the polysaccharide and the oxidant is presented. The results obtained at various hydrogen ion concentrations showed that the reaction is acid catalyzed. The added salts lead to the prediction that Mn4+ and/or Mn3+ play an important role in the autoaccleration period kinetics. A tentative reaction mechanism consistent with the kinetic results is discussed. 相似文献
16.
Shawky A. El-Shazly Abdalla A. S. Babaqi Mohamed T. Mohamed Amal A. Zaghlol Mohamed F. Amira 《Transition Metal Chemistry》1991,16(5):488-491
Summary The aquation kinetics of the chloropenta-aminecobalt(III) ion in H2O–EtOH mixtures have been determined. A new correlation is described for calculating the chemical potential from kinetic data and molar thermodynamic excess functions for binary mixtures. The rate constants correlate well with Grunwald-Winstein solvating power Y parameter and with the dielectric constant of the medium. The data supports the D mechanism. 相似文献
17.
The kinetics of oxidation of several substituted quinols by a series of Tris(1,10-phenanthroline)iron(III) complexes has been investigated with a stopped-flow technique at 6.0 and 20.0°C. The reactions were found to be first order on both reactants and independent of acidity. The second-order specific rate constants were strongly dependent on free energy of reaction. An interpretation of the mechanism in the light of Marcus theory has been developed. The first electron abstraction with semiquinone radical formation has been suggested as the rate-determining step, and on this basis, intrinsic parameters of the reactions have been derived. A good agreement was found between experimental and computed data. 相似文献
18.
《Journal of Inorganic and Nuclear Chemistry》1981,43(12):3253-3256
The presence of the unsymmetrical glycinato chelate in this complex, makes the positions of the two biguanides non-equivalent. Thus the acid-catalyzed dissociation of one or other of them, gives two different isomeric (α- and β-) diaquo- products. Up to ∼50°C, the dissociation of only one biguanide takes place with the formation of the α- diaquo product. The α- diaquo form isomerizes to the β- form at higher temperature. Direct formation of the β- form does not take place at any stage of the reaction. Aquation of the bis(biguanide) complex follows a dissociative pathway up to ∼50°C, above which it becomes a complicated one. Isomerization of the α- product takes place intramolecularly by two paths, one dependent and the other independent of acid concentration. Both the isomerization paths involve “bond-rupture” processes. 相似文献
19.
Summary In acid perchlorate media, the title complex undergoes intramolecular redox decomposition generating ultimately Ag+ ion and oxidation products of the ligand. The reaction follows a simple first-order process, and the observed pseudo-first-order rate constant is given by kobs=k0+kKa/[H+] where Ka is the deprotonation constant of the parent complex; pKa is approximately 5.9 at 30°. The values of 105 k0(s–1) and 107 kKa (Ms–1) at 30°, I=1.0 M, are 9.3±0.1 and 11.8±1.3; corresponding H (kJ/mol), S (JK–1 M–1) values are 105±0.5, 23±1 and 79±8,-96±5, respectively. The results are compared with those for similar reaction of (ethylenebisbiguanide)silver(III) and effect of change in ligand structure on kinetic behaviours of these complexes is discussed. 相似文献