Mechanistic Information on the Aquations of Complexes of the Pentaamminecobalt(III) Series from Kinetic Studies at High Pressures

Jones, W. E.; Carey, L. R.; Swaddle, Thomas W.

doi:10.1139/v72-440

Cited by 78 publications

(40 citation statements)

References 16 publications

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“…radicals and complex species of Fez+ would be generated. Although this kind of rupture is unusual, a few references were found in the literature involving complexes of cobalt, chromium, and others (28)(29)(30)(31)(32)(33)(34); it was also found in the decomposition of hexacyanomanganate(II1) and hexacyanomanganato(1V) ions in aqueous acid media (35,36). However, the best proof was recently supplied (37): potassium ferricyanide is slowly reduced under dry air atmosphere, forming cyanogen and ferricyanide in small amounts, according to reactions [8] Rhodes' test (38) for the detection of cyanogen was negative,' which means that CN.…”

Section: 13mentioning

confidence: 92%

Acid–base behaviour of the ferricyanide ion in perchloric acid media. Spectrophotometric and kinetic study

Domingo¹,

Garcı́a²,

Leal³

1990

Can. J. Chem.

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A wide study was carried out of the acid-base behaviour of ferricyanide ions in aqueous perchloric acid media in the range 0.1-1 1.5 M. 'This study shows that protonation and decomposition of the ferricyanide ions occur simultaneously. The three successive protonation equilibria were found in the acidity ranges 0.1-4.0, 3.5-8.5, and 7.0-11.5 M HC104, respectively. A kinetic study was also made of the decomposition reaction at 60°C. The kinetic data are explained by considering a reaction mechanism involving homolytic and heterolytic dissociation steps. The homolytic and heterolytic rate constants corresponding to each of the four protonated species were determined, along with the acid-base protonation constants, pK1 = -6.25 + 0.10; pK2 = -3.23 * 0.03; and pK3 = -0.60 2 0.02. Mots clis : comportement acide-base, espkces protonks, dtcomposition, dissociation homolytique, dissociation hCtCrolytique.[Traduit par la revue] Introduction In a previous paper, the acid-base behaviour of the ferrocyanide ion in perchloric acid media was studied by potentiometry and spectrophotometry ( 1). In this paper, the corresponding acid-base investigation of the ferricyanide ion is undertaken; this study, however, involves also kinetic measurements, since femcyanide ions decompose at high acid concentrations.The potentiometric titration of a sample of 0.01 N K3Fe(CN)6 with aqueous HCl shows no evidence of protonation; the curve coincides with that obtained in the titration of a blank solution containing pure water, this fact indicating that the three ionization constants of ferricyanic acid, H3Fe(CN)6, are higher than 0.1 (2,3). On the other hand, the titration curves of a sample of 0.01 M H3Fe(CN)6 with NaOH, obtained by potentiometric and conductimetric techniques, are identical to those achieved titrating 0.03 M HC1. Thus the three constants must be quite high (4). None of the three pK values was found in the literature; however, to be able to explain the effect of acidity on the rate constant, several contributions on the oxidation of organic substrates by femcyanide in acid media (5-1 1) suggest that the first protonation occurs in the range 0.1-3.8 M HC104.

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Section: 13mentioning

confidence: 92%

Acid–base behaviour of the ferricyanide ion in perchloric acid media. Spectrophotometric and kinetic study

Domingo¹,

Garcı́a²,

Leal³

1990

Can. J. Chem.

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“…The mechanism of substitution on this Co(II1) complex is presumed to proceed through a dissociative interchange mechanism (15,16).…”

Section: Discussionmentioning

confidence: 99%

The Kinetic Activation Volumes for the Binding of Iodide to Cobalamin (Vitamin B₁₂) Studied on a High Pressure Laser Temperature Jump Apparatus

Hasinoff¹

1974

Can. J. Chem.

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The relaxation kinetics of the reaction of iodide with cobalamin (vitamin B12) were studied on a high pressure laser temperature jump apparatus in aqueous solution at 25" and ionic strength 0.2 M . Analysis of the pressure dependence of the formation and dissociation rate constants gave their respective volumes of activation to be: ~V I * = 5.5 * 0.8 cm"ol-' and IV,,:': = 11.5 f 1.6 cm:' mol-'. The positive activation volume for formation of the complex, A V , * , after appropriate correction for the volume change due to formation of an outer sphere complex, is consistent with a dissociative type mechanism in which the metal ion -water bond is stretched in the activated complex. IntroductionThe macrocyclic corrin compound confers unusual properties to the ligand substitution kinetics of the Co(II1) derivative. For example, the second order rate constant for ligand substitution is about lo7 faster on cobalamin (vitamin B,,) than on other simple Co(II1) compounds (1). Previous work has measured the kinetics of the reaction of cobalamin with N3-, OCN-, and SCN-(2, 3) as well as more recently the kinetics and activation parameters for I-, S, and SO,5).The benzimidazole side chain on cobalamin coordinates with the Co3+ in one of the axial positions preventing formation of 2 : 1 complexes with small ligands; this is often a complicating factor in studying the ligand substitution kinetics on other metal ion macrocyclic complexes such as porphyrins (1).By measuring the influence of pressure on the rate constant of a reaction,

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“…It has long been recognized that the solvolysis reactions of Co(III) complexes [25,26], proceed via the Id mechanism [27,28] involving the rate-determining loss of the halide ion according to the following equations:…”

Section: Variation Of Free Energy Of Transfer With Solvent Compositionmentioning

confidence: 99%

Studies on ion-pairing effects of the kinetics of aquation of bromopentaammine cobalt(III) complex in malonate media

2011

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Mechanistic Information on the Aquations of Complexes of the Pentaamminecobalt(III) Series from Kinetic Studies at High Pressures

Cited by 78 publications

References 16 publications

Acid–base behaviour of the ferricyanide ion in perchloric acid media. Spectrophotometric and kinetic study

Acid–base behaviour of the ferricyanide ion in perchloric acid media. Spectrophotometric and kinetic study

The Kinetic Activation Volumes for the Binding of Iodide to Cobalamin (Vitamin B₁₂) Studied on a High Pressure Laser Temperature Jump Apparatus

Studies on ion-pairing effects of the kinetics of aquation of bromopentaammine cobalt(III) complex in malonate media

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Mechanistic Information on the Aquations of Complexes of the Pentaamminecobalt(III) Series from Kinetic Studies at High Pressures

Cited by 78 publications

References 16 publications

Acid–base behaviour of the ferricyanide ion in perchloric acid media. Spectrophotometric and kinetic study

Acid–base behaviour of the ferricyanide ion in perchloric acid media. Spectrophotometric and kinetic study

The Kinetic Activation Volumes for the Binding of Iodide to Cobalamin (Vitamin B12) Studied on a High Pressure Laser Temperature Jump Apparatus

Studies on ion-pairing effects of the kinetics of aquation of bromopentaammine cobalt(III) complex in malonate media

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The Kinetic Activation Volumes for the Binding of Iodide to Cobalamin (Vitamin B₁₂) Studied on a High Pressure Laser Temperature Jump Apparatus