The trans effect in cobalt(III) complexes. Kinetics and mechanism of substitution of cobalt(III) sulphito complexes

1978 ◽  
Vol 31 (3) ◽  
pp. 561 ◽  
Author(s):  
JK Yandell ◽  
LA Tomlins
Keyword(s):  
Ionic Strength ◽  
Water Molecule ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Ion Concentration ◽  
Nitrite Ion ◽  
Hydrogen Ion Concentration ◽  
Thiocyanate Ion ◽  
Order Rate ◽  
Incoming Ligand

Equilibrium constants K and rate constants kf have been measured, at 25°C and ionic strength of 1.0, for the substitution of the labile water molecule in trans-[aquabis(ethylenediamine)sulphito-cobalt(III)] ion by thiosulphate ion (K = 1.8×102 mol-1 1., kf = 1.27×103 mol-1 1. s-1), thiocyanate ion (2.5×103, 2.75×102), nitrite ion (1.0×103, 2.06×102), azide ion (2.9×102, 2.4×102) ferricyanide ion (-, 1.72×103), hydrogen azide (< 1.2,1.4×10), ammonia (3.0, 6.7) and imidazole (2.6×102, 5.2). ��� The correlation of these rate constants with charge on the incoming ligand, as well as a decrease in the apparent second-order rate constants observed at high concentrations of the anionic ligands, requires a rapid outer-sphere pre-equilibrium step followed by a rate- determining dissociative interchange of the incoming ligand with the bound water molecule. The activation energy of the thiocyanate substitution was found to be 48 kJ mol-1. Aquation of cis- [azidobis(ethylenediamine)-sulphitocobalt(III)] ion, in the range of hydrogen ion concentration between 10-2 and 0.2 M, was found to give the trans-aquasulphito complex with a first-order rate constant consistent with the equation ��������������������������� k = 4.9×10-4[H+]+1.0×10-5 s-1 at 25°C and ionic strength 1.0.

ION PAIR EFFECTS IN THE REACTION BETWEEN POTASSIUM FERROCYANIDE AND POTASSIUM PERSULFATE

1966 ◽  
Vol 44 (4) ◽  
pp. 437-445 ◽  
Author(s):  
R. W. Chlebek ◽  
M. W. Lister
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Ion Pairs ◽  
Ion Pair ◽  
Glass Electrode ◽  
Potassium Ferrocyanide ◽  
Potassium Persulfate ◽  
Ion Concentration ◽  
True Rate

The rate of the reaction between potassium ferrocyanide and potassium persulfate has been measured over a range of conditions. The rate is dependent on the potassium ion concentration, and it is shown that this is explained if it is assumed that KFe(CN)63− and KS2O8− are the reacting species. The equilibrium constants governing the formation of these ion pairs were measured with a cation-sensitive glass electrode. Similar constants for the products KFeCCN6)2− and KSO4−, and also for KNO3, were measured. From these equilibrium constants, the true rate constants of the reaction can be obtained, and it is shown that these vary with ionic strength in the manner predicted by Brönsted's equation.

Mechanistic Information from the Effect of Pressure on the Kinetics of Hydrolysis of Iodopentaaquochromium(III) Ion

1975 ◽  
Vol 53 (24) ◽  
pp. 3697-3701 ◽  
Author(s):  
Milton Cornelius Weekes ◽  
Thomas Wilson Swaddle
Keyword(s):  
Ionic Strength ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
Kinetics Of Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Aqueous Hclo ◽  
Conjugate Base

The rate of hydrolysis of iodopentaaquochromium(III) ion has been measured as a function of pressure (0.1 to 250 MPa) and hydrogen ion concentration (0.1 to 1.0 mol kg−1) at 298.2 K and ionic strength 1.0 mol kg−1 (aqueous HClO4–LiClO4). The volumes of activation for the acid independent and inversely acid dependent hydrolysis pathways are −5.4 ± 0.5 and −1.6 ± 0.3 cm3 mol−1 respectively, and are not detectably pressure-dependent. Consideration of these values, together with the molar volume change of −3.3 ± 0.3 cm3 mol−1 determined dilatometrically for the completed hydrolysis reaction, indicates that the mechanisms of the two pathways are associative interchange (Ia) and dissociative conjugate base (Dcb) respectively.

Hydrogen exchange studies. XIV. Kinetics and mechanism of base-catalyzed hydrogen exchange in 1,3-dinitrobenzene in aqueous dimethylformamide and relationship with σ-complex formation

1981 ◽  
Vol 59 (22) ◽  
pp. 3177-3187 ◽  
Author(s):  
Erwin Buncel ◽  
Allen W. Zabel
Keyword(s):  
Complex Formation ◽  
Rate Constants ◽  
Hydrogen Exchange ◽  
Equilibrium Constants ◽  
Medium Composition ◽  
Proton Exchange ◽  
Ion Concentrations ◽  
First Order ◽  
Order Rate ◽  
Insight Into

Kinetic data have been evaluated for hydrogen exchange in 1,3-dinitrobenzene (DNB), occurring at the 2-position, in dimethylformamide (DMF) – D2O mixtures containing deuteroxide ion. The pseudo first order rate constants for exchange, kobs, show inverse dependence on the initial DNB concentration, which can be quantitatively related to the extent of σ-complex formation in these systems. The profile for kobs as function of medium composition exhibits a maximum at ca. 70 mol% DMF, and εapp for σ-complex formation reaches a plateau at about the same medium composition. The equilibrium constants for σ-complex formation, Ke, are used to calculate the free, or uncomplexed, deuteroxide ion concentrations, which then allow one to calculate k2, the second order rate constants for exchange. The k2 values show a uniformly increasing tendency with increased DMF content. Correlations with medium basicity are examined, and the nature of the log k2 and log Ke vs. H− plots afford insight into the origin of the medium dependence of proton exchange. The results of the present study are consistent with the σ-complex being an unreactive form of the substrate towards exchange, which occurs via uncomplexed DNB present in small concentration. The study also rules out the possibility that the colored species present in these systems is the carbanion formed on deprotonation of DNB.

The retroaldol reaction of chalcone

1983 ◽  
Vol 61 (11) ◽  
pp. 2621-2626 ◽  
Author(s):  
J. Peter Guthrie ◽  
John Cossar ◽  
Patricia A. Cullimore ◽  
Nayyer Monshizadeh Kamkar ◽  
Kathleen F. Taylor
Keyword(s):  
Ionic Strength ◽  
Sodium Hydroxide ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Aqueous Sodium Hydroxide ◽  
Adduct Formation ◽  
Aqueous Sodium ◽  
Catalyzed Reactions

All four rate constants required to describe the hydration and aldolization/dealdolization reactions of chalcone (1,3-diphenyl-2-propen-1-one) have been determined in aqueous sodium hydroxide solutions. Kinetics were studied starting with chalcone, with its hydrate, 1,3-diphenyl-3-hydroxy-1-propanone, and with benzaldehyde in the presence of excess acetophenone. The rate constants for hydroxide catalyzed reactions, defined in terms of eq. [1] are: k12 = 10.5 ± 0.5 × 10−4 M−1 s−1; k21 = 0.026 ± 0.002 M−1 s−1; k23 = 0.194 ± 0.017 M−1 s−1; and k32 = 0.84 ± 0.12 M−2 s−1 (all at ionic strength 0.1). The corresponding equilibrium constants for aldol adduct formation and dehydration are 4.3 M−1 and 25.

scholarly journals Cooxidation of Dibenzalacetone with Oxalic Acid by Pyrazinium Chlorochromate

2020 ◽  
Vol 85 ◽  
pp. 1-14
Author(s):  
Seplapatty Kalimuthu Periyasamy ◽  
R. Ponmadasamy
Keyword(s):  
Free Radical ◽  
Ionic Strength ◽  
Oxalic Acid ◽  
Reaction Rate ◽  
Radical Reaction ◽  
Ion Concentration ◽  
Effect Of Temperature ◽  
Radical Mechanism ◽  
Free Radical Reaction ◽  
Hydrogen Ion Concentration

Oxidation of dibenzalacetone with pyrazinium chlorochromate in presence of oxalic acid has been studied at 313 K. Various reaction parameters such as effect of varying oxidant, substrate, Hydrogen ion concentration, catalyst, solvent composition, ionic strength, effect of Mn2+, effect of Al3+ and effect of temperature were studied to determine the kinetics of the reaction. Our study revealed that the reaction followed first order dependence with respect to oxidant and catalyst. The reaction followed fractional order kinetics with respect to substrate and H+. Increase in ionic strength was found to have no effect on the reaction rate and decrease in the dielectric constant of the medium decreases the reaction rate. Increase in the concentration of manganous sulphate retarded the reaction rate which confirmed the two-electron transfer involved in the mechanism. There was no possibility of free radical mechanism, which was confirmed by the addition of acrylonitrile shows no significant effect on the reaction rate indicating the non-involvement of free radical reaction.. Based on the experimental observations a mechanism and rate law has been derived. Moreover, the oxidation product was found to be chalcone epoxide, which was characterized by IR spectrum.

The Effect of Aromatic Amines on the Catalyzed Decarboxylation of 3-Oxo-glutaric Acid

1972 ◽  
Vol 50 (22) ◽  
pp. 3573-3586 ◽  
Author(s):  
K. N. Leong ◽  
M. W. Lister
Keyword(s):  
Ionic Strength ◽  
Stability Constants ◽  
Rate Constants ◽  
Aromatic Amines ◽  
Copper Complexes ◽  
Glutaric Acid ◽  
Equilibrium Constants ◽  
Nickel Compound ◽  
Ph Measurements ◽  
Cobalt Nickel

Equilibrium constants have been measured for the formation of MA species, where M is divalent manganese, cobalt, nickel, or zinc, and A2− is the 3-oxo-glutarate ion. Equilibrium constants have also been measured for the reactions [Formula: see text], where B is 2,2′-bipyridyl or 1,10-phenanthroline. These constants were obtained by pH measurements at 25 °C and an ionic strength of 0.60. The results are compared with those for similar systems, especially as regards the tendency to form ternary mixed complexes of the type MAB.The rates of decarboxylation of the various MA and MAB species have been measured. The resulting rate constants follow the Irving–Williams order for stability constants, except that in both MAB species the cobalt compound decomposed slightly faster than the nickel compound. The aromatic base, which had been found earlier to have very little effect in copper complexes, increased the rate constants appreciably with other metals, especially with manganese and zinc. Usually 1,10-phenanthroline has a larger effect than 2,2′-bipyridyl. Some possible explanations of the results are considered.

OXIDATION OF MANGANATE BY HYPOCHLORITE

1961 ◽  
Vol 39 (1) ◽  
pp. 96-101
Author(s):  
M. W. Lister ◽  
Y. Yoshino
Keyword(s):  
Activation Energy ◽  
Potassium Permanganate ◽  
Rate Constants ◽  
Effective Activation Energy ◽  
Equilibrium Constants ◽  
Intermediate Formation ◽  
Ion Concentration ◽  
Effective Activation ◽  
Text Data ◽  
Hydroxide Ion

The oxidation of potassium manganate to potassium permanganate by potassium hypochlorite has been examined. The rate of the reaction is proportional to the square of the manganate concentration and the first power of the hypochlorite, and it is inversely proportional to the permanganate concentration and to the square of the hydroxide ion concentration. It seems probable that the reaction involves the intermediate formation of hypomanganate ions from a relatively fast disproportionation of manganate, followed by a slower oxidation by hypochlorite. The following mechanism is tentatively proposed:[Formula: see text]Data on the over-all rate and effective activation energy (19.6 kcal/g-molecule) are given; but at present it is not possible to separate all the rate constants and equilibrium constants.

Reduction of chlorothallium(III) complexes by arsenic(III)

1973 ◽  
Vol 26 (10) ◽  
pp. 2115 ◽  
Author(s):  
PD Sharma ◽  
YK Gupta
Keyword(s):  
Ionic Strength ◽  
Acid Solution ◽  
Rate Constant ◽  
Perchloric Acid ◽  
Intermediate Formation ◽  
Chloride Ions ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Perchloric Acid Solution ◽  
Hydrogen Ion Concentration

The oxidation of arsenic(III) by thallium(III) in perchloric acid solution is inhibited by chloride ions. The reactivity of various chlorothallium(III) species is in the order Tl3+ > TlCl2+ > TlCl2+ > TlCl3 > TlCl4-. The rate decreases by increasing the hydrogen ion concentration and ionic strength. The redox process occurs by intermediate formation of a complex of thallium(III) and arsenic(III). The rate constant for the reaction between Tl3+ and arsenic(III) calculated from the data of the present investigation compared well with that of the reaction1 in the absence of chloride ions.

scholarly journals Kinetics of hydride transfer between nitrogen heteroaromatic cations

1988 ◽  
Vol 66 (10) ◽  
pp. 2524-2531 ◽  
Author(s):  
John W. Bunting ◽  
Mark A. Luscher
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Hydride Transfer ◽  
First Order ◽  
Order Rate ◽  
Rate Determining Step ◽  
Donor And Acceptor ◽  
Pseudo First Order ◽  
Saturation Effects ◽  
Kinetics Of

The kinetics of the reduction of the 3-cyano-1-methylquinolinium, 4-cyano-2-methylisoquinolinium, and 2-methyl-5-nitro-isoquinolinium cations by 9,10-dihydro-10-methylacridine, and also the reduction of these same three cations as well as the 10-methylacridinium cation by 5,6-dihydro-5-methylphenanthridine, have been investigated in 20% acetonitrile – 80% water, ionic strength 1.0, 25 °C. The reactions of the 2-methyl-5-nitroisoquinolinium cation with both reductants, and also of the 4-cyano-2-methylisoquinolinium cation with 9,10-dihydro-10-methylacridine, display kinetic saturation effects in the pseudo-first-order rate constants as a function of heterocyclic cation concentration. These effects are consistent with the formation of 1:1 association complexes between hydride donor and acceptor prior to the rate-determining step of the reduction. The second-order rate constants for these reactions, and also those for analogous heterocyclic cation reductions by 1,4-dihydronicotinamides, show systematic variations as a function of the hydride donor and acceptor species.

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