Showing papers on "Aquation published in 1996"

Reactivity of the Coordinated Hydroperoxo Ligand.

Abstract: The reactivity of the hydroperoxo complex [Co(CN)5OOH]3- has been studied in aqueous solution The complex undergoes acid-catalyzed aquation (k = 189(5) × 10-2 s-1, pKa = 521(4), T = 20 °C, I = 01 M) Assuming an Id mechanism, this allows the relative affinity for Co(III) to be deduced as H2O2 < H2O < HO2- and implies H2O2 to be a very weak ligand At neutral pH the hydroperoxo complex effects efficient oxygen atom transfer to l-methionine to give an intermediate identified as [Co(CN)5(l-methionine S-oxide)]2-, which then dissociates to [Co(CN)5OH2]2- and l-methionine S-oxide The reaction is acid catalyzed and is proposed to take place via nucleophilic attack of sulfur on the proximal oxygen of the hydroperoxo ligand with concerted loss of water The significance of these results for the interaction of hydrogen peroxide with labile metal ions is discussed

Equilibrium and High-Pressure Kinetic Study of Formation and Proton-Assisted Aquation of Monodentate Acetate, Propionate, and Glycolate Complexes of Palladium(II) in Aqueous Solution

Abstract: Kinetics and equilibria for reversible formation of 1:1 monodentate complexes between Pd(H2O)42+ and acetic, propionic, and glycolic acid (RCOOH) according to the equation Pd(H2O)42+ + RCOOH ⇌ Pd(H2O)3OOCR+ + H3O+ (k1, k-1) have been studied as a function of temperature and pressure in an aqueous medium with 0.60 ≤ [H+] ≤ 1.00 M, [RCOOH]/[H+] ≤ 1.0, and ionic strength 1.00 M. Stability constants β1 for the formation of acetate, propionate, and glycolate complexes are (2.19 ± 0.09) × 104, (2.10 ± 0.24) × 104, and (6.4 ± 0.1) × 103 M-1, repectively, at 25 °C and for a 1.00 M perchlorate medium. The rate expression, kobsd = k1[RCOOH] + k-1[H+], indicates that reaction between palladium and carboxylate anions is negligible under the experimental conditions used. Values for k1/M-1 s-1, k-1/M-1 s-1, ΔH1⧧/kJ mol-1, ΔH-1⧧/kJ mol-1, ΔS1⧧/J K-1 mol-1, ΔS-1⧧/J K-1 mol-1, ΔV1⧧/cm3 mol-1, and ΔV-1⧧/cm3 mol-1 at 25.0 °C are 19.3 ± 0.6, 32.8 ± 0.2, 52.5 ± 0.4, 57.5 ± 0.4, −44 ± 1, −23 ± 1, −8.1 ± 0.3, and −1.7 ± 0.2 for...

Energy of the Photosubstitutionally Reactive Excited State of Pentaammine(pyridine)ruthenium(II).

Abstract: The photosensitized aquation of pentaammine(pyridine)ruthenium(II) by several dyes has been studied under conditions where only the sensitizers absorb light. The ratio of the quantum yields for ammine and pyridine substitution was the same as that for direct photoaquation. Sensitization was effective with singlet sensitizers Rhodamine-B (17 452 cm(-)(1)) and Safranine-T (17 690 cm(-)(1)), as well as the triplet sensitizer biacetyl (19 000 cm(-)(1)), but no reaction was observed with Neutral-Red (16 900 cm(-)(1)). The results indicate that the excited state precursor of the observed photosubstitution in the complex lies in the energy range between 17 000 and 17 700 cm(-)(1).

Extraction and separation of HCl and Rh(III) with trioctylamine

Abstract: In this paper the use of trioctylamine (TOA) to extract HCl from Rh(III)-containing solutions generated by a supported liquid membrane (SLM) process is investigated. TOA was found to extract HCl readily (in a single contact of 3 min duration) at a molar ratio [HCl]/[TOA] equal to one. For each mole of HCl extracted an equivalent amount of H 2 O was found to be extracted as well. As far as Rh(III) extraction of TOA is concerned this was found to depend on the age of the solution and the Cl - concentration. Prolonged aging (accelerated by heating) or [Cl - ]≥3 M was found to completely suppress the extraction of Rh(III) by TOA. The chloride ion concentration effect was attributed to Le Chatelier's principle while the aging effect was attributed to the aquation/conversion of the extractable RhCl 6 3- complexes to RhCl 5 (H 2 O) 2- . The aquation reaction was studied with UV-Visible spectroscopy in an effort to substantiate the solvent extraction (SX) results. On the basis of the findings of this work a combined SLM/SX process flowsheet is proposed according to which the Rh(III) and HCl co-transported through the supported liquid membrane are co-extracted by TOA and subsequently separated by differential stripping; Rh(III) with 0.5 M HCl/3 M Cl - medium and HCl with NaOH.

Reactivity of a Regiospecific Ion Pair. Comparisons of Cl- and H2O Entry into the Five-Coordinate Intermediate Generated from p-[Co(tren)(NH3)OH2]3+·Cl-

Abstract: Equilibration in the system : p-[Co(tren)(NH3)OH2]3+ + Cl- ⇄ p-[Co(tren)(NH3)Cl]2+ + H2O (p-stereochemistry has the labile group (OH2, Cl-) trans to a tren NH2) in aqueous solution of variable (I = 0−2.0 M) and constant (I = 2.0 M, NaClO4) ionic strength at 37.5 °C is described by the following rate law: kobs = kaq + kanKCl[Cl-]/(1 + KCl[Cl-] + KClO4[ClO4-]); KCl (0.64 M-1) and KClO4 (0.21 M-1) correspond to ion pairing of Cl- and ClO4- to the aqua complex and kaq (1.4 × 10-5 s-1) and kan (1.2 × 10-4 s-1) to the rate constants for aquation of the chloro complex and anation of the ion-paired (Cl-) aqua complex respectively. The rate constant for loss of coordinated 17OH2 from the labeled aqua complex is the same (kOH2 ∼1.2 × 10-4 s-1) irrespective of the presence (2.0 M) or absence of NaClO4 ([H+] = 0.10 M, 37.5 °C) but increases with increasing [Cl-] to reach a limit (∼2.4 × 10-4 s-1) at high concentrations (range 0−1.90 M; I = 2.0 M, NaClO4). Water exchange in the p-[Co(tren)(NH3)OH2]3+·Cl- ion pair (k...

Kinetics of aquation of the trans-dichlorobis (N-methylethylenediamine) cobalt(III) ion in a water-methanol media

Abstract: 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.

Mechanisms and solubility equations of gas dissolving in water

Abstract: The two mechanisms of gas dissolving in water, interstice filling and aquation, are proposed. General equations of gas solubility have been deduced from the mechanisms and experimental observations. Dependence of Henry's coefficient on temperature, pressure, aquation equilibrium constant and gas molecular wlume is discussed. The theoretical equations were verified by experimental data, which shows that the theoretical results of the solubility of methane are in good agreement with the experimental data in the range of 20 -160℃ and under a pressure of less than 60 MPa.

Kinetics of aquation of cis- and trans-chloro-nitrobis(ethylenediamine) cobalt(III) ion in aqueous mixtures of ethylene carbonate and propylene carbonate

Abstract: The kinetics of aquation of cis- and trans-[Co(en)2-NO 2Cl] + were investigated in quasi-isodielectric aqueous mixtures of ethylene carbonate (EC) and propylene carbonate (PC) over a range of temperatures. Transfer Gibbs energies of reactant and transition state from H2O to aqueous mixtures of EC were evaluated from kinetic measurements and the solubilities of the complex salt. An analysis of the solvent effect on the solvation of the initial (IS) and transition (TS) state reveals that their stabilization by non-aqueous cosolvent is due to predominant ion-dipole and dispersion interactions.

Steric effects on complex formation between nickel(II) and (2- imidazoleazo)benzene, 2,2'-biimidazole and 2,2'-bibenzimidazole

Abstract: The kinetics and mechanism of reversible complexation of NiII with (2-imidazoleazo)benzene (IAB), 2,2′-biimidazole (Biim) and 2,2′-bibenzimidazole (Bibzm) have been investigated at 15–35 °C, I = 0.30 mol dm−3. The stability constants, K M, of the [NiL]2+ species vary in the sequence: [Ni(IAB)]2+ < [Ni(Bibzm)]2+ < [Ni(Biim)]2+. The values of the spontaneous dissociation rate constant (k r) at 25 °C decrease in the sequence: [Ni(IAB)]+ > [Ni(Biim)]2+ > [Ni(Bibzm)]2+. The aquation of [Ni(IAB)]2+ is insensitive to acid catalysis, whilst [Ni(Biim)]2+ is relatively more susceptible towards acid-catalysed aquation than [Ni(Bibzm)]2+. The chelate ring in [NiL]2+ (L = IAB, Biim or Bibzm) is sterically strained. The formation of [Ni(IAB)]2+ and [Ni(Bibzm)]2+ may be chelation controlled while the normal I d mechanism is supported by our data for [Ni(Biim)]2+.

Leaving-Group Effects on Volumes of Activation for Dissociative Substitution Processes.

Abstract: A simple model is proposed to explain the common observation that the activation volume for a dissociative substitution process is independent of the molar volume of the leaving group. The model is applied to substitutions of FeII(CN)5(Y) and CrIII(TPP)(Cl)(Y) and the base hydrolyses of CoIII(NH3)5(Y) and CrIII(NH3)5(Y) systems. The implications for the aquation reactions of the latter also are explored.

Salt effect on the micellar catalysis of the aquation of tris (3,4,7,8-tetramethyl-1,10-phenanthroline) iron(II) in H2O/Triton X-100 solvent system

Abstract: The effect of Na2SO4 and PhCOONa on the aquation of [Fe(Me4phen)3]2+ has been investigated in pure Triton X-100 as solvent. The rate and mechanism of the aquation are explained in terms of changes in the mobility, activity and structure of H2O in the restricted environment of water pockets in the Triton X-100 solvent.

Reaction kinetics of coordination compounds

Abstract: In the majority of chapters of this book the concern has been with an understanding of the properties of individual molecules, properties which are regarded as essentially time-independent However, no less important are the chemical reactions of these molecules and, here, changes as a function of time are of the essence This chapter is devoted to a review of our present understanding of some of the reaction types which are characteristic of coordination compounds It is as well to recognize the complexity of the problem Suppose we are interested in a reaction such as the aquation of an ion such as [Co(NH3)5Cl]2+, a much studied system: