Potentiometric study of the hydrolysis of (CH3)Hg+ in NaClO4: construction of a thermodynamic model

The hydrolysis of CH₃Hg⁺ was studied potentiometrically in NaClO₄ media in the range 0.1–3.0 mol dm⁻³ ionic strength at 25 °C. Evaluation of data with the non‐linear least‐squares computer programs BSTAC and STACO led us to propose the formation of CH₃HgOH and (CH₃Hg)₂OH⁺ species. The stoichiometric ­stability constants obtained for the two species at the different ionic strengths were correlated by means of Modified Bromley Methodology (MBM) to obtain the corresponding thermodynamic equilibrium constants, as well as the interaction parameters of the soluble species. This is the first of a series of potentiometric studies on the different equilibria of methylmercury with the majority of ions present in natural waters in order to simulate the behaviour of methylmercury in sea and estuary waters. Copyright © 2000 John Wiley & Sons, Ltd.     

Thermodynamic Model of Inorganic Arsenic Species in Aqueous Solutions. Potentiometric Study of the Hydrolytic Equilibrium of Arsenious Acid

A potentiometric study of the hydrolysis of arsenious acid was carried out to define the thermodynamic model of the inorganic arsenic species in aqueous solutions. The protonation equilibrium of arsenious acid was determined at 25^°C. The variation of the stoichiometric formation constant with the ionic strength was also studied up to ionic strength 3.0 mol-dm^–3 in aqueous NaClO₄, NaCl, and KCl. The thermodynamic formation constant of arsenious acid (log K ^o = 9.22 ± 0.01) and the various interaction parameters were computed using the Modified Bromley Methodology (MBM), for both the molar and molal concentration scales at constant temperature (25^°C). The results showed the importance, not only of ionic strength, but also of the composition of the ionic medium on the distribution of the acid-base As(III) species as a function of pH in natural waters.     

Spectrophotometric Determination of Sulfate Ion Through Copper(II)-azide System

Abstract

An indirect and alternative method for the determination of sulfate ion has been established by spectrophotometry. The procedure is based on the formation of copper(II) monoazido species, in water/acetone medium, in which a discoloration effect of system is caused by sulfate presence. In the recommended conditions, sulfate ions can be determined in the concentration range from 40 to 5000 mg/l (ppm), at 375 nm, in natural samples of waters. The best experimental conditions were determined analysing the different factors involved. Studies about the formation equilibria of the CuN₃ ⁺ and CuSO₄ species were realized in water and their respective stability constants (β₁ = 225 M^?1 and 7.15 M^?1) were determined by spectrophotometry at 25.0° C and ionic strength 1.0 M (NaClO₄). Equilibrium investigations were also made in presence of acetone. Additional studies on the ternary system Cu(II)/N₃ ^?/SO₄ ^2-) indicated some evidences of mixed complexes.     

Complexation and Precipitation of Arsenate and Iron Species in Sodium Perchlorate Solutions at 25∘C

The complexation of As(V) in aqueous solutions in the presence of iron(III) was investigated spectrophotometrically with both variable and constant ionic strengths. The determined thermodynamic and stoichiometric formation constants of the FeHAsO₄⁺ species are log₁₀^∘β = 9.21± 0.01 and log₁₀^Iβ (1.0mol⋅dm⁻³ NaClO₄) = 7.78 ± 0.01, respectively. The numerical treatment of the obtained spectral data was performed with the SPECA program. The analysis required the consideration of the hydrolysis of Fe(III) and the protonation of As(V) in the pH range studied. No significant hydrolysis was observed because of the low pH values (pH < 2.5) involved. The stabilities of the solid Fe(III) arsenates was established by solubility experiments. All of the solubility experiments were performed in aqueous NaClO₄ solutions at constant ionic strength (1.0mol⋅dm⁻³) and at 25^∘C. The experimental data were consistent with FeAsO₄⋅2H₂O being the solid phase (log₁₀ ^∘ K_so = −24.30± 0.08). The corresponding thermodynamic constants were computed by means of the Modified Bromley's Methodology (MBM) that describes the variation of the activity coefficients of all of the ions involved in the complexation and precipitation equilibria with the medium and ionic strength. Finally, the solid phase obtained in this work was also characterized by FT-IR and FT-Raman spectroscopies, and the hydration of the solid iron arsenate was confirmed by X-ray diffraction data.     

Development of a Modified Bromley's Methodology for the estimation of ionic media effects on solution equilibria: Part 4. The chemical model of Fe(III) with the halide ligands in aqueous solution at 25°C

The Modified Bromley's Methodology (MBM) has been used to construct the basic chemical model between Fe(III) and OH⁻ and the halide ligands Cl⁻, Br⁻ and F⁻ in NaClO₄ medium at 25°C, obtaining the thermodynamic constants and the corresponding interaction parameters for each equilibrium. This basic model has been extended to KNO₃, HCl, and KCl media obtaining the corresponding interaction parameters. The applicability of the model is also discussed.     

Potentiometric Study of Aluminium-Fluoride Complexation Equilibria and Definition of the Thermodynamic Model

Complexation constants of the Al³⁺/F⁻ system were determined at different ionic strengths in a NaClO₄ (1.0, 2.0 and 3.0 mol⋅dm⁻³) ionic medium by means of a potentiometry using two electrode systems: an ion fluoride selective electrode as well as a glass electrode. All the experimentation was performed at 25 °C. The main species in the complexation equilibria were determined as AlF²⁺, AlF₂⁺, AlF₃⁰, AlF₄⁻, AlF₅²⁻ and AlF₆³⁻. The differences found in the complexation constants for the ionic strength considered were explained by the different behavior of the interaction parameters for the AlF _n ³⁻ⁿ species. These parameters were calculated using the Modified Bromley’s Methodology (MBM). The corresponding thermodynamic quantities were also determined. From all the results obtained, it can be concluded that pH, fluoride concentration and ionic strength influenced the distribution of the fluoride-aluminium complexes.     

Thermal properties of sulfonic acid group functionalized Brönsted acidic ionic liquids

Thermal decomposition onset temperatures have been measured for a total of 24 methylimidazolium, triethanolammonium, and pyridinium type sulfonic acid groups functionalized Brönsted acidic ionic liquids with Cl^?, Br^?, SO₄ ^2?, PO₄ ^3?, BF₄ ^? _, CH₃CO₂ ^?, and CH₃SO₃ ^? anions, using thermogravimetric analysis. Thermal stabilities of these sulfonic acid group functionalized ionic liquids decreases in the order, methylimidazolium > triethanolammonium > pyridinium. The methylimidazolium, pyridinium, and triethanolammonium ionic liquids investigated showed decomposition onset temperatures (air) in the 213–353, 167–240, and 230–307 °C ranges, respectively. Additionally, the decomposition temperatures of these ionic liquids are highly dependent on the nature of the anion.     

Komplexone XL. Die Protonierungskonstanten einiger Komplexone in verschiedenen wässerigen Salzmedien (NaClO4, (CH3)4NCl,KNO3)

The protonation constants of the anions of thirteen polyaminocarboxylic acids have been determined in solutions containing different inert salts: KNO₃, NaClO₄ and N(CH₃)₄Cl. The formation constants of the following species: H₅EDTA+, H₆EDTA²⁺, H₅CDTA⁺ and H₄NTA⁺ have been obtained from solubility measurements with ethylenediamine tetraacetic acid (H₄EDTA), 1,2-diaminocyclohexane tetraacetic acid (H₄CDTA) and nitrilotriacetic acid (H₃NTA) in acid solutions between pH = 3 and 0 at ionic strength 1M (NaClO₄ + HClO₄).     

Development of a Modified Bromley's Methodology for the estimation of ionic media effects on solution equilibria: Part 3. Application to the construction of thermodynamic models

The development of the Modified Bromley's Methodology (MBM) is extended for the estimation of the activity coefficients of individual species in aqueous solution at 25°C in single and mixed ionic media. The estimation is compared with literature data of activity coefficients of mixtures of electrolytes in water and applied to (a) the prediction of the ionic product of water in aqueous solutions containing different salts which are commonly used as background electrolytes (NaCl, KNO₃ and NaClO₄) and (b) the equilibrium constants of the Cr(VI)–H₂O system.     

Synthesis of Pyrazolo[3,4‐d]pyrimidin‐4‐ones Catalyzed by Br?nsted‐acidic Ionic Liquids as Highly Efficient and Reusable Catalysts

A convenient and efficient method for the synthesis of pyrazolo[3,4‐d]pyrimidin‐4‐ones via heterocyclization reaction of 5‐amino‐1H‐pyrazole‐4‐carboxamides with triethyl orthoesters using two Br?nsted‐acidic ionic liquids, 3‐methyl‐1‐(4‐sulfonic acid)butylimidazolium hydrogen sulfate [MIM⁺(CH₂)₄SO₃H][HSO₄^?] or N‐(4‐sulfonic acid)butyl triethylammonium hydrogen sulfate [Et₃N⁺(CH₂)₄SO₃H][HSO₄^?], as efficient homogeneous catalysts under solvent‐free conditions is described.     

Determination and comparison of stability constants of tungsten(VI) and molybdenum(VI) with nitrilotriacetic acid and glutamic acid at different ionic strengths

The formation constants of species formed in the systems H⁺?+?W(VI)?+?nitrilotriacetic acid (NTA) and H⁺?+?NTA have been determined in aqueous solution for pH?=?4–9 at 25°C and different ionic strengths ranging from 0.1 to 1.0?mol?dm^?3 NaClO₄, using potentiometric and spectrophotometric techniques. It was shown that tungsten(VI) forms a mononuclear 1?:?1 complex with NTA of the type WO₃L^3? at pH?=?7.5. The composition of the complex was determined by the continuous variations method. The complexation of molybdenum(VI) with glutamic acid was investigated in aqueous solution ranging in pH from 4 to 9, using polarimetric, potentiometric and spectrophotometric techniques. The composition of the complex was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1?:?1 complex with glutamic acid of the type MoO₃L^2? at pH?=?6.0. The dissociation constants of glutamic acid and the stability constants of the complex were determined at 25°C and at ionic strengths ranging from 0.1 to 1.0?mol?dm^?3 sodium perchlorate. In both complex formation reactions the dependence of the dissociation and stability constants on ionic strength is described by a Debye-Huckel type equation. Finally, a comparison has been made between the patterns of ionic strength dependence for the two complexes and the results have been compared with data previously reported.     

Temperature Dependence of Interactions between Stable Piperidine‐1‐yloxyl Derivatives and an Ionic Liquid

2,2,6,6‐Tetramethylpiperidine‐1‐yloxyl derivatives substituted with either hydrogen bonding [‐OH, ‐OSO₃H] or ionic [‐OSO₃^?Na⁺, ‐OSO₃^?K⁺, N⁺(CH₃)₃I^?, N⁺(CH₃)₃ N^?(SO₂‐CF₃)₂] substituents are investigated in 1‐butyl‐3‐methylimidazolium tetrafluoroborate over a wide temperature range covering both glassy and viscous states. The Vogel–Fulcher–Tammann equation describes the temperature dependence of the ionic liquid viscosity. Quantum chemical calculations of the spin probes at the UB3LYP/6‐311(2d,p++) level are done to describe the dependence of the spin density on nitrogen on the substitution pattern of the 4‐position of the probe. The results of these calculations are also used to understand the experimental results obtained by applying the Spernol–Gierer–Wirtz theory to analyze the viscosity dependence of the rotational correlation time of the spin probes. Significant differences are found between 2,2,6,6‐tetramethylpiperidine‐1‐yloxyl and its derivatives containing substituents that are able to form hydrogen bonds with the ionic liquid. Moreover, derivatives substituted with ionic groups at the 4‐position have a large effect on temperature‐induced solvent viscosity, as this is particularly dependent on the nature of the substituent at the 4‐position. These dependencies include the temperature region that can be used to describe interactions between the spin probes and the ionic liquid, diffusion into the free volume during non‐activated (neutral spin probes) and activated (charged spin probes) processes. Additional parameters are the radii of the ionic liquid and the spin probes, which are calculated and measured approximately. In addition, the temperature dependence of the isotropic hyperfine coupling constants of the spin probes results in information about the micropolarity of the ionic liquid. At room temperature, this is comparable to that of the solvent dimethylsulfoxide.     

Mono-complex formation kinetics of 2-acetylcyclohexanonatochromium(III) in aqueous solution

The kinetics and mechanism of the reaction of complexation of chromium(III) with 2-acetyl-cyclohexanone has been investigated spectrophotometrically in aqueous solution at 50°C and ionic strength 0.5 mol dm^?3 NaClO₄. The equilibrium constants of the complex have been determined. The mechanism proposed to account for the kinetic data involves a double reversible pathway where both Cr³⁺ and Cr(OH)²⁺ react with the enol tautomer of the ligand with rate constants of 9.6 × 10^?3 dm³ mol^?1 s^?1, and 3.69 × 10^?2 dm³ mol^?1 s^?1, respectively. Some discussions are made on the basis of Eigen-Wilkins theory considering the effect of solvent exchange on the complex formation.     

Hydrolysis of (CH3)3Sn+ in Various Salt Media

The hydrolysis of trimethyltin(IV) has been studied by potentiometry (H⁺ -glass electrode) and calorimetry in various salt media (NaNO₃, NaCl, KCl, Na₂SO₄, and NaNO₃—NaCl mixtures). The effect of ionic strength on the hydrolysis constants is accounted for by a simple Debye–Hückel type equation and by Pitzer equations. The results allow us to obtain H for hydrolysis and the temperature dependence of the Pitzer parameters. The resulting coefficients can be used to examine the speciation of (CH₃)₃Sn⁺ in multicomponent electrolyte solutions, such as natural waters, over a wide range of temperature and ionic strength.     

Complex rate law for the cerium(IV) oxidation of glycolic acid in the medium HClO4–Na2SO4–NaClO4

The kinetics of the cerium(IV) oxidation of glycolic acid have been studied in the medium HClO₄? Na₂SO₄? NaClO₄ at varying organic substrate (HL), hydrogen, and bisulfate ion concentrations at 25.0°C and ionic strength 2.0M. Under the experimental conditions used (0.03 ? [H⁺] ? 0.5M; 0.02 ? [HSO₄^?] ? 0.1M; 0.01 ? [HL] ? 0.1M) the observed pseudo-first-order rate constant k_obs has been found to follow the complex expression where the values of the various constants have been estimated by a nonlinear least-squares method. According to this expression the oxidation process occurs significantly through three simultaneous pathways. Moreover three equilibria involving cerium(IV) and HSO₄^? (or SO₄^2?) ions are important from a kinetic point of view, whereas only two equilibria involving the corresponding complexes with the organic substrate are predominant.     

Approximate calculation of thermodynamic instability constants of complex compounds

A Debye-Hückel type equation is proposed for calculating thermodynamic instability constants from measurements at a single, sufficiently high, ionic strength, in solutions containing NaClO₄. The applicability of this equation to instability constants of complexes of different composition and charge is shown.     

Thermodynamics of Mixed-Ligand Complex Formation of Mercury(II) Ethylenediaminetetraacetate with Ethylenediamine and Hexamethylenediamine in an Aqueous Solution

The thermodynamic parameters (logK, Δ _r G ⁰, Δ _r H, Δ _r S) of formation of the HgEdtaL^2?, HgEdtaHL^? and (HgEdta)₂L^4? complexes (L = NH₂(CH₂)₂NH₂, NH₂(CH₂)₆NH₂) have been determined by the calorimetric and pH-metric methods at 298.15 K and the ionic strength I = 0.5 (NaClO₄). The most probable coordination mode for the complexone and an ancillary ligand in the composition of the mixed complexes was discussed.     

Die Bildungskonstanten der Wasserstoff—Fluor-Komplexe in konzentrierten Salzlösungen

Zusammenfassung Die Bildungskonstanten von HF und HF2^–in NaClO₄-Medien wurden aus Messungen mit einer Chinhydron- und einer LaF₃-Membranelektrode bestimmt. Die Bildungskonstanten bei den Ionenstärken 1–, 2–, 3– und 4M werden mit Hilfe einesDebye—Hückel-Ansatzes als Funktion der Ionenstärke dargestellt. Durch Extrapolation auf unendliche Verdünnung werden die thermodynamischen Bildungskonstanten bei 25°C erhalten. Die mit Hilfe der Chinhydronelektrode und der LaF₃-Membranelektrode erhaltenen Ergebnisse werden verglichen und kritisch gewertet.

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Stability constants of hydrogen fluorides in concentrated salt media; Measurements with aLaF ₃-membrane electrode

Formation constants of HF and HF2^– in NaClO₄ media were determined from measurements with a quinhydrone and a LaF₃-membrane electrode. The formation constants at 1,2,3, and 4M ionic strength are presented as a function of the ionic strength through aDebye—Hückel approximation. Extrapolation to infinite dilution gives the thermodynamic stability constants at 25°C. The results obtained from measurements with a quinhydrone and a LaF₃-membrane electrode are compared and critically evaluated.

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Mit 3 Abbildung     

Dimethyldithiocarbamatostibane

Dimethylaminodithiocarbamatostibanes The Halogeno-bis(dimethylaminodithiocarbamato)stibanes (dtc)₂SbCl 2 and (dtc)₂SbBr 3 are prepared from (dtc)₃Sb 1 . Reaction of 2 and 3 resp. with CF₃SO₃SiMe₃ yields the ionic compounds (dtc)₂Sb⁺CF₃SO₃^? 4 and (dtc)₂Sb⁺]₂Br^?(CF₃SO₃^?) CH₂Cl₂ 5 by elimination of Me₃SiHal. The molecular structure of 4 is determined by X-ray analysis. The vibrational and mass spectra of 1–5 are reported and briefly discussed.     

Donor ligand, basal ligand and solvent effects on the equilibrium constants of triphenylphosphinecobalt(III) Schiff base complexes with phosphite ligands

The equilibrium constants and the thermodynamic parameters were spectrophotometrically measured for the 1:1 adduct formation of [Co(Salen)(PPh₃)]ClO₄.H₂O, and [Co(7,7′-Me₂Salen)(PPh₃)]ClO₄.H₂O as acceptors, with P(OR)₃ (R = methyl, ethyl, and i-propyl) as donors, in acetonitrile (CH₃CN) and dimethylformamide (DMF) as solvents at constant ionic strength (I = 0.1 M NaClO₄), and various temperatures (t = 10–50 °C). Our results revealed the following trends: stability of the cobalt(III) Schiff base complexes toward a given phosphite donor, [Co(7,7′-Me₂Salen)(PPh₃)]⁺ < [Co(Salen)(PPh₃)]⁺; binding of the donors (phosphites) toward a given cobalt(III) Schiff base complex, P(OEt)₃ > P(OMe)₃ > P(O-ⁱPr)₃; influence of solvent on the stability of a given cobalt(III) Schiff base complex toward a given phosphite donor, CH₃CN < DMF.