Formation and stability of pyrophosphate complexes with aliphatic amines in aqueous solution

The complex formation between pyrophosphate (P(2)O(7)(4-)) and protonated methylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine, has been studied potentiometrically, in aqueous solution, at 25 degrees C. It was found that the species ALH(q)(A = amine, L = P(2)O(7)(4-)) are formed with q = 1 ... n(n = 3, 5, 6, 7, 7 and 8 for the above amines respectively). Mono- and di-amines form species A(p)LH(q) too. The stability of these species is quite high [e.g. H(4)A(4+) + HL(3-)ALH(5)(+): log K = 8.1 (A = pentaethylenehexamine)] and depends strictly on the charges involved in the formation reaction. Charges of reactants being equal, the stability trend is penten > tetren > trien > dien > en > meta and cationic mixed species are more stable than anionic ones. These results are discussed in relation to speciation problems in natural and biological fluids.     

Sorption of aliphatic amines by monocarboxycellulose from aqueous and water-ethanol solutions

The features of the sorption of hydrochlorides of lower aliphatic amines by monocarboxycellulose (MCC) from aqueous and water-ethanol solutions are studied. The ion exchange character of the sorption is shown by IR spectroscopy and potentiometry. It is found that the sorption of all studied salts of aliphatic amines by MCC from dilute aqueous and water-ethanol solutions is thermodynamically advantageous due to the great contribution of Coulomb interactions between cations and polyanions. The selectivity of sorption is predetermined by solvophobic (hydrophobic) interactions, which are thermodynamically disadvantageous at any compositions of the binary solvent due to the formation of dimeric associates of carboxyl groups in the phase of MCC, which hinder the contacts of hydrocarbon radicals of aliphatic amines with hydrophobic sites of the cellulose adsorbent matrix. At high concentrations of aliphatic amines in aqueous and water-ethanol solutions, the process of nonexchange sorption proceeds intensely through the hydrogen bonding between nitrogen atoms and hydroxyl groups of MCC.     

Estimate of the stability constants of trivalent actinide and lanthanide complexes with O-donor ligands in aqueous solutions

The stability constants of the 1: 1 complexes of trivalent actinide and lanthanide cations with O-donor ligands (OH⁻, CO₃²⁻; carboxylate anions: acetate, propionate, isobutyrate, benzoate) formed in aqueous solutions have been approximately calculated by integrating the ligand density distribution function. The contributions of the covalent interaction to the formation of coordination bonds of these cations with O-donor ligands have been estimated.     

Stability constants of tervalent actinide and lanthanide sulfate complexes in aqueous solutions

The stability constants of 1: 1 sulfate complexes (ion pairs) at 298 K are approximately calculated for all tervalent actinides and lanthanides, scandium, yttrium, and for alkali, earth-alkali, and some bivalent transition metals in aqueous solutions. The method used consists in integrating the function of the ligand distribution density with respect to a cation and allows either only solvent-separated ion pairs or all types of ion pairs to be taken into account in the calculation of constants. The dominance of solvent-separated ion pairs in infinitely dilute solutions is shown for lanthanides, actinides, and for the majority of the considered metals by comparison with experimental data.     

Evaluation of stability constants of metal complexes with sulphonated azo-ligands

An ion-exchange procedure is described for the determination of the stability constants for cadmium, copper, nickel and manganese complexes with three sulphonated azo ligands: calmagite, alizarin violet N and palatine chrome black. The results, log K values, show a good agreement with those obtained by a spectrophotometric technique.     

Temperature dependence of complex formation constants in aqueous solutions of metal acetates

The equilibrium constants of formation of inner- and outer-sphere cation-anion complexes (ion pairs) in aqueous solutions of different metal acetates in a wide temperature range have been calculated by integrating the density function of distribution of ligands around the cation. The standard Gibbs energies, enthalpies, and entropies of formation of 1: 1 complexes have been calculated. It has been shown that, in all solutions under consideration, contact and solvent-separated ion pairs coexist. A conclusion has been drawn that the temperature dependence of ion association constants is mainly determined by the temperature dependence of the water dielectric constant.     

Interaction between primary aliphatic amines and carboxylic acid esters in aqueous micellar solutions of cationic surfactants

The effects of cetylpyridinium bromide (CPB) on the acid-base equilibria of primary aliphatic amines and on the kinetics of reactions of the amines withp-nitrophenyl acetate (PNPA) andp-nitrophenyl caprylate (PNPC) were studied by potentiometric titration and UV spectroscopy. The values of apparent pK _a of the amines in the micellar phase, binding constants of their neutral forms, and the surface potentials of micelles were determined. Cetylpyridinium bromide accelerates the aminolysis of PNPA by factors of 3 to 8 by forming mixed micellar aggregates with the amines. The shift of pK _a values of the amines in micellar solutions is not the only factor that enhances their reactivity. The substrate specificity was found: in contrast to the reaction with PNPA, CPB accelerates (by factors of 15 to 65) or retards (by factors of 4 to 6) the aminolysis of PNPA depending on the hydrophobicity of the nucleophilic reagent. The binding constants of substrates, the rate constants in the micellar phase, and the critical concentrations of micellization were determined from the data obtained. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1333–1338, July, 1998.     

Raman spectroscopic determination of equilibrium constants of uranyl sulphate complexes in aqueous solutions

Raman spectra are used to determine the formation constants of uranyl sulphate complexes in aqueous solutions at 20 degrees and remedy the confusion existing in this area in the available literature. Solutions with a varying total sulphate concentration and an ionic strength lower than 0.4M are analysed. The species UO(2)SO(4) and UO(2)(SO(4))(2-)(2) are characterized by a resolved Raman band at 861 cm(-1) and an unresolved one at 852 cm(-1), corresponding to the uranyl symmetrical stretching vibration. The equilibrium constants, in term of activity (standard state 1M), are found to be about 1400 and 11, respectively, for the consecutive reactions: UO(2+)(2)(aq)+SO(2-)(4)(aq)=UO(2)SO(4)(aq) and UO(2)SO(4)(aq)+SO(2-)(4)(aq)=UO(2)(SO(4))(2-)(2)(aq).     

Redox method for the determination of stability constants of some trivalent metal complexes

Stability constants determination of very stable metal complexes using the redox method, based on the equilibrium of Fe (3+)Fe (2+) followed by a couple of platinum/reference electrodes, was undertaken and tested to complexes of some trivalent metal ions with well known polyaminopolycarboxymethylated linear ligands (edta, nta, cdta, dtpa and ttha) and also to some new macrocyclic ligands. SUPERQUAD program was used for the calculations, after adaptation of the experimental data. The method proved to be very useful for Fe(3+) and In(3+) complexes, if no polynuclear complexes are formed or/and if the kinetics of the complexation reaction is not very slow. However, for the Ga(3+) complexes the applicability of this method is very limited and the competition with OH(-) using the displacement reaction which occurs at pH higher than 6 with formation of Ga(OH)(4)(-) seems to give more accurate results. A complete data of stability constants for the case of the complexes of ttha with In(3+) is given.     

The stability constants of some bivalent metal complexes of α-hydroxyisobutyrate and lactate

The stability constants of the lactate and α-hydroxyisobutyrate complexes of Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and UO₂²⁺ were determined by potentiometric titration. The average ligand number exceeds 2, indicating the formation of ML⁺, ML₂ and ML₃^- complexes. The existence of ML₃^- complexes was confirmed by electrophoretic experiments; no polynuclear complexes were formed. α-Hydroxyisobutyrate forms stronger complexes than lactate.     

Kinetics of catalytic oxidation of aliphatic alcohols in aqueous alkaline solutions of copper phenanthroline complexes

The effect of Cu(II), phenanthroline, alcohol, NaOH and O₂ concentrations on the oxidation rates of alcohols in aqueous alkaline solutions has been studied and a reaction mechanism is proposed.

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Cu(II), , , NaOH, O₂ - . .

     

Formation constants for complexes of transition-metal cations with O- and N-donor ligands in aqueous solutions

A method has been developed for the theoretical calculation of stability constants for transitionmetal complexes proceeding from molecular properties. An analytical form of the cation-ligand interaction potential including the partial bond covalence has been developed. The potential is expressed through molecular parameters and a covalence parameter; the latter may be determined from experimentally measured or theoretically calculated gas-phase data. The stability constants have been calculated for 1: 1 complexes of divalent metal cations with hydroxide anion, acetic, glycolic, and lactic acid anions, and ammonia in aqueous solutions. The covalence parameters have been calculated for the bonds of metal cations with O-and N-donor ligands.     

Stability constants of D(−)-ribose complexes with calcium in diluted aqueous and methanolic solutions

The study of D(?)-ribose complexing with calcium in aqueous solutions less than 1.64 × 10^?1M by potentiometric measurements with a calcium selective electrode afforded the value of K₁ = 1.70 liters × mole^?1 (SD = 1.05 × 10^?3). Numerical analysis indicated that complex species with 1:1 and 1:2 calcium to D(-)-ribose ratios are present simultaneously: k₁ = 1.13 liters × mole^?1 and K₂ = 8.47 liters × mole^?1 (SD = 0.95 × 10^?3).In methanolic medium 1.24 × 10^?2M with regard to calcium chloride both stoichiometric proportions were evidenced. A large error accompanying the stability constant K₁ = 28 kg × mole^?1 (RSD = 82%) renders unreasonable the K₂ value obtained from the product K₁ × K₂ = 96.5 kg² × mole^?2.The results are discussed with respect to the data published for more concentrated (1.27 M) aqueous solutions obtained on the basis of ₁H-NMR spectroscopic investigations.     

Stoichiometries and stability constants for the cerium(IV) carbonate complexes in dilute aqueous solution

Complexation between cerium(IV) and carbonate ions in aqueous solution has been studied by UV/Visible absorption spectroscopy, ¹⁷O NMR spectroscopy and potentiometric titration, and it is shown that in dilute solutions at pH 8.8 and 10, both 1?:?1 and 1?:?2 (metal?:?ligand) complexes are formed. This contrasts with the behaviour of the corresponding Th(IV) complex, where the dominant species is the pentacarbonato complex. From the NMR spectra, it is suggested that these species involve bidentate binding of carbonate ion by the metal, while potentiometric data provided accurate formation constants and indicated the dominant species to be the 1?:?2 complex.     

Acidity constants of benzidine in aqueous solutions

The acidity constants of benzidine (Bz) in aqueous solutions determined potentiometrically at 25° were K_a1 = (1.11 ± 0.08) × 10⁻⁵, K_a2 = (1.45 ± 0.12) × 10⁻⁴. The apparent mixed constants in 0.1M sodium nitrate are K_a1 = (5.37 ± 0.28) × 10⁻⁶ and K_a2 = (1.14 ± 0.09) × 10⁻⁴. The ultraviolet spectra were recorded as a function of pH and analysed with these constants to obtain the absorption spectra of H₂Bz²⁺, HBz⁺ and Bz; the corresponding wavelengths of maximal absorption are 247, 273 and 278 nm, and molar absorptivities 1.63 × 10⁴, 1.76 × 10⁴ and 2.26 × 10⁴ 1.mole⁻¹.cm⁻¹.     

Reactions of alkali metal derivatives of some heterocyclic amines

Procedures are described for converting 2-amino-1,3,4-oxa- and thiadiazoles into various products in one-pot syntheses. The preparative method employs alkali metal derivatives of the heterocyclic amines as the reactive species.     

Determination of stability constants of some bivalent metal complexes with thiovioluric and diphenylthiovioluric acids

Stability constants of complexes of some bivalent metal ions, viz, Cu(II), Ni(II), Zn(II), Pb(II) and Mg(II) with thiovioluric and diphenylthiovioluric acid have been determined potentiometrically in 50 and 75% dioxan media, respectively. The order of stability constants for the complexes investigated has been found to be: Mn < Ni < Cu > Zn. The stability of lead complexes has been found to be intermediate between Mn(II) and Ni(II) while magnesium forms the least stable complexes.