多环芳烃在盐溶液中盐析常数和活度系数的研究

研究盐类对多环芳烃溶解度的影响,不仅涉及盐效应各种理论的研究,而且在化工分离、环境治理上也有重要的实际意义。本文研究了25℃下7种多环芳烃在NaCl水溶液中的活度系数和盐析常数。计算并比较了萘和联苯的盐析常数以及5种多环芳烃在被正辛醇饱和的NaCl水溶液中的活度系数和盐析常数。     

Modeling of Protonation Constants of Linear Aliphatic Dicarboxylates Containing -S-Groups in Aqueous Chloride Salt Solutions,at Different Ionic Strengths,Using the SIT and Pitzer Equations and Empirical Relationships

The protonation constants of ethylenedithiodiacetic, dithiodipropionic and dithiodibutyric acids were obtained from potentiometric measurements in NaCl(aq) (I≤5 mol⋅L⁻¹) and (CH₃)₄NCl(aq) (I≤3 mol⋅L⁻¹) at t=25 °C. Their dependences on ionic strength were modeled by the SIT and Pitzer approaches. The activity coefficients of the neutral species were obtained by solubility measurements. The literature values of the protonation constants of (HOOC)-(CH₂) _n -S-(CH₂) _n -(COOH) (n=1 to 3) and (HOOC)-(CH₂)-S-(CH₂) _n -S-(CH₂)-(COOH) (n=0 to 5) in NaCl(aq) and KCl(aq) (I≤3 mol⋅L⁻¹) at 18 °C were also analyzed using the above approaches. Both the log ₁₀ K _i ^H and interaction parameter values follow simple linear trends as a function of certain structural characteristics of the ligands. Examples of modeling these trends are reported. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.     

Critical Evaluation of Protonation Constants. Literature Analysis and Experimental Potentiometric and Calorimetric Data for the Thermodynamics of Phthalate Protonation in Different Ionic Media

The protonation constants of phthalate were determined in aqueous NaCl (0.1 ≤ I ≤ 5,mol⋅L⁻¹) and in aqueous Me₄NCl (0.1 mol⋅L⁻¹ ≤ I ≤ 3,mol⋅L⁻¹) at t = 25,^∘C. Experimental data were employed in conjunction with literature data from studies in different ionic media (Et₄NI: 0 ≤ I ≤ 1,mol⋅L⁻¹; NaClO₄: 0.05 mol⋅L⁻¹ ≤ I ≤ 2,mol⋅L⁻¹)to study the dependence on ionic strength using different models, such as the SIT and Pitzer equations, and an Extended Debye-Hückel type equation. Experimental calorimetric data in NaCl and protonation constants at different temperatures in Et₄NI (5 ≤ t ≤ 45^∘C) and in NaClO₄ (15 ≤ t ≤ 35 ^∘C) were also used to study their dependence on temperature. Recommended equilibrium data are reported together with a short discussion of a prospective protocol for drawing these data.     

镎和钚与环境中无机阴离子的配位化学研究进展

镎(Np)和钚(Pu)是核能领域两种重要的锕系元素,其在水溶液中的配位化学对于了解和控制其在水环境中的种态分布和迁移行为具有重要意义.综述了近十几年来国内外Np和Pu与环境中常见无机阴离子在水溶液中的配位化学研究进展,重点阐述了不同价态Np/Pu离子与OH^-、CO₃^2-、SO₄^2-、Cl^-、NO₃^-、F^-、PO₄^3-等阴离子之间形成的配位物种和配位热力学信息,并对该领域存在的关键科学问题和未来发展方向进行了分析和展望.     

Effects of Solvent, Structure, and Temperature on the Ionization Equilibrium Constants of Phenols and Pyridinium Ions in Mixtures of Water and 1,4-Dioxane

An extensive collection of data has been used to study the effects of solvent, structure, and temperature on the ionization equilibrium constants of some substituted phenols and pyridinium ions in water–1,4-dioxane mixtures (0–70% weight fraction in dioxane) and temperatures ranging from 10 to 50°C. The effects of structure and solvent are explained using Hammett's equation and the Marshall–Quist model at all temperatures. An equation allowing an analysis of the three effects together on the pK values has been developed. The pK data under all experimental conditions fit this equation well, with standard errors of less than 0.3 pH units. Hammett's reaction constant for the ionization of phenols and pyridinium ions has been obtained for all the experimental conditions. The pK and Hammett's reaction constants for the different ionizations in water–1,4-dioxane mixtures correlate well with Kamlet and Taft's solvatochromic parameters ^* and , which measure the dipolarity/polarizability and hydrogen-bonding capacity of the solvent, respectively. These correlations explain more thoroughly the different contributions and origin of the effects of the solvent on the pK.     

The Effect of Metal Cations on the Aqueous Behavior of Dopamine. Thermodynamic Investigation of the Binary and Ternary Interactions with Cd2+, Cu2+ and UO22+ in NaCl at Different Ionic Strengths and Temperatures

The interactions of dopamine [2-(3,4-Dihydroxyphenyl)ethylamine, (Dop⁻)] with cadmium(II), copper(II) and uranyl(VI) were studied in NaCl(aq) at different ionic strengths (0 ≤ I/mol dm⁻³ ≤ 1.0) and temperatures (288.15 ≤ T/K ≤ 318.15). From the elaboration of the experimental data, it was found that the speciation models are featured by species of different stoichiometry and stability. In particular for cadmium, the formation of only MLH, ML and ML₂ (M = Cd²⁺; L = dopamine) species was obtained. For uranyl(VI) (UO₂²⁺), the speciation scheme is influenced by the use of UO₂(acetate)₂ salt as a chemical; in this case, the formation of ML₂, MLOH and the ternary MLAc (Ac = acetate) species in a wide pH range was observed. The most complex speciation model was obtained for the interaction of Cu²⁺ with dopamine; in this case we observed the formation of the following species: ML₂, M₂L, M₂L₂, M₂L₂(OH)₂, M₂LOH and ML₂OH. These speciation models were determined at each ionic strength and temperature investigated. As a further contribution to this kind of investigation, the ternary interactions of dopamine with UO₂²⁺/Cd²⁺ and UO₂²⁺/Cu²⁺ were investigated at I = 0.15 mol dm⁻³ and T = 298.15K. These systems have different speciation models, with the MM’L and M₂M’L₂OH [M = UO₂²⁺; M’ = Cd²⁺ or Cu²⁺, L = dopamine] common species; the species of the mixed Cd²⁺ containing system have a higher stability with respect the Cu²⁺ containing one. The dependence on the ionic strength of complex formation constants was modelled by using both an extended Debye–Hückel equation that included the Van’t Hoff term for the calculation of the formation enthalpy change values and the Specific Ion Interaction Theory (SIT). The results highlighted that, in general, the entropy is the driving force of the process. The quantification of the effective sequestering ability of dopamine towards the studied cations was evaluated by using a Boltzmann-type equation and the calculation of pL_0.5 parameter. The sequestering ability was quantified at different ionic strengths, temperatures and pHs, and this resulted, in general, that the pL_0.5 trend was always: UO₂²⁺ > Cu²⁺ > Cd²⁺.     

Ionic Liquids in Polyethylene Glycol Aqueous Solutions: Salting-in and Salting-out Effects

Summary. Changes of the fluid phase behaviour of polyethylene glycol (PEG) aqueous solutions – viz. critical solution temperature shifts at atmospheric pressure – were produced by the addition of different ionic liquids, namely 1-ethyl-3-methylimidazolium ethyl sulfate and 1-alkyl-3-methylimidazolium chloride (alkyl = ethyl to decyl). The addition of ionic liquids with long alkyl chains improves the solubility of PEG in water (salting-in effect), whereas the impact of short-chain ionic liquids is usually the contrary (salting-out effect). The results are interpreted taking into account the kosmotropic (water-structuring) or chaotropic (water-structure-breaking) nature of ionic liquids, as compared to other inorganic salts.     

Equilibrium Constant Studies for Complexation between Ammonium Ions and 18-Crown-6 in Aqueous Solutions at 298.15 K

Osmotic vapor pressure and density measurements have been carried out for binary aqueous and ternary aqueous solutions containing a fixed concentration of 18-crown-6 (0.2 mol⋅kg⁻¹) and ammonium chloride or ammonium bromide at 298.15 K. The concentration of the ammonium salts was varied between 0.02 to 0.5 mol⋅kg⁻¹. The measured water activities were used to obtain the activity coefficient of water and the mean molal activity coefficient of the ions in binary as well as ternary solutions. Using the method developed by Patil and Dagade reported earlier in this journal and the McMillan-Meyer pair and triplet Gibbs energy interaction parameters, the thermodynamic equilibrium constant (K) for the 18-crown-6:NH₄ ⁺ complexes were determined. It is observed that the nature and polarizability of anions play important roles in imparting stability to the complexed species. The log₁₀ K values for the 18-crown-6:NH₄ ⁺ complexed species are lower than for the complexes involving alkali metal ions such as K⁺. The volume of complexation for the studied systems obtained from the apparent molar volumes of ammonium halides in ternary solutions are positive and of smaller magnitude than those reported for complexation with alkali ions. The results are further discussed in terms of water structural effects, complex formation, the role of counter anions and hydrophobic interactions.     

Rate Constants for the Reactions of NO3 and SO4 Radicals with Oxalic Acid and Oxalate Anions in Aqueous Solution

Rate constants for the reactions of NO3 and SO4 radicals with oxalic acid and oxalate anions in aqueous solution have been measured using pulse radiolysis and laser flash photolysis.     

Speciation of Phytate Ion in Aqueous Solution. Thermodynamic Parameters for Zinc(II) Sequestration at Different Ionic Strengths and Temperatures

Results of an investigation on phytate interactions with zinc(II) cation in NaNO_3aq at different ionic strengths (0.1≤I/mol⋅L⁻¹≤1.0) are reported. Stability constants of various Zn _i H _j Phy^{(12−2i−j)−} species were determined by potentiometry (ISE-H⁺ glass electrode) and the corresponding formation enthalpies by direct calorimetric titrations. Data obtained were used to provide an exhaustive speciation scheme of zinc(II) in the presence of phytate, as well as a comprehensive representation of the binding ability of phytate toward zinc(II) in different conditions. Different pL₅₀ values [an empirical parameter already proposed, expressed as the −log ₁₀ C _Phy, where C _Phy is the total phytate concentration necessary to bind 50% zinc(II)] were calculated in several conditions, and equations were formulated to model its dependence on different variables, such as ionic strength, temperature and pH. Other empirical predictive relationships are also proposed. Previous contributions to this series reviewed in ref. [1].     

有机试剂的结构与性质研究(Ⅴ)——5-Br-PADAP的酸碱平衡及其在溶液中存在形式的研究

本文用分光光度法研究了2-[2-(5-溴-吡啶)偶氮]-5-二乙胺基酚(5-Br-PADAP)的酸碱平衡,实验测得的pH和A的数据,用最小二乘法处理得到了5-Br-PADAP在30％乙醇溶液中的离解常数:pK_a1=-0.12,PK_a2=1.66,pK_a3=12.30;并用HMO量子化学计算法确定了5-Br-PADAP在溶液中可能存在的各种形式.     

Cationic Heteroconjugation Constants in the OHN+ and NHO+ Systems in Propylene Carbonate: Dependence on Difference in Basicity

Cationic heteroconjugation equilibria of more than ninety systems consisting of substituted pyridines, their N-oxides, and trimethylamine N-oxide, i. e., in systems with mixed hydrogen bridges of type OHN⁺ (NHO⁺) were studied in propylene carbonate. Both experimental systems without proton transfer, BH⁺/B₁, and those with proton transfer, B₁H⁺/B, were explored. The stability of the mixed hydrogen bridges, OHN⁺ (NHO⁺), is compared with that of the OHC⁺-type bridges. The influence of the difference in basicity of the conjugate base of the proton donor and the proton acceptor on the presence of the proton transfer equilibria, and, consequently, the possibility of determination of the cationic heteroconjugation constant values is discussed.     

Role of the activity coefficient in the dissemination of pH: comparison of primary (Harned cell) and secondary (glass electrode) measurements on phosphate buffer considering activity and concentration scales

Despite recent efforts devoted to assessing both the theoretical rationale and the experimental strategy for assignment of primary pH values, these have not yet been accomplished satisfactorily. Traceability and comparability of pH values are achieved only within the constraints of internationally accepted conventions and predefined conditions that cannot account for all possible situations when pH is measured. Critical parameters to be defined are, in particular, the activity coefficients (γ _i) of the ionic species involved in the equilibrium with the hydrogen ions in the solution, which are usually estimated with the approximation typical of the Debye–Hückel theoretical model. For this paper, primary (Harned cell) measurements (traceable to the SI system) of the pH of a phosphate buffer have been considered and the results have been compared with secondary (glass electrode) measurements obtained by considering either the activity (paH) or concentration (pcH) scale of the hydrogen ions. With conventional approaches based on measurements related to activity or concentration scale, discrepancies emerge which have been assigned to incomplete inferences of γ _i arising from chemical features of the solution. It is shown that fitting and comparable paH and pcH results are attainable if evaluation of γ _i is performed using better estimates of the ionic strength, according to an enhanced application of the Debye–Hückel theory.     

Single and Binary Dye Adsorption of Methylene Blue and Methyl Orange in Alcohol Aqueous Solution via Rice Husk Based Activated Carbon: Kinetics and Equilibrium Studies

The present work was mainly focused on the single and binary adsorption of methylene blue(MB) and methyl orange(MO) from alcohol aqueous solution over rice husk based activated carbon(RHAC). The study of single dye adsorption equilibrium experiments found that the Langmuir adsorption model was consistent with the adsorption behavior of RHAC on MB and MO, indicating that it was a single layer adsorption. The adsorption behavior conformed to the pseudo-second-order kinetic model. The binary dye adsorption experiments showed that the Langmuir-Freundlich model could be applied to describe the adsorption behavior of RHAC on MB and MO. Comparation with the single dye system, the adsorption capacity on the binary dye system was larger, and there was "competitive adsorption" and "synergistic adsorption" effects existed. Meanwhile, the pseudo-second-order kinetic model also fit for the binary dye adsorption behavior.     

Solute-Solvent Interaction Effects on Protonation Equilibrium of Substituted N-Benzylidene-2-hydroxyanilines in Aqueous Ethanol: The Application of Factor Analysis to Solvatochromic Parameters and Protonation Equilibria

Summary. In this study, the stoichiometric protonation constants, logK_OH and logK_NH, of sixteen substituted N-benzylidene-2-hydroxyanilines have been determined potentiometrically in ethanol-water mixtures of varying composition (10–80% ethanol by volume) at 25.0±0.1°C. The values of the constants, logK, were submitted to factor analysis in order to obtain the number of factors which affect the variation of the whole data sets of protonation constants and, afterwards, to target factor analysis to identify these factors. The influence of solvatochromic parameters in the interactions between Schiff bases derivatives and the solvent studied was identified and quantified. Kamlet and Taft general equations allow calculation of the logK values of Schiff bases studied in any ethanol-water mixtures up to 80% (v/v) and thus provide the knowledge of the acid-base behaviour in these solvent media. Further, the quasi-lattice quasi-chemical (QLQC) theory of preferential solvation has been applied to quantify the preferential solvation by water of electrolytes in ethanol-water mixtures.     

Hydrogen Bonding and Solvent Effects on Complexation of Alkali Metal Cations by Lower Rim Calix[4]arene Tetra(O-[N -acetyl-D -phenylglycine methyl ester]) Derivative

Complexation of alkali metal cations with 5,11,17,23-tetra-tert-butyl-26,28,25,27-tetrakis(O-methyl-D-α-phenylglycylcarbonylmethoxy)calix[4]arene (L) was studied by means of spectrophotometric, conductometric and potentiometric titrations at 25 °C. The solvent effect on the binding ability of L was examined by using two solvents with different affinities for hydrogen bonding, viz. methanol and acetonitrile. Despite the presence of intramolecular NH···O=C hydrogen bonds in L, which need to be disrupted to allow metal ion binding, this calix[4]arene amino acid derivative was shown to be an efficient binder for smaller Li⁺ and Na⁺ cations in acetonitrile (lg K_LiL > 5, lg K_NaL = 7.66), moderately efficient for K⁺ (lg K_KL = 4.62), whereas larger Rb⁺ and Cs⁺ did not fit in its hydrophilic cavity. The complex stabilities in methanol were significantly lower (lg K_NaL = 4.45, lg K_KL = 2.48). That could be explained by different solvation of the cations and by competition between the cations and methanol molecules (via hydrogen bonds) for amide carbonyl oxygens. The influence of cation solvation on complex stability was most pronounced in the case of Li⁺ for which, contrary to the quite stable LiL⁺ complex in acetonitrile, no complexation was observed in methanol under the conditions used.     

Steric and Inductive Effects on Ionic Association in Aqueous Solutions Using an ion Selective Electrode Technique. II. Magnesium Salts

The stoichiometric association constants, K, the thermodynamic association constants, K_A, and the thermodynamic parameters ΔS°, ΔH°, ΔG° for the association between Mg(II) ion with o-, m and p-toluates,o-,m, and p-chlorobenzoates, and o-, m- and p-bromobenzoates have been determined at 15°C, 25°C, 35°C and 45°C in aqueous media. Ion selective electrodes were used to measure the Mg^{2 +} activities. The trends in the association behavior of Mg(II) salts of aromatic acids connot be explained on the basis of steric effects but can be explained according to the trend of the pKa of the parent organic acids, and the Hammett function, σ, of the salts themselves relative to the corresponding benzoate salt.