Study on ion–solvent interactions of alkali metal salts in pure methanol and its binary mixtures with ethane-1,2-diol by a conductometric technique

Electrolytic conductivities of some sodium salts (NaI, NaSCN, CH₃COONa) have been studied in 0, 25, 50 and 75 mass% ethane-1,2-diol + methyl alcohol mixtures at 293.15, 298.15 and 303.15 K. The limiting molar conductivity (Λ°), the association constant (K_A) and the distance of closest approach of ion (R) have been evaluated using the Fuoss conductance equation (1978). The association constant (K_A) decreases with temperature while it tends to decrease in the order: 0 mass% > 25 mass% > 50 mass% > 75 mass% ethane-1,2-diol + methyl alcohol mixtures. Thermodynamic parameters ΔH°, ΔG° and ΔS° along with the Walden products (Λ°η) are obtained and discussed. The results have been interpreted in terms of ion–solvent interactions and structural changes in the mixed solvents.     

Thermodynamische und strukturelle Untersuchungen an den Verbindungen der Systeme KCl/MCl2 (M  Ca,Cd, Co,Ni)

Thermodynamic and Structural Investigations on Compounds of the Systems KCl/Mcl₂ (M=Ca, Cd, Co, Ni) . The formation of ternary chlorides according to the equation nKCl + MCl₂ = K_nMCl_n+2 with M = Ca, Cd, Co, Ni was investigated with a galvanic cell for solid electrolytes. Additionally to the Gibbs energies for the solid reactions, ΔG_R, the entropies, ΔS_R, and enthalpies, ΔH_R were determined by the dependence of the e.m.f. on temperature. But the stability of the double chlorides is given by the free enthalpy of synproportionation from the neighboured compounds. In case of RbSrCl₃ and RbPbCl₃ (stable only at higher temperature) the synproportionation is endothermic; the loss of enthalpy is compensated by a gain of entropy. The same is valid for K₂CoCl₄. Lattice parameters were measured for the modifications of KCaCl₃; the structure of KCdCl₃ was refined by single crystal measurements.     

Protonation equilibria studies of the standard α-amino acids in NaNO3 solutions in water and in mixtures of water and dioxane

The protonation equilibria for 20 standard α-amino acids in solutions have been studied pH-potentiometrically. The dissociation constants (pK_a) of 20 amino acids and the thermodynamic functions (ΔG^∘, ΔH^∘, ΔS^∘, and δ) for the successive and overall protonation processes of amino acids have been derived at different temperatures in water and in three different mixtures of water and dioxane (mole fractions of dioxane were 0.083, 0.174, and 0.33). Titrations were also carried out in water ionic strengths of (0.15, 0.20, and 0.25) mol · dm⁻³ NaNO₃, and the resulting dissociation constants are reported. A detailed thermodynamic analysis of the effects of organic solvent (dioxane), temperature and ionic strength influencing the protonation processes of amino acids is presented and discussed to determine the factors which control these processes.     

Thermodynamics of dimethylene urethane and poly(dimethylene urethane) in the range from T → 0 to 490 K at standard pressure

By high-precision dynamic calorimetry the temperature dependences of heat capacity of dimethylene urethane (DMU) between 320 and 370 K and partially crystalline poly(dimethylene urethane) (PDMU) in the range 326-490 K at standard pressure have been determined within ±1.5%. The thermodynamic characteristics of fusion of the substances, namely the temperature interval of melting, temperature, enthalpy and entropy of fusion, as well as the characteristics of devitrification and glassy state for poly(dimethylene urethane) have been estimated. The first and the second cryoscopic constants have been calculated for dimethylene urethane. The experimental data obtained in the present work and literature findings on the heat capacity of the substances were used to calculate their thermodynamic functions: the heat capacity C°_p (T), enthalpy H°(T)−H°(0), entropy S°(T) and Gibbs function G°(T)−H°(0) over the range from T→0 to (370-480) K. Based on the data, the thermodynamic characteristics of polymerization process with five-membered ring opening Δ_polH°, Δ_polS° and Δ_polG° of dimethylene urethane with the formation of linear partially crystalline poly(dimethylene urethane) have been evaluated.     

Investigation of interactions between some anionic dyes and cationic surfactants by conductometric method

The interactions of cationic surfactants with anionic dyes were studied by conductometric method. Benzyltrimethylammonium chloride (BTMACl), benzyltriethylammonium chloride (BTEACl) and benzyltributylammonium chloride (BTBACl) were used as cationic surfactants and indigo carmine (IC) and amaranth (Amr) were chosen as anionic dyes. The specific conductance of dye–surfactant mixtures was measured at 25, 35 and 45 °C. A decrease in measured specific conductance values of dye–surfactant mixture was caused by the formation of non-conducting or less-conducting dye–surfactant complex. The equilibrium constants, K₁, the standard free energy changes, ΔG₁°$\mathrm{\Delta }{G}_1°$, the standard enthalpy changes, ΔH₁°$\mathrm{\Delta }{H}_1°$ and the standard entropy changes, ΔS₁°$\mathrm{\Delta }{S}_1°$ for the first association step of dye–surfactant complex formation were calculated by a theoretical model. The results showed that the equilibrium constants and the negative standard free energy change values for all systems decreased as temperature increased. Also these values decreased for all systems studied with increasing alkyl chains of surfactants due to the steric effect. When the equilibrium constant values, K₁, for the first association step of IC–surfactant and Amr–surfactant systems with the same surfactant were compared, the values of K₁ for IC–surfactant system were higher than that of Amr–surfactant system.     

Combined cation-exchange and extraction chromatographic method of pre-concentration and concomitant separation of Cu(II) with high molecular mass liquid cation exchanger after its online detection

A selective method has been developed for the extraction chromatographic trace level separation of Cu(II) with Versatic 10 (liquid cation exchanger) coated on silanised silica gel (SSG-V10). Cu(II) has been extracted from 0.1 M acetate buffer at the range of pH 4.0–5.5. The effects of foreign ions, pH, flow-rate, stripping agents on extraction and elution have been investigated. Exchange capacity of the prepared exchanger at different temperatures with respect to Cu(II) has been determined. The extraction equilibrium constant (K_ex) and different standard thermodynamic parameters have also been calculated by temperature variation method. Positive value of ΔH (7.98 kJ mol⁻¹) and ΔS (0.1916 kJ mol⁻¹) and negative value of ΔG (−49.16 kJ mol⁻¹) indicated that the process was endothermic, entropy gaining and spontaneous. Preconcentration factor was optimized at 74.7 ± 0.2 and the desorption constants K_desorption¹(1.4 × 10⁻²) and K_desorption²(9.8 × 10⁻²) were determined. The effect of pH on R_f values in ion exchange paper chromatography has been investigated. In order to investigate the sorption isotherm, two equilibrium models, the Freundlich and Langmuir isotherms, were analyzed. Cu(II) has been separated from synthetic binary and multi-component mixtures containing various metal ions associated with it in ores and alloy samples. The method effectively permits sequential separation of Cu(II) from synthetic quaternary mixture containing its congeners Bi(III), Sn(II), Hg(II) and Cu(II), Cd(II), Pb(II) of same analytical group. The method was found effective for the selective detection, removal and recovery of Cu(II) from industrial waste and standard alloy samples following its preconcentration on the column. A plausible mechanism for the extraction of Cu(II) has been suggested.     

Solubility and preferential solvation of indomethacin in 1,4-dioxane + water solvent mixtures

The solubilities of indomethacin (IMC) in 1,4-dioxane + water cosolvent mixtures were determined at several temperatures, 293.15–313.15 K. The thermodynamic functions: Gibbs energy, enthalpy, and entropy of solution and of mixing were obtained from these data by using the van’t Hoff and Gibbs equations. The solubility was maximal in 0.95 mass fraction of 1,4-dioxane and very low in pure water at all the temperatures. A non-linear plot of ΔH_soln ° vs. ΔG_soln ° with negative slope from pure water up to 0.60 mass fraction of 1,4-dioxane and positive beyond this up to 0.95 mass fraction of 1,4-dioxane was obtained. Accordingly, the driving mechanism for IMC solubility in water-rich mixtures is the entropy, probably due to water-structure loss around the drug non-polar moieties by 1,4-dioxane, whereas, above 0.60 mass fraction of 1,4-dioxane the driving mechanism is the enthalpy, probably due to IMC solvation increase by the co-solvent molecules. The preferential solvation of IMC by the components of the solvent was estimated by means of the quasi-lattice quasi-chemical method, whereas the inverse Kirkwood-Buff integral method could not be applied because of divergence of the integrals in intermediate compositions.     

Reactivity of ZrCl4 and HfCl4 with silylamines and thermal decomposition of the compounds [MCl4{NH(R)(SiR′3)}] (M = Zr,Hf, R = tBu,R′ = Me; R = SiR′3 = SiMe3, SiMe2H)

The Lewis acid/base adducts [MCl₄{NH(R)(SiR′₃)}] (M = Zr, Hf; R = tBu, R′ = Me; R = SiR′₃ = SiMe₃, SiMe₂H) were synthesized by the 1:1 reaction of MCl₄ with NH(R)(SiR′₃) in dichloromethane solution at room temperature. The decomposition of [MCl₄{NH(R)(SiR′₃)}] proceeds with the elimination of R′₃SiCl, as shown by thermogravimetric analysis. Pyrolysis of the compounds at 620 °C under inert conditions (N₂, vacuum) afforded powders of composition [ClMN] or [Cl₂MNH]. Preliminary low pressure chemical vapour deposition experiments show that [MCl₄{NH(R)(SiR′₃)}] deposits thin films of metal nitride contaminated with metal oxide.     

Simultaneous determination of enthalpies of dilution and dissociation of protocatechuic acid in aqueous salt solutions by calorimetric measurements

Protocatechuic acid, a major metabolite of antioxidant polyphenols found in green tea, has been shown to prevent carcinogenesis or antitumor growth in vitro and in vivo studies. The dilution enthalpies Δ_dilH_m, dissociation enthalpies Δ_disH_m and thermodynamic dissociation constants K_a for protocatechuic acid in aqueous NaCl or KCl solutions were simultaneously determined by mixing-flow microcalorimetry at T = 298.15 K. In order to verify the reliability of the fitted dissociation parameters, the values of dissociation enthalpies and thermodynamic dissociation constants were also determined by isothermal titration calorimetry and electrical conductivity methods. The K_a values obtained through the proposed method agree well with those reported in literatures and obtained by other techniques. Enthalpic interaction coefficients (h₂, h₃ and h₄) were computed according to the McMillan–Mayer model. The trends of h₂ and Δ_disH_m for protocatechuic acid with increasing salt molality in both the salt solutions were obtained. The different influence of KCl and NaCl on the values of h₂ and Δ_disH_m were discussed in terms of (solute + solute) and (solute + solvent) interactions. The results showed that it is possible to perform in a single calorimetric experiment the simultaneous determination of dilution enthalpies, dissociation enthalpies and constants in a given solvent.     

Thermodynamic study of solid solutions in the SnTe–AgSbTe<Subscript>2</Subscript> system by means of EMF with solid electrolyte Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript>

The results from studying the SnTe–AgSbTe₂ system by means of EMF with the solid electrolyte Ag₄RbI₅ in the temperature range of 300–430 K are presented. The formation of a wide (≥80 mol % of AgSbTe₂) region of solid solutions based on SnTe is confirmed. Partial thermodynamic functions ΔG?, ΔH?, and ΔS? of silver in alloys are calculated from the equations for the EMF temperature dependences. Based on the literature data regarding solid-phase equilibria in the Ag₂Te–SnTe–Sb₂Te₃–Te system, potential-determining reactions are identified that allow us to calculate the standard thermodynamic formation functions and standard entropies of solid solutions (2SnTe) _x (AgSbTe₂)_1?x (х = 0.2, 0.4, 0.6, 0.8, and 0.9).     

Effect of Preferential Solvation on the Thermodynamic Properties of Antidepressant Drug Trazodone in Aqueous Ethanol: Linear Free‐Energy Relationships

Dissociation constants (pK_a) of trazodone hydrochloride (TZD⋅HCl) in EtOH/H₂O media containing 0, 10, 20, 30, 40, 50, 60, 70, and 80% (v/v) EtOH at 288.15, 298.15, 308.15, and 318.15 K were determined by potentiometric techniques. At any temperature, pK_a decreased as the solvent was enriched with EtOH. The dissociation and transfer thermodynamic parameters were calculated, and the results showed that a non‐spontaneous free‐energy change (Δ_dissG^o>0) and unfavorable enthalpy (Δ_dissH^o>0) and entropy (Δ_dissS^o<0) changes occurred on dissociation of trazodone hydrochloride. The free‐energy change or pK_a varied nonlinearly with the reciprocal dielectric constant, indicating the inadequacy of the electrostatic approach. The dissociation equilibria are discussed on the basis of the standard thermodynamics of transfer, solvent basicity, and solute‐solvent interactions. The values of Δ_transG^o and Δ_transH^o increased negatively with increasing EtOH content, revealing a favorable transfer of trazodone hydrochloride from H₂O to EtOH/H₂O mixtures and preferential solvation of H⁺ and trazodone (TZD). Also, Δ_transS^o values were negative and reached a minimum, in the H₂O‐rich zone that has frequently been related to the initial promotion and subsequent collapse of the lattice structure of water. The pK_a or Δ_dissG^o values correlated well with the Dimroth‐Reichardt polarity parameter E_T(30), indicating that the physicochemical properties of the solute in binary H₂O/organic solvent mixtures are better correlated with a microscopic parameter than the macroscopic one. Also, it is suggested that preferential solvation plays a significant role in influencing the solvent dependence of dissociation of trazodone hydrochloride. The solute‐solvent interactions were clarified on the basis of the linear free‐energy relationships of Kamlet and Taft. The best multiparametric fit to the Kamlet‐Taft equation was evaluated for each thermodynamic parameter. Therefore, these parameters in any EtOH/H₂O mixture up to 80% were accurately derived by means of the obtained equations.     

The monomer−dimer equilibria of liquid aliminum alkyls : III. Trimethylaluminum: the monomer−dimer equilibria of liquid and gaseous trimethylaluminum and triethylaluminum

There has been a dichotomy of opinion concerning the values for the heats of dissociation of trimethylaluminum (TMA) and triethylaluminum (TEA) in the liquid phase. It is believd that the result reported herein will enable these differences to be resolved. In the present study, the heat of dissociation (ΔH^o_d of liquid TMA is evaluated as 19.4₀±0.3₀-kcal · (mole of dimer)⁻¹ from the previously determined ΔH⁰_d of liquid TEA and new heat of mixing data for TMA−TEA. Essentially the same result is derived from the established ΔH⁰_d of gaseous TMA by application of a thermodynamic relationship between heats of dissociation and heats of vaporization (the “Dissociation−Vaporization Rule”). It is concluded that the experimental ΔH⁰_d values for liquid TEA (16.9₃ kcal · (mole of dimer)⁻¹) and gaseous TMA (20.4₀ are thermodynamically consistent. The ΔS⁰_dof liquid TMA is evaluated as 29.3±0.3 cal · K⁻¹ · (mole of dimer)⁻¹. The ΔH⁰_d valuesfor liquid adn gaseous TMA are shown to be thermodynamically consistent with vapor pressure data. Boiling points derived for pure TMA monomer and pure dimer are 8.1±2.1 and 131.95±0.02°C, respectively. Degrees of dissociation of TMA in the pure liquid state and at various mole fractions in aliphatic hydrocarbon solution are tabulated over a wide temperature range. The results indicate that the extent of dissociation of liquid TMA is 0.0047% at 20, 0.053% at 70, and 0.32% at 120°C.     

The thermodynamic parameters of the step dissociation of L-phenylalanyl in aqueous solution

The heats of interaction of L-phenylalanine with solutions of nitric acid and potassium and lithium hydroxides were determined calorimetrically at 288.15, 298.15, and 308.15 K and solution ionic strengths of 0.5, 0.75, and 1.0 in the presence of LiNO₃ and KNO₃. The standard thermodynamic characteristics (Δ_r H°, Δ_r G°, Δ_r S°, and ΔC _p ^° of acid-base interactions in aqueous solutions of L-phenylalanine were calculated. The influence of the concentration of background electrolytes and temperature on the heats of dissociation of L-phenylalanine was considered. A comparative analysis of the standard thermodynamic characteristics of step dissociation of L-phenylalanine and alanine was performed in terms of the modern concepts of the structure and physicochemical properties of these compounds and their solutions.     

Thermodynamics of the second-stage dissociation of n-(2-acetamido)iminodiacetic acid in water from 5 to 55°c

The thermodynamic second dissociation constants of the protonated form of N-(2-acetamido)iminodiacetic acid were determined at 12 temperatures from 5–55°C by measurement of the electromotive force using a cell without liquid junction, with hydrogen and silver—silver bromide electrodes. At 25°C, pK₂is 6.844. The standard changes in Gibbs energy, enthalpy, entropy and heat capacity were derived from the change of the pK₂ values with temperature. At 25°C, ΔG° = 9335 cal mol^-1, ΔH° = 2928 cal mol^-1, ΔS^o = -21.5 cal K^-1 mol^-1, and ΔC°_p = -34 cal K^-1 mol^-1. The results are interpreted and compared with those of structurally related compounds.     

New synthetic and structural studies on nitroso-ortho-carboranes RCB10H10CNO and bis(ortho-carboranyl)amines (RCB10H10C)2NH (R = Ph or Me)

Improved procedures are reported for the preparation of nitroso-carboranes RCb°NO (Cb° = 1,2-C₂B₁₀H₁₀; R = Ph, Me at cage carbon C2) in 44–77% yield, and of dicarboranylamines (RCb°)₂NH in 55–65% yield by reactions between the lithio-carboranes, RCb°Li and nitrosyl chloride, NOCl, in cold mixtures of diethyl ether and either pentane (for RCb°NO) or dimethoxyethane (for (RCb°)₂NH). Deprotonation of the amines by KO^tBu in toluene in the presence of 18-crown-6, (CH₂CH₂O)₆, affords the salts [K(18-crown-6)]⁺[(RCb°)₂N]⁻. X-ray crystal structures of PhCb°NO, (PhCb°)₂NH, (MeCb°)₂NH and [K(18-crown-6)]⁺[(PhCb°)₂N]⁻ are described, and the bonding implications of their cage C…C distances (1.68, 1.80, 1.75 and 1.99 Å, respectively) are discussed. These species provide further striking examples of the remarkable capacity of the ortho-carborane cage to act as a sensitive indicator of the π-donor characteristics of ligands attached to its cage carbon atoms.     

Ion association and solvation behavior of some alkali metal acetates in aqueous 2-butanol solutions at T = 298.15, 303.15 and 308.15 K

Molar conductance of lithium acetate, sodium acetate and potassium acetate were studied in aqueous 2-butanol solutions with an alcohol mass fraction (w₂) of 0.70, 0.80 and 0.90 at 298.15, 303.15 and 308.15 K. The conductance data were analyzed with the Fuoss conductance-concentration equation to evaluate the limiting molar conductances (Λ₀), association constants (K_A,c) and cosphere diameter (R) for ion-pair formation. Gibbs energy (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) for ion-association reaction were derived from the temperature dependence of K_A,c. Activation energy for ionic movement (ΔH^#) was derived from the temperature dependence of Λ₀. Based on the composition dependence of Walden products (Λ₀η₀) and different thermodynamic properties (ΔG⁰,ΔH⁰, ΔS⁰ and ΔH^#), the influence of the solvent composition on ion-association and solvation behavior of ions were discussed in terms of ion-solvent, ion-ion interactions and the structural changes in the mixed solvent media.     

Quantitative evaluation of catalytic effect of metal chlorides on the decomposition reaction of NaAlH4

The hydrogen desorption (or decomposition) reaction of NaAlH₄ is expressed as , and its desorption rate is accelerated by mixing metal chloride catalysts (e.g., TiCl₃). This catalytic effect of metal chlorides, MCl_n, is theoretically estimated in a quantitative way using atomization energy concept. The atomization energies, ΔE_M for metal ion and ΔE_Cl for chloride ion in various metal chlorides are evaluated using the energy density analysis of the total energy. It is shown that the hydrogen desorption reaction rate increases with increasing n × ΔE_M values of metal chlorides. This indicates that the metal ion in MCl_n interacts mainly with hydrogen or [AlH₄]^? complex anion in NaAlH₄. To confirm this calculated result, experiments are performed using NaAlH₄ mixed with Ti‐based catalysts. The hydrogen desorption rate is enhanced in the order, TiCl₃ > TiO₂ > Ti metal nanopowder, indicating that the Ti ions in TiCl₃ or TiO₂ work to promote the catalytic reaction more effectively than the neutral Ti atoms in Ti metal nanopowder. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Thermodynamics of 2D polymerized tetragonal phase of fullerene C60 in the range from T→0 to 650 K at standard pressure

By dynamic calorimetry the temperature dependence of heat capacity for two-dimensional (2D) polymerized tetragonal phase of C₆₀ has been determined over the 300-650 K range at standard pressure mainly with an uncertainty ±1.5%. In the range 490-550 K, an irreversible endothermic transition of the phase, caused by the depolymerization of the polymer, has been found and characterized. Based on the experimental data obtained and literature information, the thermodynamic functions of 2D polymerized tetragonal phase of C₆₀, namely, the heat capacity C°_p(T), enthalpy H°(T)−H°(0), entropy S°(T), and Gibbs function G°(T)−H°(0), have been calculated over the range from T→0 to 490 K. From 150 to 330 K in an adiabatic vacuum calorimeter and between 330 and 650 K in a dynamic calorimeter the thermodynamic properties of the depolymerization products have been examined and compared with the corresponding data for the monomeric phase C₆₀.