Complex Formation of Crown Ethers with Cations in Water–Organic Solvent Mixtures. III. Thermodynamics of Interaction Between Na+ Ion with 15-Crown-5 Ether in Water–Acetonitrile Mixtures at 25°C

Enthalpies of solution of 15-crown-5 ether in the acetonitrile–water–sodium iodide system have been measured at 25°C. The equilibrium constants of complex formation of 15C5 with sodium iodide have been determined by molar conductance at various mole ratios 15C5 to sodium iodide in mixtures of water with acetonitrile at 25°C. The thermodynamic functions for complexation of the crown ether with Na⁺ were calculated. From the result, the standard Gibbs energies of complex formation as a function of the normalized Lewis acidity parameters E ^N _T and enthalpy of solvation of 15C5 in the mixtures of water with acetonitrile have been analyzed. The enthalpies of transfer of the 15C5 complex with sodium iodide from pure acetonitrile to the mixtures studied were calculated and discussed.     

Enthalpies of Dilution of Aqueous Solutions of HCl, MgCl2}, CaCl2, and BaCl2 at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of BaCl₂ at 300°C and 11.0 MPa, MgCl₂, CaCl₂, and BaCl₂ at 325°C and 14.8 MPa, and at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of MgCl₂ and CaCl₂ at 300°C and 10.3 MPa and for aqueous solutions of HCl at 250, 275, and 300°C at 10.3 MPa and 320°C at 12.8 MPa were included with the new data at 300°C and 11.0 MPa and at 350°C and 17.6 MPa when fitting the Pitzer parameters. The concentration range of the chloride solutions was 0.5 to 0.02 molal. Parameters for the Pitzer excess Gibbs ion–interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat-capacity changes for the association of alkaline earth metal ions and H⁺ with chloride ion were estimated from the heat data. For all systems, the enthalpy and entropy changes are positive and show accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.     

Enthalpies of Dilution of Aqueous Solutions of NaOH, KOH, and CsOH at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of KOH and CsOH at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and for aqueous solutions of NaOH, KOH, and CsOH at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of NaOH at 300°C and 9.3 MPa and at 325°C and 12.4 MPa were included when fitting the Pitzer parameters. The concentration range of the hydroxide solutions was 0.5–0.02 molal. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for alkali metal ion association with hydroxide ion were estimated from the heat data. For all systems, the enthalpy changes and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.     

A study of metal complexes of a naturally occurring macrocyclic ionophore-monensin

The acid-base and complexing properties of a naturally occurring antibiotic ionophore-monensin (MonH)-were studied in anhydrous methanol solutions primarily by potentiometric measurements. The pK _a of the acid was found to be 10.30±0.05 at 25°C. Complexes of silver, thallium, and alkali ions with the undissociated ligand were also studied, and their stability constants were determined. The acid dissociation constant of MonH as well as the stability constants of Mon^– Na⁺ and MonH·NaClO₄ complexes were determined in the 5–45°C temperature range, and the enthalpy and entropy of the acidity and stability constants were determined from van't Hoff's plots. The formation of MonH and Mon^–Na⁺ species are both enthalpy and entropy stabilized, but the formation of the MonH·NaClO₄ complex is enthalpy stabilized but entropy destabilized.     

The state of aggregation of methyl orange in water

The electrical conductances, UV-visible absorbances, and osmotic coefficients of aqueous solutions of methyl orange, sodium 4-(4-dimethylaminophenyldiazo)-phenylsulfonate, have been measured at 25°C. From the behavior of these quantities as a function of concentration it is concluded that the methyl orange anion is almost completely dimerized above 0.2 mM and undergoes further aggregation above 1 mM. Literature values of the osmotic coefficients of aqueous methyl orange at 50 and 60°C are fitted to the monomer-dimer equilibrium yielding values of the dimer formation constant, K_d. Extrapolation to 25°C yields an estimate of K_d=9200 at this temperature. This result is shown to be consistent with the conductance data at 25°C presented here.     

Conductance and Thermodynamic Study of Thallium and Silver Ion Complexes with Crown Ethers in Different Binary Acetonitrile–Water Solvent Mixtures

The complexation reactions between Ag⁺ andTl⁺ ions with 15-crown-5 (15C5) and phenyl-aza-15-crown-5(PhA15C5) have been studied conductometrically in 90%acetonitrile-water and 50% acetonitrile - water mixed solvents attemperatures of 293, 298, 303 and 308 K. The stability constants of theresulting 1 : 1 complexes were determined, indicating that theTl⁺ complexes are more stable than the Ag⁺complexes. The enthalpy and entropy of crown complexation reactions were determined from the temperature dependence of the complexation constants.The enthalpy and entropy changes depend on solvent composition and the T S⁰ _o–H⁰ plotshows a good linear correlation, indicating the existence of entropy –enthalpy compensation in the crown complexation reactions.     

Enthalpy of dissociation of water at 325°C and LogK, ΔH, ΔS,and ΔC p values for the formation of NaOH(aq) from 250 to 325°C

The aqueous reactions H⁺+OH^–=H₂O at 325°C and Na⁺+OH^–= NaOH(aq) at 250–325°C, were studied using a flow calorimeter. Heats of mixing of aqueous NaOH and HCl solutions were measured at 325°C. The enthalpy of water formation (H=95.9 kJ-mol^–1, valid at 12.4 MPa and infinite dilution) was obtained at this temperature from the heat of mixing data but differs significantly from that calculated from the Marshall-Franck equation. This calorimetric H at 325°C was used in combination with literaturelog K and H values at lower temperatures to derive equations representinglog K, H, S, and C_p for the formation of water from 250 to 325°C. Heats of dilution of aqueous NaOH solutions were measured at 250, 275, 300, and 325°C. Log K, H, and S for the formation of NaOH(aq) were determined at these temperatures from the fits of the calculated and measured heats while C_p values were calculated from the variation of H with temperature. No previous experimental results have been reported for the formation of NaOH(aq). The isocoulombic reaction principle is tested using thelog K values obtained in this study. The plot oflog K vs. 1/T for the isocoulombic reaction NaOH(aq) +H⁺=H₂O+Na⁺ is approximately linear.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.Taken in part from the Ph.D. Dissertation of Xuemin Chen, Brigham Young University, 1991.     

Ion-solvent interactions and ionic association in ethanol solutions

The electrical conductivities of potassium halides in ethanol have been measured at 25°C. The limiting molar conductances, ionic association constants and the closest approach parameter were calculated (Justice method) and compared with existing literature data. An inversion of the anion size dependence of ionic association constants for these solutions was observed. The results are explained by what has been called localized solvolysis, in which both the cation and the anion of the solvent separated ion pair are connected with different parts of the separating solvent molecule by donor-acceptor bonding. A correlation between K _A and protonic affinity of anions was found. Similar literature data for aqueous and non-aqueous solutions are also examined.     

Potentiometric Investigation of the Weak Association of Sodium and Carbonate Ions at 25°C

The weak association between sodium and carbonate ions has been investigated at 25°C using high-precision sodium ion-selective electrode potentiometry in solutions of ionic strength ranging from 0.5 to 7.0 M in CsCl and in 1.0 M Me₄NCl media. The protonation constants of CO ₃ ^2- (aq) were also measured, using a H⁺-responsive glass electrode in 1.0 M Me₄NCl and NaCl. The value of the ion-pair association constant calculated from the difference in the protonation constants in these two media was in excellent agreement with that obtained from the Na⁺ISE measurements. Evidence is also presented for the formation of extremely weak ion pairs between Na⁺ and HCO ₃ ^- and between Cs⁺ and CO ₃ ^2- .     

Aqueous iodic acid: Conductance and thermodynamics

Precision conductance measurements are reported on aqueous solutions of iodic acid for 16 concentrations between 17 and 0.7 mM and for 20 temperatures between 5° and 100°C. RlnK _a (m) and _o were calculated at each temperature and the data expressed by suitable temperature functions. From RlnK _a (m) as a function of temperature changes in standard enthalpy, entropy, and heat capacity were calculated. C _p proved to be independent of temperature so that H⁰ was a linear function of temperature. Comparisons have been made with other published data for iodic acid. The pattern of variation of Walden products with temperature was similar to that found earlier for substituted benzoic acids.     

Potentiometric Determination of the First Hydrolysis Constant of Gallium(III) in NaCl Solution to 100°C

The hydrolysis equilibrum of gallium (III) solutions in aqueous 1 mol-kg^–1 NaCl over a range of low pH was measured potentiometrically with a hydrogen ion concentration cell at temperatures from 25 to 100°C at 25°C intervals. Potentials at temperatures above 100°C increased gradually because of further hydrolysis of the gallium(III) ion, followed by precipitation. The results were treated with a nonlinear least-squares computer program to determine the equilibrium constants for gallium(III)–hydroxo complexes using the Debye–Hückel equation. The log K (mol-kg^–1) values of the first hydrolysis constant for the reaction, Ga³⁺ + H₂O GaOH²⁺ + H⁺ were –2.85 ± 0.03 at 25°C, –2.36 ± 0.03 at 50°C, –1.98 ± 0.01 at 75°C, and –1.45 ± 0.02 at 100°C. The computed standard enthalpy and entropy changes for the hydrolysis reaction are presented over the range of experimental temperatures.     

The enthalpies of solution and crystallization of sodium nitrate in water at 25°C

The differential enthalpies of solution of sodium nitrate in water have been measured calorimetrically at 25°C, from 0.5 to 10.4 mol (kg H₂O)^–1. The concentration dependence is described by the equation H=20.4537+1.0562m^1/2-7.0568m+2.8659m^3/2-0.3382m² From the calorimetric measurements, the enthalpy of crystallization of sodium nitrate was calculated as H_c=9.98±0.16 kL-mol^-1. The literature data on the solubility, activity and osmotic coefficients of NaNO₃ at 25°C yielded a value of –9.98±0.38 kJ-mol^–1. The good agreement between the experimental and calculated H_c values indicate the reliability of the input data.     

Ionization constants of benzoic acid from 25 to 250°C and to 2000 bar

The ionization constant of benzoic acid has been determined by conductivity measurements of dilute aqueous solutions and found to vary from 6.27×10^–5 at 25°C to 0.39×10^–5 at 250°C. The pressure effect to 2000 bar has been measured, and the ratio of ionization constants K₂₀₀₀/K₁ is 2.26 at 25°C and 7.3 at 250°C. V°₁, the standard partial molar volume change for the ionization at 1 bar, varies from –11.7 cm³-mol^–1 at 25°C to –60 cm³-mol^–1 at 250°C. The volume changes are smaller at higher pressures.     

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.     

Complete Resolution and Thermodynamic Parameters of the Ionization Equilibria of Pyridoxal in Water—Dioxane Mixtures

A potentiometric method has been used to determine the thermodynamicequilibrium constants for the macroscopic ionization processes of pyridoxal inwater—1,4-dioxane mixtures (0–70% weight fraction dioxane)at temperatures ranging from 10 to 50°C. These data, combined with the equilibrium constants for the tautomericand hemiacetalization processes, allow complete resolution of the microconstantsystem and calculation of the microscopic ionization equilibrium constants underall our experimental conditions. The standard thermodynamic function changesfor the macroscopic and microscopic ionization processes were obtained in variouswater—1,4-dioxane mixtures at 25°C. The values of any given microscopic pKfor the different solvents and temperatures fit very well to a single equation. Thefree energy, enthalpy, and entropy obtained for the different ionization processesin water—dioxane mixtures correlate with Kamlet and Taft's solvatochromicparameters ^* and , which are a measure of the dipolarity/polarizability andhydrogen-bonding capacity of the solvent, respectively. These correlations explainmore fully the mutual compensation between the contributions of enthalpy andentropy and the origin of the solvent effect on the pK.     

Complex Formation of Crown Ethers with Cations in the Water–Organic Solvent Mixtures. Part VII. Thermodynamic of Interactions of Na+ Ion with 15-Crown-5 Ether in the Mixture of Water with N,N-Dimethylacetamide at 298.15 K

The thermodynamic functions of the complex formation of 15-crown-5 ether with sodium cation in mixtures of water with N,N-dimethylacetamide at 298.15K are calculated. The equilibrium constants of complex formation of 15-crown-5 ether with sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method at 298.15K. The complexes are enthalpy-stabilized but entropy-destabilized in this mixed solvent. A quantitative dependence of the excess molar enthalpy and entropy of complex formation on the structural and energetic properties of interactions between water and organic solvent molecules in the mixtures of water with N,N-dimethylacetamide, N,N-dimethylformamide and dimethylsulfoxide has been found. The linear entropy–enthalpy relationship for complex formation is also presented. The solvation enthalpy of the complex in the water–N,N-dimethylacetamide mixtures is discussed.     

Excess enthalpy and entropy of aqueous tetramethylguanidinium perchlorate and chloride and tetramethylammonium nitrate

Heats of dilution have been measured for aqueous solutions of tetramethylguanidinium perchlorate and chloride and for tetramethylammonium nitrate at 25°C. Excess enthalpies have been calculated and combined with excess free energy data which were previously published to yield excess entropy. These results furnish further evidence for the association of the tetramethylguanidinium salts in aqueous solutions.     

UV-Vis Spectrophotometric Determination of the Dissociation Constants for Monochlorophenols in Aqueous Solution at Elevated Temperatures

The dissociation constants of monochlorophenols (2-, 3-, 4-chlorophenols) were examined using direct UV-vis spectroscopy at temperatures from 25 to 175^°C and at saturated vapor pressures in a high-temperature, high-pressure cell. The dissociation constant, K _a increased under experimental temperatures in the order: 2-chlorophenol, 3-chlorophenol, and 4-chlorophenol. The dissociation constant of 4-chlorophenol increased with increasing temperature under experimental conditions, while those of 2- and 3-chlorophenol reached maximum values at around 125^°C, and then decreased with further increases in temperature. The slope of (log K)/ (1/T) was nonconstant and positive, that is, endothermic, below 150^°C. The data on dissociation constants were analyzed by simultaneous regression to yield a five-term equation that described the Van't Hoff isobar. The magnitude of enthalpy H increased at 25^°C in the order: 3-chlorophenol, 4-chlorophenol, and 2-chlorophenol. The decrease in enthalpy at the absolute temperature was larger for 3-chlorophenol than for either 2- or 4-chlorophenol. Considering the equilibrium constant K _b for the isocoulombic reaction of monochlorophenol with OH^–, the nearly linear relationship of log K _b vs. 1/T for temperatures between 25 and 175^°C indicates that the C_p values for this isocoulombic reaction are low.     

Conductance study of the thermodynamics of ammonium ion complexes with several crown ethers in acetonitrile solution

A conductance study concerning the interaction between ammonium ion and several crown ethers in acetonitrile solution has been carried out at different temperatures. The stability constants of the resulting 11 complexes at various temperatures were determined from the molar conductance-mole ratio data and found to vary in the order DC18C6>18C6>DB30C10>DB21C7>DB24C8>DB18C6>15C5>B15C5. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. The influence on the thermodynamic data of different parameters such as cavity size and dimensionality of crown ethers, nature of substituents in the polyether ring, conformations of the free and complexed ligands, solvent-ligand interaction and number of N–H bonds available for hydrogen bonding are discussed.     

Thermodynamic Studies of the Complexation between Neodymium and Acetate at Elevated Temperatures

Complexation of neodymium (III) with acetate in 2.2 mol-kg^-1 NaClO₄ solution was studied at elevated temperatures (45 and 70°C) by potentiometry, calorimetry, and optical spectroscopy. The formation constants of the consecutive complexes, Nd(OOCCH₃),²⁺ Nd(OOCCH₃) ₂ ⁺ , and Nd(OOCCH₃)₃, and the molar enthalpies of complexation at these temperatures were determined. The stability of the three complexes increases with increased temperatures, because of increased positive entropy change at higher temperatures, which exceeds the increased values of the positive (endothermic) enthalpy. The molar heat capacity changes of complexation C_p,m(MLj) (J-K^-1-mol^-1) for Nd(OOCCH₃) _j ^(3-j)+ in the temperature range from 25 to 70°C were calculated to be: 102 ± 13 (j = 1); 122 ± 19 (j = 2); and 239 ± 27 (j = 3). The effect of temperature on the complexation is discussed in terms of the electrostatic model.