Thermochemistry of Complexation of 15-Crown-5 and 18-Crown-6 with Na+and NH+4Ions in Aqueous Solutions

The complexation constants and the heats of complexation of 15-crown-5 (15C5) and 18-crown-6 (18C6) with sodium and ammonium ions in aqueous solutions at several temperatures were determined using calorimetry methods. Thermodynamic characteristics (H°, G°, S°, and C _p°) of the formation of Na(15C5)⁺, Na(18C6)⁺, and NH₄(18C6)⁺were calculated.     

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 of silver(I)-18-crown-6 perchlorate complex in methanol-acetonitrile mixtures

The standard Gibbs transfer energies of the silver(I)-18-crown-6 perchlorate complex salt from methanol to various compositions of methanol-acetonitrile mixtures were determined from solubility measurements at 30°C and these data were separated into the corresponding ionic contributions by employing the negligible liquid junction potential method of Parkeret al. The solvent transport numbers _AN, for the salt were also determined at various solvent compositions using a concentration cell with transference.The Gibbs transfer energy of the silver(I)-18-crown-6 complex cation is negative and decreases with the addition of acetonitrile but the transfer energy of the anion is positive and increases under the same conditions. The solvent transport number, _AN, increases and passes through a maximum value of 5.48 at _AN=0.55. These results indicate that the complex salt is heteroselectively solvated in these mixtures with the cation being preferentially solvated by acetonitrile and the anion by methanol molecules.     

Thermodynamics of 15-Crown-5 Complexation with Ag+ and Pb2+ Ions

Heats and constants of 15-crown-5 (R) complexation with silver and lead ions at 298, 308, and 318 K are determined using direct calorimetry. Thermodynamic parameters (G°, H°, S°, and C _p°) of formation of AgR⁺ and PbR²⁺ complexes at various temperatures are calculated. The effects of the properties of the cations and crown ethers on the thermodynamic parameters of complexation are discussed.     

Determination of enthalpy of ionization of water from 250 to 350° C

The enthalpy changes at zero ionic strength (H°) for the ionization of water (H₂O=H⁺+OH^–) were determined by flow calorimetry from the heats of mixing of aqueous NaOH and HCl solutions in the temperature range 250 to 350°C. Pitzer ion-interaction models developed by other workers were used to calculate enthalpies of dilution of aqueous NaOH, HCl, and NaCl solutions for the extrapolation of H values from the conditions of the experiment to infinite dilution. Equations are derived for thermodynamic quantities (log K, H°, S°, C _p ^° and V°) for the ionization of water using the H° values determined in this study from 250 to 350°C and literature log K and H° values from 0 to 225°C. Smoothed values of log K, H°, S°, C _p ^° , and V° are presented at rounded temperatures from 0 to 350°C and at the saturation pressure of water for each temperature. The equations in the present study provide a better representation of experimental thermodynamic data from 0 to 350°C than the Marshall-Franck equation.     

Square Wave Voltammetric-Thermodynamic Study of the Interaction Between Heavy Metal Ions and Some Macrocyclic Ligands in Water*

The interaction between Cd²⁺ and Pb²⁺ ions and 18-crown-6 (18C6), 1,10-diaza-18-crown-6 (C22) and 1,7-diaza-15-crown-5 (C21) were studied in water solvent at 25, 35, 45 and 55° using square wave voltammetric technique. The stoichiometry and stability of the complexes were determined by monitoring the shift in half-wave or peak potential of the polarographic waves of metal against the ligand concentration. Thermodynamic parameters such as G, H and S were obtained by using a polarographic double wall cell in which the temperature could be fixed to ±0.1°C. The results of all experiments show 1 : 1 complexes, but in addition to 1 : 1 ratio, a 2 : 1 ratio of ligand to cation is also obtained for C22–Pb²⁺ complex. The selectivity order for 18C6 and C22 is Pb²⁺ > Cd²⁺. The thermodynamic data G, H and S values show that the complexes are stabilized by both the enthalpy and entropy terms, but C22–Pb²⁺ complex is stabilized by only enthalpy term.     

Nuclear magnetic resonance study of the ligand interchange of Ba2+-18-crown-6 complex in methanol solution

Exchange kinetics of Ba²⁺-18-crown-6 complex in deuterated methanol solution was studied by proton NMR line-shape analysis of a series of solutions containing equal population of free and complexed 18-crown-6, but varying concentration of the macrocycle, at various temperatures. From –33 to 37°C, the predominant mechanism for the exchange of the ligand between the two sites is a bimolecular pathway which is characterized by the following activation parameters:E _a=47±2 kJ-mol^–1; H =45±2 kJ-mol^–1; S =–8±4 J-mol^–1-K^–1. However, the contribution of a dissociative mechanism with activation parametersE _a=36±5 kJ-mol^–1, H =33±5 kJ-mol^–1 and S =104±18 J-mol^–1-K^–1 becomes more important at higher temperatures.     

Thermodynamic quantities for the interaction of Cl− with Mg2+, Ca2+ and H+ in aqueous solution from 250 to 325°C

The aqueous reactions, Mg²⁺+Cl^–=MgCl⁺, Ca²⁺+Cl^–=CaCl⁺, and H⁺ +Cl^–=HCl(aq), were studied as a function of ionic strength at 250, 275, 300, and 325°C using a flow calorimetric technique. The logK, H, S and C_p values were determined from the fits of the calculated and experimental heast. The data were reduced assuming a known functionality of the activity coefficient. Hence, the logK, H, S and C_p values determined in this study are dependent on the activity coefficient model used. These thermodynamic values were compared with literature results. The logK values for the formation of MgCl⁺ agree reasonably well with those reported in the literature. The logK values for CaCl⁺ formation agree reasonably well with those reported in the literature at 300 and 325°C. At lower temperatures, the agreement is poorer. The logK values for the formation of HCl(aq) are generally lower than those reported in the literature. The logK, H, S and C_p values for all three ion association reactions are positive and increase with temperature over the temperature range studied. These values are the first determined calorimetrically for the formation of MgCl⁺ and CaCl⁺ in the temperature range 275–325°C.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.     

Thermodynamic study of complex formation of benzo-18-crown-6 with K+, Tl+, and Pb2+ in water

H ⁰ and S ⁰ values of the complex formation in water of benzo-18-crown-6 (B18C6) with K⁺, Tl⁺, and Pb²⁺ were determined and compared with those of 18-crown-6. The H⁰ values of B18C6 are negative. The stability in water of the B18C6-metal ion complex at 25°C is governed largely by the magnitude of the H ⁰ value. The B18C6-metal ion complex is less stable in water than the corresponding 18C6-metal ion complex. This is due largely to a less favorable enthalpic contribution of the B18C6-metal ion complex compared with the corresponding 18C6-metal ion complex. The two aromatic ether oxygen atoms of B18C6 are responsible for the larger H ⁰ value of the B18C6-metal ion complex compared with the corresponding 18C6-metal ion complex.     

Enthalpy of solution of carbohydrates using a modified differential scanning calorimeter

A differential scanning calorimeter (DSC) was modified for the determination of enthalpies of solution. The measurements were performed on aqueous solutions of the deoxy- and fluoro-deoxy derivatives of D-glucopyranose (Glu) where the OH group on the C1, C2, C3, and C6 is replaced by H (1HGlu, 2HGlu, 3HGlu, and 6HGlu) and by F (1FGlu, 2FGlu, 3FGlu, and 6FGlu), 4-deoxy 4-fluoro--D-glucopyranoside (4FGlu), 1-methoxy--D-glucopyranoside (MeOGlu), 1-phenoxy--D-glucopyranoside (PheOGlu), D-mannopyranose (Man), and 3-methoxy--D-glucopyranoside (3MeOGlu), at 15.1, 25.0, 35.0, and 45.1°C. The enthalpies of solution _sH⁰(T) ranged from 1.00±0.25 kJ-mol^–1 for 6HGlu at 15.1°C to 20.4±1.4 for PhOGlu at 45.1°C and were in good agreement with literature values for Man, Glu, MeOGlu, and 3MeOGlu at 25.0 and 35.0°C and for MeOMan and 2HGlu at 35.0°C. _sH⁰(T) for the derivatives were then extrapolated up to the melting temperature T_m and compared with their enthalpies of fusion, _fH also determined from DSC measurements. If the agreement between _sH⁰(T_m) and _fH was within the 95% confidence level, then it was concluded that intermolecular interactions between the carbohydrate molecules in the liquid phase were the same as between the carbohydrate and water molecules in the solution phase. This agreement was observed for aqueous solutions of Man, Glu, MeOGlu, 3HGlu, 3FGlu, and 6FGlu.     

Thermodynamics of protonation of amino acid carboxylate groups from 50 to 125°C

Flow calorimetry has been used to study the interaction of glycine, DL--alanine, DL-2-aminobutyric acid, -alanine, 4-aminobutyric acid, and 6-aminocaproic acid with protons in aqueous solutions from 323.15 K to 398.15 K and at 1.52 MPa. LogK, H°, S°, and C _p ^° for the protonation of the carboxylate groups of these amino acids have been obtained at each temperature studied. Equations are given expressing these values as functions of temperature. The protonation reactions are exothermic at lower temperatures and become endothermic as temperature increases. The logK, H°, and S° values are close together over the temperature range studied for the protonation of -amino acids, i.e., glycine, DL--alanine, and 2-aminobutyric acid. At each temperature, the magnitudes of these thermodynamic quantities increase as the number of methylene groups between the amino group and the carboxylate group increases. The C _p ^° value for the protonation of the carboxyl group is found to lie between those of an isocoulombic reaction and a charge reduction reaction. At 323.15 K, the protonation reactions of the carboxylate groups have larger C _p ^° values which approach those associated with charge reduction reactions. As the temperature increases, C _p ^° decreases and approaches those found for isocoulombic reactions. This result is explained by considering long-range and short-range solvent effects. The trend in H° and S° with temperature and with charge separation in the zwitterions is interpreted in terms of solvent-solute interactions and the electrostatic interaction of the two oppositely charged groups within the molecule.     

Strain Energies of α-Alkylsubstituted Styrenes, 1,1-Di-phenyl-ethene,Tri-, and Tetra-phenyl-ethene

The standard (p° = 0.1 MPa) molar enthalpies of formation _fH°_m (1 or cr) at the temperature T = 298.15 K were determined by using combustion calorimetry for -ethyl-styrene (A), -iso-propyl-styrene (B), -tert-butyl-styrene (C), 1,1-di-phenyl-ethene (D), tri-phenyl-ethene (E), and tetra-phenyl-ethene (F). The standard molar enthalpies of vaporization _l ^g H°_m or sublimation _cr ^g H°_m of compounds A to F were obtained from the temperature variation of the vapor pressure measured in a flow system. Molar enthalpies of fusion _cr ^l H°_m of solid compounds were measured by d.s.c. Resulting values of _fH°_m (g) were obtained at the temperature T = 298.15 K and used to derive strain enthalpies of phenylalkenes. The interactions of the substituents are discussed in terms of deviations of _fH°_m (g)from the group additivity rules. These values provide a further improvement on the group-contribution methodology for estimation of the thermodynamic properties of organic compounds.     

Thermodynamic study of solvent extraction of monovalent metal picrates with benzo-18-crown-6 into chloroform

Thermodynamic parameters (H _ex ⁰ and S _ex ⁰ ) for the overall extractions of monovalent metal (Na, K, Rb, and Tl) picrates with benzo-18-crown-6 (B18C6), and those (H _D,L ⁰ and S _D,L ⁰ ) for the distribution of B18C6 were determined between chloroform and water. All the extracted B18C6 complexes were l:1:1 complexes (B18C6:metal ion: picrate anion). The H _ex ⁰ and S _ex ⁰ values for all the metals are negative. Every extraction of the metal picrate with B18C6 is completely enthalpy driven. The H _D,L ⁰ and S _D,L ⁰ values of B18C6 are both positive, and the partition of B18C6 is entirely entropy driven. Enthalpy (H _ex,ip ⁰ ) and entropy changes (S _ex,ip ⁰ ) for ion-pair extractions of B18C6-metal ion complexes with picrate anions were calculated. All the H _ex,ip ⁰ and S _ex,ip ⁰ values are negative, and the ion-pair extractions are completely enthalpy driven.     

Systematik des Adsorptionsverhaltens homologer aliphatischer Amine an der Grenzfläche Quecksilber/Elektrolyt

Zusammenfassung Dutch die wechselstrompolarographische Kapazitäts-Potential-und Kapazitäts-Zeit-Messungen (E _m = konstant) als Funktion der Aminkonzentration wurden die Adsorptionsisothermen homologer Amine und Amin-Hydrochloride beiT = 25 °C undT = 50 °C experimentell bestimmt.Die Ads orptionsisothermen wurden mittels dimensionsloser Adsorptionstherme nachFrumkin-Damaskin ausgewertet und in Form folgender Adsorptionsparameter diskutiert und verglichen: Attraktionskonstantea; Adsorptionskoeffizientb und freie StandardadsorptionsenthalpieG _A .Der Zuwachs in denG _A -Werten pro CH₂-Gruppe läßt sich zuG _A /CH₂0,3–0,5 kcal. Mol^–1 abschätzen. Bis auf wenige Ausnahmen sind die Adsorptionsparametera, b, undG _A Temperaturfunktionen

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Summary The adsorption isotherms of homologous amines and some of their hydrochlorides were obtained from capacity-potential- und capacity-time measurements atT = 25 °C andT = 50 °C.From the adsorption isotherms we computed the thermodynamic adsorption parameters according toFrumkin andDamaskin. On the basis of the adsorption parameters attraction constant (a), adsorption coefficient (b) and free standard energy of adsorptionG _A , the results have been discussed und compared.The increase ofG _A per CH₂-group is aboutG _A /CH₂ 0,3 to 0,5 Kcal Mol^–1. In most cases the adsorption parametersa, b andG _A are temperature functions.

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Mit 3 Abbildungen und 1 Tabelle     

Evaluation of a direct1H NMR method for determining logK and ΔH values for crown ether -alkylammonium cation complexation

A direct¹H NMR method for determining logK and H values for crown ether-ammonium cation complexation using milligrams of sample was tested and evaluated for accuracy and precision by comparing the results with those obtained using a titration calorimetric method. LogK values for the interactions of a non-chiral crown ether, diketopyridino-18-crown-6 (K₂P18C6), with -phenylethylammonium (PhEt⁺) perchlorate in 50%–50% and 90%–10% (v/v) mixtures of deuterated methanol (CD₃OD) and deuterated chloroform (CDCl₃) at four temperatures and, with -(1-naphthyl)ethylammonium (NapEt⁺) perchlorate in 50%CD₃OD-50%CDCl₃ (v/v) at 25°C were determined by a direct¹H NMR method. Values of H for the interactions of K₂P18C6 with PhEt⁺ in the two solvents were calculated from the temperature dependence of logK. LogK values for the interactions of a chiral crown ether, dimethyldiketopyridino-18-crown-6 (M₂K₂P18C6), with (R) and (S) enantiomers of NapEt⁺ in pure CD₃OD at 25.0°C were also determined by the NMR method. The results were compared with those determined by a calorimetric method at 25.0°C in 50%-50% and 90%–10% (v/v) mixtures of plain methanol and chloroform, in 100% plain methanol, and in a 50%-50% mixture of partially deuterated methanol (with deuterium substitution on the methanol OH group, CH₃OD) and deuterated chloroform. The log K values determined by both methods were found to be in good agreement, but the standard deviations associated with the NMR logK values were two to three times greater. The agreement of the H values determined by the two methods was poor, differing by approximately 10 kJ/mol with the NMR method giving more negative values. The standard deviations associated with the NMR H values were approximately ten times greater than those for the calorimetric values. Ion-pairing was observed for the interaction of perchlorate ion with both free and bound PhEt⁺ in 50%methanol-50%chloroform mixture. It is concluded that the NMR procedure is satisfactory for the determination of logK, but not H values.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Ionic enthalpies of transfer from water to water-sulfolane mixtures

NaCl, NaBr, NaI, NaClO₄, KCl, KClO₄, NaBPh₄, and Ph₄PBr solution enthalpies were measured in water-sulfolane mixtures at 30°C. Ionic enthalpies of transfer from water to mixed solvents were calculated on the basis of the assumption H _s ^o (BPh ₄ ^– )=H _s ^o (Ph₄P⁺). The variation of the ionic enthalpies of transfer with solvent composition is discussed in terms of ion-solvent interactions and of the effects caused by sulfolane on the structure of water.     

Theoretical studies of [n]paracyclophanes and their valence isomers

Summary The valence isomerisations of benzene, [6]- and [7]paracyclophane to their Dewar benzene and prismane isomers are studied with the MNDO method using the unrestricted Hartree-Fock (UHF) and the configuration interaction (C.I.) approximations. The enthalpy of the reaction Dewar benzene benzene is H° _r =–68.9 kcal/mol and the activation enthalpy is H°=27.9 kcal/mol (with C.I.). The reaction path hasC _2v symmetry.The determination of several points of the lowest potential energy surface of [6]- and [7]paracyclophanes leads to a minimum reaction path having the same topology as for the potential energy surface of the nonbridged benzene. The only difference is a quantitative change in the energy values of the aromatic isomers due to the deformation introduced by the alkyl chain. For [6]paracyclophane, the activation enthalpy is H°=24.6 kcal/mol and the activation entropy is S ⁰=0.6 cal K^–1 mol^–1 calculated with C.I.The enthalpy of the reaction prismane Dewar benzene is H° _r –32 kcal/mol and the activation enthalpy is H°19 kcal/mol. The highest molecular symmetry group common to both molecules isC _2v , whereas the symmetry group of the reaction path is lowered toC _s . Along this reaction path is located a biradicaloid intermediate, separated by low activation barriers from the products. No significant changes of the potential energy surfaces are found for the bridged [n]prismanes and the [n]Dewar benzenes.All the calculated values, reaction enthalpies, activation enthalpies and entropies, are in a good agreement with literature experimental data.This article is dedicated to Professor A. Pullman     

Model calculations of changes of thermodynamic variables for the transfer of nonpolar solutes from water to water-d2

A recently introduced modified hydration shell hydrogen bond model for rationalizing the thermodynamic consequences of hydrophobic hydration is adapted for use with heavy water. The required adjustment of parameters employs the assumption that breaking hydrogen bonds in water-d₂ involves a greater enthalpy change and a larger entropy increase than bond breaking in ordinary water. It also makes some use of information derived from studies of gas solubilities in the two solvents, although a review of the data leads to serious questions about the reliability of results obtained in this way. The model permits calculations of hydrogen bonding contributions to the changes, G _t ^o , H _t ^o , S _t ^o , and C _p,t ^o , for transfer of nonpolar solutes from water to water-d₂ and implies that such data should show regular trends. Although some of the numerical results depend strongly on the values chosen for the parameters, the pattern defined by these trends is nearly independent of parameters. Predicted values of C _p,t ^o are large and positive for all nonpolar solutes, while S _t ^o is expected to be negative near 0°C, becoming progressively less negative on warming and eventually positive. Both of these quantities should be proportional to the molecular surface area of the solute. Analogous predictions regarding G _t ^o and H _t ^o can also be made, but only if it is permissible to neglect possible contributions to these quantities from van der Waals interactions.     

A Spectroscopic Study of Charge Transfer Complexes of Tetraphenylporphyrin

Summary. The fluorescence quenching and complexation behaviour of tetraphenylporphyrin (TPP) with some organic acceptors such as chloranilic acid (CHL), 5,5-dithiobis-2-nitrobenzoic acid (DTNB), or 3,4-dinitrobenzoic acid (DNB) and tetravalent metal ions such as Th⁴⁺ and Zr⁴⁺ have been studied in methanol. The second-order fluorescence quenching rate constant (k_q), the association constant (K), the molar absorption coefficient (), and the thermodynamic parameters of the complexation process (G°, H°, and S°) have been evaluated using different organic solvents.     

Study of complex formation between aluminum bromide and benzene by 27Al NMR spectroscopy

The reaction of aluminum bromide with benzene in n-hexane was studied by ²⁷Al NMR spectroscopy in the temperature range from –80 to +20 °C. The formation of C₆H₆·Al₂Br₆ (1 : 2) complexes is accompanied by broadening of the resonance line with 178. No peak splitting following a decrease in the temperature was observed but the temperature dependence of the line width passed through a maximum near –60 °C. A procedure for determination of the constant K for the formation of 1 : 2 complexes at –20, 0, and +20 °C based on the line broadening with an increase in the C₆H₆ : Al₂Br₆ molar ratio was proposed. The thermodynamic parameters of complex formation, G, H, and S, were calculated.