The enthalpies of solution and solvation of glycine in mixed water-formamide solvents at 298.15 K

The enthalpies of solution (ΔH _sol ^o ) of glycine in aqueous formamide, N-methylformamide, N,N-dimethylformamide, and N,N-diethylformamide were determined by calorimetry at 298.15 K over the concentration range x ₂=0–0.3 mole fractions. The enthalpies of glycine solvation (ΔH _solv ^o ) and transfer from water to mixed solvents (ΔH _tr ^o ) were calculated. The ΔH _sol ^o =f(x ₂) dependences for glycine in water-N-and water-N,N-substituted amide mixtures had extrema and, in water-formamide mixtures, this dependence was a smooth function, whose values changed in the opposite direction. The enthalpy coefficients of pair glycine-amide interactions were calculated. The interrelation between the enthalpy characteristics of solution, transfer, and solvation of glycine and the structure and physicochemical characteristics of solvents, on the one hand, and the composition of mixtures, on the other, was revealed.     

Thermochemistry of aqueous solutions of nucleic acid bases and their alkylated derivatives

Enthalpy of solution, ΔH _sol ^o , enthalpy of sublimation, ΔH _subl ^o , apparent partial molar volume and heat capacities,V ₂ ^o andC _p,2 ^o were determined for aqueous solutions of thirty alkylated derivatives of uracyl and adenine, eight derivatives of cytosine and guanine. Calculated accessible surface areas and molar volumes are presented, too. The values of enthalpy of solution, enthalpy of sublimation can be useful in the studies on the nature of interaction between these compounds and water molecules. Apparent partial molar volume and heat capacity give a new aspect on hydrophob properties of the examined nucleic acid base derivatives.     

Thermodynamic transfer functions for urea and thiourea from water to water-tetrahydrofuran mixtures from precise vapor-pressure measurements

The rate of change of the standard chemical potential with solvent composition, \(\partial \bar G_0 /\partial Z\) , has been calculated from precise vapor-pressure measurements for urea at three temperatures and for thiourea at 298.15°K in water-tetrahydrofuran (THF) mixtures. From these results the standard free energy of transfer ΔG _t ^o of the solutes from water to various water-THF mixtures has been obtained together with the standard molar entropy ΔS _t ^o and the standard molar enthalpy ΔH _t ^o of transfer at 298.15°K in the case of urea. The quantity ΔG _t ^o for urea is negative in the water-rich region and positive for mole fractions THF>0.2. There is a nearly complete compensation between ΔH _t ^o andTΔS _t ^o at 298.15°K up to mole fraction THF=0.5. These phenomena can be partly related to the structure in H₂O-THF mixtures.     

The enthalpies of solution of DL-α-alanine in water-organic solvent mixtures at 298.15 K

The integral enthalpies of solution (298.15 K) of DL-α-alanine in water-organic solvent mixtures were measured at organic component concentrations x ₂ = 0–0.4 mole fractions. The organic solvents used were acetonitrile (ACN), formamide (FA), N,N-dimethylformamide (DMFA), and N,N-dimethylsulfoxide (DMSO). The standard enthalpies of solution Δ_sol H ^o, solvation Δ_solv H ^o, and transfer (Δ_tr H ^o) of DL-α-alanine from water to mixed solvents were calculated. The influence of the structure and properties of solutes and mixture composition on solute thermochemical characteristics was considered. The solution of DL-α-alanine in the mixtures studied was endothermic over the whole range of organic component concentrations. The Δ_sol H ^o, Δ_tr H ^o, and Δ_solv H ^o values as functions of x ₂ can pass extrema (DMSO and DMFA), be almost independent of mixed solvent composition (FA), or be exothermic and monotonic functions (ACN). The enthalpy coefficients of pair interactions (h _xy ) between DL-α-alanine and organic solvent molecules were calculated. The linear Kamlet-Taft equation was used to correlate the h _xy values with the properties of organic solvents.     

Thermodynamic properties of alkaloids lappaconitine and glaucine

Calorimetric methods were used to study the enthalpy of solution of the alkaloids glaucine C₂₁H₂₅NO₄ and lappaconitine C₃₂H₄₄N₂O₈ in 96% ethanol and their heat capacity in the temperature ranges 173–298.15 and 173–423 K. Equations describing the dependences ΔH _sol ^m ～ f( $\sqrt m $ ) (m is molal concentration) and C _p ⁰ ～ f( $\sqrt T $ ) for the compounds under study were derived. The enthalpies of combustion, melting, and formation of C₂₁H₂₅NO₄ and C₃₂H₄₄N₂O₈ were estimated by means of theoretical calculations.     

Thermal properties of <Emphasis Type="Italic">n</Emphasis>-R<Subscript>4</Subscript>NBr solutions in binary solvents containing formamide

The enthalpies of solution of tetraethyl- and tetra-n-hexylammonium bromides have been measured in mixtures of formamide with ethylene glycol at 298.15 and 313.15 K in the whole mole fraction range by the calorimetric method. The standard enthalpies of solution in binary mixtures have been calculated with Redlich–Rosenfeld–Meyer type equation. The enthalpy and heat capacity parameters of pair interaction of organic electrolytes with EG in FA and with FA in EG have been computed and discussed. The enthalpy interaction parameters of single ions with EG in FA medium have been evaluated and compared with those for ion–water and ion–MeOH interaction in FA. The standard heat capacities of solution have been evaluated. The excess enthalpies of solution, Δ_sol H ^E, of Et₄NBr, Bu₄NBr, and Hex₄NBr have been determined. The Δ_sol H ^E values are positive for Et₄NBr and negative for Bu₄NBr and Hex₄NBr and become more negative from Bu₄NBr to Hex₄NBr.     

Thermochemical investigations of the systems KCl−KBr−H2O,K2SO4−(NH4)2SO4−H2O and KNO3−NH4NO3−H2O at 298.15 K

For the equilibrium solid phases occurring in the systems: KCl?KBr?H₂O, K₂SO₄?(NH₄)₂SO₄?H₂O and KNO₃?NH₄NO₃?H₂O, the concentration dependencies of differential solution enthalpies, Δ_sol H ₂ for several crystallization paths, were measured. The limiting differential solution enthalpies, Δ_sol H ₂ ⁰ , were determined by extrapolation of the above dependencies to the ionic strength,I _m ⁰ , corresponding to the appropriate binary solutions. For KCl?KBr?H₂O system only, the clear dependence between Δ_sol H ₂ ⁰ andI _m ⁰ values was found and discussed.     

Ionization of aqueous benzoic acid: Conductance and thermodynamics

Molar conductances of dilute aqueous benzoic acid solutions are presented for temperatures from 5 to 80°C. The data have been analyzed to give acid dissociation constants as well as ΔH ^o, ΔS ^o, and ΔC _p ^o for the ionization process and the limiting conductance of the benzoate ion. The conductance-viscosity product changes less than 4% over the temperature range, indicating that the interaction of the benzoate ion with the solvent changes little if at all with increasing temperature. The pK _a(m) vs.T data show that ΔH ^o decreases quadratically while ΔC _p ^o increases linearly withT although, over the 75°C range, ΔC _p ^o increases only about 6 cal-mole^?1 deg^?1 around an average of ?37 cal-mole^?1deg^?1. The acid dissociation constants as derived from the conductance-molal concentration analysis show an average uncertainty of about 0.1% and are fitted to within about 0.01% by the equation $$p{\text{K}}_{\text{a}} (m) = - 75.5422 + 3136.34/T + 28.7965 log T - 6.8139 {\text{x}} 10^{ - 3{\text{T}}} $$ whereT is the absolute temperature.     

Size effect on thermodynamic parameters for the peanut-like CaMoO4 micro/nano reaction systems

Peanut-like CaMoO₄ micro/nano structures with three different sizes were harvested by a simple reverse-microemulsion method at room temperature. Employing synthesized micro/nano CaMoO₄ and HCl as reaction systems, thermodynamic parameters such as standard molar enthalpy of reaction Δ_r H _m ^θ , standard molar Gibbs free energy of activation Δ _r ^≠ G _m ^θ , standard molar enthalpy of activation Δ _r ^≠ H _m ^θ , and standard molar entropy of activation Δ _r ^≠ S _m ^θ were successfully acquired for the first time by in situ microcalorimetry. Furthermore, change regularities of the thermodynamic parameters for the micro/nano reaction systems were obtained and discussed. It demonstrated that size effect has significant influence on thermodynamic parameters of micro/nano material reaction systems.     

The Standard Thermodynamic Properties of 4f Metal Dichlorides

The experimental data on heterogeneous and homogeneous equilibria with the participation of 4f metal dichlorides LnCl₂ (where Ln = La, …, Lu) were analyzed using the thermodynamic functions of these substances in the gaseous and condensed states described earlier. These data and appearance potential AP(Ln⁺/LnCl₂) measurements were used to calculate the enthalpies of sublimation Δ_sub H ₂₉₈ ^o . The enthalpies of atomization of these compounds under standard conditions were also calculated. Correlations between the enthalpies of sublimation and crystal lattice structure of 4f metal trifluorides, trichlorides, and dichlorides are described.     

Heat capacities and standard molar enthalpy of formation of pyrimethanil maleic salt and pyrimethanil fumaric salt

Novel anilino-pyrimidine fungicides, pyrimethanil maleic salt, and pyrimethanil fumaric salt (C₂₈H₃₀N₆O₄) were synthesized by a chemical reaction of pyrimethanil with maleic acid/fumaric acid. The low-temperature heat capacities of the two compounds were measured with an adiabatic calorimeter from 80 to 350 K. The heat capacities of pyrimethanil fumaric salt are bigger than that of pyrimethanil maleic salt in the measurement temperature range. The thermodynamic function data relative to 298.15 K were calculated based on the heat capacity-fitted curves. The melting points, the molar enthalpies (Δ_fus H _m), and entropies (Δ_fus S _m) of fusion of pyrimethanil maleic salt and pyrimethanil fumaric salt were determined from their DSC curves. The values indicate that pyrimethanil fumaric salt was more thermostable than pyrimethanil maleic salt. The constant-volume energies of combustion (Δ_c U _m ^o ) of pyrimethanil maleic salt and pyrimethanil fumaric salt were measured using an isoperibol oxygen bomb combustion calorimeter at T = (298.15 ± 0.001) K. From the Hess thermochemical cycle, the standard molar enthalpies of formation of the two compounds were derived and determined to be Δ_f H _m ^o (pyrimethanil maleic salt) = ?459.3 ± 4.9 kJ mol^?1 and Δ_f H _m ^o (pyrimethanil fumaric salt) = ?557.2 ± 4.8 kJ mol^?1, respectively. The results suggest that pyrimethanil fumaric salt is more chemically stable than pyrimethanil maleic salt.     

Features of the Diels-Alder reaction between 9,10-diphenylanthracene and 4-phenyl-1,2,4-triazoline-3,5-dione

The Diels-Alder reaction between substituted anthracenes 1a?1j and 4-phenyl-1,2,4-triazoline-3,5 (2) is studied. In all cases except one, the reaction proceeds on the most active 9,10-atoms of substituted anthracenes. The orthogonality of the two phenyl groups at the 9,10-position of diene 1a is found to shield 9,10-reactive centers. No dienophiles with C=C bonds are shown to participate in the Diels-Alder reaction with 1a; however, the reaction 1a + 2 proceeds with the very active dienophile 2,4-phenyl-1,2,4-triazoline-3,5-dione. It is shown that attachment occurs on the less active but sterically accessible 1,4-reactive center of diene 1a. The structure of adduct 3a is proved by ¹H and ¹³C NMR spectroscopy and X-ray diffraction analysis. The following parameters are obtained for reaction 1a + 2 ? 3a in toluene at 25°C: K _eq = 2120 M^?1, ΔH _f ^≠ = 58.6 kJ/mol, ΔS _f ^≠ = ?97 J/(mol K), ΔV _f ^≠ = ?17.2 cm³/mol, ΔH _b ^≠ = 108.8 kJ/mol, ΔS _b ^≠ = 7.3 J/(mol K), ΔV _b ^≠ = ?0.8 cm³/mol, ΔH _r-n = ?50.2 kJ/mol, ΔS _r-n = ?104.3 J/(mol K), ΔV _r-n = ?15.6 cm³/mol. It is concluded that the values of equilibrium constants of the reactions 1a?1j + 2 ? 3a?3j vary within 4 × 10¹?10¹¹ M^?1.     

Thermochemistry of Bu<Subscript>4</Subscript>NBr solutions in binary solvents containing formamide

The heats of solution of tetrabutylammonium bromide have been measured in mixtures of formamide (FA) with methanol (MeOH) and ethylene glycol (EG) at 313.15 K by calorimetric method. The standard enthalpies of solution in binary mixtures have been extrapolated to infinite dilution by Redlich–Rosenfeld–Meyer type equation using the literary data at 298.15 K and the present paper data at 313.15 K. The Debye–Hückel limiting law slope A _H required for calculation of the ∆_sol H ⁰ value has been obtained with application the new additive scheme of determination of the physic-chemical characteristics of binaries. The scheme is tested on the example of Bu₄NBr solutions in FA–MeOH mixture at 298.15 K. Its application yields the ∆_sol H ⁰ value very closed on the ones determined with the real (non-additive) characteristics of binaries. The standard enthalpies of solution extrapolated by Redlich–Rosenfeld–Meyer type equation are in a good agreement with the ones computed in terms of the Debye–Hückel theory in the second approximation. The heat capacities characteristics of Bu₄NBr have been calculated in H₂O–FA, MeOH–FA and EG–FA mixtures using the literary and present data. The sequence of solvents H₂O > FA > EG > MeOH located on their ability to solvophobic solvation found by us earlier for enthalpic characteristics is confirmed by the ∆C _p ⁰ values. The comparison of thermochemical characteristics of Bu₄NBr solutions in aqueous and non-aqueous mixtures containing FA has been carried out. The own structure of water remains in the region of small additions of formamide to co-solvents. It considerably differs the H₂O–FA mixture from the investigated non-aqueous systems.     

Decarbonation curves and associated thermodynamic data for synthetic Cd-dolomites CdMg(CO3)2, CdMn(CO3)2 and CdZn(CO3)2

Decarbonation curve for the synthetic dolomite analogues; (Cd-dolomites) were determined for CdMg(CO₃)₂, CdMn(CO₃)₂ and CdZn(CO₃)₂ under CO₂ pressure of up to 2.5 kbar. All the three double carbonates were completely disordered at the decomposition temperatures and hence the thermodynamic data (Standard enthalpy; ΔH _f ^o, Standard free energy; ΔG _f ^o) retrieved from the univariant decarbonation curve corresponds to the disordered phases. They are: The mixing enthalpies and free energies for the formation of the disordered 1∶1 solid solution phases are: The thermodynamic data (ΔH _f ^o, ΔG _f ^o and ΔH _r ^o, ΔG _r ^o) showed a positive correlation with the decomposition temperatures. The mixing energies of the disordered double carbonates also show a direct correlation with the cationic size differences.     

The thermochemical characteristics of solution of L-cysteine and L-asparagine in aqueous 1,4-dioxane and acetone

The integral heats of solution Δ_sol H ^m of L-cysteine and L-asparagine in mixtures of water with 1,4-dioxane and acetone were measured by solution calorimetry at organic solvent concentrations of up to 0.30 mole fractions. The standard enthalpies of solution (Δ_sol H ^o) and transfer (Δ_tr H ^o) of amino acids from water to mixed solvents were calculated. The calculated enthalpy coefficients of pair interactions of L-cysteine and L-asparagine with cosolvent molecules were positive. The results were interpreted from the point of view of the predominance of interactions of various types in solutions and the influence of the nature of cosolvents and amino acid side substituents on the thermochemical characteristics of solution.     

The heat capacity and thermodynamic functions of Ca0.5Zr2(PO4)3 crystalline phosphate from T → 0 to 650 K

The temperature dependence of the heat capacity C _p ^o = f(T) of crystalline calcium-zirconium phosphate was studied over the temperature range 7–650 K by precision adiabatic vacuum and dynamic scanning calorimetry. The experimental data were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o(T) ? H ^o(0), S ^o(T), and G ^o(T) ? H ^o(0) at temperatures from T → 0 to 650 K and the standard entropy of formation of Ca_0.5Zr₂(PO₄)₃ at T = 298.15 K. The data on low-temperature (30 K ≤ T ≤ 50 K) heat capacity were used to calculate fractal dimension D. Conclusions about the character of the topology of the structure of the phosphate were drawn.     

System analysis of the thermodynamic properties of binary lanthanide hydrides

Systems analysis of available data on the thermodynamic properties of binary lanthanide hydrides is carried out. The standard thermodynamic characteristics of lanthanide dihydrides (Δ_f H ^o, S ^o, C _p ^o ) and their hypothetical trihydrides (Δ_f H ^o) are calculated. The calculations are performed using a semiempirical method that takes into account the effects of the number of f-shell electrons and the spin and orbital angular moments of ground states of the lanthanide ions on the thermodynamic properties of the compounds studied. It is established that the thermodynamic characteristics of the hydrides exhibit an antibatic behavior with respect to the atomic numbers of the natural series lanthanides. The tetrad effect was revealed for these series of compounds.     

Kinetic energy release of clusters after multiphoton ionisation with time of flight and electrostatic analyser techniques

A new technique is presented which allows direct observation of initial kinetic energies in multiphoton ionisation-fragmentation processes of molecules and clusters and provides an unambiguous determination of metastable decay channels. Results are presented for the unimolecular loss of a monomer from clusters (C₆H₆) ₈ ⁺ to (C₆H₆) ₁₂ ⁺ and for the reaction C₆H ₆ ⁺ →C₄H ₄ ⁺ +C₂H₂. We also observe a significant amount of probably collision induced fragmentation processes (C₆H₆) _n ⁺ →(C₆H₆) _n?x ⁺ + (C₆H₆) _x withx much larger than 1.     

Thermochemistry of copper(II) ion solvation in aqueous organic solvents

The integral heat effects of CuCl₂ dissolution in aqueous DMSO, aqueous ethanol and aqueous acetone solutions at 298. 15 K in the electrolyte concentration range 0.001–0.01M were measured by means of calorimetry. ΔH _sol ⁰ values were obtained by extrapolation to zero electrolyte concentration. Literature data were used to determine the thermodynamic characteristics of Cu²⁺ transfer from water to aqueous organic solvents.