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The apparent molar heat capacities, Cp,ϕ, of alkaline aqueous solutions of aluminum ion in excess NaOH have been measured at temperatures between 50 and 250°C in the overall molality range 0.3–1.7 mol-kg−1. Enthalpies of dilution, ΔLϕ, have also been determined at 99°C and apparent molar relative enthalpies, Lϕ, were calculated starting from 2.16 mol-kg−1 as the maximum concentration. Measurements of the above quantities have been performed by means of a differential flow calorimeter built in our laboratory and already described. The thermodynamic data obtained and the corresponding quantities for aqueous NaOH previously determined have been fitted to the equations of the Pitzer ionic interaction model to obtain parameters relative to aqueous NaAl(OH)4. These parameters permit the calculation of Cp,ϕ, and Lϕ for this species over the examined range of temperatures and concentrations.

The limiting apparent molal adiabatic and isothermal compressibilities in aqueous solutions of alcohols and ethers at various temperatures have been determined by means of ultrasonic velocity measurements. The following compounds have been considered: secondary cyclic and open-chain alcohols (cyclopentanol, cyclohexanol, cycloheptanol, 2-butanol, 3-pentanol, 3-hexanol, 4-heptanol; cyclic ethers of the types (CH2)3On (n=1, 2, 3), (CH2)nO2 (n=3, 4, 5), and (CH2)nO (n=3, 4, 5); and the linear diethers dimethoxymethane, diethoxymethane, and 1,2-dimethoxyethane. The results indicate that both alcohols and ethers cause the water near the solute to become more resistant to pressure than the bulk. This is in agreement with the prediction of a mixture model for water.

The apparent molar heat capacity, C p,ϕ, of aqueous NaOH has been measured at temperatures between 50 and 250°C and molalities from 0.05 to 1.5 mol-kg−1. Enthalpies of dilution ΔLϕ were also determined at 99°C and apparent molar relative enthalpies Lϕ were calculated up to 1.9 m. Measurements were performed by means of a flow calorimetric apparatus constructed in our laboratory and standardized for C p,ϕ and ΔLϕ with aqueous Na2SO4 and with the formation of water from its ions, respectively. Characteristics and performance of this calorimeter are described in detail. Pitzer's semiempirical equations are used for the representation of the results and a general fitting of C p,ϕ data is reported using also recent literature values measured between 4 and 55°C. The fitted parameters are finally utilized, through an integration procedure, to derive a general equation to calculate Lϕ at any temperature between 4 and 250°C.

The temperature dependence of limiting apparent molal volumes Φ°υ in water for some alcohols (methanol, ethanol, 1-propanol, 2-butanol, 3-pentanol, 3-hexanol, 2,5-hexanediol, cyclopentanol, cyclohexanol, cycloheptanol, and 1,4-cyclohexanediol) and ethers (trimethylene oxide, tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 1,3-dioxepane, 1,3,5-trioxane, dimethoxymethane, 1,2-dimethoxyethane, diethoxymethane, and diethyl ether) has been studied in the temperature range 10–50°C by means of an automatic digital-readout dilatometer. Values of the thermal expansion coefficient α* = (1/Φ°υ)(∂Φ°υ/∂T)p have been obtained at several temperatures and discussed together with literature data on expansibilities of related compounds. The data show a wide spectrum of values of α* at low temperatures which is narrowed at the higher ones. The expansibilities of monofunctional alcohols increase with increasing temperature; the opposite effect is observed for polyhydric alcohols. The α*'s of ethers are very slightly temperature dependent and are much higher, at low temperature, than those of alcohols having the same ratio ofno/nc. These results are discussed in terms of solutewater interactions, and a possible interpretation is put forward.

Donnees pour les melanges de: heptane, cyclohexane, CCl 4 ou benzene avec cyclopentanone ou cyclohexanone

A Tian-Calvet type calorimeter has been used to determine molar excess enthalpies, HE, as a function of concentration at atmospheric pressure and 298.15 K for some binary liquid mixtures containing linear ketones with tetrachloromethane or benzene and linear diketones with n-heptane or cyclohexane. The experimental HE results are interpreted in terms of molecular interactions and of the “homoproximity effect”.

Apparent molal heat capacities of 20 organic uncharged compounds in aqueous solution have been determined at 25 and 40°C. The substances studied include mono- and polyfunctional ethers, and bifunctional open-chain compounds like aminoalcohols, aminoethers, and diamines. The results obtained support the presence of interaction between water and the hydrophilic groups −O−, −NH2, −NH−, and\(\begin{array}{*{20}c} \backslash \\ / \\ \end{array} N - \), and evidence indicates that these interactions strongly depend on the molecular structure of the compound containing the functional group.

The ΔC°p values for proton addition to some aminoalcohols, aminoethers and diamines in aqueous solution have been determined at 25 and 40°C, using partial molal heat capacity data for the neutral molecules and their hydrochlorides. A comparison is made between ΔC°p, ΔS° and ΔV° values and the corresponding values for monofunctional amines, and the following features emerge for proton addition to the nitrogen atom of saturated amines in water: (1) Either in mono- or in bifunctional amines the thermodynamic reaction parameters, ΔC°p and ΔS°, change systematically in going from primary, to secondary, to tertiary amines; the same is observed for ΔV°, but only in the case of monofunctional amines. (2) The ΔC°p and ΔS° values of protonation of bifunctional amines are higher than those of monofunctional amines of the same type.Interpretation of this behaviour is made in terms of two concurrent solvation effects: (i) the charged nitrogen–water interaction which is strongly dependent on the number of N-bonded hydrogens; (ii) the hydration of alkyl residues which is less extensive when they are bound to a charged nitrogen than when the nitrogen is neutral.

Vapor-liquid equilibria for a chloroalkane (1,2-dichloroethane or 1,1,1-trichloroethane)+a linear mono- or diether (diethyl ether, dipropyl ether, methyl buthyl ether, 1,2-dimethoxyethane) or an acetal (diethoxymethane), were determined at 298.15 K by head-space gas chromatographic analysis of the vaporphase directly withdrawn from an equilibration apparatus. Excess Gibbs energies, activity coefficients at infinite dilution, and free energies of solvation were calculated for all the systems

The ΔC°p values for proton addition to some aminoalcohols, aminoethers and diamines in aqueous solution have been determined at 25 and 40°C, using partial molal heat capacity data for the neutral molecules and their hydrochlorides. A comparison is made between ΔC°p, ΔS° and ΔV° values and the corresponding values for monofunctional amines, and the following features emerge for proton addition to the nitrogen atom of saturated amines in water: (1) Either in mono- or in bifunctional amines the thermodynamic reaction parameters, ΔC°p and ΔS°, change systematically in going from primary, to secondary, to tertiary amines; the same is observed for ΔV°, but only in the case of monofunctional amines. (2) The ΔC°p and ΔS° values of protonation of bifunctional amines are higher than those of monofunctional amines of the same type.Interpretation of this behaviour is made in terms of two concurrent solvation effects: (i) the charged nitrogen–water interaction which is strongly dependent on the number of N-bonded hydrogens; (ii) the hydration of alkyl residues which is less extensive when they are bound to a charged nitrogen than when the nitrogen is neutral.

The procedures so far adopted for interpreting the partial molal heat capacities at infinite dilution of organic compounds in water at 25°C, Φ°Cp, are critically reviewed and a new method of correlating Φ°Cp data to the molecular structure is proposed. In this method, the ΔChp values, obtained by substracting the heat capacities in the gas phase from the Φ°Cp data, are interpreted as the sum of the following terms: (i) formation of a cavity inside the solvent; (ii) interaction between the hydrocarbon part of the molecule and water; (iii) interaction between hydrophilic centres, Y, and water; (iv) a term to account for interactions among centres, Y, when more than one hydrophilic group is present in the molecule.A general equation which accounts for the formation of the cavity and for the interaction water–hydrocarbon surface is obtained on the basis of the ΔChp values of the first six n-alkanes. The values of the (iii)rd and (iv)th terms are then calculated for several types of groups Y and of couples Y1, Y2, by using the above mentioned equation in conjunction with the ΔChp values.This analysis has revealed that both the formation of the cavity and the hydrocarbon group combine to produce large positive Φ°Cp values, while all hydrophilic groups always bring about a decrease of the partial molal heat capacities. It is also shown that the interaction between hydrophilic centres in the same molecule is important in determining the Φ°Cp values, and that this may cause either ancrease or a decrease of the Φ°Cp values predicted on the basis of the Φ°Cp contribution for non-interacting groups.

The dependence of the partial molar volumes of a number of α-amino acids, ω-amino acids, dipeptides and diketopiperazines on temperature has been determined at various concentrations and for the temperature range 0–55 °C using an automatic dilatometer; the limiting partial molar expansibilities, Φ°E, have been calculated. Measurements of the sound velocity at 15 MHz and at various concentrations allowed us to determine the compressibility of the solutions at 25 °C and to calculate the limiting partial compressibilities, Φ°K,S, for some of the above mentioned compounds. Finally, by using the known values Φ°E and Φ°K,S together with the partial molar heat capacity of the solute and some physical properties of pure water, the limiting isothermal partial molar compressibilities, Φ°K,T, have been obtained.The values of Φ°E and Φ°K,S and the trends they show when the structure of the amphionic molecule is changed have been analysed by taking into account the features exhibited by Φ°E and Φ°K,S of related charged and non-charged compounds. The dependence on temperature and pressure of the internal and external proton-exchange reaction between a carboxyl and an amino group have been evaluated and compared.

The 100 MHz 1H n.m.r. spectrum of pyridine-2-carbaldehyde partially oriented in the nematic phase of a liquid crystalline solvent has been obtained and analysed. It has been shown that a conformational equilibrium is present and that theN–O-trans-form is the more stable (ca. 96%). The barrier height to cis–trans-interconversion in the pure liquid has been investigated by means of the ultrasonic relaxation technique and a value of 4.5 ± 0.3 kcal mol–1 has been found. The hindering internal potential has also been investigated by means of quantum mechanical calculations using the SCF–MO–LCAO ab initio method. The overall results have been compared with previous experimental findings and theoretical calculations.

Values of ΔG⊖s, ΔS⊖s, and ΔC⊖ps for solution of gaseous univalent ions in water from 273 to 573 K have been calculated using Abraham and Liszi's method, in which a neutral term is obtained from data on rare gases and an electrostatic term is obtained using a solvation model in which an ion of radius a is surrounded by a solvent layer of thickness (b – a) and dielectric constant Iµ1. It is shown that when (b – a) is held constant for a given ion and when Iµ1 is obtained from Iµ1= 1.87 at 298 K and ∂Iµ1/∂T=–1.6 × 10–3 K–1 there is good agreement between calculated quantities and those from Tremaine and Goldman at temperatures > ca. 423 K. There is similarly good agreement between ΔC⊖ps(calc.) and values from Cobble et al. for solution of (Na++ Cl–) above 423 K. It is suggested that below this temperature there are effects due to the structure of water that cannot be calculated on an electrostatic theory. It is shown that whereas at 298 K ions may be structure making (Na+) or structure breaking (Cs+, Cl–, Br– and I–), at temperatures > ca. 400 K all the ions studied (Na+, K+, Rb+, Cs+, Cl–, Br– and I–) are structure making. The structure-making and -breaking effects of ions in water as deduced from entropies of solvation may quantitatively be connected with ionic viscosity B coefficients at all temperatures studied (273–423 K).

Henry's-law constants for solution of all the rare gases and the n-alkanes methane to n-octane in water have been fitted to functions of temperature chosen so that not only are the experimental values of ln KH reproduced, but also that on differentiation the correct parameters for solution at 298 K (ΔG°, ΔH°, ΔS°, and ΔC°p) are obtained. These fitting equations are then used to calculate parameters for solution in water from 273 to 523 K. At elevated temperatures the rare gases dissolve in water with much more positive ΔG° and ΔH°(but not ΔS°) values than in non-aqueous solvents, but as the temperature is lowered ΔH° and ΔS° values become increasingly more negative than in non-aqueous solvents. At elevated temperatures the alkanes dissolve in water with even more positive ΔH° and ΔS° values than expected by comparison with the rare gases (we regard these exceptionally positive values as hydrophobic effects of the second kind, ΔH°II and ΔS°II). Because of complete compensation between ΔH°II and ΔS°II at elevated temperatures, ΔG°II is nearly zero, and ΔG° for solution of alkanes is comparable to ΔG° for solution of the rare gases. As the temperature is lowered, structural effects of the alkane on the surrounding water molecules become important and lead to hydrophobic effects of the first kind, with ΔH°I and ΔS°I both being negative. There is incomplete compensation between ΔH°I and ΔS°I and so ΔG°I is positive, with alkanes giving rise to more positive ΔG° values than expected from rare-gas values. These more positive ΔG° values reach a maximum at ca. 370 K depending on the alkane. The methylene increment to ΔG° for solution of the alkanes reaches a maximum at 390 K, but whether or not this methylene increment is entropy- or enthalpy-controlled depends crucially on the temperature.

Apparent molal heat capacities ΦCp of some cyclic monoethers and diethers as well as of open and cyclic secondary and tertiary amines and their chloride salts have been determined by adiabatic calorimetry in the temperature range 20–60°C, at concentrations 0.4–1.0 mol kg–1.In monofunctional compounds the contribution to ΦCp from the functional group is similar to the contribution of this group to Cp2 of the pure liquid; on the other hand the contribution to ΦCp from the methylene group is greatly enhanced with respect to the contribution to Cp2(≃ 6 cal (mol CH2)–1°C–1), ranging from 22 ± 2 for open chain compounds to 18 ± 2 cal (mol CH2)–1°C–1 for cyclic compounds. The introduction of a second polar centre brings about a large decrease in ΦCp values. Comparisons are made between ΦCp data and other thermodynamic quantities. Data are finally discussed in terms of water-hydrocarbon and water-polar centre interactions.