Luigi Marcheselli

N,N-Dimethylformamide–2-methoxyethanol solvent system. Densities and excess molar volumes at various temperatures

Densities (ρ) have been measured for N,N-dimethylformamide (1), 2-methoxyethanol (2), and for nine binary mixtures covering the whole miscibility field (0 ⩽X1⩽ 1) in the temperature range –10–+80 °C. The experimental data were used to test some empirical equations of the type ρ=ρ(t), ρ=ρ(X1) and ρ=ρ(t, X1). Furthermore, the excess volumes (VE) for these binaries have been examined and discussed at all the investigated temperatures in terms of the influence of interactions between unlike molecules.The VEvs. X1 plots suggest the presence of some stable adducts, having N,N-dimethylformamide: 2-methoxyethanol stoichiometric ratios of 1 : 2 and 1 : 1 depending on the temperature.

Dielectric behaviour of the 2-methoxyethanol–1,2-dimethoxyethane solvent system

The static relative permittivity at various temperatures ranging from –10 to +80 °C has been measured for 2-methoxyethanol, 1,2-dimethoxyethane and nine mixtures covering the whole miscibility field expressed by the mole fraction of 2-methoxyethanol (0 ⩽X1⩽ 1).Equations describing the dependence of the relative permittivity on temperature [Iµ=Iµ(T)], and binary composition [Iµ=Iµ(X1)], have been checked. Furthermore, a single function Iµ=Iµ(T, X1) has been obtained by combining the previously cited monovariant equations. As a rule, the calculated values agree very well with the experimental ones.The excess extrathermodynamic parameter IµE, which provides much useful information about the possibility of forming solvent–cosolvent complexes is briefly discussed. This fact has been interpreted on the basis of specific interactions of any kind between different molecules, taking into account geometric effects and steric hindrances.

Ethane-1,2-diol–water solvent system: relative permittivity as a function of temperature and binary composition

Relative permittivity (Iµ) data for several aqueous binary mixtures of ethane-1,2-diol at various temperatures in the range –10 to +80 °C are presented. The experimental data were processed by empirical relations stating the dependence of Iµ on temperature and binary composition expressed as mole fraction of ethane-1,2-diol. The variation of Iµ with mole fraction is non-linear at the temperatures investigated. Ethane-1,2-diol behaves as a structure breaker, showing negative deviations in Iµ vs. composition curves.Minima occur in the excess function (IµE), and the magnitude of the deviations with respect to pure species seems to be influenced by the dipolarity, polarizability and any hydrogen-bonding tendency of the two cosolvents. These empirical patterns in dielectric behaviour were very useful in order to establish the stoichiometric ratio of the ethane-1,2-diol–water solvent–cosolvent adduct which is probably formed in solution.

The relative permittivity of 1,2-dimethoxyethane and N,N-dimethylformamide mixtures from -10 to 40°C

Binary solutions of N,N-dimethylformamide and 1,2-dimethoxyethane have been investigated by means of dielectric measurements at temperatures ranging from −10 to +40°C, and for nine mixtures covering the whole miscibility field expressed by the mole fraction of one component (0≤X1≤1). The experimental data were used to study the dependence of ɛ on T and X1, of the type ɛ = ɛ(T), ɛ = ɛ(X1), and ɛ = ɛ(T,X1). Further, the excess mixing function ɛE has been evaluated in order to identify particular patterns of interaction between unlike molecules and any other factor that could modify such patterns. The minimum in the ɛE vs. composition plots suggests the formation of an adduct of stoichiometric ratio DMF∶DME=1∶1 at all the investigated temperatures.

The relative permittivity of 1,2-ethanediol+2-methoxyethanol+water ternary mixtures

The relative permittivities ∈ for the ternary 1,2-ethanediol (component 1) + 2-methoxyethanol (2) + water (3) solvent system have been measured for 66 mixtures covering the whole mole fraction composition 0≤X1/X2/X3 ≤1 range at −10, −5 and 0 °C. The experimental data were used to test some empirical relations stating the dependence of ∈=∈ (X1, X2, X3). A comparison between the calculated and experimental data show that these equations can be usefully employed to predict ∈ values in correspondence of the experimental data gaps.

2-Methoxyethanol–water solvent system: static relative permittivity from –10 to +80 °C

A detailed dielectric study of 2-methoxyethanol (ME)–water (W) mixtures has been carried out as a function of temperature in the range –10 to +80 °C and over the entire binary composition range (0 ⩽x⩽ 1). The experimental data, obtained by the heterodyne beat method at 2 MHz, were used to test some empirical relations of the type Iµ=Iµ(T), Iµ=Iµ(x) and Iµ=Iµ(T, x), in order to assess the empirical performances in dielectric behaviour of these mixtures, including the experimental conditions which are able to modify such patterns. The data reported here for ME–W binary mixtures were useful trying to understand the relative discriminating ability of both components towards cooperative intermolecular interactions in the liquid state, the quantitative similarities and differences between the chosen pure species, the intermolecular phenomena and interactions influencing the dielectric properties of the mixtures and the usefulness of a qualitative description of the possible formation of solvent–cosolvent complex species involving hydrogen-bonding, dipole–dipole and other interactions.

Thermodynamic behaviour of some electrolytes in ethane-1,2-diol from - 10 to + 80°C

Conductivities of the electrolytes NaBr, NaPi, HPi, NaBPh4, and Ph4PBr in ethane- 1,2-diol were determined in the −10 ≤ t ≤ +80 °C temperature range. The experimental data were analyzed by the Fuoss–Hsia equation, which provides further informative parameters such as the dissociation constant (K) of the ion pairs formed in solution, the limiting equivalent conductivity (Λ0), and the ion-size parameter (a). Thermodynamic behaviour of these electrolytes was derived from analysis of the K values. Single-ion conductivities were evaluated on the basis of the assumption of Ph4PBPh4 as reference electrolyte.