A volumetric and viscosity study for the mixtures of 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid with acetonitrile, dichloromethane, 2-butanone and N, N – dimethylformamide

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A simple relationship between dielectric constant of mixed solvents with solvent composition and temperature.

An innovative approach is presented to interpret the refractive index of binary liquid mixtures. The concept of refractive index "before mixing" is introduced and shown to be given by the volume-fraction mixing rule of the pure-component refractive indices (Arago-Biot formula). The refractive index of thermodynamically ideal liquid mixtures is demonstrated to be given by the volume-fraction mixing rule of the pure-component squared refractive indices (Newton formula). This theoretical formulation entails a positive change of refractive index upon ideal mixing, which is interpreted in terms of dissimilar London dispersion forces centred in the dissimilar molecules making up the mixture. For real liquid mixtures, the refractive index of mixing and the excess refractive index are introduced in a thermodynamic manner. Examples of mixtures are cited for which excess refractive indices and excess molar volumes show all of the four possible sign combinations, a fact that jeopardises the finding of a general equation linking these two excess properties. Refractive indices of 69 mixtures of water with the amphiphile (R,S)-1-propoxypropan-2-ol are reported at five temperatures in the range 283-303 K. The ideal and real refractive properties of this binary system are discussed. Pear-shaped plots of excess refractive indices against excess molar volumes show that extreme positive values of excess refractive index occur at a substantially lower mole fraction of the amphiphile than extreme negative values of excess molar volume. Analysis of these plots provides insights into the mixing schemes that occur in different composition segments. A nearly linear variation is found when Balankina's ratios between excess and ideal values of refractive indices are plotted against ratios between excess and ideal values of molar volumes. It is concluded that, when coupled with volumetric properties, the new thermodynamic functions defined for the analysis of refractive indices of liquid mixtures give important complementary information on the mixing process over the whole composition range.

Refractive Index of Liquid Mixtures: Theory and Experiment

Excess volumes, mixing viscosities, and excess Gibbs energies of activation of viscous flow of the aqueous binary mixtures of the amides formamide, N-methylformamide, N,N-dimethylformamide, pyrrolidin-2-one, and N-methyl-2-pyrrolidinone were calculated from density and viscosity measurements. The values of these functions point to strong amide−water interactions with formation of a variety of aggregates, the nature of which depends on the extent of substitution of the amides; comparison of the functions of the same amides with alkan-1-ols reveal an important hydration effect. Various one-parameter and two-parameter empirical models for prediction of mixing viscosities were in good agreement with the experimental results only for the formamide−water system; none of the models predicted satisfactorily the behavior for the aqueous mixtures of both mono- and disubstituted amides.

Solute−Solvent Interactions in Amide−Water Mixed Solvents

Thermomorphic Rhodium(I) and Palladium(0) Catalysts

Density (p), kinematic viscosity (), and absolute viscosity (η) are presented for mixtures of ethane-1,2-diol and N,N-dimethylformamide form -10 to +80 o C. The above properties were fitted by empirical equations stating their dependence on temperature and mole fraction of the mixture. Furthermore, some considerations regarding the meaning of the obtained adjustment parameters are made. The excess functions, such as molar volumes V E , have been derived

The N,N-dimethylformamide/ethane-1,2-diol solvent system. Density, viscosity, and excess molar volume at various temperatures

The extrathermodynamic parameters, relative permittivity (Iµr) and refractive index (n), have been measured for ethane-1,2-diol–2-methoxyethanol binary mixtures over the entire composition range, at various temperatures ranging between –10 and 80 °C. For this system, as far as for many solvent–cosolvent systems which are useful for analytical and electrochemical applications, the properties cited above are continuous but not linear functions of the binary composition.Various equations have been applied in order to establish the best regression models for the relationship y=f(X), where X is the composition of the mixture. On the whole, minima occurred in the excess function (IµE), showing the existence of various solvent–cosolvent complexes of different stoichiometric ratios (2 : 1, 1 : 1 or 1 : 2) and of different thermostabilities, which may be interpreted in terms of moderate interactions such as dipolarity, polarizability and hydrogen bonding between the mixed solvents. Among the above complexes, the ethane-1,2-diol–2-methoxyethanol 1 : 2 adduct is suggested to be the true ‘limiting mixture’, on the borderline between the types of behaviour typical of the two pure solvents. Furthermore, empirical patterns in the refractive index were used to scrutinize the most important mixing rules in order to determine the properties of the mixture on the basis of those of its pure components.

Ethane-1,2-diol–2-methoxyethanol solvent system. Dependence of the relative permittivity and refractive index on the temperature and composition of the binary mixture

Densities (ρ) and absolute viscosities (η) of pure 1,2-ethanediol, N,N-dimethylformamide and of their nine mixtures were determined at nineteen temperatures ranging between −10 and +80 °C. The above properties were fitted by empirical equations stating their dependence on temperature and composition of the mixtures. The extrathermodynamic excess functions, such as the excess rheochor [RE] and the excess Gibbs energy of activation of viscous flow ΔGE, have been studied. The trend of [RE] vs. composition of the mixtures shows negative deviations from ideality, indicating extensive molecular interactions between the components of the binary solvent system. Furthermore, activation enthalpies and entropies for viscous flow have been obtained and their variations with composition have also been discussed.

Viscosities and activation energies of viscous flow of the 1,2-ethanediol/N,N-dimethylformamide binary solvent system

Dielectric constant (∈) and refractive indexes (n) were measured for pure N,N-dimethylformamide, ethane-1,2-diol, and their six mixtures over the entire composition range and, where possible, at nineteen selected temperatures ranging between -10 and +80 o C. The above properties were fitted by empirical equations stating their dependence on temperature (T) and mole fraction (x 1 ) of the mixture. The refractive indexes of the binary mixtures were used to test the validity of mixing rules at different temperatures

The N,N-dimethylformamide + ethane-1,2-diol solvent system. Dielectric constant, refractive index, and related properties 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.

Mara Tagliazucchi

Papers

The N,N-dimethylformamide/ethane-1,2-diol solvent system. Density, viscosity, and excess molar volume at various temperatures

Ethane-1,2-diol–2-methoxyethanol solvent system. Dependence of the relative permittivity and refractive index on the temperature and composition of the binary mixture

Viscosities and activation energies of viscous flow of the 1,2-ethanediol/N,N-dimethylformamide binary solvent system

The N,N-dimethylformamide + ethane-1,2-diol solvent system. Dielectric constant, refractive index, and related properties at various temperatures

N,N-dimethylformamide-2-methoxyethanol solvent system : densities and excess molar volumes at various temperatures