Jan Zielkiewicz

Preferential solvation of N-methylformamide, N,N-dimethylformamide and N-methylacetamide by water and alcohols in the binary and ternary mixtures

Using the Kirkwood–Buff theory of solutions, the preferential solvation of the N-methylacetamide molecule has been investigated in the binary and ternary mixtures containing N-methylacetamide (NMA), aliphatic alcohol and water. The results are compared with those obtained previously for N-methylformamide (NMF) and N,N-dimethylformamide (DMF). The thermodynamic investigations, based on the Kirkwood–Buff theory of solutions, lead to the unexpected conclusion that both NMA and DMF are solvated in the investigated binary and ternary mixtures in a very similar manner, but solvation of NMF differs from other amides. For all the investigated amides, the local mole fractions differ only slightly from the bulk ones—the deviations are only a few per cent or less. Moreover, for the {amide+methanol} binary mixtures, where amide=NMF, DMF and NMA, molecular dynamics calculations at xamide=0.518 were performed. From the obtained molecule–molecule radial distribution functions (rdf) and atom–atom rdf, it was possible to estimate the local mole fractions around the amide molecule, the orientation effects of molecules within the solvation shell, and a possibility of the formation of complexes. The general picture obtained from analysis of the molecular dynamics results is consistent with the deductions derived from thermodynamic data.

(Vapour + liquid) equilibria in (propan-1-ol + n-hexane + n-heptane) at the temperature 313.15 K

Measurements have been made of the vapour pressure for (propan-1-ol + n -hexane + n -heptane), and for the binary constituent mixtures, at the temperature 313.15 K. The binary results have been fitted to various equations, and the possibility of predictions of the ternary quantities from binary quantities is proved using the UNIQUAC, Wilson, and NRTL equations as the basis. Moreover, the ternary quantities are correlated by taking advantage of an empirical equation with adjusted ternary parameters. The results relating to (propan-1-ol + n -hexane) and (propan-1-ol + n -heptane) have been compared with values given in the literature.

(Vapour + liquid) equilibria of (N,N-dimethylformamide + water + propan-1-ol) at the temperature 313.15 K

Vapour-pressure measurements made by a modified static method for ( N,N -dimethylformamide + water + propan-1-ol) and the binary constituent mixtures at the temperature 313.15 K are presented. Different expressions for G E m suitable for correlation of these results are tested. A prediction of ternary (vapour + liquid) equilibria from binary results is examined. Results for (water + propan-1-ol) are compared with literature values.

Preferential solvation in (amide + alcohol) binary mixtures.

The preferential solvation of N-methylpyrrolidinone by ethanol was investigated by two complementary methods. First, the thermodynamic measurements of excess Gibbs energies and excess volumes of mixing are reported for {N-methylpyrrolidinone+ethanol} binary mixture at T=313.15 K. The Kirkwood–Buff theory of solutions was used to interpret the thermodynamic data, and the results are compared with those for other amides: N-methylformamide, N,N-dimethylformamide, N-methylacetamide, N,N-dimethyl-acetamide and 2-pyrrolidinone. It was found that the presence of amide hydrogen (in the N–H group) nearly does not influence the local mole fractions. Similarly, even large hydrocarbon part in pyrrolidinones only slightly changes the local mole fractions. Second, the molecular dynamics calculations for the {N-methylpyrrolidinone+ethanol} binary mixture were performed, using various sets of parameters. The results obtained were compared with the thermodynamic data for this system, and with deductions derived from the experimental data using the Kirkwood–Buff theory of solutions. From calculated radial distribution functions, the solvation shell radius was estimated, and values of the local mole fractions were evaluated. A simple procedure for calculating the Kirkwood–Buff integrals from molecular dynamics results was proposed and examined. Moreover, the formation of hydrogen-bonded complexes was investigated; the lifetime of the N-methylpyrrolidinone–ethanol complexes created was estimated. We suppose that ethanol forms a dynamic cage around the amide molecule, and the mean lifetime of this cage was estimated. The general picture obtained from these calculations is consistent with the thermodynamic results and complements the “thermodynamic” point of view on the solvation of amides by ethanol molecules.

(Vapour + liquid) equilibria in (propan-1-ol+heptane+octane) at the temperature 313.15 K

Vapour-pressure measurements made by a modified static method for (propan-1-ol + n -heptane + n -octane) and the binary constituent mixtures at the temperature 313.15 K are presented. The binary results have been fitted to various equations, and the possibility of predictions of the ternary quantities from binary quantities is proved using the UNIQUAC, Wilson, and NRTL equations as the basis. Moreover, the ternary results are correlated by taking advantage of an empirical equation with adjusted ternary parameters. A comparison was made of the results for (propan-1-ol + n -heptane) and (propan-1-ol + n -octane) with the results given in the literature, and with predicted values from the UNIFAC model for the investigated binary and ternary mixtures.

Preferential solvation in {amide + alcohol} binary mixtures. Part 2. The N-methylpyrrolidinone + methanol mixture at T = 313.15 K: thermodynamic results and molecular dynamics calculations

The preferential solvation of N-methylpyrrolidinone by ethanol was investigated by two complementary methods. First, the thermodynamic measurements of excess Gibbs energies and excess volumes of mixing are reported for {N-methylpyrrolidinone + ethanol) binary mixture at T = 313.15 K. The Kirkwood-Buff theory of solutions was used to interpret the thermodynamic data, and the results are compared with those for other amides: N-methylformamide, N,N-dimethylformamide, N-methylacetamide, N,N-dimethyl-acetamide and 2-pyrrolidinone. It was found that the presence of amide hydrogen (in the N-H group) nearly does not influence the local mole fractions. Similarly, even large hydrocarbon part in pyrrolidinones only slightly changes the local mole fractions. Second, the molecular dynamics calculations for the {N-methylpyrrolidinone + ethanol} binary mixture were performed, using various sets of parameters. The results obtained were compared with the thermodynamic data for this system, and with deductions derived from the experimental data using the Kirkwood-Buff theory of solutions. From calculated radial distribution functions, the solvation shell radius was estimated, and values of the local mole fractions were evaluated. A simple procedure for calculating the Kirkwood-Buff integrals from molecular dynamics results was proposed and examined, Moreover, the formation of hydrogen-bonded complexes was investigated; the lifetime of the N-methylpyrrolidinone-ethanol complexes created was estimated. We suppose that ethanol forms a dynamic cage around the amide molecule, and the mean lifetime of this cage was estimated. The general picture obtained from these calculations is consistent with the thermodynamic results and complements the thermodynamic point of view on the solvation of amides by ethanol molecules.

(Vapour + liquid) equilibria in (2-methylpyridine + benzene or ethyl ethanoate or chlorobenzene) at the temperature 303.15 K

Vapour-pressure measurements have been made by a modified static method for (2-methylpyridine + benzene or ethyl ethanoate or chlorobenzene) at the temperature 303.15 K. Various equations have been fitted to the results.