Edwin F. Meyer

Thermodynamics of solution using gas-liquid chromatography: a comparison of eicosane, eicosanyl nitrile, 10-nonadecanone, and, 2-nonadecanone as solvents

Abstract Thermodynamic properties of solution have been measured for 17 solutes of varying degrees of unsaturation and polarity in n-eicosane, 2-nonadecanone, and eicosanyl nitrile using g.l.c. Inclusion of previous results for 10-nonadecanone allows evaluation of the role of dipole strength and position on these properties. The terminally located carbonyl group lends a more polar character to the solvent than the centrally located one. While the vapor pressure of a given solute is quite different over eicosane compared with the polar solvents, differences among the polar solvents are not great. Thus, for solvents containing only one dipole on a chain of 19 or 20 carbon atoms, increase in dipole strength is not strongly reflected in solute-solvent interactions, presumably because similar increases in solvent-solvent interactions oppose the solution process, masking the former effect.

Thermodynamics of solution of cyclic alkanes from C5 through C11 in n-C36H74 at 373.15 K using gas-liquid chromatography

Enthalpies and entropies of solution from the 1 atm vapor state to the infinitely dilute solution in n-C36H74 at 373.15 K have been measured for cyclic alkane solutes containing 5 through 11 carbon atoms. Enthalpies of solution are more negative than those exhibited by corresponding normal alkanes by about 0.5 kcalth mol−1. The difference is attributed to the considerably smaller molar volumes of the cyclic alkanes, requiring less energy input upon solution. While the entropies of solution of n-pentane and cyclopentane are very nearly the same, the cyclic alkanes display increasingly less negative values relative to the n-alkanes as the number of carbon atoms in the solute is increased, resulting in much lower equilibrium partial pressures for the cyclic molecules. The observed entropies of solution are predicted by a simple equation based on volume fraction. It appears that for normal and cyclic alkanes, molar volume is the most important variable in determining solution properties at infinite dilution.

A comparison of gas-liquid chromatographic enthalpies of solution with calorimetric values for four alkane systems

Abstract Using a gas-liquid-chromatography technique, specific retention volumes v g were measured in the range 293 to 303 K, for n -hexane + n -hexadecane, 2, 2-dimethyl butane + n -hexadecane, cyclohexane + n -hexadecane, and n -hexane + n -tetracosane. ΔH m ∞ for the liquids was calculated from the variation of specific retention volume with temperature for each system and from calorimetrically measured enthalpies of vaporization of the solutes. The same quantity was derived, by extrapolation, from calorimetrically measured enthalpies of mixing of the liquids. Difference between the values of ΔH m ∞ obtained in these two ways were about the same as the differences between calorimetrically determined enthalpies of mixing from different laboratories. ΔG o , ΔS o , and ΔH o of solution are also reported for each system and ΔC p ∞ is reported for n -hexane dissolving in n -tetracosane.

Thermodynamics of solution of chloroalkanes in n-heneicosane and in 1-chloroeicosane at 333.15 K using gas-liquid chromatography

Abstract Thermodynamic properties of solution at infinite dilution in n -C 21 H 44 and n -C 20 H 41 Cl at 333.15 K have been measured for several alkanes and chloroalkanes using g.l.c. The substitution of a chlorine atom for a methyl group in the solvent manifests itself in 16 per cent higher equilibrium vapor pressures for alkane solutes, and 10 to 30 per cent lower values for chloroalkanes, depending on the number of carbon atoms and the number and position of the chlorine atoms in the solute molecules. For the chloroalkanes, both enthalpy and entropy of transfer from n -C 21 H 44 to n -C 20 H 41 Cl are negative, typical values being −0.5 kcal th mol −1 and −1.0 cal th K −1 mol −1 . The same properties of transfer from the pure liquid chloroalkanes to both solvents are universally positive; however, α,ω-dichloroalkanes are the only ones studied with significantly higher escaping tendencies from the solvent relative to the pure solute, emphasizing their unusually strong dipole-dipole interaction in the latter. There is evidence that both chlorine atoms in α,ω-dichloroalkanes containing up to 5 carbon atoms interact simultaneously with the single chlorine atom in n -C 20 H 41 Cl.

Thermodynamics of solution of linear and cyclic ketones in n-C36H74 at 373.15 K using gas-liquid chromatography

Abstract Thermodynamic properties of solution at 373.15 K in n -C 36 H 74 have been measured for 2-ketones and cyclic ketones containing 5 through 11 carbon atoms, using gas-liquid chromatography (g.l.c.). The differences between the solution properties of linear and cyclic polar solutes are qualitatively the same as those between normal and cyclic alkanes, but cannot be expressed quantitatively in as simple a manner. The presence of the carbonyl group in the ketone solutes introduces a nearly constant additive contribution to the enthalpy of solution, attributed to the induction interaction between it and the methylene chain of the solvent. The same interaction is responsible for more negative entropies of solution for the ketones relative to the alkanes, particularly for the smaller solutes.

Thermodynamics of solution using gas-liquid chromatography. A comparison of n-tetracosane, didodecyl ether, and didodecyl thioether as solvents

Abstract Thermodynamic properties of solution of 24 solutes of varying degrees of unsaturation and polarity were measured at 349.15 K in n -tetracosane, di- n -dodecyl ether, and di- n -dodecyl thioether, using g.l.c. Unsaturated solutes, ethers, and polar solutes displayed increasingly lower escaping tendencies, in that order, in the ether solvents, the effect being slightly greater in the thioether. Observed enthalpies of solution did not differ significantly for a given solute in the two ether solvents, in general. A simple model was used to separate the attractive energy from the hole energy, however, which led to the conclusion that the solvent sulfur atom was responsible for an extra 2.5 kJ mol −1 of attractive energy, on the average, relative to the two other solvents.

Partial molar heat capacities at infinite dilution for alkane systems using gas-liquid chromatography☆

Abstract Measurement of the specific retention volume of n -octane and cycloheptane in n -C 36 H 74 as a function of temperature using a high-precision gas chromatograph has allowed estimation of the change in enthalpy of solution with temperature. Coupled with heat capacities for the pure solute vapor, this provides the partial molar heat capacity at infinite dilution. Comparison with calorimetric data for a similar system supports the validity of the present results.

Thermodynamics of solution of 1-, 2-, and 3-hexyne, and 1,5- and 2,4-hexadiyne in n-tetracosane, n-nonadecylcyclohexane, di-n-dodecyl ether, and di-n-dodecyl thioether at 349.15 K using gas-liquid chromatography

Abstract Thermodynamic properties of solution of five six-carbon acetylenic solutes in two alkane and two ether solvents were measured at 349.15 K using g.l.c. There is a specific attraction between the triple bond and ether oxygen or sulfur atoms, which is enhanced by the presence of an acetylenic hydrogen atom. Both triple bonds in the diynes are able to interact with solvent hetero-atoms simultaneously. The rod-like nature of 2,4-hexadiyne results in extremely strong solute-solvent attraction which is, to a large degree, independent of the solvent.