scholarly journals Solubility of Polar and Non-Polar Aromatic Molecules in Subcritical Water: The Role of the Dielectric Constant

2019 ◽  
Author(s):  
Nuno Galamba ◽  
Alexandre Paiva ◽  
Susana Barreiros ◽  
Pedro Simões
Keyword(s):  
Dielectric Constant ◽  
Free Energy ◽  
High Temperatures ◽  
High Pressures ◽  
Subcritical Water ◽  
Hot Water ◽  
Model Systems ◽  
Pure Liquid ◽  
Hydration Free Energy ◽  
Polar Solutes

Liquid water at temperatures above the boiling point and high pressures, also known as pressurized hot water, or subcritical water (SBCW), is an effective solvent for both polar and non-polar organic solutes. This is often associated to the decrease of water's dielectric constant at high temperatures, apparently allowing water to behave like an organic solvent. The decrease of the solubility at high pressures, in turn, is explained by a mild increase of the dielectric constant of water. Nevertheless, the relationship between the dielectric constant of water, hydration, and the solubility of polar and non-polar molecules in SBCW, remains poorly understood. Here, we study through molecular dynamics, the hydration thermodynamic parameters and the solubility of non-polar and polar aromatic model systems, for which a solubility increase in SBCW is observed. We show that the temperature dependence of the hydration free energy of the model non-polar solutes is nonmonotonic, exhibiting a solute size independent maximum at ~475 K, above which hydration becomes entropically favorable and enthalpically unfavorable. The monotonic increase of the solubility, separated here in hydration and vaporization or sublimation components of the pure liquid or solid solute, respectively, is, in turn, related to the temperature increase of the latter, and only to a minor extent with the decrease of the hydration free energy above ~475 K, via the hydration entropy. A solubility increase or decrease is also found at high pressures for different solutes, explained by the relative magnitude of the hydration and the vaporization or sublimation components of the solubility. For the model solid polar system studied, the hydration free energy increases monotonically with the temperature, instead, and the solubility increase is caused by the decrease of the sublimation component of the solubility. Thus, despite of the observed increase of the hydration free energy with pressure, related to the entropic component decrease, our results indicate that the dielectric constant plays no significant role on the solubility increase of non-polar and polar solutes in SBCW, opposite to the dielectric constant picture. The structure of water next to the solutes is also investigated and a structural enhancement at room temperature is observed, resulting in significantly stronger pair interactions between a water molecule and its third and fourth nearest water neighbors. This structural and energetic enhancement nearly vanishes, however, at high temperatures, contributing to a positive hydration entropy. <br>

scholarly journals Solubility of Polar and Non-Polar Aromatic Molecules in Subcritical Water: The Role of the Dielectric Constant

2019 ◽  
Author(s):  
Nuno Galamba ◽  
Alexandre Paiva ◽  
Susana Barreiros ◽  
Pedro Simões
Keyword(s):  
Dielectric Constant ◽  
Free Energy ◽  
High Temperatures ◽  
High Pressures ◽  
Subcritical Water ◽  
Hot Water ◽  
Model Systems ◽  
Pure Liquid ◽  
Hydration Free Energy ◽  
Polar Solutes

Liquid water at temperatures above the boiling point and high pressures, also known as pressurized hot water, or subcritical water (SBCW), is an effective solvent for both polar and non-polar organic solutes. This is often associated to the decrease of water's dielectric constant at high temperatures, apparently allowing water to behave like an organic solvent. The decrease of the solubility at high pressures, in turn, is explained by a mild increase of the dielectric constant of water. Nevertheless, the relationship between the dielectric constant of water, hydration, and the solubility of polar and non-polar molecules in SBCW, remains poorly understood. Here, we study through molecular dynamics, the hydration thermodynamic parameters and the solubility of non-polar and polar aromatic model systems, for which a solubility increase in SBCW is observed. We show that the temperature dependence of the hydration free energy of the model non-polar solutes is nonmonotonic, exhibiting a solute size independent maximum at ~475 K, above which hydration becomes entropically favorable and enthalpically unfavorable. The monotonic increase of the solubility, separated here in hydration and vaporization or sublimation components of the pure liquid or solid solute, respectively, is, in turn, related to the temperature increase of the latter, and only to a minor extent with the decrease of the hydration free energy above ~475 K, via the hydration entropy. A solubility increase or decrease is also found at high pressures for different solutes, explained by the relative magnitude of the hydration and the vaporization or sublimation components of the solubility. For the model solid polar system studied, the hydration free energy increases monotonically with the temperature, instead, and the solubility increase is caused by the decrease of the sublimation component of the solubility. Thus, despite of the observed increase of the hydration free energy with pressure, related to the entropic component decrease, our results indicate that the dielectric constant plays no significant role on the solubility increase of non-polar and polar solutes in SBCW, opposite to the dielectric constant picture. The structure of water next to the solutes is also investigated and a structural enhancement at room temperature is observed, resulting in significantly stronger pair interactions between a water molecule and its third and fourth nearest water neighbors. This structural and energetic enhancement nearly vanishes, however, at high temperatures, contributing to a positive hydration entropy. <br>

ΔGθ, ΔHθ, ΔSθ de transfert de H2O et du couple H+, OH− de l'eau à ses mélanges contenant jusqu'à 40% de EtOH, tert-BuOH, DMSO, acétone et urée à 25 °C

1975 ◽  
Vol 53 (3) ◽  
pp. 455-462 ◽  
Author(s):  
Henri Gillet ◽  
Lévon Avédikian ◽  
Jean-Pierre Morel
Keyword(s):  
Dielectric Constant ◽  
Free Energy ◽  
Alkali Halides ◽  
Ion Pair ◽  
Pure Liquid ◽  
Thermodynamic Quantities ◽  
Simple Correlation ◽  
Organic Mixtures ◽  
The Media ◽  
Isobaric Expansion

We have measured the heat of neutralization of dilute solutions of HCl in aqueous–organic mixtures containing up to 40% by weight of t-BuOH, DMSO, acetone, and urea; autoprotolysis constants of the mixtures H2O–DMSO and H2O–urea also were determined. Thus the usual thermodynamic quantities ΔGθ, ΔHθ, and ΔSθ could be determined for the dissociation of water in these mixtures. The results for the H2O-urea mixtures must be accepted with caution because the dissociation of urea itself is not negligible compared to that of water. Using various literature data we have calculated values of the Gibbs free energy and the enthalpy for the transfer of a molecule of water from the pure liquid to the mixtures noted above. (We also have calculated for these mixtures the coefficients of isobaric expansion and those for the variation with temperature of the dielectric constant.) In addition, the values for the transfer of the ion pair H+, OH− have been determined as well as those for the transfer from water to H2O–EtOH mixtures. These are com pared to those already known for HCl and the alkali halides. It is not possible to establish a simple correlation between the differing variations of these quantities with the structural prop erties usually considered to exist in the media studied. [Journal translation]

Brillouin scattering study of liquid methane under high pressures and high temperatures

2010 ◽  
Vol 133 (4) ◽  
pp. 044503 ◽  
Author(s):  
Min Li ◽  
Fangfei Li ◽  
Wei Gao ◽  
Chunli Ma ◽  
Liyin Huang ◽  
...  
Keyword(s):  
High Temperatures ◽  
High Pressures ◽  
Brillouin Scattering ◽  
Scattering Study ◽  
Liquid Methane

The transmission of polar effects. Part VII. A proton magnetic resonance spectra study of substituted mesitylenes, durenes, anthracenes, and triptycenes

1968 ◽  
Vol 46 (24) ◽  
pp. 3903-3908 ◽  
Author(s):  
Keith Bowden ◽  
J. G. Irving ◽  
M. J. Price
Keyword(s):  
Dielectric Constant ◽  
Free Energy ◽  
Carbon Tetrachloride ◽  
Field Effect ◽  
Proton Magnetic Resonance ◽  
Chemical Shifts ◽  
Linear Free Energy ◽  
Solvent Dependence ◽  
Similar Dependence ◽  
Energy Relations

The chemical shifts of the ring protons in a series of monosubstituted mesitylenes and durenes, and of the 10-protons of a series of 9-substituted triptycenes and anthracenes have been measured in dimethyl sulfoxide, acetone, 2-methoxyethanol, and carbon tetrachloride. The solvent dependence of the substituent chemical shifts has been analyzed by linear free energy relations. The systems all show similar dependence which increases with increasing dielectric constant of the solvent. This does not result from the field effect being transmitted through the medium, but appears to arise from the formation of a hydrogen-bonded interaction between the solvent and the hydrogen of the solute. The substituent chemical shifts appear to arise from contributions from substituent field, resonance, magnetic anisotropy, and solvent effects.

scholarly journals Gaseous combustion at high pressures. —Part X. The co-volume corrections, maximum temperatures and dissociation of steam and carbon dioxide in explosions

1928 ◽  
Vol 119 (782) ◽  
pp. 464-480
Keyword(s):  
Carbon Dioxide ◽  
High Pressure ◽  
Internal Energy ◽  
High Temperatures ◽  
High Pressures ◽  
Internal Combustion ◽  
Systematic Survey ◽  
Explosion Method ◽  
Maximum Temperatures ◽  
Very High

During the researches upon high-pressure explosions of carbonic oxide-air, hydrogen-air, etc., mixtures, which have been described in the previous papers of this series, a mass of data has been accumulated relating to the influence of density and temperature upon the internal energy of gases and the dissociation of steam and carbon dioxide. Some time ago, at Prof. Bone’s request, the author undertook a systematic survey of the data in question, and the present paper summarises some of the principal results thereof, which it is hoped will throw light upon problems interesting alike to chemists, physicists and internal-combustion engineers. The explosion method affords the only means known at present of determining the internal energies of gases at very high temperatures, and it has been used for this purpose for upwards of 50 years. Although by no means without difficulties, arising from uncertainties of some of the assumptions upon which it is based, yet, for want of a better, its results have been generally accepted as being at least provisionally valuable. Amongst the more recent investigations which have attracted attention in this connection should be mentioned those of Pier, Bjerrum, Siegel and Fenning, all of whom worked at low or medium pressures.

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