Self-association Of Ethanol Research Articles

Modeling phase behavior of poly(ethylene glycol) in supercritical fluids

The phase behavior of poly(ethylene glycol) (PEG) in supercritical solvents such as CO2, propylene, and butene, and in aqueous solution at high pressure are described using the perturbed chain statistical associating fluid (PC-SAFT) model. The effects of the molecular weight of PEG, solvent, pressure, and temperature are investigated. To model the phase behavior of PEG in supercritical solvents, the molecular weight- and temperature-dependence of the binary interaction parameter kij is considered. In addition, modeling of a PEG/CO2/ethanol mixture was carried out. The CO2 molecule was considered as a Lewis acid, and can undergo hydrogen bonding with PEG (forming a PEG-CO2 complex) and ethanol. These cross-associations, as well as the self-association of ethanol, are described in the PC-SAFT model. The correlated pressure and temperature (P-T) isopleth curves show a somewhat difference for binary system at low temperature area (<410 K), but is consistent with experimental trend for binary and ternary system.

Diffusion of Benzyl Acetate, 2-Phenylethyl Acetate, 3-Phenylpropyl Acetate, and Dibenzyl Ether in Mixtures of Carbon Dioxide and Ethanol

Diffusion coefficients of four solutes at infinite dilution (benzyl acetate, 2-phenylethyl acetate, 3-phenylpropyl acetate, and dibenzyl ether) were measured in the system CO2 + ethanol from 313.16 to 333.16 K and pressures between 15 and 35 MPa over the full concentration range of the CO2 + ethanol mixture. The diffusional behavior in the mixed solvent was compared with the estimation of seven simple predictive equations, Le Blanc, Wilke−Chang, Holmes−Olander−Wilke, Tang−Himmelblau (two formulas), Perkins−Geankoplis, and Leffler−Cullinam, observing that the first two give errors between 17 and 30% and that deviations lower than 11% are only obtained with the expressions of Tang−Himmelblau. Nevertheless, as none of the studied equations considers the self-association of ethanol nor complex formation between solute and alcohol molecules, the model of Lusis−Ratcliff and Mohan−Srnivasan was extended to a ternary liquid−supercritical system with the diffusing component dilute, obtaining average absolute deviations lower than 4.6% for the diffusivities of the four solutes. Nevertheless, the extension of this model is correlative (it needs one adjustable parameter for each solute), not predictive.

Dissociation of Selfassociation of Ethanol in nHexane and Excess Enthalpies of the Mixture

Dissociation of Selfassociation of Ethanol in nHexane and Excess Enthalpies of the Mixture

NMR Studies on hydrophobic interactions in solution Part 3 Salt effects on the self-association of ethanol in water at two different temperatures

The salt effect on the self-association of ethanol has been investigated in water-rich aqueous mixtures at 25 and 40 °C by the NMR A-parameter method. In order to investigate the anion dependence we used salts with the common sodium cation, namely Na2SO4, CF3COONa, NaBr, NaI, NaClO4 and NaSCN at fixed concentration. The association parameter A22 was obtained by means of the measurement of intermolecular 1H–1H dipole–dipole relaxation rates and self-diffusion coefficients of the ethanol molecules in D2O. The influence of the anions on the alcohol self-association at 25 °C follows the sequence: SO42− > CF3COO− > Br− > ClO4− ≈ I− > SCN−, which corresponds exactly to the well known Hofmeister or lyotropic series determining e.g. the stabilisation and destabilisation of proteins in aqueous solutions. The two salts Na2SO4 and CF3COONa promote the alcohol self-association, whereas the other salts reduce the association tendency. Thus, small organic molecules can be used for basic investigations with respect to salt effects on biologically interesting molecules. At 40 °C the relative promotingeffect of the two salts is weakened but the opposite effect of the other salts is strengthened. At this temperature the sequence ofthe anion influence is slightly different in the sense that Br− and ClO4− exchange position. Finally, we propose consideration of a special anion–apolar group interaction in water in the explanation of the anion sequence in the Hofmeister series.

NMR studies on hydrophobic interactions in solution Part 2.—Temperature and urea effect on the self-association of ethanol in water

A. Sacco and M. Holz, J. Chem. Soc., Faraday Trans., 1997, 93, 1101 DOI: 10.1039/A605867A

The self-association of ethanol in non-polar solvents

The self-association of ethanol in solutions of n-hexane, cyclopentane, cyclohexane, carbon tetrachloride and benzene is studied on the basis of heat of dilution data published in the literature. The tetramer formation model fits the experimental data better than other self-association models. The corresponding self-association constants, K 1,4, and heats of reaction, Δ H 1,4, are calculated. The solvent effect is studied using the solvent polarity factor, E T, and the existence of a linear dependance of log K 1,4 on E T values is shown.