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. Can. J. Chem. 60,2755Chem. 60, (1982. Vapor pressure osmometry was used to measure osmotic coefficients for tributylphosphate (TBP), tricresylphosphate (TCP), and triethylhexylphosphate (TEHP) in 11-octane at 30,40,50, and 60°C andat molalities up to0.3 mollkg. Activity coefficients andexcess thermodynamic properties (unsymmetrical definition) were calculated from these osmotic coefficients. At 30"C, the excess Gibbs free energies for 0.1 mol of solute in 1.0 kg 11-octane were -42 J, -66 J, and -20 J for TBP, TCP, and TEHP, respectively. Themore ideal behavior of the TEHP-octane system is attributed to the increasing importance of hydrocarbon-hydrocarbon interactions as the chain length is increased. The excess enthalpies for 0.1 mol of solute in 1.0 kg of solvent were -100 J, -300 J , and -150 J for TBP, TCP, and TEHP, respectively. Thus, association of these solutes arises primarily from entropic effects.Our data could generally be accommodated adequately by postulating association of monomers into dimers. The exception was TCP at lower temperatures, where more complex models were required. Nos donnkes peuvent gentralement s'accomoder de f a~o n adequate en postulant une association de monomeres dans les dimkres. Le TCP fait exception 2 de basses temperatures oh des modkles plus complexes sont necessaires.[Traduit par le journal] 1 Introduction Experimental IThe neutral organic phosphates, particularlyOsmotic coefficients were measured at 30, 40, 50, and 60°Ci tributylphosphate (TBP), are used in many solvent using a CoronaIWescan Model 232A vapor pressure osmom-I extraction processes. In the nuclear industry, such eter. In this apparatus, the steady-state temperature difference is measured between a drop of pure solvent (n-octane) and a I are for the reprocessing of drop of solution, both drops being maintained in a chamber irradiated fuel (1). We have begun a pro-saturated with pure solvent vapor (8,9). Thermistors areused as gram to study interfacial properties rekvant to temperature sensors, and the difference in the voltage develthese solvent extraction systems (2, 3), and thus, oped across the two thermistors, AV, is measured at aconstant we need to know activity coefficients for organic bridge current. The operation of this particular instrument is described in detail by Burge (10). To extend the range of the phosphates in various hydrocarbon and aqueous technique to higher solute molalities, solutions whose osmotic media. The purpose of this work is to measure coefficients were known were used as both reference solution activity coefficients of three triorganophosphates, and vapor-saturating solution. The AV's were obtained relative TBP, tricresylphosphate (TCP), and triethylhexyl-to these reference solutions (11).At each of the four temperatures employed, the instrument phosphate (TEHP)y in '-Octane' Osmotic coef-was calibrated using solutions of n-hexadecane in n-octane as ficients of triorgan0phosphates have been mea-standards (1 I). The voltage difference, AV, was divided by the sured previous...

. Can. J. Chem. 62, 81 (1984). The salting-out of triethylphosphate (TEP) from water was measured at 25°C for twelve inorganic electrolytes. If salting out is taken as an additive property of ions, then the effectiveness for salting TEP out of water is I-< Br-< C1-< +SO:-< $0:-for anions and $La3+ < Na+ .= NH: < Cs+ < $aZ+ = $~g " < K' < i~a " for cations. The results were fitted to three theories. The distribution theory of Conway, Desnoyers, and Smith predicts the order of magnitude of the experimental results, but does not discriminate well between salts of the same valence type. The electrostriction theory of McDevit and Long discriminates well between ions but gives results three or five times larger than those observed. Scaled particle theory predicts the results reasonably well, but the predictions depend critically on the choice of ionic and molecular parameters. Thus, none of these theories is entirely satisfactory.

The distribution of four branched chain octanols, 3-ethyl-3-hexanol, 4-ethyl-3-hexanol, 2-ethyl-4-methylpentanol, and 4-octanol, has been measured between dodecane and water. Measurements were made at alcohol concentrations in the dodecane of less than 0.1 mol/dm3, and as a function of temperature from 10 °C to 35 °C. From these distribution data, standard thermodynamic functions for transfer were calculated. Standard Gibbs energies of transfer from water to dodecane at 25 °C were in the range −14.1 to −15.1 kJ/mol, whereas the standard enthalpies of transfer at 25 °C varied from 29 to 39 kJ/mol. Thus, the change in the standard enthalpy tends to inhibit transfer, but a large standard entropy of transfer results in dodecane being the favoured phase.

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