Organic solvent-water partitioning compound

Note that if Kf has been determined from solubility measurements, ywsaU is strictly valid only for saturated conditions. For dilute solutions y,wsalt can be determined from measurements of air-water or organic solvent-water partition constants at different salt concentrations. From the few compounds for which ywsa,t has been determined by both solubility and air-water or solvent-water partitioning experiments, because of the large scatter in the data, it is not clear whether Kf varies with organic solute concentration. It can, however, be concluded that, if there is an effect, it is not very large. 

Finally, the relationships between the air-organic solvent, the air-water, and the organic solvent-water partition constants of a given compound (Eq. 6-11) will make it very easy to understand organic solvent-water partitioning, which we will treat in Chapter 7. 

LFERs Relating Partition Constants in Different Solvent-Water Systems Model for Description of Organic Solvent-Water Partitioning Illustrative Example 7.1 Evaluating the Factors that Govern the Organic Solvent-Water Partitioning of a Compound... 

Table 7.1 Organic Solvent-Water Partition Constants of a Series of Compounds for Various Organic Solvents at 25°C ... 

Which is(are) the dominating factor(s) determining the organic solvent-water partitioning of the majority of organic compounds of environmental concern ... 

Why is the effect of temperature on organic solvent-water partitioning of organic compounds in many cases not very significant What maximum A(VJHj values would you expect Give examples of solutes and organic solvents for which you would expect (a) a substantial positive (i.e., > 10 kJmol-1) and (b) a substantial negative (i.e., <-10 kJmol-1) A(viHj value. 

Any attempt to estimate a Kioc value for a compound of interest (with its particular abilities to participate in different intermolecular interactions) should take into account the structural properties of the POM present in the system considered. To this end, the use of multiparameter LFERs such as the one that we have applied for description of organic solvent-water partitioning (Eq. 7-9) would be highly desirable (Poole and Poole, 1999). Unfortunately, the available data do not allow such analyses, largely due to the very diverse solid phase sources from which reported Kioc values have been derived. 

Chapter 7 7.1 Evaluating the Factors that Govern the Organic Solvent-Water Partitioning of a Compound... 

Y. Kubota, Ion-Transfer Voltammetry of Organic Compounds at Organic Solvent/Water Interface. Study on Partition of Organic Compounds between Organic Solvent and Water, MS thesis, Fukui Prefectural University, Fukui 1998. 

To evaluate the effects of salts or organic cosolvents on air-water (or more correctly, air-aqueous phase or air-organic solvent/water mixture) partitioning, we may simply apply the approaches discussed in Section 5.4 (Eqs. 5-27 and 5-29). Thus, knowing how salt affects a compound s aqueous solubility, while having no effect on its saturation vapor pressure, we deduce that the impact of salt on Ki3V/ may be expressed by ... 

We start, however, with some general thermodynamic considerations (Section 7.2). Then, using our insights gained in Chapter 6, we compare solvent-water partition constants of a series of model compounds for different organic solvents of different polarity (Section 7.3). Finally, because n-octanol is such a widely used organic solvent in environmental chemistry, we will discuss the octanol-water partition constant in somewhat more detail (Section 7.4). 

Such multiparameter LFERs have been developed for a few organic solvent-water systems (Table 7.2.) The magnitudes of the fitted coefficients, when combined with an individual solute s Vix, nDh nit ah /3, values, reveal the importance of each inter-molecular interaction to the overall partitioning process for that chemical. To interpret the various terms, we note that these coefficients reflect the differences of the corresponding terms used to describe the partitioning of the compounds from air to water and from air to organic solvent, respectively (see Chapter 6). Some applications of Eq. 7-9 are discussed in Illustrative Example 7.1. 

The isolation method of solvent extraction has been suggested as a potentially feasible process to concentrate trace organic compounds from finished drinking water (4). One positive attribute of the solvent extraction method is that its performance for any given compound is theoretically predictable from a partition coefficient of a compound between the water sample and an organic solvent. The partition coefficient can be experimentally determined for any solute in any two-phase solvent system (7, 8). Variables of the extraction procedure such as solvent-to-water ratio and the choice of solvents can be adjusted to achieve optimum recovery. 

The organic carbon-water partition coefficient is a compound-specific term that allows the user to estimate the mobility of a solvent in saturated-soil water systems if the amount or organic carbon is known. For hydrophilic solvents, values have been measured for many compounds. Other values were derived from empirical relationships drawn between water solubility or octanol-water partition coefficients. ... 

The constant K is termed the distribution or partition coefficient. As a very rough approximation the distribution coefficient may be assumed equal to the ratio of the solubilities in the two solvents. Organic compounds are usually relatively more soluble in organic solvents than in water, hence they may be extracted from aqueous solutions. If electrolytes, e.g., sodium chloride, are added to the aqueous solution, the solubility of the organic substance is lowered, i.e., it will be salted out this will assist the extraction of the organic compound. 

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