Organic solvent-water partition constant

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. 

A more common way of expressing organic solvent-water partition constants is to use molar concentrations in both phases (Eq. 3-45) ... 

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

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... 

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). 

Figure 5.6 Illustration of the effect of a completely water-miscible solvent (CMOS, i.e., methanol) on the activity coefficient of organic compounds in water-organic solvent mixtures decadic logarithm of the activity coefficient as a function of the volume fraction of methanol. Note that the data for naphthalene (Dickhut et al., 1989 Fan and Jafvert, 1997) and for the two PCBs (Li and Andren, 1994) have been derived from solubility measurements whereas for the anilins (Jayasinghe etal., 1992), air-water partition constants determined under dilute conditions have been used to calculate y,f.

Note that many of the activity coefficients of organic compounds in dilute aqueous solution, y , that we used in Chapter 5 were derived from experimental air-water partition constants (Ki lv/) using Eq. 6-7. Finally, we should point out that in the literature, similar to air-solid surface partitioning (Section 11.1), partition constants are quite often reported as the reciprocal quantity of the air-solvent partition constants as defined above, that is, as solvent-air partition constants. However, it does not really matter in what form such constants are given, as long as we pay... 

P 7.5 Evaluating Partition Constants of Chlorinated Phenols in Two Different Organic Solvent-Water Systems... 

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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