Multicomponent Equilibrium Thermodynamics - Elements of Environmental Engineering: Thermodynamics and Kinetics - page 67

TABLE 3.10
Values of

w
i

o
i

γ and γ for Typical Organic Compounds at 298 K

o
i

w
i

Compound γ γ

2.4 × 10 3

Benzene 2.83

1.2 × 10 4

Toluene 3.18

1.4 × 10 5

Naphthalene 4.15

4.2 × 10 5

Biphenyl 5.30

6.1 × 10 4 p -Dichlorobenzene 3.54

9.6 × 10 6 Pyrene 8.66

8.6 × 10 2

Chloroform 1.40

10 4 Carbon tetrachloride 3.83 1.0 ×

Source: From Mackay, D. 1982. VolatilizationofOrganicPollutantsfromWater .
EPA Report No: 600/3-82-019, NTIS No: PB 82-230939. Springfield,
VA: National Technical Information Service; Chiou, C.T. 1981. Parti-
tion coefficient and water solubility in environmental chemistry. In: J.
Saxena and F. Fisher (eds), Hazard Assessment of Chemicals , Vol. 1.
New York: Academic Press; Yalkowsky, S.H. and Banerjee, S. 1992.
Aqueous Solubilities—Methods of Estimation for Organic Compounds .
NewYork: Marcel Dekker.

also available in pure form readily and is only sparingly soluble in water.Appendix 1
lists the log K ow values for a variety of compounds.
It is important to note that generally large K ow values are associated with com-
pounds that have low affinity with the aqueous phase. This becomes clear when one
notes that most solutes behave ideally in octanol, and hence

o

γ

i varies only slightly

i varies over several orders of magnitude (0.1-10 7 )
(see Table 3.10). Since both V o and V w are constants, the variation in K ow is entirely
due to variations in

w

(from about 1 to 10) whereas γ

w

i . In other words, K ow is a measure of the relative nonideality
of the solute in water as compared to that in octanol. Hence K ow is taken to be a
measure of the hydrophobicity or the incompatibility of the solute with water .
K ow values in the literature are reported at “room temperature.” This means the
temperature is 298 K with occasional variability of about 5 ◦ . It is important to note
that the temperature dependence is nearly negligible for these temperature variations.
Theremaybecaseswhenreliableexperimental K ow valuesarenotavailable.Under
these circumstances it is possible to estimate K ow from basic structural parameters of
the molecule (Lyman, Reehl, and Rosenblatt, 1990). Langmuir (1925) first suggested
that the interaction of a molecule with a solvent can be obtained by summing the
interactions of each fragment of the molecule with the solvent. The same principle
wasextendedtooctanol-waterpartitionratiosbyHanschandLeo(1979).Thismethod
involves assigning values of interaction parameters to the various fragments that make
up a molecule. For example, an alkane molecule (ethane, CH 3 -CH 3 ) is composed of
two -CH 3 groups, each contributing equally toward the K ow of the molecule. There
are two parts to this type of calculation: a fragmentconstant ( b) and astructuralfactor
( B) . It is presumed that from chemical to chemical these constants are the same for a

γ