Octanol-water and organic

Along with the octanol-water and octanol-air partition coefficients, KAW determines how a chemical substance will partition between the three primary media of accumulation in the environment, namely air, water, and organic matter present in soils, solids, and biota. "Volatile Organic Chemicals" such as chloroform with large values of KAW evaporate apprecia-... 

Dowdy, D.L., McKone, T.E. (1997) Predicting plant uptake of organic chemicals from soil or air using octanol/water and octanol/air partition ratios and a molecular connectivity index. Environ. Toxicol. Chem. 16, 2448-2456. 

Partition energies for the solutes were obtained from the difference of Gint in water and organic solvent according to Eq. 6.11. Where 2 GHz0 and 2 Gnonpoiar soivent are the interfacial energies from Eq. 6.10 for the solute placed in water ( = 78.5) and in the apolar phase (whith = 10 for octanol and = 2 for hydrocarbon). 

Physical and Chemical Properties. Several important physical properties of 2-butoxyethanol and 2-butoxyethanol acetate have yet to be experimentally determined. These include their octanol-water and soil-water partition coefficients, Henry s law constants, and bioconcentration factors in aquatic organisms. These data are important in estimating the fate of tlie released compounds in the environment and in determining the potential for human exposure. However, reliable estimated values for these parameters are available (ASTER 1995a, 1995b Howard 1993 HSDB 1995 Lyman et al. 1982) and there is no critical need for experimental confirmation of the estimated values. 

Many examples exist of interfaces formed between two immiscible liquids. A well-known one is the interface between a long-chain hydrocarbon, for example, dodecane, and water, which is commonly known as the oil water interface. Dodecane and water are immiscible because the hydrocarbon phase is nonpolar. Liquid liquid interfaces are also formed between water and organic liquids with polar groups such as octanol and heptanoic acid, which also have rather long hydrocarbon chains. The polar liquid nitrobenzene, which has a relative permittivity of 35, is also immiscible with water. Another well-known system is the mercury polar liquid interface. This has been studied extensively, especially for aqueous electrolyte solutions. However, the mercury polar liquid interface is also an example of a metal solution interface which was considered in the previous section. The discussion here is limited to liquids with relative dielectric permittivities falling in the range 1-200, and systems which have poor conductivities as pure liquids. 

As mentioned before, POP transport in the environment depends on their physicochemical properties [40-54], and these include saturated vapor pressure, solubility, Henry s law constant, octanol-water, octanol-air, and organic carbon-water partition coefficients. The saturated vapor pressure characterizes the capability of a substance to be transferred to the gaseous state. Eollowing the study of Wania and Mackay [40], the efficiency of POP condensation with subcooled liquid pressure (p°L) at 25°C above 1 Pa is very low. POPs with a vapor pressure between 1 and 10" Pa are condensed at a temperature of about -30°C and their deposition may be expected mostly in the polar latitudes. POPs with a vapor pressure of subcooled liquid from 10" to 10" Pa are condensed at a temperature above 0°C and they may reach to the middle latitudes. EinaUy, POPs of low volatility with a vapor pressure of subcooled liquid below 10" Pa are practically not vaporized and these substances may be transported and deposited as fine aerosols or coarse particles [39]. Using the vapor pressure of the subcooled liquid it is possible to characterize the partitioning of a POP between the gas phase and the solid phase of the atmospheric aerosol. The POPs having a lower vapor pressure are better bound with... 

The opening chapter An introduction to modelling of pollutants in the environment by Trevor M. Letcher demonstrates convincingly that equilibrium concepts and simple models lead to realistic predictions of, for example, the concentration of a polychlorinated biphenyl in the fishes of the St. Lawrence River. Relative solubilities expressed by octanol-water and air-water partition coefficients play a crucial role for estimating the distribution of chemicals in the environment. This is pointed out in the introductory chapter as well as in others such as Estimation of volatilization of organic chemicals from soil by Epaminondas Voutsas. 

These data enable assessments to be made of how chemicals in a series will differ in their environmental behaviour as they partition between air, water and organic phases. As is discussed by Gobas et al. (1987) elsewhere in this text, extreme caution must be used when calculating partitioning coefficients into organic media when log exceeds 5. It is suspected that octanol then ceases to be a satisfactory surrogate for lipids and probably also for organic matter sorption. 

M. alba fruits (28) and C soldandla (29), respectively, shows that the opposite chirahty may occur in different plants. Caution with absolute configuration assignment is therefore advised after only NMR structure elucidation. All cal5rstegines and other di- or trihydroxynortropane alkaloids are hydrophilic their octanol-water partition coefficient is well below zero (Table 1). In liquid-liquid extraction s5rstems between water and organic phase they will remain in the aqueous phase, even if the pH is elevated above 7. This property prevented their detection in former times, as classical alkaloid analysis includes liquid extraction of free alkaloid bases by organic solvents from an alkaline water extract. 

It is generally accepted that for organic substances there are three useful and fundamental physicochemical partition coefficients, Kp for air-water, ATow for octanol-water, and ffoA for octanol-air. Kqk can be estimated as Kqw/Kaw- Alternatively, log Koa can be estimated as log Afow - log Kaw- Other partition coefficients are estimated from Kqw, notably Koc, the organic carbon (OC)-water partition coefficient, ffoM, the organic matter (OM)-water partition coefficient, and ATlw, the lipid-water partition coefficient. 

The HYBOT descriptors were successfully applied to the prediction of the partition coefficient log P (>i--octanol/water) for small organic componnds with one acceptor group from their calculated polarizabilities and the free energy acceptor factor C, as well as properties like solubility log S, the permeability of drugs (Caco-2, human skin), and for the modeling of biological activities. 

Two approaches to quantify/fQ, i.e., to establish a quantitative relationship between the structural features of a compoimd and its properties, are described in this section quantitative structure-property relationships (QSPR) and linear free energy relationships (LFER) cf. Section 3.4.2.2). The LFER approach is important for historical reasons because it contributed the first attempt to predict the property of a compound from an analysis of its structure. LFERs can be established only for congeneric series of compounds, i.e., sets of compounds that share the same skeleton and only have variations in the substituents attached to this skeleton. As examples of a QSPR approach, currently available methods for the prediction of the octanol/water partition coefficient, log P, and of aqueous solubility, log S, of organic compoimds are described in Section 10.1.4 and Section 10.15, respectively. 

S. W. Karickhoff and D. S. Brown, determination of Octanol Water Distribution Coefficients, Water Solubilities, and Sediment/Water Partitions Coefficientsfor Hydrophobic Organic Pollutants, EPA-600/4-79-032, report, EPA, Washington, D.C., 1979. 

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