Organic compounds ionic distributions

The field of chemical oceanography/marine chemistry considers many processes and concepts that are not normally included in a traditional chemical curriculum. While this fact makes the application of chemistry to the study of the oceans difficult, it does not mean that fundamental chemical principles cannot be applied. The chapters included in this book provide examples of important chemical oceanographic processes, all taking place within the basic framework of fundamental chemistry. There are three principal concepts that establish many of the chemical distributions and processes and make the ocean a unique place to practice the art of chemistry (1) the high ionic strength of seawater, (2) the presence of a complex mixture of organic compounds, and (3) the sheer size of the oceans. 

For example, the ratio of the n-octanol/watcr distribution coefficient of the nondissociated species to that of the ionic species is nearly 10,000 for 3-methyl-2-nitrophenol, but only about 1000 for pentachlorophenol because of the greater significance of the hydrophobicity of the ionized form of pentachlorophenol. The logarithm of the -octanol/water distribution coefficient of pentachlorophenol as the phenolate is about 2 (determined at pH 12, and 0.1 M KC1), which indicates significant distribution of the ionized form into the n-octanol phase [8,37], Extraction of such highly hydrophobic ionogenic organic compounds can result from mixed-mode mechanisms that incorporate both the hydrophobic and ionic character of the compound. 

It may be deduced from KP = Koc x foc that partition coefficients of hydro-phobic organic compounds in general are dependent upon the chemical of interest (compound-specific properties affect the value of Koc) and the matrix properties of the medium in which it resides. In addition to the fraction of organic carbon present in the sorption phase, additional environmental factors affect partitioning. These factors include temperature, particle size distribution, the surface area of the sorbent, pH, ionic strength, the presence of suspended material or colloidal material, and the presence of surfactants. In addition, clay minerals may act as additional sorption phases for organic compounds. Nevertheless, organic carbon-normalized partition... 

The solubility of an organic compound in a micelle depends on the surfactant structure and chemical properties, micelle geometry, ionic strength and composition, temperature, and solute structure and properties. Almgren M.A. et al. (1979) and Jafvert C.T. (1991) have shown that for hydrophobic compounds solubilized within micelles, a Poisson distribution is obeyed that is the solubilization of one molecule does not affect the solubilization of another. Solubilization of compounds generally is initiated at the cmc and is proportional to the surfactant concentration beyond this point. Kile D.E. and Chiou... 

The adsorptive removal of organics and inorganics from waste water by activated carbons depends upon the surface area, the pore volume, and the pore-size distribution in carbons. Although adsorption capacity of an activated carbon depends on these parameters, it is strongly influenced by the surface chemistry of the activated carbons. Most of the as-received activated carbons are hydrophobic and are associated with small amonnts of nentral carbon-oxygen surface groups. Such activated carbons are more snitable for the adsorption of neutral or nonpolar organic compounds and they show little affinity for polar and ionic pollutants. An example is the adsorption of phenol for which the snrface chemistry " of a carbon is more important than the snrface area. 

Solutes differing significantly in polarity should have very different coefficients K for partitioning between nonpolar and polar solvents. For example, consider the distribution of two organic compounds, the first neutral and nonpolar, and the second ionic and polar, between a nonpolar solvent and a polar solvent. If a solution of these compounds in the nonpolar solvent is shaken with the polar solvent, the neutral compound will preferentially partition into the nonpolar phase, whereas the polar constituent will preferentially partition into the polar phase. Separating the two phases effects a separation of the two solutes. 

Unfortunately, cation exchange does not lend itself to simple mathematical description as does idealized sorption of hydrophobic organic compounds. For low concentrations of a contaminant ion in a constant background of other ions, however, the ion exchange process often is treated approximately as a linear partitioning process, and use of a simple retardation factor in a transport model may be justified. Distribution coefficients for ionic contaminants in an aquifer are usually determined experimentally. Typically, a batch test is performed in which the ionic concentration on a fixed volume of aquifer solids and the ionic concentration in the associated pore waters are analyzed the distribution coefficient is taken as the ratio of the concentrations. Because sorption by ion exchange is affected by the concentrations of all other ions in the groundwater, the... 

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