Solubility of organic substances

Fuhner, R. and Geiger, M. A simple method of determining the aqueous solubility of organic substances. Pestic. 5ct.. 8(4) 337-344,1977. 

There already exists a substantial literature devoted to the estimation of various material properties with the help of additive structual increments (Reid et. al, 1987, Van Krevelen, 1990). The regular solution theory in combination with additive structural increments has a wide application for estimating the relative solubilities of organic substances in polymers and the solubility of polymers in various solvents (Barton, 1983) and will be described later in this chapter. When estimating partition coefficient values, one is quickly confronted with this method s application limits, particularly with polar and non-polar structures, for example the partitioning of substances between polyolefins and alcohol (Baner and Piringer, 1991). 

The solubility of organic substances in human fatty tissues (in lipids) has been found to be roughly proportional to values. The bioconcentration factor (BCF) defined as... 

However, without dissociation, in an ideal solution at infinite dilution the contributions of the enthalpy of mixing and solvation to the dissolution process can considered to be negligible, thus giving ApH AsH. Therefore, the Schroder-van Laar equation using the melting enthalpy also for solution equilibria is often a good approximation to estimate the temperature dependence of the solubility of organic substances. 

Bumasheva lA, Gordienko AA, Toropov AP (1971) Solubility of organic substances in some fused low- melting salts and salt eutectics. Teor Rastvorov 248-50... 

Study of the solubility behaviour of the compound. A semi-quantitative study of the solubility of the substance in a hmited number of solvents (water, ether, dilute sodium hydroxide solution, dilute hydrochloric acid, sodium bicarbonate solution, concentrated sulphuric and phosphoric acid) will, if intelligently apphed, provide valuable information as to the presence or absence of certain classes of organic compounds. 

Wasik, S.P., Tewari, Y.B., Miller, M.M., Martire, D.E. (1981) Octanol/Water Partition Coefficients and Aqueous Solubilities of Organic Compounds. NBSIR 81-2406, report prepared for Office of Toxic Substances, Environmental Protection Agency, Washington, DC. 

Partitioning of PCBs into other organic compound mixtures or phases found in the environment alters environmental parameters used to estimate their fate and transport. For example, dissolved phase humic substances (i.e., DPUS) can increase the apparent solubility of organic pollutants [381-390] (see Chap. 2). 

Organic matter extracted from earth materials usually is fractionated on the basis of solubility characteristics. The fractions commonly obtained include humic acid (soluble in alkaline solution, insoluble in acidic solution), fulvic acid (soluble in aqueous media at any pH), hymatomelamic acid (alcohol-soluble part of humic acid), and humin (insoluble in alkaline solutions). This operational fractionation is based in part on the classical definition by Aiken et al. (1985). It should be noticed, however, that this fractionation of soil organic matter does not lead to a pure compound each named fraction consists of a very complicated, heterogeneous mixture of organic substances. Hayes and Malcom (2001) emphasize that biomolecules, which are not part of humic substances, also may precipitate at a pH of 1 or 2 with the humic acids. Furthermore, the more polar compounds may precipitate with fulvic acids. 

The solubility of these substances in organic solvents facilitates their initial extraction and purification from plant material using, for example, petroleum ether. Subsequent chromatographic fractionation facilitates separation of individual alkaloid components. Many alkaloids are poisonous (and have been used for this purpose), although at lower concentrations they may be useful therapeutic agents. Several of the best known alkaloid-based drugs are discussed below. The chemical structure of most of these is presented in Figure 1.11. 

To estimate the size column required to isolate more of this polar material, we used information published by Thurman et al. (16), who described an empirical relationship between aqueous solubility of organic compounds and capacity factors on XAD-8 resin. They defined capacity factor as the mass of solute sorbed on the resin divided by the mass of solute present in the void volume of the column at the 503> breakthrough point. On the basis of their data, a substance having a capacity factor of 1000 will have a solubility of about 1 X 10-3 mol/L. Examples of compounds having solubility in this range are methyl benzoate, 2,4,6-trichlorophenol, and chlorobenzene. 

The use of supercritical fluid carbon dioxide to extract low levels of organic substances from water was investigated for 23 different compounds. In general, compounds that were volatile and/or not highly soluble in water were readily extracted under the conditions used. Compounds of higher water solubility did not show evidence of extraction. In addition, those materials that tended to precipitate or form more soluble species under acidic conditions were not extracted. 

Hydrogen-bond formation is of importance also for various other properties of substances, such as the solubility of organic liquids in water and other solvents, melting points of substances under water,1 viscosity of liquids,14 second virial coefficient of gases,18 choice of crystal structure, cleavage and hardness of crystals, infrared absorption spectra, and proton magnetic resonance. Some of these are discussed in the following sections of this chapter. 

SOLUBILITY. A property of a substance by virtue of which it forms mixtures with other substances which are chemically and physically homogeneous throughout The degree of solubility is die concentration of a solute in a saturated solution at any given temperature. The degree of solubility of most substances increases widi a rise in temperature, but dicrc arc cases (notably the organic salts of calcium) where a substance is more soluble in cold Ilian in hot solvents. 

If we calculated with the idealized co-operative model by the content of spectroscopic determined Op values the number Nei of H-bonded water molecules we would get — with different 1 molar salt solutions — the result of Fig. 11. The values Nei with salt additions depend strongly on the salt concentrations because of the disturbance of the big H-bonded system3At small concentrations the Nel-N0 numbers (7V0 association number in pure water) of structure-makers are in size of the order of Debye-Sack s or Azzam s calculations. They are of the same size of order as the secondary hydration numbers calculated by solubility measurements of organic substances in water (Chapter b) or as the hydration numbers of hydrophilic organic molecules (Chapter lld-e) or biopolymers (Chapter III). 

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