Of organic acids and bases

Johansson, P.-A. Gustavii, K., Potentiometric titration of ionizable compounds in two phase systems. 2. Determination of partition coefficients of organic acids and bases, Acta Pharm. Suecica 13, 407 -20 (1976). 

Other common examples are aluminium chloride, tin(rv) chloride, zinc chloride, etc. We shall, at this point, be concerned essentially with proton acids, and the effect of structure on the strength of a number of organic acids and bases will now be considered in turn. Compounds in which it is a C—H bond that is ionised will be considered subsequently (p. 270), however. 

ESCHER, B. I., SCHWARZENBACH, R. P., Westall, J. C., Evaluation of liposome-water partitioning of organic acids and bases. 2. Comparison of experimental determination methods, Environ. Sci. Technol. 2000, 34, 3962-3968. 

The semi-empirical Yasuda-Shedlovsky technique of extrapolating a series of apparent pKa values obtained in several ratios of water/solvent to obtain an aqueous value is well established [32, 33], but three or more experiments are required and this adds significantly to assay times. A method of calculating aqueous pKas for various classes of organic acids and bases from single apparent pKa values obtained in water/solvent mixtures has been reported [34], and shows promise as a means of further speeding pKa measurement. 

FIGURE 2.6 Representative pKA values of organic acids and the conjugate acids of bases. The p values of organic acids and bases were obtained from Perrin et al. (1), of drugs from Foye et al. (2), and of amino acids from Merck Index (3). 

Extensive collections of pK values are available in the literature, e.g., [98-101]. It is also possible to predict pK values for a broad range of organic acids and bases using linear free energy relationships based on a systematic treatment of electronic (inductive, electrostatic, etc.) effects of substituents which modify the charge on the acidic and basic center. Quantitative treatment of these effects involves the use of the Hammett Equation which has been a real landmark in mechanistic organic chemistry. A Hammett parameter (a), defined as follows ... 

In addition, it is possible to extend the analysis to include an ortho substituent and the associated steric effects [98-101]. Thus it is possible by this procedure to predict with some accuracy the pKa and pKb of organic acids and bases leached from COMs. 

Wang, C., Xu, L., Xu, 0., Tian, L., and Zhang. Z. Determination of partition coefficients of organic acids and bases and the correlation of partition coefficients in different systems, HuanjingKexueXuebao, 9(4) 418-424, 1989. 

Table 13.3 Bonding strengths of organic acids and bases...

Table 3.1 Comparison Between Intestinal Absorption and Lipid Water Partition of the Nonionized Forms of Organic Acids and Bases...

Illustrative Example 8.1 Assessing the Speciation of Organic Acids and Bases in Natural Waters... 

Aqueous Solubility and Partitioning Behavior of Organic Acids and Bases Aqueous Solubility... 

Illustrative Example 8.3 Assessing the Air-Water Distribution of Organic Acids and Bases in a Cloud Organic Solvent-Water Partitioning... 

In contrast to air-water partitioning, the situation may be a little more complicated when dealing with organic solvent-water partitioning of organic acids and bases. As an example, Fig. 8.9 shows the pH dependence of the n-octanol-water distribution ratios, D,ow (HA, A"), of four pesticides exhibiting an acid function ... 

Sorption of Organic Acids and Bases to Natural Organic Matter (NOM)... 

Ion-pair partition chromatography can be a very useful technique for the analysis of organic acids and bases [72-74]. Although many of these compounds have little UV absorbance, they can be measured at low levels as an appropriate ion pair. An example of such a separation of three carboxylic acids is shown in Fig.4.38. The anions of the acids... 

Quantitative structure-activity relationship studies are of great importance in modern chemistry. From their origin in the study of organic chemistry dating back to the 19th century, these studies have relied on some empirical and qualitative rules about the reactivity similarities of compounds with similar structures. The most significant development in QSARs occurred with the work of Louis Hammett (1894-1987), who correlated some electronic properties of organic acids and bases with their equilibrium constants and reactivity (Johnson, 1973). Hammett postulated that the effect... 

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