Carboxylic acids acid-base properties

Amino acids are characterized by the presence of adjacent carboxylic (-C0 H) and amino (-NH) functional groups. The equilibrium constant for protonation or dissociation of these groups is a function of their position in the amino acid molecule. Therefore, widely differing acid-base properties of amino acids occur, depending upon the number of functional groups and their relative position in the molecule. The dissociation constants for various amino acids used in this investigation are given in Table I. 

The pXa s of substituted 2-, 4-, and 5-substituted carboxythiazoles and rates of basic hydrolysis of substituted ethyl 2-, 4-, and 5-thiazolo-carboxylates, in water and aqueous ethanol, correlate approximately with the Hammett equation,3,0,311 but the p values are much different to their benzenoid counterparts demonstrating the presence of proximity effects such as hydrogen bonding, as well as possibly tautomeric equilibria. Other correlations of acid-base properties in this area are for... 

The acid-base properties of DOM are of intrinsic interest because acidic functional groups contribute to the acid-base balance of natural waters, affect complexation and transport of dissolved metals, and interact with mineral surfaces. The concentrations of carboxyl and phenolic functional groups are among the most widely measured and reported properties of DOM. Methodologically, there are two basic approaches for measuring acidic group content—indirect titrations and direct titrations (Perdue et al., 1980 Perdue, 1985 Ritchie and Perdue, 2003). 

Many organic compounds have acid or base properties. The chemistry of organic acids and bases will be discussed in Chapters 15 (Carboxylic Acids and Carboxylic Acid Derivatives) and 16 (Amines and Amides). 

As described for neurosporaxanthin (4) [75], exhibit carotenoid carboxylic acids acidic properties, and may therefore be converted to the methyl esters with diazomethane, Fig. 14. The polar carboxylate anion is obtained upon base treatment. Thus neurosporaxanthin (4) becomes completely hypophasic when distributed between petroleum ether and 1 % NaOH in methanol-water (9 1) [75]. 

Etingov ED and Kholodova GV, Kul bakh VO and Kamatushkina AI, Acid-base properties of amphotericin B, Antibiotiki, 17, 301-305 (1972). "Titration of 66% aqueous dimethylformamide solutions of Amphotericin B with methanolic HCl and KOH yields pK s near 5.7 and 10.0. Comparison with N-acetyl-Amphotericin B (pK=6.5) and Amphotericin B-methyl ester (pK=8.8) assigns the two pK s to carboxyl and amino groups respectively. Amphotericin B is found to be almost completely zwitterionic in this solution (tautomeric equilibrium constant Kt = 1000 with respect to the neutral molecule)." S R... 

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