Equilibria in ethylenediamine. II. Hydrogen electrode studies of some acids and sodium salts

Hydrogen electrode studies of a series of pure acid solutions have yielded the dissociation constants of four phenols relative to hydrochloric acid. The behavior of these phenols indicates that the reaction HX + X^- = HX₂^-(K_HX2-) occurs. Values of K_HX2- found were 15 (phenol), 7 (thymol), 40 (o-phenylphenol), and 46 (p-phenylphenol). Studies of the acid-sodium salt mixtures permitted the determination of the relative dissociation constants of these salts. The pH of various sodium salts has been found to be independent of concentration and has yielded another means of determining the relative dissociation constants for various acids. The results obtained for pK_MX - pK_HCl are 5.40 (thymol), 4.35 (o-phenylphenol), 4.30 (phenol), 4.20 (p-phenylphenol), 2.05 (sodium thymolate), 2.10 (sodium o-phenylphenolate), 0.10 (phenylacetic acid), -0.35 (3-methyl-4-phenylazophenol), -0.60 (hydrobromic acid), and ∼ -1.4 (hydriodic acid). The value of K_NaX/K_HX for thymol is 2.1 × 10³ and 2.1 × 10² for o-phenylphenol. The difference between the negative logarithm of the autoprotolysis constant of EDA and that of the sodium salt of EDA is 7.0.