The ionization constants of p-Aminobenzoic Acid in Aqueous solution at 25°C

Abstract

The ionization constants of benzoic acid and of four esters of p-aminobenzoic acid, as well as the two ionization constants of p-aminobenzoic acid itself, have been deter- mined by spectrophotometric measurements. The extent of zwitterion formation in p-aminobenzoic acid is discussed.

Engineering cocrystal solubility, stability, and pHmax by micellar solubilization

“…Dashed line shows the SLS concentration at the CSC, where the cocrystal and drug are thermodynamically stable. Solid lines represent solubility predictions for cocrystal and drug, according to Equations 13,14,23,and 25. A CMC value of 6 mM for SLS measured at saturation with CBZD was used in these calculations.…”

“…22,23 SUC is a diprotic weak acid with pKa values of of 4.1 and 5.6. 24 4ABA is amphoteric with pKa values of 2.6 and 4.8 25. …”

Fast and direct method for measuring 1‐octanol–water partition coefficients exemplified for six local anesthetics

“…A comparison with the indirect log P OW values obtained by RP‐HPLC measurements shows large differences of 0.35–0.91 log units, resulting in a poor correlation between HPLC and our method ( r 2 = 0.823, see Figure 5). It is striking that for the more basic compounds (p K a = 8–9)12 with an amide bond (lidocaine and bupivacaine) and procaine, the partition coefficients measured with our technique are distinctly lower than the values determined by HPLC, whereas the opposite is true for the less basic substances with a structure based on 4‐aminobenzoate (methyl, ethyl, and, n ‐butyl 4‐aminobenzoate, p K a = 2.5)16. This result may be explained by different interactions between those functional groups and polar (silanol) groups in the reversed‐phase material of the HPLC system.…”

Acid-Base Relationships and Tautomeric Equilibria in m-Aminobenzoic Acid, 3-Amino-1-naphthoic Acid, and 4-Amino-2-naphthoic Acid

“…The terms pE,, pEB, pE,, and pK, with which we are particularly interested are derived from pK,, pK2, and pE,, the assumption being that the inductive effects of the COOH and COOCH, groups are equal, that is, pEE=pKB. This assumption is not necessarily justified as has been shown by Robinson and Biggs (1957) for p-aminobenzoic acid, and in this work two estimates have been made using the equivalences pEB =pKE and pKB =pE, -0.06, the correction term in the latter expression being based on the recent om values for m-COOH, m-COOCH,, and m-COOC,H, of 0.35, 0.32, and 0.34 (vanBekkum, Verkade, and Wepster 1959), the value of the reaction constant for substituted-anilines being taken as 2 -8. Furthermore, the derived values being based on three independent experimental results will bear the errors of these measurements, and additional calculations have been made on the assumptions set out in the footnote to Table 4.…”