Medium Effects on the Protonation of Carboxylic Acids at Different Temperatures

Here we report a potentiometric study (H+-glass electrode) relative to the protonation of carboxylic acids in different background salts (NaCl, KCl, Me4NCl), at different temperatures (5 ≤ t ≤ 45 °C) and ionic strengths (NaCl, 0.1 ≤ I ≤ 5; KCl, 0.1 ≤ I ≤ 4.5; Me4NCl, 0.1 ≤ I ≤ 3 mol kg-1). Dependence on ionic strength was considered using both a Debye−Hückel type equation and the Pitzer equations. Parameters for the dependence on ionic strength of protonation constants (and of activity coefficients) are reported. From the dependence on temperature of protonation constants, the enthalpy formations ΔH° were obtained. Some general relationships for the dependence on medium and on temperature of protonation constants are reported.