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, M e4NCl), at different temperatures (5 less than or equal to t less than or e qual to 45 degrees C) and ionic strengths (NaCl, 0.1 less than or equal to I less than or equal to 5; KCl, 0.1 less than or equal to I less than or eq ual to 4.5; Me4NCl, 0.1 less than or equal to I less than or equal to 3 mol kg(-1)). Dependence on ionic strength was considered using both a Debye-Hu ckel type equation and the Fitter equations. Parameters for the dependence on ionic strength of protonation constants (and of activity coefficients) a re reported. From the dependence on temperature of protonation constants, t he enthalpy formations Delta H degrees were obtained. Some general relation ships for the dependence on medium and on temperature of protonation consta nts are reported.