Thermodynamic Parameters for the Ionization of Some Amino Acids, Benzoic Acid, Aminobenzoic Acids, and Organic Nitrogen Compounds in Ethanol + Water at 25 .degree.C

Potentiometric Titration Study of the Temperature and Ionic Strength Dependence of the Acidity Constants of Nicotinic Acid (Niacin)

“…The uncertainties assigned to a , b , Δ r H m o , and Δ r S m2 o correspond to standard errors. The above Δ r H m o and Δ r S m o results are compared in Table with the analogous results taken from the literature or calculated from published data. ,,,− The poor precision of Δ r H m,l o = (4.5 ± 3.5) kJ·mol –1 reflects the difficulty in extracting proton dissociation enthalpies from the slopes of van’t Hoff plots when the variations of p K a with temperature are very weak. This is also the case of Δ r H m,l o = −(0.2 ± 1.1) kJ·mol –1 , which was derived from a van’t Hoff analysis of the single previously reported p K a1 vs T data found in the literature.…”

“… a vH = van’t Hoff plot. b This work. c Reference . d Reference . e Reference . f Reference . g Reference . h Reference . i I m = 0.25 (NaClO 4 ), reference . …”

“…At temperatures close to ambient (293 to 298 K) the reported p K a ′ or p K a values (the last often calculated from stoichiometric counterparts by using Debye–Hückel type approaches) for the first and second proton dissociation equilibriums vary in the ranges 1.87 to 3.60 and 4.67 to 5.12, respectively. ,,,− ,,− To the best of our knowledge, the temperature dependence of p K a1 or pK a2 has only been investigated twice. , These studies further afforded the corresponding enthalpies and entropies of ionization through van’t Hoff plots (second law method) . Direct measurements of the enthalpies of ionization of nicotinic acid have also been performed by calorimetry. ,,− …”

Molecular recognition of aromatic carboxylic acids by hydroxypropyl-γ-cyclodextrin: experimental and theoretical evidence

“…13 This program allows to take into account the contributions from the possible processes of dissociation/protonation of the reagents which can take place in aqueous solution together with complex formation. 14…”