The protonation equilibria for nine hydroxamic acids in solutions have been studied pH-potentiometrically
via a modified Irving and Rossotti technique. The dissociation constants (pK
a values) of hydroxamic acids
and the thermodynamic functions (ΔG°, ΔH°, ΔS°, and δ) for the successive and overall protonation
processes of hydroxamic acids have been derived at different temperatures in water and in three different
mixtures of water and dioxane (the mole fractions of dioxane were 0.083, 0.174, and 0.33). Titrations
were also carried out in water ionic strengths of (0.15, 0.20, and 0.25) mol dm-3 NaNO3, and the resulting
dissociation constants are reported. A detailed thermodynamic analysis of the effects of organic solvent
(dioxane), temperature, and ionic strength on the protonation processes of hydroxamic acids is presented
and discussed to determine the factors which control these processes.