Enthalpic and entropic contributions to dissociation of halogen–acetic acids and linear free energy relationship in EtOH–H2O mixtures at 298.15 K

On the basis of dissociation enthalpies from micro-calorimetric measurements by using LKB-2277 BioActivity Monitor, along with dissociation equilibrium constants, enthalpic and entropic contributions to substituent effects and solvent effects on the dissociation of acetic acid and three mono-substituted halogen–acetic acids (X–CH2COOH, X=H, Cl, Br, I) in binary mixtures of EtOH–H2O have been examined in terms of enthalpic and entropic reaction constants (ρH, ρS), and enthalpic and entropic substituent constants (σH, σS). A satisfactory linear free energy relationship (LFER) with the Hammett type equation has been obtained. The reaction constants have been calculated for the different EtOH–H2O mixtures and several reasonable quantitative equations have been obtained to relate them with the composition or dielectric constant of the mixed solvents.