The thermochemical characteristics of nicotinamide coordination by iron(III) and ligand protonation in aqueous-ethanolic mixtures

The heat effects of protonation of nicotinamide and formation of its complex with iron(III) were determined calorimetrically at 25.00 +/- 0.01A degrees C and ionic strength 0.25(NaClO4) in water-ethanol solvent containing 0-0.75 ethanol mol fractions. The experimental and literature data were used to construct the dependences of the enthalpy, entropy, and Gibbs energy of the reaction on the composition of the water-ethanol solvent. The dependence of the enthalpies of both reactions passed an exothermic minimum at 0.1 ethanol mol fractions. The reagent solvation contributions to the thermodynamic characteristics of transfer were analyzed.