Stability of salicylamide-caffeine complex at different temperatures and its thermodynamic parameters

The stability constants for formation of complexes of salicylamide with caffeine have been measured between 15 and 45degrees, by means of the solubility method. There was a linear solubility increase at all temperatures but phase diagrams indicated that at 15 and 25degrees an additional phase was formed which was found to be an insoluble 1 : 1 complex. The enthalpies and entropies of interactions were evaluated. They indicate that the interaction is exothermic and enthalpy controlled.