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

Abstract

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.

The dissolution mechanism in a system undergoing complexation: salicylamide in caffeine solution

“…The caffeine concentration in the dissolution medium was checked spectre photometrically before each experiment. SampleS of 5 ml were withdrawn at 15 min intervals and replaced by equal volumes of dissolution medium at the same temperature; 1 ml from each Sample was added to 5 m l modified Trinder reasent (Donbrow, Touitou & Ben-Shalom, 1976) and the concentration was measured spectrophotometridly at 525 nm. For benzoic acid, the same P r o d u f f was used except for the omission of caffeine, and the concentration was determined spectroPhot'metrically at 230 nm in 0.01 N HCI.A cumulative correction was made in d e t e e g the total amount dissolved in the dissolution medium using the equation: s=n-1 cn = C q + __ 2 c, .. .. lo00 * Correspondence.…”