Enthalpies of ionization deduced from the temperature dependence of indicator measurements for amides in concentrated aqueous solutions of perchloric acid

Abstract

The acidity function H_A has been deduced as a function of temperature from measurements of the extent of protonation of three amides in concentrated aqueous solutions of perchcloric acid. Enthalpies of dissociation of the conjugate acids of the amides have been evaluated as a function of perchloric acid concentration. The enthalpy data are in accord with theories in which acidity function behaviour is largely attributed to the release of water of hydration which occurs when a weak base combines with a proton to give its conjugate acid. The relationship between the present results and previous enthalpy data for primary amine bases is qualitatively consistent with the differences which exist between the variations with acid concentration of the H_A and H₀ acidity function scales.