Ligands containing elements of Group VIB. Part IV. Thermodynamics of proton ionization and silver complex formation of substituted phenoxyacetic, (phenylthio)acetic, and (phenylseleno)acetic acids

Abstract

The heats of proton ionization of phenoxyacetic, (phenylthio)acetic, and (phenylseleno)acetic acids have been measured with a differential reaction calorimeter using a quartz thermometer. Changes in acidity have been shown to be dependent on enthalpy changes, entropy changes remaining approximately constant. Thermodynamic constants for the formation of silver complexes of the acids, together with those of a number of substituted (phenylthio) acetic and (phenylseleno) acetic acids, have been calculated by measuring formation constants over the range 0–40°. The stability order Se > S O has been shown to be due to more favourable enthalpy changes with entropy changes opposing complex formation.