Salt effects on the proton transfer equilibria in the 3,5‐dinitro‐2‐hydroxybenzoic acid/ammonia system: A T‐jump study

Abstract

A thermodynamic study of the proton transfer equilibria involved in the system 3,5-dinitro-2-hydroxybenzoic acid/ammonia has been undertaken in LiCIO, and NaClO, aqueous solutions at different ionic strengths. The enthalpy for the different equilibria involved was measured by T-jump techniques, while the free energies were determined spectrophotometrically.The different thermodynamic magnitudes, AG, AH and TAS, are functions of the nature and concentration of the salt. However, the MSA provides a reasonable explanation for the experimental trends in most of the cases, although in this model only one parameter, the radii of the ions, is used to reproduce the mean ionic activity coefficients of electrolyte solutions at high ionic strengths.The extrapolated values at infinite dilution were also compared with the MSA prediction, and a good agreement was found.

Salt Effects on the Kinetics of the Proton-Transfer Reactions in the 3,5-Dinitrohydroxybenzoic Acid/Ammonia System

“…K HB and K HL are the acid dissociation constants of ammonia and DNSA in the different electrolyte solutions. The acid dissociation constants of ammonia were found in the literature, and those for DNSA were measured in a previous work …”

“…In previous papers we have studied the proton-transfer equilibria and kinetics of the title system and its dependence on the nature of an added supporting electrolyte. , The study of salt effects on proton-transfer reactions is of interest not only because proton-transfer reactions appear ubiquitously enough in nature but also because they take place in ionic environments . It has been shown that salt bridges may accelerate or slow charge-transfer processes by 2 orders of magnitude …”