Thermodynamic Proton Ionization Constants of some fluorinated β-ketoesters in dioxane-water mixtures. Influence of terminal group substitution

✍ Scribed by Dr. J. P. Shukla; R. S. Sharma

• Book ID: 105353733
• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 615 KB
• Volume: 332
• Category: Article
• ISSN: 1615-4150
• DOI: 10.1002/prac.19903320506

✦ Synopsis

Abstract

Thermodynamic proton ionization constants, ^T^pK~a~, of methyl trifluoroacetoacetate (HMTAA), ethyltrifluoroacetoacetate (HETAA) and ethylpentafluoropropionylacetate (HEPPA) have been determined in 10–50% dioxane‐water mixtures at 25 and 35 ± 0.1°C applying an empirical pH correction for mixed aqueous‐organic media. The ^T^pK~a~ values are calculated by subjecting the experimental data to rigorous weighted least‐squares analysis. Further, a least‐squares extrapolation technique is applied to evaluate ^T^pK~a~ in pure water (0% dioxane). All the three ligands are weak monoprotonic acids with their ^T^pK~a~ between 6.0 and 9.0. Plots of ^T^pK~a~ with the reciprocal of the dielectric constants of the medium are not linear but plots of ^T^pK~a~vs. mole fraction of dioxane are linear at a given temperature. Values of standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes, associated with their ionization are also computed. Temperature, medium and substituent effects are briefly discussed.