Isotopic fractionation factor of the hydrogen-bonded complex AcO–⋯(HOAc)n and kinetic and equilibrium solvent isotope effects on reactions of acetate ion in acetic acid

Abstract

A value of φ 0.58 ± 0.05 has been obtained for the deuterium fractionation factor of the hydrogen-bonded complex AcO–⋯(HOAc)n from 1H n.m.r. studies of solutions of potassium acetate in AcOH and 97% AcOD–3% AcOH. The result is used to account for the kinetic solvent isotope effect kAcO–AcOH/kAcO–AcOD 0.66 ± 0.10 measured for formation of acetic anhydride from 2,4,6-trinitrophenyl acetate in AcOH and AcOD in the presence of potassium acetate. The equilibrium solvent isotope effect on complex formation between 2,4,6-trinitrophenol and acetate ion in AcOH and 97% AcOD-3% AcOH, KAcOH/KAcOD 0.83 ± 0.1, leads to a value φca. 0.7 for the complex [2,4,6-(NO2)3C6H2O ⋯ H ⋯ OAc]–.