A Proton NMR Study on the Kinetics of Protolysis and Water Exchange in Mixed Solvent Systems, Beryllium(II) Nitrate in Water‐Dimethyl Sulfoxide(d6) and Water‐Acetone(d6) Mixtures

Abstract

Abstract1H spin‐echo NMR techniques were used to study the kinetics of proton exchange in the systems Be(NO3)2 in mixtures of water‐dimethyl sulfoxide(d6) and water‐acetone(d6) as a function of temperature, solvent composition and beryllium concentration. With increasing mole fraction of the organic component the total rate is reduced due to the decreasing contribution of protolysis of the hydrated beryllium(II) ion. Water exchange between coordinated sites at the beryllium(II) ion and the bulk solution dominates the proton exchange rate for DMSO mole fractions greater than 0.4 and for acetone mole fractions greater than 0.6, respectively. The calculated rates are almost independent of the solvent composition and beryllium concentration. Their values as well as the activation parameters are close to previous results on water exchange in the pure aqueous beryllium system using 17O NMR measurements [1]. For a 0.2 molal solution of beryllium(II) nitrate in water‐DMSO a temperature dependent water coordination number was found in the DMSO rich region which can be explained in terms of the extensive hydrogen bonded structure of the bulk solvent and of preferential solvation of beryllium(II) ions by water in these solutions.