Solvation of Hydrogen Ion in Oxygen-containing Solvents

Abstract

THE nature of non-aqueous solutions of the so-called ‘‘strong acids has received a good deal of attention ; but although much information is now available regarding a number of individual solvent systems, comparatively little progress has been made in establishing quantitative scales of comparison of properties such as proton-availability in different solvents. A quantity suitable for this purpose is the acidity function first introduced by Hammett¹ to deal with concentrated aqueous solutions. The acidity function is a measure of the tendency of the medium to donate a proton to a neutral base and may be defined by where B is the proton-acceptor and BH⁺ its conjugate acid, and where K_B^H₂O is the equilibrium constant of the reaction in water, SH⁺ representing the solvated proton. It can be readily shown that H = log (αc_AK_B^S/$K_B^{{\text{H}}_{\text{2}}\text{O}}$), where C_A and a are the concentration and degree of dissociation of the acid, and K_B^S the equilibrium constant of reaction (2). The ratio $K_B^{{\text{H}}_{\text{2}}\text{O}}$/K_B^S will be a measure of the proton-affinity of the solvent relative to water and can be calculated from H if a is known.