ION-PAIR CONVERSION THERMODYNAMICS IN ALCOHOL SOLUTIONS OF HYDROGEN HALIDES

Abstract

The calculation of thermodynamic characteristics of dissociation of contact and solvent-separated ion pairs into ions, conversion of contact ion pairs into solvent-separated ion pairs of ionogens HCl, HBr and HI in n-alcohols from methyl alcohol to n-octyl alcohol by the method described earlier for the systems HCl – n-alcohol in the same solvents at the same temperatures was carried out. The following regularities were established in this work: a) positive values of the change in the Gibbs energy of dissociation (ΔdisG°) of contact and solvent-separated ion pairs increase in the case of increasing temperature and the number of carbon atoms in the n-alcohol molecule and decreasing radius of the halide ion, and their sign and magnitude are determined by the entropic component (–TΔdisS°). In this case, the values of ΔdisG° of contact ion pairs exceed the same values for ion pairs separated by solvent; b) the values of the Gibbs energy change (ΔconvG°) for the studied ionogens HCl, HBr, and HI are also positive, except for the values of ΔconvG° of ionogens in methanol and HBr solutions in ethanol. In these cases, the ΔdisG° values for solvent-separated ion pairs exceed the same values for contact ion pairs, and the ΔconvG° values are negative. With increasing temperature and radius of the halide ion, ΔconvG° become more negative, and vice versa with increasing hydrocarbon radical; c) the concentration of contact ion pairs increases in the methanol – n-octanol series for all ionogens, decreases slightly with increasing temperature and radius of the anion, and varies from ~30% (methanol) to ~95% (n-octanol). In methanol, solvent-separated ion pairs predominate; in alcohols from n-propyl to n-octyl, contact ion pairs predominate, i.e., deconversion of ion pairs occurs.