ION PAIR CONVERSION THERMODYNAMICS IN HYDROGEN BROMIDE ALCOHOL SOLUTIONS

Abstract

The thermodynamic quantities of dissociation of contact and solvent-separated ion pairs into ions, conversion of contact ion pairs into solvent-separated ion pairs of HBr ionogen in n-alcohols from methyl to n-octyl have been calculated by the procedure we set forth earlier for the HCl – n-alcohol systems in the same solvents at 278.15–328.15 K. The following regularities were established in this work: a) positive values of ΔdisGº of contact and solvent-separated ion pairs increase with increasing temperature, the number of carbon atoms in the n-alcohol molecule, and decreasing radius of halide ion, and their sign and magnitude are determined by the entropic component (–TΔdis Sº). In this case, the values of ΔdisGº of contact ion pairs exceed the same values for solvent-separated ion pairs; b) ΔconvGº values for HCl and HBr are also positive, except for ΔconvGº values in methanol at 278.15–328.15 K and HBr solutions at the same temperatures in ethanol. For these cases, by contrast, ΔdisGº(RIP) > ΔdisGº(CIP) and ΔconvGº are negative. As the temperature and radius of the halide ion increase, ΔconvGº become more negative, and vice versa as the hydrocarbon radical increases; c) the concentration of contact ion pairs increases in the methanol-n-octanol series, decreases slightly with increasing temperature and anion radius, and changes within ~30 % (methanol) to 95 % (n-octanol) at 278.15 K. In methanol, solvent-separated ion pairs predominate; in ethanol, the concentration of both types of ion pairs is approximately the same; in other n-octanols, contact ion pairs predominate.