Effect of pressure on conductance. IV. Ionic association and Walden products in ethanol

The conductance at 30° of sodium bromide in methanol and in ethanol, under pressures up to 500 atm, were measured in the concentration range 3 ≤ 10⁴c ≤ 20. Confirming previous results,² the association constant in methanol increases with increasing pressure. In ethanol, the association constant is indistinguishable from zero. Solvation of bromide ions by hydrogen bonds to alcohol molecules is suggested. The conductances of tetramethylammonium bromide and tetrabutylammonium bromide and tetraphenylboride in ethanol were measured over the same range of variables. The net conductance of the three salts decreases with increasing pressure, corresponding to the increase of viscosity (relative viscosity at 5000 atm is 5.2). The association constants decrease with increasing pressure, due to the increase by 27% in dielectric constant. The association constant of Bu₄N·BPh₄ (about 300 at 30° and 1 atm) is larger than that of Me₄NBr (about 200), presumably because the excluded volume factor in the association constant is so large for the former.