CONDUCTANCE OF LARGE HYDROPHOBIC IONS IN WATER, METHANOL, AND ACETONITRILE AT 25 DEGREES

The conductance of the halides of the i-Am3BuN+ and the i-Am4N+ ions were measured in water, methanol and acetonitrile at 25°. The conductance of n-Am4NBr in water and i-Am4NClO4 in methanol are also included. The Walden products for these large cations were almost identical in acetonitrile and methanol but substantially lower in aqueous solution. This effect is attributed to the increased degree of hydrogen bonding in the water adjacent to the hydrocarbon side chains and is in agreement with the results found for the smaller tetraalkylammonium ions in aqueous solution. The degree of association into ion pairs in the hydroxylic solvents is shown to be substantially greater than that predicted by simple electrostatic theory and is attributed to a two-step process involving solvent-separated and contact ion pairs.