Ion Association and Ultrasonic Relaxation in Hydrogen-Bonding Solvents: 1:1 Electrolytes in 2-Propanol at 25 degrees C

Ultrasonic absorption measurements have been carried out in aqueous solutions of Bu(4)NCl, Bu(4)NBr, Bu(4)NI, Me(4)NCl, and LiCl in 2-propanol over the, frequency range 15-250 MHz. A single relaxation frequency was observed for each system. All the data were found to be consistent with a 2-step association mechanism in which the rate-determining step was the diffusion of the ions to form a solvent-separated ion pair, followed by rapid desolvation to form the contact ion pair. Measured association rate constants were very nearly those predicted for a diffusion-controlled process.