Ultrasonic Investigation of Acetic Acid Hydrogen Bond Formation. II Acetic Acid–Water Solutions

Abstract

Ultrasonic absorption has been measured in acetic acid–water mixtures in the range 3.6 molar acetic acid to 17.38 molar (glacial). The frequency range covered was 0.5–150 MHz and measurements were made at 18, 25, 35, and 50°C. Measurements were also made with added H+ and OAc− ions. The data for every solution measured could be fitted to a single relaxation curve. The simplest mechanism to explain the data is shown to be D⇆ lim krkfC, where D and C are believed to the “closed” and “open” forms of the acetic acid dimer. In aqueous solution this process is catalyzed by both H+ and OAc− ions. This mechanism gives a quantitative fit of the ultrasonic data and also provides complete kinetic and thermodynamic parameters. One finds that the rate constants show strong dependence on viscosity.