Hydrogen Bonding in Acetic Acid/Acetone Mixtures

Abstract

It is shown that the ultrasonic relaxation caused by hydrogen bond formation in acetic acid/acetone mixtures cannot be explained in terms of a self-association of acetic acid. The interaction of acetone, which is a strong hydrogen bond acceptor, must be introduced. The simplest way of introducing the solvent interaction is to assume that the hydrogen bonds present are established between acetic acid and acetone molecules only. However, this consideration leads to disagreement with the experimental data. It is demonstrated that a two state model which describes the kinetics of the system in terms of a transition between two states of different energy, a hydrogen bonded state, and a non-hydrogen-bonded state leads to a complete agreement with all the experimental data. Closed dimers of acetic acid, open dimers of acetic acid linked to acetone by a hydrogen bond, and monomers of acetic acid linked to acetone by a hydrogen bond contribute to the bonded state, while monomers of acetic acid and acetone contribute to the nonbonded state. The equilibrium constant and the rate constants for the transition between the two states are calculated.