Dynamic study of the interaction between diols and water by ultrasonic methods. Part 3.—2-methylpentane-2,4-diol solution

Abstract

Ultrasonic absorption, velocity, density and viscosity have been measured in aqueous solutions of 2-methylpentane-2,4-diol at 25 °C as a function of the concentration. A single relaxational absorption has been found whose cause has been attributed to the perturbation of an equilibrium associated with the solute–solvent interaction AB⇌A + B, where A is the solute and B the solvent. The forward and backward rate constants for this interaction have been evaluated from the concentration dependence of the relaxation frequency as k_f= 1.1 × 10⁸ S^–1 and k_b= 1.1 × 10⁸ dm³ mol^–1 S^–1. The standard volume and enthalpy changes of the reaction have also been determined from the concentration dependence of the maximum excess absorption per wavelength as ΔV= 0.070 cm³ mol^–1 and ΔH= 1.7 kJ mol^–1. At high concentrations (above 5.5 mol dm^–3) another relaxation, which might be due to the interconversion of rotational isomers, has been also found in the same frequency range. This is confirmed from ultrasonic-absorption measurements in toluene mixtures.