Critical Slowing Down of Chemical Reactions in Liquid Mixtures

We have observed suppression in the specific rate of hydrolysis of five organic halides in three water-based liquid mixtures near their respective equilibrium consolute points. The systems examined were tert -amyl chloride in isobutyric acid + water, tert -butyl chloride in isobutyric acid + water, tert -butyl bromide in triethylamine + water, 3-chloro-3-methylpentane in 2-butoxyethanol + water, and 4-methylbenzylbromide in 2-butoxyethanol + water. The first two have upper consolute temperatures, while the second three have lower consolute temperatures. The slowing down effect occurred within a few tenths °C on either side of the consolute temperature. In the case of tert -amyl chloride in isobutyric acid + water, the effect followed a shift in consolute temperature produced by a change in the initial concentration of tert -amyl chloride. This indicates that all points along the critical line are equivalent. These observations demonstrate the existence of critical slowing down of chemical reaction rates in liquid mixtures.